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/timing_logger.h"
26 #include "globals.h"
27 #include "jni.h"
28 #include "object_callbacks.h"
29 #include "offsets.h"
30 #include "thread_pool.h"
31 
32 namespace art {
33 namespace mirror {
34 class Reference;
35 }  // namespace mirror
36 
37 namespace gc {
38 
39 class Heap;
40 
41 // Used to temporarily store java.lang.ref.Reference(s) during GC and prior to queueing on the
42 // appropriate java.lang.ref.ReferenceQueue. The linked list is maintained in the
43 // java.lang.ref.Reference objects.
44 class ReferenceQueue {
45  public:
46   explicit ReferenceQueue(Mutex* lock);
47 
48   // Enqueue a reference if is not already enqueued. Thread safe to call from multiple threads
49   // since it uses a lock to avoid a race between checking for the references presence and adding
50   // it.
51   void AtomicEnqueueIfNotEnqueued(Thread* self, mirror::Reference* ref)
52       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) LOCKS_EXCLUDED(lock_);
53 
54   // Enqueue a reference, unlike EnqueuePendingReference, enqueue reference checks that the
55   // reference IsEnqueueable. Not thread safe, used when mutators are paused to minimize lock
56   // overhead.
57   void EnqueueReference(mirror::Reference* ref) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
58 
59   // Enqueue a reference without checking that it is enqueable.
60   void EnqueuePendingReference(mirror::Reference* ref) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
61 
62   // Dequeue the first reference (returns list_).
63   mirror::Reference* DequeuePendingReference() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
64 
65   // Enqueues finalizer references with white referents.  White referents are blackened, moved to
66   // the zombie field, and the referent field is cleared.
67   void EnqueueFinalizerReferences(ReferenceQueue* cleared_references,
68                                   IsHeapReferenceMarkedCallback* is_marked_callback,
69                                   MarkObjectCallback* mark_object_callback, void* arg)
70       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
71 
72   // Walks the reference list marking any references subject to the reference clearing policy.
73   // References with a black referent are removed from the list.  References with white referents
74   // biased toward saving are blackened and also removed from the list.
75   void ForwardSoftReferences(IsHeapReferenceMarkedCallback* preserve_callback, void* arg)
76       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
77 
78   // Unlink the reference list clearing references objects with white referents. Cleared references
79   // registered to a reference queue are scheduled for appending by the heap worker thread.
80   void ClearWhiteReferences(ReferenceQueue* cleared_references,
81                             IsHeapReferenceMarkedCallback* is_marked_callback, void* arg)
82       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
83 
84   void Dump(std::ostream& os) const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
85   size_t GetLength() const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
86 
IsEmpty()87   bool IsEmpty() const {
88     return list_ == nullptr;
89   }
Clear()90   void Clear() {
91     list_ = nullptr;
92   }
GetList()93   mirror::Reference* GetList() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
94     return list_;
95   }
96 
97   // Visits list_, currently only used for the mark compact GC.
98   void UpdateRoots(IsMarkedCallback* callback, void* arg)
99       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
100 
101  private:
102   // Lock, used for parallel GC reference enqueuing. It allows for multiple threads simultaneously
103   // calling AtomicEnqueueIfNotEnqueued.
104   Mutex* const lock_;
105   // The actual reference list. Only a root for the mark compact GC since it will be null for other
106   // GC types.
107   mirror::Reference* list_;
108 
109   DISALLOW_IMPLICIT_CONSTRUCTORS(ReferenceQueue);
110 };
111 
112 }  // namespace gc
113 }  // namespace art
114 
115 #endif  // ART_RUNTIME_GC_REFERENCE_QUEUE_H_
116