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 #ifndef ART_RUNTIME_GC_REFERENCE_QUEUE_H_ 18 #define ART_RUNTIME_GC_REFERENCE_QUEUE_H_ 19 20 #include <iosfwd> 21 #include <string> 22 #include <vector> 23 24 #include "base/atomic.h" 25 #include "base/locks.h" 26 #include "base/timing_logger.h" 27 #include "jni.h" 28 #include "obj_ptr.h" 29 #include "offsets.h" 30 #include "runtime_globals.h" 31 #include "thread_pool.h" 32 33 namespace art { 34 35 class Mutex; 36 37 namespace mirror { 38 class Reference; 39 } // namespace mirror 40 41 class IsMarkedVisitor; 42 class MarkObjectVisitor; 43 44 namespace gc { 45 46 namespace collector { 47 class GarbageCollector; 48 } // namespace collector 49 50 class Heap; 51 52 struct FinalizerStats { FinalizerStatsFinalizerStats53 FinalizerStats(size_t num_refs, size_t num_enqueued) 54 : num_refs_(num_refs), num_enqueued_(num_enqueued) {} 55 const uint32_t num_refs_; 56 const uint32_t num_enqueued_; 57 }; 58 59 // Used to temporarily store java.lang.ref.Reference(s) during GC and prior to queueing on the 60 // appropriate java.lang.ref.ReferenceQueue. The linked list is maintained as an unordered, 61 // circular, and singly-linked list using the pendingNext fields of the java.lang.ref.Reference 62 // objects. 63 class ReferenceQueue { 64 public: 65 explicit ReferenceQueue(Mutex* lock); 66 67 // Enqueue a reference if it is unprocessed. Thread safe to call from multiple 68 // threads since it uses a lock to avoid a race between checking for the references presence and 69 // adding it. 70 void AtomicEnqueueIfNotEnqueued(Thread* self, ObjPtr<mirror::Reference> ref) 71 REQUIRES_SHARED(Locks::mutator_lock_) REQUIRES(!*lock_); 72 73 // Enqueue a reference. The reference must be unprocessed. 74 // Not thread safe, used when mutators are paused to minimize lock overhead. 75 void EnqueueReference(ObjPtr<mirror::Reference> ref) REQUIRES_SHARED(Locks::mutator_lock_); 76 77 // Dequeue a reference from the queue and return that dequeued reference. 78 // Call DisableReadBarrierForReference for the reference that's returned from this function. 79 ObjPtr<mirror::Reference> DequeuePendingReference() REQUIRES_SHARED(Locks::mutator_lock_); 80 81 // If applicable, disable the read barrier for the reference after its referent is handled (see 82 // ConcurrentCopying::ProcessMarkStackRef.) This must be called for a reference that's dequeued 83 // from pending queue (DequeuePendingReference). 84 void DisableReadBarrierForReference(ObjPtr<mirror::Reference> ref) 85 REQUIRES_SHARED(Locks::mutator_lock_); 86 87 // Enqueues finalizer references with white referents. White referents are blackened, moved to 88 // the zombie field, and the referent field is cleared. 89 FinalizerStats EnqueueFinalizerReferences(ReferenceQueue* cleared_references, 90 collector::GarbageCollector* collector) 91 REQUIRES_SHARED(Locks::mutator_lock_); 92 93 // Walks the reference list marking and dequeuing any references subject to the reference 94 // clearing policy. References with a black referent are removed from the list. References 95 // with white referents biased toward saving are blackened and also removed from the list. 96 // Returns the number of non-null soft references. May be called concurrently with 97 // AtomicEnqueueIfNotEnqueued(). 98 uint32_t ForwardSoftReferences(MarkObjectVisitor* visitor) 99 REQUIRES(!*lock_) 100 REQUIRES_SHARED(Locks::mutator_lock_); 101 102 // Unlink the reference list clearing references objects with white referents. Cleared references 103 // registered to a reference queue are scheduled for appending by the heap worker thread. 104 void ClearWhiteReferences(ReferenceQueue* cleared_references, 105 collector::GarbageCollector* collector, 106 bool report_cleared = false) 107 REQUIRES_SHARED(Locks::mutator_lock_); 108 109 void Dump(std::ostream& os) const REQUIRES_SHARED(Locks::mutator_lock_); 110 size_t GetLength() const REQUIRES_SHARED(Locks::mutator_lock_); 111 IsEmpty()112 bool IsEmpty() const { 113 return list_ == nullptr; 114 } 115 116 // Clear this queue. Only safe after handing off the contents elsewhere for further processing. Clear()117 void Clear() { 118 list_ = nullptr; 119 } 120 GetList()121 mirror::Reference* GetList() REQUIRES_SHARED(Locks::mutator_lock_) { 122 return list_; 123 } 124 125 // Visits list_, currently only used for the mark compact GC. 126 void UpdateRoots(IsMarkedVisitor* visitor) 127 REQUIRES_SHARED(Locks::mutator_lock_); 128 129 private: 130 // Lock, used for parallel GC reference enqueuing. It allows for multiple threads simultaneously 131 // calling AtomicEnqueueIfNotEnqueued. 132 Mutex* const lock_; 133 // The actual reference list. Only a root for the mark compact GC since it 134 // will be null during root marking for other GC types. Not an ObjPtr since it 135 // is accessed from multiple threads. Points to a singly-linked circular list 136 // using the pendingNext field. 137 mirror::Reference* list_; 138 139 DISALLOW_IMPLICIT_CONSTRUCTORS(ReferenceQueue); 140 }; 141 142 } // namespace gc 143 } // namespace art 144 145 #endif // ART_RUNTIME_GC_REFERENCE_QUEUE_H_ 146