1 /*
2 * Copyright (C) 2013 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "reference_queue.h"
18
19 #include "accounting/card_table-inl.h"
20 #include "collector/concurrent_copying.h"
21 #include "heap.h"
22 #include "mirror/class-inl.h"
23 #include "mirror/object-inl.h"
24 #include "mirror/reference-inl.h"
25 #include "object_callbacks.h"
26
27 namespace art {
28 namespace gc {
29
ReferenceQueue(Mutex * lock)30 ReferenceQueue::ReferenceQueue(Mutex* lock) : lock_(lock), list_(nullptr) {
31 }
32
AtomicEnqueueIfNotEnqueued(Thread * self,ObjPtr<mirror::Reference> ref)33 void ReferenceQueue::AtomicEnqueueIfNotEnqueued(Thread* self, ObjPtr<mirror::Reference> ref) {
34 DCHECK(ref != nullptr);
35 MutexLock mu(self, *lock_);
36 if (ref->IsUnprocessed()) {
37 EnqueueReference(ref);
38 }
39 }
40
EnqueueReference(ObjPtr<mirror::Reference> ref)41 void ReferenceQueue::EnqueueReference(ObjPtr<mirror::Reference> ref) {
42 DCHECK(ref != nullptr);
43 CHECK(ref->IsUnprocessed());
44 if (IsEmpty()) {
45 // 1 element cyclic queue, ie: Reference ref = ..; ref.pendingNext = ref;
46 list_ = ref.Ptr();
47 } else {
48 // The list is owned by the GC, everything that has been inserted must already be at least
49 // gray.
50 ObjPtr<mirror::Reference> head = list_->GetPendingNext<kWithoutReadBarrier>();
51 DCHECK(head != nullptr);
52 ref->SetPendingNext(head);
53 }
54 // Add the reference in the middle to preserve the cycle.
55 list_->SetPendingNext(ref);
56 }
57
DequeuePendingReference()58 ObjPtr<mirror::Reference> ReferenceQueue::DequeuePendingReference() {
59 DCHECK(!IsEmpty());
60 ObjPtr<mirror::Reference> ref = list_->GetPendingNext<kWithoutReadBarrier>();
61 DCHECK(ref != nullptr);
62 // Note: the following code is thread-safe because it is only called from ProcessReferences which
63 // is single threaded.
64 if (list_ == ref) {
65 list_ = nullptr;
66 } else {
67 ObjPtr<mirror::Reference> next = ref->GetPendingNext<kWithoutReadBarrier>();
68 list_->SetPendingNext(next);
69 }
70 ref->SetPendingNext(nullptr);
71 return ref;
72 }
73
74 // This must be called whenever DequeuePendingReference is called.
DisableReadBarrierForReference(ObjPtr<mirror::Reference> ref)75 void ReferenceQueue::DisableReadBarrierForReference(ObjPtr<mirror::Reference> ref) {
76 Heap* heap = Runtime::Current()->GetHeap();
77 if (kUseBakerOrBrooksReadBarrier && heap->CurrentCollectorType() == kCollectorTypeCC &&
78 heap->ConcurrentCopyingCollector()->IsActive()) {
79 // Change the gray ptr we left in ConcurrentCopying::ProcessMarkStackRef() to white.
80 // We check IsActive() above because we don't want to do this when the zygote compaction
81 // collector (SemiSpace) is running.
82 CHECK(ref != nullptr);
83 collector::ConcurrentCopying* concurrent_copying = heap->ConcurrentCopyingCollector();
84 uint32_t rb_state = ref->GetReadBarrierState();
85 if (rb_state == ReadBarrier::GrayState()) {
86 ref->AtomicSetReadBarrierState(ReadBarrier::GrayState(), ReadBarrier::WhiteState());
87 CHECK_EQ(ref->GetReadBarrierState(), ReadBarrier::WhiteState());
88 } else {
89 // In ConcurrentCopying::ProcessMarkStackRef() we may leave a white reference in the queue and
90 // find it here, which is OK.
91 CHECK_EQ(rb_state, ReadBarrier::WhiteState()) << "ref=" << ref << " rb_state=" << rb_state;
92 ObjPtr<mirror::Object> referent = ref->GetReferent<kWithoutReadBarrier>();
93 // The referent could be null if it's cleared by a mutator (Reference.clear()).
94 if (referent != nullptr) {
95 CHECK(concurrent_copying->IsInToSpace(referent.Ptr()))
96 << "ref=" << ref << " rb_state=" << ref->GetReadBarrierState()
97 << " referent=" << referent;
98 }
99 }
100 }
101 }
102
Dump(std::ostream & os) const103 void ReferenceQueue::Dump(std::ostream& os) const {
104 ObjPtr<mirror::Reference> cur = list_;
105 os << "Reference starting at list_=" << list_ << "\n";
106 if (cur == nullptr) {
107 return;
108 }
109 do {
110 ObjPtr<mirror::Reference> pending_next = cur->GetPendingNext();
111 os << "Reference= " << cur << " PendingNext=" << pending_next;
112 if (cur->IsFinalizerReferenceInstance()) {
113 os << " Zombie=" << cur->AsFinalizerReference()->GetZombie();
114 }
115 os << "\n";
116 cur = pending_next;
117 } while (cur != list_);
118 }
119
GetLength() const120 size_t ReferenceQueue::GetLength() const {
121 size_t count = 0;
122 ObjPtr<mirror::Reference> cur = list_;
123 if (cur != nullptr) {
124 do {
125 ++count;
126 cur = cur->GetPendingNext();
127 } while (cur != list_);
128 }
129 return count;
130 }
131
ClearWhiteReferences(ReferenceQueue * cleared_references,collector::GarbageCollector * collector)132 void ReferenceQueue::ClearWhiteReferences(ReferenceQueue* cleared_references,
133 collector::GarbageCollector* collector) {
134 while (!IsEmpty()) {
135 ObjPtr<mirror::Reference> ref = DequeuePendingReference();
136 mirror::HeapReference<mirror::Object>* referent_addr = ref->GetReferentReferenceAddr();
137 // do_atomic_update is false because this happens during the reference processing phase where
138 // Reference.clear() would block.
139 if (!collector->IsNullOrMarkedHeapReference(referent_addr, /*do_atomic_update*/false)) {
140 // Referent is white, clear it.
141 if (Runtime::Current()->IsActiveTransaction()) {
142 ref->ClearReferent<true>();
143 } else {
144 ref->ClearReferent<false>();
145 }
146 cleared_references->EnqueueReference(ref);
147 }
148 // Delay disabling the read barrier until here so that the ClearReferent call above in
149 // transaction mode will trigger the read barrier.
150 DisableReadBarrierForReference(ref);
151 }
152 }
153
EnqueueFinalizerReferences(ReferenceQueue * cleared_references,collector::GarbageCollector * collector)154 void ReferenceQueue::EnqueueFinalizerReferences(ReferenceQueue* cleared_references,
155 collector::GarbageCollector* collector) {
156 while (!IsEmpty()) {
157 ObjPtr<mirror::FinalizerReference> ref = DequeuePendingReference()->AsFinalizerReference();
158 mirror::HeapReference<mirror::Object>* referent_addr = ref->GetReferentReferenceAddr();
159 // do_atomic_update is false because this happens during the reference processing phase where
160 // Reference.clear() would block.
161 if (!collector->IsNullOrMarkedHeapReference(referent_addr, /*do_atomic_update*/false)) {
162 ObjPtr<mirror::Object> forward_address = collector->MarkObject(referent_addr->AsMirrorPtr());
163 // Move the updated referent to the zombie field.
164 if (Runtime::Current()->IsActiveTransaction()) {
165 ref->SetZombie<true>(forward_address);
166 ref->ClearReferent<true>();
167 } else {
168 ref->SetZombie<false>(forward_address);
169 ref->ClearReferent<false>();
170 }
171 cleared_references->EnqueueReference(ref);
172 }
173 // Delay disabling the read barrier until here so that the ClearReferent call above in
174 // transaction mode will trigger the read barrier.
175 DisableReadBarrierForReference(ref->AsReference());
176 }
177 }
178
ForwardSoftReferences(MarkObjectVisitor * visitor)179 void ReferenceQueue::ForwardSoftReferences(MarkObjectVisitor* visitor) {
180 if (UNLIKELY(IsEmpty())) {
181 return;
182 }
183 ObjPtr<mirror::Reference> const head = list_;
184 ObjPtr<mirror::Reference> ref = head;
185 do {
186 mirror::HeapReference<mirror::Object>* referent_addr = ref->GetReferentReferenceAddr();
187 if (referent_addr->AsMirrorPtr() != nullptr) {
188 // do_atomic_update is false because mutators can't access the referent due to the weak ref
189 // access blocking.
190 visitor->MarkHeapReference(referent_addr, /*do_atomic_update*/ false);
191 }
192 ref = ref->GetPendingNext();
193 } while (LIKELY(ref != head));
194 }
195
UpdateRoots(IsMarkedVisitor * visitor)196 void ReferenceQueue::UpdateRoots(IsMarkedVisitor* visitor) {
197 if (list_ != nullptr) {
198 list_ = down_cast<mirror::Reference*>(visitor->IsMarked(list_));
199 }
200 }
201
202 } // namespace gc
203 } // namespace art
204