1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 // This is a low level implementation of atomic semantics for reference
6 // counting. Please use base/memory/ref_counted.h directly instead.
7 //
8 // The implementation includes annotations to avoid some false positives
9 // when using data race detection tools.
10
11 #ifndef BASE_ATOMIC_REF_COUNT_H_
12 #define BASE_ATOMIC_REF_COUNT_H_
13
14 #include "base/atomicops.h"
15
16 namespace base {
17
18 typedef subtle::Atomic32 AtomicRefCount;
19
20 // Increment a reference count by "increment", which must exceed 0.
AtomicRefCountIncN(volatile AtomicRefCount * ptr,AtomicRefCount increment)21 inline void AtomicRefCountIncN(volatile AtomicRefCount *ptr,
22 AtomicRefCount increment) {
23 subtle::NoBarrier_AtomicIncrement(ptr, increment);
24 }
25
26 // Decrement a reference count by "decrement", which must exceed 0,
27 // and return whether the result is non-zero.
28 // Insert barriers to ensure that state written before the reference count
29 // became zero will be visible to a thread that has just made the count zero.
AtomicRefCountDecN(volatile AtomicRefCount * ptr,AtomicRefCount decrement)30 inline bool AtomicRefCountDecN(volatile AtomicRefCount *ptr,
31 AtomicRefCount decrement) {
32 bool res = (subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0);
33 return res;
34 }
35
36 // Increment a reference count by 1.
AtomicRefCountInc(volatile AtomicRefCount * ptr)37 inline void AtomicRefCountInc(volatile AtomicRefCount *ptr) {
38 base::AtomicRefCountIncN(ptr, 1);
39 }
40
41 // Decrement a reference count by 1 and return whether the result is non-zero.
42 // Insert barriers to ensure that state written before the reference count
43 // became zero will be visible to a thread that has just made the count zero.
AtomicRefCountDec(volatile AtomicRefCount * ptr)44 inline bool AtomicRefCountDec(volatile AtomicRefCount *ptr) {
45 return base::AtomicRefCountDecN(ptr, 1);
46 }
47
48 // Return whether the reference count is one. If the reference count is used
49 // in the conventional way, a refrerence count of 1 implies that the current
50 // thread owns the reference and no other thread shares it. This call performs
51 // the test for a reference count of one, and performs the memory barrier
52 // needed for the owning thread to act on the object, knowing that it has
53 // exclusive access to the object.
AtomicRefCountIsOne(volatile AtomicRefCount * ptr)54 inline bool AtomicRefCountIsOne(volatile AtomicRefCount *ptr) {
55 bool res = (subtle::Acquire_Load(ptr) == 1);
56 return res;
57 }
58
59 // Return whether the reference count is zero. With conventional object
60 // referencing counting, the object will be destroyed, so the reference count
61 // should never be zero. Hence this is generally used for a debug check.
AtomicRefCountIsZero(volatile AtomicRefCount * ptr)62 inline bool AtomicRefCountIsZero(volatile AtomicRefCount *ptr) {
63 bool res = (subtle::Acquire_Load(ptr) == 0);
64 return res;
65 }
66
67 } // namespace base
68
69 #endif // BASE_ATOMIC_REF_COUNT_H_
70