1/*
2 * Copyright (C) 2008, 2016 Apple Inc. All rights reserved.
3 * Copyright (C) 2009 Jian Li <[email protected]>
4 * Copyright (C) 2012 Patrick Gansterer <[email protected]>
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 *
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of Apple Inc. ("Apple") nor the names of
16 * its contributors may be used to endorse or promote products derived
17 * from this software without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
20 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
21 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
22 * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
23 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
24 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
25 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
26 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
28 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30
31/* Thread local storage is implemented by using either pthread API or Windows
32 * native API. There is subtle semantic discrepancy for the cleanup function
33 * implementation as noted below:
34 * @ In pthread implementation, the destructor function will be called
35 * repeatedly if there is still non-NULL value associated with the function.
36 * @ In Windows native implementation, the destructor function will be called
37 * only once.
38 * This semantic discrepancy does not impose any problem because nowhere in
39 * WebKit the repeated call bahavior is utilized.
40 */
41
42#pragma once
43
44#include <wtf/MainThread.h>
45#include <wtf/Noncopyable.h>
46#include <wtf/StdLibExtras.h>
47#include <wtf/Threading.h>
48
49namespace WTF {
50
51enum class CanBeGCThread {
52 False,
53 True
54};
55
56template<typename T, CanBeGCThread canBeGCThread = CanBeGCThread::False> class ThreadSpecific {
57 WTF_MAKE_NONCOPYABLE(ThreadSpecific);
58 WTF_MAKE_FAST_ALLOCATED;
59public:
60 ThreadSpecific();
61 bool isSet(); // Useful as a fast check to see if this thread has set this value.
62 T* operator->();
63 operator T*();
64 T& operator*();
65
66private:
67 // Not implemented. It's technically possible to destroy a thread specific key, but one would need
68 // to make sure that all values have been destroyed already (usually, that all threads that used it
69 // have exited). It's unlikely that any user of this call will be in that situation - and having
70 // a destructor defined can be confusing, given that it has such strong pre-requisites to work correctly.
71 ~ThreadSpecific();
72
73 struct Data {
74 WTF_MAKE_NONCOPYABLE(Data);
75 WTF_MAKE_FAST_ALLOCATED;
76 public:
77 using PointerType = typename std::remove_const<T>::type*;
78
79 Data(ThreadSpecific<T, canBeGCThread>* owner)
80 : owner(owner)
81 {
82 // Set up thread-specific value's memory pointer before invoking constructor, in case any function it calls
83 // needs to access the value, to avoid recursion.
84 owner->setInTLS(this);
85 new (NotNull, storagePointer()) T();
86 }
87
88 ~Data()
89 {
90 storagePointer()->~T();
91 owner->setInTLS(nullptr);
92 }
93
94 PointerType storagePointer() const { return const_cast<PointerType>(reinterpret_cast<const T*>(&m_storage)); }
95
96 typename std::aligned_storage<sizeof(T), std::alignment_of<T>::value>::type m_storage;
97 ThreadSpecific<T, canBeGCThread>* owner;
98 };
99
100 T* get();
101 T* set();
102 void setInTLS(Data*);
103 void static destroy(void* ptr);
104
105#if USE(PTHREADS)
106 pthread_key_t m_key { };
107#elif OS(WINDOWS)
108 int m_key;
109#endif
110};
111
112#if USE(PTHREADS)
113
114template<typename T, CanBeGCThread canBeGCThread>
115inline ThreadSpecific<T, canBeGCThread>::ThreadSpecific()
116{
117 int error = pthread_key_create(&m_key, destroy);
118 if (error)
119 CRASH();
120}
121
122template<typename T, CanBeGCThread canBeGCThread>
123inline T* ThreadSpecific<T, canBeGCThread>::get()
124{
125 Data* data = static_cast<Data*>(pthread_getspecific(m_key));
126 if (data)
127 return data->storagePointer();
128 return nullptr;
129}
130
131template<typename T, CanBeGCThread canBeGCThread>
132inline void ThreadSpecific<T, canBeGCThread>::setInTLS(Data* data)
133{
134 pthread_setspecific(m_key, data);
135}
136
137#elif OS(WINDOWS)
138
139template<typename T, CanBeGCThread canBeGCThread>
140inline ThreadSpecific<T, canBeGCThread>::ThreadSpecific()
141 : m_key(-1)
142{
143 bool ok = Thread::SpecificStorage::allocateKey(m_key, destroy);
144 if (!ok)
145 CRASH();
146}
147
148template<typename T, CanBeGCThread canBeGCThread>
149inline T* ThreadSpecific<T, canBeGCThread>::get()
150{
151 auto data = static_cast<Data*>(Thread::current().specificStorage().get(m_key));
152 if (!data)
153 return nullptr;
154 return data->storagePointer();
155}
156
157template<typename T, CanBeGCThread canBeGCThread>
158inline void ThreadSpecific<T, canBeGCThread>::setInTLS(Data* data)
159{
160 return Thread::current().specificStorage().set(m_key, data);
161}
162
163#else
164#error ThreadSpecific is not implemented for this platform.
165#endif
166
167template<typename T, CanBeGCThread canBeGCThread>
168inline void ThreadSpecific<T, canBeGCThread>::destroy(void* ptr)
169{
170 Data* data = static_cast<Data*>(ptr);
171
172#if USE(PTHREADS)
173 // We want get() to keep working while data destructor works, because it can be called indirectly by the destructor.
174 // Some pthreads implementations zero out the pointer before calling destroy(), so we temporarily reset it.
175 pthread_setspecific(data->owner->m_key, ptr);
176#endif
177
178 delete data;
179}
180
181template<typename T, CanBeGCThread canBeGCThread>
182inline T* ThreadSpecific<T, canBeGCThread>::set()
183{
184 RELEASE_ASSERT(canBeGCThread == CanBeGCThread::True || !Thread::mayBeGCThread());
185 ASSERT(!get());
186 Data* data = new Data(this); // Data will set itself into TLS.
187 ASSERT(get() == data->storagePointer());
188 return data->storagePointer();
189}
190
191template<typename T, CanBeGCThread canBeGCThread>
192inline bool ThreadSpecific<T, canBeGCThread>::isSet()
193{
194 return !!get();
195}
196
197template<typename T, CanBeGCThread canBeGCThread>
198inline ThreadSpecific<T, canBeGCThread>::operator T*()
199{
200 if (T* ptr = get())
201 return ptr;
202 return set();
203}
204
205template<typename T, CanBeGCThread canBeGCThread>
206inline T* ThreadSpecific<T, canBeGCThread>::operator->()
207{
208 return operator T*();
209}
210
211template<typename T, CanBeGCThread canBeGCThread>
212inline T& ThreadSpecific<T, canBeGCThread>::operator*()
213{
214 return *operator T*();
215}
216
217} // namespace WTF
218
219using WTF::ThreadSpecific;
220