blob: 0b61b9ab653641937263ac8a2ba8e45fdcf65394 [file] [log] [blame]
// Copyright 2011 Google Inc. All Rights Reserved.
#include "mark_sweep.h"
#include <climits>
#include <vector>
#include "heap.h"
#include "logging.h"
#include "macros.h"
#include "mark_stack.h"
#include "object.h"
#include "class_loader.h"
#include "runtime.h"
#include "space.h"
#include "thread.h"
namespace art {
bool MarkSweep::Init() {
mark_stack_ = MarkStack::Create();
if (mark_stack_ == NULL) {
return false;
}
mark_bitmap_ = Heap::GetMarkBits();
live_bitmap_ = Heap::GetLiveBits();
// TODO: if concurrent, clear the card table.
// TODO: check that the mark bitmap is entirely clear.
return true;
}
void MarkSweep::MarkObject0(const Object* obj, bool check_finger) {
DCHECK(obj != NULL);
if (obj < condemned_) {
DCHECK(IsMarked(obj));
return;
}
bool is_marked = mark_bitmap_->Test(obj);
// This object was not previously marked.
if (!is_marked) {
mark_bitmap_->Set(obj);
if (check_finger && obj < finger_) {
// The object must be pushed on to the mark stack.
mark_stack_->Push(obj);
}
}
}
// Used to mark objects when recursing. Recursion is done by moving
// the finger across the bitmaps in address order and marking child
// objects. Any newly-marked objects whose addresses are lower than
// the finger won't be visited by the bitmap scan, so those objects
// need to be added to the mark stack.
void MarkSweep::MarkObject(const Object* obj) {
if (obj != NULL) {
MarkObject0(obj, true);
}
}
void MarkSweep::MarkObjectVisitor(const Object* root, void* arg) {
DCHECK(root != NULL);
DCHECK(arg != NULL);
MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg);
mark_sweep->MarkObject0(root, true);
}
// Marks all objects in the root set.
void MarkSweep::MarkRoots() {
Runtime::Current()->VisitRoots(MarkObjectVisitor, this);
}
void MarkSweep::ScanBitmapCallback(Object* obj, void* finger, void* arg) {
MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg);
mark_sweep->finger_ = reinterpret_cast<Object*>(finger);
mark_sweep->ScanObject(obj);
}
// Populates the mark stack based on the set of marked objects and
// recursively marks until the mark stack is emptied.
void MarkSweep::RecursiveMark() {
// RecursiveMark will build the lists of known instances of the Reference classes.
// See DelayReferenceReferent for details.
CHECK(soft_reference_list_ == NULL);
CHECK(weak_reference_list_ == NULL);
CHECK(finalizer_reference_list_ == NULL);
CHECK(phantom_reference_list_ == NULL);
CHECK(cleared_reference_list_ == NULL);
void* arg = reinterpret_cast<void*>(this);
const std::vector<Space*>& spaces = Heap::GetSpaces();
for (size_t i = 0; i < spaces.size(); ++i) {
if (spaces[i]->IsCondemned()) {
uintptr_t base = reinterpret_cast<uintptr_t>(spaces[i]->GetBase());
mark_bitmap_->ScanWalk(base, &MarkSweep::ScanBitmapCallback, arg);
}
}
finger_ = reinterpret_cast<Object*>(~0);
ProcessMarkStack();
}
void MarkSweep::ReMarkRoots() {
UNIMPLEMENTED(FATAL);
}
void MarkSweep::SweepSystemWeaks() {
//Runtime::Current()->GetInternTable().RemoveWeakIf(isUnmarkedObject);
UNIMPLEMENTED(FATAL);
//dvmSweepMonitorList(&gDvm.monitorList, isUnmarkedObject);
//sweepWeakJniGlobals();
}
void MarkSweep::SweepCallback(size_t num_ptrs, void **ptrs, void *arg) {
// TODO, lock heap if concurrent
Space* space = static_cast<Space*>(arg);
for (size_t i = 0; i < num_ptrs; ++i) {
Object* obj = static_cast<Object*>(ptrs[i]);
space->Free(obj);
}
// TODO, unlock heap if concurrent
}
void MarkSweep::Sweep() {
const std::vector<Space*>& spaces = Heap::GetSpaces();
for (size_t i = 0; i < spaces.size(); ++i) {
if (spaces[i]->IsCondemned()) {
uintptr_t base = reinterpret_cast<uintptr_t>(spaces[i]->GetBase());
uintptr_t limit = reinterpret_cast<uintptr_t>(spaces[i]->GetLimit());
void* arg = static_cast<void*>(spaces[i]);
HeapBitmap::SweepWalk(*live_bitmap_, *mark_bitmap_, base, limit,
&MarkSweep::SweepCallback, arg);
}
}
}
// Scans instance fields.
void MarkSweep::ScanInstanceFields(const Object* obj) {
DCHECK(obj != NULL);
Class* klass = obj->GetClass();
DCHECK(klass != NULL);
ScanFields(obj,
klass->GetReferenceInstanceOffsets(),
false);
}
// Scans static storage on a Class.
void MarkSweep::ScanStaticFields(const Class* klass) {
DCHECK(klass != NULL);
ScanFields(klass,
klass->GetReferenceStaticOffsets(),
true);
}
void MarkSweep::ScanFields(const Object* obj,
uint32_t ref_offsets,
bool is_static) {
if (ref_offsets != CLASS_WALK_SUPER) {
// Found a reference offset bitmap. Mark the specified offsets.
while (ref_offsets != 0) {
size_t right_shift = CLZ(ref_offsets);
size_t byte_offset = CLASS_OFFSET_FROM_CLZ(right_shift);
const Object* ref = obj->GetFieldObject(byte_offset);
MarkObject(ref);
ref_offsets &= ~(CLASS_HIGH_BIT >> right_shift);
}
} else {
// There is no reference offset bitmap. In the non-static case,
// walk up the class inheritance hierarchy and find reference
// offsets the hard way. In the static case, just consider this
// class.
for (const Class* klass = is_static ? obj->AsClass() : obj->GetClass();
klass != NULL;
klass = is_static ? NULL : klass->GetSuperClass()) {
size_t num_reference_fields = (is_static
? klass->NumReferenceStaticFields()
: klass->NumReferenceInstanceFields());
for (size_t i = 0; i < num_reference_fields; ++i) {
Field* field = (is_static
? klass->GetStaticField(i)
: klass->GetInstanceField(i));
size_t field_offset = field->GetOffset();
const Object* ref = obj->GetFieldObject(field_offset);
MarkObject(ref);
}
}
}
}
void MarkSweep::ScanInterfaces(const Class* klass) {
DCHECK(klass != NULL);
for (size_t i = 0; i < klass->NumInterfaces(); ++i) {
MarkObject(klass->GetInterface(i));
}
}
// Scans the header, static field references, and interface pointers
// of a class object.
void MarkSweep::ScanClass(const Object* obj) {
DCHECK(obj != NULL);
DCHECK(obj->IsClass());
const Class* klass = obj->AsClass();
MarkObject(klass->GetClass());
if (klass->IsArrayClass()) {
MarkObject(klass->GetComponentType());
}
if (klass->IsLoaded()) {
MarkObject(klass->GetSuperClass());
}
MarkObject(klass->GetClassLoader());
ScanInstanceFields(obj);
ScanStaticFields(klass);
// TODO: scan methods
// TODO: scan instance fields
if (klass->IsLoaded()) {
ScanInterfaces(klass);
}
}
// Scans the header of all array objects. If the array object is
// specialized to a reference type, scans the array data as well.
void MarkSweep::ScanArray(const Object* obj) {
DCHECK(obj != NULL);
DCHECK(obj->GetClass() != NULL);
MarkObject(obj->GetClass());
if (obj->IsObjectArray()) {
const ObjectArray<Object>* array = obj->AsObjectArray<Object>();
for (int32_t i = 0; i < array->GetLength(); ++i) {
const Object* element = array->Get(i);
MarkObject(element);
}
}
}
void MarkSweep::EnqueuePendingReference(Object* ref, Object** list) {
DCHECK(ref != NULL);
DCHECK(list != NULL);
size_t offset = Heap::GetReferencePendingNextOffset();
if (*list == NULL) {
ref->SetFieldObject(offset, ref);
*list = ref;
} else {
Object* head = (*list)->GetFieldObject(offset);
ref->SetFieldObject(offset, head);
(*list)->SetFieldObject(offset, ref);
}
}
Object* MarkSweep::DequeuePendingReference(Object** list) {
DCHECK(list != NULL);
DCHECK(*list != NULL);
size_t offset = Heap::GetReferencePendingNextOffset();
Object* head = (*list)->GetFieldObject(offset);
Object* ref;
if (*list == head) {
ref = *list;
*list = NULL;
} else {
Object* next = head->GetFieldObject(offset);
(*list)->SetFieldObject(offset, next);
ref = head;
}
ref->SetFieldObject(offset, NULL);
return ref;
}
// Process the "referent" field in a java.lang.ref.Reference. If the
// referent has not yet been marked, put it on the appropriate list in
// the gcHeap for later processing.
void MarkSweep::DelayReferenceReferent(Object* obj) {
DCHECK(obj != NULL);
Class* klass = obj->GetClass();
DCHECK(klass != NULL);
DCHECK(klass->IsReference());
Object* pending = obj->GetFieldObject(Heap::GetReferencePendingNextOffset());
Object* referent = obj->GetFieldObject(Heap::GetReferenceReferentOffset());
if (pending == NULL && referent != NULL && !IsMarked(referent)) {
Object** list = NULL;
if (klass->IsSoftReference()) {
list = &soft_reference_list_;
} else if (klass->IsWeakReference()) {
list = &weak_reference_list_;
} else if (klass->IsFinalizerReference()) {
list = &finalizer_reference_list_;
} else if (klass->IsPhantomReference()) {
list = &phantom_reference_list_;
}
DCHECK(list != NULL);
EnqueuePendingReference(obj, list);
}
}
// Scans the header and field references of a data object. If the
// scanned object is a reference subclass, it is scheduled for later
// processing
void MarkSweep::ScanOther(const Object* obj) {
DCHECK(obj != NULL);
Class* klass = obj->GetClass();
DCHECK(klass != NULL);
MarkObject(klass);
ScanInstanceFields(obj);
if (klass->IsReference()) {
DelayReferenceReferent(const_cast<Object*>(obj));
}
}
// Scans an object reference. Determines the type of the reference
// and dispatches to a specialized scanning routine.
void MarkSweep::ScanObject(const Object* obj) {
DCHECK(obj != NULL);
DCHECK(obj->GetClass() != NULL);
DCHECK(IsMarked(obj));
if (obj->IsClass()) {
ScanClass(obj);
} else if (obj->IsArrayInstance()) {
ScanArray(obj);
} else {
ScanOther(obj);
}
}
// Scan anything that's on the mark stack. We can't use the bitmaps
// anymore, so use a finger that points past the end of them.
void MarkSweep::ProcessMarkStack() {
while (!mark_stack_->IsEmpty()) {
const Object* obj = mark_stack_->Pop();
ScanObject(obj);
}
}
void MarkSweep::ScanDirtyObjects() {
ProcessMarkStack();
}
void MarkSweep::ClearReference(Object* ref) {
DCHECK(ref != NULL);
ref->SetFieldObject(Heap::GetReferenceReferentOffset(), NULL);
}
bool MarkSweep::IsEnqueuable(const Object* ref) {
DCHECK(ref != NULL);
const Object* queue = ref->GetFieldObject(Heap::GetReferenceQueueOffset());
const Object* queue_next = ref->GetFieldObject(Heap::GetReferenceQueueNextOffset());
return (queue != NULL) && (queue_next == NULL);
}
void MarkSweep::EnqueueReference(Object* ref) {
DCHECK(ref != NULL);
CHECK(ref->GetFieldObject(Heap::GetReferenceQueueOffset()) != NULL);
CHECK(ref->GetFieldObject(Heap::GetReferenceQueueNextOffset()) == NULL);
EnqueuePendingReference(ref, &cleared_reference_list_);
}
// Walks the reference list marking any references subject to the
// reference clearing policy. References with a black referent are
// removed from the list. References with white referents biased
// toward saving are blackened and also removed from the list.
void MarkSweep::PreserveSomeSoftReferences(Object** list) {
DCHECK(list != NULL);
Object* clear = NULL;
size_t counter = 0;
while (*list != NULL) {
Object* ref = DequeuePendingReference(list);
Object* referent = ref->GetFieldObject(Heap::GetReferenceReferentOffset());
if (referent == NULL) {
// Referent was cleared by the user during marking.
continue;
}
bool is_marked = IsMarked(referent);
if (!is_marked && ((++counter) & 1)) {
// Referent is white and biased toward saving, mark it.
MarkObject(referent);
is_marked = true;
}
if (!is_marked) {
// Referent is white, queue it for clearing.
EnqueuePendingReference(ref, &clear);
}
}
*list = clear;
// Restart the mark with the newly black references added to the
// root set.
ProcessMarkStack();
}
// Unlink the reference list clearing references objects with white
// referents. Cleared references registered to a reference queue are
// scheduled for appending by the heap worker thread.
void MarkSweep::ClearWhiteReferences(Object** list) {
DCHECK(list != NULL);
size_t offset = Heap::GetReferenceReferentOffset();
while (*list != NULL) {
Object* ref = DequeuePendingReference(list);
Object* referent = ref->GetFieldObject(offset);
if (referent != NULL && !IsMarked(referent)) {
// Referent is white, clear it.
ClearReference(ref);
if (IsEnqueuable(ref)) {
EnqueueReference(ref);
}
}
}
DCHECK(*list == NULL);
}
// Enqueues finalizer references with white referents. White
// referents are blackened, moved to the zombie field, and the
// referent field is cleared.
void MarkSweep::EnqueueFinalizerReferences(Object** list) {
DCHECK(list != NULL);
size_t referent_offset = Heap::GetReferenceReferentOffset();
size_t zombie_offset = Heap::GetFinalizerReferenceZombieOffset();
bool has_enqueued = false;
while (*list != NULL) {
Object* ref = DequeuePendingReference(list);
Object* referent = ref->GetFieldObject(referent_offset);
if (referent != NULL && !IsMarked(referent)) {
MarkObject(referent);
// If the referent is non-null the reference must queuable.
DCHECK(IsEnqueuable(ref));
ref->SetFieldObject(zombie_offset, referent);
ClearReference(ref);
EnqueueReference(ref);
has_enqueued = true;
}
}
if (has_enqueued) {
ProcessMarkStack();
}
DCHECK(*list == NULL);
}
// Process reference class instances and schedule finalizations.
void MarkSweep::ProcessReferences(Object** soft_references, bool clear_soft,
Object** weak_references,
Object** finalizer_references,
Object** phantom_references) {
DCHECK(soft_references != NULL);
DCHECK(weak_references != NULL);
DCHECK(finalizer_references != NULL);
DCHECK(phantom_references != NULL);
// Unless we are in the zygote or required to clear soft references
// with white references, preserve some white referents.
if (clear_soft) {
PreserveSomeSoftReferences(soft_references);
}
// Clear all remaining soft and weak references with white
// referents.
ClearWhiteReferences(soft_references);
ClearWhiteReferences(weak_references);
// Preserve all white objects with finalize methods and schedule
// them for finalization.
EnqueueFinalizerReferences(finalizer_references);
// Clear all f-reachable soft and weak references with white
// referents.
ClearWhiteReferences(soft_references);
ClearWhiteReferences(weak_references);
// Clear all phantom references with white referents.
ClearWhiteReferences(phantom_references);
// At this point all reference lists should be empty.
DCHECK(*soft_references == NULL);
DCHECK(*weak_references == NULL);
DCHECK(*finalizer_references == NULL);
DCHECK(*phantom_references == NULL);
}
// Pushes a list of cleared references out to the managed heap.
void MarkSweep::EnqueueClearedReferences(Object** cleared) {
DCHECK(cleared != NULL);
if (*cleared != NULL) {
Thread* self = Thread::Current();
DCHECK(self != NULL);
// TODO: Method *meth = gDvm.methJavaLangRefReferenceQueueAdd;
// DCHECK(meth != NULL);
// JValue unused;
// Object* reference = *cleared;
// TODO: dvmCallMethod(self, meth, NULL, &unused, reference);
UNIMPLEMENTED(FATAL);
*cleared = NULL;
}
}
MarkSweep::~MarkSweep() {
delete mark_stack_;
mark_bitmap_->Clear();
}
} // namespace art