atomic_ref_count.h revision c7f5f8508d98d5952d42ed7648c2a8f30a4da156
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// 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#include "base/dynamic_annotations.h" 16 17namespace base { 18 19typedef subtle::Atomic32 AtomicRefCount; 20 21// Increment a reference count by "increment", which must exceed 0. 22inline void AtomicRefCountIncN(volatile AtomicRefCount *ptr, 23 AtomicRefCount increment) { 24 subtle::NoBarrier_AtomicIncrement(ptr, increment); 25} 26 27// Decrement a reference count by "decrement", which must exceed 0, 28// and return whether the result is non-zero. 29// Insert barriers to ensure that state written before the reference count 30// became zero will be visible to a thread that has just made the count zero. 31inline bool AtomicRefCountDecN(volatile AtomicRefCount *ptr, 32 AtomicRefCount decrement) { 33 ANNOTATE_HAPPENS_BEFORE(ptr); 34 bool res = (subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0); 35 if (!res) { 36 ANNOTATE_HAPPENS_AFTER(ptr); 37 } 38 return res; 39} 40 41// Increment a reference count by 1. 42inline void AtomicRefCountInc(volatile AtomicRefCount *ptr) { 43 base::AtomicRefCountIncN(ptr, 1); 44} 45 46// Decrement a reference count by 1 and return whether the result is non-zero. 47// Insert barriers to ensure that state written before the reference count 48// became zero will be visible to a thread that has just made the count zero. 49inline bool AtomicRefCountDec(volatile AtomicRefCount *ptr) { 50 return base::AtomicRefCountDecN(ptr, 1); 51} 52 53// Return whether the reference count is one. If the reference count is used 54// in the conventional way, a refrerence count of 1 implies that the current 55// thread owns the reference and no other thread shares it. This call performs 56// the test for a reference count of one, and performs the memory barrier 57// needed for the owning thread to act on the object, knowing that it has 58// exclusive access to the object. 59inline bool AtomicRefCountIsOne(volatile AtomicRefCount *ptr) { 60 bool res = (subtle::Acquire_Load(ptr) == 1); 61 if (res) { 62 ANNOTATE_HAPPENS_AFTER(ptr); 63 } 64 return res; 65} 66 67// Return whether the reference count is zero. With conventional object 68// referencing counting, the object will be destroyed, so the reference count 69// should never be zero. Hence this is generally used for a debug check. 70inline bool AtomicRefCountIsZero(volatile AtomicRefCount *ptr) { 71 bool res = (subtle::Acquire_Load(ptr) == 0); 72 if (res) { 73 ANNOTATE_HAPPENS_AFTER(ptr); 74 } 75 return res; 76} 77 78} // namespace base 79 80#endif // BASE_ATOMIC_REF_COUNT_H_ 81