third_party/WebKit/Source/wtf/WeakPtr.h

   1 /*
   2  * Copyright (C) 2013 Google, 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. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef WTF_WeakPtr_h
  27 #define WTF_WeakPtr_h
  28
  29 #include "wtf/Noncopyable.h"
  30 #include "wtf/PassRefPtr.h"
  31 #include "wtf/RefPtr.h"
  32 #include "wtf/ThreadSafeRefCounted.h"
  33 #include "wtf/Threading.h"
  34
  35 namespace WTF {
  36
  37 template<typename T>
  38 class WeakReference : public ThreadSafeRefCounted<WeakReference<T>> {
  39     WTF_MAKE_NONCOPYABLE(WeakReference<T>);
  40     WTF_MAKE_FAST_ALLOCATED(WeakReference);
  41 public:
  42     static PassRefPtr<WeakReference<T>> create(T* ptr) { return adoptRef(new WeakReference(ptr)); }
  43     static PassRefPtr<WeakReference<T>> createUnbound() { return adoptRef(new WeakReference()); }
  44
  45     T* get() const
  46     {
  47         ASSERT(m_boundThread == currentThread());
  48         return m_ptr;
  49     }
  50
  51     void clear()
  52     {
  53         ASSERT(m_boundThread == currentThread());
  54         m_ptr = 0;
  55     }
  56
  57     void bindTo(T* ptr)
  58     {
  59         ASSERT(!m_ptr);
  60 #if ENABLE(ASSERT)
  61         m_boundThread = currentThread();
  62 #endif
  63         m_ptr = ptr;
  64     }
  65
  66 private:
  67     WeakReference() : m_ptr(0) { }
  68
  69     explicit WeakReference(T* ptr)
  70         : m_ptr(ptr)
  71 #if ENABLE(ASSERT)
  72         , m_boundThread(currentThread())
  73 #endif
  74     {
  75     }
  76
  77     T* m_ptr;
  78 #if ENABLE(ASSERT)
  79     ThreadIdentifier m_boundThread;
  80 #endif
  81 };
  82
  83 template<typename T>
  84 class WeakPtr {
  85     WTF_MAKE_FAST_ALLOCATED(WeakPtr);
  86 public:
  87     WeakPtr() { }
  88     WeakPtr(std::nullptr_t) { }
  89     WeakPtr(PassRefPtr<WeakReference<T>> ref) : m_ref(ref) { }
  90
  91     T* get() const { return m_ref ? m_ref->get() : 0; }
  92     void clear() { m_ref.clear(); }
  93
  94     T* operator->() const
  95     {
  96         ASSERT(get());
  97         return get();
  98     }
  99
 100     typedef RefPtr<WeakReference<T>> (WeakPtr::*UnspecifiedBoolType);
 101     operator UnspecifiedBoolType() const { return get() ? &WeakPtr::m_ref : 0; }
 102
 103 private:
 104     RefPtr<WeakReference<T>> m_ref;
 105 };
 106
 107 template<typename T, typename U> inline bool operator==(const WeakPtr<T>& a, const WeakPtr<U>& b)
 108 {
 109     return a.get() == b.get();
 110 }
 111
 112 template<typename T, typename U> inline bool operator!=(const WeakPtr<T>& a, const WeakPtr<U>& b)
 113 {
 114     return a.get() != b.get();
 115 }
 116
 117 template<typename T>
 118 class WeakPtrFactory {
 119     WTF_MAKE_NONCOPYABLE(WeakPtrFactory<T>);
 120     WTF_MAKE_FAST_ALLOCATED(WeakPtrFactory);
 121 public:
 122     explicit WeakPtrFactory(T* ptr) : m_ref(WeakReference<T>::create(ptr)) { }
 123
 124     WeakPtrFactory(PassRefPtr<WeakReference<T>> ref, T* ptr)
 125         : m_ref(ref)
 126     {
 127         m_ref->bindTo(ptr);
 128     }
 129
 130     ~WeakPtrFactory() { m_ref->clear(); }
 131
 132     // We should consider having createWeakPtr populate m_ref the first time createWeakPtr is called.
 133     WeakPtr<T> createWeakPtr() { return WeakPtr<T>(m_ref); }
 134
 135     void revokeAll()
 136     {
 137         T* ptr = m_ref->get();
 138         m_ref->clear();
 139         // We create a new WeakReference so that future calls to createWeakPtr() create nonzero WeakPtrs.
 140         m_ref = WeakReference<T>::create(ptr);
 141     }
 142
 143     bool hasWeakPtrs() const
 144     {
 145         return m_ref->refCount() > 1;
 146     }
 147
 148 private:
 149     RefPtr<WeakReference<T>> m_ref;
 150 };
 151
 152 } // namespace WTF
 153
 154 using WTF::WeakPtr;
 155 using WTF::WeakPtrFactory;
 156 using WTF::WeakReference;
 157
 158 #endif