license.bot | f003cfe | 2008-08-24 09:55:55 +0900 | [diff] [blame^] | 1 | // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
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| 2 | // Use of this source code is governed by a BSD-style license that can be
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| 3 | // found in the LICENSE file.
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| 4 |
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| 5 | // This is a low level implementation of atomic semantics for reference
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| 6 | // counting. Please use base/ref_counted.h directly instead.
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| 7 |
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| 8 | #ifndef BASE_ATOMIC_REF_COUNT_H_
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| 9 | #define BASE_ATOMIC_REF_COUNT_H_
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| 10 |
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| 11 | #include "base/atomicops.h"
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| 12 | #include "base/basictypes.h"
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| 13 |
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| 14 | namespace base {
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| 15 |
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| 16 | typedef base::subtle::Atomic32 AtomicRefCount;
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| 17 |
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| 18 | // Increment a reference count by "increment", which must exceed 0.
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| 19 | inline void AtomicRefCountIncN(volatile AtomicRefCount *ptr,
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| 20 | AtomicRefCount increment) {
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| 21 | base::subtle::NoBarrier_AtomicIncrement(ptr, increment);
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| 22 | }
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| 23 |
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| 24 | // Decrement a reference count by "decrement", which must exceed 0,
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| 25 | // and return whether the result is non-zero.
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| 26 | // Insert barriers to ensure that state written before the reference count
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| 27 | // became zero will be visible to a thread that has just made the count zero.
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| 28 | inline bool AtomicRefCountDecN(volatile AtomicRefCount *ptr,
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| 29 | AtomicRefCount decrement) {
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| 30 | return base::subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0;
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| 31 | }
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| 32 |
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| 33 | // Increment a reference count by 1.
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| 34 | inline void AtomicRefCountInc(volatile AtomicRefCount *ptr) {
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| 35 | base::AtomicRefCountIncN(ptr, 1);
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| 36 | }
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| 37 |
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| 38 | // Decrement a reference count by 1 and return whether the result is non-zero.
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| 39 | // Insert barriers to ensure that state written before the reference count
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| 40 | // became zero will be visible to a thread that has just made the count zero.
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| 41 | inline bool AtomicRefCountDec(volatile AtomicRefCount *ptr) {
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| 42 | return base::AtomicRefCountDecN(ptr, 1);
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| 43 | }
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| 44 |
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| 45 | // Return whether the reference count is one. If the reference count is used
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| 46 | // in the conventional way, a refrerence count of 1 implies that the current
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| 47 | // thread owns the reference and no other thread shares it. This call performs
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| 48 | // the test for a reference count of one, and performs the memory barrier
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| 49 | // needed for the owning thread to act on the object, knowing that it has
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| 50 | // exclusive access to the object.
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| 51 | inline bool AtomicRefCountIsOne(volatile AtomicRefCount *ptr) {
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| 52 | return base::subtle::Acquire_Load(ptr) == 1;
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| 53 | }
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| 54 |
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| 55 | // Return whether the reference count is zero. With conventional object
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| 56 | // referencing counting, the object will be destroyed, so the reference count
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| 57 | // should never be zero. Hence this is generally used for a debug check.
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| 58 | inline bool AtomicRefCountIsZero(volatile AtomicRefCount *ptr) {
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| 59 | return base::subtle::Acquire_Load(ptr) == 0;
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| 60 | }
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| 61 |
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| 62 | } // namespace base
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| 63 |
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| 64 | #endif // BASE_ATOMIC_REF_COUNT_H_
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| 65 |
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