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gerrit-public.fairphone.software / platform / art / 8b1ac802f539cab4832831824a043ce936920c4c / . / runtime / gc / collector / concurrent_copying.cc
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/*
* Copyright (C) 2014 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "concurrent_copying.h"
#include "art_field-inl.h"
#include "barrier.h"
#include "base/enums.h"
#include "base/file_utils.h"
#include "base/histogram-inl.h"
#include "base/quasi_atomic.h"
#include "base/stl_util.h"
#include "base/systrace.h"
#include "class_root.h"
#include "debugger.h"
#include "gc/accounting/atomic_stack.h"
#include "gc/accounting/heap_bitmap-inl.h"
#include "gc/accounting/mod_union_table-inl.h"
#include "gc/accounting/read_barrier_table.h"
#include "gc/accounting/space_bitmap-inl.h"
#include "gc/gc_pause_listener.h"
#include "gc/reference_processor.h"
#include "gc/space/image_space.h"
#include "gc/space/space-inl.h"
#include "gc/verification.h"
#include "image-inl.h"
#include "intern_table.h"
#include "mirror/class-inl.h"
#include "mirror/object-inl.h"
#include "mirror/object-refvisitor-inl.h"
#include "mirror/object_reference.h"
#include "scoped_thread_state_change-inl.h"
#include "thread-inl.h"
#include "thread_list.h"
#include "well_known_classes.h"
namespace art {
namespace gc {
namespace collector {
static constexpr size_t kDefaultGcMarkStackSize = 2 * MB;
// If kFilterModUnionCards then we attempt to filter cards that don't need to be dirty in the mod
// union table. Disabled since it does not seem to help the pause much.
static constexpr bool kFilterModUnionCards = kIsDebugBuild;
// If kDisallowReadBarrierDuringScan is true then the GC aborts if there are any read barrier that
// occur during ConcurrentCopying::Scan in GC thread. May be used to diagnose possibly unnecessary
// read barriers. Only enabled for kIsDebugBuild to avoid performance hit.
static constexpr bool kDisallowReadBarrierDuringScan = kIsDebugBuild;
// Slow path mark stack size, increase this if the stack is getting full and it is causing
// performance problems.
static constexpr size_t kReadBarrierMarkStackSize = 512 * KB;
// Size (in the number of objects) of the sweep array free buffer.
static constexpr size_t kSweepArrayChunkFreeSize = 1024;
// Verify that there are no missing card marks.
static constexpr bool kVerifyNoMissingCardMarks = kIsDebugBuild;
ConcurrentCopying::ConcurrentCopying(Heap* heap,
bool young_gen,
bool use_generational_cc,
const std::string& name_prefix,
bool measure_read_barrier_slow_path)
: GarbageCollector(heap,
name_prefix + (name_prefix.empty() ? "" : " ") +
"concurrent copying"),
region_space_(nullptr),
gc_barrier_(new Barrier(0)),
gc_mark_stack_(accounting::ObjectStack::Create("concurrent copying gc mark stack",
kDefaultGcMarkStackSize,
kDefaultGcMarkStackSize)),
use_generational_cc_(use_generational_cc),
young_gen_(young_gen),
rb_mark_bit_stack_(accounting::ObjectStack::Create("rb copying gc mark stack",
kReadBarrierMarkStackSize,
kReadBarrierMarkStackSize)),
rb_mark_bit_stack_full_(false),
mark_stack_lock_("concurrent copying mark stack lock", kMarkSweepMarkStackLock),
thread_running_gc_(nullptr),
is_marking_(false),
is_using_read_barrier_entrypoints_(false),
is_active_(false),
is_asserting_to_space_invariant_(false),
region_space_bitmap_(nullptr),
heap_mark_bitmap_(nullptr),
live_stack_freeze_size_(0),
from_space_num_objects_at_first_pause_(0),
from_space_num_bytes_at_first_pause_(0),
mark_stack_mode_(kMarkStackModeOff),
weak_ref_access_enabled_(true),
copied_live_bytes_ratio_sum_(0.f),
gc_count_(0),
region_space_inter_region_bitmap_(nullptr),
non_moving_space_inter_region_bitmap_(nullptr),
reclaimed_bytes_ratio_sum_(0.f),
skipped_blocks_lock_("concurrent copying bytes blocks lock", kMarkSweepMarkStackLock),
measure_read_barrier_slow_path_(measure_read_barrier_slow_path),
mark_from_read_barrier_measurements_(false),
rb_slow_path_ns_(0),
rb_slow_path_count_(0),
rb_slow_path_count_gc_(0),
rb_slow_path_histogram_lock_("Read barrier histogram lock"),
rb_slow_path_time_histogram_("Mutator time in read barrier slow path", 500, 32),
rb_slow_path_count_total_(0),
rb_slow_path_count_gc_total_(0),
rb_table_(heap_->GetReadBarrierTable()),
force_evacuate_all_(false),
gc_grays_immune_objects_(false),
immune_gray_stack_lock_("concurrent copying immune gray stack lock",
kMarkSweepMarkStackLock),
num_bytes_allocated_before_gc_(0) {
static_assert(space::RegionSpace::kRegionSize == accounting::ReadBarrierTable::kRegionSize,
"The region space size and the read barrier table region size must match");
CHECK(use_generational_cc_ || !young_gen_);
Thread* self = Thread::Current();
{
ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
// Cache this so that we won't have to lock heap_bitmap_lock_ in
// Mark() which could cause a nested lock on heap_bitmap_lock_
// when GC causes a RB while doing GC or a lock order violation
// (class_linker_lock_ and heap_bitmap_lock_).
heap_mark_bitmap_ = heap->GetMarkBitmap();
}
{
MutexLock mu(self, mark_stack_lock_);
for (size_t i = 0; i < kMarkStackPoolSize; ++i) {
accounting::AtomicStack<mirror::Object>* mark_stack =
accounting::AtomicStack<mirror::Object>::Create(
"thread local mark stack", kMarkStackSize, kMarkStackSize);
pooled_mark_stacks_.push_back(mark_stack);
}
}
if (use_generational_cc_) {
// Allocate sweep array free buffer.
std::string error_msg;
sweep_array_free_buffer_mem_map_ = MemMap::MapAnonymous(
"concurrent copying sweep array free buffer",
RoundUp(kSweepArrayChunkFreeSize * sizeof(mirror::Object*), kPageSize),
PROT_READ | PROT_WRITE,
/*low_4gb=*/ false,
&error_msg);
CHECK(sweep_array_free_buffer_mem_map_.IsValid())
<< "Couldn't allocate sweep array free buffer: " << error_msg;
}
}
void ConcurrentCopying::MarkHeapReference(mirror::HeapReference<mirror::Object>* field,
bool do_atomic_update) {
Thread* const self = Thread::Current();
if (UNLIKELY(do_atomic_update)) {
// Used to mark the referent in DelayReferenceReferent in transaction mode.
mirror::Object* from_ref = field->AsMirrorPtr();
if (from_ref == nullptr) {
return;
}
mirror::Object* to_ref = Mark(self, from_ref);
if (from_ref != to_ref) {
do {
if (field->AsMirrorPtr() != from_ref) {
// Concurrently overwritten by a mutator.
break;
}
} while (!field->CasWeakRelaxed(from_ref, to_ref));
}
} else {
// Used for preserving soft references, should be OK to not have a CAS here since there should be
// no other threads which can trigger read barriers on the same referent during reference
// processing.
field->Assign(Mark(self, field->AsMirrorPtr()));
}
}
ConcurrentCopying::~ConcurrentCopying() {
STLDeleteElements(&pooled_mark_stacks_);
}
void ConcurrentCopying::RunPhases() {
CHECK(kUseBakerReadBarrier || kUseTableLookupReadBarrier);
CHECK(!is_active_);
is_active_ = true;
Thread* self = Thread::Current();
thread_running_gc_ = self;
Locks::mutator_lock_->AssertNotHeld(self);
{
ReaderMutexLock mu(self, *Locks::mutator_lock_);
InitializePhase();
// In case of forced evacuation, all regions are evacuated and hence no
// need to compute live_bytes.
if (use_generational_cc_ && !young_gen_ && !force_evacuate_all_) {
MarkingPhase();
}
}
if (kUseBakerReadBarrier && kGrayDirtyImmuneObjects) {
// Switch to read barrier mark entrypoints before we gray the objects. This is required in case
// a mutator sees a gray bit and dispatches on the entrypoint. (b/37876887).
ActivateReadBarrierEntrypoints();
// Gray dirty immune objects concurrently to reduce GC pause times. We re-process gray cards in
// the pause.
ReaderMutexLock mu(self, *Locks::mutator_lock_);
GrayAllDirtyImmuneObjects();
}
FlipThreadRoots();
{
ReaderMutexLock mu(self, *Locks::mutator_lock_);
CopyingPhase();
}
// Verify no from space refs. This causes a pause.
if (kEnableNoFromSpaceRefsVerification) {
TimingLogger::ScopedTiming split("(Paused)VerifyNoFromSpaceReferences", GetTimings());
ScopedPause pause(this, false);
CheckEmptyMarkStack();
if (kVerboseMode) {
LOG(INFO) << "Verifying no from-space refs";
}
VerifyNoFromSpaceReferences();
if (kVerboseMode) {
LOG(INFO) << "Done verifying no from-space refs";
}
CheckEmptyMarkStack();
}
{
ReaderMutexLock mu(self, *Locks::mutator_lock_);
ReclaimPhase();
}
FinishPhase();
CHECK(is_active_);
is_active_ = false;
thread_running_gc_ = nullptr;
}
class ConcurrentCopying::ActivateReadBarrierEntrypointsCheckpoint : public Closure {
public:
explicit ActivateReadBarrierEntrypointsCheckpoint(ConcurrentCopying* concurrent_copying)
: concurrent_copying_(concurrent_copying) {}
void Run(Thread* thread) override NO_THREAD_SAFETY_ANALYSIS {
// Note: self is not necessarily equal to thread since thread may be suspended.
Thread* self = Thread::Current();
DCHECK(thread == self || thread->IsSuspended() || thread->GetState() == kWaitingPerformingGc)
<< thread->GetState() << " thread " << thread << " self " << self;
// Switch to the read barrier entrypoints.
thread->SetReadBarrierEntrypoints();
// If thread is a running mutator, then act on behalf of the garbage collector.
// See the code in ThreadList::RunCheckpoint.
concurrent_copying_->GetBarrier().Pass(self);
}
private:
ConcurrentCopying* const concurrent_copying_;
};
class ConcurrentCopying::ActivateReadBarrierEntrypointsCallback : public Closure {
public:
explicit ActivateReadBarrierEntrypointsCallback(ConcurrentCopying* concurrent_copying)
: concurrent_copying_(concurrent_copying) {}
void Run(Thread* self ATTRIBUTE_UNUSED) override REQUIRES(Locks::thread_list_lock_) {
// This needs to run under the thread_list_lock_ critical section in ThreadList::RunCheckpoint()
// to avoid a race with ThreadList::Register().
CHECK(!concurrent_copying_->is_using_read_barrier_entrypoints_);
concurrent_copying_->is_using_read_barrier_entrypoints_ = true;
}
private:
ConcurrentCopying* const concurrent_copying_;
};
void ConcurrentCopying::ActivateReadBarrierEntrypoints() {
Thread* const self = Thread::Current();
ActivateReadBarrierEntrypointsCheckpoint checkpoint(this);
ThreadList* thread_list = Runtime::Current()->GetThreadList();
gc_barrier_->Init(self, 0);
ActivateReadBarrierEntrypointsCallback callback(this);
const size_t barrier_count = thread_list->RunCheckpoint(&checkpoint, &callback);
// If there are no threads to wait which implies that all the checkpoint functions are finished,
// then no need to release the mutator lock.
if (barrier_count == 0) {
return;
}
ScopedThreadStateChange tsc(self, kWaitingForCheckPointsToRun);
gc_barrier_->Increment(self, barrier_count);
}
void ConcurrentCopying::CreateInterRegionRefBitmaps() {
DCHECK(use_generational_cc_);
DCHECK(region_space_inter_region_bitmap_ == nullptr);
DCHECK(non_moving_space_inter_region_bitmap_ == nullptr);
DCHECK(region_space_ != nullptr);
DCHECK(heap_->non_moving_space_ != nullptr);
// Region-space
region_space_inter_region_bitmap_.reset(accounting::ContinuousSpaceBitmap::Create(
"region-space inter region ref bitmap",
reinterpret_cast<uint8_t*>(region_space_->Begin()),
region_space_->Limit() - region_space_->Begin()));
CHECK(region_space_inter_region_bitmap_ != nullptr)
<< "Couldn't allocate region-space inter region ref bitmap";
// non-moving-space
non_moving_space_inter_region_bitmap_.reset(accounting::ContinuousSpaceBitmap::Create(
"non-moving-space inter region ref bitmap",
reinterpret_cast<uint8_t*>(heap_->non_moving_space_->Begin()),
heap_->non_moving_space_->Limit() - heap_->non_moving_space_->Begin()));
CHECK(non_moving_space_inter_region_bitmap_ != nullptr)
<< "Couldn't allocate non-moving-space inter region ref bitmap";
}
void ConcurrentCopying::BindBitmaps() {
Thread* self = Thread::Current();
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
// Mark all of the spaces we never collect as immune.
for (const auto& space : heap_->GetContinuousSpaces()) {
if (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyNeverCollect ||
space->GetGcRetentionPolicy() == space::kGcRetentionPolicyFullCollect) {
CHECK(space->IsZygoteSpace() || space->IsImageSpace());
immune_spaces_.AddSpace(space);
} else {
CHECK(!space->IsZygoteSpace());
CHECK(!space->IsImageSpace());
CHECK(space == region_space_ || space == heap_->non_moving_space_);
if (use_generational_cc_) {
if (space == region_space_) {
region_space_bitmap_ = region_space_->GetMarkBitmap();
} else if (young_gen_ && space->IsContinuousMemMapAllocSpace()) {
DCHECK_EQ(space->GetGcRetentionPolicy(), space::kGcRetentionPolicyAlwaysCollect);
space->AsContinuousMemMapAllocSpace()->BindLiveToMarkBitmap();
}
if (young_gen_) {
// Age all of the cards for the region space so that we know which evac regions to scan.
heap_->GetCardTable()->ModifyCardsAtomic(space->Begin(),
space->End(),
AgeCardVisitor(),
VoidFunctor());
} else {
// In a full-heap GC cycle, the card-table corresponding to region-space and
// non-moving space can be cleared, because this cycle only needs to
// capture writes during the marking phase of this cycle to catch
// objects that skipped marking due to heap mutation. Furthermore,
// if the next GC is a young-gen cycle, then it only needs writes to
// be captured after the thread-flip of this GC cycle, as that is when
// the young-gen for the next GC cycle starts getting populated.
heap_->GetCardTable()->ClearCardRange(space->Begin(), space->Limit());
}
} else {
if (space == region_space_) {
// It is OK to clear the bitmap with mutators running since the only place it is read is
// VisitObjects which has exclusion with CC.
region_space_bitmap_ = region_space_->GetMarkBitmap();
region_space_bitmap_->Clear();
}
}
}
}
if (use_generational_cc_ && young_gen_) {
for (const auto& space : GetHeap()->GetDiscontinuousSpaces()) {
CHECK(space->IsLargeObjectSpace());
space->AsLargeObjectSpace()->CopyLiveToMarked();
}
}
}
void ConcurrentCopying::InitializePhase() {
TimingLogger::ScopedTiming split("InitializePhase", GetTimings());
num_bytes_allocated_before_gc_ = static_cast<int64_t>(heap_->GetBytesAllocated());
if (kVerboseMode) {
LOG(INFO) << "GC InitializePhase";
LOG(INFO) << "Region-space : " << reinterpret_cast<void*>(region_space_->Begin()) << "-"
<< reinterpret_cast<void*>(region_space_->Limit());
}
CheckEmptyMarkStack();
rb_mark_bit_stack_full_ = false;
mark_from_read_barrier_measurements_ = measure_read_barrier_slow_path_;
if (measure_read_barrier_slow_path_) {
rb_slow_path_ns_.store(0, std::memory_order_relaxed);
rb_slow_path_count_.store(0, std::memory_order_relaxed);
rb_slow_path_count_gc_.store(0, std::memory_order_relaxed);
}
immune_spaces_.Reset();
bytes_moved_.store(0, std::memory_order_relaxed);
objects_moved_.store(0, std::memory_order_relaxed);
bytes_moved_gc_thread_ = 0;
objects_moved_gc_thread_ = 0;
GcCause gc_cause = GetCurrentIteration()->GetGcCause();
force_evacuate_all_ = false;
if (!use_generational_cc_ || !young_gen_) {
if (gc_cause == kGcCauseExplicit ||
gc_cause == kGcCauseCollectorTransition ||
GetCurrentIteration()->GetClearSoftReferences()) {
force_evacuate_all_ = true;
}
}
if (kUseBakerReadBarrier) {
updated_all_immune_objects_.store(false, std::memory_order_relaxed);
// GC may gray immune objects in the thread flip.
gc_grays_immune_objects_ = true;
if (kIsDebugBuild) {
MutexLock mu(Thread::Current(), immune_gray_stack_lock_);
DCHECK(immune_gray_stack_.empty());
}
}
if (use_generational_cc_) {
done_scanning_.store(false, std::memory_order_release);
}
BindBitmaps();
if (kVerboseMode) {
LOG(INFO) << "young_gen=" << std::boolalpha << young_gen_ << std::noboolalpha;
LOG(INFO) << "force_evacuate_all=" << std::boolalpha << force_evacuate_all_ << std::noboolalpha;
LOG(INFO) << "Largest immune region: " << immune_spaces_.GetLargestImmuneRegion().Begin()
<< "-" << immune_spaces_.GetLargestImmuneRegion().End();
for (space::ContinuousSpace* space : immune_spaces_.GetSpaces()) {
LOG(INFO) << "Immune space: " << *space;
}
LOG(INFO) << "GC end of InitializePhase";
}
if (use_generational_cc_ && !young_gen_) {
region_space_bitmap_->Clear();
}
mark_stack_mode_.store(ConcurrentCopying::kMarkStackModeThreadLocal, std::memory_order_relaxed);
// Mark all of the zygote large objects without graying them.
MarkZygoteLargeObjects();
}
// Used to switch the thread roots of a thread from from-space refs to to-space refs.
class ConcurrentCopying::ThreadFlipVisitor : public Closure, public RootVisitor {
public:
ThreadFlipVisitor(ConcurrentCopying* concurrent_copying, bool use_tlab)
: concurrent_copying_(concurrent_copying), use_tlab_(use_tlab) {
}
void Run(Thread* thread) override REQUIRES_SHARED(Locks::mutator_lock_) {
// Note: self is not necessarily equal to thread since thread may be suspended.
Thread* self = Thread::Current();
CHECK(thread == self || thread->IsSuspended() || thread->GetState() == kWaitingPerformingGc)
<< thread->GetState() << " thread " << thread << " self " << self;
thread->SetIsGcMarkingAndUpdateEntrypoints(true);
if (use_tlab_ && thread->HasTlab()) {
if (ConcurrentCopying::kEnableFromSpaceAccountingCheck) {
// This must come before the revoke.
size_t thread_local_objects = thread->GetThreadLocalObjectsAllocated();
concurrent_copying_->region_space_->RevokeThreadLocalBuffers(thread);
reinterpret_cast<Atomic<size_t>*>(
&concurrent_copying_->from_space_num_objects_at_first_pause_)->
fetch_add(thread_local_objects, std::memory_order_relaxed);
} else {
concurrent_copying_->region_space_->RevokeThreadLocalBuffers(thread);
}
}
if (kUseThreadLocalAllocationStack) {
thread->RevokeThreadLocalAllocationStack();
}
ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
// We can use the non-CAS VisitRoots functions below because we update thread-local GC roots
// only.
thread->VisitRoots(this, kVisitRootFlagAllRoots);
concurrent_copying_->GetBarrier().Pass(self);
}
void VisitRoots(mirror::Object*** roots,
size_t count,
const RootInfo& info ATTRIBUTE_UNUSED) override
REQUIRES_SHARED(Locks::mutator_lock_) {
Thread* self = Thread::Current();
for (size_t i = 0; i < count; ++i) {
mirror::Object** root = roots[i];
mirror::Object* ref = *root;
if (ref != nullptr) {
mirror::Object* to_ref = concurrent_copying_->Mark(self, ref);
if (to_ref != ref) {
*root = to_ref;
}
}
}
}
void VisitRoots(mirror::CompressedReference<mirror::Object>** roots,
size_t count,
const RootInfo& info ATTRIBUTE_UNUSED) override
REQUIRES_SHARED(Locks::mutator_lock_) {
Thread* self = Thread::Current();
for (size_t i = 0; i < count; ++i) {
mirror::CompressedReference<mirror::Object>* const root = roots[i];
if (!root->IsNull()) {
mirror::Object* ref = root->AsMirrorPtr();
mirror::Object* to_ref = concurrent_copying_->Mark(self, ref);
if (to_ref != ref) {
root->Assign(to_ref);
}
}
}
}
private:
ConcurrentCopying* const concurrent_copying_;
const bool use_tlab_;
};
// Called back from Runtime::FlipThreadRoots() during a pause.
class ConcurrentCopying::FlipCallback : public Closure {
public:
explicit FlipCallback(ConcurrentCopying* concurrent_copying)
: concurrent_copying_(concurrent_copying) {
}
void Run(Thread* thread) override REQUIRES(Locks::mutator_lock_) {
ConcurrentCopying* cc = concurrent_copying_;
TimingLogger::ScopedTiming split("(Paused)FlipCallback", cc->GetTimings());
// Note: self is not necessarily equal to thread since thread may be suspended.
Thread* self = Thread::Current();
if (kVerifyNoMissingCardMarks && cc->young_gen_) {
cc->VerifyNoMissingCardMarks();
}
CHECK_EQ(thread, self);
Locks::mutator_lock_->AssertExclusiveHeld(self);
space::RegionSpace::EvacMode evac_mode = space::RegionSpace::kEvacModeLivePercentNewlyAllocated;
if (cc->young_gen_) {
CHECK(!cc->force_evacuate_all_);
evac_mode = space::RegionSpace::kEvacModeNewlyAllocated;
} else if (cc->force_evacuate_all_) {
evac_mode = space::RegionSpace::kEvacModeForceAll;
}
{
TimingLogger::ScopedTiming split2("(Paused)SetFromSpace", cc->GetTimings());
// Only change live bytes for 1-phase full heap CC.
cc->region_space_->SetFromSpace(
cc->rb_table_,
evac_mode,
/*clear_live_bytes=*/ !cc->use_generational_cc_);
}
cc->SwapStacks();
if (ConcurrentCopying::kEnableFromSpaceAccountingCheck) {
cc->RecordLiveStackFreezeSize(self);
cc->from_space_num_objects_at_first_pause_ = cc->region_space_->GetObjectsAllocated();
cc->from_space_num_bytes_at_first_pause_ = cc->region_space_->GetBytesAllocated();
}
cc->is_marking_ = true;
if (kIsDebugBuild && !cc->use_generational_cc_) {
cc->region_space_->AssertAllRegionLiveBytesZeroOrCleared();
}
if (UNLIKELY(Runtime::Current()->IsActiveTransaction())) {
CHECK(Runtime::Current()->IsAotCompiler());
TimingLogger::ScopedTiming split3("(Paused)VisitTransactionRoots", cc->GetTimings());
Runtime::Current()->VisitTransactionRoots(cc);
}
if (kUseBakerReadBarrier && kGrayDirtyImmuneObjects) {
cc->GrayAllNewlyDirtyImmuneObjects();
if (kIsDebugBuild) {
// Check that all non-gray immune objects only reference immune objects.
cc->VerifyGrayImmuneObjects();
}
}
// May be null during runtime creation, in this case leave java_lang_Object null.
// This is safe since single threaded behavior should mean FillDummyObject does not
// happen when java_lang_Object_ is null.
if (WellKnownClasses::java_lang_Object != nullptr) {
cc->java_lang_Object_ = down_cast<mirror::Class*>(cc->Mark(thread,
WellKnownClasses::ToClass(WellKnownClasses::java_lang_Object).Ptr()));
} else {
cc->java_lang_Object_ = nullptr;
}
}
private:
ConcurrentCopying* const concurrent_copying_;
};
class ConcurrentCopying::VerifyGrayImmuneObjectsVisitor {
public:
explicit VerifyGrayImmuneObjectsVisitor(ConcurrentCopying* collector)
: collector_(collector) {}
void operator()(ObjPtr<mirror::Object> obj, MemberOffset offset, bool /* is_static */)
const ALWAYS_INLINE REQUIRES_SHARED(Locks::mutator_lock_)
REQUIRES_SHARED(Locks::heap_bitmap_lock_) {
CheckReference(obj->GetFieldObject<mirror::Object, kVerifyNone, kWithoutReadBarrier>(offset),
obj, offset);
}
void operator()(ObjPtr<mirror::Class> klass, ObjPtr<mirror::Reference> ref) const
REQUIRES_SHARED(Locks::mutator_lock_) ALWAYS_INLINE {
CHECK(klass->IsTypeOfReferenceClass());
CheckReference(ref->GetReferent<kWithoutReadBarrier>(),
ref,
mirror::Reference::ReferentOffset());
}
void VisitRootIfNonNull(mirror::CompressedReference<mirror::Object>* root) const
ALWAYS_INLINE
REQUIRES_SHARED(Locks::mutator_lock_) {
if (!root->IsNull()) {
VisitRoot(root);
}
}
void VisitRoot(mirror::CompressedReference<mirror::Object>* root) const
ALWAYS_INLINE
REQUIRES_SHARED(Locks::mutator_lock_) {
CheckReference(root->AsMirrorPtr(), nullptr, MemberOffset(0));
}
private:
ConcurrentCopying* const collector_;
void CheckReference(ObjPtr<mirror::Object> ref,
ObjPtr<mirror::Object> holder,
MemberOffset offset) const
REQUIRES_SHARED(Locks::mutator_lock_) {
if (ref != nullptr) {
if (!collector_->immune_spaces_.ContainsObject(ref.Ptr())) {
// Not immune, must be a zygote large object.
space::LargeObjectSpace* large_object_space =
Runtime::Current()->GetHeap()->GetLargeObjectsSpace();
CHECK(large_object_space->Contains(ref.Ptr()) &&
large_object_space->IsZygoteLargeObject(Thread::Current(), ref.Ptr()))
<< "Non gray object references non immune, non zygote large object "<< ref << " "
<< mirror::Object::PrettyTypeOf(ref) << " in holder " << holder << " "
<< mirror::Object::PrettyTypeOf(holder) << " offset=" << offset.Uint32Value();
} else {
// Make sure the large object class is immune since we will never scan the large object.
CHECK(collector_->immune_spaces_.ContainsObject(
ref->GetClass<kVerifyNone, kWithoutReadBarrier>()));
}
}
}
};
void ConcurrentCopying::VerifyGrayImmuneObjects() {
TimingLogger::ScopedTiming split(__FUNCTION__, GetTimings());
for (auto& space : immune_spaces_.GetSpaces()) {
DCHECK(space->IsImageSpace() || space->IsZygoteSpace());
accounting::ContinuousSpaceBitmap* live_bitmap = space->GetLiveBitmap();
VerifyGrayImmuneObjectsVisitor visitor(this);
live_bitmap->VisitMarkedRange(reinterpret_cast<uintptr_t>(space->Begin()),
reinterpret_cast<uintptr_t>(space->Limit()),
[&visitor](mirror::Object* obj)
REQUIRES_SHARED(Locks::mutator_lock_) {
// If an object is not gray, it should only have references to things in the immune spaces.
if (obj->GetReadBarrierState() != ReadBarrier::GrayState()) {
obj->VisitReferences</*kVisitNativeRoots=*/true,
kDefaultVerifyFlags,
kWithoutReadBarrier>(visitor, visitor);
}
});
}
}
class ConcurrentCopying::VerifyNoMissingCardMarkVisitor {
public:
VerifyNoMissingCardMarkVisitor(ConcurrentCopying* cc, ObjPtr<mirror::Object> holder)
: cc_(cc),
holder_(holder) {}
void operator()(ObjPtr<mirror::Object> obj,
MemberOffset offset,
bool is_static ATTRIBUTE_UNUSED) const
REQUIRES_SHARED(Locks::mutator_lock_) ALWAYS_INLINE {
if (offset.Uint32Value() != mirror::Object::ClassOffset().Uint32Value()) {
CheckReference(obj->GetFieldObject<mirror::Object, kDefaultVerifyFlags, kWithoutReadBarrier>(
offset), offset.Uint32Value());
}
}
void operator()(ObjPtr<mirror::Class> klass,
ObjPtr<mirror::Reference> ref) const
REQUIRES_SHARED(Locks::mutator_lock_) ALWAYS_INLINE {
CHECK(klass->IsTypeOfReferenceClass());
this->operator()(ref, mirror::Reference::ReferentOffset(), false);
}
void VisitRootIfNonNull(mirror::CompressedReference<mirror::Object>* root) const
REQUIRES_SHARED(Locks::mutator_lock_) {
if (!root->IsNull()) {
VisitRoot(root);
}
}
void VisitRoot(mirror::CompressedReference<mirror::Object>* root) const
REQUIRES_SHARED(Locks::mutator_lock_) {
CheckReference(root->AsMirrorPtr());
}
void CheckReference(mirror::Object* ref, int32_t offset = -1) const
REQUIRES_SHARED(Locks::mutator_lock_) {
if (ref != nullptr && cc_->region_space_->IsInNewlyAllocatedRegion(ref)) {
LOG(FATAL_WITHOUT_ABORT)
<< holder_->PrettyTypeOf() << "(" << holder_.Ptr() << ") references object "
<< ref->PrettyTypeOf() << "(" << ref << ") in newly allocated region at offset=" << offset;
LOG(FATAL_WITHOUT_ABORT) << "time=" << cc_->region_space_->Time();
constexpr const char* kIndent = " ";
LOG(FATAL_WITHOUT_ABORT) << cc_->DumpReferenceInfo(holder_.Ptr(), "holder_", kIndent);
LOG(FATAL_WITHOUT_ABORT) << cc_->DumpReferenceInfo(ref, "ref", kIndent);
LOG(FATAL) << "Unexpected reference to newly allocated region.";
}
}
private:
ConcurrentCopying* const cc_;
const ObjPtr<mirror::Object> holder_;
};
void ConcurrentCopying::VerifyNoMissingCardMarks() {
auto visitor = [&](mirror::Object* obj)
REQUIRES(Locks::mutator_lock_)
REQUIRES(!mark_stack_lock_) {
// Objects on clean cards should never have references to newly allocated regions. Note
// that aged cards are also not clean.
if (heap_->GetCardTable()->GetCard(obj) == gc::accounting::CardTable::kCardClean) {
VerifyNoMissingCardMarkVisitor internal_visitor(this, /*holder=*/ obj);
obj->VisitReferences</*kVisitNativeRoots=*/true, kVerifyNone, kWithoutReadBarrier>(
internal_visitor, internal_visitor);
}
};
TimingLogger::ScopedTiming split(__FUNCTION__, GetTimings());
region_space_->Walk(visitor);
{
ReaderMutexLock rmu(Thread::Current(), *Locks::heap_bitmap_lock_);
heap_->GetLiveBitmap()->Visit(visitor);
}
}
// Switch threads that from from-space to to-space refs. Forward/mark the thread roots.
void ConcurrentCopying::FlipThreadRoots() {
TimingLogger::ScopedTiming split("FlipThreadRoots", GetTimings());
if (kVerboseMode || heap_->dump_region_info_before_gc_) {
LOG(INFO) << "time=" << region_space_->Time();
region_space_->DumpNonFreeRegions(LOG_STREAM(INFO));
}
Thread* self = Thread::Current();
Locks::mutator_lock_->AssertNotHeld(self);
gc_barrier_->Init(self, 0);
ThreadFlipVisitor thread_flip_visitor(this, heap_->use_tlab_);
FlipCallback flip_callback(this);
size_t barrier_count = Runtime::Current()->GetThreadList()->FlipThreadRoots(
&thread_flip_visitor, &flip_callback, this, GetHeap()->GetGcPauseListener());
{
ScopedThreadStateChange tsc(self, kWaitingForCheckPointsToRun);
gc_barrier_->Increment(self, barrier_count);
}
is_asserting_to_space_invariant_ = true;
QuasiAtomic::ThreadFenceForConstructor();
if (kVerboseMode) {
LOG(INFO) << "time=" << region_space_->Time();
region_space_->DumpNonFreeRegions(LOG_STREAM(INFO));
LOG(INFO) << "GC end of FlipThreadRoots";
}
}
template <bool kConcurrent>
class ConcurrentCopying::GrayImmuneObjectVisitor {
public:
explicit GrayImmuneObjectVisitor(Thread* self) : self_(self) {}
ALWAYS_INLINE void operator()(mirror::Object* obj) const REQUIRES_SHARED(Locks::mutator_lock_) {
if (kUseBakerReadBarrier && obj->GetReadBarrierState() == ReadBarrier::NonGrayState()) {
if (kConcurrent) {
Locks::mutator_lock_->AssertSharedHeld(self_);
obj->AtomicSetReadBarrierState(ReadBarrier::NonGrayState(), ReadBarrier::GrayState());
// Mod union table VisitObjects may visit the same object multiple times so we can't check
// the result of the atomic set.
} else {
Locks::mutator_lock_->AssertExclusiveHeld(self_);
obj->SetReadBarrierState(ReadBarrier::GrayState());
}
}
}
static void Callback(mirror::Object* obj, void* arg) REQUIRES_SHARED(Locks::mutator_lock_) {
reinterpret_cast<GrayImmuneObjectVisitor<kConcurrent>*>(arg)->operator()(obj);
}
private:
Thread* const self_;
};
void ConcurrentCopying::GrayAllDirtyImmuneObjects() {
TimingLogger::ScopedTiming split("GrayAllDirtyImmuneObjects", GetTimings());
accounting::CardTable* const card_table = heap_->GetCardTable();
Thread* const self = Thread::Current();
using VisitorType = GrayImmuneObjectVisitor</* kIsConcurrent= */ true>;
VisitorType visitor(self);
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
for (space::ContinuousSpace* space : immune_spaces_.GetSpaces()) {
DCHECK(space->IsImageSpace() || space->IsZygoteSpace());
accounting::ModUnionTable* table = heap_->FindModUnionTableFromSpace(space);
// Mark all the objects on dirty cards since these may point to objects in other space.
// Once these are marked, the GC will eventually clear them later.
// Table is non null for boot image and zygote spaces. It is only null for application image
// spaces.
if (table != nullptr) {
table->ProcessCards();
table->VisitObjects(&VisitorType::Callback, &visitor);
// Don't clear cards here since we need to rescan in the pause. If we cleared the cards here,
// there would be races with the mutator marking new cards.
} else {
// Keep cards aged if we don't have a mod-union table since we may need to scan them in future
// GCs. This case is for app images.
card_table->ModifyCardsAtomic(
space->Begin(),
space->End(),
[](uint8_t card) {
return (card != gc::accounting::CardTable::kCardClean)
? gc::accounting::CardTable::kCardAged
: card;
},
/* card modified visitor */ VoidFunctor());
card_table->Scan</*kClearCard=*/ false>(space->GetMarkBitmap(),
space->Begin(),
space->End(),
visitor,
gc::accounting::CardTable::kCardAged);
}
}
}
void ConcurrentCopying::GrayAllNewlyDirtyImmuneObjects() {
TimingLogger::ScopedTiming split("(Paused)GrayAllNewlyDirtyImmuneObjects", GetTimings());
accounting::CardTable* const card_table = heap_->GetCardTable();
using VisitorType = GrayImmuneObjectVisitor</* kIsConcurrent= */ false>;
Thread* const self = Thread::Current();
VisitorType visitor(self);
WriterMutexLock mu(Thread::Current(), *Locks::heap_bitmap_lock_);
for (space::ContinuousSpace* space : immune_spaces_.GetSpaces()) {
DCHECK(space->IsImageSpace() || space->IsZygoteSpace());
accounting::ModUnionTable* table = heap_->FindModUnionTableFromSpace(space);
// Don't need to scan aged cards since we did these before the pause. Note that scanning cards
// also handles the mod-union table cards.
card_table->Scan</*kClearCard=*/ false>(space->GetMarkBitmap(),
space->Begin(),
space->End(),
visitor,
gc::accounting::CardTable::kCardDirty);
if (table != nullptr) {
// Add the cards to the mod-union table so that we can clear cards to save RAM.
table->ProcessCards();
TimingLogger::ScopedTiming split2("(Paused)ClearCards", GetTimings());
card_table->ClearCardRange(space->Begin(),
AlignDown(space->End(), accounting::CardTable::kCardSize));
}
}
// Since all of the objects that may point to other spaces are gray, we can avoid all the read
// barriers in the immune spaces.
updated_all_immune_objects_.store(true, std::memory_order_relaxed);
}
void ConcurrentCopying::SwapStacks() {
heap_->SwapStacks();
}
void ConcurrentCopying::RecordLiveStackFreezeSize(Thread* self) {
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
live_stack_freeze_size_ = heap_->GetLiveStack()->Size();
}
// Used to visit objects in the immune spaces.
inline void ConcurrentCopying::ScanImmuneObject(mirror::Object* obj) {
DCHECK(obj != nullptr);
DCHECK(immune_spaces_.ContainsObject(obj));
// Update the fields without graying it or pushing it onto the mark stack.
if (use_generational_cc_ && young_gen_) {
// Young GC does not care about references to unevac space. It is safe to not gray these as
// long as scan immune objects happens after scanning the dirty cards.
Scan<true>(obj);
} else {
Scan<false>(obj);
}
}
class ConcurrentCopying::ImmuneSpaceScanObjVisitor {
public:
explicit ImmuneSpaceScanObjVisitor(ConcurrentCopying* cc)
: collector_(cc) {}
ALWAYS_INLINE void operator()(mirror::Object* obj) const REQUIRES_SHARED(Locks::mutator_lock_) {
if (kUseBakerReadBarrier && kGrayDirtyImmuneObjects) {
// Only need to scan gray objects.
if (obj->GetReadBarrierState() == ReadBarrier::GrayState()) {
collector_->ScanImmuneObject(obj);
// Done scanning the object, go back to black (non-gray).
bool success = obj->AtomicSetReadBarrierState(ReadBarrier::GrayState(),
ReadBarrier::NonGrayState());
CHECK(success)
<< Runtime::Current()->GetHeap()->GetVerification()->DumpObjectInfo(obj, "failed CAS");
}
} else {
collector_->ScanImmuneObject(obj);
}
}
static void Callback(mirror::Object* obj, void* arg) REQUIRES_SHARED(Locks::mutator_lock_) {
reinterpret_cast<ImmuneSpaceScanObjVisitor*>(arg)->operator()(obj);
}
private:
ConcurrentCopying* const collector_;
};
template <bool kAtomicTestAndSet>
class ConcurrentCopying::CaptureRootsForMarkingVisitor : public RootVisitor {
public:
explicit CaptureRootsForMarkingVisitor(ConcurrentCopying* cc, Thread* self)
: collector_(cc), self_(self) {}
void VisitRoots(mirror::Object*** roots,
size_t count,
const RootInfo& info ATTRIBUTE_UNUSED) override
REQUIRES_SHARED(Locks::mutator_lock_) {
for (size_t i = 0; i < count; ++i) {
mirror::Object** root = roots[i];
mirror::Object* ref = *root;
if (ref != nullptr && !collector_->TestAndSetMarkBitForRef<kAtomicTestAndSet>(ref)) {
collector_->PushOntoMarkStack(self_, ref);
}
}
}
void VisitRoots(mirror::CompressedReference<mirror::Object>** roots,
size_t count,
const RootInfo& info ATTRIBUTE_UNUSED) override
REQUIRES_SHARED(Locks::mutator_lock_) {
for (size_t i = 0; i < count; ++i) {
mirror::CompressedReference<mirror::Object>* const root = roots[i];
if (!root->IsNull()) {
mirror::Object* ref = root->AsMirrorPtr();
if (!collector_->TestAndSetMarkBitForRef<kAtomicTestAndSet>(ref)) {
collector_->PushOntoMarkStack(self_, ref);
}
}
}
}
private:
ConcurrentCopying* const collector_;
Thread* const self_;
};
class ConcurrentCopying::RevokeThreadLocalMarkStackCheckpoint : public Closure {
public:
RevokeThreadLocalMarkStackCheckpoint(ConcurrentCopying* concurrent_copying,
bool disable_weak_ref_access)
: concurrent_copying_(concurrent_copying),
disable_weak_ref_access_(disable_weak_ref_access) {
}
void Run(Thread* thread) override NO_THREAD_SAFETY_ANALYSIS {
// Note: self is not necessarily equal to thread since thread may be suspended.
Thread* const self = Thread::Current();
CHECK(thread == self || thread->IsSuspended() || thread->GetState() == kWaitingPerformingGc)
<< thread->GetState() << " thread " << thread << " self " << self;
// Revoke thread local mark stacks.
accounting::AtomicStack<mirror::Object>* tl_mark_stack = thread->GetThreadLocalMarkStack();
if (tl_mark_stack != nullptr) {
MutexLock mu(self, concurrent_copying_->mark_stack_lock_);
concurrent_copying_->revoked_mark_stacks_.push_back(tl_mark_stack);
thread->SetThreadLocalMarkStack(nullptr);
}
// Disable weak ref access.
if (disable_weak_ref_access_) {
thread->SetWeakRefAccessEnabled(false);
}
// If thread is a running mutator, then act on behalf of the garbage collector.
// See the code in ThreadList::RunCheckpoint.
concurrent_copying_->GetBarrier().Pass(self);
}
protected:
ConcurrentCopying* const concurrent_copying_;
private:
const bool disable_weak_ref_access_;
};
class ConcurrentCopying::CaptureThreadRootsForMarkingAndCheckpoint :
public RevokeThreadLocalMarkStackCheckpoint {
public:
explicit CaptureThreadRootsForMarkingAndCheckpoint(ConcurrentCopying* cc) :
RevokeThreadLocalMarkStackCheckpoint(cc, /* disable_weak_ref_access */ false) {}
void Run(Thread* thread) override
REQUIRES_SHARED(Locks::mutator_lock_) {
Thread* const self = Thread::Current();
ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
// We can use the non-CAS VisitRoots functions below because we update thread-local GC roots
// only.
CaptureRootsForMarkingVisitor</*kAtomicTestAndSet*/ true> visitor(concurrent_copying_, self);
thread->VisitRoots(&visitor, kVisitRootFlagAllRoots);
// Barrier handling is done in the base class' Run() below.
RevokeThreadLocalMarkStackCheckpoint::Run(thread);
}
};
void ConcurrentCopying::CaptureThreadRootsForMarking() {
TimingLogger::ScopedTiming split("CaptureThreadRootsForMarking", GetTimings());
if (kVerboseMode) {
LOG(INFO) << "time=" << region_space_->Time();
region_space_->DumpNonFreeRegions(LOG_STREAM(INFO));
}
Thread* const self = Thread::Current();
CaptureThreadRootsForMarkingAndCheckpoint check_point(this);
ThreadList* thread_list = Runtime::Current()->GetThreadList();
gc_barrier_->Init(self, 0);
size_t barrier_count = thread_list->RunCheckpoint(&check_point, /* callback */ nullptr);
// If there are no threads to wait which implys that all the checkpoint functions are finished,
// then no need to release the mutator lock.
if (barrier_count == 0) {
return;
}
Locks::mutator_lock_->SharedUnlock(self);
{
ScopedThreadStateChange tsc(self, kWaitingForCheckPointsToRun);
gc_barrier_->Increment(self, barrier_count);
}
Locks::mutator_lock_->SharedLock(self);
if (kVerboseMode) {
LOG(INFO) << "time=" << region_space_->Time();
region_space_->DumpNonFreeRegions(LOG_STREAM(INFO));
LOG(INFO) << "GC end of CaptureThreadRootsForMarking";
}
}
// Used to scan ref fields of an object.
template <bool kHandleInterRegionRefs>
class ConcurrentCopying::ComputeLiveBytesAndMarkRefFieldsVisitor {
public:
explicit ComputeLiveBytesAndMarkRefFieldsVisitor(ConcurrentCopying* collector,
size_t obj_region_idx)
: collector_(collector),
obj_region_idx_(obj_region_idx),
contains_inter_region_idx_(false) {}
void operator()(mirror::Object* obj, MemberOffset offset, bool /* is_static */) const
ALWAYS_INLINE
REQUIRES_SHARED(Locks::mutator_lock_)
REQUIRES_SHARED(Locks::heap_bitmap_lock_) {
DCHECK_EQ(collector_->RegionSpace()->RegionIdxForRef(obj), obj_region_idx_);
DCHECK(kHandleInterRegionRefs || collector_->immune_spaces_.ContainsObject(obj));
CheckReference(obj->GetFieldObject<mirror::Object, kVerifyNone, kWithoutReadBarrier>(offset));
}
void operator()(ObjPtr<mirror::Class> klass, ObjPtr<mirror::Reference> ref) const
REQUIRES_SHARED(Locks::mutator_lock_) ALWAYS_INLINE {
DCHECK(klass->IsTypeOfReferenceClass());
// If the referent is not null, then we must re-visit the object during
// copying phase to enqueue it for delayed processing and setting
// read-barrier state to gray to ensure that call to GetReferent() triggers
// the read-barrier. We use same data structure that is used to remember
// objects with inter-region refs for this purpose too.
if (kHandleInterRegionRefs
&& !contains_inter_region_idx_
&& ref->AsReference()->GetReferent<kWithoutReadBarrier>() != nullptr) {
contains_inter_region_idx_ = true;
}
}
void VisitRootIfNonNull(mirror::CompressedReference<mirror::Object>* root) const
ALWAYS_INLINE
REQUIRES_SHARED(Locks::mutator_lock_) {
if (!root->IsNull()) {
VisitRoot(root);
}
}
void VisitRoot(mirror::CompressedReference<mirror::Object>* root) const
ALWAYS_INLINE
REQUIRES_SHARED(Locks::mutator_lock_) {
CheckReference(root->AsMirrorPtr());
}
bool ContainsInterRegionRefs() const ALWAYS_INLINE REQUIRES_SHARED(Locks::mutator_lock_) {
return contains_inter_region_idx_;
}
private:
void CheckReference(mirror::Object* ref) const
REQUIRES_SHARED(Locks::mutator_lock_) {
if (ref == nullptr) {
// Nothing to do.
return;
}
if (!collector_->TestAndSetMarkBitForRef(ref)) {
collector_->PushOntoLocalMarkStack(ref);
}
if (kHandleInterRegionRefs && !contains_inter_region_idx_) {
size_t ref_region_idx = collector_->RegionSpace()->RegionIdxForRef(ref);
// If a region-space object refers to an outside object, we will have a
// mismatch of region idx, but the object need not be re-visited in
// copying phase.
if (ref_region_idx != static_cast<size_t>(-1) && obj_region_idx_ != ref_region_idx) {
contains_inter_region_idx_ = true;
}
}
}
ConcurrentCopying* const collector_;
const size_t obj_region_idx_;
mutable bool contains_inter_region_idx_;
};
void ConcurrentCopying::AddLiveBytesAndScanRef(mirror::Object* ref) {
DCHECK(ref != nullptr);
DCHECK(!immune_spaces_.ContainsObject(ref));
DCHECK(TestMarkBitmapForRef(ref));
size_t obj_region_idx = static_cast<size_t>(-1);
if (LIKELY(region_space_->HasAddress(ref))) {
obj_region_idx = region_space_->RegionIdxForRefUnchecked(ref);
// Add live bytes to the corresponding region
if (!region_space_->IsRegionNewlyAllocated(obj_region_idx)) {
// Newly Allocated regions are always chosen for evacuation. So no need
// to update live_bytes_.
size_t obj_size = ref->SizeOf<kDefaultVerifyFlags>();
size_t alloc_size = RoundUp(obj_size, space::RegionSpace::kAlignment);
region_space_->AddLiveBytes(ref, alloc_size);
}
}
ComputeLiveBytesAndMarkRefFieldsVisitor</*kHandleInterRegionRefs*/ true>
visitor(this, obj_region_idx);
ref->VisitReferences</*kVisitNativeRoots=*/ true, kDefaultVerifyFlags, kWithoutReadBarrier>(
visitor, visitor);
// Mark the corresponding card dirty if the object contains any
// inter-region reference.
if (visitor.ContainsInterRegionRefs()) {
if (obj_region_idx == static_cast<size_t>(-1)) {
// If an inter-region ref has been found in a non-region-space, then it
// must be non-moving-space. This is because this function cannot be
// called on a immune-space object, and a large-object-space object has
// only class object reference, which is either in some immune-space, or
// in non-moving-space.
DCHECK(heap_->non_moving_space_->HasAddress(ref));
non_moving_space_inter_region_bitmap_->Set(ref);
} else {
region_space_inter_region_bitmap_->Set(ref);
}
}
}
template <bool kAtomic>
bool ConcurrentCopying::TestAndSetMarkBitForRef(mirror::Object* ref) {
accounting::ContinuousSpaceBitmap* bitmap = nullptr;
accounting::LargeObjectBitmap* los_bitmap = nullptr;
if (LIKELY(region_space_->HasAddress(ref))) {
bitmap = region_space_bitmap_;
} else if (heap_->GetNonMovingSpace()->HasAddress(ref)) {
bitmap = heap_->GetNonMovingSpace()->GetMarkBitmap();
} else if (immune_spaces_.ContainsObject(ref)) {
// References to immune space objects are always live.
DCHECK(heap_mark_bitmap_->GetContinuousSpaceBitmap(ref)->Test(ref));
return true;
} else {
// Should be a large object. Must be page aligned and the LOS must exist.
if (kIsDebugBuild
&& (!IsAligned<kPageSize>(ref) || heap_->GetLargeObjectsSpace() == nullptr)) {
// It must be heap corruption. Remove memory protection and dump data.
region_space_->Unprotect();
heap_->GetVerification()->LogHeapCorruption(/* obj */ nullptr,
MemberOffset(0),
ref,
/* fatal */ true);
}
los_bitmap = heap_->GetLargeObjectsSpace()->GetMarkBitmap();
}
if (kAtomic) {
return (bitmap != nullptr) ? bitmap->AtomicTestAndSet(ref) : los_bitmap->AtomicTestAndSet(ref);
} else {
return (bitmap != nullptr) ? bitmap->Set(ref) : los_bitmap->Set(ref);
}
}
bool ConcurrentCopying::TestMarkBitmapForRef(mirror::Object* ref) {
if (LIKELY(region_space_->HasAddress(ref))) {
return region_space_bitmap_->Test(ref);
} else if (heap_->GetNonMovingSpace()->HasAddress(ref)) {
return heap_->GetNonMovingSpace()->GetMarkBitmap()->Test(ref);
} else if (immune_spaces_.ContainsObject(ref)) {
// References to immune space objects are always live.
DCHECK(heap_mark_bitmap_->GetContinuousSpaceBitmap(ref)->Test(ref));
return true;
} else {
// Should be a large object. Must be page aligned and the LOS must exist.
if (kIsDebugBuild
&& (!IsAligned<kPageSize>(ref) || heap_->GetLargeObjectsSpace() == nullptr)) {
// It must be heap corruption. Remove memory protection and dump data.
region_space_->Unprotect();
heap_->GetVerification()->LogHeapCorruption(/* obj */ nullptr,
MemberOffset(0),
ref,
/* fatal */ true);
}
return heap_->GetLargeObjectsSpace()->GetMarkBitmap()->Test(ref);
}
}
void ConcurrentCopying::PushOntoLocalMarkStack(mirror::Object* ref) {
if (kIsDebugBuild) {
Thread *self = Thread::Current();
DCHECK_EQ(thread_running_gc_, self);
DCHECK(self->GetThreadLocalMarkStack() == nullptr);
}
DCHECK_EQ(mark_stack_mode_.load(std::memory_order_relaxed), kMarkStackModeThreadLocal);
if (UNLIKELY(gc_mark_stack_->IsFull())) {
ExpandGcMarkStack();
}
gc_mark_stack_->PushBack(ref);
}
void ConcurrentCopying::ProcessMarkStackForMarkingAndComputeLiveBytes() {
// Process thread-local mark stack containing thread roots
ProcessThreadLocalMarkStacks(/* disable_weak_ref_access */ false,
/* checkpoint_callback */ nullptr,
[this] (mirror::Object* ref)
REQUIRES_SHARED(Locks::mutator_lock_) {
AddLiveBytesAndScanRef(ref);
});
while (!gc_mark_stack_->IsEmpty()) {
mirror::Object* ref = gc_mark_stack_->PopBack();
AddLiveBytesAndScanRef(ref);
}
}
class ConcurrentCopying::ImmuneSpaceCaptureRefsVisitor {
public:
explicit ImmuneSpaceCaptureRefsVisitor(ConcurrentCopying* cc) : collector_(cc) {}
ALWAYS_INLINE void operator()(mirror::Object* obj) const REQUIRES_SHARED(Locks::mutator_lock_) {
ComputeLiveBytesAndMarkRefFieldsVisitor</*kHandleInterRegionRefs*/ false>
visitor(collector_, /*obj_region_idx*/ static_cast<size_t>(-1));
obj->VisitReferences</*kVisitNativeRoots=*/true, kDefaultVerifyFlags, kWithoutReadBarrier>(
visitor, visitor);
}
static void Callback(mirror::Object* obj, void* arg) REQUIRES_SHARED(Locks::mutator_lock_) {
reinterpret_cast<ImmuneSpaceScanObjVisitor*>(arg)->operator()(obj);
}
private:
ConcurrentCopying* const collector_;
};
/* Invariants for two-phase CC
* ===========================
* A) Definitions
* ---------------
* 1) Black: marked in bitmap, rb_state is non-gray, and not in mark stack
* 2) Black-clean: marked in bitmap, and corresponding card is clean/aged
* 3) Black-dirty: marked in bitmap, and corresponding card is dirty
* 4) Gray: marked in bitmap, and exists in mark stack
* 5) Gray-dirty: marked in bitmap, rb_state is gray, corresponding card is
* dirty, and exists in mark stack
* 6) White: unmarked in bitmap, rb_state is non-gray, and not in mark stack
*
* B) Before marking phase
* -----------------------
* 1) All objects are white
* 2) Cards are either clean or aged (cannot be asserted without a STW pause)
* 3) Mark bitmap is cleared
* 4) Mark stack is empty
*
* C) During marking phase
* ------------------------
* 1) If a black object holds an inter-region or white reference, then its
* corresponding card is dirty. In other words, it changes from being
* black-clean to black-dirty
* 2) No black-clean object points to a white object
*
* D) After marking phase
* -----------------------
* 1) There are no gray objects
* 2) All newly allocated objects are in from space
* 3) No white object can be reachable, directly or otherwise, from a
* black-clean object
*
* E) During copying phase
* ------------------------
* 1) Mutators cannot observe white and black-dirty objects
* 2) New allocations are in to-space (newly allocated regions are part of to-space)
* 3) An object in mark stack must have its rb_state = Gray
*
* F) During card table scan
* --------------------------
* 1) Referents corresponding to root references are gray or in to-space
* 2) Every path from an object that is read or written by a mutator during
* this period to a dirty black object goes through some gray object.
* Mutators preserve this by graying black objects as needed during this
* period. Ensures that a mutator never encounters a black dirty object.
*
* G) After card table scan
* ------------------------
* 1) There are no black-dirty objects
* 2) Referents corresponding to root references are gray, black-clean or in
* to-space
*
* H) After copying phase
* -----------------------
* 1) Mark stack is empty
* 2) No references into evacuated from-space
* 3) No reference to an object which is unmarked and is also not in newly
* allocated region. In other words, no reference to white objects.
*/
void ConcurrentCopying::MarkingPhase() {
TimingLogger::ScopedTiming split("MarkingPhase", GetTimings());
if (kVerboseMode) {
LOG(INFO) << "GC MarkingPhase";
}
accounting::CardTable* const card_table = heap_->GetCardTable();
Thread* const self = Thread::Current();
// Clear live_bytes_ of every non-free region, except the ones that are newly
// allocated.
region_space_->SetAllRegionLiveBytesZero();
if (kIsDebugBuild) {
region_space_->AssertAllRegionLiveBytesZeroOrCleared();
}
// Scan immune spaces
{
TimingLogger::ScopedTiming split2("ScanImmuneSpaces", GetTimings());
for (auto& space : immune_spaces_.GetSpaces()) {
DCHECK(space->IsImageSpace() || space->IsZygoteSpace());
accounting::ContinuousSpaceBitmap* live_bitmap = space->GetLiveBitmap();
accounting::ModUnionTable* table = heap_->FindModUnionTableFromSpace(space);
ImmuneSpaceCaptureRefsVisitor visitor(this);
if (table != nullptr) {
table->VisitObjects(ImmuneSpaceCaptureRefsVisitor::Callback, &visitor);
} else {
WriterMutexLock rmu(Thread::Current(), *Locks::heap_bitmap_lock_);
card_table->Scan<false>(
live_bitmap,
space->Begin(),
space->Limit(),
visitor,
accounting::CardTable::kCardDirty - 1);
}
}
}
// Scan runtime roots
{
TimingLogger::ScopedTiming split2("VisitConcurrentRoots", GetTimings());
CaptureRootsForMarkingVisitor visitor(this, self);
Runtime::Current()->VisitConcurrentRoots(&visitor, kVisitRootFlagAllRoots);
}
{
// TODO: don't visit the transaction roots if it's not active.
TimingLogger::ScopedTiming split2("VisitNonThreadRoots", GetTimings());
CaptureRootsForMarkingVisitor visitor(this, self);
Runtime::Current()->VisitNonThreadRoots(&visitor);
}
// Capture thread roots
CaptureThreadRootsForMarking();
// Process mark stack
ProcessMarkStackForMarkingAndComputeLiveBytes();
if (kVerboseMode) {
LOG(INFO) << "GC end of MarkingPhase";
}
}
template <bool kNoUnEvac>
void ConcurrentCopying::ScanDirtyObject(mirror::Object* obj) {
Scan<kNoUnEvac>(obj);
// Set the read-barrier state of a reference-type object to gray if its
// referent is not marked yet. This is to ensure that if GetReferent() is
// called, it triggers the read-barrier to process the referent before use.
if (UNLIKELY((obj->GetClass<kVerifyNone, kWithoutReadBarrier>()->IsTypeOfReferenceClass()))) {
mirror::Object* referent =
obj->AsReference<kVerifyNone, kWithoutReadBarrier>()->GetReferent<kWithoutReadBarrier>();
if (referent != nullptr && !IsInToSpace(referent)) {
obj->AtomicSetReadBarrierState(ReadBarrier::NonGrayState(), ReadBarrier::GrayState());
}
}
}
// Concurrently mark roots that are guarded by read barriers and process the mark stack.
void ConcurrentCopying::CopyingPhase() {
TimingLogger::ScopedTiming split("CopyingPhase", GetTimings());
if (kVerboseMode) {
LOG(INFO) << "GC CopyingPhase";
}
Thread* self = Thread::Current();
accounting::CardTable* const card_table = heap_->GetCardTable();
if (kIsDebugBuild) {
MutexLock mu(self, *Locks::thread_list_lock_);
CHECK(weak_ref_access_enabled_);
}
// Scan immune spaces.
// Update all the fields in the immune spaces first without graying the objects so that we
// minimize dirty pages in the immune spaces. Note mutators can concurrently access and gray some
// of the objects.
if (kUseBakerReadBarrier) {
gc_grays_immune_objects_ = false;
}
if (use_generational_cc_) {
if (kVerboseMode) {
LOG(INFO) << "GC ScanCardsForSpace";
}
TimingLogger::ScopedTiming split2("ScanCardsForSpace", GetTimings());
WriterMutexLock rmu(Thread::Current(), *Locks::heap_bitmap_lock_);
CHECK(!done_scanning_.load(std::memory_order_relaxed));
if (kIsDebugBuild) {
// Leave some time for mutators to race ahead to try and find races between the GC card
// scanning and mutators reading references.
usleep(10 * 1000);
}
for (space::ContinuousSpace* space : GetHeap()->GetContinuousSpaces()) {
if (space->IsImageSpace() || space->IsZygoteSpace()) {
// Image and zygote spaces are already handled since we gray the objects in the pause.
continue;
}
// Scan all of the objects on dirty cards in unevac from space, and non moving space. These
// are from previous GCs (or from marking phase of 2-phase full GC) and may reference things
// in the from space.
//
// Note that we do not need to process the large-object space (the only discontinuous space)
// as it contains only large string objects and large primitive array objects, that have no
// reference to other objects, except their class. There is no need to scan these large
// objects, as the String class and the primitive array classes are expected to never move
// during a collection:
// - In the case where we run with a boot image, these classes are part of the image space,
// which is an immune space.
// - In the case where we run without a boot image, these classes are allocated in the
// non-moving space (see art::ClassLinker::InitWithoutImage).
card_table->Scan<false>(
space->GetMarkBitmap(),
space->Begin(),
space->End(),
[this, space](mirror::Object* obj)
REQUIRES(Locks::heap_bitmap_lock_)
REQUIRES_SHARED(Locks::mutator_lock_) {
// TODO: This code may be refactored to avoid scanning object while
// done_scanning_ is false by setting rb_state to gray, and pushing the
// object on mark stack. However, it will also require clearing the
// corresponding mark-bit and, for region space objects,
// decrementing the object's size from the corresponding region's
// live_bytes.
if (young_gen_) {
// Don't push or gray unevac refs.
if (kIsDebugBuild && space == region_space_) {
// We may get unevac large objects.
if (!region_space_->IsInUnevacFromSpace(obj)) {
CHECK(region_space_bitmap_->Test(obj));
region_space_->DumpRegionForObject(LOG_STREAM(FATAL_WITHOUT_ABORT), obj);
LOG(FATAL) << "Scanning " << obj << " not in unevac space";
}
}
ScanDirtyObject</*kNoUnEvac*/ true>(obj);
} else if (space != region_space_) {
DCHECK(space == heap_->non_moving_space_);
// We need to process un-evac references as they may be unprocessed,
// if they skipped the marking phase due to heap mutation.
ScanDirtyObject</*kNoUnEvac*/ false>(obj);
non_moving_space_inter_region_bitmap_->Clear(obj);
} else if (region_space_->IsInUnevacFromSpace(obj)) {
ScanDirtyObject</*kNoUnEvac*/ false>(obj);
region_space_inter_region_bitmap_->Clear(obj);
}
},
accounting::CardTable::kCardAged);
if (!young_gen_) {
auto visitor = [this](mirror::Object* obj) REQUIRES_SHARED(Locks::mutator_lock_) {
// We don't need to process un-evac references as any unprocessed
// ones will be taken care of in the card-table scan above.
ScanDirtyObject</*kNoUnEvac*/ true>(obj);
};
if (space == region_space_) {
region_space_->ScanUnevacFromSpace(region_space_inter_region_bitmap_.get(), visitor);
} else {
DCHECK(space == heap_->non_moving_space_);
non_moving_space_inter_region_bitmap_->VisitMarkedRange(
reinterpret_cast<uintptr_t>(space->Begin()),
reinterpret_cast<uintptr_t>(space->End()),
visitor);
}
}
}
// Done scanning unevac space.
done_scanning_.store(true, std::memory_order_release);
// NOTE: inter-region-ref bitmaps can be cleared here to release memory, if needed.
// Currently we do it in ReclaimPhase().
if (kVerboseMode) {
LOG(INFO) << "GC end of ScanCardsForSpace";
}
}
{
// For a sticky-bit collection, this phase needs to be after the card scanning since the
// mutator may read an unevac space object out of an image object. If the image object is no
// longer gray it will trigger a read barrier for the unevac space object.
TimingLogger::ScopedTiming split2("ScanImmuneSpaces", GetTimings());
for (auto& space : immune_spaces_.GetSpaces()) {
DCHECK(space->IsImageSpace() || space->IsZygoteSpace());
accounting::ContinuousSpaceBitmap* live_bitmap = space->GetLiveBitmap();
accounting::ModUnionTable* table = heap_->FindModUnionTableFromSpace(space);
ImmuneSpaceScanObjVisitor visitor(this);
if (kUseBakerReadBarrier && kGrayDirtyImmuneObjects && table != nullptr) {
table->VisitObjects(ImmuneSpaceScanObjVisitor::Callback, &visitor);
} else {
WriterMutexLock rmu(Thread::Current(), *Locks::heap_bitmap_lock_);
card_table->Scan<false>(
live_bitmap,
space->Begin(),
space->Limit(),
visitor,
accounting::CardTable::kCardDirty - 1);
}
}
}
if (kUseBakerReadBarrier) {
// This release fence makes the field updates in the above loop visible before allowing mutator
// getting access to immune objects without graying it first.
updated_all_immune_objects_.store(true, std::memory_order_release);
// Now "un-gray" (conceptually blacken) immune objects concurrently accessed and grayed by
// mutators. We can't do this in the above loop because we would incorrectly disable the read
// barrier by un-graying (conceptually blackening) an object which may point to an unscanned,
// white object, breaking the to-space invariant (a mutator shall never observe a from-space
// (white) object).
//
// Make sure no mutators are in the middle of marking an immune object before un-graying
// (blackening) immune objects.
IssueEmptyCheckpoint();
MutexLock mu(Thread::Current(), immune_gray_stack_lock_);
if (kVerboseMode) {
LOG(INFO) << "immune gray stack size=" << immune_gray_stack_.size();
}
for (mirror::Object* obj : immune_gray_stack_) {
DCHECK_EQ(obj->GetReadBarrierState(), ReadBarrier::GrayState());
bool success = obj->AtomicSetReadBarrierState(ReadBarrier::GrayState(),
ReadBarrier::NonGrayState());
DCHECK(success);
}
immune_gray_stack_.clear();
}
{
TimingLogger::ScopedTiming split2("VisitConcurrentRoots", GetTimings());
Runtime::Current()->VisitConcurrentRoots(this, kVisitRootFlagAllRoots);
}
{
// TODO: don't visit the transaction roots if it's not active.
TimingLogger::ScopedTiming split5("VisitNonThreadRoots", GetTimings());
Runtime::Current()->VisitNonThreadRoots(this);
}
{
TimingLogger::ScopedTiming split7("ProcessMarkStack", GetTimings());
// We transition through three mark stack modes (thread-local, shared, GC-exclusive). The
// primary reasons are the fact that we need to use a checkpoint to process thread-local mark
// stacks, but after we disable weak refs accesses, we can't use a checkpoint due to a deadlock
// issue because running threads potentially blocking at WaitHoldingLocks, and that once we
// reach the point where we process weak references, we can avoid using a lock when accessing
// the GC mark stack, which makes mark stack processing more efficient.
// Process the mark stack once in the thread local stack mode. This marks most of the live
// objects, aside from weak ref accesses with read barriers (Reference::GetReferent() and system
// weaks) that may happen concurrently while we processing the mark stack and newly mark/gray
// objects and push refs on the mark stack.
ProcessMarkStack();
// Switch to the shared mark stack mode. That is, revoke and process thread-local mark stacks
// for the last time before transitioning to the shared mark stack mode, which would process new
// refs that may have been concurrently pushed onto the mark stack during the ProcessMarkStack()
// call above. At the same time, disable weak ref accesses using a per-thread flag. It's
// important to do these together in a single checkpoint so that we can ensure that mutators
// won't newly gray objects and push new refs onto the mark stack due to weak ref accesses and
// mutators safely transition to the shared mark stack mode (without leaving unprocessed refs on
// the thread-local mark stacks), without a race. This is why we use a thread-local weak ref
// access flag Thread::tls32_.weak_ref_access_enabled_ instead of the global ones.
SwitchToSharedMarkStackMode();
CHECK(!self->GetWeakRefAccessEnabled());
// Now that weak refs accesses are disabled, once we exhaust the shared mark stack again here
// (which may be non-empty if there were refs found on thread-local mark stacks during the above
// SwitchToSharedMarkStackMode() call), we won't have new refs to process, that is, mutators
// (via read barriers) have no way to produce any more refs to process. Marking converges once
// before we process weak refs below.
ProcessMarkStack();
CheckEmptyMarkStack();
// Switch to the GC exclusive mark stack mode so that we can process the mark stack without a
// lock from this point on.
SwitchToGcExclusiveMarkStackMode();
CheckEmptyMarkStack();
if (kVerboseMode) {
LOG(INFO) << "ProcessReferences";
}
// Process weak references. This may produce new refs to process and have them processed via
// ProcessMarkStack (in the GC exclusive mark stack mode).
ProcessReferences(self);
CheckEmptyMarkStack();
if (kVerboseMode) {
LOG(INFO) << "SweepSystemWeaks";
}
SweepSystemWeaks(self);
if (kVerboseMode) {
LOG(INFO) << "SweepSystemWeaks done";
}
// Process the mark stack here one last time because the above SweepSystemWeaks() call may have
// marked some objects (strings alive) as hash_set::Erase() can call the hash function for
// arbitrary elements in the weak intern table in InternTable::Table::SweepWeaks().
ProcessMarkStack();
CheckEmptyMarkStack();
// Re-enable weak ref accesses.
ReenableWeakRefAccess(self);
// Free data for class loaders that we unloaded.
Runtime::Current()->GetClassLinker()->CleanupClassLoaders();
// Marking is done. Disable marking.
DisableMarking();
CheckEmptyMarkStack();
}
if (kIsDebugBuild) {
MutexLock mu(self, *Locks::thread_list_lock_);
CHECK(weak_ref_access_enabled_);
}
if (kVerboseMode) {
LOG(INFO) << "GC end of CopyingPhase";
}
}
void ConcurrentCopying::ReenableWeakRefAccess(Thread* self) {
if (kVerboseMode) {
LOG(INFO) << "ReenableWeakRefAccess";
}
// Iterate all threads (don't need to or can't use a checkpoint) and re-enable weak ref access.
{
MutexLock mu(self, *Locks::thread_list_lock_);
weak_ref_access_enabled_ = true; // This is for new threads.
std::list<Thread*> thread_list = Runtime::Current()->GetThreadList()->GetList();
for (Thread* thread : thread_list) {
thread->SetWeakRefAccessEnabled(true);
}
}
// Unblock blocking threads.
GetHeap()->GetReferenceProcessor()->BroadcastForSlowPath(self);
Runtime::Current()->BroadcastForNewSystemWeaks();
}
class ConcurrentCopying::DisableMarkingCheckpoint : public Closure {
public:
explicit DisableMarkingCheckpoint(ConcurrentCopying* concurrent_copying)
: concurrent_copying_(concurrent_copying) {
}
void Run(Thread* thread) override NO_THREAD_SAFETY_ANALYSIS {
// Note: self is not necessarily equal to thread since thread may be suspended.
Thread* self = Thread::Current();
DCHECK(thread == self || thread->IsSuspended() || thread->GetState() == kWaitingPerformingGc)
<< thread->GetState() << " thread " << thread << " self " << self;
// Disable the thread-local is_gc_marking flag.
// Note a thread that has just started right before this checkpoint may have already this flag
// set to false, which is ok.
thread->SetIsGcMarkingAndUpdateEntrypoints(false);
// If thread is a running mutator, then act on behalf of the garbage collector.
// See the code in ThreadList::RunCheckpoint.
concurrent_copying_->GetBarrier().Pass(self);
}
private:
ConcurrentCopying* const concurrent_copying_;
};
class ConcurrentCopying::DisableMarkingCallback : public Closure {
public:
explicit DisableMarkingCallback(ConcurrentCopying* concurrent_copying)
: concurrent_copying_(concurrent_copying) {
}
void Run(Thread* self ATTRIBUTE_UNUSED) override REQUIRES(Locks::thread_list_lock_) {
// This needs to run under the thread_list_lock_ critical section in ThreadList::RunCheckpoint()
// to avoid a race with ThreadList::Register().
CHECK(concurrent_copying_->is_marking_);
concurrent_copying_->is_marking_ = false;
if (kUseBakerReadBarrier && kGrayDirtyImmuneObjects) {
CHECK(concurrent_copying_->is_using_read_barrier_entrypoints_);
concurrent_copying_->is_using_read_barrier_entrypoints_ = false;
} else {
CHECK(!concurrent_copying_->is_using_read_barrier_entrypoints_);
}
}
private:
ConcurrentCopying* const concurrent_copying_;
};
void ConcurrentCopying::IssueDisableMarkingCheckpoint() {
Thread* self = Thread::Current();
DisableMarkingCheckpoint check_point(this);
ThreadList* thread_list = Runtime::Current()->GetThreadList();
gc_barrier_->Init(self, 0);
DisableMarkingCallback dmc(this);
size_t barrier_count = thread_list->RunCheckpoint(&check_point, &dmc);
// If there are no threads to wait which implies that all the checkpoint functions are finished,
// then no need to release the mutator lock.
if (barrier_count == 0) {
return;
}
// Release locks then wait for all mutator threads to pass the barrier.
Locks::mutator_lock_->SharedUnlock(self);
{
ScopedThreadStateChange tsc(self, kWaitingForCheckPointsToRun);
gc_barrier_->Increment(self, barrier_count);
}
Locks::mutator_lock_->SharedLock(self);
}
void ConcurrentCopying::DisableMarking() {
// Use a checkpoint to turn off the global is_marking and the thread-local is_gc_marking flags and
// to ensure no threads are still in the middle of a read barrier which may have a from-space ref
// cached in a local variable.
IssueDisableMarkingCheckpoint();
if (kUseTableLookupReadBarrier) {
heap_->rb_table_->ClearAll();
DCHECK(heap_->rb_table_->IsAllCleared());
}
is_mark_stack_push_disallowed_.store(1, std::memory_order_seq_cst);
mark_stack_mode_.store(kMarkStackModeOff, std::memory_order_seq_cst);
}
void ConcurrentCopying::IssueEmptyCheckpoint() {
Thread* self = Thread::Current();
ThreadList* thread_list = Runtime::Current()->GetThreadList();
// Release locks then wait for all mutator threads to pass the barrier.
Locks::mutator_lock_->SharedUnlock(self);
thread_list->RunEmptyCheckpoint();
Locks::mutator_lock_->SharedLock(self);
}
void ConcurrentCopying::ExpandGcMarkStack() {
DCHECK(gc_mark_stack_->IsFull());
const size_t new_size = gc_mark_stack_->Capacity() * 2;
std::vector<StackReference<mirror::Object>> temp(gc_mark_stack_->Begin(),
gc_mark_stack_->End());
gc_mark_stack_->Resize(new_size);
for (auto& ref : temp) {
gc_mark_stack_->PushBack(ref.AsMirrorPtr());
}
DCHECK(!gc_mark_stack_->IsFull());
}
void ConcurrentCopying::PushOntoMarkStack(Thread* const self, mirror::Object* to_ref) {
CHECK_EQ(is_mark_stack_push_disallowed_.load(std::memory_order_relaxed), 0)
<< " " << to_ref << " " << mirror::Object::PrettyTypeOf(to_ref);
CHECK(thread_running_gc_ != nullptr);
MarkStackMode mark_stack_mode = mark_stack_mode_.load(std::memory_order_relaxed);
if (LIKELY(mark_stack_mode == kMarkStackModeThreadLocal)) {
if (LIKELY(self == thread_running_gc_)) {
// If GC-running thread, use the GC mark stack instead of a thread-local mark stack.
CHECK(self->GetThreadLocalMarkStack() == nullptr);
if (UNLIKELY(gc_mark_stack_->IsFull())) {
ExpandGcMarkStack();
}
gc_mark_stack_->PushBack(to_ref);
} else {
// Otherwise, use a thread-local mark stack.
accounting::AtomicStack<mirror::Object>* tl_mark_stack = self->GetThreadLocalMarkStack();
if (UNLIKELY(tl_mark_stack == nullptr || tl_mark_stack->IsFull())) {
MutexLock mu(self, mark_stack_lock_);
// Get a new thread local mark stack.
accounting::AtomicStack<mirror::Object>* new_tl_mark_stack;
if (!pooled_mark_stacks_.empty()) {
// Use a pooled mark stack.
new_tl_mark_stack = pooled_mark_stacks_.back();
pooled_mark_stacks_.pop_back();
} else {
// None pooled. Create a new one.
new_tl_mark_stack =
accounting::AtomicStack<mirror::Object>::Create(
"thread local mark stack", 4 * KB, 4 * KB);
}
DCHECK(new_tl_mark_stack != nullptr);
DCHECK(new_tl_mark_stack->IsEmpty());
new_tl_mark_stack->PushBack(to_ref);
self->SetThreadLocalMarkStack(new_tl_mark_stack);
if (tl_mark_stack != nullptr) {
// Store the old full stack into a vector.
revoked_mark_stacks_.push_back(tl_mark_stack);
}
} else {
tl_mark_stack->PushBack(to_ref);
}
}
} else if (mark_stack_mode == kMarkStackModeShared) {
// Access the shared GC mark stack with a lock.
MutexLock mu(self, mark_stack_lock_);
if (UNLIKELY(gc_mark_stack_->IsFull())) {
ExpandGcMarkStack();
}
gc_mark_stack_->PushBack(to_ref);
} else {
CHECK_EQ(static_cast<uint32_t>(mark_stack_mode),
static_cast<uint32_t>(kMarkStackModeGcExclusive))
<< "ref=" << to_ref
<< " self->gc_marking=" << self->GetIsGcMarking()
<< " cc->is_marking=" << is_marking_;
CHECK(self == thread_running_gc_)
<< "Only GC-running thread should access the mark stack "
<< "in the GC exclusive mark stack mode";
// Access the GC mark stack without a lock.
if (UNLIKELY(gc_mark_stack_->IsFull())) {
ExpandGcMarkStack();
}
gc_mark_stack_->PushBack(to_ref);
}
}
accounting::ObjectStack* ConcurrentCopying::GetAllocationStack() {
return heap_->allocation_stack_.get();
}
accounting::ObjectStack* ConcurrentCopying::GetLiveStack() {
return heap_->live_stack_.get();
}
// The following visitors are used to verify that there's no references to the from-space left after
// marking.
class ConcurrentCopying::VerifyNoFromSpaceRefsVisitor : public SingleRootVisitor {
public:
explicit VerifyNoFromSpaceRefsVisitor(ConcurrentCopying* collector)
: collector_(collector) {}
void operator()(mirror::Object* ref,
MemberOffset offset = MemberOffset(0),
mirror::Object* holder = nullptr) const
REQUIRES_SHARED(Locks::mutator_lock_) ALWAYS_INLINE {
if (ref == nullptr) {
// OK.
return;
}
collector_->AssertToSpaceInvariant(holder, offset, ref);
if (kUseBakerReadBarrier) {
CHECK_EQ(ref->GetReadBarrierState(), ReadBarrier::NonGrayState())
<< "Ref " << ref << " " << ref->PrettyTypeOf() << " has gray rb_state";
}
}
void VisitRoot(mirror::Object* root, const RootInfo& info ATTRIBUTE_UNUSED)
override REQUIRES_SHARED(Locks::mutator_lock_) {
DCHECK(root != nullptr);
operator()(root);
}
private:
ConcurrentCopying* const collector_;
};
class ConcurrentCopying::VerifyNoFromSpaceRefsFieldVisitor {
public:
explicit VerifyNoFromSpaceRefsFieldVisitor(ConcurrentCopying* collector)
: collector_(collector) {}
void operator()(ObjPtr<mirror::Object> obj,
MemberOffset offset,
bool is_static ATTRIBUTE_UNUSED) const
REQUIRES_SHARED(Locks::mutator_lock_) ALWAYS_INLINE {
mirror::Object* ref =
obj->GetFieldObject<mirror::Object, kDefaultVerifyFlags, kWithoutReadBarrier>(offset);
VerifyNoFromSpaceRefsVisitor visitor(collector_);
visitor(ref, offset, obj.Ptr());
}
void operator()(ObjPtr<mirror::Class> klass,
ObjPtr<mirror::Reference> ref) const
REQUIRES_SHARED(Locks::mutator_lock_) ALWAYS_INLINE {
CHECK(klass->IsTypeOfReferenceClass());
this->operator()(ref, mirror::Reference::ReferentOffset(), false);
}
void VisitRootIfNonNull(mirror::CompressedReference<mirror::Object>* root) const
REQUIRES_SHARED(Locks::mutator_lock_) {
if (!root->IsNull()) {
VisitRoot(root);
}
}
void VisitRoot(mirror::CompressedReference<mirror::Object>* root) const
REQUIRES_SHARED(Locks::mutator_lock_) {
VerifyNoFromSpaceRefsVisitor visitor(collector_);
visitor(root->AsMirrorPtr());
}
private:
ConcurrentCopying* const collector_;
};
// Verify there's no from-space references left after the marking phase.
void ConcurrentCopying::VerifyNoFromSpaceReferences() {
Thread* self = Thread::Current();
DCHECK(Locks::mutator_lock_->IsExclusiveHeld(self));
// Verify all threads have is_gc_marking to be false
{
MutexLock mu(self, *Locks::thread_list_lock_);
std::list<Thread*> thread_list = Runtime::Current()->GetThreadList()->GetList();
for (Thread* thread : thread_list) {
CHECK(!thread->GetIsGcMarking());
}
}
auto verify_no_from_space_refs_visitor = [&](mirror::Object* obj)
REQUIRES_SHARED(Locks::mutator_lock_) {
CHECK(obj != nullptr);
space::RegionSpace* region_space = RegionSpace();
CHECK(!region_space->IsInFromSpace(obj)) << "Scanning object " << obj << " in from space";
VerifyNoFromSpaceRefsFieldVisitor visitor(this);
obj->VisitReferences</*kVisitNativeRoots=*/true, kDefaultVerifyFlags, kWithoutReadBarrier>(
visitor,
visitor);
if (kUseBakerReadBarrier) {
CHECK_EQ(obj->GetReadBarrierState(), ReadBarrier::NonGrayState())
<< "obj=" << obj << " has gray rb_state " << obj->GetReadBarrierState();
}
};
// Roots.
{
ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
VerifyNoFromSpaceRefsVisitor ref_visitor(this);
Runtime::Current()->VisitRoots(&ref_visitor);
}
// The to-space.
region_space_->WalkToSpace(verify_no_from_space_refs_visitor);
// Non-moving spaces.
{
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
heap_->GetMarkBitmap()->Visit(verify_no_from_space_refs_visitor);
}
// The alloc stack.
{
VerifyNoFromSpaceRefsVisitor ref_visitor(this);
for (auto* it = heap_->allocation_stack_->Begin(), *end = heap_->allocation_stack_->End();
it < end; ++it) {
mirror::Object* const obj = it->AsMirrorPtr();
if (obj != nullptr && obj->GetClass() != nullptr) {
// TODO: need to call this only if obj is alive?
ref_visitor(obj);
verify_no_from_space_refs_visitor(obj);
}
}
}
// TODO: LOS. But only refs in LOS are classes.
}
// The following visitors are used to assert the to-space invariant.
class ConcurrentCopying::AssertToSpaceInvariantFieldVisitor {
public:
explicit AssertToSpaceInvariantFieldVisitor(ConcurrentCopying* collector)
: collector_(collector) {}
void operator()(ObjPtr<mirror::Object> obj,
MemberOffset offset,
bool is_static ATTRIBUTE_UNUSED) const
REQUIRES_SHARED(Locks::mutator_lock_) ALWAYS_INLINE {
mirror::Object* ref =
obj->GetFieldObject<mirror::Object, kDefaultVerifyFlags, kWithoutReadBarrier>(offset);
collector_->AssertToSpaceInvariant(obj.Ptr(), offset, ref);
}
void operator()(ObjPtr<mirror::Class> klass, ObjPtr<mirror::Reference> ref ATTRIBUTE_UNUSED) const
REQUIRES_SHARED(Locks::mutator_lock_) ALWAYS_INLINE {
CHECK(klass->IsTypeOfReferenceClass());
}
void VisitRootIfNonNull(mirror::CompressedReference<mirror::Object>* root) const
REQUIRES_SHARED(Locks::mutator_lock_) {
if (!root->IsNull()) {
VisitRoot(root);
}
}
void VisitRoot(mirror::CompressedReference<mirror::Object>* root) const
REQUIRES_SHARED(Locks::mutator_lock_) {
mirror::Object* ref = root->AsMirrorPtr();
collector_->AssertToSpaceInvariant(/* obj */ nullptr, MemberOffset(0), ref);
}
private:
ConcurrentCopying* const collector_;
};
void ConcurrentCopying::RevokeThreadLocalMarkStacks(bool disable_weak_ref_access,
Closure* checkpoint_callback) {
Thread* self = Thread::Current();
RevokeThreadLocalMarkStackCheckpoint check_point(this, disable_weak_ref_access);
ThreadList* thread_list = Runtime::Current()->GetThreadList();
gc_barrier_->Init(self, 0);
size_t barrier_count = thread_list->RunCheckpoint(&check_point, checkpoint_callback);
// If there are no threads to wait which implys that all the checkpoint functions are finished,
// then no need to release the mutator lock.
if (barrier_count == 0) {
return;
}
Locks::mutator_lock_->SharedUnlock(self);
{
ScopedThreadStateChange tsc(self, kWaitingForCheckPointsToRun);
gc_barrier_->Increment(self, barrier_count);
}
Locks::mutator_lock_->SharedLock(self);
}
void ConcurrentCopying::RevokeThreadLocalMarkStack(Thread* thread) {
Thread* self = Thread::Current();
CHECK_EQ(self, thread);
accounting::AtomicStack<mirror::Object>* tl_mark_stack = thread->GetThreadLocalMarkStack();
if (tl_mark_stack != nullptr) {
CHECK(is_marking_);
MutexLock mu(self, mark_stack_lock_);
revoked_mark_stacks_.push_back(tl_mark_stack);
thread->SetThreadLocalMarkStack(nullptr);
}
}
void ConcurrentCopying::ProcessMarkStack() {
if (kVerboseMode) {
LOG(INFO) << "ProcessMarkStack. ";
}
bool empty_prev = false;
while (true) {
bool empty = ProcessMarkStackOnce();
if (empty_prev && empty) {
// Saw empty mark stack for a second time, done.
break;
}
empty_prev = empty;
}
}
bool ConcurrentCopying::ProcessMarkStackOnce() {
DCHECK(thread_running_gc_ != nullptr);
Thread* const self = Thread::Current();
DCHECK(self == thread_running_gc_);
DCHECK(thread_running_gc_->GetThreadLocalMarkStack() == nullptr);
size_t count = 0;
MarkStackMode mark_stack_mode = mark_stack_mode_.load(std::memory_order_relaxed);
if (mark_stack_mode == kMarkStackModeThreadLocal) {
// Process the thread-local mark stacks and the GC mark stack.
count += ProcessThreadLocalMarkStacks(/* disable_weak_ref_access= */ false,
/* checkpoint_callback= */ nullptr,
[this] (mirror::Object* ref)
REQUIRES_SHARED(Locks::mutator_lock_) {
ProcessMarkStackRef(ref);
});
while (!gc_mark_stack_->IsEmpty()) {
mirror::Object* to_ref = gc_mark_stack_->PopBack();
ProcessMarkStackRef(to_ref);
++count;
}
gc_mark_stack_->Reset();
} else if (mark_stack_mode == kMarkStackModeShared) {
// Do an empty checkpoint to avoid a race with a mutator preempted in the middle of a read
// barrier but before pushing onto the mark stack. b/32508093. Note the weak ref access is
// disabled at this point.
IssueEmptyCheckpoint();
// Process the shared GC mark stack with a lock.
{
MutexLock mu(thread_running_gc_, mark_stack_lock_);
CHECK(revoked_mark_stacks_.empty());
}
while (true) {
std::vector<mirror::Object*> refs;
{
// Copy refs with lock. Note the number of refs should be small.
MutexLock mu(thread_running_gc_, mark_stack_lock_);
if (gc_mark_stack_->IsEmpty()) {
break;
}
for (StackReference<mirror::Object>* p = gc_mark_stack_->Begin();
p != gc_mark_stack_->End(); ++p) {
refs.push_back(p->AsMirrorPtr());
}
gc_mark_stack_->Reset();
}
for (mirror::Object* ref : refs) {
ProcessMarkStackRef(ref);
++count;
}
}
} else {
CHECK_EQ(static_cast<uint32_t>(mark_stack_mode),
static_cast<uint32_t>(kMarkStackModeGcExclusive));
{
MutexLock mu(thread_running_gc_, mark_stack_lock_);
CHECK(revoked_mark_stacks_.empty());
}
// Process the GC mark stack in the exclusive mode. No need to take the lock.
while (!gc_mark_stack_->IsEmpty()) {
mirror::Object* to_ref = gc_mark_stack_->PopBack();
ProcessMarkStackRef(to_ref);
++count;
}
gc_mark_stack_->Reset();
}
// Return true if the stack was empty.
return count == 0;
}
template <typename Processor>
size_t ConcurrentCopying::ProcessThreadLocalMarkStacks(bool disable_weak_ref_access,
Closure* checkpoint_callback,
const Processor& processor) {
// Run a checkpoint to collect all thread local mark stacks and iterate over them all.
RevokeThreadLocalMarkStacks(disable_weak_ref_access, checkpoint_callback);
size_t count = 0;
std::vector<accounting::AtomicStack<mirror::Object>*> mark_stacks;
{
MutexLock mu(thread_running_gc_, mark_stack_lock_);
// Make a copy of the mark stack vector.
mark_stacks = revoked_mark_stacks_;
revoked_mark_stacks_.clear();
}
for (accounting::AtomicStack<mirror::Object>* mark_stack : mark_stacks) {
for (StackReference<mirror::Object>* p = mark_stack->Begin(); p != mark_stack->End(); ++p) {
mirror::Object* to_ref = p->AsMirrorPtr();
processor(to_ref);
++count;
}
{
MutexLock mu(thread_running_gc_, mark_stack_lock_);
if (pooled_mark_stacks_.size() >= kMarkStackPoolSize) {
// The pool has enough. Delete it.
delete mark_stack;
} else {
// Otherwise, put it into the pool for later reuse.
mark_stack->Reset();
pooled_mark_stacks_.push_back(mark_stack);
}
}
}
return count;
}
inline void ConcurrentCopying::ProcessMarkStackRef(mirror::Object* to_ref) {
DCHECK(!region_space_->IsInFromSpace(to_ref));
space::RegionSpace::RegionType rtype = region_space_->GetRegionType(to_ref);
if (kUseBakerReadBarrier) {
DCHECK(to_ref->GetReadBarrierState() == ReadBarrier::GrayState())
<< " to_ref=" << to_ref
<< " rb_state=" << to_ref->GetReadBarrierState()
<< " is_marked=" << IsMarked(to_ref)
<< " type=" << to_ref->PrettyTypeOf()
<< " young_gen=" << std::boolalpha << young_gen_ << std::noboolalpha
<< " space=" << heap_->DumpSpaceNameFromAddress(to_ref)
<< " region_type=" << rtype
// TODO: Temporary; remove this when this is no longer needed (b/116087961).
<< " runtime->sentinel=" << Runtime::Current()->GetSentinel().Read<kWithoutReadBarrier>();
}
bool add_to_live_bytes = false;
// Invariant: There should be no object from a newly-allocated
// region (either large or non-large) on the mark stack.
DCHECK(!region_space_->IsInNewlyAllocatedRegion(to_ref)) << to_ref;
bool perform_scan = false;
switch (rtype) {
case space::RegionSpace::RegionType::kRegionTypeUnevacFromSpace:
// Mark the bitmap only in the GC thread here so that we don't need a CAS.
if (!kUseBakerReadBarrier || !region_space_bitmap_->Set(to_ref)) {
// It may be already marked if we accidentally pushed the same object twice due to the racy
// bitmap read in MarkUnevacFromSpaceRegion.
if (use_generational_cc_ && young_gen_) {
CHECK(region_space_->IsLargeObject(to_ref));
region_space_->ZeroLiveBytesForLargeObject(to_ref);
}
perform_scan = true;
// Only add to the live bytes if the object was not already marked and we are not the young
// GC.
// Why add live bytes even after 2-phase GC?
// We need to ensure that if there is a unevac region with any live
// objects, then its live_bytes must be non-zero. Otherwise,
// ClearFromSpace() will clear the region. Considering, that we may skip
// live objects during marking phase of 2-phase GC, we have to take care
// of such objects here.
add_to_live_bytes = true;
}
break;
case space::RegionSpace::RegionType::kRegionTypeToSpace:
if (use_generational_cc_) {
// Copied to to-space, set the bit so that the next GC can scan objects.
region_space_bitmap_->Set(to_ref);
}
perform_scan = true;
break;
default:
DCHECK(!region_space_->HasAddress(to_ref)) << to_ref;
DCHECK(!immune_spaces_.ContainsObject(to_ref));
// Non-moving or large-object space.
if (kUseBakerReadBarrier) {
accounting::ContinuousSpaceBitmap* mark_bitmap =
heap_->GetNonMovingSpace()->GetMarkBitmap();
const bool is_los = !mark_bitmap->HasAddress(to_ref);
if (is_los) {
if (!IsAligned<kPageSize>(to_ref)) {
// Ref is a large object that is not aligned, it must be heap
// corruption. Remove memory protection and dump data before
// AtomicSetReadBarrierState since it will fault if the address is not
// valid.
region_space_->Unprotect();
heap_->GetVerification()->LogHeapCorruption(/* obj */ nullptr,
MemberOffset(0),
to_ref,
/* fatal */ true);
}
DCHECK(heap_->GetLargeObjectsSpace())
<< "ref=" << to_ref
<< " doesn't belong to non-moving space and large object space doesn't exist";
accounting::LargeObjectBitmap* los_bitmap =
heap_->GetLargeObjectsSpace()->GetMarkBitmap();
DCHECK(los_bitmap->HasAddress(to_ref));
// Only the GC thread could be setting the LOS bit map hence doesn't
// need to be atomically done.
perform_scan = !los_bitmap->Set(to_ref);
} else {
// Only the GC thread could be setting the non-moving space bit map
// hence doesn't need to be atomically done.
perform_scan = !mark_bitmap->Set(to_ref);
}
} else {
perform_scan = true;
}
}
if (perform_scan) {
if (use_generational_cc_ && young_gen_) {
Scan<true>(to_ref);
} else {
Scan<false>(to_ref);
}
}
if (kUseBakerReadBarrier) {
DCHECK(to_ref->GetReadBarrierState() == ReadBarrier::GrayState())
<< " to_ref=" << to_ref
<< " rb_state=" << to_ref->GetReadBarrierState()
<< " is_marked=" << IsMarked(to_ref)
<< " type=" << to_ref->PrettyTypeOf()
<< " young_gen=" << std::boolalpha << young_gen_ << std::noboolalpha
<< " space=" << heap_->DumpSpaceNameFromAddress(to_ref)
<< " region_type=" << rtype
// TODO: Temporary; remove this when this is no longer needed (b/116087961).
<< " runtime->sentinel=" << Runtime::Current()->GetSentinel().Read<kWithoutReadBarrier>();
}
#ifdef USE_BAKER_OR_BROOKS_READ_BARRIER
mirror::Object* referent = nullptr;
if (UNLIKELY((to_ref->GetClass<kVerifyNone, kWithoutReadBarrier>()->IsTypeOfReferenceClass() &&
(referent = to_ref->AsReference()->GetReferent<kWithoutReadBarrier>()) != nullptr &&
!IsInToSpace(referent)))) {
// Leave this reference gray in the queue so that GetReferent() will trigger a read barrier. We
// will change it to non-gray later in ReferenceQueue::DisableReadBarrierForReference.
DCHECK(to_ref->AsReference()->GetPendingNext() != nullptr)
<< "Left unenqueued ref gray " << to_ref;
} else {
// We may occasionally leave a reference non-gray in the queue if its referent happens to be
// concurrently marked after the Scan() call above has enqueued the Reference, in which case the
// above IsInToSpace() evaluates to true and we change the color from gray to non-gray here in
// this else block.
if (kUseBakerReadBarrier) {
bool success = to_ref->AtomicSetReadBarrierState<std::memory_order_release>(
ReadBarrier::GrayState(),
ReadBarrier::NonGrayState());
DCHECK(success) << "Must succeed as we won the race.";
}
}
#else
DCHECK(!kUseBakerReadBarrier);
#endif
if (add_to_live_bytes) {
// Add to the live bytes per unevacuated from-space. Note this code is always run by the
// GC-running thread (no synchronization required).
DCHECK(region_space_bitmap_->Test(to_ref));
size_t obj_size = to_ref->SizeOf<kDefaultVerifyFlags>();
size_t alloc_size = RoundUp(obj_size, space::RegionSpace::kAlignment);
region_space_->AddLiveBytes(to_ref, alloc_size);
}
if (ReadBarrier::kEnableToSpaceInvariantChecks) {
CHECK(to_ref != nullptr);
space::RegionSpace* region_space = RegionSpace();
CHECK(!region_space->IsInFromSpace(to_ref)) << "Scanning object " << to_ref << " in from space";
AssertToSpaceInvariant(nullptr, MemberOffset(0), to_ref);
AssertToSpaceInvariantFieldVisitor visitor(this);
to_ref->VisitReferences</*kVisitNativeRoots=*/true, kDefaultVerifyFlags, kWithoutReadBarrier>(
visitor,
visitor);
}
}
class ConcurrentCopying::DisableWeakRefAccessCallback : public Closure {
public:
explicit DisableWeakRefAccessCallback(ConcurrentCopying* concurrent_copying)
: concurrent_copying_(concurrent_copying) {
}
void Run(Thread* self ATTRIBUTE_UNUSED) override REQUIRES(Locks::thread_list_lock_) {
// This needs to run under the thread_list_lock_ critical section in ThreadList::RunCheckpoint()
// to avoid a deadlock b/31500969.
CHECK(concurrent_copying_->weak_ref_access_enabled_);
concurrent_copying_->weak_ref_access_enabled_ = false;
}
private:
ConcurrentCopying* const concurrent_copying_;
};
void ConcurrentCopying::SwitchToSharedMarkStackMode() {
Thread* self = Thread::Current();
DCHECK(thread_running_gc_ != nullptr);
DCHECK(self == thread_running_gc_);
DCHECK(thread_running_gc_->GetThreadLocalMarkStack() == nullptr);
MarkStackMode before_mark_stack_mode = mark_stack_mode_.load(std::memory_order_relaxed);
CHECK_EQ(static_cast<uint32_t>(before_mark_stack_mode),
static_cast<uint32_t>(kMarkStackModeThreadLocal));
mark_stack_mode_.store(kMarkStackModeShared, std::memory_order_relaxed);
DisableWeakRefAccessCallback dwrac(this);
// Process the thread local mark stacks one last time after switching to the shared mark stack
// mode and disable weak ref accesses.
ProcessThreadLocalMarkStacks(/* disable_weak_ref_access= */ true,
&dwrac,
[this] (mirror::Object* ref)
REQUIRES_SHARED(Locks::mutator_lock_) {
ProcessMarkStackRef(ref);
});
if (kVerboseMode) {
LOG(INFO) << "Switched to shared mark stack mode and disabled weak ref access";
}
}
void ConcurrentCopying::SwitchToGcExclusiveMarkStackMode() {
Thread* self = Thread::Current();
DCHECK(thread_running_gc_ != nullptr);
DCHECK(self == thread_running_gc_);
DCHECK(thread_running_gc_->GetThreadLocalMarkStack() == nullptr);
MarkStackMode before_mark_stack_mode = mark_stack_mode_.load(std::memory_order_relaxed);
CHECK_EQ(static_cast<uint32_t>(before_mark_stack_mode),
static_cast<uint32_t>(kMarkStackModeShared));
mark_stack_mode_.store(kMarkStackModeGcExclusive, std::memory_order_relaxed);
QuasiAtomic::ThreadFenceForConstructor();
if (kVerboseMode) {
LOG(INFO) << "Switched to GC exclusive mark stack mode";
}
}
void ConcurrentCopying::CheckEmptyMarkStack() {
Thread* self = Thread::Current();
DCHECK(thread_running_gc_ != nullptr);
DCHECK(self == thread_running_gc_);
DCHECK(thread_running_gc_->GetThreadLocalMarkStack() == nullptr);
MarkStackMode mark_stack_mode = mark_stack_mode_.load(std::memory_order_relaxed);
if (mark_stack_mode == kMarkStackModeThreadLocal) {
// Thread-local mark stack mode.
RevokeThreadLocalMarkStacks(false, nullptr);
MutexLock mu(thread_running_gc_, mark_stack_lock_);
if (!revoked_mark_stacks_.empty()) {
for (accounting::AtomicStack<mirror::Object>* mark_stack : revoked_mark_stacks_) {
while (!mark_stack->IsEmpty()) {
mirror::Object* obj = mark_stack->PopBack();
if (kUseBakerReadBarrier) {
uint32_t rb_state = obj->GetReadBarrierState();
LOG(INFO) << "On mark queue : " << obj << " " << obj->PrettyTypeOf() << " rb_state="
<< rb_state << " is_marked=" << IsMarked(obj);
} else {
LOG(INFO) << "On mark queue : " << obj << " " << obj->PrettyTypeOf()
<< " is_marked=" << IsMarked(obj);
}
}
}
LOG(FATAL) << "mark stack is not empty";
}
} else {
// Shared, GC-exclusive, or off.
MutexLock mu(thread_running_gc_, mark_stack_lock_);
CHECK(gc_mark_stack_->IsEmpty());
CHECK(revoked_mark_stacks_.empty());
}
}
void ConcurrentCopying::SweepSystemWeaks(Thread* self) {
TimingLogger::ScopedTiming split("SweepSystemWeaks", GetTimings());
ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
Runtime::Current()->SweepSystemWeaks(this);
}
void ConcurrentCopying::Sweep(bool swap_bitmaps) {
if (use_generational_cc_ && young_gen_) {
// Only sweep objects on the live stack.
SweepArray(heap_->GetLiveStack(), /* swap_bitmaps= */ false);
} else {
{
TimingLogger::ScopedTiming t("MarkStackAsLive", GetTimings());
accounting::ObjectStack* live_stack = heap_->GetLiveStack();
if (kEnableFromSpaceAccountingCheck) {
// Ensure that nobody inserted items in the live stack after we swapped the stacks.
CHECK_GE(live_stack_freeze_size_, live_stack->Size());
}
heap_->MarkAllocStackAsLive(live_stack);
live_stack->Reset();
}
CheckEmptyMarkStack();
TimingLogger::ScopedTiming split("Sweep", GetTimings());
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
if (space->IsContinuousMemMapAllocSpace() && space != region_space_
&& !immune_spaces_.ContainsSpace(space)) {
space::ContinuousMemMapAllocSpace* alloc_space = space->AsContinuousMemMapAllocSpace();
TimingLogger::ScopedTiming split2(
alloc_space->IsZygoteSpace() ? "SweepZygoteSpace" : "SweepAllocSpace", GetTimings());
RecordFree(alloc_space->Sweep(swap_bitmaps));
}
}
SweepLargeObjects(swap_bitmaps);
}
}
// Copied and adapted from MarkSweep::SweepArray.
void ConcurrentCopying::SweepArray(accounting::ObjectStack* allocations, bool swap_bitmaps) {
// This method is only used when Generational CC collection is enabled.
DCHECK(use_generational_cc_);
CheckEmptyMarkStack();
TimingLogger::ScopedTiming t("SweepArray", GetTimings());
Thread* self = Thread::Current();
mirror::Object** chunk_free_buffer = reinterpret_cast<mirror::Object**>(
sweep_array_free_buffer_mem_map_.BaseBegin());
size_t chunk_free_pos = 0;
ObjectBytePair freed;
ObjectBytePair freed_los;
// How many objects are left in the array, modified after each space is swept.
StackReference<mirror::Object>* objects = allocations->Begin();
size_t count = allocations->Size();
// Start by sweeping the continuous spaces.
for (space::ContinuousSpace* space : heap_->GetContinuousSpaces()) {
if (!space->IsAllocSpace() ||
space == region_space_ ||
immune_spaces_.ContainsSpace(space) ||
space->GetLiveBitmap() == nullptr) {
continue;
}
space::AllocSpace* alloc_space = space->AsAllocSpace();
accounting::ContinuousSpaceBitmap* live_bitmap = space->GetLiveBitmap();
accounting::ContinuousSpaceBitmap* mark_bitmap = space->GetMarkBitmap();
if (swap_bitmaps) {
std::swap(live_bitmap, mark_bitmap);
}
StackReference<mirror::Object>* out = objects;
for (size_t i = 0; i < count; ++i) {
mirror::Object* const obj = objects[i].AsMirrorPtr();
if (kUseThreadLocalAllocationStack && obj == nullptr) {
continue;
}
if (space->HasAddress(obj)) {
// This object is in the space, remove it from the array and add it to the sweep buffer
// if needed.
if (!mark_bitmap->Test(obj)) {
if (chunk_free_pos >= kSweepArrayChunkFreeSize) {
TimingLogger::ScopedTiming t2("FreeList", GetTimings());
freed.objects += chunk_free_pos;
freed.bytes += alloc_space->FreeList(self, chunk_free_pos, chunk_free_buffer);
chunk_free_pos = 0;
}
chunk_free_buffer[chunk_free_pos++] = obj;
}
} else {
(out++)->Assign(obj);
}
}
if (chunk_free_pos > 0) {
TimingLogger::ScopedTiming t2("FreeList", GetTimings());
freed.objects += chunk_free_pos;
freed.bytes += alloc_space->FreeList(self, chunk_free_pos, chunk_free_buffer);
chunk_free_pos = 0;
}
// All of the references which space contained are no longer in the allocation stack, update
// the count.
count = out - objects;
}
// Handle the large object space.
space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace();
if (large_object_space != nullptr) {
accounting::LargeObjectBitmap* large_live_objects = large_object_space->GetLiveBitmap();
accounting::LargeObjectBitmap* large_mark_objects = large_object_space->GetMarkBitmap();
if (swap_bitmaps) {
std::swap(large_live_objects, large_mark_objects);
}
for (size_t i = 0; i < count; ++i) {
mirror::Object* const obj = objects[i].AsMirrorPtr();
// Handle large objects.
if (kUseThreadLocalAllocationStack && obj == nullptr) {
continue;
}
if (!large_mark_objects->Test(obj)) {
++freed_los.objects;
freed_los.bytes += large_object_space->Free(self, obj);
}
}
}
{
TimingLogger::ScopedTiming t2("RecordFree", GetTimings());
RecordFree(freed);
RecordFreeLOS(freed_los);
t2.NewTiming("ResetStack");
allocations->Reset();
}
sweep_array_free_buffer_mem_map_.MadviseDontNeedAndZero();
}
void ConcurrentCopying::MarkZygoteLargeObjects() {
TimingLogger::ScopedTiming split(__FUNCTION__, GetTimings());
Thread* const self = Thread::Current();
WriterMutexLock rmu(self, *Locks::heap_bitmap_lock_);
space::LargeObjectSpace* const los = heap_->GetLargeObjectsSpace();
if (los != nullptr) {
// Pick the current live bitmap (mark bitmap if swapped).
accounting::LargeObjectBitmap* const live_bitmap = los->GetLiveBitmap();
accounting::LargeObjectBitmap* const mark_bitmap = los->GetMarkBitmap();
// Walk through all of the objects and explicitly mark the zygote ones so they don't get swept.
std::pair<uint8_t*, uint8_t*> range = los->GetBeginEndAtomic();
live_bitmap->VisitMarkedRange(reinterpret_cast<uintptr_t>(range.first),
reinterpret_cast<uintptr_t>(range.second),
[mark_bitmap, los, self](mirror::Object* obj)
REQUIRES(Locks::heap_bitmap_lock_)
REQUIRES_SHARED(Locks::mutator_lock_) {
if (los->IsZygoteLargeObject(self, obj)) {
mark_bitmap->Set(obj);
}
});
}
}
void ConcurrentCopying::SweepLargeObjects(bool swap_bitmaps) {
TimingLogger::ScopedTiming split("SweepLargeObjects", GetTimings());
if (heap_->GetLargeObjectsSpace() != nullptr) {
RecordFreeLOS(heap_->GetLargeObjectsSpace()->Sweep(swap_bitmaps));
}
}
void ConcurrentCopying::CaptureRssAtPeak() {
using range_t = std::pair<void*, void*>;
// This operation is expensive as several calls to mincore() are performed.
// Also, this must be called before clearing regions in ReclaimPhase().
// Therefore, we make it conditional on the flag that enables dumping GC
// performance info on shutdown.
if (Runtime::Current()->GetDumpGCPerformanceOnShutdown()) {
std::list<range_t> gc_ranges;
auto add_gc_range = [&gc_ranges](void* start, size_t size) {
void* end = static_cast<char*>(start) + RoundUp(size, kPageSize);
gc_ranges.emplace_back(range_t(start, end));
};
// region space
DCHECK(IsAligned<kPageSize>(region_space_->Limit()));
gc_ranges.emplace_back(range_t(region_space_->Begin(), region_space_->Limit()));
// mark bitmap
add_gc_range(region_space_bitmap_->Begin(), region_space_bitmap_->Size());
// non-moving space
{
DCHECK(IsAligned<kPageSize>(heap_->non_moving_space_->Limit()));
gc_ranges.emplace_back(range_t(heap_->non_moving_space_->Begin(),
heap_->non_moving_space_->Limit()));
// mark bitmap
accounting::ContinuousSpaceBitmap *bitmap = heap_->non_moving_space_->GetMarkBitmap();
add_gc_range(bitmap->Begin(), bitmap->Size());
// live bitmap. Deal with bound bitmaps.
ReaderMutexLock mu(Thread::Current(), *Locks::heap_bitmap_lock_);
if (heap_->non_moving_space_->HasBoundBitmaps()) {
DCHECK_EQ(bitmap, heap_->non_moving_space_->GetLiveBitmap());
bitmap = heap_->non_moving_space_->GetTempBitmap();
} else {
bitmap = heap_->non_moving_space_->GetLiveBitmap();
}
add_gc_range(bitmap->Begin(), bitmap->Size());
}
// large-object space
if (heap_->GetLargeObjectsSpace()) {
heap_->GetLargeObjectsSpace()->ForEachMemMap([&add_gc_range](const MemMap& map) {
DCHECK(IsAligned<kPageSize>(map.BaseSize()));
add_gc_range(map.BaseBegin(), map.BaseSize());
});
// mark bitmap
accounting::LargeObjectBitmap* bitmap = heap_->GetLargeObjectsSpace()->GetMarkBitmap();
add_gc_range(bitmap->Begin(), bitmap->Size());
// live bitmap
bitmap = heap_->GetLargeObjectsSpace()->GetLiveBitmap();
add_gc_range(bitmap->Begin(), bitmap->Size());
}
// card table
add_gc_range(heap_->GetCardTable()->MemMapBegin(), heap_->GetCardTable()->MemMapSize());
// inter-region refs
if (use_generational_cc_ && !young_gen_) {
// region space
add_gc_range(region_space_inter_region_bitmap_->Begin(),
region_space_inter_region_bitmap_->Size());
// non-moving space
add_gc_range(non_moving_space_inter_region_bitmap_->Begin(),
non_moving_space_inter_region_bitmap_->Size());
}
// Extract RSS using mincore(). Updates the cummulative RSS counter.
ExtractRssFromMincore(&gc_ranges);
}
}
void ConcurrentCopying::ReclaimPhase() {
TimingLogger::ScopedTiming split("ReclaimPhase", GetTimings());
if (kVerboseMode) {
LOG(INFO) << "GC ReclaimPhase";
}
Thread* self = Thread::Current();
{
// Double-check that the mark stack is empty.
// Note: need to set this after VerifyNoFromSpaceRef().
is_asserting_to_space_invariant_ = false;
QuasiAtomic::ThreadFenceForConstructor();
if (kVerboseMode) {
LOG(INFO) << "Issue an empty check point. ";
}
IssueEmptyCheckpoint();
// Disable the check.
is_mark_stack_push_disallowed_.store(0, std::memory_order_seq_cst);
if (kUseBakerReadBarrier) {
updated_all_immune_objects_.store(false, std::memory_order_seq_cst);
}
CheckEmptyMarkStack();
}
// Capture RSS at the time when memory usage is at its peak. All GC related
// memory ranges like java heap, card table, bitmap etc. are taken into
// account.
// TODO: We can fetch resident memory for region space directly by going
// through list of allocated regions. This way we can avoid calling mincore on
// the biggest memory range, thereby reducing the cost of this function.
CaptureRssAtPeak();
// Sweep the malloc spaces before clearing the from space since the memory tool mode might
// access the object classes in the from space for dead objects.
{
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
Sweep(/* swap_bitmaps= */ false);
SwapBitmaps();
heap_->UnBindBitmaps();
// The bitmap was cleared at the start of the GC, there is nothing we need to do here.
DCHECK(region_space_bitmap_ != nullptr);
region_space_bitmap_ = nullptr;
}
{
// Record freed objects.
TimingLogger::ScopedTiming split2("RecordFree", GetTimings());
// Don't include thread-locals that are in the to-space.
const uint64_t from_bytes = region_space_->GetBytesAllocatedInFromSpace();
const uint64_t from_objects = region_space_->GetObjectsAllocatedInFromSpace();
const uint64_t unevac_from_bytes = region_space_->GetBytesAllocatedInUnevacFromSpace();
const uint64_t unevac_from_objects = region_space_->GetObjectsAllocatedInUnevacFromSpace();
uint64_t to_bytes = bytes_moved_.load(std::memory_order_relaxed) + bytes_moved_gc_thread_;
cumulative_bytes_moved_.fetch_add(to_bytes, std::memory_order_relaxed);
uint64_t to_objects = objects_moved_.load(std::memory_order_relaxed) + objects_moved_gc_thread_;
cumulative_objects_moved_.fetch_add(to_objects, std::memory_order_relaxed);
if (kEnableFromSpaceAccountingCheck) {
CHECK_EQ(from_space_num_objects_at_first_pause_, from_objects + unevac_from_objects);
CHECK_EQ(from_space_num_bytes_at_first_pause_, from_bytes + unevac_from_bytes);
}
CHECK_LE(to_objects, from_objects);
// to_bytes <= from_bytes is only approximately true, because objects expand a little when
// copying to non-moving space in near-OOM situations.
if (from_bytes > 0) {
copied_live_bytes_ratio_sum_ += static_cast<float>(to_bytes) / from_bytes;
gc_count_++;
}
// Cleared bytes and objects, populated by the call to RegionSpace::ClearFromSpace below.
uint64_t cleared_bytes;
uint64_t cleared_objects;
{
TimingLogger::ScopedTiming split4("ClearFromSpace", GetTimings());
region_space_->ClearFromSpace(&cleared_bytes, &cleared_objects, /*clear_bitmap*/ !young_gen_);
// `cleared_bytes` and `cleared_objects` may be greater than the from space equivalents since
// RegionSpace::ClearFromSpace may clear empty unevac regions.
CHECK_GE(cleared_bytes, from_bytes);
CHECK_GE(cleared_objects, from_objects);
}
// freed_bytes could conceivably be negative if we fall back to nonmoving space and have to
// pad to a larger size.
int64_t freed_bytes = (int64_t)cleared_bytes - (int64_t)to_bytes;
uint64_t freed_objects = cleared_objects - to_objects;
if (kVerboseMode) {
LOG(INFO) << "RecordFree:"
<< " from_bytes=" << from_bytes << " from_objects=" << from_objects
<< " unevac_from_bytes=" << unevac_from_bytes
<< " unevac_from_objects=" << unevac_from_objects
<< " to_bytes=" << to_bytes << " to_objects=" << to_objects
<< " freed_bytes=" << freed_bytes << " freed_objects=" << freed_objects
<< " from_space size=" << region_space_->FromSpaceSize()
<< " unevac_from_space size=" << region_space_->UnevacFromSpaceSize()
<< " to_space size=" << region_space_->ToSpaceSize();
LOG(INFO) << "(before) num_bytes_allocated="
<< heap_->num_bytes_allocated_.load();
}
RecordFree(ObjectBytePair(freed_objects, freed_bytes));
if (kVerboseMode) {
LOG(INFO) << "(after) num_bytes_allocated="
<< heap_->num_bytes_allocated_.load();
}
float reclaimed_bytes_ratio = static_cast<float>(freed_bytes) / num_bytes_allocated_before_gc_;
reclaimed_bytes_ratio_sum_ += reclaimed_bytes_ratio;
}
CheckEmptyMarkStack();
if (heap_->dump_region_info_after_gc_) {
LOG(INFO) << "time=" << region_space_->Time();
region_space_->DumpNonFreeRegions(LOG_STREAM(INFO));
}
if (kVerboseMode) {
LOG(INFO) << "GC end of ReclaimPhase";
}
}
std::string ConcurrentCopying::DumpReferenceInfo(mirror::Object* ref,
const char* ref_name,
const char* indent) {
std::ostringstream oss;
oss << indent << heap_->GetVerification()->DumpObjectInfo(ref, ref_name) << '\n';
if (ref != nullptr) {
if (kUseBakerReadBarrier) {
oss << indent << ref_name << "->GetMarkBit()=" << ref->GetMarkBit() << '\n';
oss << indent << ref_name << "->GetReadBarrierState()=" << ref->GetReadBarrierState() << '\n';
}
}
if (region_space_->HasAddress(ref)) {
oss << indent << "Region containing " << ref_name << ":" << '\n';
region_space_->DumpRegionForObject(oss, ref);
if (region_space_bitmap_ != nullptr) {
oss << indent << "region_space_bitmap_->Test(" << ref_name << ")="
<< std::boolalpha << region_space_bitmap_->Test(ref) << std::noboolalpha;
}
}
return oss.str();
}
std::string ConcurrentCopying::DumpHeapReference(mirror::Object* obj,
MemberOffset offset,
mirror::Object* ref) {
std::ostringstream oss;
constexpr const char* kIndent = " ";
oss << kIndent << "Invalid reference: ref=" << ref
<< " referenced from: object=" << obj << " offset= " << offset << '\n';
// Information about `obj`.
oss << DumpReferenceInfo(obj, "obj", kIndent) << '\n';
// Information about `ref`.
oss << DumpReferenceInfo(ref, "ref", kIndent);
return oss.str();
}
void ConcurrentCopying::AssertToSpaceInvariant(mirror::Object* obj,
MemberOffset offset,
mirror::Object* ref) {
CHECK_EQ(heap_->collector_type_, kCollectorTypeCC) << static_cast<size_t>(heap_->collector_type_);
if (is_asserting_to_space_invariant_) {
if (ref == nullptr) {
// OK.
return;
} else if (region_space_->HasAddress(ref)) {
// Check to-space invariant in region space (moving space).
using RegionType = space::RegionSpace::RegionType;
space::RegionSpace::RegionType type = region_space_->GetRegionTypeUnsafe(ref);
if (type == RegionType::kRegionTypeToSpace) {
// OK.
return;
} else if (type == RegionType::kRegionTypeUnevacFromSpace) {
if (!IsMarkedInUnevacFromSpace(ref)) {
LOG(FATAL_WITHOUT_ABORT) << "Found unmarked reference in unevac from-space:";
// Remove memory protection from the region space and log debugging information.
region_space_->Unprotect();
LOG(FATAL_WITHOUT_ABORT) << DumpHeapReference(obj, offset, ref);
Thread::Current()->DumpJavaStack(LOG_STREAM(FATAL_WITHOUT_ABORT));
}
CHECK(IsMarkedInUnevacFromSpace(ref)) << ref;
} else {
// Not OK: either a from-space ref or a reference in an unused region.
if (type == RegionType::kRegionTypeFromSpace) {
LOG(FATAL_WITHOUT_ABORT) << "Found from-space reference:";
} else {
LOG(FATAL_WITHOUT_ABORT) << "Found reference in region with type " << type << ":";
}
// Remove memory protection from the region space and log debugging information.
region_space_->Unprotect();
LOG(FATAL_WITHOUT_ABORT) << DumpHeapReference(obj, offset, ref);
if (obj != nullptr) {
LogFromSpaceRefHolder(obj, offset);
LOG(FATAL_WITHOUT_ABORT) << "UNEVAC " << region_space_->IsInUnevacFromSpace(obj) << " "
<< obj << " " << obj->GetMarkBit();
if (region_space_->HasAddress(obj)) {
region_space_->DumpRegionForObject(LOG_STREAM(FATAL_WITHOUT_ABORT), obj);
}
LOG(FATAL_WITHOUT_ABORT) << "CARD " << static_cast<size_t>(
*Runtime::Current()->GetHeap()->GetCardTable()->CardFromAddr(
reinterpret_cast<uint8_t*>(obj)));
if (region_space_->HasAddress(obj)) {
LOG(FATAL_WITHOUT_ABORT) << "BITMAP " << region_space_bitmap_->Test(obj);
} else {
accounting::ContinuousSpaceBitmap* mark_bitmap =
heap_mark_bitmap_->GetContinuousSpaceBitmap(obj);
if (mark_bitmap != nullptr) {
LOG(FATAL_WITHOUT_ABORT) << "BITMAP " << mark_bitmap->Test(obj);
} else {
accounting::LargeObjectBitmap* los_bitmap =
heap_mark_bitmap_->GetLargeObjectBitmap(obj);
LOG(FATAL_WITHOUT_ABORT) << "BITMAP " << los_bitmap->Test(obj);
}
}
}
ref->GetLockWord(false).Dump(LOG_STREAM(FATAL_WITHOUT_ABORT));
LOG(FATAL_WITHOUT_ABORT) << "Non-free regions:";
region_space_->DumpNonFreeRegions(LOG_STREAM(FATAL_WITHOUT_ABORT));
PrintFileToLog("/proc/self/maps", LogSeverity::FATAL_WITHOUT_ABORT);
MemMap::DumpMaps(LOG_STREAM(FATAL_WITHOUT_ABORT), /* terse= */ true);
LOG(FATAL) << "Invalid reference " << ref
<< " referenced from object " << obj << " at offset " << offset;
}
} else {
// Check to-space invariant in non-moving space.
AssertToSpaceInvariantInNonMovingSpace(obj, ref);
}
}
}
class RootPrinter {
public:
RootPrinter() { }
template <class MirrorType>
ALWAYS_INLINE void VisitRootIfNonNull(mirror::CompressedReference<MirrorType>* root)
REQUIRES_SHARED(Locks::mutator_lock_) {
if (!root->IsNull()) {
VisitRoot(root);
}
}
template <class MirrorType>
void VisitRoot(mirror::Object** root)
REQUIRES_SHARED(Locks::mutator_lock_) {
LOG(FATAL_WITHOUT_ABORT) << "root=" << root << " ref=" << *root;
}
template <class MirrorType>
void VisitRoot(mirror::CompressedReference<MirrorType>* root)
REQUIRES_SHARED(Locks::mutator_lock_) {
LOG(FATAL_WITHOUT_ABORT) << "root=" << root << " ref=" << root->AsMirrorPtr();
}
};
std::string ConcurrentCopying::DumpGcRoot(mirror::Object* ref) {
std::ostringstream oss;
constexpr const char* kIndent = " ";
oss << kIndent << "Invalid GC root: ref=" << ref << '\n';
// Information about `ref`.
oss << DumpReferenceInfo(ref, "ref", kIndent);
return oss.str();
}
void ConcurrentCopying::AssertToSpaceInvariant(GcRootSource* gc_root_source,
mirror::Object* ref) {
CHECK_EQ(heap_->collector_type_, kCollectorTypeCC) << static_cast<size_t>(heap_->collector_type_);
if (is_asserting_to_space_invariant_) {
if (ref == nullptr) {
// OK.
return;
} else if (region_space_->HasAddress(ref)) {
// Check to-space invariant in region space (moving space).
using RegionType = space::RegionSpace::RegionType;
space::RegionSpace::RegionType type = region_space_->GetRegionTypeUnsafe(ref);
if (type == RegionType::kRegionTypeToSpace) {
// OK.
return;
} else if (type == RegionType::kRegionTypeUnevacFromSpace) {
if (!IsMarkedInUnevacFromSpace(ref)) {
LOG(FATAL_WITHOUT_ABORT) << "Found unmarked reference in unevac from-space:";
// Remove memory protection from the region space and log debugging information.
region_space_->Unprotect();
LOG(FATAL_WITHOUT_ABORT) << DumpGcRoot(ref);
}
CHECK(IsMarkedInUnevacFromSpace(ref)) << ref;
} else {
// Not OK: either a from-space ref or a reference in an unused region.
if (type == RegionType::kRegionTypeFromSpace) {
LOG(FATAL_WITHOUT_ABORT) << "Found from-space reference:";
} else {
LOG(FATAL_WITHOUT_ABORT) << "Found reference in region with type " << type << ":";
}
// Remove memory protection from the region space and log debugging information.
region_space_->Unprotect();
LOG(FATAL_WITHOUT_ABORT) << DumpGcRoot(ref);
if (gc_root_source == nullptr) {
// No info.
} else if (gc_root_source->HasArtField()) {
ArtField* field = gc_root_source->GetArtField();
LOG(FATAL_WITHOUT_ABORT) << "gc root in field " << field << " "
<< ArtField::PrettyField(field);
RootPrinter root_printer;
field->VisitRoots(root_printer);
} else if (gc_root_source->HasArtMethod()) {
ArtMethod* method = gc_root_source->GetArtMethod();
LOG(FATAL_WITHOUT_ABORT) << "gc root in method " << method << " "
<< ArtMethod::PrettyMethod(method);
RootPrinter root_printer;
method->VisitRoots(root_printer, kRuntimePointerSize);
}
ref->GetLockWord(false).Dump(LOG_STREAM(FATAL_WITHOUT_ABORT));
LOG(FATAL_WITHOUT_ABORT) << "Non-free regions:";
region_space_->DumpNonFreeRegions(LOG_STREAM(FATAL_WITHOUT_ABORT));
PrintFileToLog("/proc/self/maps", LogSeverity::FATAL_WITHOUT_ABORT);
MemMap::DumpMaps(LOG_STREAM(FATAL_WITHOUT_ABORT), /* terse= */ true);
LOG(FATAL) << "Invalid reference " << ref;
}
} else {
// Check to-space invariant in non-moving space.
AssertToSpaceInvariantInNonMovingSpace(/* obj= */ nullptr, ref);
}
}
}
void ConcurrentCopying::LogFromSpaceRefHolder(mirror::Object* obj, MemberOffset offset) {
if (kUseBakerReadBarrier) {
LOG(INFO) << "holder=" << obj << " " << obj->PrettyTypeOf()
<< " holder rb_state=" << obj->GetReadBarrierState();
} else {
LOG(INFO) << "holder=" << obj << " " << obj->PrettyTypeOf();
}
if (region_space_->IsInFromSpace(obj)) {
LOG(INFO) << "holder is in the from-space.";
} else if (region_space_->IsInToSpace(obj)) {
LOG(INFO) << "holder is in the to-space.";
} else if (region_space_->IsInUnevacFromSpace(obj)) {
LOG(INFO) << "holder is in the unevac from-space.";
if (IsMarkedInUnevacFromSpace(obj)) {
LOG(INFO) << "holder is marked in the region space bitmap.";
} else {
LOG(INFO) << "holder is not marked in the region space bitmap.";
}
} else {
// In a non-moving space.
if (immune_spaces_.ContainsObject(obj)) {
LOG(INFO) << "holder is in an immune image or the zygote space.";
} else {
LOG(INFO) << "holder is in a non-immune, non-moving (or main) space.";
accounting::ContinuousSpaceBitmap* mark_bitmap = heap_->GetNonMovingSpace()->GetMarkBitmap();
accounting::LargeObjectBitmap* los_bitmap = nullptr;
const bool is_los = !mark_bitmap->HasAddress(obj);
if (is_los) {
DCHECK(heap_->GetLargeObjectsSpace() && heap_->GetLargeObjectsSpace()->Contains(obj))
<< "obj=" << obj
<< " LOS bit map covers the entire lower 4GB address range";
los_bitmap = heap_->GetLargeObjectsSpace()->GetMarkBitmap();
}
if (!is_los && mark_bitmap->Test(obj)) {
LOG(INFO) << "holder is marked in the non-moving space mark bit map.";
} else if (is_los && los_bitmap->Test(obj)) {
LOG(INFO) << "holder is marked in the los bit map.";
} else {
// If ref is on the allocation stack, then it is considered
// mark/alive (but not necessarily on the live stack.)
if (IsOnAllocStack(obj)) {
LOG(INFO) << "holder is on the alloc stack.";
} else {
LOG(INFO) << "holder is not marked or on the alloc stack.";
}
}
}
}
LOG(INFO) << "offset=" << offset.SizeValue();
}
bool ConcurrentCopying::IsMarkedInNonMovingSpace(mirror::Object* from_ref) {
DCHECK(!region_space_->HasAddress(from_ref)) << "ref=" << from_ref;
DCHECK(!immune_spaces_.ContainsObject(from_ref)) << "ref=" << from_ref;
if (kUseBakerReadBarrier && from_ref->GetReadBarrierStateAcquire() == ReadBarrier::GrayState()) {
return true;
} else if (!use_generational_cc_ || done_scanning_.load(std::memory_order_acquire)) {
// Read the comment in IsMarkedInUnevacFromSpace()
accounting::ContinuousSpaceBitmap* mark_bitmap = heap_->GetNonMovingSpace()->GetMarkBitmap();
accounting::LargeObjectBitmap* los_bitmap = nullptr;
const bool is_los = !mark_bitmap->HasAddress(from_ref);
if (is_los) {
DCHECK(heap_->GetLargeObjectsSpace() && heap_->GetLargeObjectsSpace()->Contains(from_ref))
<< "ref=" << from_ref
<< " doesn't belong to non-moving space and large object space doesn't exist";
los_bitmap = heap_->GetLargeObjectsSpace()->GetMarkBitmap();
}
if (is_los ? los_bitmap->Test(from_ref) : mark_bitmap->Test(from_ref)) {
return true;
}
}
return IsOnAllocStack(from_ref);
}
void ConcurrentCopying::AssertToSpaceInvariantInNonMovingSpace(mirror::Object* obj,
mirror::Object* ref) {
CHECK(ref != nullptr);
CHECK(!region_space_->HasAddress(ref)) << "obj=" << obj << " ref=" << ref;
// In a non-moving space. Check that the ref is marked.
if (immune_spaces_.ContainsObject(ref)) {
// Immune space case.
if (kUseBakerReadBarrier) {
// Immune object may not be gray if called from the GC.
if (Thread::Current() == thread_running_gc_ && !gc_grays_immune_objects_) {
return;
}
bool updated_all_immune_objects = updated_all_immune_objects_.load(std::memory_order_seq_cst);
CHECK(updated_all_immune_objects || ref->GetReadBarrierState() == ReadBarrier::GrayState())
<< "Unmarked immune space ref. obj=" << obj << " rb_state="
<< (obj != nullptr ? obj->GetReadBarrierState() : 0U)
<< " ref=" << ref << " ref rb_state=" << ref->GetReadBarrierState()
<< " updated_all_immune_objects=" << updated_all_immune_objects;
}
} else {
// Non-moving space and large-object space (LOS) cases.
// If `ref` is on the allocation stack, then it may not be
// marked live, but considered marked/alive (but not
// necessarily on the live stack).
CHECK(IsMarkedInNonMovingSpace(ref))
<< "Unmarked ref that's not on the allocation stack."
<< " obj=" << obj
<< " ref=" << ref
<< " rb_state=" << ref->GetReadBarrierState()
<< " is_marking=" << std::boolalpha << is_marking_ << std::noboolalpha
<< " young_gen=" << std::boolalpha << young_gen_ << std::noboolalpha
<< " done_scanning="
<< std::boolalpha << done_scanning_.load(std::memory_order_acquire) << std::noboolalpha
<< " self=" << Thread::Current();
}
}
// Used to scan ref fields of an object.
template <bool kNoUnEvac>
class ConcurrentCopying::RefFieldsVisitor {
public:
explicit RefFieldsVisitor(ConcurrentCopying* collector, Thread* const thread)
: collector_(collector), thread_(thread) {
// Cannot have `kNoUnEvac` when Generational CC collection is disabled.
DCHECK(!kNoUnEvac || collector_->use_generational_cc_);
}
void operator()(mirror::Object* obj, MemberOffset offset, bool /* is_static */)
const ALWAYS_INLINE REQUIRES_SHARED(Locks::mutator_lock_)
REQUIRES_SHARED(Locks::heap_bitmap_lock_) {
collector_->Process<kNoUnEvac>(obj, offset);
}
void operator()(ObjPtr<mirror::Class> klass, ObjPtr<mirror::Reference> ref) const
REQUIRES_SHARED(Locks::mutator_lock_) ALWAYS_INLINE {
CHECK(klass->IsTypeOfReferenceClass());
collector_->DelayReferenceReferent(klass, ref);
}
void VisitRootIfNonNull(mirror::CompressedReference<mirror::Object>* root) const
ALWAYS_INLINE
REQUIRES_SHARED(Locks::mutator_lock_) {
if (!root->IsNull()) {
VisitRoot(root);
}
}
void VisitRoot(mirror::CompressedReference<mirror::Object>* root) const
ALWAYS_INLINE
REQUIRES_SHARED(Locks::mutator_lock_) {
collector_->MarkRoot</*kGrayImmuneObject=*/false>(thread_, root);
}
private:
ConcurrentCopying* const collector_;
Thread* const thread_;
};
template <bool kNoUnEvac>
inline void ConcurrentCopying::Scan(mirror::Object* to_ref) {
// Cannot have `kNoUnEvac` when Generational CC collection is disabled.
DCHECK(!kNoUnEvac || use_generational_cc_);
if (kDisallowReadBarrierDuringScan && !Runtime::Current()->IsActiveTransaction()) {
// Avoid all read barriers during visit references to help performance.
// Don't do this in transaction mode because we may read the old value of an field which may
// trigger read barriers.
Thread::Current()->ModifyDebugDisallowReadBarrier(1);
}
DCHECK(!region_space_->IsInFromSpace(to_ref));
DCHECK_EQ(Thread::Current(), thread_running_gc_);
RefFieldsVisitor<kNoUnEvac> visitor(this, thread_running_gc_);
// Disable the read barrier for a performance reason.
to_ref->VisitReferences</*kVisitNativeRoots=*/true, kDefaultVerifyFlags, kWithoutReadBarrier>(
visitor, visitor);
if (kDisallowReadBarrierDuringScan && !Runtime::Current()->IsActiveTransaction()) {
thread_running_gc_->ModifyDebugDisallowReadBarrier(-1);
}
}
template <bool kNoUnEvac>
inline void ConcurrentCopying::Process(mirror::Object* obj, MemberOffset offset) {
// Cannot have `kNoUnEvac` when Generational CC collection is disabled.
DCHECK(!kNoUnEvac || use_generational_cc_);
DCHECK_EQ(Thread::Current(), thread_running_gc_);
mirror::Object* ref = obj->GetFieldObject<
mirror::Object, kVerifyNone, kWithoutReadBarrier, false>(offset);
mirror::Object* to_ref = Mark</*kGrayImmuneObject=*/false, kNoUnEvac, /*kFromGCThread=*/true>(
thread_running_gc_,
ref,
/*holder=*/ obj,
offset);
if (to_ref == ref) {
return;
}
// This may fail if the mutator writes to the field at the same time. But it's ok.
mirror::Object* expected_ref = ref;
mirror::Object* new_ref = to_ref;
do {
if (expected_ref !=
obj->GetFieldObject<mirror::Object, kVerifyNone, kWithoutReadBarrier, false>(offset)) {
// It was updated by the mutator.
break;
}
// Use release CAS to make sure threads reading the reference see contents of copied objects.
} while (!obj->CasFieldObjectWithoutWriteBarrier<false, false, kVerifyNone>(
offset,
expected_ref,
new_ref,
CASMode::kWeak,
std::memory_order_release));
}
// Process some roots.
inline void ConcurrentCopying::VisitRoots(
mirror::Object*** roots, size_t count, const RootInfo& info ATTRIBUTE_UNUSED) {
Thread* const self = Thread::Current();
for (size_t i = 0; i < count; ++i) {
mirror::Object** root = roots[i];
mirror::Object* ref = *root;
mirror::Object* to_ref = Mark(self, ref);
if (to_ref == ref) {
continue;
}
Atomic<mirror::Object*>* addr = reinterpret_cast<Atomic<mirror::Object*>*>(root);
mirror::Object* expected_ref = ref;
mirror::Object* new_ref = to_ref;
do {
if (expected_ref != addr->load(std::memory_order_relaxed)) {
// It was updated by the mutator.
break;
}
} while (!addr->CompareAndSetWeakRelaxed(expected_ref, new_ref));
}
}
template<bool kGrayImmuneObject>
inline void ConcurrentCopying::MarkRoot(Thread* const self,
mirror::CompressedReference<mirror::Object>* root) {
DCHECK(!root->IsNull());
mirror::Object* const ref = root->AsMirrorPtr();
mirror::Object* to_ref = Mark<kGrayImmuneObject>(self, ref);
if (to_ref != ref) {
auto* addr = reinterpret_cast<Atomic<mirror::CompressedReference<mirror::Object>>*>(root);
auto expected_ref = mirror::CompressedReference<mirror::Object>::FromMirrorPtr(ref);
auto new_ref = mirror::CompressedReference<mirror::Object>::FromMirrorPtr(to_ref);
// If the cas fails, then it was updated by the mutator.
do {
if (ref != addr->load(std::memory_order_relaxed).AsMirrorPtr()) {
// It was updated by the mutator.
break;
}
} while (!addr->CompareAndSetWeakRelaxed(expected_ref, new_ref));
}
}
inline void ConcurrentCopying::VisitRoots(
mirror::CompressedReference<mirror::Object>** roots, size_t count,
const RootInfo& info ATTRIBUTE_UNUSED) {
Thread* const self = Thread::Current();
for (size_t i = 0; i < count; ++i) {
mirror::CompressedReference<mirror::Object>* const root = roots[i];
if (!root->IsNull()) {
// kGrayImmuneObject is true because this is used for the thread flip.
MarkRoot</*kGrayImmuneObject=*/true>(self, root);
}
}
}
// Temporary set gc_grays_immune_objects_ to true in a scope if the current thread is GC.
class ConcurrentCopying::ScopedGcGraysImmuneObjects {
public:
explicit ScopedGcGraysImmuneObjects(ConcurrentCopying* collector)
: collector_(collector), enabled_(false) {
if (kUseBakerReadBarrier &&
collector_->thread_running_gc_ == Thread::Current() &&
!collector_->gc_grays_immune_objects_) {
collector_->gc_grays_immune_objects_ = true;
enabled_ = true;
}
}
~ScopedGcGraysImmuneObjects() {
if (kUseBakerReadBarrier &&
collector_->thread_running_gc_ == Thread::Current() &&
enabled_) {
DCHECK(collector_->gc_grays_immune_objects_);
collector_->gc_grays_immune_objects_ = false;
}
}
private:
ConcurrentCopying* const collector_;
bool enabled_;
};
// Fill the given memory block with a dummy object. Used to fill in a
// copy of objects that was lost in race.
void ConcurrentCopying::FillWithDummyObject(Thread* const self,
mirror::Object* dummy_obj,
size_t byte_size) {
// GC doesn't gray immune objects while scanning immune objects. But we need to trigger the read
// barriers here because we need the updated reference to the int array class, etc. Temporary set
// gc_grays_immune_objects_ to true so that we won't cause a DCHECK failure in MarkImmuneSpace().
ScopedGcGraysImmuneObjects scoped_gc_gray_immune_objects(this);
CHECK_ALIGNED(byte_size, kObjectAlignment);
memset(dummy_obj, 0, byte_size);
// Avoid going through read barrier for since kDisallowReadBarrierDuringScan may be enabled.
// Explicitly mark to make sure to get an object in the to-space.
mirror::Class* int_array_class = down_cast<mirror::Class*>(
Mark(self, GetClassRoot<mirror::IntArray, kWithoutReadBarrier>().Ptr()));
CHECK(int_array_class != nullptr);
if (ReadBarrier::kEnableToSpaceInvariantChecks) {
AssertToSpaceInvariant(nullptr, MemberOffset(0), int_array_class);
}
size_t component_size = int_array_class->GetComponentSize();
CHECK_EQ(component_size, sizeof(int32_t));
size_t data_offset = mirror::Array::DataOffset(component_size).SizeValue();
if (data_offset > byte_size) {
// An int array is too big. Use java.lang.Object.
CHECK(java_lang_Object_ != nullptr);
if (ReadBarrier::kEnableToSpaceInvariantChecks) {
AssertToSpaceInvariant(nullptr, MemberOffset(0), java_lang_Object_);
}
CHECK_EQ(byte_size, java_lang_Object_->GetObjectSize<kVerifyNone>());
dummy_obj->SetClass(java_lang_Object_);
CHECK_EQ(byte_size, (dummy_obj->SizeOf<kVerifyNone>()));
} else {
// Use an int array.
dummy_obj->SetClass(int_array_class);
CHECK(dummy_obj->IsArrayInstance<kVerifyNone>());
int32_t length = (byte_size - data_offset) / component_size;
ObjPtr<mirror::Array> dummy_arr = dummy_obj->AsArray<kVerifyNone>();
dummy_arr->SetLength(length);
CHECK_EQ(dummy_arr->GetLength(), length)
<< "byte_size=" << byte_size << " length=" << length
<< " component_size=" << component_size << " data_offset=" << data_offset;
CHECK_EQ(byte_size, (dummy_obj->SizeOf<kVerifyNone>()))
<< "byte_size=" << byte_size << " length=" << length
<< " component_size=" << component_size << " data_offset=" << data_offset;
}
}
// Reuse the memory blocks that were copy of objects that were lost in race.
mirror::Object* ConcurrentCopying::AllocateInSkippedBlock(Thread* const self, size_t alloc_size) {
// Try to reuse the blocks that were unused due to CAS failures.
CHECK_ALIGNED(alloc_size, space::RegionSpace::kAlignment);
size_t min_object_size = RoundUp(sizeof(mirror::Object), space::RegionSpace::kAlignment);
size_t byte_size;
uint8_t* addr;
{
MutexLock mu(self, skipped_blocks_lock_);
auto it = skipped_blocks_map_.lower_bound(alloc_size);
if (it == skipped_blocks_map_.end()) {
// Not found.
return nullptr;
}
byte_size = it->first;
CHECK_GE(byte_size, alloc_size);
if (byte_size > alloc_size && byte_size - alloc_size < min_object_size) {
// If remainder would be too small for a dummy object, retry with a larger request size.
it = skipped_blocks_map_.lower_bound(alloc_size + min_object_size);
if (it == skipped_blocks_map_.end()) {
// Not found.
return nullptr;
}
CHECK_ALIGNED(it->first - alloc_size, space::RegionSpace::kAlignment);
CHECK_GE(it->first - alloc_size, min_object_size)
<< "byte_size=" << byte_size << " it->first=" << it->first << " alloc_size=" << alloc_size;
}
// Found a block.
CHECK(it != skipped_blocks_map_.end());
byte_size = it->first;
addr = it->second;
CHECK_GE(byte_size, alloc_size);
CHECK(region_space_->IsInToSpace(reinterpret_cast<mirror::Object*>(addr)));
CHECK_ALIGNED(byte_size, space::RegionSpace::kAlignment);
if (kVerboseMode) {
LOG(INFO) << "Reusing skipped bytes : " << reinterpret_cast<void*>(addr) << ", " << byte_size;
}
skipped_blocks_map_.erase(it);
}
memset(addr, 0, byte_size);
if (byte_size > alloc_size) {
// Return the remainder to the map.
CHECK_ALIGNED(byte_size - alloc_size, space::RegionSpace::kAlignment);
CHECK_GE(byte_size - alloc_size, min_object_size);
// FillWithDummyObject may mark an object, avoid holding skipped_blocks_lock_ to prevent lock
// violation and possible deadlock. The deadlock case is a recursive case:
// FillWithDummyObject -> Mark(IntArray.class) -> Copy -> AllocateInSkippedBlock.
FillWithDummyObject(self,
reinterpret_cast<mirror::Object*>(addr + alloc_size),
byte_size - alloc_size);
CHECK(region_space_->IsInToSpace(reinterpret_cast<mirror::Object*>(addr + alloc_size)));
{
MutexLock mu(self, skipped_blocks_lock_);
skipped_blocks_map_.insert(std::make_pair(byte_size - alloc_size, addr + alloc_size));
}
}
return reinterpret_cast<mirror::Object*>(addr);
}
mirror::Object* ConcurrentCopying::Copy(Thread* const self,
mirror::Object* from_ref,
mirror::Object* holder,
MemberOffset offset) {
DCHECK(region_space_->IsInFromSpace(from_ref));
// If the class pointer is null, the object is invalid. This could occur for a dangling pointer
// from a previous GC that is either inside or outside the allocated region.
mirror::Class* klass = from_ref->GetClass<kVerifyNone, kWithoutReadBarrier>();
if (UNLIKELY(klass == nullptr)) {
// Remove memory protection from the region space and log debugging information.
region_space_->Unprotect();
heap_->GetVerification()->LogHeapCorruption(holder, offset, from_ref, /* fatal= */ true);
}
// There must not be a read barrier to avoid nested RB that might violate the to-space invariant.
// Note that from_ref is a from space ref so the SizeOf() call will access the from-space meta
// objects, but it's ok and necessary.
size_t obj_size = from_ref->SizeOf<kDefaultVerifyFlags>();
size_t region_space_alloc_size = (obj_size <= space::RegionSpace::kRegionSize)
? RoundUp(obj_size, space::RegionSpace::kAlignment)
: RoundUp(obj_size, space::RegionSpace::kRegionSize);
size_t region_space_bytes_allocated = 0U;
size_t non_moving_space_bytes_allocated = 0U;
size_t bytes_allocated = 0U;
size_t dummy;
bool fall_back_to_non_moving = false;
mirror::Object* to_ref = region_space_->AllocNonvirtual</*kForEvac=*/ true>(
region_space_alloc_size, &region_space_bytes_allocated, nullptr, &dummy);
bytes_allocated = region_space_bytes_allocated;
if (LIKELY(to_ref != nullptr)) {
DCHECK_EQ(region_space_alloc_size, region_space_bytes_allocated);
} else {
// Failed to allocate in the region space. Try the skipped blocks.
to_ref = AllocateInSkippedBlock(self, region_space_alloc_size);
if (to_ref != nullptr) {
// Succeeded to allocate in a skipped block.
if (heap_->use_tlab_) {
// This is necessary for the tlab case as it's not accounted in the space.
region_space_->RecordAlloc(to_ref);
}
bytes_allocated = region_space_alloc_size;
heap_->num_bytes_allocated_.fetch_sub(bytes_allocated, std::memory_order_relaxed);
to_space_bytes_skipped_.fetch_sub(bytes_allocated, std::memory_order_relaxed);
to_space_objects_skipped_.fetch_sub(1, std::memory_order_relaxed);
} else {
// Fall back to the non-moving space.
fall_back_to_non_moving = true;
if (kVerboseMode) {
LOG(INFO) << "Out of memory in the to-space. Fall back to non-moving. skipped_bytes="
<< to_space_bytes_skipped_.load(std::memory_order_relaxed)
<< " skipped_objects="
<< to_space_objects_skipped_.load(std::memory_order_relaxed);
}
to_ref = heap_->non_moving_space_->Alloc(self, obj_size,
&non_moving_space_bytes_allocated, nullptr, &dummy);
if (UNLIKELY(to_ref == nullptr)) {
LOG(FATAL_WITHOUT_ABORT) << "Fall-back non-moving space allocation failed for a "
<< obj_size << " byte object in region type "
<< region_space_->GetRegionType(from_ref);
LOG(FATAL) << "Object address=" << from_ref << " type=" << from_ref->PrettyTypeOf();
}
bytes_allocated = non_moving_space_bytes_allocated;
}
}
DCHECK(to_ref != nullptr);
// Copy the object excluding the lock word since that is handled in the loop.
to_ref->SetClass(klass);
const size_t kObjectHeaderSize = sizeof(mirror::Object);
DCHECK_GE(obj_size, kObjectHeaderSize);
static_assert(kObjectHeaderSize == sizeof(mirror::HeapReference<mirror::Class>) +
sizeof(LockWord),
"Object header size does not match");
// Memcpy can tear for words since it may do byte copy. It is only safe to do this since the
// object in the from space is immutable other than the lock word. b/31423258
memcpy(reinterpret_cast<uint8_t*>(to_ref) + kObjectHeaderSize,
reinterpret_cast<const uint8_t*>(from_ref) + kObjectHeaderSize,
obj_size - kObjectHeaderSize);
// Attempt to install the forward pointer. This is in a loop as the
// lock word atomic write can fail.
while (true) {
LockWord old_lock_word = from_ref->GetLockWord(false);
if (old_lock_word.GetState() == LockWord::kForwardingAddress) {
// Lost the race. Another thread (either GC or mutator) stored
// the forwarding pointer first. Make the lost copy (to_ref)
// look like a valid but dead (dummy) object and keep it for
// future reuse.
FillWithDummyObject(self, to_ref, bytes_allocated);
if (!fall_back_to_non_moving) {
DCHECK(region_space_->IsInToSpace(to_ref));
if (bytes_allocated > space::RegionSpace::kRegionSize) {
// Free the large alloc.
region_space_->FreeLarge</*kForEvac=*/ true>(to_ref, bytes_allocated);
} else {
// Record the lost copy for later reuse.
heap_->num_bytes_allocated_.fetch_add(bytes_allocated, std::memory_order_relaxed);
to_space_bytes_skipped_.fetch_add(bytes_allocated, std::memory_order_relaxed);
to_space_objects_skipped_.fetch_add(1, std::memory_order_relaxed);
MutexLock mu(self, skipped_blocks_lock_);
skipped_blocks_map_.insert(std::make_pair(bytes_allocated,
reinterpret_cast<uint8_t*>(to_ref)));
}
} else {
DCHECK(heap_->non_moving_space_->HasAddress(to_ref));
DCHECK_EQ(bytes_allocated, non_moving_space_bytes_allocated);
// Free the non-moving-space chunk.
heap_->non_moving_space_->Free(self, to_ref);
}
// Get the winner's forward ptr.
mirror::Object* lost_fwd_ptr = to_ref;
to_ref = reinterpret_cast<mirror::Object*>(old_lock_word.ForwardingAddress());
CHECK(to_ref != nullptr);
CHECK_NE(to_ref, lost_fwd_ptr);
CHECK(region_space_->IsInToSpace(to_ref) || heap_->non_moving_space_->HasAddress(to_ref))
<< "to_ref=" << to_ref << " " << heap_->DumpSpaces();
CHECK_NE(to_ref->GetLockWord(false).GetState(), LockWord::kForwardingAddress);
return to_ref;
}
// Copy the old lock word over since we did not copy it yet.
to_ref->SetLockWord(old_lock_word, false);
// Set the gray ptr.
if (kUseBakerReadBarrier) {
to_ref->SetReadBarrierState(ReadBarrier::GrayState());
}
// Do a fence to prevent the field CAS in ConcurrentCopying::Process from possibly reordering
// before the object copy.
std::atomic_thread_fence(std::memory_order_release);
LockWord new_lock_word = LockWord::FromForwardingAddress(reinterpret_cast<size_t>(to_ref));
// Try to atomically write the fwd ptr.
bool success = from_ref->CasLockWord(old_lock_word,
new_lock_word,
CASMode::kWeak,
std::memory_order_relaxed);
if (LIKELY(success)) {
// The CAS succeeded.
DCHECK(thread_running_gc_ != nullptr);
if (LIKELY(self == thread_running_gc_)) {
objects_moved_gc_thread_ += 1;
bytes_moved_gc_thread_ += bytes_allocated;
} else {
objects_moved_.fetch_add(1, std::memory_order_relaxed);
bytes_moved_.fetch_add(bytes_allocated, std::memory_order_relaxed);
}
if (LIKELY(!fall_back_to_non_moving)) {
DCHECK(region_space_->IsInToSpace(to_ref));
} else {
DCHECK(heap_->non_moving_space_->HasAddress(to_ref));
DCHECK_EQ(bytes_allocated, non_moving_space_bytes_allocated);
if (!use_generational_cc_ || !young_gen_) {
// Mark it in the live bitmap.
CHECK(!heap_->non_moving_space_->GetLiveBitmap()->AtomicTestAndSet(to_ref));
}
if (!kUseBakerReadBarrier) {
// Mark it in the mark bitmap.
CHECK(!heap_->non_moving_space_->GetMarkBitmap()->AtomicTestAndSet(to_ref));
}
}
if (kUseBakerReadBarrier) {
DCHECK(to_ref->GetReadBarrierState() == ReadBarrier::GrayState());
}
DCHECK(GetFwdPtr(from_ref) == to_ref);
CHECK_NE(to_ref->GetLockWord(false).GetState(), LockWord::kForwardingAddress);
PushOntoMarkStack(self, to_ref);
return to_ref;
} else {
// The CAS failed. It may have lost the race or may have failed
// due to monitor/hashcode ops. Either way, retry.
}
}
}
mirror::Object* ConcurrentCopying::IsMarked(mirror::Object* from_ref) {
DCHECK(from_ref != nullptr);
space::RegionSpace::RegionType rtype = region_space_->GetRegionType(from_ref);
if (rtype == space::RegionSpace::RegionType::kRegionTypeToSpace) {
// It's already marked.
return from_ref;
}
mirror::Object* to_ref;
if (rtype == space::RegionSpace::RegionType::kRegionTypeFromSpace) {
to_ref = GetFwdPtr(from_ref);
DCHECK(to_ref == nullptr || region_space_->IsInToSpace(to_ref) ||
heap_->non_moving_space_->HasAddress(to_ref))
<< "from_ref=" << from_ref << " to_ref=" << to_ref;
} else if (rtype == space::RegionSpace::RegionType::kRegionTypeUnevacFromSpace) {
if (IsMarkedInUnevacFromSpace(from_ref)) {
to_ref = from_ref;
} else {
to_ref = nullptr;
}
} else {
// At this point, `from_ref` should not be in the region space
// (i.e. within an "unused" region).
DCHECK(!region_space_->HasAddress(from_ref)) << from_ref;
// from_ref is in a non-moving space.
if (immune_spaces_.ContainsObject(from_ref)) {
// An immune object is alive.
to_ref = from_ref;
} else {
// Non-immune non-moving space. Use the mark bitmap.
if (IsMarkedInNonMovingSpace(from_ref)) {
// Already marked.
to_ref = from_ref;
} else {
to_ref = nullptr;
}
}
}
return to_ref;
}
bool ConcurrentCopying::IsOnAllocStack(mirror::Object* ref) {
// TODO: Explain why this is here. What release operation does it pair with?
std::atomic_thread_fence(std::memory_order_acquire);
accounting::ObjectStack* alloc_stack = GetAllocationStack();
return alloc_stack->Contains(ref);
}
mirror::Object* ConcurrentCopying::MarkNonMoving(Thread* const self,
mirror::Object* ref,
mirror::Object* holder,
MemberOffset offset) {
// ref is in a non-moving space (from_ref == to_ref).
DCHECK(!region_space_->HasAddress(ref)) << ref;
DCHECK(!immune_spaces_.ContainsObject(ref));
// Use the mark bitmap.
accounting::ContinuousSpaceBitmap* mark_bitmap = heap_->GetNonMovingSpace()->GetMarkBitmap();
accounting::LargeObjectBitmap* los_bitmap = nullptr;
const bool is_los = !mark_bitmap->HasAddress(ref);
if (is_los) {
if (!IsAligned<kPageSize>(ref)) {
// Ref is a large object that is not aligned, it must be heap
// corruption. Remove memory protection and dump data before
// AtomicSetReadBarrierState since it will fault if the address is not
// valid.
region_space_->Unprotect();
heap_->GetVerification()->LogHeapCorruption(holder, offset, ref, /* fatal= */ true);
}
DCHECK(heap_->GetLargeObjectsSpace())
<< "ref=" << ref
<< " doesn't belong to non-moving space and large object space doesn't exist";
los_bitmap = heap_->GetLargeObjectsSpace()->GetMarkBitmap();
DCHECK(los_bitmap->HasAddress(ref));
}
if (use_generational_cc_) {
// The sticky-bit CC collector is only compatible with Baker-style read barriers.
DCHECK(kUseBakerReadBarrier);
// Not done scanning, use AtomicSetReadBarrierPointer.
if (!done_scanning_.load(std::memory_order_acquire)) {
// Since the mark bitmap is still filled in from last GC, we can not use that or else the
// mutator may see references to the from space. Instead, use the Baker pointer itself as
// the mark bit.
//
// We need to avoid marking objects that are on allocation stack as that will lead to a
// situation (after this GC cycle is finished) where some object(s) are on both allocation
// stack and live bitmap. This leads to visiting the same object(s) twice during a heapdump
// (b/117426281).
if (!IsOnAllocStack(ref) &&
ref->AtomicSetReadBarrierState(ReadBarrier::NonGrayState(), ReadBarrier::GrayState())) {
// TODO: We don't actually need to scan this object later, we just need to clear the gray
// bit.
// We don't need to mark newly allocated objects (those in allocation stack) as they can
// only point to to-space objects. Also, they are considered live till the next GC cycle.
PushOntoMarkStack(self, ref);
}
return ref;
}
}
if (!is_los && mark_bitmap->Test(ref)) {
// Already marked.
} else if (is_los && los_bitmap->Test(ref)) {
// Already marked in LOS.
} else if (IsOnAllocStack(ref)) {
// If it's on the allocation stack, it's considered marked. Keep it white (non-gray).
// Objects on the allocation stack need not be marked.
if (!is_los) {
DCHECK(!mark_bitmap->Test(ref));
} else {
DCHECK(!los_bitmap->Test(ref));
}
if (kUseBakerReadBarrier) {
DCHECK_EQ(ref->GetReadBarrierState(), ReadBarrier::NonGrayState());
}
} else {
// Not marked nor on the allocation stack. Try to mark it.
// This may or may not succeed, which is ok.
bool success = false;
if (kUseBakerReadBarrier) {
success = ref->AtomicSetReadBarrierState(ReadBarrier::NonGrayState(),
ReadBarrier::GrayState());
} else {
success = is_los ?
!los_bitmap->AtomicTestAndSet(ref) :
!mark_bitmap->AtomicTestAndSet(ref);
}
if (success) {
if (kUseBakerReadBarrier) {
DCHECK_EQ(ref->GetReadBarrierState(), ReadBarrier::GrayState());
}
PushOntoMarkStack(self, ref);
}
}
return ref;
}
void ConcurrentCopying::FinishPhase() {
Thread* const self = Thread::Current();
{
MutexLock mu(self, mark_stack_lock_);
CHECK_EQ(pooled_mark_stacks_.size(), kMarkStackPoolSize);
}
// kVerifyNoMissingCardMarks relies on the region space cards not being cleared to avoid false
// positives.
if (!kVerifyNoMissingCardMarks && !use_generational_cc_) {
TimingLogger::ScopedTiming split("ClearRegionSpaceCards", GetTimings());
// We do not currently use the region space cards at all, madvise them away to save ram.
heap_->GetCardTable()->ClearCardRange(region_space_->Begin(), region_space_->Limit());
} else if (use_generational_cc_ && !young_gen_) {
region_space_inter_region_bitmap_->Clear();
non_moving_space_inter_region_bitmap_->Clear();
}
{
MutexLock mu(self, skipped_blocks_lock_);
skipped_blocks_map_.clear();
}
{
ReaderMutexLock mu(self, *Locks::mutator_lock_);
{
WriterMutexLock mu2(self, *Locks::heap_bitmap_lock_);
heap_->ClearMarkedObjects();
}
if (kUseBakerReadBarrier && kFilterModUnionCards) {
TimingLogger::ScopedTiming split("FilterModUnionCards", GetTimings());
ReaderMutexLock mu2(self, *Locks::heap_bitmap_lock_);
for (space::ContinuousSpace* space : immune_spaces_.GetSpaces()) {
DCHECK(space->IsImageSpace() || space->IsZygoteSpace());
accounting::ModUnionTable* table = heap_->FindModUnionTableFromSpace(space);
// Filter out cards that don't need to be set.
if (table != nullptr) {
table->FilterCards();
}
}
}
if (kUseBakerReadBarrier) {
TimingLogger::ScopedTiming split("EmptyRBMarkBitStack", GetTimings());
DCHECK(rb_mark_bit_stack_ != nullptr);
const auto* limit = rb_mark_bit_stack_->End();
for (StackReference<mirror::Object>* it = rb_mark_bit_stack_->Begin(); it != limit; ++it) {
CHECK(it->AsMirrorPtr()->AtomicSetMarkBit(1, 0))
<< "rb_mark_bit_stack_->Begin()" << rb_mark_bit_stack_->Begin() << '\n'
<< "rb_mark_bit_stack_->End()" << rb_mark_bit_stack_->End() << '\n'
<< "rb_mark_bit_stack_->IsFull()"
<< std::boolalpha << rb_mark_bit_stack_->IsFull() << std::noboolalpha << '\n'
<< DumpReferenceInfo(it->AsMirrorPtr(), "*it");
}
rb_mark_bit_stack_->Reset();
}
}
if (measure_read_barrier_slow_path_) {
MutexLock mu(self, rb_slow_path_histogram_lock_);
rb_slow_path_time_histogram_.AdjustAndAddValue(
rb_slow_path_ns_.load(std::memory_order_relaxed));
rb_slow_path_count_total_ += rb_slow_path_count_.load(std::memory_order_relaxed);
rb_slow_path_count_gc_total_ += rb_slow_path_count_gc_.load(std::memory_order_relaxed);
}
}
bool ConcurrentCopying::IsNullOrMarkedHeapReference(mirror::HeapReference<mirror::Object>* field,
bool do_atomic_update) {
mirror::Object* from_ref = field->AsMirrorPtr();
if (from_ref == nullptr) {
return true;
}
mirror::Object* to_ref = IsMarked(from_ref);
if (to_ref == nullptr) {
return false;
}
if (from_ref != to_ref) {
if (do_atomic_update) {
do {
if (field->AsMirrorPtr() != from_ref) {
// Concurrently overwritten by a mutator.
break;
}
} while (!field->CasWeakRelaxed(from_ref, to_ref));
} else {
// TODO: Why is this seq_cst when the above is relaxed? Document memory ordering.
field->Assign</* kIsVolatile= */ true>(to_ref);
}
}
return true;
}
mirror::Object* ConcurrentCopying::MarkObject(mirror::Object* from_ref) {
return Mark(Thread::Current(), from_ref);
}
void ConcurrentCopying::DelayReferenceReferent(ObjPtr<mirror::Class> klass,
ObjPtr<mirror::Reference> reference) {
heap_->GetReferenceProcessor()->DelayReferenceReferent(klass, reference, this);
}
void ConcurrentCopying::ProcessReferences(Thread* self) {
TimingLogger::ScopedTiming split("ProcessReferences", GetTimings());
// We don't really need to lock the heap bitmap lock as we use CAS to mark in bitmaps.
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
GetHeap()->GetReferenceProcessor()->ProcessReferences(
/*concurrent=*/ true, GetTimings(), GetCurrentIteration()->GetClearSoftReferences(), this);
}
void ConcurrentCopying::RevokeAllThreadLocalBuffers() {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
region_space_->RevokeAllThreadLocalBuffers();
}
mirror::Object* ConcurrentCopying::MarkFromReadBarrierWithMeasurements(Thread* const self,
mirror::Object* from_ref) {
if (self != thread_running_gc_) {
rb_slow_path_count_.fetch_add(1u, std::memory_order_relaxed);
} else {
rb_slow_path_count_gc_.fetch_add(1u, std::memory_order_relaxed);
}
ScopedTrace tr(__FUNCTION__);
const uint64_t start_time = measure_read_barrier_slow_path_ ? NanoTime() : 0u;
mirror::Object* ret =
Mark</*kGrayImmuneObject=*/true, /*kNoUnEvac=*/false, /*kFromGCThread=*/false>(self,
from_ref);
if (measure_read_barrier_slow_path_) {
rb_slow_path_ns_.fetch_add(NanoTime() - start_time, std::memory_order_relaxed);
}
return ret;
}
void ConcurrentCopying::DumpPerformanceInfo(std::ostream& os) {
GarbageCollector::DumpPerformanceInfo(os);
size_t num_gc_cycles = GetCumulativeTimings().GetIterations();
MutexLock mu(Thread::Current(), rb_slow_path_histogram_lock_);
if (rb_slow_path_time_histogram_.SampleSize() > 0) {
Histogram<uint64_t>::CumulativeData cumulative_data;
rb_slow_path_time_histogram_.CreateHistogram(&cumulative_data);
rb_slow_path_time_histogram_.PrintConfidenceIntervals(os, 0.99, cumulative_data);
}
if (rb_slow_path_count_total_ > 0) {
os << "Slow path count " << rb_slow_path_count_total_ << "\n";
}
if (rb_slow_path_count_gc_total_ > 0) {
os << "GC slow path count " << rb_slow_path_count_gc_total_ << "\n";
}
os << "Average " << (young_gen_ ? "minor" : "major") << " GC reclaim bytes ratio "
<< (reclaimed_bytes_ratio_sum_ / num_gc_cycles) << " over " << num_gc_cycles
<< " GC cycles\n";
os << "Average " << (young_gen_ ? "minor" : "major") << " GC copied live bytes ratio "
<< (copied_live_bytes_ratio_sum_ / gc_count_) << " over " << gc_count_
<< " " << (young_gen_ ? "minor" : "major") << " GCs\n";
os << "Cumulative bytes moved "
<< cumulative_bytes_moved_.load(std::memory_order_relaxed) << "\n";
os << "Cumulative objects moved "
<< cumulative_objects_moved_.load(std::memory_order_relaxed) << "\n";
os << "Peak regions allocated "
<< region_space_->GetMaxPeakNumNonFreeRegions() << " ("
<< PrettySize(region_space_->GetMaxPeakNumNonFreeRegions() * space::RegionSpace::kRegionSize)
<< ") / " << region_space_->GetNumRegions() / 2 << " ("
<< PrettySize(region_space_->GetNumRegions() * space::RegionSpace::kRegionSize / 2)
<< ")\n";
}
} // namespace collector
} // namespace gc
} // namespace art