heap/Handle.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 Handle_h
  27 #define Handle_h
  28
  29 #include "HandleTypes.h"
  30
  31 namespace JSC {
  32
  33 /*
  34     A Handle is a smart pointer that updates automatically when the garbage
  35     collector moves the object to which it points.
  36
  37     The base Handle class represents a temporary reference to a pointer whose
  38     lifetime is guaranteed by something else.
  39 */
  40
  41 template <class T> class Handle;
  42
  43 // Creating a JSValue Handle is invalid
  44 template <> class Handle<JSValue>;
  45
  46 class HandleBase {
  47     template <typename T> friend class Weak;
  48     template <typename T> friend class Strong;
  49     friend class HandleSet;
  50     friend struct JSCallbackObjectData;
  51
  52 public:
  53     bool operator!() const { return !m_slot || !*m_slot; }
  54
  55     // This conversion operator allows implicit conversion to bool but not to other integer types.
  56     typedef JSValue (HandleBase::*UnspecifiedBoolType);
  57     operator UnspecifiedBoolType*() const { return (m_slot && *m_slot) ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0; }
  58
  59     HandleSlot slot() const { return m_slot; }
  60
  61 protected:
  62     HandleBase(HandleSlot slot)
  63         : m_slot(slot)
  64     {
  65     }
  66
  67     void swap(HandleBase& other) { std::swap(m_slot, other.m_slot); }
  68
  69     void setSlot(HandleSlot slot)
  70     {
  71         m_slot = slot;
  72     }
  73
  74 private:
  75     HandleSlot m_slot;
  76 };
  77
  78 template <typename Base, typename T> struct HandleConverter {
  79     T* operator->()
  80     {
  81         return static_cast<Base*>(this)->get();
  82     }
  83     const T* operator->() const
  84     {
  85         return static_cast<const Base*>(this)->get();
  86     }
  87
  88     T* operator*()
  89     {
  90         return static_cast<Base*>(this)->get();
  91     }
  92     const T* operator*() const
  93     {
  94         return static_cast<const Base*>(this)->get();
  95     }
  96 };
  97
  98 template <typename Base> struct HandleConverter<Base, Unknown> {
  99     Handle<JSObject> asObject() const;
 100     bool isObject() const { return jsValue().isObject(); }
 101     bool getNumber(double number) const { return jsValue().getNumber(number); }
 102     WTF::String getString(ExecState*) const;
 103     bool isUndefinedOrNull() const { return jsValue().isUndefinedOrNull(); }
 104
 105 private:
 106     JSValue jsValue() const
 107     {
 108         return static_cast<const Base*>(this)->get();
 109     }
 110 };
 111
 112 template <typename T> class Handle : public HandleBase, public HandleConverter<Handle<T>, T> {
 113 public:
 114     template <typename A, typename B> friend struct HandleConverter;
 115     typedef typename HandleTypes<T>::ExternalType ExternalType;
 116     template <typename U> Handle(Handle<U> o)
 117     {
 118         typename HandleTypes<T>::template validateUpcast<U>();
 119         setSlot(o.slot());
 120     }
 121
 122     void swap(Handle& other) { HandleBase::swap(other); }
 123
 124     ExternalType get() const { return HandleTypes<T>::getFromSlot(this->slot()); }
 125
 126 protected:
 127     Handle(HandleSlot slot = 0)
 128         : HandleBase(slot)
 129     {
 130     }
 131
 132 private:
 133     friend class HandleSet;
 134     friend class WeakBlock;
 135
 136     static Handle<T> wrapSlot(HandleSlot slot)
 137     {
 138         return Handle<T>(slot);
 139     }
 140 };
 141
 142 template <typename Base> Handle<JSObject> HandleConverter<Base, Unknown>::asObject() const
 143 {
 144     return Handle<JSObject>::wrapSlot(static_cast<const Base*>(this)->slot());
 145 }
 146
 147 template <typename T, typename U> inline bool operator==(const Handle<T>& a, const Handle<U>& b)
 148 {
 149     return a.get() == b.get();
 150 }
 151
 152 template <typename T, typename U> inline bool operator==(const Handle<T>& a, U* b)
 153 {
 154     return a.get() == b;
 155 }
 156
 157 template <typename T, typename U> inline bool operator==(T* a, const Handle<U>& b)
 158 {
 159     return a == b.get();
 160 }
 161
 162 template <typename T, typename U> inline bool operator!=(const Handle<T>& a, const Handle<U>& b)
 163 {
 164     return a.get() != b.get();
 165 }
 166
 167 template <typename T, typename U> inline bool operator!=(const Handle<T>& a, U* b)
 168 {
 169     return a.get() != b;
 170 }
 171
 172 template <typename T, typename U> inline bool operator!=(T* a, const Handle<U>& b)
 173 {
 174     return a != b.get();
 175 }
 176
 177 template <typename T, typename U> inline bool operator!=(const Handle<T>& a, JSValue b)
 178 {
 179     return a.get() != b;
 180 }
 181
 182 template <typename T, typename U> inline bool operator!=(JSValue a, const Handle<U>& b)
 183 {
 184     return a != b.get();
 185 }
 186
 187 }
 188
 189 #endif