Add IndirectReferenceTable and initialize all the instances.
We're not _using_ any of the tables yet (except in tests), but all the
reference tables are now in place.
Change-Id: Ifd3fc114254460b4a1302520f2a4653319b113e5
diff --git a/src/indirect_reference_table.h b/src/indirect_reference_table.h
new file mode 100644
index 0000000..857b9cd
--- /dev/null
+++ b/src/indirect_reference_table.h
@@ -0,0 +1,365 @@
+/*
+ * Copyright (C) 2009 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.
+ */
+
+#ifndef ART_SRC_INDIRECT_REFERENCE_TABLE_H_
+#define ART_SRC_INDIRECT_REFERENCE_TABLE_H_
+
+#include "logging.h"
+
+#include <iosfwd>
+#include <stdint.h>
+#include <string>
+
+namespace art {
+
+class Object;
+
+/*
+ * Maintain a table of indirect references. Used for local/global JNI
+ * references.
+ *
+ * The table contains object references that are part of the GC root set.
+ * When an object is added we return an IndirectRef that is not a valid
+ * pointer but can be used to find the original value in O(1) time.
+ * Conversions to and from indirect refs are performed on JNI method calls
+ * in and out of the VM, so they need to be very fast.
+ *
+ * To be efficient for JNI local variable storage, we need to provide
+ * operations that allow us to operate on segments of the table, where
+ * segments are pushed and popped as if on a stack. For example, deletion
+ * of an entry should only succeed if it appears in the current segment,
+ * and we want to be able to strip off the current segment quickly when
+ * a method returns. Additions to the table must be made in the current
+ * segment even if space is available in an earlier area.
+ *
+ * A new segment is created when we call into native code from interpreted
+ * code, or when we handle the JNI PushLocalFrame function.
+ *
+ * The GC must be able to scan the entire table quickly.
+ *
+ * In summary, these must be very fast:
+ * - adding or removing a segment
+ * - adding references to a new segment
+ * - converting an indirect reference back to an Object
+ * These can be a little slower, but must still be pretty quick:
+ * - adding references to a "mature" segment
+ * - removing individual references
+ * - scanning the entire table straight through
+ *
+ * If there's more than one segment, we don't guarantee that the table
+ * will fill completely before we fail due to lack of space. We do ensure
+ * that the current segment will pack tightly, which should satisfy JNI
+ * requirements (e.g. EnsureLocalCapacity).
+ *
+ * To make everything fit nicely in 32-bit integers, the maximum size of
+ * the table is capped at 64K.
+ *
+ * None of the table functions are synchronized.
+ */
+
+/*
+ * Indirect reference definition. This must be interchangeable with JNI's
+ * jobject, and it's convenient to let null be null, so we use void*.
+ *
+ * We need a 16-bit table index and a 2-bit reference type (global, local,
+ * weak global). Real object pointers will have zeroes in the low 2 or 3
+ * bits (4- or 8-byte alignment), so it's useful to put the ref type
+ * in the low bits and reserve zero as an invalid value.
+ *
+ * The remaining 14 bits can be used to detect stale indirect references.
+ * For example, if objects don't move, we can use a hash of the original
+ * Object* to make sure the entry hasn't been re-used. (If the Object*
+ * we find there doesn't match because of heap movement, we could do a
+ * secondary check on the preserved hash value; this implies that creating
+ * a global/local ref queries the hash value and forces it to be saved.)
+ *
+ * A more rigorous approach would be to put a serial number in the extra
+ * bits, and keep a copy of the serial number in a parallel table. This is
+ * easier when objects can move, but requires 2x the memory and additional
+ * memory accesses on add/get. It will catch additional problems, e.g.:
+ * create iref1 for obj, delete iref1, create iref2 for same obj, lookup
+ * iref1. A pattern based on object bits will miss this.
+ */
+typedef void* IndirectRef;
+
+/* magic failure values; must not pass dvmIsHeapAddress() */
+static Object* const kInvalidIndirectRefObject = reinterpret_cast<Object*>(0xdead4321);
+static Object* const kClearedJniWeakGlobal = reinterpret_cast<Object*>(0xdead1234);
+
+/*
+ * Indirect reference kind, used as the two low bits of IndirectRef.
+ *
+ * For convenience these match up with enum jobjectRefType from jni.h.
+ */
+enum IndirectRefKind {
+ kInvalid = 0,
+ kLocal = 1,
+ kGlobal = 2,
+ kWeakGlobal = 3
+};
+std::ostream& operator<<(std::ostream& os, IndirectRefKind rhs);
+
+/*
+ * Determine what kind of indirect reference this is.
+ */
+static inline IndirectRefKind GetIndirectRefKind(IndirectRef iref) {
+ return static_cast<IndirectRefKind>(reinterpret_cast<uintptr_t>(iref) & 0x03);
+}
+
+/*
+ * Extended debugging structure. We keep a parallel array of these, one
+ * per slot in the table.
+ */
+static const size_t kIRTPrevCount = 4;
+struct IndirectRefSlot {
+ uint32_t serial;
+ Object* previous[kIRTPrevCount];
+};
+
+/* use as initial value for "cookie", and when table has only one segment */
+static const uint32_t IRT_FIRST_SEGMENT = 0;
+
+/*
+ * Table definition.
+ *
+ * For the global reference table, the expected common operations are
+ * adding a new entry and removing a recently-added entry (usually the
+ * most-recently-added entry). For JNI local references, the common
+ * operations are adding a new entry and removing an entire table segment.
+ *
+ * If "alloc_entries_" is not equal to "max_entries_", the table may expand
+ * when entries are added, which means the memory may move. If you want
+ * to keep pointers into "table" rather than offsets, you must use a
+ * fixed-size table.
+ *
+ * If we delete entries from the middle of the list, we will be left with
+ * "holes". We track the number of holes so that, when adding new elements,
+ * we can quickly decide to do a trivial append or go slot-hunting.
+ *
+ * When the top-most entry is removed, any holes immediately below it are
+ * also removed. Thus, deletion of an entry may reduce "topIndex" by more
+ * than one.
+ *
+ * To get the desired behavior for JNI locals, we need to know the bottom
+ * and top of the current "segment". The top is managed internally, and
+ * the bottom is passed in as a function argument (the VM keeps it in a
+ * slot in the interpreted stack frame). When we call a native method or
+ * push a local frame, the current top index gets pushed on, and serves
+ * as the new bottom. When we pop a frame off, the value from the stack
+ * becomes the new top index, and the value stored in the previous frame
+ * becomes the new bottom.
+ *
+ * To avoid having to re-scan the table after a pop, we want to push the
+ * number of holes in the table onto the stack. Because of our 64K-entry
+ * cap, we can combine the two into a single unsigned 32-bit value.
+ * Instead of a "bottom" argument we take a "cookie", which includes the
+ * bottom index and the count of holes below the bottom.
+ *
+ * We need to minimize method call/return overhead. If we store the
+ * "cookie" externally, on the interpreted call stack, the VM can handle
+ * pushes and pops with a single 4-byte load and store. (We could also
+ * store it internally in a public structure, but the local JNI refs are
+ * logically tied to interpreted stack frames anyway.)
+ *
+ * Common alternative implementation: make IndirectRef a pointer to the
+ * actual reference slot. Instead of getting a table and doing a lookup,
+ * the lookup can be done instantly. Operations like determining the
+ * type and deleting the reference are more expensive because the table
+ * must be hunted for (i.e. you have to do a pointer comparison to see
+ * which table it's in), you can't move the table when expanding it (so
+ * realloc() is out), and tricks like serial number checking to detect
+ * stale references aren't possible (though we may be able to get similar
+ * benefits with other approaches).
+ *
+ * TODO: consider a "lastDeleteIndex" for quick hole-filling when an
+ * add immediately follows a delete; must invalidate after segment pop
+ * (which could increase the cost/complexity of method call/return).
+ * Might be worth only using it for JNI globals.
+ *
+ * TODO: may want completely different add/remove algorithms for global
+ * and local refs to improve performance. A large circular buffer might
+ * reduce the amortized cost of adding global references.
+ *
+ * TODO: if we can guarantee that the underlying storage doesn't move,
+ * e.g. by using oversized mmap regions to handle expanding tables, we may
+ * be able to avoid having to synchronize lookups. Might make sense to
+ * add a "synchronized lookup" call that takes the mutex as an argument,
+ * and either locks or doesn't lock based on internal details.
+ */
+union IRTSegmentState {
+ uint32_t all;
+ struct {
+ uint32_t topIndex:16; /* index of first unused entry */
+ uint32_t numHoles:16; /* #of holes in entire table */
+ } parts;
+};
+
+class IrtIterator {
+ public:
+ explicit IrtIterator(Object** table, size_t i, size_t capacity)
+ : table_(table), i_(i), capacity_(capacity) {
+ SkipNullsAndTombstones();
+ }
+
+ IrtIterator& operator++() {
+ ++i_;
+ SkipNullsAndTombstones();
+ return *this;
+ }
+
+ Object** operator*() {
+ return &table_[i_];
+ }
+
+ bool equals(const IrtIterator& rhs) const {
+ return (i_ == rhs.i_ && table_ == rhs.table_);
+ }
+
+ private:
+ void SkipNullsAndTombstones() {
+ // We skip NULLs and tombstones. Clients don't want to see implementation details.
+ while (i_ < capacity_ && (table_[i_] == NULL || table_[i_] == kClearedJniWeakGlobal)) {
+ ++i_;
+ }
+ }
+
+ Object** table_;
+ size_t i_;
+ size_t capacity_;
+};
+
+bool inline operator!=(const IrtIterator& lhs, const IrtIterator& rhs) {
+ return !lhs.equals(rhs);
+}
+
+class IndirectReferenceTable {
+ public:
+ typedef IrtIterator iterator;
+
+ IndirectReferenceTable(size_t initialCount, size_t maxCount, IndirectRefKind kind);
+
+ ~IndirectReferenceTable();
+
+ /*
+ * Add a new entry. "obj" must be a valid non-NULL object reference
+ * (though it's okay if it's not fully-formed, e.g. the result from
+ * dvmMalloc doesn't have obj->clazz set).
+ *
+ * Returns NULL if the table is full (max entries reached, or alloc
+ * failed during expansion).
+ */
+ IndirectRef Add(uint32_t cookie, Object* obj);
+
+ /*
+ * Given an IndirectRef in the table, return the Object it refers to.
+ *
+ * Returns kInvalidIndirectRefObject if iref is invalid.
+ */
+ Object* Get(IndirectRef iref) const {
+ if (!GetChecked(iref)) {
+ return kInvalidIndirectRefObject;
+ }
+ return table_[ExtractIndex(iref)];
+ }
+
+ // TODO: only used for workAroundAppJniBugs support.
+ bool Contains(IndirectRef iref) const;
+
+ /*
+ * Remove an existing entry.
+ *
+ * If the entry is not between the current top index and the bottom index
+ * specified by the cookie, we don't remove anything. This is the behavior
+ * required by JNI's DeleteLocalRef function.
+ *
+ * Returns "false" if nothing was removed.
+ */
+ bool Remove(uint32_t cookie, IndirectRef iref);
+
+ void Dump() const;
+
+ /*
+ * Return the #of entries in the entire table. This includes holes, and
+ * so may be larger than the actual number of "live" entries.
+ */
+ size_t Capacity() const {
+ return segmentState.parts.topIndex;
+ }
+
+ iterator begin() {
+ return iterator(table_, 0, Capacity());
+ }
+
+ iterator end() {
+ return iterator(table_, Capacity(), Capacity());
+ }
+
+ private:
+ /*
+ * Extract the table index from an indirect reference.
+ */
+ static uint32_t ExtractIndex(IndirectRef iref) {
+ uint32_t uref = (uint32_t) iref;
+ return (uref >> 2) & 0xffff;
+ }
+
+ /*
+ * The object pointer itself is subject to relocation in some GC
+ * implementations, so we shouldn't really be using it here.
+ */
+ IndirectRef ToIndirectRef(Object* obj, uint32_t tableIndex) const {
+ DCHECK_LT(tableIndex, 65536U);
+ uint32_t serialChunk = slot_data_[tableIndex].serial;
+ uint32_t uref = serialChunk << 20 | (tableIndex << 2) | kind_;
+ return (IndirectRef) uref;
+ }
+
+ /*
+ * Update extended debug info when an entry is added.
+ *
+ * We advance the serial number, invalidating any outstanding references to
+ * this slot.
+ */
+ void UpdateSlotAdd(Object* obj, int slot) {
+ if (slot_data_ != NULL) {
+ IndirectRefSlot* pSlot = &slot_data_[slot];
+ pSlot->serial++;
+ pSlot->previous[pSlot->serial % kIRTPrevCount] = obj;
+ }
+ }
+
+ /* extra debugging checks */
+ bool GetChecked(IndirectRef) const;
+ bool CheckEntry(const char*, IndirectRef, int) const;
+
+ /* semi-public - read/write by interpreter in native call handler */
+ IRTSegmentState segmentState;
+
+ /* bottom of the stack */
+ Object** table_;
+ /* bit mask, ORed into all irefs */
+ IndirectRefKind kind_;
+ /* extended debugging info */
+ IndirectRefSlot* slot_data_;
+ /* #of entries we have space for */
+ size_t alloc_entries_;
+ /* max #of entries allowed */
+ size_t max_entries_;
+};
+
+} // namespace art
+
+#endif // ART_SRC_INDIRECT_REFERENCE_TABLE_H_