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. 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. 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. 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. 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. 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. 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
