206 lines
8.4 KiB
C++
206 lines
8.4 KiB
C++
/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef ART_RUNTIME_GC_COLLECTOR_CONCURRENT_COPYING_INL_H_
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#define ART_RUNTIME_GC_COLLECTOR_CONCURRENT_COPYING_INL_H_
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#include "concurrent_copying.h"
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#include "gc/accounting/atomic_stack.h"
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#include "gc/accounting/space_bitmap-inl.h"
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#include "gc/heap.h"
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#include "gc/space/region_space.h"
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#include "lock_word.h"
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#include "mirror/object-readbarrier-inl.h"
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namespace art {
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namespace gc {
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namespace collector {
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inline mirror::Object* ConcurrentCopying::MarkUnevacFromSpaceRegion(
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mirror::Object* ref, accounting::ContinuousSpaceBitmap* bitmap) {
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// For the Baker-style RB, in a rare case, we could incorrectly change the object from white
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// to gray even though the object has already been marked through. This happens if a mutator
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// thread gets preempted before the AtomicSetReadBarrierState below, GC marks through the
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// object (changes it from white to gray and back to white), and the thread runs and
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// incorrectly changes it from white to gray. If this happens, the object will get added to the
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// mark stack again and get changed back to white after it is processed.
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if (kUseBakerReadBarrier) {
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// Test the bitmap first to avoid graying an object that has already been marked through most
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// of the time.
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if (bitmap->Test(ref)) {
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return ref;
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}
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}
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// This may or may not succeed, which is ok because the object may already be gray.
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bool success = false;
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if (kUseBakerReadBarrier) {
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// GC will mark the bitmap when popping from mark stack. If only the GC is touching the bitmap
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// we can avoid an expensive CAS.
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// For the baker case, an object is marked if either the mark bit marked or the bitmap bit is
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// set.
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success = ref->AtomicSetReadBarrierState(ReadBarrier::WhiteState(), ReadBarrier::GrayState());
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} else {
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success = !bitmap->AtomicTestAndSet(ref);
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}
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if (success) {
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// Newly marked.
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if (kUseBakerReadBarrier) {
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DCHECK_EQ(ref->GetReadBarrierState(), ReadBarrier::GrayState());
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}
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PushOntoMarkStack(ref);
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}
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return ref;
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}
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template<bool kGrayImmuneObject>
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inline mirror::Object* ConcurrentCopying::MarkImmuneSpace(mirror::Object* ref) {
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if (kUseBakerReadBarrier) {
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// The GC-running thread doesn't (need to) gray immune objects except when updating thread roots
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// in the thread flip on behalf of suspended threads (when gc_grays_immune_objects_ is
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// true). Also, a mutator doesn't (need to) gray an immune object after GC has updated all
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// immune space objects (when updated_all_immune_objects_ is true).
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if (kIsDebugBuild) {
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if (Thread::Current() == thread_running_gc_) {
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DCHECK(!kGrayImmuneObject ||
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updated_all_immune_objects_.LoadRelaxed() ||
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gc_grays_immune_objects_);
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} else {
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DCHECK(kGrayImmuneObject);
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}
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}
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if (!kGrayImmuneObject || updated_all_immune_objects_.LoadRelaxed()) {
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return ref;
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}
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// This may or may not succeed, which is ok because the object may already be gray.
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bool success = ref->AtomicSetReadBarrierState(ReadBarrier::WhiteState(),
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ReadBarrier::GrayState());
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if (success) {
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MutexLock mu(Thread::Current(), immune_gray_stack_lock_);
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immune_gray_stack_.push_back(ref);
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}
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}
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return ref;
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}
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template<bool kGrayImmuneObject, bool kFromGCThread>
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inline mirror::Object* ConcurrentCopying::Mark(mirror::Object* from_ref,
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mirror::Object* holder,
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MemberOffset offset) {
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if (from_ref == nullptr) {
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return nullptr;
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}
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DCHECK(heap_->collector_type_ == kCollectorTypeCC);
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if (kFromGCThread) {
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DCHECK(is_active_);
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DCHECK_EQ(Thread::Current(), thread_running_gc_);
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} else if (UNLIKELY(kUseBakerReadBarrier && !is_active_)) {
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// In the lock word forward address state, the read barrier bits
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// in the lock word are part of the stored forwarding address and
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// invalid. This is usually OK as the from-space copy of objects
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// aren't accessed by mutators due to the to-space
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// invariant. However, during the dex2oat image writing relocation
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// and the zygote compaction, objects can be in the forward
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// address state (to store the forward/relocation addresses) and
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// they can still be accessed and the invalid read barrier bits
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// are consulted. If they look like gray but aren't really, the
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// read barriers slow path can trigger when it shouldn't. To guard
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// against this, return here if the CC collector isn't running.
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return from_ref;
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}
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DCHECK(region_space_ != nullptr) << "Read barrier slow path taken when CC isn't running?";
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space::RegionSpace::RegionType rtype = region_space_->GetRegionType(from_ref);
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switch (rtype) {
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case space::RegionSpace::RegionType::kRegionTypeToSpace:
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// It's already marked.
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return from_ref;
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case space::RegionSpace::RegionType::kRegionTypeFromSpace: {
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mirror::Object* to_ref = GetFwdPtr(from_ref);
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if (to_ref == nullptr) {
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// It isn't marked yet. Mark it by copying it to the to-space.
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to_ref = Copy(from_ref, holder, offset);
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}
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DCHECK(region_space_->IsInToSpace(to_ref) || heap_->non_moving_space_->HasAddress(to_ref))
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<< "from_ref=" << from_ref << " to_ref=" << to_ref;
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return to_ref;
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}
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case space::RegionSpace::RegionType::kRegionTypeUnevacFromSpace: {
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return MarkUnevacFromSpaceRegion(from_ref, region_space_bitmap_);
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}
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case space::RegionSpace::RegionType::kRegionTypeNone:
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if (immune_spaces_.ContainsObject(from_ref)) {
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return MarkImmuneSpace<kGrayImmuneObject>(from_ref);
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} else {
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return MarkNonMoving(from_ref, holder, offset);
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}
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default:
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UNREACHABLE();
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}
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}
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inline mirror::Object* ConcurrentCopying::MarkFromReadBarrier(mirror::Object* from_ref) {
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mirror::Object* ret;
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// We can get here before marking starts since we gray immune objects before the marking phase.
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if (from_ref == nullptr || !Thread::Current()->GetIsGcMarking()) {
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return from_ref;
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}
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// TODO: Consider removing this check when we are done investigating slow paths. b/30162165
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if (UNLIKELY(mark_from_read_barrier_measurements_)) {
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ret = MarkFromReadBarrierWithMeasurements(from_ref);
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} else {
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ret = Mark(from_ref);
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}
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// Only set the mark bit for baker barrier.
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if (kUseBakerReadBarrier && LIKELY(!rb_mark_bit_stack_full_ && ret->AtomicSetMarkBit(0, 1))) {
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// If the mark stack is full, we may temporarily go to mark and back to unmarked. Seeing both
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// values are OK since the only race is doing an unnecessary Mark.
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if (!rb_mark_bit_stack_->AtomicPushBack(ret)) {
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// Mark stack is full, set the bit back to zero.
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CHECK(ret->AtomicSetMarkBit(1, 0));
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// Set rb_mark_bit_stack_full_, this is racy but OK since AtomicPushBack is thread safe.
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rb_mark_bit_stack_full_ = true;
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}
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}
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return ret;
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}
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inline mirror::Object* ConcurrentCopying::GetFwdPtr(mirror::Object* from_ref) {
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DCHECK(region_space_->IsInFromSpace(from_ref));
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LockWord lw = from_ref->GetLockWord(false);
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if (lw.GetState() == LockWord::kForwardingAddress) {
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mirror::Object* fwd_ptr = reinterpret_cast<mirror::Object*>(lw.ForwardingAddress());
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DCHECK(fwd_ptr != nullptr);
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return fwd_ptr;
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} else {
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return nullptr;
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}
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}
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inline bool ConcurrentCopying::IsMarkedInUnevacFromSpace(mirror::Object* from_ref) {
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// Use load acquire on the read barrier pointer to ensure that we never see a white read barrier
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// state with an unmarked bit due to reordering.
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DCHECK(region_space_->IsInUnevacFromSpace(from_ref));
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if (kUseBakerReadBarrier && from_ref->GetReadBarrierStateAcquire() == ReadBarrier::GrayState()) {
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return true;
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}
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return region_space_bitmap_->Test(from_ref);
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}
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} // namespace collector
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} // namespace gc
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} // namespace art
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#endif // ART_RUNTIME_GC_COLLECTOR_CONCURRENT_COPYING_INL_H_
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