heap/CopyWriteBarrier.h

   1 /*
   2  * Copyright (C) 2014 Apple Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
  14  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  15  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
  17  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  18  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  19  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  20  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  21  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  22  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
  23  * THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef CopyWriteBarrier_h
  27 #define CopyWriteBarrier_h
  28
  29 #include "Heap.h"
  30
  31 namespace JSC {
  32
  33 template <typename T>
  34 class CopyWriteBarrier {
  35 public:
  36     CopyWriteBarrier()
  37         : m_value(0)
  38     {
  39     }
  40
  41     CopyWriteBarrier(VM& vm, const JSCell* owner, T& value)
  42     {
  43         this->set(vm, owner, &value);
  44     }
  45
  46     CopyWriteBarrier(VM& vm, const JSCell* owner, T* value)
  47     {
  48         this->set(vm, owner, value);
  49     }
  50
  51     bool operator!() const { return !m_value; }
  52
  53     typedef T* (CopyWriteBarrier::*UnspecifiedBoolType);
  54     operator UnspecifiedBoolType*() const { return m_value ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
  55
  56     T* get() const
  57     {
  58         return m_value;
  59     }
  60
  61     T* operator*() const
  62     {
  63         return get();
  64     }
  65
  66     T* operator->() const
  67     {
  68         return get();
  69     }
  70
  71     void set(VM& vm, const JSCell* owner, T* value)
  72     {
  73         this->m_value = value;
  74         vm.heap.writeBarrier(owner);
  75     }
  76
  77     void setWithoutWriteBarrier(T* value)
  78     {
  79         this->m_value = value;
  80     }
  81
  82     void clear() { m_value = 0; }
  83
  84 private:
  85     T* m_value;
  86 };
  87
  88 } // namespace JSC
  89
  90 #endif // CopyWriteBarrier_h