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 #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.
AtomicRefCountIncN(volatile AtomicRefCount * ptr,AtomicRefCount increment)18 inline void AtomicRefCountIncN(volatile AtomicRefCount *ptr,
19 AtomicRefCount increment) {
20 subtle::NoBarrier_AtomicIncrement(ptr, increment);
21 }
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.
AtomicRefCountDecN(volatile AtomicRefCount * ptr,AtomicRefCount decrement)27 inline bool AtomicRefCountDecN(volatile AtomicRefCount *ptr,
28 AtomicRefCount decrement) {
29 bool res = (subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0);
30 return res;
31 }
32
33 // Increment a reference count by 1.
AtomicRefCountInc(volatile AtomicRefCount * ptr)34 inline void AtomicRefCountInc(volatile AtomicRefCount *ptr) {
35 base::AtomicRefCountIncN(ptr, 1);
36 }
37
38 // Decrement a reference count by 1 and return whether the result is non-zero.
39 // Insert barriers to ensure that state written before the reference count
40 // became zero will be visible to a thread that has just made the count zero.
AtomicRefCountDec(volatile AtomicRefCount * ptr)41 inline bool AtomicRefCountDec(volatile AtomicRefCount *ptr) {
42 return base::AtomicRefCountDecN(ptr, 1);
43 }
44
45 // Return whether the reference count is one. If the reference count is used
46 // in the conventional way, a refrerence count of 1 implies that the current
47 // thread owns the reference and no other thread shares it. This call performs
48 // the test for a reference count of one, and performs the memory barrier
49 // needed for the owning thread to act on the object, knowing that it has
50 // exclusive access to the object.
AtomicRefCountIsOne(volatile AtomicRefCount * ptr)51 inline bool AtomicRefCountIsOne(volatile AtomicRefCount *ptr) {
52 bool res = (subtle::Acquire_Load(ptr) == 1);
53 return res;
54 }
55
56 // Return whether the reference count is zero. With conventional object
57 // referencing counting, the object will be destroyed, so the reference count
58 // should never be zero. Hence this is generally used for a debug check.
AtomicRefCountIsZero(volatile AtomicRefCount * ptr)59 inline bool AtomicRefCountIsZero(volatile AtomicRefCount *ptr) {
60 bool res = (subtle::Acquire_Load(ptr) == 0);
61 return res;
62 }
63
64 } // namespace base
65
66 #endif // BASE_ATOMIC_REF_COUNT_H_
67