1/*
2 * Copyright (C) 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. ``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#pragma once
27
28#include <wtf/Assertions.h>
29#include <wtf/FastMalloc.h>
30#include <wtf/Noncopyable.h>
31
32namespace WTF {
33
34// A variant of RefCounted that allows reference counting to be deferred,
35// and can tell you if that has happened. You can think of a deferral as
36// just being an additional "ref", except that you can detect if it has
37// specifically happened - this can be useful either for debugging, or
38// sometimes even for some additional functionality.
39
40class DeferrableRefCountedBase {
41 static const unsigned deferredFlag = 1;
42 static const unsigned normalIncrement = 2;
43
44public:
45 void ref() const
46 {
47 m_refCount += normalIncrement;
48 }
49
50 bool hasOneRef() const
51 {
52 return refCount() == 1;
53 }
54
55 unsigned refCount() const
56 {
57 return m_refCount / normalIncrement;
58 }
59
60 bool isDeferred() const
61 {
62 return !!(m_refCount & deferredFlag);
63 }
64
65protected:
66 DeferrableRefCountedBase()
67 : m_refCount(normalIncrement)
68 {
69 }
70
71 ~DeferrableRefCountedBase()
72 {
73 }
74
75 bool derefBase() const
76 {
77 m_refCount -= normalIncrement;
78 return !m_refCount;
79 }
80
81 bool setIsDeferredBase(bool value)
82 {
83 if (value) {
84 m_refCount |= deferredFlag;
85 return false;
86 }
87 m_refCount &= ~deferredFlag;
88 return !m_refCount;
89 }
90
91private:
92 mutable unsigned m_refCount;
93};
94
95template<typename T>
96class DeferrableRefCounted : public DeferrableRefCountedBase {
97 WTF_MAKE_NONCOPYABLE(DeferrableRefCounted); WTF_MAKE_FAST_ALLOCATED;
98public:
99 void deref() const
100 {
101 if (derefBase())
102 delete static_cast<const T*>(this);
103 }
104
105 bool setIsDeferred(bool value)
106 {
107 if (!setIsDeferredBase(value))
108 return false;
109 delete static_cast<T*>(this);
110 return true;
111 }
112
113protected:
114 DeferrableRefCounted() { }
115 ~DeferrableRefCounted() { }
116};
117
118} // namespace WTF
119
120using WTF::DeferrableRefCounted;
121