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