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v8/src/mark-compact.cc

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// Copyright 2012 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following
// disclaimer in the documentation and/or other materials provided
// with the distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#include "v8.h"
#include "code-stubs.h"
#include "compilation-cache.h"
#include "cpu-profiler.h"
#include "deoptimizer.h"
#include "execution.h"
#include "gdb-jit.h"
#include "global-handles.h"
#include "heap-profiler.h"
#include "ic-inl.h"
#include "incremental-marking.h"
#include "mark-compact.h"
#include "marking-thread.h"
#include "objects-visiting.h"
#include "objects-visiting-inl.h"
#include "stub-cache.h"
#include "sweeper-thread.h"
namespace v8 {
namespace internal {
const char* Marking::kWhiteBitPattern = "00";
const char* Marking::kBlackBitPattern = "10";
const char* Marking::kGreyBitPattern = "11";
const char* Marking::kImpossibleBitPattern = "01";
// -------------------------------------------------------------------------
// MarkCompactCollector
MarkCompactCollector::MarkCompactCollector() : // NOLINT
#ifdef DEBUG
state_(IDLE),
#endif
sweep_precisely_(false),
reduce_memory_footprint_(false),
abort_incremental_marking_(false),
marking_parity_(ODD_MARKING_PARITY),
compacting_(false),
was_marked_incrementally_(false),
sweeping_pending_(false),
sequential_sweeping_(false),
tracer_(NULL),
migration_slots_buffer_(NULL),
heap_(NULL),
code_flusher_(NULL),
encountered_weak_collections_(NULL),
have_code_to_deoptimize_(false) { }
#ifdef VERIFY_HEAP
class VerifyMarkingVisitor: public ObjectVisitor {
public:
explicit VerifyMarkingVisitor(Heap* heap) : heap_(heap) {}
void VisitPointers(Object** start, Object** end) {
for (Object** current = start; current < end; current++) {
if ((*current)->IsHeapObject()) {
HeapObject* object = HeapObject::cast(*current);
CHECK(heap_->mark_compact_collector()->IsMarked(object));
}
}
}
void VisitEmbeddedPointer(RelocInfo* rinfo) {
ASSERT(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
if (!FLAG_weak_embedded_maps_in_optimized_code || !FLAG_collect_maps ||
rinfo->host()->kind() != Code::OPTIMIZED_FUNCTION ||
!rinfo->target_object()->IsMap() ||
!Map::cast(rinfo->target_object())->CanTransition()) {
VisitPointer(rinfo->target_object_address());
}
}
private:
Heap* heap_;
};
static void VerifyMarking(Heap* heap, Address bottom, Address top) {
VerifyMarkingVisitor visitor(heap);
HeapObject* object;
Address next_object_must_be_here_or_later = bottom;
for (Address current = bottom;
current < top;
current += kPointerSize) {
object = HeapObject::FromAddress(current);
if (MarkCompactCollector::IsMarked(object)) {
CHECK(current >= next_object_must_be_here_or_later);
object->Iterate(&visitor);
next_object_must_be_here_or_later = current + object->Size();
}
}
}
static void VerifyMarking(NewSpace* space) {
Address end = space->top();
NewSpacePageIterator it(space->bottom(), end);
// The bottom position is at the start of its page. Allows us to use
// page->area_start() as start of range on all pages.
CHECK_EQ(space->bottom(),
NewSpacePage::FromAddress(space->bottom())->area_start());
while (it.has_next()) {
NewSpacePage* page = it.next();
Address limit = it.has_next() ? page->area_end() : end;
CHECK(limit == end || !page->Contains(end));
VerifyMarking(space->heap(), page->area_start(), limit);
}
}
static void VerifyMarking(PagedSpace* space) {
PageIterator it(space);
while (it.has_next()) {
Page* p = it.next();
VerifyMarking(space->heap(), p->area_start(), p->area_end());
}
}
static void VerifyMarking(Heap* heap) {
VerifyMarking(heap->old_pointer_space());
VerifyMarking(heap->old_data_space());
VerifyMarking(heap->code_space());
VerifyMarking(heap->cell_space());
VerifyMarking(heap->property_cell_space());
VerifyMarking(heap->map_space());
VerifyMarking(heap->new_space());
VerifyMarkingVisitor visitor(heap);
LargeObjectIterator it(heap->lo_space());
for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
if (MarkCompactCollector::IsMarked(obj)) {
obj->Iterate(&visitor);
}
}
heap->IterateStrongRoots(&visitor, VISIT_ONLY_STRONG);
}
class VerifyEvacuationVisitor: public ObjectVisitor {
public:
void VisitPointers(Object** start, Object** end) {
for (Object** current = start; current < end; current++) {
if ((*current)->IsHeapObject()) {
HeapObject* object = HeapObject::cast(*current);
CHECK(!MarkCompactCollector::IsOnEvacuationCandidate(object));
}
}
}
};
static void VerifyEvacuation(Address bottom, Address top) {
VerifyEvacuationVisitor visitor;
HeapObject* object;
Address next_object_must_be_here_or_later = bottom;
for (Address current = bottom;
current < top;
current += kPointerSize) {
object = HeapObject::FromAddress(current);
if (MarkCompactCollector::IsMarked(object)) {
CHECK(current >= next_object_must_be_here_or_later);
object->Iterate(&visitor);
next_object_must_be_here_or_later = current + object->Size();
}
}
}
static void VerifyEvacuation(NewSpace* space) {
NewSpacePageIterator it(space->bottom(), space->top());
VerifyEvacuationVisitor visitor;
while (it.has_next()) {
NewSpacePage* page = it.next();
Address current = page->area_start();
Address limit = it.has_next() ? page->area_end() : space->top();
CHECK(limit == space->top() || !page->Contains(space->top()));
while (current < limit) {
HeapObject* object = HeapObject::FromAddress(current);
object->Iterate(&visitor);
current += object->Size();
}
}
}
static void VerifyEvacuation(PagedSpace* space) {
PageIterator it(space);
while (it.has_next()) {
Page* p = it.next();
if (p->IsEvacuationCandidate()) continue;
VerifyEvacuation(p->area_start(), p->area_end());
}
}
static void VerifyEvacuation(Heap* heap) {
VerifyEvacuation(heap->old_pointer_space());
VerifyEvacuation(heap->old_data_space());
VerifyEvacuation(heap->code_space());
VerifyEvacuation(heap->cell_space());
VerifyEvacuation(heap->property_cell_space());
VerifyEvacuation(heap->map_space());
VerifyEvacuation(heap->new_space());
VerifyEvacuationVisitor visitor;
heap->IterateStrongRoots(&visitor, VISIT_ALL);
}
#endif // VERIFY_HEAP
#ifdef DEBUG
class VerifyNativeContextSeparationVisitor: public ObjectVisitor {
public:
VerifyNativeContextSeparationVisitor() : current_native_context_(NULL) {}
void VisitPointers(Object** start, Object** end) {
for (Object** current = start; current < end; current++) {
if ((*current)->IsHeapObject()) {
HeapObject* object = HeapObject::cast(*current);
if (object->IsString()) continue;
switch (object->map()->instance_type()) {
case JS_FUNCTION_TYPE:
CheckContext(JSFunction::cast(object)->context());
break;
case JS_GLOBAL_PROXY_TYPE:
CheckContext(JSGlobalProxy::cast(object)->native_context());
break;
case JS_GLOBAL_OBJECT_TYPE:
case JS_BUILTINS_OBJECT_TYPE:
CheckContext(GlobalObject::cast(object)->native_context());
break;
case JS_ARRAY_TYPE:
case JS_DATE_TYPE:
case JS_OBJECT_TYPE:
case JS_REGEXP_TYPE:
VisitPointer(HeapObject::RawField(object, JSObject::kMapOffset));
break;
case MAP_TYPE:
VisitPointer(HeapObject::RawField(object, Map::kPrototypeOffset));
VisitPointer(HeapObject::RawField(object, Map::kConstructorOffset));
break;
case FIXED_ARRAY_TYPE:
if (object->IsContext()) {
CheckContext(object);
} else {
FixedArray* array = FixedArray::cast(object);
int length = array->length();
// Set array length to zero to prevent cycles while iterating
// over array bodies, this is easier than intrusive marking.
array->set_length(0);
array->IterateBody(
FIXED_ARRAY_TYPE, FixedArray::SizeFor(length), this);
array->set_length(length);
}
break;
case CELL_TYPE:
case JS_PROXY_TYPE:
case JS_VALUE_TYPE:
case TYPE_FEEDBACK_INFO_TYPE:
object->Iterate(this);
break;
case DECLARED_ACCESSOR_INFO_TYPE:
case EXECUTABLE_ACCESSOR_INFO_TYPE:
case BYTE_ARRAY_TYPE:
case CALL_HANDLER_INFO_TYPE:
case CODE_TYPE:
case FIXED_DOUBLE_ARRAY_TYPE:
case HEAP_NUMBER_TYPE:
case INTERCEPTOR_INFO_TYPE:
case ODDBALL_TYPE:
case SCRIPT_TYPE:
case SHARED_FUNCTION_INFO_TYPE:
break;
default:
UNREACHABLE();
}
}
}
}
private:
void CheckContext(Object* context) {
if (!context->IsContext()) return;
Context* native_context = Context::cast(context)->native_context();
if (current_native_context_ == NULL) {
current_native_context_ = native_context;
} else {
CHECK_EQ(current_native_context_, native_context);
}
}
Context* current_native_context_;
};
static void VerifyNativeContextSeparation(Heap* heap) {
HeapObjectIterator it(heap->code_space());
for (Object* object = it.Next(); object != NULL; object = it.Next()) {
VerifyNativeContextSeparationVisitor visitor;
Code::cast(object)->CodeIterateBody(&visitor);
}
}
#endif
void MarkCompactCollector::TearDown() {
AbortCompaction();
}
void MarkCompactCollector::AddEvacuationCandidate(Page* p) {
p->MarkEvacuationCandidate();
evacuation_candidates_.Add(p);
}
static void TraceFragmentation(PagedSpace* space) {
int number_of_pages = space->CountTotalPages();
intptr_t reserved = (number_of_pages * space->AreaSize());
intptr_t free = reserved - space->SizeOfObjects();
PrintF("[%s]: %d pages, %d (%.1f%%) free\n",
AllocationSpaceName(space->identity()),
number_of_pages,
static_cast<int>(free),
static_cast<double>(free) * 100 / reserved);
}
bool MarkCompactCollector::StartCompaction(CompactionMode mode) {
if (!compacting_) {
ASSERT(evacuation_candidates_.length() == 0);
#ifdef ENABLE_GDB_JIT_INTERFACE
// If GDBJIT interface is active disable compaction.
if (FLAG_gdbjit) return false;
#endif
CollectEvacuationCandidates(heap()->old_pointer_space());
CollectEvacuationCandidates(heap()->old_data_space());
if (FLAG_compact_code_space &&
(mode == NON_INCREMENTAL_COMPACTION ||
FLAG_incremental_code_compaction)) {
CollectEvacuationCandidates(heap()->code_space());
} else if (FLAG_trace_fragmentation) {
TraceFragmentation(heap()->code_space());
}
if (FLAG_trace_fragmentation) {
TraceFragmentation(heap()->map_space());
TraceFragmentation(heap()->cell_space());
TraceFragmentation(heap()->property_cell_space());
}
heap()->old_pointer_space()->EvictEvacuationCandidatesFromFreeLists();
heap()->old_data_space()->EvictEvacuationCandidatesFromFreeLists();
heap()->code_space()->EvictEvacuationCandidatesFromFreeLists();
compacting_ = evacuation_candidates_.length() > 0;
}
return compacting_;
}
void MarkCompactCollector::CollectGarbage() {
// Make sure that Prepare() has been called. The individual steps below will
// update the state as they proceed.
ASSERT(state_ == PREPARE_GC);
ASSERT(encountered_weak_collections_ == Smi::FromInt(0));
MarkLiveObjects();
ASSERT(heap_->incremental_marking()->IsStopped());
if (FLAG_collect_maps) ClearNonLiveReferences();
ClearWeakCollections();
#ifdef VERIFY_HEAP
if (FLAG_verify_heap) {
VerifyMarking(heap_);
}
#endif
SweepSpaces();
if (!FLAG_collect_maps) ReattachInitialMaps();
#ifdef DEBUG
if (FLAG_verify_native_context_separation) {
VerifyNativeContextSeparation(heap_);
}
#endif
#ifdef VERIFY_HEAP
if (FLAG_collect_maps && FLAG_weak_embedded_maps_in_optimized_code &&
heap()->weak_embedded_maps_verification_enabled()) {
VerifyWeakEmbeddedMapsInOptimizedCode();
}
if (FLAG_collect_maps && FLAG_omit_map_checks_for_leaf_maps) {
VerifyOmittedMapChecks();
}
#endif
Finish();
if (marking_parity_ == EVEN_MARKING_PARITY) {
marking_parity_ = ODD_MARKING_PARITY;
} else {
ASSERT(marking_parity_ == ODD_MARKING_PARITY);
marking_parity_ = EVEN_MARKING_PARITY;
}
tracer_ = NULL;
}
#ifdef VERIFY_HEAP
void MarkCompactCollector::VerifyMarkbitsAreClean(PagedSpace* space) {
PageIterator it(space);
while (it.has_next()) {
Page* p = it.next();
CHECK(p->markbits()->IsClean());
CHECK_EQ(0, p->LiveBytes());
}
}
void MarkCompactCollector::VerifyMarkbitsAreClean(NewSpace* space) {
NewSpacePageIterator it(space->bottom(), space->top());
while (it.has_next()) {
NewSpacePage* p = it.next();
CHECK(p->markbits()->IsClean());
CHECK_EQ(0, p->LiveBytes());
}
}
void MarkCompactCollector::VerifyMarkbitsAreClean() {
VerifyMarkbitsAreClean(heap_->old_pointer_space());
VerifyMarkbitsAreClean(heap_->old_data_space());
VerifyMarkbitsAreClean(heap_->code_space());
VerifyMarkbitsAreClean(heap_->cell_space());
VerifyMarkbitsAreClean(heap_->property_cell_space());
VerifyMarkbitsAreClean(heap_->map_space());
VerifyMarkbitsAreClean(heap_->new_space());
LargeObjectIterator it(heap_->lo_space());
for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
MarkBit mark_bit = Marking::MarkBitFrom(obj);
CHECK(Marking::IsWhite(mark_bit));
CHECK_EQ(0, Page::FromAddress(obj->address())->LiveBytes());
}
}
void MarkCompactCollector::VerifyWeakEmbeddedMapsInOptimizedCode() {
HeapObjectIterator code_iterator(heap()->code_space());
for (HeapObject* obj = code_iterator.Next();
obj != NULL;
obj = code_iterator.Next()) {
Code* code = Code::cast(obj);
if (code->kind() != Code::OPTIMIZED_FUNCTION) continue;
if (WillBeDeoptimized(code)) continue;
code->VerifyEmbeddedMapsDependency();
}
}
void MarkCompactCollector::VerifyOmittedMapChecks() {
HeapObjectIterator iterator(heap()->map_space());
for (HeapObject* obj = iterator.Next();
obj != NULL;
obj = iterator.Next()) {
Map* map = Map::cast(obj);
map->VerifyOmittedMapChecks();
}
}
#endif // VERIFY_HEAP
static void ClearMarkbitsInPagedSpace(PagedSpace* space) {
PageIterator it(space);
while (it.has_next()) {
Bitmap::Clear(it.next());
}
}
static void ClearMarkbitsInNewSpace(NewSpace* space) {
NewSpacePageIterator it(space->ToSpaceStart(), space->ToSpaceEnd());
while (it.has_next()) {
Bitmap::Clear(it.next());
}
}
void MarkCompactCollector::ClearMarkbits() {
ClearMarkbitsInPagedSpace(heap_->code_space());
ClearMarkbitsInPagedSpace(heap_->map_space());
ClearMarkbitsInPagedSpace(heap_->old_pointer_space());
ClearMarkbitsInPagedSpace(heap_->old_data_space());
ClearMarkbitsInPagedSpace(heap_->cell_space());
ClearMarkbitsInPagedSpace(heap_->property_cell_space());
ClearMarkbitsInNewSpace(heap_->new_space());
LargeObjectIterator it(heap_->lo_space());
for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
MarkBit mark_bit = Marking::MarkBitFrom(obj);
mark_bit.Clear();
mark_bit.Next().Clear();
Page::FromAddress(obj->address())->ResetProgressBar();
Page::FromAddress(obj->address())->ResetLiveBytes();
}
}
void MarkCompactCollector::StartSweeperThreads() {
sweeping_pending_ = true;
for (int i = 0; i < FLAG_sweeper_threads; i++) {
isolate()->sweeper_threads()[i]->StartSweeping();
}
}
void MarkCompactCollector::WaitUntilSweepingCompleted() {
ASSERT(sweeping_pending_ == true);
for (int i = 0; i < FLAG_sweeper_threads; i++) {
isolate()->sweeper_threads()[i]->WaitForSweeperThread();
}
sweeping_pending_ = false;
StealMemoryFromSweeperThreads(heap()->paged_space(OLD_DATA_SPACE));
StealMemoryFromSweeperThreads(heap()->paged_space(OLD_POINTER_SPACE));
heap()->paged_space(OLD_DATA_SPACE)->ResetUnsweptFreeBytes();
heap()->paged_space(OLD_POINTER_SPACE)->ResetUnsweptFreeBytes();
}
intptr_t MarkCompactCollector::
StealMemoryFromSweeperThreads(PagedSpace* space) {
intptr_t freed_bytes = 0;
for (int i = 0; i < FLAG_sweeper_threads; i++) {
freed_bytes += isolate()->sweeper_threads()[i]->StealMemory(space);
}
space->AddToAccountingStats(freed_bytes);
space->DecrementUnsweptFreeBytes(freed_bytes);
return freed_bytes;
}
bool MarkCompactCollector::AreSweeperThreadsActivated() {
return isolate()->sweeper_threads() != NULL;
}
bool MarkCompactCollector::IsConcurrentSweepingInProgress() {
return sweeping_pending_;
}
void MarkCompactCollector::MarkInParallel() {
for (int i = 0; i < FLAG_marking_threads; i++) {
isolate()->marking_threads()[i]->StartMarking();
}
}
void MarkCompactCollector::WaitUntilMarkingCompleted() {
for (int i = 0; i < FLAG_marking_threads; i++) {
isolate()->marking_threads()[i]->WaitForMarkingThread();
}
}
bool Marking::TransferMark(Address old_start, Address new_start) {
// This is only used when resizing an object.
ASSERT(MemoryChunk::FromAddress(old_start) ==
MemoryChunk::FromAddress(new_start));
// If the mark doesn't move, we don't check the color of the object.
// It doesn't matter whether the object is black, since it hasn't changed
// size, so the adjustment to the live data count will be zero anyway.
if (old_start == new_start) return false;
MarkBit new_mark_bit = MarkBitFrom(new_start);
MarkBit old_mark_bit = MarkBitFrom(old_start);
#ifdef DEBUG
ObjectColor old_color = Color(old_mark_bit);
#endif
if (Marking::IsBlack(old_mark_bit)) {
old_mark_bit.Clear();
ASSERT(IsWhite(old_mark_bit));
Marking::MarkBlack(new_mark_bit);
return true;
} else if (Marking::IsGrey(old_mark_bit)) {
ASSERT(heap_->incremental_marking()->IsMarking());
old_mark_bit.Clear();
old_mark_bit.Next().Clear();
ASSERT(IsWhite(old_mark_bit));
heap_->incremental_marking()->WhiteToGreyAndPush(
HeapObject::FromAddress(new_start), new_mark_bit);
heap_->incremental_marking()->RestartIfNotMarking();
}
#ifdef DEBUG
ObjectColor new_color = Color(new_mark_bit);
ASSERT(new_color == old_color);
#endif
return false;
}
const char* AllocationSpaceName(AllocationSpace space) {
switch (space) {
case NEW_SPACE: return "NEW_SPACE";
case OLD_POINTER_SPACE: return "OLD_POINTER_SPACE";
case OLD_DATA_SPACE: return "OLD_DATA_SPACE";
case CODE_SPACE: return "CODE_SPACE";
case MAP_SPACE: return "MAP_SPACE";
case CELL_SPACE: return "CELL_SPACE";
case PROPERTY_CELL_SPACE:
return "PROPERTY_CELL_SPACE";
case LO_SPACE: return "LO_SPACE";
default:
UNREACHABLE();
}
return NULL;
}
// Returns zero for pages that have so little fragmentation that it is not
// worth defragmenting them. Otherwise a positive integer that gives an
// estimate of fragmentation on an arbitrary scale.
static int FreeListFragmentation(PagedSpace* space, Page* p) {
// If page was not swept then there are no free list items on it.
if (!p->WasSwept()) {
if (FLAG_trace_fragmentation) {
PrintF("%p [%s]: %d bytes live (unswept)\n",
reinterpret_cast<void*>(p),
AllocationSpaceName(space->identity()),
p->LiveBytes());
}
return 0;
}
PagedSpace::SizeStats sizes;
space->ObtainFreeListStatistics(p, &sizes);
intptr_t ratio;
intptr_t ratio_threshold;
intptr_t area_size = space->AreaSize();
if (space->identity() == CODE_SPACE) {
ratio = (sizes.medium_size_ * 10 + sizes.large_size_ * 2) * 100 /
area_size;
ratio_threshold = 10;
} else {
ratio = (sizes.small_size_ * 5 + sizes.medium_size_) * 100 /
area_size;
ratio_threshold = 15;
}
if (FLAG_trace_fragmentation) {
PrintF("%p [%s]: %d (%.2f%%) %d (%.2f%%) %d (%.2f%%) %d (%.2f%%) %s\n",
reinterpret_cast<void*>(p),
AllocationSpaceName(space->identity()),
static_cast<int>(sizes.small_size_),
static_cast<double>(sizes.small_size_ * 100) /
area_size,
static_cast<int>(sizes.medium_size_),
static_cast<double>(sizes.medium_size_ * 100) /
area_size,
static_cast<int>(sizes.large_size_),
static_cast<double>(sizes.large_size_ * 100) /
area_size,
static_cast<int>(sizes.huge_size_),
static_cast<double>(sizes.huge_size_ * 100) /
area_size,
(ratio > ratio_threshold) ? "[fragmented]" : "");
}
if (FLAG_always_compact && sizes.Total() != area_size) {
return 1;
}
if (ratio <= ratio_threshold) return 0; // Not fragmented.
return static_cast<int>(ratio - ratio_threshold);
}
void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
ASSERT(space->identity() == OLD_POINTER_SPACE ||
space->identity() == OLD_DATA_SPACE ||
space->identity() == CODE_SPACE);
static const int kMaxMaxEvacuationCandidates = 1000;
int number_of_pages = space->CountTotalPages();
int max_evacuation_candidates =
static_cast<int>(sqrt(number_of_pages / 2.0) + 1);
if (FLAG_stress_compaction || FLAG_always_compact) {
max_evacuation_candidates = kMaxMaxEvacuationCandidates;
}
class Candidate {
public:
Candidate() : fragmentation_(0), page_(NULL) { }
Candidate(int f, Page* p) : fragmentation_(f), page_(p) { }
int fragmentation() { return fragmentation_; }
Page* page() { return page_; }
private:
int fragmentation_;
Page* page_;
};
enum CompactionMode {
COMPACT_FREE_LISTS,
REDUCE_MEMORY_FOOTPRINT
};
CompactionMode mode = COMPACT_FREE_LISTS;
intptr_t reserved = number_of_pages * space->AreaSize();
intptr_t over_reserved = reserved - space->SizeOfObjects();
static const intptr_t kFreenessThreshold = 50;
if (reduce_memory_footprint_ && over_reserved >= space->AreaSize()) {
// If reduction of memory footprint was requested, we are aggressive
// about choosing pages to free. We expect that half-empty pages
// are easier to compact so slightly bump the limit.
mode = REDUCE_MEMORY_FOOTPRINT;
max_evacuation_candidates += 2;
}
if (over_reserved > reserved / 3 && over_reserved >= 2 * space->AreaSize()) {
// If over-usage is very high (more than a third of the space), we
// try to free all mostly empty pages. We expect that almost empty
// pages are even easier to compact so bump the limit even more.
mode = REDUCE_MEMORY_FOOTPRINT;
max_evacuation_candidates *= 2;
}
if (FLAG_trace_fragmentation && mode == REDUCE_MEMORY_FOOTPRINT) {
PrintF("Estimated over reserved memory: %.1f / %.1f MB (threshold %d), "
"evacuation candidate limit: %d\n",
static_cast<double>(over_reserved) / MB,
static_cast<double>(reserved) / MB,
static_cast<int>(kFreenessThreshold),
max_evacuation_candidates);
}
intptr_t estimated_release = 0;
Candidate candidates[kMaxMaxEvacuationCandidates];
max_evacuation_candidates =
Min(kMaxMaxEvacuationCandidates, max_evacuation_candidates);
int count = 0;
int fragmentation = 0;
Candidate* least = NULL;
PageIterator it(space);
if (it.has_next()) it.next(); // Never compact the first page.
while (it.has_next()) {
Page* p = it.next();
p->ClearEvacuationCandidate();
if (FLAG_stress_compaction) {
unsigned int counter = space->heap()->ms_count();
uintptr_t page_number = reinterpret_cast<uintptr_t>(p) >> kPageSizeBits;
if ((counter & 1) == (page_number & 1)) fragmentation = 1;
} else if (mode == REDUCE_MEMORY_FOOTPRINT) {
// Don't try to release too many pages.
if (estimated_release >= over_reserved) {
continue;
}
intptr_t free_bytes = 0;
if (!p->WasSwept()) {
free_bytes = (p->area_size() - p->LiveBytes());
} else {
PagedSpace::SizeStats sizes;
space->ObtainFreeListStatistics(p, &sizes);
free_bytes = sizes.Total();
}
int free_pct = static_cast<int>(free_bytes * 100) / p->area_size();
if (free_pct >= kFreenessThreshold) {
estimated_release += free_bytes;
fragmentation = free_pct;
} else {
fragmentation = 0;
}
if (FLAG_trace_fragmentation) {
PrintF("%p [%s]: %d (%.2f%%) free %s\n",
reinterpret_cast<void*>(p),
AllocationSpaceName(space->identity()),
static_cast<int>(free_bytes),
static_cast<double>(free_bytes * 100) / p->area_size(),
(fragmentation > 0) ? "[fragmented]" : "");
}
} else {
fragmentation = FreeListFragmentation(space, p);
}
if (fragmentation != 0) {
if (count < max_evacuation_candidates) {
candidates[count++] = Candidate(fragmentation, p);
} else {
if (least == NULL) {
for (int i = 0; i < max_evacuation_candidates; i++) {
if (least == NULL ||
candidates[i].fragmentation() < least->fragmentation()) {
least = candidates + i;
}
}
}
if (least->fragmentation() < fragmentation) {
*least = Candidate(fragmentation, p);
least = NULL;
}
}
}
}
for (int i = 0; i < count; i++) {
AddEvacuationCandidate(candidates[i].page());
}
if (count > 0 && FLAG_trace_fragmentation) {
PrintF("Collected %d evacuation candidates for space %s\n",
count,
AllocationSpaceName(space->identity()));
}
}
void MarkCompactCollector::AbortCompaction() {
if (compacting_) {
int npages = evacuation_candidates_.length();
for (int i = 0; i < npages; i++) {
Page* p = evacuation_candidates_[i];
slots_buffer_allocator_.DeallocateChain(p->slots_buffer_address());
p->ClearEvacuationCandidate();
p->ClearFlag(MemoryChunk::RESCAN_ON_EVACUATION);
}
compacting_ = false;
evacuation_candidates_.Rewind(0);
invalidated_code_.Rewind(0);
}
ASSERT_EQ(0, evacuation_candidates_.length());
}
void MarkCompactCollector::Prepare(GCTracer* tracer) {
was_marked_incrementally_ = heap()->incremental_marking()->IsMarking();
// Rather than passing the tracer around we stash it in a static member
// variable.
tracer_ = tracer;
#ifdef DEBUG
ASSERT(state_ == IDLE);
state_ = PREPARE_GC;
#endif
ASSERT(!FLAG_never_compact || !FLAG_always_compact);
if (IsConcurrentSweepingInProgress()) {
// Instead of waiting we could also abort the sweeper threads here.
WaitUntilSweepingCompleted();
}
// Clear marking bits if incremental marking is aborted.
if (was_marked_incrementally_ && abort_incremental_marking_) {
heap()->incremental_marking()->Abort();
ClearMarkbits();
AbortCompaction();
was_marked_incrementally_ = false;
}
// Don't start compaction if we are in the middle of incremental
// marking cycle. We did not collect any slots.
if (!FLAG_never_compact && !was_marked_incrementally_) {
StartCompaction(NON_INCREMENTAL_COMPACTION);
}
PagedSpaces spaces(heap());
for (PagedSpace* space = spaces.next();
space != NULL;
space = spaces.next()) {
space->PrepareForMarkCompact();
}
#ifdef VERIFY_HEAP
if (!was_marked_incrementally_ && FLAG_verify_heap) {
VerifyMarkbitsAreClean();
}
#endif
}
void MarkCompactCollector::Finish() {
#ifdef DEBUG
ASSERT(state_ == SWEEP_SPACES || state_ == RELOCATE_OBJECTS);
state_ = IDLE;
#endif
// The stub cache is not traversed during GC; clear the cache to
// force lazy re-initialization of it. This must be done after the
// GC, because it relies on the new address of certain old space
// objects (empty string, illegal builtin).
isolate()->stub_cache()->Clear();
if (have_code_to_deoptimize_) {
// Some code objects were marked for deoptimization during the GC.
Deoptimizer::DeoptimizeMarkedCode(isolate());
have_code_to_deoptimize_ = false;
}
}
// -------------------------------------------------------------------------
// Phase 1: tracing and marking live objects.
// before: all objects are in normal state.
// after: a live object's map pointer is marked as '00'.
// Marking all live objects in the heap as part of mark-sweep or mark-compact
// collection. Before marking, all objects are in their normal state. After
// marking, live objects' map pointers are marked indicating that the object
// has been found reachable.
//
// The marking algorithm is a (mostly) depth-first (because of possible stack
// overflow) traversal of the graph of objects reachable from the roots. It
// uses an explicit stack of pointers rather than recursion. The young
// generation's inactive ('from') space is used as a marking stack. The
// objects in the marking stack are the ones that have been reached and marked
// but their children have not yet been visited.
//
// The marking stack can overflow during traversal. In that case, we set an
// overflow flag. When the overflow flag is set, we continue marking objects
// reachable from the objects on the marking stack, but no longer push them on
// the marking stack. Instead, we mark them as both marked and overflowed.
// When the stack is in the overflowed state, objects marked as overflowed
// have been reached and marked but their children have not been visited yet.
// After emptying the marking stack, we clear the overflow flag and traverse
// the heap looking for objects marked as overflowed, push them on the stack,
// and continue with marking. This process repeats until all reachable
// objects have been marked.
void CodeFlusher::ProcessJSFunctionCandidates() {
Code* lazy_compile = isolate_->builtins()->builtin(Builtins::kLazyCompile);
Object* undefined = isolate_->heap()->undefined_value();
JSFunction* candidate = jsfunction_candidates_head_;
JSFunction* next_candidate;
while (candidate != NULL) {
next_candidate = GetNextCandidate(candidate);
ClearNextCandidate(candidate, undefined);
SharedFunctionInfo* shared = candidate->shared();
Code* code = shared->code();
MarkBit code_mark = Marking::MarkBitFrom(code);
if (!code_mark.Get()) {
if (FLAG_trace_code_flushing && shared->is_compiled()) {
PrintF("[code-flushing clears: ");
shared->ShortPrint();
PrintF(" - age: %d]\n", code->GetAge());
}
shared->set_code(lazy_compile);
candidate->set_code(lazy_compile);
} else {
candidate->set_code(code);
}
// We are in the middle of a GC cycle so the write barrier in the code
// setter did not record the slot update and we have to do that manually.
Address slot = candidate->address() + JSFunction::kCodeEntryOffset;
Code* target = Code::cast(Code::GetObjectFromEntryAddress(slot));
isolate_->heap()->mark_compact_collector()->
RecordCodeEntrySlot(slot, target);
Object** shared_code_slot =
HeapObject::RawField(shared, SharedFunctionInfo::kCodeOffset);
isolate_->heap()->mark_compact_collector()->
RecordSlot(shared_code_slot, shared_code_slot, *shared_code_slot);
candidate = next_candidate;
}
jsfunction_candidates_head_ = NULL;
}
void CodeFlusher::ProcessSharedFunctionInfoCandidates() {
Code* lazy_compile = isolate_->builtins()->builtin(Builtins::kLazyCompile);
SharedFunctionInfo* candidate = shared_function_info_candidates_head_;
SharedFunctionInfo* next_candidate;
while (candidate != NULL) {
next_candidate = GetNextCandidate(candidate);
ClearNextCandidate(candidate);
Code* code = candidate->code();
MarkBit code_mark = Marking::MarkBitFrom(code);
if (!code_mark.Get()) {
if (FLAG_trace_code_flushing && candidate->is_compiled()) {
PrintF("[code-flushing clears: ");
candidate->ShortPrint();
PrintF(" - age: %d]\n", code->GetAge());
}
candidate->set_code(lazy_compile);
}
Object** code_slot =
HeapObject::RawField(candidate, SharedFunctionInfo::kCodeOffset);
isolate_->heap()->mark_compact_collector()->
RecordSlot(code_slot, code_slot, *code_slot);
candidate = next_candidate;
}
shared_function_info_candidates_head_ = NULL;
}
void CodeFlusher::ProcessOptimizedCodeMaps() {
static const int kEntriesStart = SharedFunctionInfo::kEntriesStart;
static const int kEntryLength = SharedFunctionInfo::kEntryLength;
static const int kContextOffset = 0;
static const int kCodeOffset = 1;
static const int kLiteralsOffset = 2;
STATIC_ASSERT(kEntryLength == 3);
SharedFunctionInfo* holder = optimized_code_map_holder_head_;
SharedFunctionInfo* next_holder;
while (holder != NULL) {
next_holder = GetNextCodeMap(holder);
ClearNextCodeMap(holder);
FixedArray* code_map = FixedArray::cast(holder->optimized_code_map());
int new_length = kEntriesStart;
int old_length = code_map->length();
for (int i = kEntriesStart; i < old_length; i += kEntryLength) {
Code* code = Code::cast(code_map->get(i + kCodeOffset));
MarkBit code_mark = Marking::MarkBitFrom(code);
if (!code_mark.Get()) {
continue;
}
// Update and record the context slot in the optimized code map.
Object** context_slot = HeapObject::RawField(code_map,
FixedArray::OffsetOfElementAt(new_length));
code_map->set(new_length++, code_map->get(i + kContextOffset));
ASSERT(Marking::IsBlack(
Marking::MarkBitFrom(HeapObject::cast(*context_slot))));
isolate_->heap()->mark_compact_collector()->
RecordSlot(context_slot, context_slot, *context_slot);
// Update and record the code slot in the optimized code map.
Object** code_slot = HeapObject::RawField(code_map,
FixedArray::OffsetOfElementAt(new_length));
code_map->set(new_length++, code_map->get(i + kCodeOffset));
ASSERT(Marking::IsBlack(
Marking::MarkBitFrom(HeapObject::cast(*code_slot))));
isolate_->heap()->mark_compact_collector()->
RecordSlot(code_slot, code_slot, *code_slot);
// Update and record the literals slot in the optimized code map.
Object** literals_slot = HeapObject::RawField(code_map,
FixedArray::OffsetOfElementAt(new_length));
code_map->set(new_length++, code_map->get(i + kLiteralsOffset));
ASSERT(Marking::IsBlack(
Marking::MarkBitFrom(HeapObject::cast(*literals_slot))));
isolate_->heap()->mark_compact_collector()->
RecordSlot(literals_slot, literals_slot, *literals_slot);
}
// Trim the optimized code map if entries have been removed.
if (new_length < old_length) {
holder->TrimOptimizedCodeMap(old_length - new_length);
}
holder = next_holder;
}
optimized_code_map_holder_head_ = NULL;
}
void CodeFlusher::EvictCandidate(SharedFunctionInfo* shared_info) {
// Make sure previous flushing decisions are revisited.
isolate_->heap()->incremental_marking()->RecordWrites(shared_info);
if (FLAG_trace_code_flushing) {
PrintF("[code-flushing abandons function-info: ");
shared_info->ShortPrint();
PrintF("]\n");
}
SharedFunctionInfo* candidate = shared_function_info_candidates_head_;
SharedFunctionInfo* next_candidate;
if (candidate == shared_info) {
next_candidate = GetNextCandidate(shared_info);
shared_function_info_candidates_head_ = next_candidate;
ClearNextCandidate(shared_info);
} else {
while (candidate != NULL) {
next_candidate = GetNextCandidate(candidate);
if (next_candidate == shared_info) {
next_candidate = GetNextCandidate(shared_info);
SetNextCandidate(candidate, next_candidate);
ClearNextCandidate(shared_info);
break;
}
candidate = next_candidate;
}
}
}
void CodeFlusher::EvictCandidate(JSFunction* function) {
ASSERT(!function->next_function_link()->IsUndefined());
Object* undefined = isolate_->heap()->undefined_value();
// Make sure previous flushing decisions are revisited.
isolate_->heap()->incremental_marking()->RecordWrites(function);
isolate_->heap()->incremental_marking()->RecordWrites(function->shared());
if (FLAG_trace_code_flushing) {
PrintF("[code-flushing abandons closure: ");
function->shared()->ShortPrint();
PrintF("]\n");
}
JSFunction* candidate = jsfunction_candidates_head_;
JSFunction* next_candidate;
if (candidate == function) {
next_candidate = GetNextCandidate(function);
jsfunction_candidates_head_ = next_candidate;
ClearNextCandidate(function, undefined);
} else {
while (candidate != NULL) {
next_candidate = GetNextCandidate(candidate);
if (next_candidate == function) {
next_candidate = GetNextCandidate(function);
SetNextCandidate(candidate, next_candidate);
ClearNextCandidate(function, undefined);
break;
}
candidate = next_candidate;
}
}
}
void CodeFlusher::EvictOptimizedCodeMap(SharedFunctionInfo* code_map_holder) {
ASSERT(!FixedArray::cast(code_map_holder->optimized_code_map())->
get(SharedFunctionInfo::kNextMapIndex)->IsUndefined());
// Make sure previous flushing decisions are revisited.
isolate_->heap()->incremental_marking()->RecordWrites(code_map_holder);
if (FLAG_trace_code_flushing) {
PrintF("[code-flushing abandons code-map: ");
code_map_holder->ShortPrint();
PrintF("]\n");
}
SharedFunctionInfo* holder = optimized_code_map_holder_head_;
SharedFunctionInfo* next_holder;
if (holder == code_map_holder) {
next_holder = GetNextCodeMap(code_map_holder);
optimized_code_map_holder_head_ = next_holder;
ClearNextCodeMap(code_map_holder);
} else {
while (holder != NULL) {
next_holder = GetNextCodeMap(holder);
if (next_holder == code_map_holder) {
next_holder = GetNextCodeMap(code_map_holder);
SetNextCodeMap(holder, next_holder);
ClearNextCodeMap(code_map_holder);
break;
}
holder = next_holder;
}
}
}
void CodeFlusher::EvictJSFunctionCandidates() {
JSFunction* candidate = jsfunction_candidates_head_;
JSFunction* next_candidate;
while (candidate != NULL) {
next_candidate = GetNextCandidate(candidate);
EvictCandidate(candidate);
candidate = next_candidate;
}
ASSERT(jsfunction_candidates_head_ == NULL);
}
void CodeFlusher::EvictSharedFunctionInfoCandidates() {
SharedFunctionInfo* candidate = shared_function_info_candidates_head_;
SharedFunctionInfo* next_candidate;
while (candidate != NULL) {
next_candidate = GetNextCandidate(candidate);
EvictCandidate(candidate);
candidate = next_candidate;
}
ASSERT(shared_function_info_candidates_head_ == NULL);
}
void CodeFlusher::EvictOptimizedCodeMaps() {
SharedFunctionInfo* holder = optimized_code_map_holder_head_;
SharedFunctionInfo* next_holder;
while (holder != NULL) {
next_holder = GetNextCodeMap(holder);
EvictOptimizedCodeMap(holder);
holder = next_holder;
}
ASSERT(optimized_code_map_holder_head_ == NULL);
}
void CodeFlusher::IteratePointersToFromSpace(ObjectVisitor* v) {
Heap* heap = isolate_->heap();
JSFunction** slot = &jsfunction_candidates_head_;
JSFunction* candidate = jsfunction_candidates_head_;
while (candidate != NULL) {
if (heap->InFromSpace(candidate)) {
v->VisitPointer(reinterpret_cast<Object**>(slot));
}
candidate = GetNextCandidate(*slot);
slot = GetNextCandidateSlot(*slot);
}
}
MarkCompactCollector::~MarkCompactCollector() {
if (code_flusher_ != NULL) {
delete code_flusher_;
code_flusher_ = NULL;
}
}
static inline HeapObject* ShortCircuitConsString(Object** p) {
// Optimization: If the heap object pointed to by p is a non-internalized
// cons string whose right substring is HEAP->empty_string, update
// it in place to its left substring. Return the updated value.
//
// Here we assume that if we change *p, we replace it with a heap object
// (i.e., the left substring of a cons string is always a heap object).
//
// The check performed is:
// object->IsConsString() && !object->IsInternalizedString() &&
// (ConsString::cast(object)->second() == HEAP->empty_string())
// except the maps for the object and its possible substrings might be
// marked.
HeapObject* object = HeapObject::cast(*p);
if (!FLAG_clever_optimizations) return object;
Map* map = object->map();
InstanceType type = map->instance_type();
if ((type & kShortcutTypeMask) != kShortcutTypeTag) return object;
Object* second = reinterpret_cast<ConsString*>(object)->second();
Heap* heap = map->GetHeap();
if (second != heap->empty_string()) {
return object;
}
// Since we don't have the object's start, it is impossible to update the
// page dirty marks. Therefore, we only replace the string with its left
// substring when page dirty marks do not change.
Object* first = reinterpret_cast<ConsString*>(object)->first();
if (!heap->InNewSpace(object) && heap->InNewSpace(first)) return object;
*p = first;
return HeapObject::cast(first);
}
class MarkCompactMarkingVisitor
: public StaticMarkingVisitor<MarkCompactMarkingVisitor> {
public:
static void ObjectStatsVisitBase(StaticVisitorBase::VisitorId id,
Map* map, HeapObject* obj);
static void ObjectStatsCountFixedArray(
FixedArrayBase* fixed_array,
FixedArraySubInstanceType fast_type,
FixedArraySubInstanceType dictionary_type);
template<MarkCompactMarkingVisitor::VisitorId id>
class ObjectStatsTracker {
public:
static inline void Visit(Map* map, HeapObject* obj);
};
static void Initialize();
INLINE(static void VisitPointer(Heap* heap, Object** p)) {
MarkObjectByPointer(heap->mark_compact_collector(), p, p);
}
INLINE(static void VisitPointers(Heap* heap, Object** start, Object** end)) {
// Mark all objects pointed to in [start, end).
const int kMinRangeForMarkingRecursion = 64;
if (end - start >= kMinRangeForMarkingRecursion) {
if (VisitUnmarkedObjects(heap, start, end)) return;
// We are close to a stack overflow, so just mark the objects.
}
MarkCompactCollector* collector = heap->mark_compact_collector();
for (Object** p = start; p < end; p++) {
MarkObjectByPointer(collector, start, p);
}
}
// Marks the object black and pushes it on the marking stack.
INLINE(static void MarkObject(Heap* heap, HeapObject* object)) {
MarkBit mark = Marking::MarkBitFrom(object);
heap->mark_compact_collector()->MarkObject(object, mark);
}
// Marks the object black without pushing it on the marking stack.
// Returns true if object needed marking and false otherwise.
INLINE(static bool MarkObjectWithoutPush(Heap* heap, HeapObject* object)) {
MarkBit mark_bit = Marking::MarkBitFrom(object);
if (!mark_bit.Get()) {
heap->mark_compact_collector()->SetMark(object, mark_bit);
return true;
}
return false;
}
// Mark object pointed to by p.
INLINE(static void MarkObjectByPointer(MarkCompactCollector* collector,
Object** anchor_slot,
Object** p)) {
if (!(*p)->IsHeapObject()) return;
HeapObject* object = ShortCircuitConsString(p);
collector->RecordSlot(anchor_slot, p, object);
MarkBit mark = Marking::MarkBitFrom(object);
collector->MarkObject(object, mark);
}
// Visit an unmarked object.
INLINE(static void VisitUnmarkedObject(MarkCompactCollector* collector,
HeapObject* obj)) {
#ifdef DEBUG
ASSERT(collector->heap()->Contains(obj));
ASSERT(!collector->heap()->mark_compact_collector()->IsMarked(obj));
#endif
Map* map = obj->map();
Heap* heap = obj->GetHeap();
MarkBit mark = Marking::MarkBitFrom(obj);
heap->mark_compact_collector()->SetMark(obj, mark);
// Mark the map pointer and the body.
MarkBit map_mark = Marking::MarkBitFrom(map);
heap->mark_compact_collector()->MarkObject(map, map_mark);
IterateBody(map, obj);
}
// Visit all unmarked objects pointed to by [start, end).
// Returns false if the operation fails (lack of stack space).
INLINE(static bool VisitUnmarkedObjects(Heap* heap,
Object** start,
Object** end)) {
// Return false is we are close to the stack limit.
StackLimitCheck check(heap->isolate());
if (check.HasOverflowed()) return false;
MarkCompactCollector* collector = heap->mark_compact_collector();
// Visit the unmarked objects.
for (Object** p = start; p < end; p++) {
Object* o = *p;
if (!o->IsHeapObject()) continue;
collector->RecordSlot(start, p, o);
HeapObject* obj = HeapObject::cast(o);
MarkBit mark = Marking::MarkBitFrom(obj);
if (mark.Get()) continue;
VisitUnmarkedObject(collector, obj);
}
return true;
}
INLINE(static void BeforeVisitingSharedFunctionInfo(HeapObject* object)) {
SharedFunctionInfo* shared = SharedFunctionInfo::cast(object);
shared->BeforeVisitingPointers();
}
static void VisitWeakCollection(Map* map, HeapObject* object) {
MarkCompactCollector* collector = map->GetHeap()->mark_compact_collector();
JSWeakCollection* weak_collection =
reinterpret_cast<JSWeakCollection*>(object);
// Enqueue weak map in linked list of encountered weak maps.
if (weak_collection->next() == Smi::FromInt(0)) {
weak_collection->set_next(collector->encountered_weak_collections());
collector->set_encountered_weak_collections(weak_collection);
}
// Skip visiting the backing hash table containing the mappings.
int object_size = JSWeakCollection::BodyDescriptor::SizeOf(map, object);
BodyVisitorBase<MarkCompactMarkingVisitor>::IteratePointers(
map->GetHeap(),
object,
JSWeakCollection::BodyDescriptor::kStartOffset,
JSWeakCollection::kTableOffset);
BodyVisitorBase<MarkCompactMarkingVisitor>::IteratePointers(
map->GetHeap(),
object,
JSWeakCollection::kTableOffset + kPointerSize,
object_size);
// Mark the backing hash table without pushing it on the marking stack.
Object* table_object = weak_collection->table();
if (!table_object->IsHashTable()) return;
ObjectHashTable* table = ObjectHashTable::cast(table_object);
Object** table_slot =
HeapObject::RawField(weak_collection, JSWeakCollection::kTableOffset);
MarkBit table_mark = Marking::MarkBitFrom(table);
collector->RecordSlot(table_slot, table_slot, table);
if (!table_mark.Get()) collector->SetMark(table, table_mark);
// Recording the map slot can be skipped, because maps are not compacted.
collector->MarkObject(table->map(), Marking::MarkBitFrom(table->map()));
ASSERT(MarkCompactCollector::IsMarked(table->map()));
}
private:
template<int id>
static inline void TrackObjectStatsAndVisit(Map* map, HeapObject* obj);
// Code flushing support.
static const int kRegExpCodeThreshold = 5;
static void UpdateRegExpCodeAgeAndFlush(Heap* heap,
JSRegExp* re,
bool is_ascii) {
// Make sure that the fixed array is in fact initialized on the RegExp.
// We could potentially trigger a GC when initializing the RegExp.
if (HeapObject::cast(re->data())->map()->instance_type() !=
FIXED_ARRAY_TYPE) return;
// Make sure this is a RegExp that actually contains code.
if (re->TypeTag() != JSRegExp::IRREGEXP) return;
Object* code = re->DataAt(JSRegExp::code_index(is_ascii));
if (!code->IsSmi() &&
HeapObject::cast(code)->map()->instance_type() == CODE_TYPE) {
// Save a copy that can be reinstated if we need the code again.
re->SetDataAt(JSRegExp::saved_code_index(is_ascii), code);
// Saving a copy might create a pointer into compaction candidate
// that was not observed by marker. This might happen if JSRegExp data
// was marked through the compilation cache before marker reached JSRegExp
// object.
FixedArray* data = FixedArray::cast(re->data());
Object** slot = data->data_start() + JSRegExp::saved_code_index(is_ascii);
heap->mark_compact_collector()->
RecordSlot(slot, slot, code);
// Set a number in the 0-255 range to guarantee no smi overflow.
re->SetDataAt(JSRegExp::code_index(is_ascii),
Smi::FromInt(heap->sweep_generation() & 0xff));
} else if (code->IsSmi()) {
int value = Smi::cast(code)->value();
// The regexp has not been compiled yet or there was a compilation error.
if (value == JSRegExp::kUninitializedValue ||
value == JSRegExp::kCompilationErrorValue) {
return;
}
// Check if we should flush now.
if (value == ((heap->sweep_generation() - kRegExpCodeThreshold) & 0xff)) {
re->SetDataAt(JSRegExp::code_index(is_ascii),
Smi::FromInt(JSRegExp::kUninitializedValue));
re->SetDataAt(JSRegExp::saved_code_index(is_ascii),
Smi::FromInt(JSRegExp::kUninitializedValue));
}
}
}
// Works by setting the current sweep_generation (as a smi) in the
// code object place in the data array of the RegExp and keeps a copy
// around that can be reinstated if we reuse the RegExp before flushing.
// If we did not use the code for kRegExpCodeThreshold mark sweep GCs
// we flush the code.
static void VisitRegExpAndFlushCode(Map* map, HeapObject* object) {
Heap* heap = map->GetHeap();
MarkCompactCollector* collector = heap->mark_compact_collector();
if (!collector->is_code_flushing_enabled()) {
VisitJSRegExp(map, object);
return;
}
JSRegExp* re = reinterpret_cast<JSRegExp*>(object);
// Flush code or set age on both ASCII and two byte code.
UpdateRegExpCodeAgeAndFlush(heap, re, true);
UpdateRegExpCodeAgeAndFlush(heap, re, false);
// Visit the fields of the RegExp, including the updated FixedArray.
VisitJSRegExp(map, object);
}
static VisitorDispatchTable<Callback> non_count_table_;
};
void MarkCompactMarkingVisitor::ObjectStatsCountFixedArray(
FixedArrayBase* fixed_array,
FixedArraySubInstanceType fast_type,
FixedArraySubInstanceType dictionary_type) {
Heap* heap = fixed_array->map()->GetHeap();
if (fixed_array->map() != heap->fixed_cow_array_map() &&
fixed_array->map() != heap->fixed_double_array_map() &&
fixed_array != heap->empty_fixed_array()) {
if (fixed_array->IsDictionary()) {
heap->RecordObjectStats(FIXED_ARRAY_TYPE,
dictionary_type,
fixed_array->Size());
} else {
heap->RecordObjectStats(FIXED_ARRAY_TYPE,
fast_type,
fixed_array->Size());
}
}
}
void MarkCompactMarkingVisitor::ObjectStatsVisitBase(
MarkCompactMarkingVisitor::VisitorId id, Map* map, HeapObject* obj) {
Heap* heap = map->GetHeap();
int object_size = obj->Size();
heap->RecordObjectStats(map->instance_type(), -1, object_size);
non_count_table_.GetVisitorById(id)(map, obj);
if (obj->IsJSObject()) {
JSObject* object = JSObject::cast(obj);
ObjectStatsCountFixedArray(object->elements(),
DICTIONARY_ELEMENTS_SUB_TYPE,
FAST_ELEMENTS_SUB_TYPE);
ObjectStatsCountFixedArray(object->properties(),
DICTIONARY_PROPERTIES_SUB_TYPE,
FAST_PROPERTIES_SUB_TYPE);
}
}
template<MarkCompactMarkingVisitor::VisitorId id>
void MarkCompactMarkingVisitor::ObjectStatsTracker<id>::Visit(
Map* map, HeapObject* obj) {
ObjectStatsVisitBase(id, map, obj);
}
template<>
class MarkCompactMarkingVisitor::ObjectStatsTracker<
MarkCompactMarkingVisitor::kVisitMap> {
public:
static inline void Visit(Map* map, HeapObject* obj) {
Heap* heap = map->GetHeap();
Map* map_obj = Map::cast(obj);
ASSERT(map->instance_type() == MAP_TYPE);
DescriptorArray* array = map_obj->instance_descriptors();
if (map_obj->owns_descriptors() &&
array != heap->empty_descriptor_array()) {
int fixed_array_size = array->Size();
heap->RecordObjectStats(FIXED_ARRAY_TYPE,
DESCRIPTOR_ARRAY_SUB_TYPE,
fixed_array_size);
}
if (map_obj->HasTransitionArray()) {
int fixed_array_size = map_obj->transitions()->Size();
heap->RecordObjectStats(FIXED_ARRAY_TYPE,
TRANSITION_ARRAY_SUB_TYPE,
fixed_array_size);
}
if (map_obj->has_code_cache()) {
CodeCache* cache = CodeCache::cast(map_obj->code_cache());
heap->RecordObjectStats(
FIXED_ARRAY_TYPE,
MAP_CODE_CACHE_SUB_TYPE,
cache->default_cache()->Size());
if (!cache->normal_type_cache()->IsUndefined()) {
heap->RecordObjectStats(
FIXED_ARRAY_TYPE,
MAP_CODE_CACHE_SUB_TYPE,
FixedArray::cast(cache->normal_type_cache())->Size());
}
}
ObjectStatsVisitBase(kVisitMap, map, obj);
}
};
template<>
class MarkCompactMarkingVisitor::ObjectStatsTracker<
MarkCompactMarkingVisitor::kVisitCode> {
public:
static inline void Visit(Map* map, HeapObject* obj) {
Heap* heap = map->GetHeap();
int object_size = obj->Size();
ASSERT(map->instance_type() == CODE_TYPE);
heap->RecordObjectStats(CODE_TYPE, Code::cast(obj)->kind(), object_size);
ObjectStatsVisitBase(kVisitCode, map, obj);
}
};
template<>
class MarkCompactMarkingVisitor::ObjectStatsTracker<
MarkCompactMarkingVisitor::kVisitSharedFunctionInfo> {
public:
static inline void Visit(Map* map, HeapObject* obj) {
Heap* heap = map->GetHeap();
SharedFunctionInfo* sfi = SharedFunctionInfo::cast(obj);
if (sfi->scope_info() != heap->empty_fixed_array()) {
heap->RecordObjectStats(
FIXED_ARRAY_TYPE,
SCOPE_INFO_SUB_TYPE,
FixedArray::cast(sfi->scope_info())->Size());
}
ObjectStatsVisitBase(kVisitSharedFunctionInfo, map, obj);
}
};
template<>
class MarkCompactMarkingVisitor::ObjectStatsTracker<
MarkCompactMarkingVisitor::kVisitFixedArray> {
public:
static inline void Visit(Map* map, HeapObject* obj) {
Heap* heap = map->GetHeap();
FixedArray* fixed_array = FixedArray::cast(obj);
if (fixed_array == heap->string_table()) {
heap->RecordObjectStats(
FIXED_ARRAY_TYPE,
STRING_TABLE_SUB_TYPE,
fixed_array->Size());
}
ObjectStatsVisitBase(kVisitFixedArray, map, obj);
}
};
void MarkCompactMarkingVisitor::Initialize() {
StaticMarkingVisitor<MarkCompactMarkingVisitor>::Initialize();
table_.Register(kVisitJSRegExp,
&VisitRegExpAndFlushCode);
if (FLAG_track_gc_object_stats) {
// Copy the visitor table to make call-through possible.
non_count_table_.CopyFrom(&table_);
#define VISITOR_ID_COUNT_FUNCTION(id) \
table_.Register(kVisit##id, ObjectStatsTracker<kVisit##id>::Visit);
VISITOR_ID_LIST(VISITOR_ID_COUNT_FUNCTION)
#undef VISITOR_ID_COUNT_FUNCTION
}
}
VisitorDispatchTable<MarkCompactMarkingVisitor::Callback>
MarkCompactMarkingVisitor::non_count_table_;
class CodeMarkingVisitor : public ThreadVisitor {
public:
explicit CodeMarkingVisitor(MarkCompactCollector* collector)
: collector_(collector) {}
void VisitThread(Isolate* isolate, ThreadLocalTop* top) {
collector_->PrepareThreadForCodeFlushing(isolate, top);
}
private:
MarkCompactCollector* collector_;
};
class SharedFunctionInfoMarkingVisitor : public ObjectVisitor {
public:
explicit SharedFunctionInfoMarkingVisitor(MarkCompactCollector* collector)
: collector_(collector) {}
void VisitPointers(Object** start, Object** end) {
for (Object** p = start; p < end; p++) VisitPointer(p);
}
void VisitPointer(Object** slot) {
Object* obj = *slot;
if (obj->IsSharedFunctionInfo()) {
SharedFunctionInfo* shared = reinterpret_cast<SharedFunctionInfo*>(obj);
MarkBit shared_mark = Marking::MarkBitFrom(shared);
MarkBit code_mark = Marking::MarkBitFrom(shared->code());
collector_->MarkObject(shared->code(), code_mark);
collector_->MarkObject(shared, shared_mark);
}
}
private:
MarkCompactCollector* collector_;
};
void MarkCompactCollector::PrepareThreadForCodeFlushing(Isolate* isolate,
ThreadLocalTop* top) {
for (StackFrameIterator it(isolate, top); !it.done(); it.Advance()) {
// Note: for the frame that has a pending lazy deoptimization
// StackFrame::unchecked_code will return a non-optimized code object for
// the outermost function and StackFrame::LookupCode will return
// actual optimized code object.
StackFrame* frame = it.frame();
Code* code = frame->unchecked_code();
MarkBit code_mark = Marking::MarkBitFrom(code);
MarkObject(code, code_mark);
if (frame->is_optimized()) {
MarkCompactMarkingVisitor::MarkInlinedFunctionsCode(heap(),
frame->LookupCode());
}
}
}
void MarkCompactCollector::PrepareForCodeFlushing() {
// Enable code flushing for non-incremental cycles.
if (FLAG_flush_code && !FLAG_flush_code_incrementally) {
EnableCodeFlushing(!was_marked_incrementally_);
}
// If code flushing is disabled, there is no need to prepare for it.
if (!is_code_flushing_enabled()) return;
// Ensure that empty descriptor array is marked. Method MarkDescriptorArray
// relies on it being marked before any other descriptor array.
HeapObject* descriptor_array = heap()->empty_descriptor_array();
MarkBit descriptor_array_mark = Marking::MarkBitFrom(descriptor_array);
MarkObject(descriptor_array, descriptor_array_mark);
// Make sure we are not referencing the code from the stack.
ASSERT(this == heap()->mark_compact_collector());
PrepareThreadForCodeFlushing(heap()->isolate(),
heap()->isolate()->thread_local_top());
// Iterate the archived stacks in all threads to check if
// the code is referenced.
CodeMarkingVisitor code_marking_visitor(this);
heap()->isolate()->thread_manager()->IterateArchivedThreads(
&code_marking_visitor);
SharedFunctionInfoMarkingVisitor visitor(this);
heap()->isolate()->compilation_cache()->IterateFunctions(&visitor);
heap()->isolate()->handle_scope_implementer()->Iterate(&visitor);
ProcessMarkingDeque();
}
// Visitor class for marking heap roots.
class RootMarkingVisitor : public ObjectVisitor {
public:
explicit RootMarkingVisitor(Heap* heap)
: collector_(heap->mark_compact_collector()) { }
void VisitPointer(Object** p) {
MarkObjectByPointer(p);
}
void VisitPointers(Object** start, Object** end) {
for (Object** p = start; p < end; p++) MarkObjectByPointer(p);
}
private:
void MarkObjectByPointer(Object** p) {
if (!(*p)->IsHeapObject()) return;
// Replace flat cons strings in place.
HeapObject* object = ShortCircuitConsString(p);
MarkBit mark_bit = Marking::MarkBitFrom(object);
if (mark_bit.Get()) return;
Map* map = object->map();
// Mark the object.
collector_->SetMark(object, mark_bit);
// Mark the map pointer and body, and push them on the marking stack.
MarkBit map_mark = Marking::MarkBitFrom(map);
collector_->MarkObject(map, map_mark);
MarkCompactMarkingVisitor::IterateBody(map, object);
// Mark all the objects reachable from the map and body. May leave
// overflowed objects in the heap.
collector_->EmptyMarkingDeque();
}
MarkCompactCollector* collector_;
};
// Helper class for pruning the string table.
class StringTableCleaner : public ObjectVisitor {
public:
explicit StringTableCleaner(Heap* heap)
: heap_(heap), pointers_removed_(0) { }
virtual void VisitPointers(Object** start, Object** end) {
// Visit all HeapObject pointers in [start, end).
for (Object** p = start; p < end; p++) {
Object* o = *p;
if (o->IsHeapObject() &&
!Marking::MarkBitFrom(HeapObject::cast(o)).Get()) {
// Check if the internalized string being pruned is external. We need to
// delete the associated external data as this string is going away.
// Since no objects have yet been moved we can safely access the map of
// the object.
if (o->IsExternalString()) {
heap_->FinalizeExternalString(String::cast(*p));
}
// Set the entry to the_hole_value (as deleted).
*p = heap_->the_hole_value();
pointers_removed_++;
}
}
}
int PointersRemoved() {
return pointers_removed_;
}
private:
Heap* heap_;
int pointers_removed_;
};
// Implementation of WeakObjectRetainer for mark compact GCs. All marked objects
// are retained.
class MarkCompactWeakObjectRetainer : public WeakObjectRetainer {
public:
virtual Object* RetainAs(Object* object) {
if (Marking::MarkBitFrom(HeapObject::cast(object)).Get()) {
return object;
} else {
return NULL;
}
}
};
// Fill the marking stack with overflowed objects returned by the given
// iterator. Stop when the marking stack is filled or the end of the space
// is reached, whichever comes first.
template<class T>
static void DiscoverGreyObjectsWithIterator(Heap* heap,
MarkingDeque* marking_deque,
T* it) {
// The caller should ensure that the marking stack is initially not full,
// so that we don't waste effort pointlessly scanning for objects.
ASSERT(!marking_deque->IsFull());
Map* filler_map = heap->one_pointer_filler_map();
for (HeapObject* object = it->Next();
object != NULL;
object = it->Next()) {
MarkBit markbit = Marking::MarkBitFrom(object);
if ((object->map() != filler_map) && Marking::IsGrey(markbit)) {
Marking::GreyToBlack(markbit);
MemoryChunk::IncrementLiveBytesFromGC(object->address(), object->Size());
marking_deque->PushBlack(object);
if (marking_deque->IsFull()) return;
}
}
}
static inline int MarkWordToObjectStarts(uint32_t mark_bits, int* starts);
static void DiscoverGreyObjectsOnPage(MarkingDeque* marking_deque,
MemoryChunk* p) {
ASSERT(!marking_deque->IsFull());
ASSERT(strcmp(Marking::kWhiteBitPattern, "00") == 0);
ASSERT(strcmp(Marking::kBlackBitPattern, "10") == 0);
ASSERT(strcmp(Marking::kGreyBitPattern, "11") == 0);
ASSERT(strcmp(Marking::kImpossibleBitPattern, "01") == 0);
for (MarkBitCellIterator it(p); !it.Done(); it.Advance()) {
Address cell_base = it.CurrentCellBase();
MarkBit::CellType* cell = it.CurrentCell();
const MarkBit::CellType current_cell = *cell;
if (current_cell == 0) continue;
MarkBit::CellType grey_objects;
if (it.HasNext()) {
const MarkBit::CellType next_cell = *(cell+1);
grey_objects = current_cell &
((current_cell >> 1) | (next_cell << (Bitmap::kBitsPerCell - 1)));
} else {
grey_objects = current_cell & (current_cell >> 1);
}
int offset = 0;
while (grey_objects != 0) {
int trailing_zeros = CompilerIntrinsics::CountTrailingZeros(grey_objects);
grey_objects >>= trailing_zeros;
offset += trailing_zeros;
MarkBit markbit(cell, 1 << offset, false);
ASSERT(Marking::IsGrey(markbit));
Marking::GreyToBlack(markbit);
Address addr = cell_base + offset * kPointerSize;
HeapObject* object = HeapObject::FromAddress(addr);
MemoryChunk::IncrementLiveBytesFromGC(object->address(), object->Size());
marking_deque->PushBlack(object);
if (marking_deque->IsFull()) return;
offset += 2;
grey_objects >>= 2;
}
grey_objects >>= (Bitmap::kBitsPerCell - 1);
}
}
int MarkCompactCollector::DiscoverAndPromoteBlackObjectsOnPage(
NewSpace* new_space,
NewSpacePage* p) {
ASSERT(strcmp(Marking::kWhiteBitPattern, "00") == 0);
ASSERT(strcmp(Marking::kBlackBitPattern, "10") == 0);
ASSERT(strcmp(Marking::kGreyBitPattern, "11") == 0);
ASSERT(strcmp(Marking::kImpossibleBitPattern, "01") == 0);
MarkBit::CellType* cells = p->markbits()->cells();
int survivors_size = 0;
for (MarkBitCellIterator it(p); !it.Done(); it.Advance()) {
Address cell_base = it.CurrentCellBase();
MarkBit::CellType* cell = it.CurrentCell();
MarkBit::CellType current_cell = *cell;
if (current_cell == 0) continue;
int offset = 0;
while (current_cell != 0) {
int trailing_zeros = CompilerIntrinsics::CountTrailingZeros(current_cell);
current_cell >>= trailing_zeros;
offset += trailing_zeros;
Address address = cell_base + offset * kPointerSize;
HeapObject* object = HeapObject::FromAddress(address);
int size = object->Size();
survivors_size += size;
offset++;
current_cell >>= 1;
// Aggressively promote young survivors to the old space.
if (TryPromoteObject(object, size)) {
continue;
}
// Promotion failed. Just migrate object to another semispace.
MaybeObject* allocation = new_space->AllocateRaw(size);
if (allocation->IsFailure()) {
if (!new_space->AddFreshPage()) {
// Shouldn't happen. We are sweeping linearly, and to-space
// has the same number of pages as from-space, so there is
// always room.
UNREACHABLE();
}
allocation = new_space->AllocateRaw(size);
ASSERT(!allocation->IsFailure());
}
Object* target = allocation->ToObjectUnchecked();
MigrateObject(HeapObject::cast(target)->address(),
object->address(),
size,
NEW_SPACE);
}
*cells = 0;
}
return survivors_size;
}
static void DiscoverGreyObjectsInSpace(Heap* heap,
MarkingDeque* marking_deque,
PagedSpace* space) {
if (!space->was_swept_conservatively()) {
HeapObjectIterator it(space);
DiscoverGreyObjectsWithIterator(heap, marking_deque, &it);
} else {
PageIterator it(space);
while (it.has_next()) {
Page* p = it.next();
DiscoverGreyObjectsOnPage(marking_deque, p);
if (marking_deque->IsFull()) return;
}
}
}
static void DiscoverGreyObjectsInNewSpace(Heap* heap,
MarkingDeque* marking_deque) {
NewSpace* space = heap->new_space();
NewSpacePageIterator it(space->bottom(), space->top());
while (it.has_next()) {
NewSpacePage* page = it.next();
DiscoverGreyObjectsOnPage(marking_deque, page);
if (marking_deque->IsFull()) return;
}
}
bool MarkCompactCollector::IsUnmarkedHeapObject(Object** p) {
Object* o = *p;
if (!o->IsHeapObject()) return false;
HeapObject* heap_object = HeapObject::cast(o);
MarkBit mark = Marking::MarkBitFrom(heap_object);
return !mark.Get();
}
bool MarkCompactCollector::IsUnmarkedHeapObjectWithHeap(Heap* heap,
Object** p) {
Object* o = *p;
ASSERT(o->IsHeapObject());
HeapObject* heap_object = HeapObject::cast(o);
MarkBit mark = Marking::MarkBitFrom(heap_object);
return !mark.Get();
}
void MarkCompactCollector::MarkStringTable(RootMarkingVisitor* visitor) {
StringTable* string_table = heap()->string_table();
// Mark the string table itself.
MarkBit string_table_mark = Marking::MarkBitFrom(string_table);
SetMark(string_table, string_table_mark);
// Explicitly mark the prefix.
string_table->IteratePrefix(visitor);
ProcessMarkingDeque();
}
void MarkCompactCollector::MarkRoots(RootMarkingVisitor* visitor) {
// Mark the heap roots including global variables, stack variables,
// etc., and all objects reachable from them.
heap()->IterateStrongRoots(visitor, VISIT_ONLY_STRONG);
// Handle the string table specially.
MarkStringTable(visitor);
// There may be overflowed objects in the heap. Visit them now.
while (marking_deque_.overflowed()) {
RefillMarkingDeque();
EmptyMarkingDeque();
}
}
void MarkCompactCollector::MarkImplicitRefGroups() {
List<ImplicitRefGroup*>* ref_groups =
isolate()->global_handles()->implicit_ref_groups();
int last = 0;
for (int i = 0; i < ref_groups->length(); i++) {
ImplicitRefGroup* entry = ref_groups->at(i);
ASSERT(entry != NULL);
if (!IsMarked(*entry->parent)) {
(*ref_groups)[last++] = entry;
continue;
}
Object*** children = entry->children;
// A parent object is marked, so mark all child heap objects.
for (size_t j = 0; j < entry->length; ++j) {
if ((*children[j])->IsHeapObject()) {
HeapObject* child = HeapObject::cast(*children[j]);
MarkBit mark = Marking::MarkBitFrom(child);
MarkObject(child, mark);
}
}
// Once the entire group has been marked, dispose it because it's
// not needed anymore.
delete entry;
}
ref_groups->Rewind(last);
}
// Mark all objects reachable from the objects on the marking stack.
// Before: the marking stack contains zero or more heap object pointers.
// After: the marking stack is empty, and all objects reachable from the
// marking stack have been marked, or are overflowed in the heap.
void MarkCompactCollector::EmptyMarkingDeque() {
while (!marking_deque_.IsEmpty()) {
HeapObject* object = marking_deque_.Pop();
ASSERT(object->IsHeapObject());
ASSERT(heap()->Contains(object));
ASSERT(Marking::IsBlack(Marking::MarkBitFrom(object)));
Map* map = object->map();
MarkBit map_mark = Marking::MarkBitFrom(map);
MarkObject(map, map_mark);
MarkCompactMarkingVisitor::IterateBody(map, object);
}
}
// Sweep the heap for overflowed objects, clear their overflow bits, and
// push them on the marking stack. Stop early if the marking stack fills
// before sweeping completes. If sweeping completes, there are no remaining
// overflowed objects in the heap so the overflow flag on the markings stack
// is cleared.
void MarkCompactCollector::RefillMarkingDeque() {
ASSERT(marking_deque_.overflowed());
DiscoverGreyObjectsInNewSpace(heap(), &marking_deque_);
if (marking_deque_.IsFull()) return;
DiscoverGreyObjectsInSpace(heap(),
&marking_deque_,
heap()->old_pointer_space());
if (marking_deque_.IsFull()) return;
DiscoverGreyObjectsInSpace(heap(),
&marking_deque_,
heap()->old_data_space());
if (marking_deque_.IsFull()) return;
DiscoverGreyObjectsInSpace(heap(),
&marking_deque_,
heap()->code_space());
if (marking_deque_.IsFull()) return;
DiscoverGreyObjectsInSpace(heap(),
&marking_deque_,
heap()->map_space());
if (marking_deque_.IsFull()) return;
DiscoverGreyObjectsInSpace(heap(),
&marking_deque_,
heap()->cell_space());
if (marking_deque_.IsFull()) return;
DiscoverGreyObjectsInSpace(heap(),
&marking_deque_,
heap()->property_cell_space());
if (marking_deque_.IsFull()) return;
LargeObjectIterator lo_it(heap()->lo_space());
DiscoverGreyObjectsWithIterator(heap(),
&marking_deque_,
&lo_it);
if (marking_deque_.IsFull()) return;
marking_deque_.ClearOverflowed();
}
// Mark all objects reachable (transitively) from objects on the marking
// stack. Before: the marking stack contains zero or more heap object
// pointers. After: the marking stack is empty and there are no overflowed
// objects in the heap.
void MarkCompactCollector::ProcessMarkingDeque() {
EmptyMarkingDeque();
while (marking_deque_.overflowed()) {
RefillMarkingDeque();
EmptyMarkingDeque();
}
}
// Mark all objects reachable (transitively) from objects on the marking
// stack including references only considered in the atomic marking pause.
void MarkCompactCollector::ProcessEphemeralMarking(ObjectVisitor* visitor) {
bool work_to_do = true;
ASSERT(marking_deque_.IsEmpty());
while (work_to_do) {
isolate()->global_handles()->IterateObjectGroups(
visitor, &IsUnmarkedHeapObjectWithHeap);
MarkImplicitRefGroups();
ProcessWeakCollections();
work_to_do = !marking_deque_.IsEmpty();
ProcessMarkingDeque();
}
}
void MarkCompactCollector::ProcessTopOptimizedFrame(ObjectVisitor* visitor) {
for (StackFrameIterator it(isolate(), isolate()->thread_local_top());
!it.done(); it.Advance()) {
if (it.frame()->type() == StackFrame::JAVA_SCRIPT) {
return;
}
if (it.frame()->type() == StackFrame::OPTIMIZED) {
Code* code = it.frame()->LookupCode();
if (!code->CanDeoptAt(it.frame()->pc())) {
code->CodeIterateBody(visitor);
}
ProcessMarkingDeque();
return;
}
}
}
void MarkCompactCollector::MarkLiveObjects() {
GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_MARK);
// The recursive GC marker detects when it is nearing stack overflow,
// and switches to a different marking system. JS interrupts interfere
// with the C stack limit check.
PostponeInterruptsScope postpone(isolate());
bool incremental_marking_overflowed = false;
IncrementalMarking* incremental_marking = heap_->incremental_marking();
if (was_marked_incrementally_) {
// Finalize the incremental marking and check whether we had an overflow.
// Both markers use grey color to mark overflowed objects so
// non-incremental marker can deal with them as if overflow
// occured during normal marking.
// But incremental marker uses a separate marking deque
// so we have to explicitly copy its overflow state.
incremental_marking->Finalize();
incremental_marking_overflowed =
incremental_marking->marking_deque()->overflowed();
incremental_marking->marking_deque()->ClearOverflowed();
} else {
// Abort any pending incremental activities e.g. incremental sweeping.
incremental_marking->Abort();
}
#ifdef DEBUG
ASSERT(state_ == PREPARE_GC);
state_ = MARK_LIVE_OBJECTS;
#endif
// The to space contains live objects, a page in from space is used as a
// marking stack.
Address marking_deque_start = heap()->new_space()->FromSpacePageLow();
Address marking_deque_end = heap()->new_space()->FromSpacePageHigh();
if (FLAG_force_marking_deque_overflows) {
marking_deque_end = marking_deque_start + 64 * kPointerSize;
}
marking_deque_.Initialize(marking_deque_start,
marking_deque_end);
ASSERT(!marking_deque_.overflowed());
if (incremental_marking_overflowed) {
// There are overflowed objects left in the heap after incremental marking.
marking_deque_.SetOverflowed();
}
PrepareForCodeFlushing();
if (was_marked_incrementally_) {
// There is no write barrier on cells so we have to scan them now at the end
// of the incremental marking.
{
HeapObjectIterator cell_iterator(heap()->cell_space());
HeapObject* cell;
while ((cell = cell_iterator.Next()) != NULL) {
ASSERT(cell->IsCell());
if (IsMarked(cell)) {
int offset = Cell::kValueOffset;
MarkCompactMarkingVisitor::VisitPointer(
heap(),
reinterpret_cast<Object**>(cell->address() + offset));
}
}
}
{
HeapObjectIterator js_global_property_cell_iterator(
heap()->property_cell_space());
HeapObject* cell;
while ((cell = js_global_property_cell_iterator.Next()) != NULL) {
ASSERT(cell->IsPropertyCell());
if (IsMarked(cell)) {
MarkCompactMarkingVisitor::VisitPropertyCell(cell->map(), cell);
}
}
}
}
RootMarkingVisitor root_visitor(heap());
MarkRoots(&root_visitor);
ProcessTopOptimizedFrame(&root_visitor);
// The objects reachable from the roots are marked, yet unreachable
// objects are unmarked. Mark objects reachable due to host
// application specific logic or through Harmony weak maps.
ProcessEphemeralMarking(&root_visitor);
// The objects reachable from the roots, weak maps or object groups
// are marked, yet unreachable objects are unmarked. Mark objects
// reachable only from weak global handles.
//
// First we identify nonlive weak handles and mark them as pending
// destruction.
heap()->isolate()->global_handles()->IdentifyWeakHandles(
&IsUnmarkedHeapObject);
// Then we mark the objects and process the transitive closure.
heap()->isolate()->global_handles()->IterateWeakRoots(&root_visitor);
while (marking_deque_.overflowed()) {
RefillMarkingDeque();
EmptyMarkingDeque();
}
// Repeat host application specific and Harmony weak maps marking to
// mark unmarked objects reachable from the weak roots.
ProcessEphemeralMarking(&root_visitor);
AfterMarking();
}
void MarkCompactCollector::AfterMarking() {
// Object literal map caches reference strings (cache keys) and maps
// (cache values). At this point still useful maps have already been
// marked. Mark the keys for the alive values before we process the
// string table.
ProcessMapCaches();
// Prune the string table removing all strings only pointed to by the
// string table. Cannot use string_table() here because the string
// table is marked.
StringTable* string_table = heap()->string_table();
StringTableCleaner v(heap());
string_table->IterateElements(&v);
string_table->ElementsRemoved(v.PointersRemoved());
heap()->external_string_table_.Iterate(&v);
heap()->external_string_table_.CleanUp();
// Process the weak references.
MarkCompactWeakObjectRetainer mark_compact_object_retainer;
heap()->ProcessWeakReferences(&mark_compact_object_retainer);
// Remove object groups after marking phase.
heap()->isolate()->global_handles()->RemoveObjectGroups();
heap()->isolate()->global_handles()->RemoveImplicitRefGroups();
// Flush code from collected candidates.
if (is_code_flushing_enabled()) {
code_flusher_->ProcessCandidates();
// If incremental marker does not support code flushing, we need to
// disable it before incremental marking steps for next cycle.
if (FLAG_flush_code && !FLAG_flush_code_incrementally) {
EnableCodeFlushing(false);
}
}
if (!FLAG_watch_ic_patching) {
// Clean up dead objects from the runtime profiler.
heap()->isolate()->runtime_profiler()->RemoveDeadSamples();
}
if (FLAG_track_gc_object_stats) {
heap()->CheckpointObjectStats();
}
}
void MarkCompactCollector::ProcessMapCaches() {
Object* raw_context = heap()->native_contexts_list_;
while (raw_context != heap()->undefined_value()) {
Context* context = reinterpret_cast<Context*>(raw_context);
if (IsMarked(context)) {
HeapObject* raw_map_cache =
HeapObject::cast(context->get(Context::MAP_CACHE_INDEX));
// A map cache may be reachable from the stack. In this case
// it's already transitively marked and it's too late to clean
// up its parts.
if (!IsMarked(raw_map_cache) &&
raw_map_cache != heap()->undefined_value()) {
MapCache* map_cache = reinterpret_cast<MapCache*>(raw_map_cache);
int existing_elements = map_cache->NumberOfElements();
int used_elements = 0;
for (int i = MapCache::kElementsStartIndex;
i < map_cache->length();
i += MapCache::kEntrySize) {
Object* raw_key = map_cache->get(i);
if (raw_key == heap()->undefined_value() ||
raw_key == heap()->the_hole_value()) continue;
STATIC_ASSERT(MapCache::kEntrySize == 2);
Object* raw_map = map_cache->get(i + 1);
if (raw_map->IsHeapObject() && IsMarked(raw_map)) {
++used_elements;
} else {
// Delete useless entries with unmarked maps.
ASSERT(raw_map->IsMap());
map_cache->set_the_hole(i);
map_cache->set_the_hole(i + 1);
}
}
if (used_elements == 0) {
context->set(Context::MAP_CACHE_INDEX, heap()->undefined_value());
} else {
// Note: we don't actually shrink the cache here to avoid
// extra complexity during GC. We rely on subsequent cache
// usages (EnsureCapacity) to do this.
map_cache->ElementsRemoved(existing_elements - used_elements);
MarkBit map_cache_markbit = Marking::MarkBitFrom(map_cache);
MarkObject(map_cache, map_cache_markbit);
}
}
}
// Move to next element in the list.
raw_context = context->get(Context::NEXT_CONTEXT_LINK);
}
ProcessMarkingDeque();
}
void MarkCompactCollector::ReattachInitialMaps() {
HeapObjectIterator map_iterator(heap()->map_space());
for (HeapObject* obj = map_iterator.Next();
obj != NULL;
obj = map_iterator.Next()) {
Map* map = Map::cast(obj);
STATIC_ASSERT(LAST_TYPE == LAST_JS_RECEIVER_TYPE);
if (map->instance_type() < FIRST_JS_RECEIVER_TYPE) continue;
if (map->attached_to_shared_function_info()) {
JSFunction::cast(map->constructor())->shared()->AttachInitialMap(map);
}
}
}
void MarkCompactCollector::ClearNonLiveReferences() {
// Iterate over the map space, setting map transitions that go from
// a marked map to an unmarked map to null transitions. This action
// is carried out only on maps of JSObjects and related subtypes.
HeapObjectIterator map_iterator(heap()->map_space());
for (HeapObject* obj = map_iterator.Next();
obj != NULL;
obj = map_iterator.Next()) {
Map* map = Map::cast(obj);
if (!map->CanTransition()) continue;
MarkBit map_mark = Marking::MarkBitFrom(map);
if (map_mark.Get() && map->attached_to_shared_function_info()) {
// This map is used for inobject slack tracking and has been detached
// from SharedFunctionInfo during the mark phase.
// Since it survived the GC, reattach it now.
JSFunction::cast(map->constructor())->shared()->AttachInitialMap(map);
}
ClearNonLivePrototypeTransitions(map);
ClearNonLiveMapTransitions(map, map_mark);
if (map_mark.Get()) {
ClearNonLiveDependentCode(map->dependent_code());
} else {
ClearAndDeoptimizeDependentCode(map);
}
}
// Iterate over property cell space, removing dependent code that is not
// otherwise kept alive by strong references.
HeapObjectIterator cell_iterator(heap_->property_cell_space());
for (HeapObject* cell = cell_iterator.Next();
cell != NULL;
cell = cell_iterator.Next()) {
if (IsMarked(cell)) {
ClearNonLiveDependentCode(PropertyCell::cast(cell)->dependent_code());
}
}
}
void MarkCompactCollector::ClearNonLivePrototypeTransitions(Map* map) {
int number_of_transitions = map->NumberOfProtoTransitions();
FixedArray* prototype_transitions = map->GetPrototypeTransitions();
int new_number_of_transitions = 0;
const int header = Map::kProtoTransitionHeaderSize;
const int proto_offset = header + Map::kProtoTransitionPrototypeOffset;
const int map_offset = header + Map::kProtoTransitionMapOffset;
const int step = Map::kProtoTransitionElementsPerEntry;
for (int i = 0; i < number_of_transitions; i++) {
Object* prototype = prototype_transitions->get(proto_offset + i * step);
Object* cached_map = prototype_transitions->get(map_offset + i * step);
if (IsMarked(prototype) && IsMarked(cached_map)) {
int proto_index = proto_offset + new_number_of_transitions * step;
int map_index = map_offset + new_number_of_transitions * step;
if (new_number_of_transitions != i) {
prototype_transitions->set(
proto_index,
prototype,
UPDATE_WRITE_BARRIER);
prototype_transitions->set(
map_index,
cached_map,
SKIP_WRITE_BARRIER);
}
Object** slot =
HeapObject::RawField(prototype_transitions,
FixedArray::OffsetOfElementAt(proto_index));
RecordSlot(slot, slot, prototype);
new_number_of_transitions++;
}
}
if (new_number_of_transitions != number_of_transitions) {
map->SetNumberOfProtoTransitions(new_number_of_transitions);
}
// Fill slots that became free with undefined value.
for (int i = new_number_of_transitions * step;
i < number_of_transitions * step;
i++) {
prototype_transitions->set_undefined(header + i);
}
}
void MarkCompactCollector::ClearNonLiveMapTransitions(Map* map,
MarkBit map_mark) {
Object* potential_parent = map->GetBackPointer();
if (!potential_parent->IsMap()) return;
Map* parent = Map::cast(potential_parent);
// Follow back pointer, check whether we are dealing with a map transition
// from a live map to a dead path and in case clear transitions of parent.
bool current_is_alive = map_mark.Get();
bool parent_is_alive = Marking::MarkBitFrom(parent).Get();
if (!current_is_alive && parent_is_alive) {
parent->ClearNonLiveTransitions(heap());
}
}
void MarkCompactCollector::ClearAndDeoptimizeDependentCode(Map* map) {
DisallowHeapAllocation no_allocation;
DependentCode* entries = map->dependent_code();
DependentCode::GroupStartIndexes starts(entries);
int number_of_entries = starts.number_of_entries();
if (number_of_entries == 0) return;
for (int i = 0; i < number_of_entries; i++) {
// If the entry is compilation info then the map must be alive,
// and ClearAndDeoptimizeDependentCode shouldn't be called.
ASSERT(entries->is_code_at(i));
Code* code = entries->code_at(i);
if (IsMarked(code) && !code->marked_for_deoptimization()) {
code->set_marked_for_deoptimization(true);
have_code_to_deoptimize_ = true;
}
entries->clear_at(i);
}
map->set_dependent_code(DependentCode::cast(heap()->empty_fixed_array()));
}
void MarkCompactCollector::ClearNonLiveDependentCode(DependentCode* entries) {
DisallowHeapAllocation no_allocation;
DependentCode::GroupStartIndexes starts(entries);
int number_of_entries = starts.number_of_entries();
if (number_of_entries == 0) return;
int new_number_of_entries = 0;
// Go through all groups, remove dead codes and compact.
for (int g = 0; g < DependentCode::kGroupCount; g++) {
int group_number_of_entries = 0;
for (int i = starts.at(g); i < starts.at(g + 1); i++) {
Object* obj = entries->object_at(i);
ASSERT(obj->IsCode() || IsMarked(obj));
if (IsMarked(obj) &&
(!obj->IsCode() || !WillBeDeoptimized(Code::cast(obj)))) {
if (new_number_of_entries + group_number_of_entries != i) {
entries->set_object_at(
new_number_of_entries + group_number_of_entries, obj);
}
Object** slot = entries->slot_at(new_number_of_entries +
group_number_of_entries);
RecordSlot(slot, slot, obj);
group_number_of_entries++;
}
}
entries->set_number_of_entries(
static_cast<DependentCode::DependencyGroup>(g),
group_number_of_entries);
new_number_of_entries += group_number_of_entries;
}
for (int i = new_number_of_entries; i < number_of_entries; i++) {
entries->clear_at(i);
}
}
void MarkCompactCollector::ProcessWeakCollections() {
GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_WEAKCOLLECTION_PROCESS);
Object* weak_collection_obj = encountered_weak_collections();
while (weak_collection_obj != Smi::FromInt(0)) {
ASSERT(MarkCompactCollector::IsMarked(
HeapObject::cast(weak_collection_obj)));
JSWeakCollection* weak_collection =
reinterpret_cast<JSWeakCollection*>(weak_collection_obj);
ObjectHashTable* table = ObjectHashTable::cast(weak_collection->table());
Object** anchor = reinterpret_cast<Object**>(table->address());
for (int i = 0; i < table->Capacity(); i++) {
if (MarkCompactCollector::IsMarked(HeapObject::cast(table->KeyAt(i)))) {
Object** key_slot =
HeapObject::RawField(table, FixedArray::OffsetOfElementAt(
ObjectHashTable::EntryToIndex(i)));
RecordSlot(anchor, key_slot, *key_slot);
Object** value_slot =
HeapObject::RawField(table, FixedArray::OffsetOfElementAt(
ObjectHashTable::EntryToValueIndex(i)));
MarkCompactMarkingVisitor::MarkObjectByPointer(
this, anchor, value_slot);
}
}
weak_collection_obj = weak_collection->next();
}
}
void MarkCompactCollector::ClearWeakCollections() {
GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_WEAKCOLLECTION_CLEAR);
Object* weak_collection_obj = encountered_weak_collections();
while (weak_collection_obj != Smi::FromInt(0)) {
ASSERT(MarkCompactCollector::IsMarked(
HeapObject::cast(weak_collection_obj)));
JSWeakCollection* weak_collection =
reinterpret_cast<JSWeakCollection*>(weak_collection_obj);
ObjectHashTable* table = ObjectHashTable::cast(weak_collection->table());
for (int i = 0; i < table->Capacity(); i++) {
if (!MarkCompactCollector::IsMarked(HeapObject::cast(table->KeyAt(i)))) {
table->RemoveEntry(i);
}
}
weak_collection_obj = weak_collection->next();
weak_collection->set_next(Smi::FromInt(0));
}
set_encountered_weak_collections(Smi::FromInt(0));
}
// We scavange new space simultaneously with sweeping. This is done in two
// passes.
//
// The first pass migrates all alive objects from one semispace to another or
// promotes them to old space. Forwarding address is written directly into
// first word of object without any encoding. If object is dead we write
// NULL as a forwarding address.
//
// The second pass updates pointers to new space in all spaces. It is possible
// to encounter pointers to dead new space objects during traversal of pointers
// to new space. We should clear them to avoid encountering them during next
// pointer iteration. This is an issue if the store buffer overflows and we
// have to scan the entire old space, including dead objects, looking for
// pointers to new space.
void MarkCompactCollector::MigrateObject(Address dst,
Address src,
int size,
AllocationSpace dest) {
HEAP_PROFILE(heap(), ObjectMoveEvent(src, dst));
// TODO(hpayer): Replace these checks with asserts.
CHECK(heap()->AllowedToBeMigrated(HeapObject::FromAddress(src), dest));
CHECK(dest != LO_SPACE && size <= Page::kMaxNonCodeHeapObjectSize);
if (dest == OLD_POINTER_SPACE) {
Address src_slot = src;
Address dst_slot = dst;
ASSERT(IsAligned(size, kPointerSize));
for (int remaining = size / kPointerSize; remaining > 0; remaining--) {
Object* value = Memory::Object_at(src_slot);
Memory::Object_at(dst_slot) = value;
if (heap_->InNewSpace(value)) {
heap_->store_buffer()->Mark(dst_slot);
} else if (value->IsHeapObject() && IsOnEvacuationCandidate(value)) {
SlotsBuffer::AddTo(&slots_buffer_allocator_,
&migration_slots_buffer_,
reinterpret_cast<Object**>(dst_slot),
SlotsBuffer::IGNORE_OVERFLOW);
}
src_slot += kPointerSize;
dst_slot += kPointerSize;
}
if (compacting_ && HeapObject::FromAddress(dst)->IsJSFunction()) {
Address code_entry_slot = dst + JSFunction::kCodeEntryOffset;
Address code_entry = Memory::Address_at(code_entry_slot);
if (Page::FromAddress(code_entry)->IsEvacuationCandidate()) {
SlotsBuffer::AddTo(&slots_buffer_allocator_,
&migration_slots_buffer_,
SlotsBuffer::CODE_ENTRY_SLOT,
code_entry_slot,
SlotsBuffer::IGNORE_OVERFLOW);
}
}
} else if (dest == CODE_SPACE) {
PROFILE(isolate(), CodeMoveEvent(src, dst));
heap()->MoveBlock(dst, src, size);
SlotsBuffer::AddTo(&slots_buffer_allocator_,
&migration_slots_buffer_,
SlotsBuffer::RELOCATED_CODE_OBJECT,
dst,
SlotsBuffer::IGNORE_OVERFLOW);
Code::cast(HeapObject::FromAddress(dst))->Relocate(dst - src);
} else {
ASSERT(dest == OLD_DATA_SPACE || dest == NEW_SPACE);
heap()->MoveBlock(dst, src, size);
}
Memory::Address_at(src) = dst;
}
// Visitor for updating pointers from live objects in old spaces to new space.
// It does not expect to encounter pointers to dead objects.
class PointersUpdatingVisitor: public ObjectVisitor {
public:
explicit PointersUpdatingVisitor(Heap* heap) : heap_(heap) { }
void VisitPointer(Object** p) {
UpdatePointer(p);
}
void VisitPointers(Object** start, Object** end) {
for (Object** p = start; p < end; p++) UpdatePointer(p);
}
void VisitEmbeddedPointer(RelocInfo* rinfo) {
ASSERT(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
Object* target = rinfo->target_object();
Object* old_target = target;
VisitPointer(&target);
// Avoid unnecessary changes that might unnecessary flush the instruction
// cache.
if (target != old_target) {
rinfo->set_target_object(target);
}
}
void VisitCodeTarget(RelocInfo* rinfo) {
ASSERT(RelocInfo::IsCodeTarget(rinfo->rmode()));
Object* target = Code::GetCodeFromTargetAddress(rinfo->target_address());
Object* old_target = target;
VisitPointer(&target);
if (target != old_target) {
rinfo->set_target_address(Code::cast(target)->instruction_start());
}
}
void VisitCodeAgeSequence(RelocInfo* rinfo) {
ASSERT(RelocInfo::IsCodeAgeSequence(rinfo->rmode()));
Object* stub = rinfo->code_age_stub();
ASSERT(stub != NULL);
VisitPointer(&stub);
if (stub != rinfo->code_age_stub()) {
rinfo->set_code_age_stub(Code::cast(stub));
}
}
void VisitDebugTarget(RelocInfo* rinfo) {
ASSERT((RelocInfo::IsJSReturn(rinfo->rmode()) &&
rinfo->IsPatchedReturnSequence()) ||
(RelocInfo::IsDebugBreakSlot(rinfo->rmode()) &&
rinfo->IsPatchedDebugBreakSlotSequence()));
Object* target = Code::GetCodeFromTargetAddress(rinfo->call_address());
VisitPointer(&target);
rinfo->set_call_address(Code::cast(target)->instruction_start());
}
static inline void UpdateSlot(Heap* heap, Object** slot) {
Object* obj = *slot;
if (!obj->IsHeapObject()) return;
HeapObject* heap_obj = HeapObject::cast(obj);
MapWord map_word = heap_obj->map_word();
if (map_word.IsForwardingAddress()) {
ASSERT(heap->InFromSpace(heap_obj) ||
MarkCompactCollector::IsOnEvacuationCandidate(heap_obj));
HeapObject* target = map_word.ToForwardingAddress();
*slot = target;
ASSERT(!heap->InFromSpace(target) &&
!MarkCompactCollector::IsOnEvacuationCandidate(target));
}
}
private:
inline void UpdatePointer(Object** p) {
UpdateSlot(heap_, p);
}
Heap* heap_;
};
static void UpdatePointer(HeapObject** p, HeapObject* object) {
ASSERT(*p == object);
Address old_addr = object->address();
Address new_addr = Memory::Address_at(old_addr);
// The new space sweep will overwrite the map word of dead objects
// with NULL. In this case we do not need to transfer this entry to
// the store buffer which we are rebuilding.
if (new_addr != NULL) {
*p = HeapObject::FromAddress(new_addr);
} else {
// We have to zap this pointer, because the store buffer may overflow later,
// and then we have to scan the entire heap and we don't want to find
// spurious newspace pointers in the old space.
// TODO(mstarzinger): This was changed to a sentinel value to track down
// rare crashes, change it back to Smi::FromInt(0) later.
*p = reinterpret_cast<HeapObject*>(Smi::FromInt(0x0f100d00 >> 1)); // flood
}
}
static String* UpdateReferenceInExternalStringTableEntry(Heap* heap,
Object** p) {
MapWord map_word = HeapObject::cast(*p)->map_word();
if (map_word.IsForwardingAddress()) {
return String::cast(map_word.ToForwardingAddress());
}
return String::cast(*p);
}
bool MarkCompactCollector::TryPromoteObject(HeapObject* object,
int object_size) {
// TODO(hpayer): Replace that check with an assert.
CHECK(object_size <= Page::kMaxNonCodeHeapObjectSize);
OldSpace* target_space = heap()->TargetSpace(object);
ASSERT(target_space == heap()->old_pointer_space() ||
target_space == heap()->old_data_space());
Object* result;
MaybeObject* maybe_result = target_space->AllocateRaw(object_size);
if (maybe_result->ToObject(&result)) {
HeapObject* target = HeapObject::cast(result);
MigrateObject(target->address(),
object->address(),
object_size,
target_space->identity());
heap()->mark_compact_collector()->tracer()->
increment_promoted_objects_size(object_size);
return true;
}
return false;
}
void MarkCompactCollector::EvacuateNewSpace() {
// There are soft limits in the allocation code, designed trigger a mark
// sweep collection by failing allocations. But since we are already in
// a mark-sweep allocation, there is no sense in trying to trigger one.
AlwaysAllocateScope scope;
heap()->CheckNewSpaceExpansionCriteria();
NewSpace* new_space = heap()->new_space();
// Store allocation range before flipping semispaces.
Address from_bottom = new_space->bottom();
Address from_top = new_space->top();
// Flip the semispaces. After flipping, to space is empty, from space has
// live objects.
new_space->Flip();
new_space->ResetAllocationInfo();
int survivors_size = 0;
// First pass: traverse all objects in inactive semispace, remove marks,
// migrate live objects and write forwarding addresses. This stage puts
// new entries in the store buffer and may cause some pages to be marked
// scan-on-scavenge.
NewSpacePageIterator it(from_bottom, from_top);
while (it.has_next()) {
NewSpacePage* p = it.next();
survivors_size += DiscoverAndPromoteBlackObjectsOnPage(new_space, p);
}
heap_->IncrementYoungSurvivorsCounter(survivors_size);
new_space->set_age_mark(new_space->top());
}
void MarkCompactCollector::EvacuateLiveObjectsFromPage(Page* p) {
AlwaysAllocateScope always_allocate;
PagedSpace* space = static_cast<PagedSpace*>(p->owner());
ASSERT(p->IsEvacuationCandidate() && !p->WasSwept());
p->MarkSweptPrecisely();
int offsets[16];
for (MarkBitCellIterator it(p); !it.Done(); it.Advance()) {
Address cell_base = it.CurrentCellBase();
MarkBit::CellType* cell = it.CurrentCell();
if (*cell == 0) continue;
int live_objects = MarkWordToObjectStarts(*cell, offsets);
for (int i = 0; i < live_objects; i++) {
Address object_addr = cell_base + offsets[i] * kPointerSize;
HeapObject* object = HeapObject::FromAddress(object_addr);
ASSERT(Marking::IsBlack(Marking::MarkBitFrom(object)));
int size = object->Size();
MaybeObject* target = space->AllocateRaw(size);
if (target->IsFailure()) {
// OS refused to give us memory.
V8::FatalProcessOutOfMemory("Evacuation");
return;
}
Object* target_object = target->ToObjectUnchecked();
MigrateObject(HeapObject::cast(target_object)->address(),
object_addr,
size,
space->identity());
ASSERT(object->map_word().IsForwardingAddress());
}
// Clear marking bits for current cell.
*cell = 0;
}
p->ResetLiveBytes();
}
void MarkCompactCollector::EvacuatePages() {
int npages = evacuation_candidates_.length();
for (int i = 0; i < npages; i++) {
Page* p = evacuation_candidates_[i];
ASSERT(p->IsEvacuationCandidate() ||
p->IsFlagSet(Page::RESCAN_ON_EVACUATION));
if (p->IsEvacuationCandidate()) {
// During compaction we might have to request a new page.
// Check that space still have room for that.
if (static_cast<PagedSpace*>(p->owner())->CanExpand()) {
EvacuateLiveObjectsFromPage(p);
} else {
// Without room for expansion evacuation is not guaranteed to succeed.
// Pessimistically abandon unevacuated pages.
for (int j = i; j < npages; j++) {
Page* page = evacuation_candidates_[j];
slots_buffer_allocator_.DeallocateChain(page->slots_buffer_address());
page->ClearEvacuationCandidate();
page->SetFlag(Page::RESCAN_ON_EVACUATION);
page->InsertAfter(static_cast<PagedSpace*>(page->owner())->anchor());
}
return;
}
}
}
}
class EvacuationWeakObjectRetainer : public WeakObjectRetainer {
public:
virtual Object* RetainAs(Object* object) {
if (object->IsHeapObject()) {
HeapObject* heap_object = HeapObject::cast(object);
MapWord map_word = heap_object->map_word();
if (map_word.IsForwardingAddress()) {
return map_word.ToForwardingAddress();
}
}
return object;
}
};
static inline void UpdateSlot(Isolate* isolate,
ObjectVisitor* v,
SlotsBuffer::SlotType slot_type,
Address addr) {
switch (slot_type) {
case SlotsBuffer::CODE_TARGET_SLOT: {
RelocInfo rinfo(addr, RelocInfo::CODE_TARGET, 0, NULL);
rinfo.Visit(isolate, v);
break;
}
case SlotsBuffer::CODE_ENTRY_SLOT: {
v->VisitCodeEntry(addr);
break;
}
case SlotsBuffer::RELOCATED_CODE_OBJECT: {
HeapObject* obj = HeapObject::FromAddress(addr);
Code::cast(obj)->CodeIterateBody(v);
break;
}
case SlotsBuffer::DEBUG_TARGET_SLOT: {
RelocInfo rinfo(addr, RelocInfo::DEBUG_BREAK_SLOT, 0, NULL);
if (rinfo.IsPatchedDebugBreakSlotSequence()) rinfo.Visit(isolate, v);
break;
}
case SlotsBuffer::JS_RETURN_SLOT: {
RelocInfo rinfo(addr, RelocInfo::JS_RETURN, 0, NULL);
if (rinfo.IsPatchedReturnSequence()) rinfo.Visit(isolate, v);
break;
}
case SlotsBuffer::EMBEDDED_OBJECT_SLOT: {
RelocInfo rinfo(addr, RelocInfo::EMBEDDED_OBJECT, 0, NULL);
rinfo.Visit(isolate, v);
break;
}
default:
UNREACHABLE();
break;
}
}
enum SweepingMode {
SWEEP_ONLY,
SWEEP_AND_VISIT_LIVE_OBJECTS
};
enum SkipListRebuildingMode {
REBUILD_SKIP_LIST,
IGNORE_SKIP_LIST
};
// Sweep a space precisely. After this has been done the space can
// be iterated precisely, hitting only the live objects. Code space
// is always swept precisely because we want to be able to iterate
// over it. Map space is swept precisely, because it is not compacted.
// Slots in live objects pointing into evacuation candidates are updated
// if requested.
template<SweepingMode sweeping_mode, SkipListRebuildingMode skip_list_mode>
static void SweepPrecisely(PagedSpace* space,
Page* p,
ObjectVisitor* v) {
ASSERT(!p->IsEvacuationCandidate() && !p->WasSwept());
ASSERT_EQ(skip_list_mode == REBUILD_SKIP_LIST,
space->identity() == CODE_SPACE);
ASSERT((p->skip_list() == NULL) || (skip_list_mode == REBUILD_SKIP_LIST));
double start_time = 0.0;
if (FLAG_print_cumulative_gc_stat) {
start_time = OS::TimeCurrentMillis();
}
p->MarkSweptPrecisely();
Address free_start = p->area_start();
ASSERT(reinterpret_cast<intptr_t>(free_start) % (32 * kPointerSize) == 0);
int offsets[16];
SkipList* skip_list = p->skip_list();
int curr_region = -1;
if ((skip_list_mode == REBUILD_SKIP_LIST) && skip_list) {
skip_list->Clear();
}
for (MarkBitCellIterator it(p); !it.Done(); it.Advance()) {
Address cell_base = it.CurrentCellBase();
MarkBit::CellType* cell = it.CurrentCell();
int live_objects = MarkWordToObjectStarts(*cell, offsets);
int live_index = 0;
for ( ; live_objects != 0; live_objects--) {
Address free_end = cell_base + offsets[live_index++] * kPointerSize;
if (free_end != free_start) {
space->Free(free_start, static_cast<int>(free_end - free_start));
#ifdef ENABLE_GDB_JIT_INTERFACE
if (FLAG_gdbjit && space->identity() == CODE_SPACE) {
GDBJITInterface::RemoveCodeRange(free_start, free_end);
}
#endif
}
HeapObject* live_object = HeapObject::FromAddress(free_end);
ASSERT(Marking::IsBlack(Marking::MarkBitFrom(live_object)));
Map* map = live_object->map();
int size = live_object->SizeFromMap(map);
if (sweeping_mode == SWEEP_AND_VISIT_LIVE_OBJECTS) {
live_object->IterateBody(map->instance_type(), size, v);
}
if ((skip_list_mode == REBUILD_SKIP_LIST) && skip_list != NULL) {
int new_region_start =
SkipList::RegionNumber(free_end);
int new_region_end =
SkipList::RegionNumber(free_end + size - kPointerSize);
if (new_region_start != curr_region ||
new_region_end != curr_region) {
skip_list->AddObject(free_end, size);
curr_region = new_region_end;
}
}
free_start = free_end + size;
}
// Clear marking bits for current cell.
*cell = 0;
}
if (free_start != p->area_end()) {
space->Free(free_start, static_cast<int>(p->area_end() - free_start));
#ifdef ENABLE_GDB_JIT_INTERFACE
if (FLAG_gdbjit && space->identity() == CODE_SPACE) {
GDBJITInterface::RemoveCodeRange(free_start, p->area_end());
}
#endif
}
p->ResetLiveBytes();
if (FLAG_print_cumulative_gc_stat) {
space->heap()->AddSweepingTime(OS::TimeCurrentMillis() - start_time);
}
}
static bool SetMarkBitsUnderInvalidatedCode(Code* code, bool value) {
Page* p = Page::FromAddress(code->address());
if (p->IsEvacuationCandidate() ||
p->IsFlagSet(Page::RESCAN_ON_EVACUATION)) {
return false;
}
Address code_start = code->address();
Address code_end = code_start + code->Size();
uint32_t start_index = MemoryChunk::FastAddressToMarkbitIndex(code_start);
uint32_t end_index =
MemoryChunk::FastAddressToMarkbitIndex(code_end - kPointerSize);
Bitmap* b = p->markbits();
MarkBit start_mark_bit = b->MarkBitFromIndex(start_index);
MarkBit end_mark_bit = b->MarkBitFromIndex(end_index);
MarkBit::CellType* start_cell = start_mark_bit.cell();
MarkBit::CellType* end_cell = end_mark_bit.cell();
if (value) {
MarkBit::CellType start_mask = ~(start_mark_bit.mask() - 1);
MarkBit::CellType end_mask = (end_mark_bit.mask() << 1) - 1;
if (start_cell == end_cell) {
*start_cell |= start_mask & end_mask;
} else {
*start_cell |= start_mask;
for (MarkBit::CellType* cell = start_cell + 1; cell < end_cell; cell++) {
*cell = ~0;
}
*end_cell |= end_mask;
}
} else {
for (MarkBit::CellType* cell = start_cell ; cell <= end_cell; cell++) {
*cell = 0;
}
}
return true;
}
static bool IsOnInvalidatedCodeObject(Address addr) {
// We did not record any slots in large objects thus
// we can safely go to the page from the slot address.
Page* p = Page::FromAddress(addr);
// First check owner's identity because old pointer and old data spaces
// are swept lazily and might still have non-zero mark-bits on some
// pages.
if (p->owner()->identity() != CODE_SPACE) return false;
// In code space only bits on evacuation candidates (but we don't record
// any slots on them) and under invalidated code objects are non-zero.
MarkBit mark_bit =
p->markbits()->MarkBitFromIndex(Page::FastAddressToMarkbitIndex(addr));
return mark_bit.Get();
}
void MarkCompactCollector::InvalidateCode(Code* code) {
if (heap_->incremental_marking()->IsCompacting() &&
!ShouldSkipEvacuationSlotRecording(code)) {
ASSERT(compacting_);
// If the object is white than no slots were recorded on it yet.
MarkBit mark_bit = Marking::MarkBitFrom(code);
if (Marking::IsWhite(mark_bit)) return;
invalidated_code_.Add(code);
}
}
// Return true if the given code is deoptimized or will be deoptimized.
bool MarkCompactCollector::WillBeDeoptimized(Code* code) {
return code->marked_for_deoptimization();
}
bool MarkCompactCollector::MarkInvalidatedCode() {
bool code_marked = false;
int length = invalidated_code_.length();
for (int i = 0; i < length; i++) {
Code* code = invalidated_code_[i];
if (SetMarkBitsUnderInvalidatedCode(code, true)) {
code_marked = true;
}
}
return code_marked;
}
void MarkCompactCollector::RemoveDeadInvalidatedCode() {
int length = invalidated_code_.length();
for (int i = 0; i < length; i++) {
if (!IsMarked(invalidated_code_[i])) invalidated_code_[i] = NULL;
}
}
void MarkCompactCollector::ProcessInvalidatedCode(ObjectVisitor* visitor) {
int length = invalidated_code_.length();
for (int i = 0; i < length; i++) {
Code* code = invalidated_code_[i];
if (code != NULL) {
code->Iterate(visitor);
SetMarkBitsUnderInvalidatedCode(code, false);
}
}
invalidated_code_.Rewind(0);
}
void MarkCompactCollector::EvacuateNewSpaceAndCandidates() {
Heap::RelocationLock relocation_lock(heap());
bool code_slots_filtering_required;
{ GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_SWEEP_NEWSPACE);
code_slots_filtering_required = MarkInvalidatedCode();
EvacuateNewSpace();
}
{ GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_EVACUATE_PAGES);
EvacuatePages();
}
// Second pass: find pointers to new space and update them.
PointersUpdatingVisitor updating_visitor(heap());
{ GCTracer::Scope gc_scope(tracer_,
GCTracer::Scope::MC_UPDATE_NEW_TO_NEW_POINTERS);
// Update pointers in to space.
SemiSpaceIterator to_it(heap()->new_space()->bottom(),
heap()->new_space()->top());
for (HeapObject* object = to_it.Next();
object != NULL;
object = to_it.Next()) {
Map* map = object->map();
object->IterateBody(map->instance_type(),
object->SizeFromMap(map),
&updating_visitor);
}
}
{ GCTracer::Scope gc_scope(tracer_,
GCTracer::Scope::MC_UPDATE_ROOT_TO_NEW_POINTERS);
// Update roots.
heap_->IterateRoots(&updating_visitor, VISIT_ALL_IN_SWEEP_NEWSPACE);
}
{ GCTracer::Scope gc_scope(tracer_,
GCTracer::Scope::MC_UPDATE_OLD_TO_NEW_POINTERS);
StoreBufferRebuildScope scope(heap_,
heap_->store_buffer(),
&Heap::ScavengeStoreBufferCallback);
heap_->store_buffer()->IteratePointersToNewSpaceAndClearMaps(
&UpdatePointer);
}
{ GCTracer::Scope gc_scope(tracer_,
GCTracer::Scope::MC_UPDATE_POINTERS_TO_EVACUATED);
SlotsBuffer::UpdateSlotsRecordedIn(heap_,
migration_slots_buffer_,
code_slots_filtering_required);
if (FLAG_trace_fragmentation) {
PrintF(" migration slots buffer: %d\n",
SlotsBuffer::SizeOfChain(migration_slots_buffer_));
}
if (compacting_ && was_marked_incrementally_) {
// It's difficult to filter out slots recorded for large objects.
LargeObjectIterator it(heap_->lo_space());
for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
// LargeObjectSpace is not swept yet thus we have to skip
// dead objects explicitly.
if (!IsMarked(obj)) continue;
Page* p = Page::FromAddress(obj->address());
if (p->IsFlagSet(Page::RESCAN_ON_EVACUATION)) {
obj->Iterate(&updating_visitor);
p->ClearFlag(Page::RESCAN_ON_EVACUATION);
}
}
}
}
int npages = evacuation_candidates_.length();
{ GCTracer::Scope gc_scope(
tracer_, GCTracer::Scope::MC_UPDATE_POINTERS_BETWEEN_EVACUATED);
for (int i = 0; i < npages; i++) {
Page* p = evacuation_candidates_[i];
ASSERT(p->IsEvacuationCandidate() ||
p->IsFlagSet(Page::RESCAN_ON_EVACUATION));
if (p->IsEvacuationCandidate()) {
SlotsBuffer::UpdateSlotsRecordedIn(heap_,
p->slots_buffer(),
code_slots_filtering_required);
if (FLAG_trace_fragmentation) {
PrintF(" page %p slots buffer: %d\n",
reinterpret_cast<void*>(p),
SlotsBuffer::SizeOfChain(p->slots_buffer()));
}
// Important: skip list should be cleared only after roots were updated
// because root iteration traverses the stack and might have to find
// code objects from non-updated pc pointing into evacuation candidate.
SkipList* list = p->skip_list();
if (list != NULL) list->Clear();
} else {
if (FLAG_gc_verbose) {
PrintF("Sweeping 0x%" V8PRIxPTR " during evacuation.\n",
reinterpret_cast<intptr_t>(p));
}
PagedSpace* space = static_cast<PagedSpace*>(p->owner());
p->ClearFlag(MemoryChunk::RESCAN_ON_EVACUATION);
switch (space->identity()) {
case OLD_DATA_SPACE:
SweepConservatively<SWEEP_SEQUENTIALLY>(space, NULL, p);
break;
case OLD_POINTER_SPACE:
SweepPrecisely<SWEEP_AND_VISIT_LIVE_OBJECTS, IGNORE_SKIP_LIST>(
space, p, &updating_visitor);
break;
case CODE_SPACE:
SweepPrecisely<SWEEP_AND_VISIT_LIVE_OBJECTS, REBUILD_SKIP_LIST>(
space, p, &updating_visitor);
break;
default:
UNREACHABLE();
break;
}
}
}
}
GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_UPDATE_MISC_POINTERS);
// Update pointers from cells.
HeapObjectIterator cell_iterator(heap_->cell_space());
for (HeapObject* cell = cell_iterator.Next();
cell != NULL;
cell = cell_iterator.Next()) {
if (cell->IsCell()) {
Cell::BodyDescriptor::IterateBody(cell, &updating_visitor);
}
}
HeapObjectIterator js_global_property_cell_iterator(
heap_->property_cell_space());
for (HeapObject* cell = js_global_property_cell_iterator.Next();
cell != NULL;
cell = js_global_property_cell_iterator.Next()) {
if (cell->IsPropertyCell()) {
PropertyCell::BodyDescriptor::IterateBody(cell, &updating_visitor);
}
}
// Update the head of the native contexts list in the heap.
updating_visitor.VisitPointer(heap_->native_contexts_list_address());
heap_->string_table()->Iterate(&updating_visitor);
// Update pointers from external string table.
heap_->UpdateReferencesInExternalStringTable(
&UpdateReferenceInExternalStringTableEntry);
if (!FLAG_watch_ic_patching) {
// Update JSFunction pointers from the runtime profiler.
heap()->isolate()->runtime_profiler()->UpdateSamplesAfterCompact(
&updating_visitor);
}
EvacuationWeakObjectRetainer evacuation_object_retainer;
heap()->ProcessWeakReferences(&evacuation_object_retainer);
// Visit invalidated code (we ignored all slots on it) and clear mark-bits
// under it.
ProcessInvalidatedCode(&updating_visitor);
heap_->isolate()->inner_pointer_to_code_cache()->Flush();
#ifdef VERIFY_HEAP
if (FLAG_verify_heap) {
VerifyEvacuation(heap_);
}
#endif
slots_buffer_allocator_.DeallocateChain(&migration_slots_buffer_);
ASSERT(migration_slots_buffer_ == NULL);
}
void MarkCompactCollector::UnlinkEvacuationCandidates() {
int npages = evacuation_candidates_.length();
for (int i = 0; i < npages; i++) {
Page* p = evacuation_candidates_[i];
if (!p->IsEvacuationCandidate()) continue;
p->Unlink();
p->ClearSweptPrecisely();
p->ClearSweptConservatively();
}
}
void MarkCompactCollector::ReleaseEvacuationCandidates() {
int npages = evacuation_candidates_.length();
for (int i = 0; i < npages; i++) {
Page* p = evacuation_candidates_[i];
if (!p->IsEvacuationCandidate()) continue;
PagedSpace* space = static_cast<PagedSpace*>(p->owner());
space->Free(p->area_start(), p->area_size());
p->set_scan_on_scavenge(false);
slots_buffer_allocator_.DeallocateChain(p->slots_buffer_address());
p->ResetLiveBytes();
space->ReleasePage(p, false);
}
evacuation_candidates_.Rewind(0);
compacting_ = false;
heap()->FreeQueuedChunks();
}
static const int kStartTableEntriesPerLine = 5;
static const int kStartTableLines = 171;
static const int kStartTableInvalidLine = 127;
static const int kStartTableUnusedEntry = 126;
#define _ kStartTableUnusedEntry
#define X kStartTableInvalidLine
// Mark-bit to object start offset table.
//
// The line is indexed by the mark bits in a byte. The first number on
// the line describes the number of live object starts for the line and the
// other numbers on the line describe the offsets (in words) of the object
// starts.
//
// Since objects are at least 2 words large we don't have entries for two
// consecutive 1 bits. All entries after 170 have at least 2 consecutive bits.
char kStartTable[kStartTableLines * kStartTableEntriesPerLine] = {
0, _, _, _, _, // 0
1, 0, _, _, _, // 1
1, 1, _, _, _, // 2
X, _, _, _, _, // 3
1, 2, _, _, _, // 4
2, 0, 2, _, _, // 5
X, _, _, _, _, // 6
X, _, _, _, _, // 7
1, 3, _, _, _, // 8
2, 0, 3, _, _, // 9
2, 1, 3, _, _, // 10
X, _, _, _, _, // 11
X, _, _, _, _, // 12
X, _, _, _, _, // 13
X, _, _, _, _, // 14
X, _, _, _, _, // 15
1, 4, _, _, _, // 16
2, 0, 4, _, _, // 17
2, 1, 4, _, _, // 18
X, _, _, _, _, // 19
2, 2, 4, _, _, // 20
3, 0, 2, 4, _, // 21
X, _, _, _, _, // 22
X, _, _, _, _, // 23
X, _, _, _, _, // 24
X, _, _, _, _, // 25
X, _, _, _, _, // 26
X, _, _, _, _, // 27
X, _, _, _, _, // 28
X, _, _, _, _, // 29
X, _, _, _, _, // 30
X, _, _, _, _, // 31
1, 5, _, _, _, // 32
2, 0, 5, _, _, // 33
2, 1, 5, _, _, // 34
X, _, _, _, _, // 35
2, 2, 5, _, _, // 36
3, 0, 2, 5, _, // 37
X, _, _, _, _, // 38
X, _, _, _, _, // 39
2, 3, 5, _, _, // 40
3, 0, 3, 5, _, // 41
3, 1, 3, 5, _, // 42
X, _, _, _, _, // 43
X, _, _, _, _, // 44
X, _, _, _, _, // 45
X, _, _, _, _, // 46
X, _, _, _, _, // 47
X, _, _, _, _, // 48
X, _, _, _, _, // 49
X, _, _, _, _, // 50
X, _, _, _, _, // 51
X, _, _, _, _, // 52
X, _, _, _, _, // 53
X, _, _, _, _, // 54
X, _, _, _, _, // 55
X, _, _, _, _, // 56
X, _, _, _, _, // 57
X, _, _, _, _, // 58
X, _, _, _, _, // 59
X, _, _, _, _, // 60
X, _, _, _, _, // 61
X, _, _, _, _, // 62
X, _, _, _, _, // 63
1, 6, _, _, _, // 64
2, 0, 6, _, _, // 65
2, 1, 6, _, _, // 66
X, _, _, _, _, // 67
2, 2, 6, _, _, // 68
3, 0, 2, 6, _, // 69
X, _, _, _, _, // 70
X, _, _, _, _, // 71
2, 3, 6, _, _, // 72
3, 0, 3, 6, _, // 73
3, 1, 3, 6, _, // 74
X, _, _, _, _, // 75
X, _, _, _, _, // 76
X, _, _, _, _, // 77
X, _, _, _, _, // 78
X, _, _, _, _, // 79
2, 4, 6, _, _, // 80
3, 0, 4, 6, _, // 81
3, 1, 4, 6, _, // 82
X, _, _, _, _, // 83
3, 2, 4, 6, _, // 84
4, 0, 2, 4, 6, // 85
X, _, _, _, _, // 86
X, _, _, _, _, // 87
X, _, _, _, _, // 88
X, _, _, _, _, // 89
X, _, _, _, _, // 90
X, _, _, _, _, // 91
X, _, _, _, _, // 92
X, _, _, _, _, // 93
X, _, _, _, _, // 94
X, _, _, _, _, // 95
X, _, _, _, _, // 96
X, _, _, _, _, // 97
X, _, _, _, _, // 98
X, _, _, _, _, // 99
X, _, _, _, _, // 100
X, _, _, _, _, // 101
X, _, _, _, _, // 102
X, _, _, _, _, // 103
X, _, _, _, _, // 104
X, _, _, _, _, // 105
X, _, _, _, _, // 106
X, _, _, _, _, // 107
X, _, _, _, _, // 108
X, _, _, _, _, // 109
X, _, _, _, _, // 110
X, _, _, _, _, // 111
X, _, _, _, _, // 112
X, _, _, _, _, // 113
X, _, _, _, _, // 114
X, _, _, _, _, // 115
X, _, _, _, _, // 116
X, _, _, _, _, // 117
X, _, _, _, _, // 118
X, _, _, _, _, // 119
X, _, _, _, _, // 120
X, _, _, _, _, // 121
X, _, _, _, _, // 122
X, _, _, _, _, // 123
X, _, _, _, _, // 124
X, _, _, _, _, // 125
X, _, _, _, _, // 126
X, _, _, _, _, // 127
1, 7, _, _, _, // 128
2, 0, 7, _, _, // 129
2, 1, 7, _, _, // 130
X, _, _, _, _, // 131
2, 2, 7, _, _, // 132
3, 0, 2, 7, _, // 133
X, _, _, _, _, // 134
X, _, _, _, _, // 135
2, 3, 7, _, _, // 136
3, 0, 3, 7, _, // 137
3, 1, 3, 7, _, // 138
X, _, _, _, _, // 139
X, _, _, _, _, // 140
X, _, _, _, _, // 141
X, _, _, _, _, // 142
X, _, _, _, _, // 143
2, 4, 7, _, _, // 144
3, 0, 4, 7, _, // 145
3, 1, 4, 7, _, // 146
X, _, _, _, _, // 147
3, 2, 4, 7, _, // 148
4, 0, 2, 4, 7, // 149
X, _, _, _, _, // 150
X, _, _, _, _, // 151
X, _, _, _, _, // 152
X, _, _, _, _, // 153
X, _, _, _, _, // 154
X, _, _, _, _, // 155
X, _, _, _, _, // 156
X, _, _, _, _, // 157
X, _, _, _, _, // 158
X, _, _, _, _, // 159
2, 5, 7, _, _, // 160
3, 0, 5, 7, _, // 161
3, 1, 5, 7, _, // 162
X, _, _, _, _, // 163
3, 2, 5, 7, _, // 164
4, 0, 2, 5, 7, // 165
X, _, _, _, _, // 166
X, _, _, _, _, // 167
3, 3, 5, 7, _, // 168
4, 0, 3, 5, 7, // 169
4, 1, 3, 5, 7 // 170
};
#undef _
#undef X
// Takes a word of mark bits. Returns the number of objects that start in the
// range. Puts the offsets of the words in the supplied array.
static inline int MarkWordToObjectStarts(uint32_t mark_bits, int* starts) {
int objects = 0;
int offset = 0;
// No consecutive 1 bits.
ASSERT((mark_bits & 0x180) != 0x180);
ASSERT((mark_bits & 0x18000) != 0x18000);
ASSERT((mark_bits & 0x1800000) != 0x1800000);
while (mark_bits != 0) {
int byte = (mark_bits & 0xff);
mark_bits >>= 8;
if (byte != 0) {
ASSERT(byte < kStartTableLines); // No consecutive 1 bits.
char* table = kStartTable + byte * kStartTableEntriesPerLine;
int objects_in_these_8_words = table[0];
ASSERT(objects_in_these_8_words != kStartTableInvalidLine);
ASSERT(objects_in_these_8_words < kStartTableEntriesPerLine);
for (int i = 0; i < objects_in_these_8_words; i++) {
starts[objects++] = offset + table[1 + i];
}
}
offset += 8;
}
return objects;
}
static inline Address DigestFreeStart(Address approximate_free_start,
uint32_t free_start_cell) {
ASSERT(free_start_cell != 0);
// No consecutive 1 bits.
ASSERT((free_start_cell & (free_start_cell << 1)) == 0);
int offsets[16];
uint32_t cell = free_start_cell;
int offset_of_last_live;
if ((cell & 0x80000000u) != 0) {
// This case would overflow below.
offset_of_last_live = 31;
} else {
// Remove all but one bit, the most significant. This is an optimization
// that may or may not be worthwhile.
cell |= cell >> 16;
cell |= cell >> 8;
cell |= cell >> 4;
cell |= cell >> 2;
cell |= cell >> 1;
cell = (cell + 1) >> 1;
int live_objects = MarkWordToObjectStarts(cell, offsets);
ASSERT(live_objects == 1);
offset_of_last_live = offsets[live_objects - 1];
}
Address last_live_start =
approximate_free_start + offset_of_last_live * kPointerSize;
HeapObject* last_live = HeapObject::FromAddress(last_live_start);
Address free_start = last_live_start + last_live->Size();
return free_start;
}
static inline Address StartOfLiveObject(Address block_address, uint32_t cell) {
ASSERT(cell != 0);
// No consecutive 1 bits.
ASSERT((cell & (cell << 1)) == 0);
int offsets[16];
if (cell == 0x80000000u) { // Avoid overflow below.
return block_address + 31 * kPointerSize;
}
uint32_t first_set_bit = ((cell ^ (cell - 1)) + 1) >> 1;
ASSERT((first_set_bit & cell) == first_set_bit);
int live_objects = MarkWordToObjectStarts(first_set_bit, offsets);
ASSERT(live_objects == 1);
USE(live_objects);
return block_address + offsets[0] * kPointerSize;
}
template<MarkCompactCollector::SweepingParallelism mode>
static intptr_t Free(PagedSpace* space,
FreeList* free_list,
Address start,
int size) {
if (mode == MarkCompactCollector::SWEEP_SEQUENTIALLY) {
return space->Free(start, size);
} else {
return size - free_list->Free(start, size);
}
}
// Force instantiation of templatized SweepConservatively method for
// SWEEP_SEQUENTIALLY mode.
template intptr_t MarkCompactCollector::
SweepConservatively<MarkCompactCollector::SWEEP_SEQUENTIALLY>(
PagedSpace*, FreeList*, Page*);
// Force instantiation of templatized SweepConservatively method for
// SWEEP_IN_PARALLEL mode.
template intptr_t MarkCompactCollector::
SweepConservatively<MarkCompactCollector::SWEEP_IN_PARALLEL>(
PagedSpace*, FreeList*, Page*);
// Sweeps a space conservatively. After this has been done the larger free
// spaces have been put on the free list and the smaller ones have been
// ignored and left untouched. A free space is always either ignored or put
// on the free list, never split up into two parts. This is important
// because it means that any FreeSpace maps left actually describe a region of
// memory that can be ignored when scanning. Dead objects other than free
// spaces will not contain the free space map.
template<MarkCompactCollector::SweepingParallelism mode>
intptr_t MarkCompactCollector::SweepConservatively(PagedSpace* space,
FreeList* free_list,
Page* p) {
ASSERT(!p->IsEvacuationCandidate() && !p->WasSwept());
ASSERT((mode == MarkCompactCollector::SWEEP_IN_PARALLEL &&
free_list != NULL) ||
(mode == MarkCompactCollector::SWEEP_SEQUENTIALLY &&
free_list == NULL));
p->MarkSweptConservatively();
intptr_t freed_bytes = 0;
size_t size = 0;
// Skip over all the dead objects at the start of the page and mark them free.
Address cell_base = 0;
MarkBit::CellType* cell = NULL;
MarkBitCellIterator it(p);
for (; !it.Done(); it.Advance()) {
cell_base = it.CurrentCellBase();
cell = it.CurrentCell();
if (*cell != 0) break;
}
if (it.Done()) {
size = p->area_end() - p->area_start();
freed_bytes += Free<mode>(space, free_list, p->area_start(),
static_cast<int>(size));
ASSERT_EQ(0, p->LiveBytes());
return freed_bytes;
}
// Grow the size of the start-of-page free space a little to get up to the
// first live object.
Address free_end = StartOfLiveObject(cell_base, *cell);
// Free the first free space.
size = free_end - p->area_start();
freed_bytes += Free<mode>(space, free_list, p->area_start(),
static_cast<int>(size));
// The start of the current free area is represented in undigested form by
// the address of the last 32-word section that contained a live object and
// the marking bitmap for that cell, which describes where the live object
// started. Unless we find a large free space in the bitmap we will not
// digest this pair into a real address. We start the iteration here at the
// first word in the marking bit map that indicates a live object.
Address free_start = cell_base;
MarkBit::CellType free_start_cell = *cell;
for (; !it.Done(); it.Advance()) {
cell_base = it.CurrentCellBase();
cell = it.CurrentCell();
if (*cell != 0) {
// We have a live object. Check approximately whether it is more than 32
// words since the last live object.
if (cell_base - free_start > 32 * kPointerSize) {
free_start = DigestFreeStart(free_start, free_start_cell);
if (cell_base - free_start > 32 * kPointerSize) {
// Now that we know the exact start of the free space it still looks
// like we have a large enough free space to be worth bothering with.
// so now we need to find the start of the first live object at the
// end of the free space.
free_end = StartOfLiveObject(cell_base, *cell);
freed_bytes += Free<mode>(space, free_list, free_start,
static_cast<int>(free_end - free_start));
}
}
// Update our undigested record of where the current free area started.
free_start = cell_base;
free_start_cell = *cell;
// Clear marking bits for current cell.
*cell = 0;
}
}
// Handle the free space at the end of the page.
if (cell_base - free_start > 32 * kPointerSize) {
free_start = DigestFreeStart(free_start, free_start_cell);
freed_bytes += Free<mode>(space, free_list, free_start,
static_cast<int>(p->area_end() - free_start));
}
p->ResetLiveBytes();
return freed_bytes;
}
void MarkCompactCollector::SweepInParallel(PagedSpace* space,
FreeList* private_free_list,
FreeList* free_list) {
PageIterator it(space);
while (it.has_next()) {
Page* p = it.next();
if (p->TryParallelSweeping()) {
SweepConservatively<SWEEP_IN_PARALLEL>(space, private_free_list, p);
free_list->Concatenate(private_free_list);
}
}
}
void MarkCompactCollector::SweepSpace(PagedSpace* space, SweeperType sweeper) {
space->set_was_swept_conservatively(sweeper == CONSERVATIVE ||
sweeper == LAZY_CONSERVATIVE ||
sweeper == PARALLEL_CONSERVATIVE ||
sweeper == CONCURRENT_CONSERVATIVE);
space->ClearStats();
PageIterator it(space);
int pages_swept = 0;
bool lazy_sweeping_active = false;
bool unused_page_present = false;
bool parallel_sweeping_active = false;
while (it.has_next()) {
Page* p = it.next();
ASSERT(p->parallel_sweeping() == 0);
ASSERT(!p->IsEvacuationCandidate());
// Clear sweeping flags indicating that marking bits are still intact.
p->ClearSweptPrecisely();
p->ClearSweptConservatively();
if (p->IsFlagSet(Page::RESCAN_ON_EVACUATION)) {
// Will be processed in EvacuateNewSpaceAndCandidates.
ASSERT(evacuation_candidates_.length() > 0);
continue;
}
// One unused page is kept, all further are released before sweeping them.
if (p->LiveBytes() == 0) {
if (unused_page_present) {
if (FLAG_gc_verbose) {
PrintF("Sweeping 0x%" V8PRIxPTR " released page.\n",
reinterpret_cast<intptr_t>(p));
}
// Adjust unswept free bytes because releasing a page expects said
// counter to be accurate for unswept pages.
space->IncreaseUnsweptFreeBytes(p);
space->ReleasePage(p, true);
continue;
}
unused_page_present = true;
}
switch (sweeper) {
case CONSERVATIVE: {
if (FLAG_gc_verbose) {
PrintF("Sweeping 0x%" V8PRIxPTR " conservatively.\n",
reinterpret_cast<intptr_t>(p));
}
SweepConservatively<SWEEP_SEQUENTIALLY>(space, NULL, p);
pages_swept++;
break;
}
case LAZY_CONSERVATIVE: {
if (lazy_sweeping_active) {
if (FLAG_gc_verbose) {
PrintF("Sweeping 0x%" V8PRIxPTR " lazily postponed.\n",
reinterpret_cast<intptr_t>(p));
}
space->IncreaseUnsweptFreeBytes(p);
} else {
if (FLAG_gc_verbose) {
PrintF("Sweeping 0x%" V8PRIxPTR " conservatively.\n",
reinterpret_cast<intptr_t>(p));
}
SweepConservatively<SWEEP_SEQUENTIALLY>(space, NULL, p);
pages_swept++;
space->SetPagesToSweep(p->next_page());
lazy_sweeping_active = true;
}
break;
}
case CONCURRENT_CONSERVATIVE:
case PARALLEL_CONSERVATIVE: {
if (!parallel_sweeping_active) {
if (FLAG_gc_verbose) {
PrintF("Sweeping 0x%" V8PRIxPTR " conservatively.\n",
reinterpret_cast<intptr_t>(p));
}
SweepConservatively<SWEEP_SEQUENTIALLY>(space, NULL, p);
pages_swept++;
parallel_sweeping_active = true;
} else {
if (FLAG_gc_verbose) {
PrintF("Sweeping 0x%" V8PRIxPTR " conservatively in parallel.\n",
reinterpret_cast<intptr_t>(p));
}
p->set_parallel_sweeping(1);
space->IncreaseUnsweptFreeBytes(p);
}
break;
}
case PRECISE: {
if (FLAG_gc_verbose) {
PrintF("Sweeping 0x%" V8PRIxPTR " precisely.\n",
reinterpret_cast<intptr_t>(p));
}
if (space->identity() == CODE_SPACE) {
SweepPrecisely<SWEEP_ONLY, REBUILD_SKIP_LIST>(space, p, NULL);
} else {
SweepPrecisely<SWEEP_ONLY, IGNORE_SKIP_LIST>(space, p, NULL);
}
pages_swept++;
break;
}
default: {
UNREACHABLE();
}
}
}
if (FLAG_gc_verbose) {
PrintF("SweepSpace: %s (%d pages swept)\n",
AllocationSpaceName(space->identity()),
pages_swept);
}
// Give pages that are queued to be freed back to the OS.
heap()->FreeQueuedChunks();
}
void MarkCompactCollector::SweepSpaces() {
GCTracer::Scope gc_scope(tracer_, GCTracer::Scope::MC_SWEEP);
#ifdef DEBUG
state_ = SWEEP_SPACES;
#endif
SweeperType how_to_sweep =
FLAG_lazy_sweeping ? LAZY_CONSERVATIVE : CONSERVATIVE;
if (FLAG_parallel_sweeping) how_to_sweep = PARALLEL_CONSERVATIVE;
if (FLAG_concurrent_sweeping) how_to_sweep = CONCURRENT_CONSERVATIVE;
if (FLAG_expose_gc) how_to_sweep = CONSERVATIVE;
if (sweep_precisely_) how_to_sweep = PRECISE;
// Unlink evacuation candidates before sweeper threads access the list of
// pages to avoid race condition.
UnlinkEvacuationCandidates();
// Noncompacting collections simply sweep the spaces to clear the mark
// bits and free the nonlive blocks (for old and map spaces). We sweep
// the map space last because freeing non-live maps overwrites them and
// the other spaces rely on possibly non-live maps to get the sizes for
// non-live objects.
SequentialSweepingScope scope(this);
SweepSpace(heap()->old_pointer_space(), how_to_sweep);
SweepSpace(heap()->old_data_space(), how_to_sweep);
if (how_to_sweep == PARALLEL_CONSERVATIVE ||
how_to_sweep == CONCURRENT_CONSERVATIVE) {
// TODO(hpayer): fix race with concurrent sweeper
StartSweeperThreads();
}
if (how_to_sweep == PARALLEL_CONSERVATIVE) {
WaitUntilSweepingCompleted();
}
RemoveDeadInvalidatedCode();
SweepSpace(heap()->code_space(), PRECISE);
SweepSpace(heap()->cell_space(), PRECISE);
SweepSpace(heap()->property_cell_space(), PRECISE);
EvacuateNewSpaceAndCandidates();
// ClearNonLiveTransitions depends on precise sweeping of map space to
// detect whether unmarked map became dead in this collection or in one
// of the previous ones.
SweepSpace(heap()->map_space(), PRECISE);
// Deallocate unmarked objects and clear marked bits for marked objects.
heap_->lo_space()->FreeUnmarkedObjects();
// Deallocate evacuated candidate pages.
ReleaseEvacuationCandidates();
}
void MarkCompactCollector::EnableCodeFlushing(bool enable) {
#ifdef ENABLE_DEBUGGER_SUPPORT
if (isolate()->debug()->IsLoaded() ||
isolate()->debug()->has_break_points()) {
enable = false;
}
#endif
if (enable) {
if (code_flusher_ != NULL) return;
code_flusher_ = new CodeFlusher(isolate());
} else {
if (code_flusher_ == NULL) return;
code_flusher_->EvictAllCandidates();
delete code_flusher_;
code_flusher_ = NULL;
}
if (FLAG_trace_code_flushing) {
PrintF("[code-flushing is now %s]\n", enable ? "on" : "off");
}
}
// TODO(1466) ReportDeleteIfNeeded is not called currently.
// Our profiling tools do not expect intersections between
// code objects. We should either reenable it or change our tools.
void MarkCompactCollector::ReportDeleteIfNeeded(HeapObject* obj,
Isolate* isolate) {
#ifdef ENABLE_GDB_JIT_INTERFACE
if (obj->IsCode()) {
GDBJITInterface::RemoveCode(reinterpret_cast<Code*>(obj));
}
#endif
if (obj->IsCode()) {
PROFILE(isolate, CodeDeleteEvent(obj->address()));
}
}
Isolate* MarkCompactCollector::isolate() const {
return heap_->isolate();
}
void MarkCompactCollector::Initialize() {
MarkCompactMarkingVisitor::Initialize();
IncrementalMarking::Initialize();
}
bool SlotsBuffer::IsTypedSlot(ObjectSlot slot) {
return reinterpret_cast<uintptr_t>(slot) < NUMBER_OF_SLOT_TYPES;
}
bool SlotsBuffer::AddTo(SlotsBufferAllocator* allocator,
SlotsBuffer** buffer_address,
SlotType type,
Address addr,
AdditionMode mode) {
SlotsBuffer* buffer = *buffer_address;
if (buffer == NULL || !buffer->HasSpaceForTypedSlot()) {
if (mode == FAIL_ON_OVERFLOW && ChainLengthThresholdReached(buffer)) {
allocator->DeallocateChain(buffer_address);
return false;
}
buffer = allocator->AllocateBuffer(buffer);
*buffer_address = buffer;
}
ASSERT(buffer->HasSpaceForTypedSlot());
buffer->Add(reinterpret_cast<ObjectSlot>(type));
buffer->Add(reinterpret_cast<ObjectSlot>(addr));
return true;
}
static inline SlotsBuffer::SlotType SlotTypeForRMode(RelocInfo::Mode rmode) {
if (RelocInfo::IsCodeTarget(rmode)) {
return SlotsBuffer::CODE_TARGET_SLOT;
} else if (RelocInfo::IsEmbeddedObject(rmode)) {
return SlotsBuffer::EMBEDDED_OBJECT_SLOT;
} else if (RelocInfo::IsDebugBreakSlot(rmode)) {
return SlotsBuffer::DEBUG_TARGET_SLOT;
} else if (RelocInfo::IsJSReturn(rmode)) {
return SlotsBuffer::JS_RETURN_SLOT;
}
UNREACHABLE();
return SlotsBuffer::NUMBER_OF_SLOT_TYPES;
}
void MarkCompactCollector::RecordRelocSlot(RelocInfo* rinfo, Object* target) {
Page* target_page = Page::FromAddress(reinterpret_cast<Address>(target));
if (target_page->IsEvacuationCandidate() &&
(rinfo->host() == NULL ||
!ShouldSkipEvacuationSlotRecording(rinfo->host()))) {
if (!SlotsBuffer::AddTo(&slots_buffer_allocator_,
target_page->slots_buffer_address(),
SlotTypeForRMode(rinfo->rmode()),
rinfo->pc(),
SlotsBuffer::FAIL_ON_OVERFLOW)) {
EvictEvacuationCandidate(target_page);
}
}
}
void MarkCompactCollector::RecordCodeEntrySlot(Address slot, Code* target) {
Page* target_page = Page::FromAddress(reinterpret_cast<Address>(target));
if (target_page->IsEvacuationCandidate() &&
!ShouldSkipEvacuationSlotRecording(reinterpret_cast<Object**>(slot))) {
if (!SlotsBuffer::AddTo(&slots_buffer_allocator_,
target_page->slots_buffer_address(),
SlotsBuffer::CODE_ENTRY_SLOT,
slot,
SlotsBuffer::FAIL_ON_OVERFLOW)) {
EvictEvacuationCandidate(target_page);
}
}
}
void MarkCompactCollector::RecordCodeTargetPatch(Address pc, Code* target) {
ASSERT(heap()->gc_state() == Heap::MARK_COMPACT);
if (is_compacting()) {
Code* host = isolate()->inner_pointer_to_code_cache()->
GcSafeFindCodeForInnerPointer(pc);
MarkBit mark_bit = Marking::MarkBitFrom(host);
if (Marking::IsBlack(mark_bit)) {
RelocInfo rinfo(pc, RelocInfo::CODE_TARGET, 0, host);
RecordRelocSlot(&rinfo, target);
}
}
}
static inline SlotsBuffer::SlotType DecodeSlotType(
SlotsBuffer::ObjectSlot slot) {
return static_cast<SlotsBuffer::SlotType>(reinterpret_cast<intptr_t>(slot));
}
void SlotsBuffer::UpdateSlots(Heap* heap) {
PointersUpdatingVisitor v(heap);
for (int slot_idx = 0; slot_idx < idx_; ++slot_idx) {
ObjectSlot slot = slots_[slot_idx];
if (!IsTypedSlot(slot)) {
PointersUpdatingVisitor::UpdateSlot(heap, slot);
} else {
++slot_idx;
ASSERT(slot_idx < idx_);
UpdateSlot(heap->isolate(),
&v,
DecodeSlotType(slot),
reinterpret_cast<Address>(slots_[slot_idx]));
}
}
}
void SlotsBuffer::UpdateSlotsWithFilter(Heap* heap) {
PointersUpdatingVisitor v(heap);
for (int slot_idx = 0; slot_idx < idx_; ++slot_idx) {
ObjectSlot slot = slots_[slot_idx];
if (!IsTypedSlot(slot)) {
if (!IsOnInvalidatedCodeObject(reinterpret_cast<Address>(slot))) {
PointersUpdatingVisitor::UpdateSlot(heap, slot);
}
} else {
++slot_idx;
ASSERT(slot_idx < idx_);
Address pc = reinterpret_cast<Address>(slots_[slot_idx]);
if (!IsOnInvalidatedCodeObject(pc)) {
UpdateSlot(heap->isolate(),
&v,
DecodeSlotType(slot),
reinterpret_cast<Address>(slots_[slot_idx]));
}
}
}
}
SlotsBuffer* SlotsBufferAllocator::AllocateBuffer(SlotsBuffer* next_buffer) {
return new SlotsBuffer(next_buffer);
}
void SlotsBufferAllocator::DeallocateBuffer(SlotsBuffer* buffer) {
delete buffer;
}
void SlotsBufferAllocator::DeallocateChain(SlotsBuffer** buffer_address) {
SlotsBuffer* buffer = *buffer_address;
while (buffer != NULL) {
SlotsBuffer* next_buffer = buffer->next();
DeallocateBuffer(buffer);
buffer = next_buffer;
}
*buffer_address = NULL;
}
} } // namespace v8::internal
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