| /* |
| * Copyright (C) 2015 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. |
| */ |
| |
| #ifndef ART_RUNTIME_GC_COLLECTOR_CONCURRENT_COPYING_INL_H_ |
| #define ART_RUNTIME_GC_COLLECTOR_CONCURRENT_COPYING_INL_H_ |
| |
| #include "concurrent_copying.h" |
| |
| #include "gc/accounting/atomic_stack.h" |
| #include "gc/accounting/space_bitmap-inl.h" |
| #include "gc/heap.h" |
| #include "gc/space/region_space-inl.h" |
| #include "gc/verification.h" |
| #include "lock_word.h" |
| #include "mirror/class.h" |
| #include "mirror/object-readbarrier-inl.h" |
| |
| namespace art { |
| namespace gc { |
| namespace collector { |
| |
| inline mirror::Object* ConcurrentCopying::MarkUnevacFromSpaceRegion( |
| Thread* const self, |
| mirror::Object* ref, |
| accounting::ContinuousSpaceBitmap* bitmap) { |
| if (use_generational_cc_ && !done_scanning_.load(std::memory_order_acquire)) { |
| // Everything in the unevac space should be marked for young generation CC, |
| // except for large objects. |
| DCHECK(!young_gen_ || region_space_bitmap_->Test(ref) || region_space_->IsLargeObject(ref)) |
| << ref << " " |
| << ref->GetClass<kVerifyNone, kWithoutReadBarrier>()->PrettyClass(); |
| // Since the mark bitmap is still filled in from last GC (or from marking phase of 2-phase CC, |
| // we can not use that or else the mutator may see references to the from space. Instead, use |
| // the baker pointer itself as the mark bit. |
| if (ref->AtomicSetReadBarrierState(ReadBarrier::NonGrayState(), ReadBarrier::GrayState())) { |
| // TODO: We don't actually need to scan this object later, we just need to clear the gray |
| // bit. |
| // TODO: We could also set the mark bit here for "free" since this case comes from the |
| // read barrier. |
| PushOntoMarkStack(self, ref); |
| } |
| DCHECK_EQ(ref->GetReadBarrierState(), ReadBarrier::GrayState()); |
| return ref; |
| } |
| // For the Baker-style RB, in a rare case, we could incorrectly change the object from non-gray |
| // (black) to gray even though the object has already been marked through. This happens if a |
| // mutator thread gets preempted before the AtomicSetReadBarrierState below, GC marks through the |
| // object (changes it from non-gray (white) to gray and back to non-gray (black)), and the thread |
| // runs and incorrectly changes it from non-gray (black) to gray. If this happens, the object |
| // will get added to the mark stack again and get changed back to non-gray (black) after it is |
| // processed. |
| if (kUseBakerReadBarrier) { |
| // Test the bitmap first to avoid graying an object that has already been marked through most |
| // of the time. |
| if (bitmap->Test(ref)) { |
| return ref; |
| } |
| } |
| // This may or may not succeed, which is ok because the object may already be gray. |
| bool success = false; |
| if (kUseBakerReadBarrier) { |
| // GC will mark the bitmap when popping from mark stack. If only the GC is touching the bitmap |
| // we can avoid an expensive CAS. |
| // For the baker case, an object is marked if either the mark bit marked or the bitmap bit is |
| // set. |
| success = ref->AtomicSetReadBarrierState(/* expected_rb_state= */ ReadBarrier::NonGrayState(), |
| /* rb_state= */ ReadBarrier::GrayState()); |
| } else { |
| success = !bitmap->AtomicTestAndSet(ref); |
| } |
| if (success) { |
| // Newly marked. |
| if (kUseBakerReadBarrier) { |
| DCHECK_EQ(ref->GetReadBarrierState(), ReadBarrier::GrayState()); |
| } |
| PushOntoMarkStack(self, ref); |
| } |
| return ref; |
| } |
| |
| template<bool kGrayImmuneObject> |
| inline mirror::Object* ConcurrentCopying::MarkImmuneSpace(Thread* const self, |
| mirror::Object* ref) { |
| if (kUseBakerReadBarrier) { |
| // The GC-running thread doesn't (need to) gray immune objects except when updating thread roots |
| // in the thread flip on behalf of suspended threads (when gc_grays_immune_objects_ is |
| // true). Also, a mutator doesn't (need to) gray an immune object after GC has updated all |
| // immune space objects (when updated_all_immune_objects_ is true). |
| if (kIsDebugBuild) { |
| if (self == thread_running_gc_) { |
| DCHECK(!kGrayImmuneObject || |
| updated_all_immune_objects_.load(std::memory_order_relaxed) || |
| gc_grays_immune_objects_); |
| } else { |
| DCHECK(kGrayImmuneObject); |
| } |
| } |
| if (!kGrayImmuneObject || updated_all_immune_objects_.load(std::memory_order_relaxed)) { |
| return ref; |
| } |
| // This may or may not succeed, which is ok because the object may already be gray. |
| bool success = |
| ref->AtomicSetReadBarrierState(/* expected_rb_state= */ ReadBarrier::NonGrayState(), |
| /* rb_state= */ ReadBarrier::GrayState()); |
| if (success) { |
| MutexLock mu(self, immune_gray_stack_lock_); |
| immune_gray_stack_.push_back(ref); |
| } |
| } |
| return ref; |
| } |
| |
| template<bool kGrayImmuneObject, bool kNoUnEvac, bool kFromGCThread> |
| inline mirror::Object* ConcurrentCopying::Mark(Thread* const self, |
| mirror::Object* from_ref, |
| mirror::Object* holder, |
| MemberOffset offset) { |
| // Cannot have `kNoUnEvac` when Generational CC collection is disabled. |
| DCHECK_IMPLIES(kNoUnEvac, use_generational_cc_); |
| if (from_ref == nullptr) { |
| return nullptr; |
| } |
| DCHECK(heap_->collector_type_ == kCollectorTypeCC); |
| if (kFromGCThread) { |
| DCHECK(is_active_); |
| DCHECK_EQ(self, thread_running_gc_); |
| } else if (UNLIKELY(kUseBakerReadBarrier && !is_active_)) { |
| // In the lock word forward address state, the read barrier bits |
| // in the lock word are part of the stored forwarding address and |
| // invalid. This is usually OK as the from-space copy of objects |
| // aren't accessed by mutators due to the to-space |
| // invariant. However, during the dex2oat image writing relocation |
| // and the zygote compaction, objects can be in the forward |
| // address state (to store the forward/relocation addresses) and |
| // they can still be accessed and the invalid read barrier bits |
| // are consulted. If they look like gray but aren't really, the |
| // read barriers slow path can trigger when it shouldn't. To guard |
| // against this, return here if the CC collector isn't running. |
| return from_ref; |
| } |
| DCHECK(region_space_ != nullptr) << "Read barrier slow path taken when CC isn't running?"; |
| if (region_space_->HasAddress(from_ref)) { |
| space::RegionSpace::RegionType rtype = region_space_->GetRegionTypeUnsafe(from_ref); |
| switch (rtype) { |
| case space::RegionSpace::RegionType::kRegionTypeToSpace: |
| // It's already marked. |
| return from_ref; |
| case space::RegionSpace::RegionType::kRegionTypeFromSpace: { |
| mirror::Object* to_ref = GetFwdPtr(from_ref); |
| if (to_ref == nullptr) { |
| // It isn't marked yet. Mark it by copying it to the to-space. |
| to_ref = Copy(self, from_ref, holder, offset); |
| } |
| // The copy should either be in a to-space region, or in the |
| // non-moving space, if it could not fit in a to-space region. |
| DCHECK(region_space_->IsInToSpace(to_ref) || heap_->non_moving_space_->HasAddress(to_ref)) |
| << "from_ref=" << from_ref << " to_ref=" << to_ref; |
| return to_ref; |
| } |
| case space::RegionSpace::RegionType::kRegionTypeUnevacFromSpace: |
| if (kNoUnEvac && use_generational_cc_ && !region_space_->IsLargeObject(from_ref)) { |
| if (!kFromGCThread) { |
| DCHECK(IsMarkedInUnevacFromSpace(from_ref)) << "Returning unmarked object to mutator"; |
| } |
| return from_ref; |
| } |
| return MarkUnevacFromSpaceRegion(self, from_ref, region_space_bitmap_); |
| default: |
| // The reference is in an unused region. Remove memory protection from |
| // the region space and log debugging information. |
| region_space_->Unprotect(); |
| LOG(FATAL_WITHOUT_ABORT) << DumpHeapReference(holder, offset, from_ref); |
| region_space_->DumpNonFreeRegions(LOG_STREAM(FATAL_WITHOUT_ABORT)); |
| heap_->GetVerification()->LogHeapCorruption(holder, offset, from_ref, /* fatal= */ true); |
| UNREACHABLE(); |
| } |
| } else { |
| if (immune_spaces_.ContainsObject(from_ref)) { |
| return MarkImmuneSpace<kGrayImmuneObject>(self, from_ref); |
| } else { |
| return MarkNonMoving(self, from_ref, holder, offset); |
| } |
| } |
| } |
| |
| inline mirror::Object* ConcurrentCopying::MarkFromReadBarrier(mirror::Object* from_ref) { |
| mirror::Object* ret; |
| Thread* const self = Thread::Current(); |
| // We can get here before marking starts since we gray immune objects before the marking phase. |
| if (from_ref == nullptr || !self->GetIsGcMarking()) { |
| return from_ref; |
| } |
| // TODO: Consider removing this check when we are done investigating slow paths. b/30162165 |
| if (UNLIKELY(mark_from_read_barrier_measurements_)) { |
| ret = MarkFromReadBarrierWithMeasurements(self, from_ref); |
| } else { |
| ret = Mark</*kGrayImmuneObject=*/true, /*kNoUnEvac=*/false, /*kFromGCThread=*/false>(self, |
| from_ref); |
| } |
| // Only set the mark bit for baker barrier. |
| if (kUseBakerReadBarrier && LIKELY(!rb_mark_bit_stack_full_ && ret->AtomicSetMarkBit(0, 1))) { |
| // If the mark stack is full, we may temporarily go to mark and back to unmarked. Seeing both |
| // values are OK since the only race is doing an unnecessary Mark. |
| if (!rb_mark_bit_stack_->AtomicPushBack(ret)) { |
| // Mark stack is full, set the bit back to zero. |
| CHECK(ret->AtomicSetMarkBit(1, 0)); |
| // Set rb_mark_bit_stack_full_, this is racy but OK since AtomicPushBack is thread safe. |
| rb_mark_bit_stack_full_ = true; |
| } |
| } |
| return ret; |
| } |
| |
| inline mirror::Object* ConcurrentCopying::GetFwdPtrUnchecked(mirror::Object* from_ref) { |
| LockWord lw = from_ref->GetLockWord(false); |
| if (lw.GetState() == LockWord::kForwardingAddress) { |
| mirror::Object* fwd_ptr = reinterpret_cast<mirror::Object*>(lw.ForwardingAddress()); |
| DCHECK(fwd_ptr != nullptr); |
| return fwd_ptr; |
| } else { |
| return nullptr; |
| } |
| } |
| |
| inline mirror::Object* ConcurrentCopying::GetFwdPtr(mirror::Object* from_ref) { |
| DCHECK(region_space_->IsInFromSpace(from_ref)); |
| return GetFwdPtrUnchecked(from_ref); |
| } |
| |
| inline bool ConcurrentCopying::IsMarkedInUnevacFromSpace(mirror::Object* from_ref) { |
| // Use load-acquire on the read barrier pointer to ensure that we never see a black (non-gray) |
| // read barrier state with an unmarked bit due to reordering. |
| DCHECK(region_space_->IsInUnevacFromSpace(from_ref)); |
| if (kUseBakerReadBarrier && from_ref->GetReadBarrierStateAcquire() == ReadBarrier::GrayState()) { |
| return true; |
| } else if (!use_generational_cc_ || done_scanning_.load(std::memory_order_acquire)) { |
| // If the card table scanning is not finished yet, then only read-barrier |
| // state should be checked. Checking the mark bitmap is unreliable as there |
| // may be some objects - whose corresponding card is dirty - which are |
| // marked in the mark bitmap, but cannot be considered marked unless their |
| // read-barrier state is set to Gray. |
| // |
| // Why read read-barrier state before checking done_scanning_? |
| // If the read-barrier state was read *after* done_scanning_, then there |
| // exists a concurrency race due to which even after the object is marked, |
| // read-barrier state is checked *after* that, this function will return |
| // false. The following scenario may cause the race: |
| // |
| // 1. Mutator thread reads done_scanning_ and upon finding it false, gets |
| // suspended before reading the object's read-barrier state. |
| // 2. GC thread finishes card-table scan and then sets done_scanning_ to |
| // true. |
| // 3. GC thread grays the object, scans it, marks in the bitmap, and then |
| // changes its read-barrier state back to non-gray. |
| // 4. Mutator thread resumes, reads the object's read-barrier state and |
| // returns false. |
| return region_space_bitmap_->Test(from_ref); |
| } |
| return false; |
| } |
| |
| } // namespace collector |
| } // namespace gc |
| } // namespace art |
| |
| #endif // ART_RUNTIME_GC_COLLECTOR_CONCURRENT_COPYING_INL_H_ |