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. 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 NeverDestroyed_h
27#define NeverDestroyed_h
28
29#include <wtf/Alignment.h>
30#include <wtf/Noncopyable.h>
31#include <wtf/StdLibExtras.h>
32#include <wtf/TypeTraits.h>
33
34// NeverDestroyed is a smart pointer like class who ensures that the destructor
35// for the given object is never called, but doesn't use the heap to allocate it.
36// It's useful for static local variables, and can be used like so:
37//
38// MySharedGlobal& mySharedGlobal()
39// {
40// static NeverDestroyed<MySharedGlobal> myGlobal("Hello", 42);
41// return myGlobal;
42// }
43//
44
45namespace WTF {
46
47template<typename T> class NeverDestroyed {
48 WTF_MAKE_NONCOPYABLE(NeverDestroyed);
49
50public:
51#if COMPILER_SUPPORTS(CXX_VARIADIC_TEMPLATES)
52 template<typename... Args>
53 NeverDestroyed(Args&&... args)
54 {
55 new (asPtr()) T(std::forward<Args>(args)...);
56 }
57#else
58 NeverDestroyed()
59 {
60 new (NotNull, asPtr()) T;
61 }
62
63 template<typename P1>
64 NeverDestroyed(const P1& p1)
65 {
66 new (NotNull, asPtr()) T(p1);
67 }
68#endif
69
70 operator T&() { return *asPtr(); }
71
72private:
73#if COMPILER_SUPPORTS(CXX_RVALUE_REFERENCES)
74 NeverDestroyed(NeverDestroyed&&) WTF_DELETED_FUNCTION;
75#endif
76
77 typedef typename WTF::RemoveConst<T>::Type *PointerType;
78
79 PointerType asPtr() { return reinterpret_cast<PointerType>(&m_storage); }
80
81 // FIXME: Investigate whether we should allocate a hunk of virtual memory
82 // and hand out chunks of it to NeverDestroyed instead, to reduce fragmentation.
83 AlignedBuffer<sizeof(T), WTF_ALIGN_OF(T)> m_storage;
84};
85
86} // namespace WTF;
87
88using WTF::NeverDestroyed;
89
90#endif // NeverDestroyed_h