| // Copyright 2008, Google Inc. |
| // All rights reserved. |
| // |
| // Redistribution and use in source and binary forms, with or without |
| // modification, are permitted provided that the following conditions are |
| // met: |
| // |
| // * Redistributions of source code must retain the above copyright |
| // notice, this list of conditions and the following disclaimer. |
| // * Redistributions in binary form must reproduce the above |
| // copyright notice, this list of conditions and the following disclaimer |
| // in the documentation and/or other materials provided with the |
| // distribution. |
| // * Neither the name of Google Inc. nor the names of its |
| // contributors may be used to endorse or promote products derived from |
| // this software without specific prior written permission. |
| // |
| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| // This is a low level implementation of atomic semantics for reference |
| // counting. Please use base/ref_counted.h directly instead. |
| |
| #ifndef BASE_ATOMIC_REF_COUNT_H_ |
| #define BASE_ATOMIC_REF_COUNT_H_ |
| |
| #include "base/atomicops.h" |
| #include "base/basictypes.h" |
| |
| namespace base { |
| |
| typedef base::subtle::Atomic32 AtomicRefCount; |
| |
| // Increment a reference count by "increment", which must exceed 0. |
| inline void AtomicRefCountIncN(volatile AtomicRefCount *ptr, |
| AtomicRefCount increment) { |
| base::subtle::NoBarrier_AtomicIncrement(ptr, increment); |
| } |
| |
| // Decrement a reference count by "decrement", which must exceed 0, |
| // and return whether the result is non-zero. |
| // Insert barriers to ensure that state written before the reference count |
| // became zero will be visible to a thread that has just made the count zero. |
| inline bool AtomicRefCountDecN(volatile AtomicRefCount *ptr, |
| AtomicRefCount decrement) { |
| return base::subtle::Barrier_AtomicIncrement(ptr, -decrement) != 0; |
| } |
| |
| // Increment a reference count by 1. |
| inline void AtomicRefCountInc(volatile AtomicRefCount *ptr) { |
| base::AtomicRefCountIncN(ptr, 1); |
| } |
| |
| // Decrement a reference count by 1 and return whether the result is non-zero. |
| // Insert barriers to ensure that state written before the reference count |
| // became zero will be visible to a thread that has just made the count zero. |
| inline bool AtomicRefCountDec(volatile AtomicRefCount *ptr) { |
| return base::AtomicRefCountDecN(ptr, 1); |
| } |
| |
| // Return whether the reference count is one. If the reference count is used |
| // in the conventional way, a refrerence count of 1 implies that the current |
| // thread owns the reference and no other thread shares it. This call performs |
| // the test for a reference count of one, and performs the memory barrier |
| // needed for the owning thread to act on the object, knowing that it has |
| // exclusive access to the object. |
| inline bool AtomicRefCountIsOne(volatile AtomicRefCount *ptr) { |
| return base::subtle::Acquire_Load(ptr) == 1; |
| } |
| |
| // Return whether the reference count is zero. With conventional object |
| // referencing counting, the object will be destroyed, so the reference count |
| // should never be zero. Hence this is generally used for a debug check. |
| inline bool AtomicRefCountIsZero(volatile AtomicRefCount *ptr) { |
| return base::subtle::Acquire_Load(ptr) == 0; |
| } |
| |
| } // namespace base |
| |
| #endif // BASE_ATOMIC_REF_COUNT_H_ |