wtf/ThreadSafeShared.h

   1 /*
   2  * Copyright (C) 2007, 2008, 2010 Apple Inc. All rights reserved.
   3  * Copyright (C) 2007 Justin Haygood (jhaygood@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 ThreadSafeShared_h
  60 #define ThreadSafeShared_h
  61
  62 #include "Platform.h"
  63
  64 #include <wtf/Atomics.h>
  65 #include <wtf/Noncopyable.h>
  66 #include <wtf/ThreadingPrimitives.h>
  67
  68 namespace WTF {
  69
  70 class ThreadSafeSharedBase : public Noncopyable {
  71 public:
  72     ThreadSafeSharedBase(int initialRefCount = 1)
  73         : m_refCount(initialRefCount)
  74     {
  75     }
  76
  77     void ref()
  78     {
  79 #if USE(LOCKFREE_THREADSAFESHARED)
  80         atomicIncrement(&m_refCount);
  81 #else
  82         MutexLocker locker(m_mutex);
  83         ++m_refCount;
  84 #endif
  85     }
  86
  87     bool hasOneRef()
  88     {
  89         return refCount() == 1;
  90     }
  91
  92     int refCount() const
  93     {
  94 #if !USE(LOCKFREE_THREADSAFESHARED)
  95         MutexLocker locker(m_mutex);
  96 #endif
  97         return static_cast<int const volatile &>(m_refCount);
  98     }
  99
 100 protected:
 101     // Returns whether the pointer should be freed or not.
 102     bool derefBase()
 103     {
 104 #if USE(LOCKFREE_THREADSAFESHARED)
 105         if (atomicDecrement(&m_refCount) <= 0)
 106             return true;
 107 #else
 108         int refCount;
 109         {
 110             MutexLocker locker(m_mutex);
 111             --m_refCount;
 112             refCount = m_refCount;
 113         }
 114         if (refCount <= 0)
 115             return true;
 116 #endif
 117         return false;
 118     }
 119
 120 private:
 121     template<class T>
 122     friend class CrossThreadRefCounted;
 123
 124     int m_refCount;
 125 #if !USE(LOCKFREE_THREADSAFESHARED)
 126     mutable Mutex m_mutex;
 127 #endif
 128 };
 129
 130 template<class T> class ThreadSafeShared : public ThreadSafeSharedBase {
 131 public:
 132     ThreadSafeShared(int initialRefCount = 1)
 133         : ThreadSafeSharedBase(initialRefCount)
 134     {
 135     }
 136
 137     void deref()
 138     {
 139         if (derefBase())
 140             delete static_cast<T*>(this);
 141     }
 142 };
 143
 144 } // namespace WTF
 145
 146 using WTF::ThreadSafeShared;
 147
 148 #endif // ThreadSafeShared_h