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android / platform / art / ba311b4 / . / runtime / gc / collector / mark_sweep.cc
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/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "mark_sweep.h"
#include <functional>
#include <numeric>
#include <climits>
#include <vector>
#include "base/bounded_fifo.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/mutex-inl.h"
#include "base/timing_logger.h"
#include "gc/accounting/card_table-inl.h"
#include "gc/accounting/heap_bitmap.h"
#include "gc/accounting/space_bitmap-inl.h"
#include "gc/heap.h"
#include "gc/space/image_space.h"
#include "gc/space/large_object_space.h"
#include "gc/space/space-inl.h"
#include "indirect_reference_table.h"
#include "intern_table.h"
#include "jni_internal.h"
#include "monitor.h"
#include "mark_sweep-inl.h"
#include "mirror/art_field.h"
#include "mirror/art_field-inl.h"
#include "mirror/class-inl.h"
#include "mirror/class_loader.h"
#include "mirror/dex_cache.h"
#include "mirror/object-inl.h"
#include "mirror/object_array.h"
#include "mirror/object_array-inl.h"
#include "runtime.h"
#include "thread-inl.h"
#include "thread_list.h"
#include "verifier/method_verifier.h"
using ::art::mirror::ArtField;
using ::art::mirror::Class;
using ::art::mirror::Object;
using ::art::mirror::ObjectArray;
namespace art {
namespace gc {
namespace collector {
// Performance options.
constexpr bool kUseRecursiveMark = false;
constexpr bool kUseMarkStackPrefetch = true;
constexpr size_t kSweepArrayChunkFreeSize = 1024;
// Parallelism options.
constexpr bool kParallelCardScan = true;
constexpr bool kParallelRecursiveMark = true;
// Don't attempt to parallelize mark stack processing unless the mark stack is at least n
// elements. This is temporary until we reduce the overhead caused by allocating tasks, etc.. Not
// having this can add overhead in ProcessReferences since we may end up doing many calls of
// ProcessMarkStack with very small mark stacks.
constexpr size_t kMinimumParallelMarkStackSize = 128;
constexpr bool kParallelProcessMarkStack = true;
// Profiling and information flags.
constexpr bool kCountClassesMarked = false;
constexpr bool kProfileLargeObjects = false;
constexpr bool kMeasureOverhead = false;
constexpr bool kCountTasks = false;
constexpr bool kCountJavaLangRefs = false;
// Turn off kCheckLocks when profiling the GC since it slows the GC down by up to 40%.
constexpr bool kCheckLocks = kDebugLocking;
void MarkSweep::ImmuneSpace(space::ContinuousSpace* space) {
// Bind live to mark bitmap if necessary.
if (space->GetLiveBitmap() != space->GetMarkBitmap()) {
BindLiveToMarkBitmap(space);
}
// Add the space to the immune region.
if (immune_begin_ == NULL) {
DCHECK(immune_end_ == NULL);
SetImmuneRange(reinterpret_cast<Object*>(space->Begin()),
reinterpret_cast<Object*>(space->End()));
} else {
const space::ContinuousSpace* prev_space = nullptr;
// Find out if the previous space is immune.
for (space::ContinuousSpace* cur_space : GetHeap()->GetContinuousSpaces()) {
if (cur_space == space) {
break;
}
prev_space = cur_space;
}
// If previous space was immune, then extend the immune region. Relies on continuous spaces
// being sorted by Heap::AddContinuousSpace.
if (prev_space != NULL &&
immune_begin_ <= reinterpret_cast<Object*>(prev_space->Begin()) &&
immune_end_ >= reinterpret_cast<Object*>(prev_space->End())) {
immune_begin_ = std::min(reinterpret_cast<Object*>(space->Begin()), immune_begin_);
immune_end_ = std::max(reinterpret_cast<Object*>(space->End()), immune_end_);
}
}
}
void MarkSweep::BindBitmaps() {
timings_.StartSplit("BindBitmaps");
WriterMutexLock mu(Thread::Current(), *Locks::heap_bitmap_lock_);
// Mark all of the spaces we never collect as immune.
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
if (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyNeverCollect) {
ImmuneSpace(space);
}
}
timings_.EndSplit();
}
MarkSweep::MarkSweep(Heap* heap, bool is_concurrent, const std::string& name_prefix)
: GarbageCollector(heap,
name_prefix + (name_prefix.empty() ? "" : " ") +
(is_concurrent ? "concurrent mark sweep": "mark sweep")),
current_mark_bitmap_(NULL),
java_lang_Class_(NULL),
mark_stack_(NULL),
immune_begin_(NULL),
immune_end_(NULL),
soft_reference_list_(NULL),
weak_reference_list_(NULL),
finalizer_reference_list_(NULL),
phantom_reference_list_(NULL),
cleared_reference_list_(NULL),
gc_barrier_(new Barrier(0)),
large_object_lock_("mark sweep large object lock", kMarkSweepLargeObjectLock),
mark_stack_lock_("mark sweep mark stack lock"),
is_concurrent_(is_concurrent),
clear_soft_references_(false) {
}
void MarkSweep::InitializePhase() {
timings_.Reset();
base::TimingLogger::ScopedSplit split("InitializePhase", &timings_);
mark_stack_ = heap_->mark_stack_.get();
DCHECK(mark_stack_ != nullptr);
SetImmuneRange(nullptr, nullptr);
soft_reference_list_ = nullptr;
weak_reference_list_ = nullptr;
finalizer_reference_list_ = nullptr;
phantom_reference_list_ = nullptr;
cleared_reference_list_ = nullptr;
freed_bytes_ = 0;
freed_large_object_bytes_ = 0;
freed_objects_ = 0;
freed_large_objects_ = 0;
class_count_ = 0;
array_count_ = 0;
other_count_ = 0;
large_object_test_ = 0;
large_object_mark_ = 0;
classes_marked_ = 0;
overhead_time_ = 0;
work_chunks_created_ = 0;
work_chunks_deleted_ = 0;
reference_count_ = 0;
java_lang_Class_ = Class::GetJavaLangClass();
CHECK(java_lang_Class_ != nullptr);
FindDefaultMarkBitmap();
// Do any pre GC verification.
timings_.NewSplit("PreGcVerification");
heap_->PreGcVerification(this);
}
void MarkSweep::ProcessReferences(Thread* self) {
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
ProcessReferences(&soft_reference_list_, clear_soft_references_, &weak_reference_list_,
&finalizer_reference_list_, &phantom_reference_list_);
}
bool MarkSweep::HandleDirtyObjectsPhase() {
base::TimingLogger::ScopedSplit split("HandleDirtyObjectsPhase", &timings_);
Thread* self = Thread::Current();
Locks::mutator_lock_->AssertExclusiveHeld(self);
{
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
// Re-mark root set.
ReMarkRoots();
// Scan dirty objects, this is only required if we are not doing concurrent GC.
RecursiveMarkDirtyObjects(true, accounting::CardTable::kCardDirty);
}
ProcessReferences(self);
// Only need to do this if we have the card mark verification on, and only during concurrent GC.
if (GetHeap()->verify_missing_card_marks_) {
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
// This second sweep makes sure that we don't have any objects in the live stack which point to
// freed objects. These cause problems since their references may be previously freed objects.
SweepArray(GetHeap()->allocation_stack_.get(), false);
}
return true;
}
bool MarkSweep::IsConcurrent() const {
return is_concurrent_;
}
void MarkSweep::MarkingPhase() {
base::TimingLogger::ScopedSplit split("MarkingPhase", &timings_);
Heap* heap = GetHeap();
Thread* self = Thread::Current();
BindBitmaps();
FindDefaultMarkBitmap();
// Process dirty cards and add dirty cards to mod union tables.
heap->ProcessCards(timings_);
// Need to do this before the checkpoint since we don't want any threads to add references to
// the live stack during the recursive mark.
timings_.NewSplit("SwapStacks");
heap->SwapStacks();
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
if (Locks::mutator_lock_->IsExclusiveHeld(self)) {
// If we exclusively hold the mutator lock, all threads must be suspended.
MarkRoots();
} else {
MarkThreadRoots(self);
MarkNonThreadRoots();
}
MarkConcurrentRoots();
heap->UpdateAndMarkModUnion(this, timings_, GetGcType());
MarkReachableObjects();
}
void MarkSweep::MarkThreadRoots(Thread* self) {
MarkRootsCheckpoint(self);
}
void MarkSweep::MarkReachableObjects() {
// Mark everything allocated since the last as GC live so that we can sweep concurrently,
// knowing that new allocations won't be marked as live.
timings_.StartSplit("MarkStackAsLive");
accounting::ObjectStack* live_stack = heap_->GetLiveStack();
heap_->MarkAllocStack(heap_->alloc_space_->GetLiveBitmap(),
heap_->large_object_space_->GetLiveObjects(), live_stack);
live_stack->Reset();
timings_.EndSplit();
// Recursively mark all the non-image bits set in the mark bitmap.
RecursiveMark();
}
void MarkSweep::ReclaimPhase() {
base::TimingLogger::ScopedSplit split("ReclaimPhase", &timings_);
Thread* self = Thread::Current();
if (!IsConcurrent()) {
base::TimingLogger::ScopedSplit split("ProcessReferences", &timings_);
ProcessReferences(self);
} else {
base::TimingLogger::ScopedSplit split("UnMarkAllocStack", &timings_);
accounting::ObjectStack* allocation_stack = GetHeap()->allocation_stack_.get();
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
// The allocation stack contains things allocated since the start of the GC. These may have been
// marked during this GC meaning they won't be eligible for reclaiming in the next sticky GC.
// Remove these objects from the mark bitmaps so that they will be eligible for sticky
// collection.
// There is a race here which is safely handled. Another thread such as the hprof could
// have flushed the alloc stack after we resumed the threads. This is safe however, since
// reseting the allocation stack zeros it out with madvise. This means that we will either
// read NULLs or attempt to unmark a newly allocated object which will not be marked in the
// first place.
mirror::Object** end = allocation_stack->End();
for (mirror::Object** it = allocation_stack->Begin(); it != end; ++it) {
const Object* obj = *it;
if (obj != NULL) {
UnMarkObjectNonNull(obj);
}
}
}
// Before freeing anything, lets verify the heap.
if (kIsDebugBuild) {
ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
VerifyImageRoots();
}
timings_.StartSplit("PreSweepingGcVerification");
heap_->PreSweepingGcVerification(this);
timings_.EndSplit();
{
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
// Reclaim unmarked objects.
Sweep(false);
// Swap the live and mark bitmaps for each space which we modified space. This is an
// optimization that enables us to not clear live bits inside of the sweep. Only swaps unbound
// bitmaps.
timings_.StartSplit("SwapBitmaps");
SwapBitmaps();
timings_.EndSplit();
// Unbind the live and mark bitmaps.
UnBindBitmaps();
}
}
void MarkSweep::SetImmuneRange(Object* begin, Object* end) {
immune_begin_ = begin;
immune_end_ = end;
}
void MarkSweep::FindDefaultMarkBitmap() {
base::TimingLogger::ScopedSplit split("FindDefaultMarkBitmap", &timings_);
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
if (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect) {
current_mark_bitmap_ = space->GetMarkBitmap();
CHECK(current_mark_bitmap_ != NULL);
return;
}
}
GetHeap()->DumpSpaces();
LOG(FATAL) << "Could not find a default mark bitmap";
}
void MarkSweep::ExpandMarkStack() {
ResizeMarkStack(mark_stack_->Capacity() * 2);
}
void MarkSweep::ResizeMarkStack(size_t new_size) {
// Rare case, no need to have Thread::Current be a parameter.
if (UNLIKELY(mark_stack_->Size() < mark_stack_->Capacity())) {
// Someone else acquired the lock and expanded the mark stack before us.
return;
}
std::vector<Object*> temp(mark_stack_->Begin(), mark_stack_->End());
CHECK_LE(mark_stack_->Size(), new_size);
mark_stack_->Resize(new_size);
for (const auto& obj : temp) {
mark_stack_->PushBack(obj);
}
}
inline void MarkSweep::MarkObjectNonNullParallel(const Object* obj) {
DCHECK(obj != NULL);
if (MarkObjectParallel(obj)) {
MutexLock mu(Thread::Current(), mark_stack_lock_);
if (UNLIKELY(mark_stack_->Size() >= mark_stack_->Capacity())) {
ExpandMarkStack();
}
// The object must be pushed on to the mark stack.
mark_stack_->PushBack(const_cast<Object*>(obj));
}
}
inline void MarkSweep::UnMarkObjectNonNull(const Object* obj) {
DCHECK(!IsImmune(obj));
// Try to take advantage of locality of references within a space, failing this find the space
// the hard way.
accounting::SpaceBitmap* object_bitmap = current_mark_bitmap_;
if (UNLIKELY(!object_bitmap->HasAddress(obj))) {
accounting::SpaceBitmap* new_bitmap = heap_->GetMarkBitmap()->GetContinuousSpaceBitmap(obj);
if (LIKELY(new_bitmap != NULL)) {
object_bitmap = new_bitmap;
} else {
MarkLargeObject(obj, false);
return;
}
}
DCHECK(object_bitmap->HasAddress(obj));
object_bitmap->Clear(obj);
}
inline void MarkSweep::MarkObjectNonNull(const Object* obj) {
DCHECK(obj != NULL);
if (IsImmune(obj)) {
DCHECK(IsMarked(obj));
return;
}
// Try to take advantage of locality of references within a space, failing this find the space
// the hard way.
accounting::SpaceBitmap* object_bitmap = current_mark_bitmap_;
if (UNLIKELY(!object_bitmap->HasAddress(obj))) {
accounting::SpaceBitmap* new_bitmap = heap_->GetMarkBitmap()->GetContinuousSpaceBitmap(obj);
if (LIKELY(new_bitmap != NULL)) {
object_bitmap = new_bitmap;
} else {
MarkLargeObject(obj, true);
return;
}
}
// This object was not previously marked.
if (!object_bitmap->Test(obj)) {
object_bitmap->Set(obj);
// Lock is not needed but is here anyways to please annotalysis.
MutexLock mu(Thread::Current(), mark_stack_lock_);
if (UNLIKELY(mark_stack_->Size() >= mark_stack_->Capacity())) {
ExpandMarkStack();
}
// The object must be pushed on to the mark stack.
mark_stack_->PushBack(const_cast<Object*>(obj));
}
}
// Rare case, probably not worth inlining since it will increase instruction cache miss rate.
bool MarkSweep::MarkLargeObject(const Object* obj, bool set) {
// TODO: support >1 discontinuous space.
space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace();
accounting::SpaceSetMap* large_objects = large_object_space->GetMarkObjects();
if (kProfileLargeObjects) {
++large_object_test_;
}
if (UNLIKELY(!large_objects->Test(obj))) {
if (!large_object_space->Contains(obj)) {
LOG(ERROR) << "Tried to mark " << obj << " not contained by any spaces";
LOG(ERROR) << "Attempting see if it's a bad root";
VerifyRoots();
LOG(FATAL) << "Can't mark bad root";
}
if (kProfileLargeObjects) {
++large_object_mark_;
}
if (set) {
large_objects->Set(obj);
} else {
large_objects->Clear(obj);
}
return true;
}
return false;
}
inline bool MarkSweep::MarkObjectParallel(const Object* obj) {
DCHECK(obj != NULL);
if (IsImmune(obj)) {
DCHECK(IsMarked(obj));
return false;
}
// Try to take advantage of locality of references within a space, failing this find the space
// the hard way.
accounting::SpaceBitmap* object_bitmap = current_mark_bitmap_;
if (UNLIKELY(!object_bitmap->HasAddress(obj))) {
accounting::SpaceBitmap* new_bitmap = heap_->GetMarkBitmap()->GetContinuousSpaceBitmap(obj);
if (new_bitmap != NULL) {
object_bitmap = new_bitmap;
} else {
// TODO: Remove the Thread::Current here?
// TODO: Convert this to some kind of atomic marking?
MutexLock mu(Thread::Current(), large_object_lock_);
return MarkLargeObject(obj, true);
}
}
// Return true if the object was not previously marked.
return !object_bitmap->AtomicTestAndSet(obj);
}
// Used to mark objects when recursing. Recursion is done by moving
// the finger across the bitmaps in address order and marking child
// objects. Any newly-marked objects whose addresses are lower than
// the finger won't be visited by the bitmap scan, so those objects
// need to be added to the mark stack.
inline void MarkSweep::MarkObject(const Object* obj) {
if (obj != NULL) {
MarkObjectNonNull(obj);
}
}
void MarkSweep::MarkRoot(const Object* obj) {
if (obj != NULL) {
MarkObjectNonNull(obj);
}
}
void MarkSweep::MarkRootParallelCallback(const Object* root, void* arg) {
DCHECK(root != NULL);
DCHECK(arg != NULL);
reinterpret_cast<MarkSweep*>(arg)->MarkObjectNonNullParallel(root);
}
void MarkSweep::MarkObjectCallback(const Object* root, void* arg) {
DCHECK(root != NULL);
DCHECK(arg != NULL);
MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg);
mark_sweep->MarkObjectNonNull(root);
}
void MarkSweep::ReMarkObjectVisitor(const Object* root, void* arg) {
DCHECK(root != NULL);
DCHECK(arg != NULL);
MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg);
mark_sweep->MarkObjectNonNull(root);
}
void MarkSweep::VerifyRootCallback(const Object* root, void* arg, size_t vreg,
const StackVisitor* visitor) {
reinterpret_cast<MarkSweep*>(arg)->VerifyRoot(root, vreg, visitor);
}
void MarkSweep::VerifyRoot(const Object* root, size_t vreg, const StackVisitor* visitor) {
// See if the root is on any space bitmap.
if (GetHeap()->GetLiveBitmap()->GetContinuousSpaceBitmap(root) == NULL) {
space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace();
if (!large_object_space->Contains(root)) {
LOG(ERROR) << "Found invalid root: " << root;
if (visitor != NULL) {
LOG(ERROR) << visitor->DescribeLocation() << " in VReg: " << vreg;
}
}
}
}
void MarkSweep::VerifyRoots() {
Runtime::Current()->GetThreadList()->VerifyRoots(VerifyRootCallback, this);
}
// Marks all objects in the root set.
void MarkSweep::MarkRoots() {
timings_.StartSplit("MarkRoots");
Runtime::Current()->VisitNonConcurrentRoots(MarkObjectCallback, this);
timings_.EndSplit();
}
void MarkSweep::MarkNonThreadRoots() {
timings_.StartSplit("MarkNonThreadRoots");
Runtime::Current()->VisitNonThreadRoots(MarkObjectCallback, this);
timings_.EndSplit();
}
void MarkSweep::MarkConcurrentRoots() {
timings_.StartSplit("MarkConcurrentRoots");
// Visit all runtime roots and clear dirty flags.
Runtime::Current()->VisitConcurrentRoots(MarkObjectCallback, this, false, true);
timings_.EndSplit();
}
void MarkSweep::CheckObject(const Object* obj) {
DCHECK(obj != NULL);
VisitObjectReferences(obj, [this](const Object* obj, const Object* ref, MemberOffset offset,
bool is_static) NO_THREAD_SAFETY_ANALYSIS {
Locks::heap_bitmap_lock_->AssertSharedHeld(Thread::Current());
CheckReference(obj, ref, offset, is_static);
});
}
void MarkSweep::VerifyImageRootVisitor(Object* root, void* arg) {
DCHECK(root != NULL);
DCHECK(arg != NULL);
MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg);
DCHECK(mark_sweep->heap_->GetMarkBitmap()->Test(root));
mark_sweep->CheckObject(root);
}
void MarkSweep::BindLiveToMarkBitmap(space::ContinuousSpace* space) {
CHECK(space->IsDlMallocSpace());
space::DlMallocSpace* alloc_space = space->AsDlMallocSpace();
accounting::SpaceBitmap* live_bitmap = space->GetLiveBitmap();
accounting::SpaceBitmap* mark_bitmap = alloc_space->mark_bitmap_.release();
GetHeap()->GetMarkBitmap()->ReplaceBitmap(mark_bitmap, live_bitmap);
alloc_space->temp_bitmap_.reset(mark_bitmap);
alloc_space->mark_bitmap_.reset(live_bitmap);
}
class ScanObjectVisitor {
public:
explicit ScanObjectVisitor(MarkSweep* const mark_sweep) ALWAYS_INLINE
: mark_sweep_(mark_sweep) {}
// TODO: Fixme when anotatalysis works with visitors.
void operator()(const Object* obj) const ALWAYS_INLINE NO_THREAD_SAFETY_ANALYSIS {
if (kCheckLocks) {
Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current());
}
mark_sweep_->ScanObject(obj);
}
private:
MarkSweep* const mark_sweep_;
};
template <bool kUseFinger = false>
class MarkStackTask : public Task {
public:
MarkStackTask(ThreadPool* thread_pool, MarkSweep* mark_sweep, size_t mark_stack_size,
const Object** mark_stack)
: mark_sweep_(mark_sweep),
thread_pool_(thread_pool),
mark_stack_pos_(mark_stack_size) {
// We may have to copy part of an existing mark stack when another mark stack overflows.
if (mark_stack_size != 0) {
DCHECK(mark_stack != NULL);
// TODO: Check performance?
std::copy(mark_stack, mark_stack + mark_stack_size, mark_stack_);
}
if (kCountTasks) {
++mark_sweep_->work_chunks_created_;
}
}
static const size_t kMaxSize = 1 * KB;
protected:
class ScanObjectParallelVisitor {
public:
explicit ScanObjectParallelVisitor(MarkStackTask<kUseFinger>* chunk_task) ALWAYS_INLINE
: chunk_task_(chunk_task) {}
void operator()(const Object* obj) const {
MarkSweep* mark_sweep = chunk_task_->mark_sweep_;
mark_sweep->ScanObjectVisit(obj,
[mark_sweep, this](const Object* /* obj */, const Object* ref,
const MemberOffset& /* offset */, bool /* is_static */) ALWAYS_INLINE {
if (ref != nullptr && mark_sweep->MarkObjectParallel(ref)) {
if (kUseFinger) {
android_memory_barrier();
if (reinterpret_cast<uintptr_t>(ref) >=
static_cast<uintptr_t>(mark_sweep->atomic_finger_)) {
return;
}
}
chunk_task_->MarkStackPush(ref);
}
});
}
private:
MarkStackTask<kUseFinger>* const chunk_task_;
};
virtual ~MarkStackTask() {
// Make sure that we have cleared our mark stack.
DCHECK_EQ(mark_stack_pos_, 0U);
if (kCountTasks) {
++mark_sweep_->work_chunks_deleted_;
}
}
MarkSweep* const mark_sweep_;
ThreadPool* const thread_pool_;
// Thread local mark stack for this task.
const Object* mark_stack_[kMaxSize];
// Mark stack position.
size_t mark_stack_pos_;
void MarkStackPush(const Object* obj) ALWAYS_INLINE {
if (UNLIKELY(mark_stack_pos_ == kMaxSize)) {
// Mark stack overflow, give 1/2 the stack to the thread pool as a new work task.
mark_stack_pos_ /= 2;
auto* task = new MarkStackTask(thread_pool_, mark_sweep_, kMaxSize - mark_stack_pos_,
mark_stack_ + mark_stack_pos_);
thread_pool_->AddTask(Thread::Current(), task);
}
DCHECK(obj != nullptr);
DCHECK(mark_stack_pos_ < kMaxSize);
mark_stack_[mark_stack_pos_++] = obj;
}
virtual void Finalize() {
delete this;
}
// Scans all of the objects
virtual void Run(Thread* self) {
ScanObjectParallelVisitor visitor(this);
// TODO: Tune this.
static const size_t kFifoSize = 4;
BoundedFifoPowerOfTwo<const Object*, kFifoSize> prefetch_fifo;
for (;;) {
const Object* obj = NULL;
if (kUseMarkStackPrefetch) {
while (mark_stack_pos_ != 0 && prefetch_fifo.size() < kFifoSize) {
const Object* obj = mark_stack_[--mark_stack_pos_];
DCHECK(obj != NULL);
__builtin_prefetch(obj);
prefetch_fifo.push_back(obj);
}
if (UNLIKELY(prefetch_fifo.empty())) {
break;
}
obj = prefetch_fifo.front();
prefetch_fifo.pop_front();
} else {
if (UNLIKELY(mark_stack_pos_ == 0)) {
break;
}
obj = mark_stack_[--mark_stack_pos_];
}
DCHECK(obj != NULL);
visitor(obj);
}
}
};
class CardScanTask : public MarkStackTask<false> {
public:
CardScanTask(ThreadPool* thread_pool, MarkSweep* mark_sweep, accounting::SpaceBitmap* bitmap,
byte* begin, byte* end, byte minimum_age, size_t mark_stack_size,
const Object** mark_stack_obj)
: MarkStackTask<false>(thread_pool, mark_sweep, mark_stack_size, mark_stack_obj),
bitmap_(bitmap),
begin_(begin),
end_(end),
minimum_age_(minimum_age) {
}
protected:
accounting::SpaceBitmap* const bitmap_;
byte* const begin_;
byte* const end_;
const byte minimum_age_;
virtual void Finalize() {
delete this;
}
virtual void Run(Thread* self) NO_THREAD_SAFETY_ANALYSIS {
ScanObjectParallelVisitor visitor(this);
accounting::CardTable* card_table = mark_sweep_->GetHeap()->GetCardTable();
card_table->Scan(bitmap_, begin_, end_, visitor, minimum_age_);
// Finish by emptying our local mark stack.
MarkStackTask::Run(self);
}
};
size_t MarkSweep::GetThreadCount(bool paused) const {
if (heap_->GetThreadPool() == nullptr || !heap_->CareAboutPauseTimes()) {
return 0;
}
if (paused) {
return heap_->GetParallelGCThreadCount() + 1;
} else {
return heap_->GetConcGCThreadCount() + 1;
}
}
void MarkSweep::ScanGrayObjects(bool paused, byte minimum_age) {
accounting::CardTable* card_table = GetHeap()->GetCardTable();
ThreadPool* thread_pool = GetHeap()->GetThreadPool();
size_t thread_count = GetThreadCount(paused);
// The parallel version with only one thread is faster for card scanning, TODO: fix.
if (kParallelCardScan && thread_count > 0) {
Thread* self = Thread::Current();
// Can't have a different split for each space since multiple spaces can have their cards being
// scanned at the same time.
timings_.StartSplit(paused ? "(Paused)ScanGrayObjects" : "ScanGrayObjects");
// Try to take some of the mark stack since we can pass this off to the worker tasks.
const Object** mark_stack_begin = const_cast<const Object**>(mark_stack_->Begin());
const Object** mark_stack_end = const_cast<const Object**>(mark_stack_->End());
const size_t mark_stack_size = mark_stack_end - mark_stack_begin;
// Estimated number of work tasks we will create.
const size_t mark_stack_tasks = GetHeap()->GetContinuousSpaces().size() * thread_count;
DCHECK_NE(mark_stack_tasks, 0U);
const size_t mark_stack_delta = std::min(CardScanTask::kMaxSize / 2,
mark_stack_size / mark_stack_tasks + 1);
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
byte* card_begin = space->Begin();
byte* card_end = space->End();
// Calculate how many bytes of heap we will scan,
const size_t address_range = card_end - card_begin;
// Calculate how much address range each task gets.
const size_t card_delta = RoundUp(address_range / thread_count + 1,
accounting::CardTable::kCardSize);
// Create the worker tasks for this space.
while (card_begin != card_end) {
// Add a range of cards.
size_t addr_remaining = card_end - card_begin;
size_t card_increment = std::min(card_delta, addr_remaining);
// Take from the back of the mark stack.
size_t mark_stack_remaining = mark_stack_end - mark_stack_begin;
size_t mark_stack_increment = std::min(mark_stack_delta, mark_stack_remaining);
mark_stack_end -= mark_stack_increment;
mark_stack_->PopBackCount(static_cast<int32_t>(mark_stack_increment));
DCHECK_EQ(mark_stack_end, mark_stack_->End());
// Add the new task to the thread pool.
auto* task = new CardScanTask(thread_pool, this, space->GetMarkBitmap(), card_begin,
card_begin + card_increment, minimum_age,
mark_stack_increment, mark_stack_end);
thread_pool->AddTask(self, task);
card_begin += card_increment;
}
}
thread_pool->SetMaxActiveWorkers(thread_count - 1);
thread_pool->StartWorkers(self);
thread_pool->Wait(self, true, true);
thread_pool->StopWorkers(self);
timings_.EndSplit();
} else {
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
// Image spaces are handled properly since live == marked for them.
switch (space->GetGcRetentionPolicy()) {
case space::kGcRetentionPolicyNeverCollect:
timings_.StartSplit(paused ? "(Paused)ScanGrayImageSpaceObjects" :
"ScanGrayImageSpaceObjects");
break;
case space::kGcRetentionPolicyFullCollect:
timings_.StartSplit(paused ? "(Paused)ScanGrayZygoteSpaceObjects" :
"ScanGrayZygoteSpaceObjects");
break;
case space::kGcRetentionPolicyAlwaysCollect:
timings_.StartSplit(paused ? "(Paused)ScanGrayAllocSpaceObjects" :
"ScanGrayAllocSpaceObjects");
break;
}
ScanObjectVisitor visitor(this);
card_table->Scan(space->GetMarkBitmap(), space->Begin(), space->End(), visitor, minimum_age);
timings_.EndSplit();
}
}
}
void MarkSweep::VerifyImageRoots() {
// Verify roots ensures that all the references inside the image space point
// objects which are either in the image space or marked objects in the alloc
// space
timings_.StartSplit("VerifyImageRoots");
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
if (space->IsImageSpace()) {
space::ImageSpace* image_space = space->AsImageSpace();
uintptr_t begin = reinterpret_cast<uintptr_t>(image_space->Begin());
uintptr_t end = reinterpret_cast<uintptr_t>(image_space->End());
accounting::SpaceBitmap* live_bitmap = image_space->GetLiveBitmap();
DCHECK(live_bitmap != NULL);
live_bitmap->VisitMarkedRange(begin, end, [this](const Object* obj) {
if (kCheckLocks) {
Locks::heap_bitmap_lock_->AssertSharedHeld(Thread::Current());
}
DCHECK(obj != NULL);
CheckObject(obj);
});
}
}
timings_.EndSplit();
}
class RecursiveMarkTask : public MarkStackTask<false> {
public:
RecursiveMarkTask(ThreadPool* thread_pool, MarkSweep* mark_sweep,
accounting::SpaceBitmap* bitmap, uintptr_t begin, uintptr_t end)
: MarkStackTask<false>(thread_pool, mark_sweep, 0, NULL),
bitmap_(bitmap),
begin_(begin),
end_(end) {
}
protected:
accounting::SpaceBitmap* const bitmap_;
const uintptr_t begin_;
const uintptr_t end_;
virtual void Finalize() {
delete this;
}
// Scans all of the objects
virtual void Run(Thread* self) NO_THREAD_SAFETY_ANALYSIS {
ScanObjectParallelVisitor visitor(this);
bitmap_->VisitMarkedRange(begin_, end_, visitor);
// Finish by emptying our local mark stack.
MarkStackTask::Run(self);
}
};
// Populates the mark stack based on the set of marked objects and
// recursively marks until the mark stack is emptied.
void MarkSweep::RecursiveMark() {
base::TimingLogger::ScopedSplit split("RecursiveMark", &timings_);
// RecursiveMark will build the lists of known instances of the Reference classes.
// See DelayReferenceReferent for details.
CHECK(soft_reference_list_ == NULL);
CHECK(weak_reference_list_ == NULL);
CHECK(finalizer_reference_list_ == NULL);
CHECK(phantom_reference_list_ == NULL);
CHECK(cleared_reference_list_ == NULL);
if (kUseRecursiveMark) {
const bool partial = GetGcType() == kGcTypePartial;
ScanObjectVisitor scan_visitor(this);
auto* self = Thread::Current();
ThreadPool* thread_pool = heap_->GetThreadPool();
size_t thread_count = GetThreadCount(false);
const bool parallel = kParallelRecursiveMark && thread_count > 1;
mark_stack_->Reset();
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
if ((space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect) ||
(!partial && space->GetGcRetentionPolicy() == space::kGcRetentionPolicyFullCollect)) {
current_mark_bitmap_ = space->GetMarkBitmap();
if (current_mark_bitmap_ == NULL) {
GetHeap()->DumpSpaces();
LOG(FATAL) << "invalid bitmap";
}
if (parallel) {
// We will use the mark stack the future.
// CHECK(mark_stack_->IsEmpty());
// This function does not handle heap end increasing, so we must use the space end.
uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin());
uintptr_t end = reinterpret_cast<uintptr_t>(space->End());
atomic_finger_ = static_cast<int32_t>(0xFFFFFFFF);
// Create a few worker tasks.
const size_t n = thread_count * 2;
while (begin != end) {
uintptr_t start = begin;
uintptr_t delta = (end - begin) / n;
delta = RoundUp(delta, KB);
if (delta < 16 * KB) delta = end - begin;
begin += delta;
auto* task = new RecursiveMarkTask(thread_pool, this, current_mark_bitmap_, start,
begin);
thread_pool->AddTask(self, task);
}
thread_pool->SetMaxActiveWorkers(thread_count - 1);
thread_pool->StartWorkers(self);
thread_pool->Wait(self, true, true);
thread_pool->StopWorkers(self);
} else {
// This function does not handle heap end increasing, so we must use the space end.
uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin());
uintptr_t end = reinterpret_cast<uintptr_t>(space->End());
current_mark_bitmap_->VisitMarkedRange(begin, end, scan_visitor);
}
}
}
}
ProcessMarkStack(false);
}
bool MarkSweep::IsMarkedCallback(const Object* object, void* arg) {
return
reinterpret_cast<MarkSweep*>(arg)->IsMarked(object) ||
!reinterpret_cast<MarkSweep*>(arg)->GetHeap()->GetLiveBitmap()->Test(object);
}
void MarkSweep::RecursiveMarkDirtyObjects(bool paused, byte minimum_age) {
ScanGrayObjects(paused, minimum_age);
ProcessMarkStack(paused);
}
void MarkSweep::ReMarkRoots() {
timings_.StartSplit("ReMarkRoots");
Runtime::Current()->VisitRoots(ReMarkObjectVisitor, this, true, true);
timings_.EndSplit();
}
void MarkSweep::SweepJniWeakGlobals(IsMarkedTester is_marked, void* arg) {
JavaVMExt* vm = Runtime::Current()->GetJavaVM();
WriterMutexLock mu(Thread::Current(), vm->weak_globals_lock);
for (const Object** entry : vm->weak_globals) {
if (!is_marked(*entry, arg)) {
*entry = kClearedJniWeakGlobal;
}
}
}
struct ArrayMarkedCheck {
accounting::ObjectStack* live_stack;
MarkSweep* mark_sweep;
};
// Either marked or not live.
bool MarkSweep::IsMarkedArrayCallback(const Object* object, void* arg) {
ArrayMarkedCheck* array_check = reinterpret_cast<ArrayMarkedCheck*>(arg);
if (array_check->mark_sweep->IsMarked(object)) {
return true;
}
accounting::ObjectStack* live_stack = array_check->live_stack;
return std::find(live_stack->Begin(), live_stack->End(), object) == live_stack->End();
}
void MarkSweep::SweepSystemWeaksArray(accounting::ObjectStack* allocations) {
Runtime* runtime = Runtime::Current();
// The callbacks check
// !is_marked where is_marked is the callback but we want
// !IsMarked && IsLive
// So compute !(!IsMarked && IsLive) which is equal to (IsMarked || !IsLive).
// Or for swapped (IsLive || !IsMarked).
timings_.StartSplit("SweepSystemWeaksArray");
ArrayMarkedCheck visitor;
visitor.live_stack = allocations;
visitor.mark_sweep = this;
runtime->GetInternTable()->SweepInternTableWeaks(IsMarkedArrayCallback, &visitor);
runtime->GetMonitorList()->SweepMonitorList(IsMarkedArrayCallback, &visitor);
SweepJniWeakGlobals(IsMarkedArrayCallback, &visitor);
timings_.EndSplit();
}
void MarkSweep::SweepSystemWeaks() {
Runtime* runtime = Runtime::Current();
// The callbacks check
// !is_marked where is_marked is the callback but we want
// !IsMarked && IsLive
// So compute !(!IsMarked && IsLive) which is equal to (IsMarked || !IsLive).
// Or for swapped (IsLive || !IsMarked).
timings_.StartSplit("SweepSystemWeaks");
runtime->GetInternTable()->SweepInternTableWeaks(IsMarkedCallback, this);
runtime->GetMonitorList()->SweepMonitorList(IsMarkedCallback, this);
SweepJniWeakGlobals(IsMarkedCallback, this);
timings_.EndSplit();
}
bool MarkSweep::VerifyIsLiveCallback(const Object* obj, void* arg) {
reinterpret_cast<MarkSweep*>(arg)->VerifyIsLive(obj);
// We don't actually want to sweep the object, so lets return "marked"
return true;
}
void MarkSweep::VerifyIsLive(const Object* obj) {
Heap* heap = GetHeap();
if (!heap->GetLiveBitmap()->Test(obj)) {
space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace();
if (!large_object_space->GetLiveObjects()->Test(obj)) {
if (std::find(heap->allocation_stack_->Begin(), heap->allocation_stack_->End(), obj) ==
heap->allocation_stack_->End()) {
// Object not found!
heap->DumpSpaces();
LOG(FATAL) << "Found dead object " << obj;
}
}
}
}
void MarkSweep::VerifySystemWeaks() {
Runtime* runtime = Runtime::Current();
// Verify system weaks, uses a special IsMarked callback which always returns true.
runtime->GetInternTable()->SweepInternTableWeaks(VerifyIsLiveCallback, this);
runtime->GetMonitorList()->SweepMonitorList(VerifyIsLiveCallback, this);
JavaVMExt* vm = runtime->GetJavaVM();
ReaderMutexLock mu(Thread::Current(), vm->weak_globals_lock);
for (const Object** entry : vm->weak_globals) {
VerifyIsLive(*entry);
}
}
struct SweepCallbackContext {
MarkSweep* mark_sweep;
space::AllocSpace* space;
Thread* self;
};
class CheckpointMarkThreadRoots : public Closure {
public:
explicit CheckpointMarkThreadRoots(MarkSweep* mark_sweep) : mark_sweep_(mark_sweep) {}
virtual void Run(Thread* thread) NO_THREAD_SAFETY_ANALYSIS {
// Note: self is not necessarily equal to thread since thread may be suspended.
Thread* self = Thread::Current();
CHECK(thread == self || thread->IsSuspended() || thread->GetState() == kWaitingPerformingGc)
<< thread->GetState() << " thread " << thread << " self " << self;
thread->VisitRoots(MarkSweep::MarkRootParallelCallback, mark_sweep_);
mark_sweep_->GetBarrier().Pass(self);
}
private:
MarkSweep* mark_sweep_;
};
void MarkSweep::MarkRootsCheckpoint(Thread* self) {
CheckpointMarkThreadRoots check_point(this);
timings_.StartSplit("MarkRootsCheckpoint");
ThreadList* thread_list = Runtime::Current()->GetThreadList();
// Request the check point is run on all threads returning a count of the threads that must
// run through the barrier including self.
size_t barrier_count = thread_list->RunCheckpoint(&check_point);
// Release locks then wait for all mutator threads to pass the barrier.
// TODO: optimize to not release locks when there are no threads to wait for.
Locks::heap_bitmap_lock_->ExclusiveUnlock(self);
Locks::mutator_lock_->SharedUnlock(self);
ThreadState old_state = self->SetState(kWaitingForCheckPointsToRun);
CHECK_EQ(old_state, kWaitingPerformingGc);
gc_barrier_->Increment(self, barrier_count);
self->SetState(kWaitingPerformingGc);
Locks::mutator_lock_->SharedLock(self);
Locks::heap_bitmap_lock_->ExclusiveLock(self);
timings_.EndSplit();
}
void MarkSweep::SweepCallback(size_t num_ptrs, Object** ptrs, void* arg) {
SweepCallbackContext* context = static_cast<SweepCallbackContext*>(arg);
MarkSweep* mark_sweep = context->mark_sweep;
Heap* heap = mark_sweep->GetHeap();
space::AllocSpace* space = context->space;
Thread* self = context->self;
Locks::heap_bitmap_lock_->AssertExclusiveHeld(self);
// Use a bulk free, that merges consecutive objects before freeing or free per object?
// Documentation suggests better free performance with merging, but this may be at the expensive
// of allocation.
size_t freed_objects = num_ptrs;
// AllocSpace::FreeList clears the value in ptrs, so perform after clearing the live bit
size_t freed_bytes = space->FreeList(self, num_ptrs, ptrs);
heap->RecordFree(freed_objects, freed_bytes);
mark_sweep->freed_objects_.fetch_add(freed_objects);
mark_sweep->freed_bytes_.fetch_add(freed_bytes);
}
void MarkSweep::ZygoteSweepCallback(size_t num_ptrs, Object** ptrs, void* arg) {
SweepCallbackContext* context = static_cast<SweepCallbackContext*>(arg);
Locks::heap_bitmap_lock_->AssertExclusiveHeld(context->self);
Heap* heap = context->mark_sweep->GetHeap();
// We don't free any actual memory to avoid dirtying the shared zygote pages.
for (size_t i = 0; i < num_ptrs; ++i) {
Object* obj = static_cast<Object*>(ptrs[i]);
heap->GetLiveBitmap()->Clear(obj);
heap->GetCardTable()->MarkCard(obj);
}
}
void MarkSweep::SweepArray(accounting::ObjectStack* allocations, bool swap_bitmaps) {
space::DlMallocSpace* space = heap_->GetAllocSpace();
// If we don't swap bitmaps then newly allocated Weaks go into the live bitmap but not mark
// bitmap, resulting in occasional frees of Weaks which are still in use.
SweepSystemWeaksArray(allocations);
timings_.StartSplit("SweepArray");
// Newly allocated objects MUST be in the alloc space and those are the only objects which we are
// going to free.
accounting::SpaceBitmap* live_bitmap = space->GetLiveBitmap();
accounting::SpaceBitmap* mark_bitmap = space->GetMarkBitmap();
space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace();
accounting::SpaceSetMap* large_live_objects = large_object_space->GetLiveObjects();
accounting::SpaceSetMap* large_mark_objects = large_object_space->GetMarkObjects();
if (swap_bitmaps) {
std::swap(live_bitmap, mark_bitmap);
std::swap(large_live_objects, large_mark_objects);
}
size_t freed_bytes = 0;
size_t freed_large_object_bytes = 0;
size_t freed_objects = 0;
size_t freed_large_objects = 0;
size_t count = allocations->Size();
Object** objects = const_cast<Object**>(allocations->Begin());
Object** out = objects;
Object** objects_to_chunk_free = out;
// Empty the allocation stack.
Thread* self = Thread::Current();
for (size_t i = 0; i < count; ++i) {
Object* obj = objects[i];
// There should only be objects in the AllocSpace/LargeObjectSpace in the allocation stack.
if (LIKELY(mark_bitmap->HasAddress(obj))) {
if (!mark_bitmap->Test(obj)) {
// Don't bother un-marking since we clear the mark bitmap anyways.
*(out++) = obj;
// Free objects in chunks.
DCHECK_GE(out, objects_to_chunk_free);
DCHECK_LE(static_cast<size_t>(out - objects_to_chunk_free), kSweepArrayChunkFreeSize);
if (static_cast<size_t>(out - objects_to_chunk_free) == kSweepArrayChunkFreeSize) {
timings_.StartSplit("FreeList");
size_t chunk_freed_objects = out - objects_to_chunk_free;
freed_objects += chunk_freed_objects;
freed_bytes += space->FreeList(self, chunk_freed_objects, objects_to_chunk_free);
objects_to_chunk_free = out;
timings_.EndSplit();
}
}
} else if (!large_mark_objects->Test(obj)) {
++freed_large_objects;
freed_large_object_bytes += large_object_space->Free(self, obj);
}
}
// Free the remaining objects in chunks.
DCHECK_GE(out, objects_to_chunk_free);
DCHECK_LE(static_cast<size_t>(out - objects_to_chunk_free), kSweepArrayChunkFreeSize);
if (out - objects_to_chunk_free > 0) {
timings_.StartSplit("FreeList");
size_t chunk_freed_objects = out - objects_to_chunk_free;
freed_objects += chunk_freed_objects;
freed_bytes += space->FreeList(self, chunk_freed_objects, objects_to_chunk_free);
timings_.EndSplit();
}
CHECK_EQ(count, allocations->Size());
timings_.EndSplit();
timings_.StartSplit("RecordFree");
VLOG(heap) << "Freed " << freed_objects << "/" << count
<< " objects with size " << PrettySize(freed_bytes);
heap_->RecordFree(freed_objects + freed_large_objects, freed_bytes + freed_large_object_bytes);
freed_objects_.fetch_add(freed_objects);
freed_large_objects_.fetch_add(freed_large_objects);
freed_bytes_.fetch_add(freed_bytes);
freed_large_object_bytes_.fetch_add(freed_large_object_bytes);
timings_.EndSplit();
timings_.StartSplit("ResetStack");
allocations->Reset();
timings_.EndSplit();
}
void MarkSweep::Sweep(bool swap_bitmaps) {
DCHECK(mark_stack_->IsEmpty());
base::TimingLogger::ScopedSplit("Sweep", &timings_);
// If we don't swap bitmaps then newly allocated Weaks go into the live bitmap but not mark
// bitmap, resulting in occasional frees of Weaks which are still in use.
SweepSystemWeaks();
const bool partial = (GetGcType() == kGcTypePartial);
SweepCallbackContext scc;
scc.mark_sweep = this;
scc.self = Thread::Current();
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
// We always sweep always collect spaces.
bool sweep_space = (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect);
if (!partial && !sweep_space) {
// We sweep full collect spaces when the GC isn't a partial GC (ie its full).
sweep_space = (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyFullCollect);
}
if (sweep_space) {
uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin());
uintptr_t end = reinterpret_cast<uintptr_t>(space->End());
scc.space = space->AsDlMallocSpace();
accounting::SpaceBitmap* live_bitmap = space->GetLiveBitmap();
accounting::SpaceBitmap* mark_bitmap = space->GetMarkBitmap();
if (swap_bitmaps) {
std::swap(live_bitmap, mark_bitmap);
}
if (!space->IsZygoteSpace()) {
base::TimingLogger::ScopedSplit split("SweepAllocSpace", &timings_);
// Bitmaps are pre-swapped for optimization which enables sweeping with the heap unlocked.
accounting::SpaceBitmap::SweepWalk(*live_bitmap, *mark_bitmap, begin, end,
&SweepCallback, reinterpret_cast<void*>(&scc));
} else {
base::TimingLogger::ScopedSplit split("SweepZygote", &timings_);
// Zygote sweep takes care of dirtying cards and clearing live bits, does not free actual
// memory.
accounting::SpaceBitmap::SweepWalk(*live_bitmap, *mark_bitmap, begin, end,
&ZygoteSweepCallback, reinterpret_cast<void*>(&scc));
}
}
}
SweepLargeObjects(swap_bitmaps);
}
void MarkSweep::SweepLargeObjects(bool swap_bitmaps) {
base::TimingLogger::ScopedSplit("SweepLargeObjects", &timings_);
// Sweep large objects
space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace();
accounting::SpaceSetMap* large_live_objects = large_object_space->GetLiveObjects();
accounting::SpaceSetMap* large_mark_objects = large_object_space->GetMarkObjects();
if (swap_bitmaps) {
std::swap(large_live_objects, large_mark_objects);
}
// O(n*log(n)) but hopefully there are not too many large objects.
size_t freed_objects = 0;
size_t freed_bytes = 0;
Thread* self = Thread::Current();
for (const Object* obj : large_live_objects->GetObjects()) {
if (!large_mark_objects->Test(obj)) {
freed_bytes += large_object_space->Free(self, const_cast<Object*>(obj));
++freed_objects;
}
}
freed_large_objects_.fetch_add(freed_objects);
freed_large_object_bytes_.fetch_add(freed_bytes);
GetHeap()->RecordFree(freed_objects, freed_bytes);
}
void MarkSweep::CheckReference(const Object* obj, const Object* ref, MemberOffset offset, bool is_static) {
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
if (space->IsDlMallocSpace() && space->Contains(ref)) {
DCHECK(IsMarked(obj));
bool is_marked = IsMarked(ref);
if (!is_marked) {
LOG(INFO) << *space;
LOG(WARNING) << (is_static ? "Static ref'" : "Instance ref'") << PrettyTypeOf(ref)
<< "' (" << reinterpret_cast<const void*>(ref) << ") in '" << PrettyTypeOf(obj)
<< "' (" << reinterpret_cast<const void*>(obj) << ") at offset "
<< reinterpret_cast<void*>(offset.Int32Value()) << " wasn't marked";
const Class* klass = is_static ? obj->AsClass() : obj->GetClass();
DCHECK(klass != NULL);
const ObjectArray<ArtField>* fields = is_static ? klass->GetSFields() : klass->GetIFields();
DCHECK(fields != NULL);
bool found = false;
for (int32_t i = 0; i < fields->GetLength(); ++i) {
const ArtField* cur = fields->Get(i);
if (cur->GetOffset().Int32Value() == offset.Int32Value()) {
LOG(WARNING) << "Field referencing the alloc space was " << PrettyField(cur);
found = true;
break;
}
}
if (!found) {
LOG(WARNING) << "Could not find field in object alloc space with offset " << offset.Int32Value();
}
bool obj_marked = heap_->GetCardTable()->IsDirty(obj);
if (!obj_marked) {
LOG(WARNING) << "Object '" << PrettyTypeOf(obj) << "' "
<< "(" << reinterpret_cast<const void*>(obj) << ") contains references to "
<< "the alloc space, but wasn't card marked";
}
}
}
break;
}
}
// Process the "referent" field in a java.lang.ref.Reference. If the
// referent has not yet been marked, put it on the appropriate list in
// the heap for later processing.
void MarkSweep::DelayReferenceReferent(mirror::Class* klass, Object* obj) {
DCHECK(klass != nullptr);
DCHECK(klass->IsReferenceClass());
DCHECK(obj != NULL);
Object* referent = heap_->GetReferenceReferent(obj);
if (referent != NULL && !IsMarked(referent)) {
if (kCountJavaLangRefs) {
++reference_count_;
}
Thread* self = Thread::Current();
// TODO: Remove these locks, and use atomic stacks for storing references?
if (klass->IsSoftReferenceClass()) {
MutexLock mu(self, *heap_->GetSoftRefQueueLock());
heap_->EnqueuePendingReference(obj, &soft_reference_list_);
} else if (klass->IsWeakReferenceClass()) {
MutexLock mu(self, *heap_->GetWeakRefQueueLock());
heap_->EnqueuePendingReference(obj, &weak_reference_list_);
} else if (klass->IsFinalizerReferenceClass()) {
MutexLock mu(self, *heap_->GetFinalizerRefQueueLock());
heap_->EnqueuePendingReference(obj, &finalizer_reference_list_);
} else if (klass->IsPhantomReferenceClass()) {
MutexLock mu(self, *heap_->GetPhantomRefQueueLock());
heap_->EnqueuePendingReference(obj, &phantom_reference_list_);
} else {
LOG(FATAL) << "Invalid reference type " << PrettyClass(klass)
<< " " << std::hex << klass->GetAccessFlags();
}
}
}
void MarkSweep::ScanRoot(const Object* obj) {
ScanObject(obj);
}
class MarkObjectVisitor {
public:
explicit MarkObjectVisitor(MarkSweep* const mark_sweep) ALWAYS_INLINE : mark_sweep_(mark_sweep) {}
// TODO: Fixme when anotatalysis works with visitors.
void operator()(const Object* /* obj */, const Object* ref, const MemberOffset& /* offset */,
bool /* is_static */) const ALWAYS_INLINE
NO_THREAD_SAFETY_ANALYSIS {
if (kCheckLocks) {
Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current());
}
mark_sweep_->MarkObject(ref);
}
private:
MarkSweep* const mark_sweep_;
};
// Scans an object reference. Determines the type of the reference
// and dispatches to a specialized scanning routine.
void MarkSweep::ScanObject(const Object* obj) {
MarkObjectVisitor visitor(this);
ScanObjectVisit(obj, visitor);
}
void MarkSweep::ProcessMarkStackParallel(size_t thread_count) {
Thread* self = Thread::Current();
ThreadPool* thread_pool = GetHeap()->GetThreadPool();
const size_t chunk_size = std::min(mark_stack_->Size() / thread_count + 1,
static_cast<size_t>(MarkStackTask<false>::kMaxSize));
CHECK_GT(chunk_size, 0U);
// Split the current mark stack up into work tasks.
for (mirror::Object **it = mark_stack_->Begin(), **end = mark_stack_->End(); it < end; ) {
const size_t delta = std::min(static_cast<size_t>(end - it), chunk_size);
thread_pool->AddTask(self, new MarkStackTask<false>(thread_pool, this, delta,
const_cast<const mirror::Object**>(it)));
it += delta;
}
thread_pool->SetMaxActiveWorkers(thread_count - 1);
thread_pool->StartWorkers(self);
thread_pool->Wait(self, true, true);
thread_pool->StopWorkers(self);
mark_stack_->Reset();
CHECK_EQ(work_chunks_created_, work_chunks_deleted_) << " some of the work chunks were leaked";
}
// Scan anything that's on the mark stack.
void MarkSweep::ProcessMarkStack(bool paused) {
timings_.StartSplit("ProcessMarkStack");
size_t thread_count = GetThreadCount(paused);
if (kParallelProcessMarkStack && thread_count > 1 &&
mark_stack_->Size() >= kMinimumParallelMarkStackSize) {
ProcessMarkStackParallel(thread_count);
} else {
// TODO: Tune this.
static const size_t kFifoSize = 4;
BoundedFifoPowerOfTwo<const Object*, kFifoSize> prefetch_fifo;
for (;;) {
const Object* obj = NULL;
if (kUseMarkStackPrefetch) {
while (!mark_stack_->IsEmpty() && prefetch_fifo.size() < kFifoSize) {
const Object* obj = mark_stack_->PopBack();
DCHECK(obj != NULL);
__builtin_prefetch(obj);
prefetch_fifo.push_back(obj);
}
if (prefetch_fifo.empty()) {
break;
}
obj = prefetch_fifo.front();
prefetch_fifo.pop_front();
} else {
if (mark_stack_->IsEmpty()) {
break;
}
obj = mark_stack_->PopBack();
}
DCHECK(obj != NULL);
ScanObject(obj);
}
}
timings_.EndSplit();
}
// Walks the reference list marking any references subject to the
// reference clearing policy. References with a black referent are
// removed from the list. References with white referents biased
// toward saving are blackened and also removed from the list.
void MarkSweep::PreserveSomeSoftReferences(Object** list) {
DCHECK(list != NULL);
Object* clear = NULL;
size_t counter = 0;
DCHECK(mark_stack_->IsEmpty());
timings_.StartSplit("PreserveSomeSoftReferences");
while (*list != NULL) {
Object* ref = heap_->DequeuePendingReference(list);
Object* referent = heap_->GetReferenceReferent(ref);
if (referent == NULL) {
// Referent was cleared by the user during marking.
continue;
}
bool is_marked = IsMarked(referent);
if (!is_marked && ((++counter) & 1)) {
// Referent is white and biased toward saving, mark it.
MarkObject(referent);
is_marked = true;
}
if (!is_marked) {
// Referent is white, queue it for clearing.
heap_->EnqueuePendingReference(ref, &clear);
}
}
*list = clear;
timings_.EndSplit();
// Restart the mark with the newly black references added to the root set.
ProcessMarkStack(true);
}
inline bool MarkSweep::IsMarked(const Object* object) const
SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_) {
if (IsImmune(object)) {
return true;
}
DCHECK(current_mark_bitmap_ != NULL);
if (current_mark_bitmap_->HasAddress(object)) {
return current_mark_bitmap_->Test(object);
}
return heap_->GetMarkBitmap()->Test(object);
}
// Unlink the reference list clearing references objects with white
// referents. Cleared references registered to a reference queue are
// scheduled for appending by the heap worker thread.
void MarkSweep::ClearWhiteReferences(Object** list) {
DCHECK(list != NULL);
while (*list != NULL) {
Object* ref = heap_->DequeuePendingReference(list);
Object* referent = heap_->GetReferenceReferent(ref);
if (referent != NULL && !IsMarked(referent)) {
// Referent is white, clear it.
heap_->ClearReferenceReferent(ref);
if (heap_->IsEnqueuable(ref)) {
heap_->EnqueueReference(ref, &cleared_reference_list_);
}
}
}
DCHECK(*list == NULL);
}
// Enqueues finalizer references with white referents. White
// referents are blackened, moved to the zombie field, and the
// referent field is cleared.
void MarkSweep::EnqueueFinalizerReferences(Object** list) {
DCHECK(list != NULL);
timings_.StartSplit("EnqueueFinalizerReferences");
MemberOffset zombie_offset = heap_->GetFinalizerReferenceZombieOffset();
bool has_enqueued = false;
while (*list != NULL) {
Object* ref = heap_->DequeuePendingReference(list);
Object* referent = heap_->GetReferenceReferent(ref);
if (referent != NULL && !IsMarked(referent)) {
MarkObject(referent);
// If the referent is non-null the reference must queuable.
DCHECK(heap_->IsEnqueuable(ref));
ref->SetFieldObject(zombie_offset, referent, false);
heap_->ClearReferenceReferent(ref);
heap_->EnqueueReference(ref, &cleared_reference_list_);
has_enqueued = true;
}
}
timings_.EndSplit();
if (has_enqueued) {
ProcessMarkStack(true);
}
DCHECK(*list == NULL);
}
// Process reference class instances and schedule finalizations.
void MarkSweep::ProcessReferences(Object** soft_references, bool clear_soft,
Object** weak_references,
Object** finalizer_references,
Object** phantom_references) {
DCHECK(soft_references != NULL);
DCHECK(weak_references != NULL);
DCHECK(finalizer_references != NULL);
DCHECK(phantom_references != NULL);
// Unless we are in the zygote or required to clear soft references
// with white references, preserve some white referents.
if (!clear_soft && !Runtime::Current()->IsZygote()) {
PreserveSomeSoftReferences(soft_references);
}
timings_.StartSplit("ProcessReferences");
// Clear all remaining soft and weak references with white
// referents.
ClearWhiteReferences(soft_references);
ClearWhiteReferences(weak_references);
timings_.EndSplit();
// Preserve all white objects with finalize methods and schedule
// them for finalization.
EnqueueFinalizerReferences(finalizer_references);
timings_.StartSplit("ProcessReferences");
// Clear all f-reachable soft and weak references with white
// referents.
ClearWhiteReferences(soft_references);
ClearWhiteReferences(weak_references);
// Clear all phantom references with white referents.
ClearWhiteReferences(phantom_references);
// At this point all reference lists should be empty.
DCHECK(*soft_references == NULL);
DCHECK(*weak_references == NULL);
DCHECK(*finalizer_references == NULL);
DCHECK(*phantom_references == NULL);
timings_.EndSplit();
}
void MarkSweep::UnBindBitmaps() {
base::TimingLogger::ScopedSplit split("UnBindBitmaps", &timings_);
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
if (space->IsDlMallocSpace()) {
space::DlMallocSpace* alloc_space = space->AsDlMallocSpace();
if (alloc_space->temp_bitmap_.get() != NULL) {
// At this point, the temp_bitmap holds our old mark bitmap.
accounting::SpaceBitmap* new_bitmap = alloc_space->temp_bitmap_.release();
GetHeap()->GetMarkBitmap()->ReplaceBitmap(alloc_space->mark_bitmap_.get(), new_bitmap);
CHECK_EQ(alloc_space->mark_bitmap_.release(), alloc_space->live_bitmap_.get());
alloc_space->mark_bitmap_.reset(new_bitmap);
DCHECK(alloc_space->temp_bitmap_.get() == NULL);
}
}
}
}
void MarkSweep::FinishPhase() {
base::TimingLogger::ScopedSplit split("FinishPhase", &timings_);
// Can't enqueue references if we hold the mutator lock.
Object* cleared_references = GetClearedReferences();
Heap* heap = GetHeap();
timings_.NewSplit("EnqueueClearedReferences");
heap->EnqueueClearedReferences(&cleared_references);
timings_.NewSplit("PostGcVerification");
heap->PostGcVerification(this);
timings_.NewSplit("GrowForUtilization");
heap->GrowForUtilization(GetGcType(), GetDurationNs());
timings_.NewSplit("RequestHeapTrim");
heap->RequestHeapTrim();
// Update the cumulative statistics
total_time_ns_ += GetDurationNs();
total_paused_time_ns_ += std::accumulate(GetPauseTimes().begin(), GetPauseTimes().end(), 0,
std::plus<uint64_t>());
total_freed_objects_ += GetFreedObjects() + GetFreedLargeObjects();
total_freed_bytes_ += GetFreedBytes() + GetFreedLargeObjectBytes();
// Ensure that the mark stack is empty.
CHECK(mark_stack_->IsEmpty());
if (kCountScannedTypes) {
VLOG(gc) << "MarkSweep scanned classes=" << class_count_ << " arrays=" << array_count_
<< " other=" << other_count_;
}
if (kCountTasks) {
VLOG(gc) << "Total number of work chunks allocated: " << work_chunks_created_;
}
if (kMeasureOverhead) {
VLOG(gc) << "Overhead time " << PrettyDuration(overhead_time_);
}
if (kProfileLargeObjects) {
VLOG(gc) << "Large objects tested " << large_object_test_ << " marked " << large_object_mark_;
}
if (kCountClassesMarked) {
VLOG(gc) << "Classes marked " << classes_marked_;
}
if (kCountJavaLangRefs) {
VLOG(gc) << "References scanned " << reference_count_;
}
// Update the cumulative loggers.
cumulative_timings_.Start();
cumulative_timings_.AddLogger(timings_);
cumulative_timings_.End();
// Clear all of the spaces' mark bitmaps.
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
if (space->GetGcRetentionPolicy() != space::kGcRetentionPolicyNeverCollect) {
space->GetMarkBitmap()->Clear();
}
}
mark_stack_->Reset();
// Reset the marked large objects.
space::LargeObjectSpace* large_objects = GetHeap()->GetLargeObjectsSpace();
large_objects->GetMarkObjects()->Clear();
}
} // namespace collector
} // namespace gc
} // namespace art