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      1 /*
      2  * Copyright (C) 2007, 2008, 2010 Apple Inc. All rights reserved.
      3  * Copyright (C) 2007 Justin Haygood (jhaygood (at) reaktix.com)
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions
      7  * are met:
      8  *
      9  * 1.  Redistributions of source code must retain the above copyright
     10  *     notice, this list of conditions and the following disclaimer.
     11  * 2.  Redistributions in binary form must reproduce the above copyright
     12  *     notice, this list of conditions and the following disclaimer in the
     13  *     documentation and/or other materials provided with the distribution.
     14  * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
     15  *     its contributors may be used to endorse or promote products derived
     16  *     from this software without specific prior written permission.
     17  *
     18  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
     19  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
     20  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
     21  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
     22  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
     23  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
     24  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
     25  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     26  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     27  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     28  *
     29  *
     30  * Note: The implementations of InterlockedIncrement and InterlockedDecrement are based
     31  * on atomic_increment and atomic_exchange_and_add from the Boost C++ Library. The license
     32  * is virtually identical to the Apple license above but is included here for completeness.
     33  *
     34  * Boost Software License - Version 1.0 - August 17th, 2003
     35  *
     36  * Permission is hereby granted, free of charge, to any person or organization
     37  * obtaining a copy of the software and accompanying documentation covered by
     38  * this license (the "Software") to use, reproduce, display, distribute,
     39  * execute, and transmit the Software, and to prepare derivative works of the
     40  * Software, and to permit third-parties to whom the Software is furnished to
     41  * do so, all subject to the following:
     42  *
     43  * The copyright notices in the Software and this entire statement, including
     44  * the above license grant, this restriction and the following disclaimer,
     45  * must be included in all copies of the Software, in whole or in part, and
     46  * all derivative works of the Software, unless such copies or derivative
     47  * works are solely in the form of machine-executable object code generated by
     48  * a source language processor.
     49  *
     50  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     51  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     52  * FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
     53  * SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
     54  * FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
     55  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
     56  * DEALINGS IN THE SOFTWARE.
     57  */
     58 
     59 #ifndef ThreadSafeRefCounted_h
     60 #define ThreadSafeRefCounted_h
     61 
     62 #include "Platform.h"
     63 
     64 #include <wtf/Atomics.h>
     65 #include <wtf/DynamicAnnotations.h>
     66 #include <wtf/ThreadingPrimitives.h>
     67 
     68 namespace WTF {
     69 
     70 class ThreadSafeRefCountedBase {
     71     WTF_MAKE_NONCOPYABLE(ThreadSafeRefCountedBase);
     72     WTF_MAKE_FAST_ALLOCATED;
     73 public:
     74     ThreadSafeRefCountedBase(int initialRefCount = 1)
     75         : m_refCount(initialRefCount)
     76     {
     77     }
     78 
     79     void ref()
     80     {
     81 #if USE(LOCKFREE_THREADSAFEREFCOUNTED)
     82         atomicIncrement(&m_refCount);
     83 #else
     84         MutexLocker locker(m_mutex);
     85         ++m_refCount;
     86 #endif
     87     }
     88 
     89     bool hasOneRef()
     90     {
     91         return refCount() == 1;
     92     }
     93 
     94     int refCount() const
     95     {
     96 #if !USE(LOCKFREE_THREADSAFEREFCOUNTED)
     97         MutexLocker locker(m_mutex);
     98 #endif
     99         return static_cast<int const volatile &>(m_refCount);
    100     }
    101 
    102 protected:
    103     // Returns whether the pointer should be freed or not.
    104     bool derefBase()
    105     {
    106 #if USE(LOCKFREE_THREADSAFEREFCOUNTED)
    107         WTF_ANNOTATE_HAPPENS_BEFORE(&m_refCount);
    108         if (atomicDecrement(&m_refCount) <= 0) {
    109             WTF_ANNOTATE_HAPPENS_AFTER(&m_refCount);
    110             return true;
    111         }
    112 #else
    113         int refCount;
    114         {
    115             MutexLocker locker(m_mutex);
    116             --m_refCount;
    117             refCount = m_refCount;
    118         }
    119         if (refCount <= 0)
    120             return true;
    121 #endif
    122         return false;
    123     }
    124 
    125 private:
    126     template<class T>
    127     friend class CrossThreadRefCounted;
    128 
    129     int m_refCount;
    130 #if !USE(LOCKFREE_THREADSAFEREFCOUNTED)
    131     mutable Mutex m_mutex;
    132 #endif
    133 };
    134 
    135 template<class T> class ThreadSafeRefCounted : public ThreadSafeRefCountedBase {
    136 public:
    137     void deref()
    138     {
    139         if (derefBase())
    140             delete static_cast<T*>(this);
    141     }
    142 
    143 protected:
    144     ThreadSafeRefCounted()
    145     {
    146     }
    147 };
    148 
    149 } // namespace WTF
    150 
    151 using WTF::ThreadSafeRefCounted;
    152 
    153 #endif // ThreadSafeRefCounted_h
    154