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
35namespace WTF {
36
37template<typename T>
38class WeakReference : public ThreadSafeRefCounted<WeakReference<T> > {
39    WTF_MAKE_NONCOPYABLE(WeakReference<T>);
40    WTF_MAKE_FAST_ALLOCATED;
41public:
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
66private:
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
83template<typename T>
84class WeakPtr {
85    WTF_MAKE_FAST_ALLOCATED;
86public:
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
103private:
104    RefPtr<WeakReference<T> > m_ref;
105};
106
107template<typename T, typename U> inline bool operator==(const WeakPtr<T>& a, const WeakPtr<U>& b)
108{
109    return a.get() == b.get();
110}
111
112template<typename T, typename U> inline bool operator!=(const WeakPtr<T>& a, const WeakPtr<U>& b)
113{
114    return a.get() != b.get();
115}
116
117template<typename T>
118class WeakPtrFactory {
119    WTF_MAKE_NONCOPYABLE(WeakPtrFactory<T>);
120    WTF_MAKE_FAST_ALLOCATED;
121public:
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
143private:
144    RefPtr<WeakReference<T> > m_ref;
145};
146
147} // namespace WTF
148
149using WTF::WeakPtr;
150using WTF::WeakPtrFactory;
151using WTF::WeakReference;
152
153#endif
154