heap/Strong.h

   1 /*
   2  * Copyright (C) 2011 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 Strong_h
  27 #define Strong_h
  28
  29 #include <wtf/Assertions.h>
  30 #include "Handle.h"
  31 #include "HandleSet.h"
  32
  33 namespace JSC {
  34
  35 class VM;
  36
  37 // A strongly referenced handle that prevents the object it points to from being garbage collected.
  38 template <typename T> class Strong : public Handle<T> {
  39     using Handle<T>::slot;
  40     using Handle<T>::setSlot;
  41     template <typename U> friend class Strong;
  42
  43 public:
  44     typedef typename Handle<T>::ExternalType ExternalType;
  45
  46     Strong()
  47         : Handle<T>()
  48     {
  49     }
  50
  51     Strong(VM&, ExternalType = ExternalType());
  52
  53     Strong(VM&, Handle<T>);
  54
  55     Strong(const Strong& other)
  56         : Handle<T>()
  57     {
  58         if (!other.slot())
  59             return;
  60         setSlot(HandleSet::heapFor(other.slot())->allocate());
  61         set(other.get());
  62     }
  63
  64     template <typename U> Strong(const Strong<U>& other)
  65         : Handle<T>()
  66     {
  67         if (!other.slot())
  68             return;
  69         setSlot(HandleSet::heapFor(other.slot())->allocate());
  70         set(other.get());
  71     }
  72
  73     enum HashTableDeletedValueTag { HashTableDeletedValue };
  74     bool isHashTableDeletedValue() const { return slot() == hashTableDeletedValue(); }
  75     Strong(HashTableDeletedValueTag)
  76         : Handle<T>(hashTableDeletedValue())
  77     {
  78     }
  79
  80     ~Strong()
  81     {
  82         clear();
  83     }
  84
  85     bool operator!() const { return !slot() || !*slot(); }
  86
  87     // This conversion operator allows implicit conversion to bool but not to other integer types.
  88     typedef JSValue (HandleBase::*UnspecifiedBoolType);
  89     operator UnspecifiedBoolType*() const { return !!*this ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
  90
  91     void swap(Strong& other)
  92     {
  93         Handle<T>::swap(other);
  94     }
  95
  96     ExternalType get() const { return HandleTypes<T>::getFromSlot(this->slot()); }
  97
  98     void set(VM&, ExternalType);
  99
 100     template <typename U> Strong& operator=(const Strong<U>& other)
 101     {
 102         if (!other.slot()) {
 103             clear();
 104             return *this;
 105         }
 106
 107         set(*HandleSet::heapFor(other.slot())->vm(), other.get());
 108         return *this;
 109     }
 110
 111     Strong& operator=(const Strong& other)
 112     {
 113         if (!other.slot()) {
 114             clear();
 115             return *this;
 116         }
 117
 118         set(*HandleSet::heapFor(other.slot())->vm(), other.get());
 119         return *this;
 120     }
 121
 122     void clear()
 123     {
 124         if (!slot())
 125             return;
 126         HandleSet::heapFor(slot())->deallocate(slot());
 127         setSlot(0);
 128     }
 129
 130 private:
 131     static HandleSlot hashTableDeletedValue() { return reinterpret_cast<HandleSlot>(-1); }
 132
 133     void set(ExternalType externalType)
 134     {
 135         ASSERT(slot());
 136         JSValue value = HandleTypes<T>::toJSValue(externalType);
 137         HandleSet::heapFor(slot())->writeBarrier(slot(), value);
 138         *slot() = value;
 139     }
 140 };
 141
 142 template<class T> inline void swap(Strong<T>& a, Strong<T>& b)
 143 {
 144     a.swap(b);
 145 }
 146
 147 } // namespace JSC
 148
 149 namespace WTF {
 150
 151 template<typename T> struct VectorTraits<JSC::Strong<T>> : SimpleClassVectorTraits {
 152     static const bool canCompareWithMemcmp = false;
 153 };
 154
 155 template<typename P> struct HashTraits<JSC::Strong<P>> : SimpleClassHashTraits<JSC::Strong<P>> { };
 156
 157 }
 158
 159 #endif // Strong_h