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