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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 #ifndef ThreadSafeRefCounted_h
     31 #define ThreadSafeRefCounted_h
     32 
     33 #include "wtf/Atomics.h"
     34 #include "wtf/DynamicAnnotations.h"
     35 #include "wtf/FastAllocBase.h"
     36 #include "wtf/Noncopyable.h"
     37 #include "wtf/Platform.h"
     38 #include "wtf/WTFExport.h"
     39 
     40 namespace WTF {
     41 
     42 class WTF_EXPORT ThreadSafeRefCountedBase {
     43     WTF_MAKE_NONCOPYABLE(ThreadSafeRefCountedBase);
     44     WTF_MAKE_FAST_ALLOCATED;
     45 public:
     46     ThreadSafeRefCountedBase(int initialRefCount = 1)
     47         : m_refCount(initialRefCount)
     48     {
     49     }
     50 
     51     void ref()
     52     {
     53         atomicIncrement(&m_refCount);
     54     }
     55 
     56     bool hasOneRef()
     57     {
     58         return refCount() == 1;
     59     }
     60 
     61     int refCount() const
     62     {
     63         return static_cast<int const volatile &>(m_refCount);
     64     }
     65 
     66 protected:
     67     // Returns whether the pointer should be freed or not.
     68     bool derefBase()
     69     {
     70         WTF_ANNOTATE_HAPPENS_BEFORE(&m_refCount);
     71         if (atomicDecrement(&m_refCount) <= 0) {
     72             WTF_ANNOTATE_HAPPENS_AFTER(&m_refCount);
     73             return true;
     74         }
     75         return false;
     76     }
     77 
     78 private:
     79     int m_refCount;
     80 };
     81 
     82 template<class T> class ThreadSafeRefCounted : public ThreadSafeRefCountedBase {
     83 public:
     84     void deref()
     85     {
     86         if (derefBase())
     87             delete static_cast<T*>(this);
     88     }
     89 
     90 protected:
     91     ThreadSafeRefCounted()
     92     {
     93     }
     94 };
     95 
     96 } // namespace WTF
     97 
     98 using WTF::ThreadSafeRefCounted;
     99 
    100 #endif // ThreadSafeRefCounted_h
    101