Gitiles
Code Review Sign In
LeafOS / LeafOS-Project / android_art / 465455f6538a4b624a8482e8927f5cbb929c2f5c / . / runtime / gc / collector / mark_sweep.cc
blob: 984d71ca252a3b76a33fdc4e0789d3d5180607e8 [file] [log] [blame]
/*
* 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 <atomic>
#include <climits>
#include <functional>
#include <numeric>
#include <vector>
#include "base/bounded_fifo.h"
#include "base/enums.h"
#include "base/file_utils.h"
#include "base/logging.h" // For VLOG.
#include "base/macros.h"
#include "base/mutex-inl.h"
#include "base/systrace.h"
#include "base/time_utils.h"
#include "base/timing_logger.h"
#include "gc/accounting/card_table-inl.h"
#include "gc/accounting/heap_bitmap-inl.h"
#include "gc/accounting/mod_union_table.h"
#include "gc/accounting/space_bitmap-inl.h"
#include "gc/heap.h"
#include "gc/reference_processor.h"
#include "gc/space/large_object_space.h"
#include "gc/space/space-inl.h"
#include "mark_sweep-inl.h"
#include "mirror/object-inl.h"
#include "runtime.h"
#include "scoped_thread_state_change-inl.h"
#include "thread-current-inl.h"
#include "thread_list.h"
namespace art HIDDEN {
namespace gc {
namespace collector {
// Performance options.
static constexpr bool kUseRecursiveMark = false;
static constexpr bool kUseMarkStackPrefetch = true;
static constexpr size_t kSweepArrayChunkFreeSize = 1024;
static constexpr bool kPreCleanCards = true;
// Parallelism options.
static constexpr bool kParallelCardScan = true;
static 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.
static constexpr size_t kMinimumParallelMarkStackSize = 128;
static constexpr bool kParallelProcessMarkStack = true;
// Profiling and information flags.
static constexpr bool kProfileLargeObjects = false;
static constexpr bool kMeasureOverhead = false;
static constexpr bool kCountTasks = false;
static constexpr bool kCountMarkedObjects = false;
// Turn off kCheckLocks when profiling the GC since it slows the GC down by up to 40%.
static constexpr bool kCheckLocks = kDebugLocking;
static constexpr bool kVerifyRootsMarked = kIsDebugBuild;
// If true, revoke the rosalloc thread-local buffers at the
// checkpoint, as opposed to during the pause.
static constexpr bool kRevokeRosAllocThreadLocalBuffersAtCheckpoint = true;
void MarkSweep::BindBitmaps() {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
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) {
immune_spaces_.AddSpace(space);
}
}
}
MarkSweep::MarkSweep(Heap* heap, bool is_concurrent, const std::string& name_prefix)
: GarbageCollector(heap,
name_prefix +
(is_concurrent ? "concurrent mark sweep": "mark sweep")),
current_space_bitmap_(nullptr),
mark_bitmap_(nullptr),
mark_stack_(nullptr),
gc_barrier_(new Barrier(0)),
mark_stack_lock_("mark sweep mark stack lock", kMarkSweepMarkStackLock),
is_concurrent_(is_concurrent),
live_stack_freeze_size_(0) {
std::string error_msg;
sweep_array_free_buffer_mem_map_ = MemMap::MapAnonymous(
"mark sweep sweep array free buffer",
RoundUp(kSweepArrayChunkFreeSize * sizeof(mirror::Object*), gPageSize),
PROT_READ | PROT_WRITE,
/*low_4gb=*/ false,
&error_msg);
CHECK(sweep_array_free_buffer_mem_map_.IsValid())
<< "Couldn't allocate sweep array free buffer: " << error_msg;
}
void MarkSweep::InitializePhase() {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
mark_stack_ = heap_->GetMarkStack();
DCHECK(mark_stack_ != nullptr);
immune_spaces_.Reset();
no_reference_class_count_.store(0, std::memory_order_relaxed);
normal_count_.store(0, std::memory_order_relaxed);
class_count_.store(0, std::memory_order_relaxed);
object_array_count_.store(0, std::memory_order_relaxed);
other_count_.store(0, std::memory_order_relaxed);
reference_count_.store(0, std::memory_order_relaxed);
large_object_test_.store(0, std::memory_order_relaxed);
large_object_mark_.store(0, std::memory_order_relaxed);
overhead_time_ .store(0, std::memory_order_relaxed);
work_chunks_created_.store(0, std::memory_order_relaxed);
work_chunks_deleted_.store(0, std::memory_order_relaxed);
mark_null_count_.store(0, std::memory_order_relaxed);
mark_immune_count_.store(0, std::memory_order_relaxed);
mark_fastpath_count_.store(0, std::memory_order_relaxed);
mark_slowpath_count_.store(0, std::memory_order_relaxed);
{
// TODO: I don't think we should need heap bitmap lock to Get the mark bitmap.
ReaderMutexLock mu(Thread::Current(), *Locks::heap_bitmap_lock_);
mark_bitmap_ = heap_->GetMarkBitmap();
}
if (!GetCurrentIteration()->GetClearSoftReferences()) {
// Always clear soft references if a non-sticky collection.
GetCurrentIteration()->SetClearSoftReferences(GetGcType() != collector::kGcTypeSticky);
}
}
void MarkSweep::RunPhases() {
Thread* self = Thread::Current();
InitializePhase();
Locks::mutator_lock_->AssertNotHeld(self);
if (IsConcurrent()) {
GetHeap()->PreGcVerification(this);
{
ReaderMutexLock mu(self, *Locks::mutator_lock_);
MarkingPhase();
}
ScopedPause pause(this);
GetHeap()->PrePauseRosAllocVerification(this);
PausePhase();
RevokeAllThreadLocalBuffers();
} else {
ScopedPause pause(this);
GetHeap()->PreGcVerificationPaused(this);
MarkingPhase();
GetHeap()->PrePauseRosAllocVerification(this);
PausePhase();
RevokeAllThreadLocalBuffers();
}
{
// Sweeping always done concurrently, even for non concurrent mark sweep.
ReaderMutexLock mu(self, *Locks::mutator_lock_);
ReclaimPhase();
}
GetHeap()->PostGcVerification(this);
FinishPhase();
}
void MarkSweep::ProcessReferences(Thread* self) {
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
GetHeap()->GetReferenceProcessor()->ProcessReferences(self, GetTimings());
}
void MarkSweep::PausePhase() {
TimingLogger::ScopedTiming t("(Paused)PausePhase", GetTimings());
Thread* self = Thread::Current();
Locks::mutator_lock_->AssertExclusiveHeld(self);
if (IsConcurrent()) {
// Handle the dirty objects if we are a concurrent GC.
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
// Re-mark root set.
ReMarkRoots();
// Scan dirty objects, this is only required if we are doing concurrent GC.
RecursiveMarkDirtyObjects(true, accounting::CardTable::kCardDirty);
}
{
TimingLogger::ScopedTiming t2("SwapStacks", GetTimings());
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
heap_->SwapStacks();
live_stack_freeze_size_ = heap_->GetLiveStack()->Size();
// Need to revoke all the thread local allocation stacks since we just swapped the allocation
// stacks and don't want anybody to allocate into the live stack.
RevokeAllThreadLocalAllocationStacks(self);
}
heap_->PreSweepingGcVerification(this);
// Disallow new system weaks to prevent a race which occurs when someone adds a new system
// weak before we sweep them. Since this new system weak may not be marked, the GC may
// incorrectly sweep it. This also fixes a race where interning may attempt to return a strong
// reference to a string that is about to be swept.
Runtime::Current()->DisallowNewSystemWeaks();
// Enable the reference processing slow path, needs to be done with mutators paused since there
// is no lock in the GetReferent fast path.
ReferenceProcessor* rp = GetHeap()->GetReferenceProcessor();
rp->Setup(self, this, /*concurrent=*/true, GetCurrentIteration()->GetClearSoftReferences());
rp->EnableSlowPath();
}
void MarkSweep::PreCleanCards() {
// Don't do this for non concurrent GCs since they don't have any dirty cards.
if (kPreCleanCards && IsConcurrent()) {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
Thread* self = Thread::Current();
CHECK(!Locks::mutator_lock_->IsExclusiveHeld(self));
// Process dirty cards and add dirty cards to mod union tables, also ages cards.
heap_->ProcessCards(GetTimings(), false, true, false);
// The checkpoint root marking is required to avoid a race condition which occurs if the
// following happens during a reference write:
// 1. mutator dirties the card (write barrier)
// 2. GC ages the card (the above ProcessCards call)
// 3. GC scans the object (the RecursiveMarkDirtyObjects call below)
// 4. mutator writes the value (corresponding to the write barrier in 1.)
// This causes the GC to age the card but not necessarily mark the reference which the mutator
// wrote into the object stored in the card.
// Having the checkpoint fixes this issue since it ensures that the card mark and the
// reference write are visible to the GC before the card is scanned (this is due to locks being
// acquired / released in the checkpoint code).
// The other roots are also marked to help reduce the pause.
MarkRootsCheckpoint(self, false);
MarkNonThreadRoots();
MarkConcurrentRoots(
static_cast<VisitRootFlags>(kVisitRootFlagClearRootLog | kVisitRootFlagNewRoots));
// Process the newly aged cards.
RecursiveMarkDirtyObjects(false, accounting::CardTable::kCardDirty - 1);
// TODO: Empty allocation stack to reduce the number of objects we need to test / mark as live
// in the next GC.
}
}
void MarkSweep::RevokeAllThreadLocalAllocationStacks(Thread* self) {
if (kUseThreadLocalAllocationStack) {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
Locks::mutator_lock_->AssertExclusiveHeld(self);
heap_->RevokeAllThreadLocalAllocationStacks(self);
}
}
void MarkSweep::MarkingPhase() {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
Thread* self = Thread::Current();
BindBitmaps();
FindDefaultSpaceBitmap();
// Process dirty cards and add dirty cards to mod union tables.
// If the GC type is non sticky, then we just clear the cards of the
// alloc space instead of aging them.
//
// Note that it is fine to clear the cards of the alloc space here,
// in the case of a concurrent (non-sticky) mark-sweep GC (whose
// marking phase _is_ performed concurrently with mutator threads
// running and possibly dirtying cards), as the whole alloc space
// will be traced in that case, starting *after* this call to
// Heap::ProcessCards (see calls to MarkSweep::MarkRoots and
// MarkSweep::MarkReachableObjects). References held by objects on
// cards that became dirty *after* the actual marking work started
// will be marked in the pause (see MarkSweep::PausePhase), in a
// *non-concurrent* way to prevent races with mutator threads.
//
// TODO: Do we need some sort of fence between the call to
// Heap::ProcessCard and the calls to MarkSweep::MarkRoot /
// MarkSweep::MarkReachableObjects below to make sure write
// operations in the card table clearing the alloc space's dirty
// cards (during the call to Heap::ProcessCard) are not reordered
// *after* marking actually starts?
heap_->ProcessCards(GetTimings(),
/* use_rem_sets= */ false,
/* process_alloc_space_cards= */ true,
/* clear_alloc_space_cards= */ GetGcType() != kGcTypeSticky);
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
MarkRoots(self);
MarkReachableObjects();
// Pre-clean dirtied cards to reduce pauses.
PreCleanCards();
}
class MarkSweep::ScanObjectVisitor {
public:
explicit ScanObjectVisitor(MarkSweep* const mark_sweep) ALWAYS_INLINE
: mark_sweep_(mark_sweep) {}
void operator()(ObjPtr<mirror::Object> obj) const
ALWAYS_INLINE
REQUIRES(Locks::heap_bitmap_lock_)
REQUIRES_SHARED(Locks::mutator_lock_) {
if (kCheckLocks) {
Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current());
}
mark_sweep_->ScanObject(obj.Ptr());
}
private:
MarkSweep* const mark_sweep_;
};
void MarkSweep::UpdateAndMarkModUnion() {
for (const auto& space : immune_spaces_.GetSpaces()) {
const char* name = space->IsZygoteSpace()
? "UpdateAndMarkZygoteModUnionTable"
: "UpdateAndMarkImageModUnionTable";
DCHECK(space->IsZygoteSpace() || space->IsImageSpace()) << *space;
TimingLogger::ScopedTiming t(name, GetTimings());
accounting::ModUnionTable* mod_union_table = heap_->FindModUnionTableFromSpace(space);
if (mod_union_table != nullptr) {
mod_union_table->UpdateAndMarkReferences(this);
} else {
// No mod-union table, scan all the live bits. This can only occur for app images.
space->GetLiveBitmap()->VisitMarkedRange(reinterpret_cast<uintptr_t>(space->Begin()),
reinterpret_cast<uintptr_t>(space->End()),
ScanObjectVisitor(this));
}
}
}
void MarkSweep::MarkReachableObjects() {
UpdateAndMarkModUnion();
// Recursively mark all the non-image bits set in the mark bitmap.
RecursiveMark();
}
void MarkSweep::ReclaimPhase() {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
Thread* const self = Thread::Current();
// Process the references concurrently.
ProcessReferences(self);
// There is no need to sweep interpreter caches as this GC doesn't move
// objects and hence would be a nop.
SweepSystemWeaks(self);
Runtime* const runtime = Runtime::Current();
runtime->AllowNewSystemWeaks();
// Clean up class loaders after system weaks are swept since that is how we know if class
// unloading occurred.
runtime->GetClassLinker()->CleanupClassLoaders();
{
WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
GetHeap()->RecordFreeRevoke();
// 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.
SwapBitmaps();
// Unbind the live and mark bitmaps.
GetHeap()->UnBindBitmaps();
}
}
void MarkSweep::FindDefaultSpaceBitmap() {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
accounting::ContinuousSpaceBitmap* bitmap = space->GetMarkBitmap();
// We want to have the main space instead of non moving if possible.
if (bitmap != nullptr &&
space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect) {
current_space_bitmap_ = bitmap;
// If we are not the non moving space exit the loop early since this will be good enough.
if (space != heap_->GetNonMovingSpace()) {
break;
}
}
}
CHECK(current_space_bitmap_ != nullptr) << "Could not find a default mark bitmap\n"
<< heap_->DumpSpaces();
}
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<StackReference<mirror::Object>> temp(mark_stack_->Begin(), mark_stack_->End());
CHECK_LE(mark_stack_->Size(), new_size);
mark_stack_->Resize(new_size);
for (auto& obj : temp) {
mark_stack_->PushBack(obj.AsMirrorPtr());
}
}
mirror::Object* MarkSweep::MarkObject(mirror::Object* obj) {
MarkObject(obj, nullptr, MemberOffset(0));
return obj;
}
inline void MarkSweep::MarkObjectNonNullParallel(mirror::Object* obj) {
DCHECK(obj != nullptr);
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(obj);
}
}
bool MarkSweep::IsNullOrMarkedHeapReference(mirror::HeapReference<mirror::Object>* ref,
[[maybe_unused]] bool do_atomic_update) {
mirror::Object* obj = ref->AsMirrorPtr();
if (obj == nullptr) {
return true;
}
return IsMarked(obj);
}
class MarkSweep::MarkObjectSlowPath {
public:
explicit MarkObjectSlowPath(MarkSweep* mark_sweep,
mirror::Object* holder = nullptr,
MemberOffset offset = MemberOffset(0))
: mark_sweep_(mark_sweep),
holder_(holder),
offset_(offset) {}
void operator()(const mirror::Object* obj) const NO_THREAD_SAFETY_ANALYSIS {
if (kProfileLargeObjects) {
// TODO: Differentiate between marking and testing somehow.
++mark_sweep_->large_object_test_;
++mark_sweep_->large_object_mark_;
}
space::LargeObjectSpace* large_object_space = mark_sweep_->GetHeap()->GetLargeObjectsSpace();
if (UNLIKELY(obj == nullptr ||
!IsAlignedParam(obj, space::LargeObjectSpace::ObjectAlignment()) ||
(kIsDebugBuild && large_object_space != nullptr &&
!large_object_space->Contains(obj)))) {
// Lowest priority logging first:
PrintFileToLog("/proc/self/maps", LogSeverity::FATAL_WITHOUT_ABORT);
MemMap::DumpMaps(LOG_STREAM(FATAL_WITHOUT_ABORT), /* terse= */ true);
// Buffer the output in the string stream since it is more important than the stack traces
// and we want it to have log priority. The stack traces are printed from Runtime::Abort
// which is called from LOG(FATAL) but before the abort message.
std::ostringstream oss;
oss << "Tried to mark " << obj << " not contained by any spaces" << std::endl;
if (holder_ != nullptr) {
size_t holder_size = holder_->SizeOf();
ArtField* field = holder_->FindFieldByOffset(offset_);
oss << "Field info: "
<< " holder=" << holder_
<< " holder is "
<< (mark_sweep_->GetHeap()->IsLiveObjectLocked(holder_)
? "alive" : "dead")
<< " holder_size=" << holder_size
<< " holder_type=" << holder_->PrettyTypeOf()
<< " offset=" << offset_.Uint32Value()
<< " field=" << (field != nullptr ? field->GetName() : "nullptr")
<< " field_type="
<< (field != nullptr ? field->GetTypeDescriptor() : "")
<< " first_ref_field_offset="
<< (holder_->IsClass()
? holder_->AsClass()->GetFirstReferenceStaticFieldOffset(
kRuntimePointerSize)
: holder_->GetClass()->GetFirstReferenceInstanceFieldOffset())
<< " num_of_ref_fields="
<< (holder_->IsClass()
? holder_->AsClass()->NumReferenceStaticFields()
: holder_->GetClass()->NumReferenceInstanceFields())
<< std::endl;
// Print the memory content of the holder.
for (size_t i = 0; i < holder_size / sizeof(uint32_t); ++i) {
uint32_t* p = reinterpret_cast<uint32_t*>(holder_);
oss << &p[i] << ": " << "holder+" << (i * sizeof(uint32_t)) << " = " << std::hex << p[i]
<< std::endl;
}
}
oss << "Attempting see if it's a bad thread root" << std::endl;
mark_sweep_->VerifySuspendedThreadRoots(oss);
LOG(FATAL) << oss.str();
}
}
private:
MarkSweep* const mark_sweep_;
mirror::Object* const holder_;
MemberOffset offset_;
};
inline void MarkSweep::MarkObjectNonNull(mirror::Object* obj,
mirror::Object* holder,
MemberOffset offset) {
DCHECK(obj != nullptr);
if (kUseBakerReadBarrier) {
// Verify all the objects have the correct state installed.
obj->AssertReadBarrierState();
}
if (immune_spaces_.IsInImmuneRegion(obj)) {
if (kCountMarkedObjects) {
++mark_immune_count_;
}
DCHECK(mark_bitmap_->Test(obj));
} else if (LIKELY(current_space_bitmap_->HasAddress(obj))) {
if (kCountMarkedObjects) {
++mark_fastpath_count_;
}
if (UNLIKELY(!current_space_bitmap_->Set(obj))) {
PushOnMarkStack(obj); // This object was not previously marked.
}
} else {
if (kCountMarkedObjects) {
++mark_slowpath_count_;
}
MarkObjectSlowPath visitor(this, holder, offset);
// TODO: We already know that the object is not in the current_space_bitmap_ but MarkBitmap::Set
// will check again.
if (!mark_bitmap_->Set(obj, visitor)) {
PushOnMarkStack(obj); // Was not already marked, push.
}
}
}
inline void MarkSweep::PushOnMarkStack(mirror::Object* obj) {
if (UNLIKELY(mark_stack_->Size() >= mark_stack_->Capacity())) {
// Lock is not needed but is here anyways to please annotalysis.
MutexLock mu(Thread::Current(), mark_stack_lock_);
ExpandMarkStack();
}
// The object must be pushed on to the mark stack.
mark_stack_->PushBack(obj);
}
inline bool MarkSweep::MarkObjectParallel(mirror::Object* obj) {
DCHECK(obj != nullptr);
if (kUseBakerReadBarrier) {
// Verify all the objects have the correct state installed.
obj->AssertReadBarrierState();
}
if (immune_spaces_.IsInImmuneRegion(obj)) {
DCHECK(IsMarked(obj) != nullptr);
return false;
}
// Try to take advantage of locality of references within a space, failing this find the space
// the hard way.
accounting::ContinuousSpaceBitmap* object_bitmap = current_space_bitmap_;
if (LIKELY(object_bitmap->HasAddress(obj))) {
return !object_bitmap->AtomicTestAndSet(obj);
}
MarkObjectSlowPath visitor(this);
return !mark_bitmap_->AtomicTestAndSet(obj, visitor);
}
void MarkSweep::MarkHeapReference(mirror::HeapReference<mirror::Object>* ref,
[[maybe_unused]] bool do_atomic_update) {
MarkObject(ref->AsMirrorPtr(), nullptr, MemberOffset(0));
}
// Used to mark objects when processing the mark stack. If an object is null, it is not marked.
inline void MarkSweep::MarkObject(mirror::Object* obj,
mirror::Object* holder,
MemberOffset offset) {
if (obj != nullptr) {
MarkObjectNonNull(obj, holder, offset);
} else if (kCountMarkedObjects) {
++mark_null_count_;
}
}
class MarkSweep::VerifyRootMarkedVisitor : public SingleRootVisitor {
public:
explicit VerifyRootMarkedVisitor(MarkSweep* collector) : collector_(collector) { }
void VisitRoot(mirror::Object* root, const RootInfo& info) override
REQUIRES_SHARED(Locks::mutator_lock_, Locks::heap_bitmap_lock_) {
CHECK(collector_->IsMarked(root) != nullptr) << info.ToString();
}
private:
MarkSweep* const collector_;
};
void MarkSweep::VisitRoots(mirror::Object*** roots,
size_t count,
[[maybe_unused]] const RootInfo& info) {
for (size_t i = 0; i < count; ++i) {
MarkObjectNonNull(*roots[i]);
}
}
void MarkSweep::VisitRoots(mirror::CompressedReference<mirror::Object>** roots,
size_t count,
[[maybe_unused]] const RootInfo& info) {
for (size_t i = 0; i < count; ++i) {
MarkObjectNonNull(roots[i]->AsMirrorPtr());
}
}
class MarkSweep::VerifyRootVisitor : public SingleRootVisitor {
public:
explicit VerifyRootVisitor(std::ostream& os) : os_(os) {}
void VisitRoot(mirror::Object* root, const RootInfo& info) override
REQUIRES_SHARED(Locks::mutator_lock_, Locks::heap_bitmap_lock_) {
// See if the root is on any space bitmap.
auto* heap = Runtime::Current()->GetHeap();
if (heap->GetLiveBitmap()->GetContinuousSpaceBitmap(root) == nullptr) {
space::LargeObjectSpace* large_object_space = heap->GetLargeObjectsSpace();
if (large_object_space != nullptr && !large_object_space->Contains(root)) {
os_ << "Found invalid root: " << root << " " << info << std::endl;
}
}
}
private:
std::ostream& os_;
};
void MarkSweep::VerifySuspendedThreadRoots(std::ostream& os) {
VerifyRootVisitor visitor(os);
Runtime::Current()->GetThreadList()->VisitRootsForSuspendedThreads(&visitor);
}
void MarkSweep::MarkRoots(Thread* self) {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
if (Locks::mutator_lock_->IsExclusiveHeld(self)) {
// If we exclusively hold the mutator lock, all threads must be suspended.
Runtime::Current()->VisitRoots(this);
RevokeAllThreadLocalAllocationStacks(self);
} else {
MarkRootsCheckpoint(self, kRevokeRosAllocThreadLocalBuffersAtCheckpoint);
// At this point the live stack should no longer have any mutators which push into it.
MarkNonThreadRoots();
MarkConcurrentRoots(
static_cast<VisitRootFlags>(kVisitRootFlagAllRoots | kVisitRootFlagStartLoggingNewRoots));
}
}
void MarkSweep::MarkNonThreadRoots() {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
Runtime::Current()->VisitNonThreadRoots(this);
}
void MarkSweep::MarkConcurrentRoots(VisitRootFlags flags) {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
// Visit all runtime roots and clear dirty flags.
Runtime::Current()->VisitConcurrentRoots(this, flags);
}
class MarkSweep::DelayReferenceReferentVisitor {
public:
explicit DelayReferenceReferentVisitor(MarkSweep* collector) : collector_(collector) {}
void operator()(ObjPtr<mirror::Class> klass, ObjPtr<mirror::Reference> ref) const
REQUIRES(Locks::heap_bitmap_lock_)
REQUIRES_SHARED(Locks::mutator_lock_) {
collector_->DelayReferenceReferent(klass, ref);
}
private:
MarkSweep* const collector_;
};
template <bool kUseFinger = false>
class MarkSweep::MarkStackTask : public Task {
public:
MarkStackTask(ThreadPool* thread_pool,
MarkSweep* mark_sweep,
size_t mark_stack_size,
StackReference<mirror::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 != nullptr);
// TODO: Check performance?
std::copy(mark_stack, mark_stack + mark_stack_size, mark_stack_);
}
if (kCountTasks) {
++mark_sweep_->work_chunks_created_;
}
}
static constexpr size_t kMaxSize = 1 * KB;
protected:
class MarkObjectParallelVisitor {
public:
ALWAYS_INLINE MarkObjectParallelVisitor(MarkStackTask<kUseFinger>* chunk_task,
MarkSweep* mark_sweep)
: chunk_task_(chunk_task), mark_sweep_(mark_sweep) {}
ALWAYS_INLINE void operator()(mirror::Object* obj,
MemberOffset offset,
[[maybe_unused]] bool is_static) const
REQUIRES_SHARED(Locks::mutator_lock_) {
Mark(obj->GetFieldObject<mirror::Object>(offset));
}
void VisitRootIfNonNull(mirror::CompressedReference<mirror::Object>* root) const
REQUIRES_SHARED(Locks::mutator_lock_) {
if (!root->IsNull()) {
VisitRoot(root);
}
}
void VisitRoot(mirror::CompressedReference<mirror::Object>* root) const
REQUIRES_SHARED(Locks::mutator_lock_) {
if (kCheckLocks) {
Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current());
}
Mark(root->AsMirrorPtr());
}
private:
ALWAYS_INLINE void Mark(mirror::Object* ref) const REQUIRES_SHARED(Locks::mutator_lock_) {
if (ref != nullptr && mark_sweep_->MarkObjectParallel(ref)) {
if (kUseFinger) {
std::atomic_thread_fence(std::memory_order_seq_cst);
if (reinterpret_cast<uintptr_t>(ref) >=
static_cast<uintptr_t>(mark_sweep_->atomic_finger_.load(std::memory_order_relaxed))) {
return;
}
}
chunk_task_->MarkStackPush(ref);
}
}
MarkStackTask<kUseFinger>* const chunk_task_;
MarkSweep* const mark_sweep_;
};
class ScanObjectParallelVisitor {
public:
ALWAYS_INLINE explicit ScanObjectParallelVisitor(MarkStackTask<kUseFinger>* chunk_task)
: chunk_task_(chunk_task) {}
// No thread safety analysis since multiple threads will use this visitor.
void operator()(mirror::Object* obj) const
REQUIRES(Locks::heap_bitmap_lock_)
REQUIRES_SHARED(Locks::mutator_lock_) {
MarkSweep* const mark_sweep = chunk_task_->mark_sweep_;
MarkObjectParallelVisitor mark_visitor(chunk_task_, mark_sweep);
DelayReferenceReferentVisitor ref_visitor(mark_sweep);
mark_sweep->ScanObjectVisit(obj, mark_visitor, ref_visitor);
}
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.
StackReference<mirror::Object> mark_stack_[kMaxSize];
// Mark stack position.
size_t mark_stack_pos_;
ALWAYS_INLINE void MarkStackPush(mirror::Object* obj)
REQUIRES_SHARED(Locks::mutator_lock_) {
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_LT(mark_stack_pos_, kMaxSize);
mark_stack_[mark_stack_pos_++].Assign(obj);
}
void Finalize() override {
delete this;
}
// Scans all of the objects
void Run([[maybe_unused]] Thread* self) override REQUIRES(Locks::heap_bitmap_lock_)
REQUIRES_SHARED(Locks::mutator_lock_) {
ScanObjectParallelVisitor visitor(this);
// TODO: Tune this.
static const size_t kFifoSize = 4;
BoundedFifoPowerOfTwo<mirror::Object*, kFifoSize> prefetch_fifo;
for (;;) {
mirror::Object* obj = nullptr;
if (kUseMarkStackPrefetch) {
while (mark_stack_pos_ != 0 && prefetch_fifo.size() < kFifoSize) {
mirror::Object* const mark_stack_obj = mark_stack_[--mark_stack_pos_].AsMirrorPtr();
DCHECK(mark_stack_obj != nullptr);
__builtin_prefetch(mark_stack_obj);
prefetch_fifo.push_back(mark_stack_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_].AsMirrorPtr();
}
DCHECK(obj != nullptr);
visitor(obj);
}
}
};
class MarkSweep::CardScanTask : public MarkStackTask<false> {
public:
CardScanTask(ThreadPool* thread_pool,
MarkSweep* mark_sweep,
accounting::ContinuousSpaceBitmap* bitmap,
uint8_t* begin,
uint8_t* end,
uint8_t minimum_age,
size_t mark_stack_size,
StackReference<mirror::Object>* mark_stack_obj,
bool clear_card)
: MarkStackTask<false>(thread_pool, mark_sweep, mark_stack_size, mark_stack_obj),
bitmap_(bitmap),
begin_(begin),
end_(end),
minimum_age_(minimum_age),
clear_card_(clear_card) {}
protected:
accounting::ContinuousSpaceBitmap* const bitmap_;
uint8_t* const begin_;
uint8_t* const end_;
const uint8_t minimum_age_;
const bool clear_card_;
void Finalize() override {
delete this;
}
void Run(Thread* self) override NO_THREAD_SAFETY_ANALYSIS {
ScanObjectParallelVisitor visitor(this);
accounting::CardTable* card_table = mark_sweep_->GetHeap()->GetCardTable();
size_t cards_scanned = clear_card_
? card_table->Scan<true>(bitmap_, begin_, end_, visitor, minimum_age_)
: card_table->Scan<false>(bitmap_, begin_, end_, visitor, minimum_age_);
VLOG(heap) << "Parallel scanning cards " << reinterpret_cast<void*>(begin_) << " - "
<< reinterpret_cast<void*>(end_) << " = " << cards_scanned;
// Finish by emptying our local mark stack.
MarkStackTask::Run(self);
}
};
size_t MarkSweep::GetThreadCount(bool paused) const {
// Use less threads if we are in a background state (non jank perceptible) since we want to leave
// more CPU time for the foreground apps.
if (heap_->GetThreadPool() == nullptr || !Runtime::Current()->InJankPerceptibleProcessState()) {
return 1;
}
return (paused ? heap_->GetParallelGCThreadCount() : heap_->GetConcGCThreadCount()) + 1;
}
void MarkSweep::ScanGrayObjects(bool paused, uint8_t 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 > 1) {
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.
TimingLogger::ScopedTiming t(paused ? "(Paused)ScanGrayObjects" : __FUNCTION__,
GetTimings());
// Try to take some of the mark stack since we can pass this off to the worker tasks.
StackReference<mirror::Object>* mark_stack_begin = mark_stack_->Begin();
StackReference<mirror::Object>* mark_stack_end = 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()) {
if (space->GetMarkBitmap() == nullptr) {
continue;
}
uint8_t* card_begin = space->Begin();
uint8_t* card_end = space->End();
// Align up the end address. For example, the image space's end
// may not be card-size-aligned.
card_end = AlignUp(card_end, accounting::CardTable::kCardSize);
DCHECK_ALIGNED(card_begin, accounting::CardTable::kCardSize);
DCHECK_ALIGNED(card_end, accounting::CardTable::kCardSize);
// 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);
// If paused and the space is neither zygote nor image space, we could clear the dirty
// cards to avoid accumulating them to increase card scanning load in the following GC
// cycles. We need to keep dirty cards of image space and zygote space in order to track
// references to the other spaces.
bool clear_card = paused && !space->IsZygoteSpace() && !space->IsImageSpace();
// 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,
clear_card);
thread_pool->AddTask(self, task);
card_begin += card_increment;
}
}
// Note: the card scan below may dirty new cards (and scan them)
// as a side effect when a Reference object is encountered and
// queued during the marking. See b/11465268.
thread_pool->SetMaxActiveWorkers(thread_count - 1);
thread_pool->StartWorkers(self);
thread_pool->Wait(self, true, true);
thread_pool->StopWorkers(self);
} else {
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
if (space->GetMarkBitmap() != nullptr) {
// Image spaces are handled properly since live == marked for them.
const char* name = nullptr;
switch (space->GetGcRetentionPolicy()) {
case space::kGcRetentionPolicyNeverCollect:
name = paused ? "(Paused)ScanGrayImageSpaceObjects" : "ScanGrayImageSpaceObjects";
break;
case space::kGcRetentionPolicyFullCollect:
name = paused ? "(Paused)ScanGrayZygoteSpaceObjects" : "ScanGrayZygoteSpaceObjects";
break;
case space::kGcRetentionPolicyAlwaysCollect:
name = paused ? "(Paused)ScanGrayAllocSpaceObjects" : "ScanGrayAllocSpaceObjects";
break;
default:
LOG(FATAL) << "Unreachable";
UNREACHABLE();
}
TimingLogger::ScopedTiming t(name, GetTimings());
ScanObjectVisitor visitor(this);
bool clear_card = paused && !space->IsZygoteSpace() && !space->IsImageSpace();
if (clear_card) {
card_table->Scan<true>(space->GetMarkBitmap(),
space->Begin(),
space->End(),
visitor,
minimum_age);
} else {
card_table->Scan<false>(space->GetMarkBitmap(),
space->Begin(),
space->End(),
visitor,
minimum_age);
}
}
}
}
}
class MarkSweep::RecursiveMarkTask : public MarkStackTask<false> {
public:
RecursiveMarkTask(ThreadPool* thread_pool,
MarkSweep* mark_sweep,
accounting::ContinuousSpaceBitmap* bitmap,
uintptr_t begin,
uintptr_t end)
: MarkStackTask<false>(thread_pool, mark_sweep, 0, nullptr),
bitmap_(bitmap),
begin_(begin),
end_(end) {}
protected:
accounting::ContinuousSpaceBitmap* const bitmap_;
const uintptr_t begin_;
const uintptr_t end_;
void Finalize() override {
delete this;
}
// Scans all of the objects
void Run(Thread* self) override 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() {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
// RecursiveMark will build the lists of known instances of the Reference classes. See
// DelayReferenceReferent for details.
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_space_bitmap_ = space->GetMarkBitmap();
if (current_space_bitmap_ == nullptr) {
continue;
}
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_.store(AtomicInteger::MaxValue(), std::memory_order_relaxed);
// 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_space_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_space_bitmap_->VisitMarkedRange(begin, end, scan_visitor);
}
}
}
}
ProcessMarkStack(false);
}
void MarkSweep::RecursiveMarkDirtyObjects(bool paused, uint8_t minimum_age) {
ScanGrayObjects(paused, minimum_age);
ProcessMarkStack(paused);
}
void MarkSweep::ReMarkRoots() {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
Locks::mutator_lock_->AssertExclusiveHeld(Thread::Current());
Runtime::Current()->VisitRoots(this, static_cast<VisitRootFlags>(
kVisitRootFlagNewRoots | kVisitRootFlagStopLoggingNewRoots | kVisitRootFlagClearRootLog));
if (kVerifyRootsMarked) {
TimingLogger::ScopedTiming t2("(Paused)VerifyRoots", GetTimings());
VerifyRootMarkedVisitor visitor(this);
Runtime::Current()->VisitRoots(&visitor);
}
}
void MarkSweep::SweepSystemWeaks(Thread* self) {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
Runtime::Current()->SweepSystemWeaks(this);
}
class MarkSweep::VerifySystemWeakVisitor : public IsMarkedVisitor {
public:
explicit VerifySystemWeakVisitor(MarkSweep* mark_sweep) : mark_sweep_(mark_sweep) {}
mirror::Object* IsMarked(mirror::Object* obj) override
REQUIRES_SHARED(Locks::mutator_lock_, Locks::heap_bitmap_lock_) {
mark_sweep_->VerifyIsLive(obj);
return obj;
}
MarkSweep* const mark_sweep_;
};
void MarkSweep::VerifyIsLive(const mirror::Object* obj) {
if (!heap_->GetLiveBitmap()->Test(obj)) {
// TODO: Consider live stack? Has this code bitrotted?
CHECK(!heap_->allocation_stack_->Contains(obj))
<< "Found dead object " << obj << "\n" << heap_->DumpSpaces();
}
}
void MarkSweep::VerifySystemWeaks() {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
// Verify system weaks, uses a special object visitor which returns the input object.
VerifySystemWeakVisitor visitor(this);
Runtime* runtime = Runtime::Current();
runtime->SweepSystemWeaks(&visitor);
}
class MarkSweep::CheckpointMarkThreadRoots : public Closure, public RootVisitor {
public:
CheckpointMarkThreadRoots(MarkSweep* mark_sweep,
bool revoke_ros_alloc_thread_local_buffers_at_checkpoint)
: mark_sweep_(mark_sweep),
revoke_ros_alloc_thread_local_buffers_at_checkpoint_(
revoke_ros_alloc_thread_local_buffers_at_checkpoint) {
}
void VisitRoots(mirror::Object*** roots,
size_t count,
[[maybe_unused]] const RootInfo& info) override
REQUIRES_SHARED(Locks::mutator_lock_) REQUIRES(Locks::heap_bitmap_lock_) {
for (size_t i = 0; i < count; ++i) {
mark_sweep_->MarkObjectNonNullParallel(*roots[i]);
}
}
void VisitRoots(mirror::CompressedReference<mirror::Object>** roots,
size_t count,
[[maybe_unused]] const RootInfo& info) override
REQUIRES_SHARED(Locks::mutator_lock_) REQUIRES(Locks::heap_bitmap_lock_) {
for (size_t i = 0; i < count; ++i) {
mark_sweep_->MarkObjectNonNullParallel(roots[i]->AsMirrorPtr());
}
}
void Run(Thread* thread) override NO_THREAD_SAFETY_ANALYSIS {
ScopedTrace trace("Marking thread roots");
// Note: self is not necessarily equal to thread since thread may be suspended.
Thread* const self = Thread::Current();
CHECK(thread == self ||
thread->IsSuspended() ||
thread->GetState() == ThreadState::kWaitingPerformingGc)
<< thread->GetState() << " thread " << thread << " self " << self;
thread->VisitRoots(this, kVisitRootFlagAllRoots);
if (revoke_ros_alloc_thread_local_buffers_at_checkpoint_) {
ScopedTrace trace2("RevokeRosAllocThreadLocalBuffers");
mark_sweep_->GetHeap()->RevokeRosAllocThreadLocalBuffers(thread);
}
// If thread is a running mutator, then act on behalf of the garbage collector.
// See the code in ThreadList::RunCheckpoint.
mark_sweep_->GetBarrier().Pass(self);
}
private:
MarkSweep* const mark_sweep_;
const bool revoke_ros_alloc_thread_local_buffers_at_checkpoint_;
};
void MarkSweep::MarkRootsCheckpoint(Thread* self,
bool revoke_ros_alloc_thread_local_buffers_at_checkpoint) {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
CheckpointMarkThreadRoots check_point(this, revoke_ros_alloc_thread_local_buffers_at_checkpoint);
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.
// If there are no threads to wait which implys that all the checkpoint functions are finished,
// then no need to release locks.
if (barrier_count == 0) {
return;
}
Locks::heap_bitmap_lock_->ExclusiveUnlock(self);
Locks::mutator_lock_->SharedUnlock(self);
{
ScopedThreadStateChange tsc(self, ThreadState::kWaitingForCheckPointsToRun);
gc_barrier_->Increment(self, barrier_count);
}
Locks::mutator_lock_->SharedLock(self);
Locks::heap_bitmap_lock_->ExclusiveLock(self);
}
void MarkSweep::SweepArray(accounting::ObjectStack* allocations, bool swap_bitmaps) {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
Thread* self = Thread::Current();
mirror::Object** chunk_free_buffer = reinterpret_cast<mirror::Object**>(
sweep_array_free_buffer_mem_map_.BaseBegin());
size_t chunk_free_pos = 0;
ObjectBytePair freed;
ObjectBytePair freed_los;
// How many objects are left in the array, modified after each space is swept.
StackReference<mirror::Object>* objects = allocations->Begin();
size_t count = allocations->Size();
// Change the order to ensure that the non-moving space last swept as an optimization.
std::vector<space::ContinuousSpace*> sweep_spaces;
space::ContinuousSpace* non_moving_space = nullptr;
for (space::ContinuousSpace* space : heap_->GetContinuousSpaces()) {
if (space->IsAllocSpace() &&
!immune_spaces_.ContainsSpace(space) &&
space->GetLiveBitmap() != nullptr) {
if (space == heap_->GetNonMovingSpace()) {
non_moving_space = space;
} else {
sweep_spaces.push_back(space);
}
}
}
// Unlikely to sweep a significant amount of non_movable objects, so we do these after
// the other alloc spaces as an optimization.
if (non_moving_space != nullptr) {
sweep_spaces.push_back(non_moving_space);
}
// Start by sweeping the continuous spaces.
for (space::ContinuousSpace* space : sweep_spaces) {
space::AllocSpace* alloc_space = space->AsAllocSpace();
accounting::ContinuousSpaceBitmap* live_bitmap = space->GetLiveBitmap();
accounting::ContinuousSpaceBitmap* mark_bitmap = space->GetMarkBitmap();
if (swap_bitmaps) {
std::swap(live_bitmap, mark_bitmap);
}
StackReference<mirror::Object>* out = objects;
for (size_t i = 0; i < count; ++i) {
mirror::Object* const obj = objects[i].AsMirrorPtr();
if (kUseThreadLocalAllocationStack && obj == nullptr) {
continue;
}
if (space->HasAddress(obj)) {
// This object is in the space, remove it from the array and add it to the sweep buffer
// if needed.
if (!mark_bitmap->Test(obj)) {
if (chunk_free_pos >= kSweepArrayChunkFreeSize) {
TimingLogger::ScopedTiming t2("FreeList", GetTimings());
freed.objects += chunk_free_pos;
freed.bytes += alloc_space->FreeList(self, chunk_free_pos, chunk_free_buffer);
chunk_free_pos = 0;
}
chunk_free_buffer[chunk_free_pos++] = obj;
}
} else {
(out++)->Assign(obj);
}
}
if (chunk_free_pos > 0) {
TimingLogger::ScopedTiming t2("FreeList", GetTimings());
freed.objects += chunk_free_pos;
freed.bytes += alloc_space->FreeList(self, chunk_free_pos, chunk_free_buffer);
chunk_free_pos = 0;
}
// All of the references which space contained are no longer in the allocation stack, update
// the count.
count = out - objects;
}
// Handle the large object space.
space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace();
if (large_object_space != nullptr) {
accounting::LargeObjectBitmap* large_live_objects = large_object_space->GetLiveBitmap();
accounting::LargeObjectBitmap* large_mark_objects = large_object_space->GetMarkBitmap();
if (swap_bitmaps) {
std::swap(large_live_objects, large_mark_objects);
}
for (size_t i = 0; i < count; ++i) {
mirror::Object* const obj = objects[i].AsMirrorPtr();
// Handle large objects.
if (kUseThreadLocalAllocationStack && obj == nullptr) {
continue;
}
if (!large_mark_objects->Test(obj)) {
++freed_los.objects;
freed_los.bytes += large_object_space->Free(self, obj);
}
}
}
{
TimingLogger::ScopedTiming t2("RecordFree", GetTimings());
RecordFree(freed);
RecordFreeLOS(freed_los);
t2.NewTiming("ResetStack");
allocations->Reset();
}
sweep_array_free_buffer_mem_map_.MadviseDontNeedAndZero();
}
void MarkSweep::Sweep(bool swap_bitmaps) {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
// Ensure that nobody inserted items in the live stack after we swapped the stacks.
CHECK_GE(live_stack_freeze_size_, GetHeap()->GetLiveStack()->Size());
{
TimingLogger::ScopedTiming t2("MarkAllocStackAsLive", GetTimings());
// Mark everything allocated since the last GC as live so that we can sweep concurrently,
// knowing that new allocations won't be marked as live.
accounting::ObjectStack* live_stack = heap_->GetLiveStack();
heap_->MarkAllocStackAsLive(live_stack);
live_stack->Reset();
DCHECK(mark_stack_->IsEmpty());
}
for (const auto& space : GetHeap()->GetContinuousSpaces()) {
if (space->IsContinuousMemMapAllocSpace()) {
space::ContinuousMemMapAllocSpace* alloc_space = space->AsContinuousMemMapAllocSpace();
TimingLogger::ScopedTiming split(
alloc_space->IsZygoteSpace() ? "SweepZygoteSpace" : "SweepMallocSpace",
GetTimings());
RecordFree(alloc_space->Sweep(swap_bitmaps));
}
}
SweepLargeObjects(swap_bitmaps);
}
void MarkSweep::SweepLargeObjects(bool swap_bitmaps) {
space::LargeObjectSpace* los = heap_->GetLargeObjectsSpace();
if (los != nullptr) {
TimingLogger::ScopedTiming split(__FUNCTION__, GetTimings());
RecordFreeLOS(los->Sweep(swap_bitmaps));
}
}
// Process the "referent" field lin 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(ObjPtr<mirror::Class> klass, ObjPtr<mirror::Reference> ref) {
heap_->GetReferenceProcessor()->DelayReferenceReferent(klass, ref, this);
}
class MarkVisitor {
public:
ALWAYS_INLINE explicit MarkVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) {}
ALWAYS_INLINE void operator()(mirror::Object* obj,
MemberOffset offset,
[[maybe_unused]] bool is_static) const
REQUIRES(Locks::heap_bitmap_lock_) REQUIRES_SHARED(Locks::mutator_lock_) {
if (kCheckLocks) {
Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current());
}
mark_sweep_->MarkObject(obj->GetFieldObject<mirror::Object>(offset), obj, offset);
}
void VisitRootIfNonNull(mirror::CompressedReference<mirror::Object>* root) const
REQUIRES(Locks::heap_bitmap_lock_)
REQUIRES_SHARED(Locks::mutator_lock_) {
if (!root->IsNull()) {
VisitRoot(root);
}
}
void VisitRoot(mirror::CompressedReference<mirror::Object>* root) const
REQUIRES(Locks::heap_bitmap_lock_)
REQUIRES_SHARED(Locks::mutator_lock_) {
if (kCheckLocks) {
Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current());
}
mark_sweep_->MarkObject(root->AsMirrorPtr());
}
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(mirror::Object* obj) {
MarkVisitor mark_visitor(this);
DelayReferenceReferentVisitor ref_visitor(this);
ScanObjectVisit(obj, mark_visitor, ref_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 (auto* 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, 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_.load(std::memory_order_seq_cst),
work_chunks_deleted_.load(std::memory_order_seq_cst))
<< " some of the work chunks were leaked";
}
// Scan anything that's on the mark stack.
void MarkSweep::ProcessMarkStack(bool paused) {
TimingLogger::ScopedTiming t(paused ? "(Paused)ProcessMarkStack" : __FUNCTION__, GetTimings());
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<mirror::Object*, kFifoSize> prefetch_fifo;
for (;;) {
mirror::Object* obj = nullptr;
if (kUseMarkStackPrefetch) {
while (!mark_stack_->IsEmpty() && prefetch_fifo.size() < kFifoSize) {
mirror::Object* mark_stack_obj = mark_stack_->PopBack();
DCHECK(mark_stack_obj != nullptr);
__builtin_prefetch(mark_stack_obj);
prefetch_fifo.push_back(mark_stack_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 != nullptr);
ScanObject(obj);
}
}
}
inline mirror::Object* MarkSweep::IsMarked(mirror::Object* object) {
if (immune_spaces_.IsInImmuneRegion(object)) {
return object;
}
if (current_space_bitmap_->HasAddress(object)) {
return current_space_bitmap_->Test(object) ? object : nullptr;
}
// This function returns nullptr for objects allocated after marking phase as
// they are not marked in the bitmap.
return mark_bitmap_->Test(object) ? object : nullptr;
}
void MarkSweep::FinishPhase() {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
if (kCountScannedTypes) {
VLOG(gc)
<< "MarkSweep scanned"
<< " no reference objects=" << no_reference_class_count_.load(std::memory_order_relaxed)
<< " normal objects=" << normal_count_.load(std::memory_order_relaxed)
<< " classes=" << class_count_.load(std::memory_order_relaxed)
<< " object arrays=" << object_array_count_.load(std::memory_order_relaxed)
<< " references=" << reference_count_.load(std::memory_order_relaxed)
<< " other=" << other_count_.load(std::memory_order_relaxed);
}
if (kCountTasks) {
VLOG(gc)
<< "Total number of work chunks allocated: "
<< work_chunks_created_.load(std::memory_order_relaxed);
}
if (kMeasureOverhead) {
VLOG(gc) << "Overhead time " << PrettyDuration(overhead_time_.load(std::memory_order_relaxed));
}
if (kProfileLargeObjects) {
VLOG(gc)
<< "Large objects tested " << large_object_test_.load(std::memory_order_relaxed)
<< " marked " << large_object_mark_.load(std::memory_order_relaxed);
}
if (kCountMarkedObjects) {
VLOG(gc)
<< "Marked: null=" << mark_null_count_.load(std::memory_order_relaxed)
<< " immune=" << mark_immune_count_.load(std::memory_order_relaxed)
<< " fastpath=" << mark_fastpath_count_.load(std::memory_order_relaxed)
<< " slowpath=" << mark_slowpath_count_.load(std::memory_order_relaxed);
}
CHECK(mark_stack_->IsEmpty()); // Ensure that the mark stack is empty.
mark_stack_->Reset();
Thread* const self = Thread::Current();
ReaderMutexLock mu(self, *Locks::mutator_lock_);
WriterMutexLock mu2(self, *Locks::heap_bitmap_lock_);
heap_->ClearMarkedObjects();
}
void MarkSweep::RevokeAllThreadLocalBuffers() {
if (kRevokeRosAllocThreadLocalBuffersAtCheckpoint && IsConcurrent()) {
// If concurrent, rosalloc thread-local buffers are revoked at the
// thread checkpoint. Bump pointer space thread-local buffers must
// not be in use.
GetHeap()->AssertAllBumpPointerSpaceThreadLocalBuffersAreRevoked();
} else {
TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
GetHeap()->RevokeAllThreadLocalBuffers();
}
}
} // namespace collector
} // namespace gc
} // namespace art