heap/Weak.h

   1 /*
   2  * Copyright (C) 2009 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 Weak_h
  27 #define Weak_h
  28
  29 #include "Assertions.h"
  30 #include "Handle.h"
  31 #include "HandleHeap.h"
  32 #include "JSGlobalData.h"
  33
  34 namespace JSC {
  35
  36 // A weakly referenced handle that becomes 0 when the value it points to is garbage collected.
  37 template <typename T> class Weak : public Handle<T> {
  38     using Handle<T>::slot;
  39     using Handle<T>::setSlot;
  40
  41 public:
  42     typedef typename Handle<T>::ExternalType ExternalType;
  43
  44     Weak()
  45         : Handle<T>()
  46     {
  47     }
  48
  49     Weak(JSGlobalData& globalData, ExternalType value = ExternalType(), WeakHandleOwner* weakOwner = 0, void* context = 0)
  50         : Handle<T>(globalData.allocateGlobalHandle())
  51     {
  52         HandleHeap::heapFor(slot())->makeWeak(slot(), weakOwner, context);
  53         set(value);
  54     }
  55
  56     enum AdoptTag { Adopt };
  57     template<typename U> Weak(AdoptTag, Handle<U> handle)
  58         : Handle<T>(handle.slot())
  59     {
  60         validateCell(get());
  61     }
  62
  63     Weak(const Weak& other)
  64         : Handle<T>()
  65     {
  66         if (!other.slot())
  67             return;
  68         setSlot(HandleHeap::heapFor(other.slot())->copyWeak(other.slot()));
  69     }
  70
  71     template <typename U> Weak(const Weak<U>& other)
  72         : Handle<T>()
  73     {
  74         if (!other.slot())
  75             return;
  76         setSlot(HandleHeap::heapFor(other.slot())->copyWeak(other.slot()));
  77     }
  78
  79     enum HashTableDeletedValueTag { HashTableDeletedValue };
  80     bool isHashTableDeletedValue() const { return slot() == hashTableDeletedValue(); }
  81     Weak(HashTableDeletedValueTag)
  82         : Handle<T>(hashTableDeletedValue())
  83     {
  84     }
  85
  86     ~Weak()
  87     {
  88         clear();
  89     }
  90
  91     void swap(Weak& other)
  92     {
  93         Handle<T>::swap(other);
  94     }
  95
  96     ExternalType get() const { return  HandleTypes<T>::getFromSlot(slot()); }
  97
  98     void clear()
  99     {
 100         if (!slot())
 101             return;
 102         HandleHeap::heapFor(slot())->deallocate(slot());
 103         setSlot(0);
 104     }
 105
 106     void set(JSGlobalData& globalData, ExternalType value, WeakHandleOwner* weakOwner = 0, void* context = 0)
 107     {
 108         if (!slot()) {
 109             setSlot(globalData.allocateGlobalHandle());
 110             HandleHeap::heapFor(slot())->makeWeak(slot(), weakOwner, context);
 111         }
 112         ASSERT(HandleHeap::heapFor(slot())->hasWeakOwner(slot(), weakOwner));
 113         set(value);
 114     }
 115
 116     template <typename U> Weak& operator=(const Weak<U>& other)
 117     {
 118         clear();
 119         if (other.slot())
 120             setSlot(HandleHeap::heapFor(other.slot())->copyWeak(other.slot()));
 121         return *this;
 122     }
 123
 124     Weak& operator=(const Weak& other)
 125     {
 126         clear();
 127         if (other.slot())
 128             setSlot(HandleHeap::heapFor(other.slot())->copyWeak(other.slot()));
 129         return *this;
 130     }
 131
 132     HandleSlot leakHandle()
 133     {
 134         ASSERT(HandleHeap::heapFor(slot())->hasFinalizer(slot()));
 135         HandleSlot result = slot();
 136         setSlot(0);
 137         return result;
 138     }
 139
 140 private:
 141     static HandleSlot hashTableDeletedValue() { return reinterpret_cast<HandleSlot>(-1); }
 142
 143     void set(ExternalType externalType)
 144     {
 145         ASSERT(slot());
 146         JSValue value = HandleTypes<T>::toJSValue(externalType);
 147         ASSERT(!value || !value.isCell() || Heap::isMarked(value.asCell()));
 148         HandleHeap::heapFor(slot())->writeBarrier(slot(), value);
 149         *slot() = value;
 150     }
 151 };
 152
 153 template<class T> inline void swap(Weak<T>& a, Weak<T>& b)
 154 {
 155     a.swap(b);
 156 }
 157
 158 } // namespace JSC
 159
 160 namespace WTF {
 161
 162 template<typename T> struct VectorTraits<JSC::Weak<T> > : SimpleClassVectorTraits {
 163     static const bool canCompareWithMemcmp = false;
 164 };
 165
 166 template<typename P> struct HashTraits<JSC::Weak<P> > : SimpleClassHashTraits<JSC::Weak<P> > { };
 167
 168 }
 169
 170 #endif // Weak_h