1 : // Copyright (c) 2006-2008 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/ref_counted.h directly instead.
7 :
8 : #ifndef BASE_ATOMIC_REF_COUNT_H_
9 : #define BASE_ATOMIC_REF_COUNT_H_
10 :
11 : #include "base/atomicops.h"
12 :
13 : namespace base {
14 :
15 : typedef subtle::Atomic32 AtomicRefCount;
16 :
17 : // Increment a reference count by "increment", which must exceed 0.
18 8564 : inline void AtomicRefCountIncN(volatile AtomicRefCount *ptr,
19 : AtomicRefCount increment) {
20 8564 : subtle::NoBarrier_AtomicIncrement(ptr, increment);
21 8564 : }
22 :
23 : // Decrement a reference count by "decrement", which must exceed 0,
24 : // and return whether the result is non-zero.
25 : // Insert barriers to ensure that state written before the reference count
26 : // became zero will be visible to a thread that has just made the count zero.
27 7096 : inline bool AtomicRefCountDecN(volatile AtomicRefCount *ptr,
28 : AtomicRefCount decrement) {
29 7096 : return subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0;
30 : }
31 :
32 : // Increment a reference count by 1.
33 8564 : inline void AtomicRefCountInc(volatile AtomicRefCount *ptr) {
34 8564 : base::AtomicRefCountIncN(ptr, 1);
35 8564 : }
36 :
37 : // Decrement a reference count by 1 and return whether the result is non-zero.
38 : // Insert barriers to ensure that state written before the reference count
39 : // became zero will be visible to a thread that has just made the count zero.
40 7096 : inline bool AtomicRefCountDec(volatile AtomicRefCount *ptr) {
41 7096 : return base::AtomicRefCountDecN(ptr, 1);
42 : }
43 :
44 : // Return whether the reference count is one. If the reference count is used
45 : // in the conventional way, a refrerence count of 1 implies that the current
46 : // thread owns the reference and no other thread shares it. This call performs
47 : // the test for a reference count of one, and performs the memory barrier
48 : // needed for the owning thread to act on the object, knowing that it has
49 : // exclusive access to the object.
50 : inline bool AtomicRefCountIsOne(volatile AtomicRefCount *ptr) {
51 : return subtle::Acquire_Load(ptr) == 1;
52 : }
53 :
54 : // Return whether the reference count is zero. With conventional object
55 : // referencing counting, the object will be destroyed, so the reference count
56 : // should never be zero. Hence this is generally used for a debug check.
57 7096 : inline bool AtomicRefCountIsZero(volatile AtomicRefCount *ptr) {
58 7096 : return subtle::Acquire_Load(ptr) == 0;
59 : }
60 :
61 : } // namespace base
62 :
63 : #endif // BASE_ATOMIC_REF_COUNT_H_
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