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 #pragma once 14 15 #include "base/atomicops.h" 16 #include "base/third_party/dynamic_annotations/dynamic_annotations.h" 17 18 namespace base { 19 20 typedef subtle::Atomic32 AtomicRefCount; 21 22 // Increment a reference count by "increment", which must exceed 0. 23 inline void AtomicRefCountIncN(volatile AtomicRefCount *ptr, 24 AtomicRefCount increment) { 25 subtle::NoBarrier_AtomicIncrement(ptr, increment); 26 } 27 28 // Decrement a reference count by "decrement", which must exceed 0, 29 // and return whether the result is non-zero. 30 // Insert barriers to ensure that state written before the reference count 31 // became zero will be visible to a thread that has just made the count zero. 32 inline bool AtomicRefCountDecN(volatile AtomicRefCount *ptr, 33 AtomicRefCount decrement) { 34 ANNOTATE_HAPPENS_BEFORE(ptr); 35 bool res = (subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0); 36 if (!res) { 37 ANNOTATE_HAPPENS_AFTER(ptr); 38 } 39 return res; 40 } 41 42 // Increment a reference count by 1. 43 inline void AtomicRefCountInc(volatile AtomicRefCount *ptr) { 44 base::AtomicRefCountIncN(ptr, 1); 45 } 46 47 // Decrement a reference count by 1 and return whether the result is non-zero. 48 // Insert barriers to ensure that state written before the reference count 49 // became zero will be visible to a thread that has just made the count zero. 50 inline bool AtomicRefCountDec(volatile AtomicRefCount *ptr) { 51 return base::AtomicRefCountDecN(ptr, 1); 52 } 53 54 // Return whether the reference count is one. If the reference count is used 55 // in the conventional way, a refrerence count of 1 implies that the current 56 // thread owns the reference and no other thread shares it. This call performs 57 // the test for a reference count of one, and performs the memory barrier 58 // needed for the owning thread to act on the object, knowing that it has 59 // exclusive access to the object. 60 inline bool AtomicRefCountIsOne(volatile AtomicRefCount *ptr) { 61 bool res = (subtle::Acquire_Load(ptr) == 1); 62 if (res) { 63 ANNOTATE_HAPPENS_AFTER(ptr); 64 } 65 return res; 66 } 67 68 // Return whether the reference count is zero. With conventional object 69 // referencing counting, the object will be destroyed, so the reference count 70 // should never be zero. Hence this is generally used for a debug check. 71 inline bool AtomicRefCountIsZero(volatile AtomicRefCount *ptr) { 72 bool res = (subtle::Acquire_Load(ptr) == 0); 73 if (res) { 74 ANNOTATE_HAPPENS_AFTER(ptr); 75 } 76 return res; 77 } 78 79 } // namespace base 80 81 #endif // BASE_ATOMIC_REF_COUNT_H_ 82
