heap/Weak.h

   1 /*
   2  * Copyright (C) 2009, 2012, 2013 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 <wtf/Noncopyable.h>
  30 #include <wtf/NullPtr.h>
  31
  32 namespace JSC {
  33
  34 template<typename T> class PassWeak;
  35 class WeakImpl;
  36 class WeakHandleOwner;
  37
  38 // This is a free function rather than a Weak<T> member function so we can put it in Weak.cpp.
  39 JS_EXPORT_PRIVATE void weakClearSlowCase(WeakImpl*&);
  40
  41 template<typename T> class Weak {
  42     WTF_MAKE_NONCOPYABLE(Weak);
  43 public:
  44     Weak()
  45         : m_impl(0)
  46     {
  47     }
  48
  49     explicit Weak(std::nullptr_t)
  50         : m_impl(0)
  51     {
  52     }
  53
  54     explicit Weak(T*, WeakHandleOwner* = 0, void* context = 0);
  55
  56     enum HashTableDeletedValueTag { HashTableDeletedValue };
  57     bool isHashTableDeletedValue() const;
  58     Weak(HashTableDeletedValueTag);
  59
  60     template<typename U> Weak(const PassWeak<U>&);
  61
  62     ~Weak()
  63     {
  64         clear();
  65     }
  66
  67     void swap(Weak&);
  68     Weak& operator=(const PassWeak<T>&);
  69
  70     bool operator!() const;
  71     T* operator->() const;
  72     T& operator*() const;
  73     T* get() const;
  74
  75     bool was(T*) const;
  76
  77     // This conversion operator allows implicit conversion to bool but not to other integer types.
  78     typedef void* (Weak::*UnspecifiedBoolType);
  79     operator UnspecifiedBoolType*() const;
  80
  81     PassWeak<T> release();
  82     void clear()
  83     {
  84         if (!m_impl)
  85             return;
  86         weakClearSlowCase(m_impl);
  87     }
  88
  89 private:
  90     static WeakImpl* hashTableDeletedValue();
  91
  92     WeakImpl* m_impl;
  93 };
  94
  95 } // namespace JSC
  96
  97 #endif // Weak_h