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// Copyright 2011 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_STORE_BUFFER_H_
#define V8_STORE_BUFFER_H_
#include "src/allocation.h"
#include "src/checks.h"
#include "src/globals.h"
#include "src/platform.h"
namespace v8 {
namespace internal {
class Page;
class PagedSpace;
class StoreBuffer;
typedef void (*ObjectSlotCallback)(HeapObject** from, HeapObject* to);
typedef void (StoreBuffer::*RegionCallback)(Address start,
Address end,
ObjectSlotCallback slot_callback,
bool clear_maps);
// Used to implement the write barrier by collecting addresses of pointers
// between spaces.
class StoreBuffer {
explicit StoreBuffer(Heap* heap);
static void StoreBufferOverflow(Isolate* isolate);
inline Address TopAddress();
void SetUp();
void TearDown();
// This is used by the mutator to enter addresses into the store buffer.
inline void Mark(Address addr);
// This is used by the heap traversal to enter the addresses into the store
// buffer that should still be in the store buffer after GC. It enters
// addresses directly into the old buffer because the GC starts by wiping the
// old buffer and thereafter only visits each cell once so there is no need
// to attempt to remove any dupes. During the first part of a GC we
// are using the store buffer to access the old spaces and at the same time
// we are rebuilding the store buffer using this function. There is, however
// no issue of overwriting the buffer we are iterating over, because this
// stage of the scavenge can only reduce the number of addresses in the store
// buffer (some objects are promoted so pointers to them do not need to be in
// the store buffer). The later parts of the GC scan the pages that are
// exempt from the store buffer and process the promotion queue. These steps
// can overflow this buffer. We check for this and on overflow we call the
// callback set up with the StoreBufferRebuildScope object.
inline void EnterDirectlyIntoStoreBuffer(Address addr);
// Iterates over all pointers that go from old space to new space. It will
// delete the store buffer as it starts so the callback should reenter
// surviving old-to-new pointers into the store buffer to rebuild it.
void IteratePointersToNewSpace(ObjectSlotCallback callback);
// Same as IteratePointersToNewSpace but additonally clears maps in objects
// referenced from the store buffer that do not contain a forwarding pointer.
void IteratePointersToNewSpaceAndClearMaps(ObjectSlotCallback callback);
static const int kStoreBufferOverflowBit = 1 << (14 + kPointerSizeLog2);
static const int kStoreBufferSize = kStoreBufferOverflowBit;
static const int kStoreBufferLength = kStoreBufferSize / sizeof(Address);
static const int kOldStoreBufferLength = kStoreBufferLength * 16;
static const int kHashSetLengthLog2 = 12;
static const int kHashSetLength = 1 << kHashSetLengthLog2;
void Compact();
void GCPrologue();
void GCEpilogue();
Object*** Limit() { return reinterpret_cast<Object***>(old_limit_); }
Object*** Start() { return reinterpret_cast<Object***>(old_start_); }
Object*** Top() { return reinterpret_cast<Object***>(old_top_); }
void SetTop(Object*** top) {
ASSERT(top >= Start());
ASSERT(top <= Limit());
old_top_ = reinterpret_cast<Address*>(top);
bool old_buffer_is_sorted() { return old_buffer_is_sorted_; }
bool old_buffer_is_filtered() { return old_buffer_is_filtered_; }
// Goes through the store buffer removing pointers to things that have
// been promoted. Rebuilds the store buffer completely if it overflowed.
void SortUniq();
void EnsureSpace(intptr_t space_needed);
void Verify();
bool PrepareForIteration();
#ifdef DEBUG
void Clean();
// Slow, for asserts only.
bool CellIsInStoreBuffer(Address cell);
void Filter(int flag);
Heap* heap_;
// The store buffer is divided up into a new buffer that is constantly being
// filled by mutator activity and an old buffer that is filled with the data
// from the new buffer after compression.
Address* start_;
Address* limit_;
Address* old_start_;
Address* old_limit_;
Address* old_top_;
Address* old_reserved_limit_;
VirtualMemory* old_virtual_memory_;
bool old_buffer_is_sorted_;
bool old_buffer_is_filtered_;
bool during_gc_;
// The garbage collector iterates over many pointers to new space that are not
// handled by the store buffer. This flag indicates whether the pointers
// found by the callbacks should be added to the store buffer or not.
bool store_buffer_rebuilding_enabled_;
StoreBufferCallback callback_;
bool may_move_store_buffer_entries_;
VirtualMemory* virtual_memory_;
// Two hash sets used for filtering.
// If address is in the hash set then it is guaranteed to be in the
// old part of the store buffer.
uintptr_t* hash_set_1_;
uintptr_t* hash_set_2_;
bool hash_sets_are_empty_;
void ClearFilteringHashSets();
bool SpaceAvailable(intptr_t space_needed);
void Uniq();
void ExemptPopularPages(int prime_sample_step, int threshold);
// Set the map field of the object to NULL if contains a map.
inline void ClearDeadObject(HeapObject *object);
void IteratePointersToNewSpace(ObjectSlotCallback callback, bool clear_maps);
void FindPointersToNewSpaceInRegion(Address start,
Address end,
ObjectSlotCallback slot_callback,
bool clear_maps);
// For each region of pointers on a page in use from an old space call
// visit_pointer_region callback.
// If either visit_pointer_region or callback can cause an allocation
// in old space and changes in allocation watermark then
// can_preallocate_during_iteration should be set to true.
void IteratePointersOnPage(
PagedSpace* space,
Page* page,
RegionCallback region_callback,
ObjectSlotCallback slot_callback);
void FindPointersToNewSpaceInMaps(
Address start,
Address end,
ObjectSlotCallback slot_callback,
bool clear_maps);
void FindPointersToNewSpaceInMapsRegion(
Address start,
Address end,
ObjectSlotCallback slot_callback,
bool clear_maps);
void IteratePointersInStoreBuffer(ObjectSlotCallback slot_callback,
bool clear_maps);
void VerifyPointers(LargeObjectSpace* space);
friend class StoreBufferRebuildScope;
friend class DontMoveStoreBufferEntriesScope;
class StoreBufferRebuildScope {
explicit StoreBufferRebuildScope(Heap* heap,
StoreBuffer* store_buffer,
StoreBufferCallback callback)
: store_buffer_(store_buffer),
stored_callback_(store_buffer->callback_) {
store_buffer_->store_buffer_rebuilding_enabled_ = true;
store_buffer_->callback_ = callback;
(*callback)(heap, NULL, kStoreBufferStartScanningPagesEvent);
~StoreBufferRebuildScope() {
store_buffer_->callback_ = stored_callback_;
store_buffer_->store_buffer_rebuilding_enabled_ = stored_state_;
StoreBuffer* store_buffer_;
bool stored_state_;
StoreBufferCallback stored_callback_;
class DontMoveStoreBufferEntriesScope {
explicit DontMoveStoreBufferEntriesScope(StoreBuffer* store_buffer)
: store_buffer_(store_buffer),
stored_state_(store_buffer->may_move_store_buffer_entries_) {
store_buffer_->may_move_store_buffer_entries_ = false;
~DontMoveStoreBufferEntriesScope() {
store_buffer_->may_move_store_buffer_entries_ = stored_state_;
StoreBuffer* store_buffer_;
bool stored_state_;
} } // namespace v8::internal
#endif // V8_STORE_BUFFER_H_