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1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 // WARNING: Thread local storage is a bit tricky to get right. Please make | 5 // WARNING: Thread local storage is a bit tricky to get right. Please make sure |
6 // sure that this is really the proper solution for what you're trying to | 6 // that this is really the proper solution for what you're trying to achieve. |
7 // achieve. Don't prematurely optimize, most likely you can just use a Lock. | 7 // Don't prematurely optimize, most likely you can just use a Lock. |
8 // | 8 // |
9 // These classes implement a wrapper around the platform's TLS storage | 9 // These classes implement a wrapper around ThreadLocalStorage::Slot. On |
brettw
2016/02/25 22:57:45
At the top of thread_local_storage.h it says you s
robliao
2016/02/26 00:02:51
Done. Updated to...
// WARNING: You should *NOT*
| |
10 // mechanism. On construction, they will allocate a TLS slot, and free the | 10 // construction, they will allocate a TLS slot, and free the TLS slot on |
11 // TLS slot on destruction. No memory management (creation or destruction) is | 11 // destruction. No memory management (creation or destruction) is handled. This |
12 // handled. This means for uses of ThreadLocalPointer, you must correctly | 12 // means for uses of ThreadLocalPointer, you must correctly manage the memory |
13 // manage the memory yourself, these classes will not destroy the pointer for | 13 // yourself, these classes will not destroy the pointer for you. There are no |
14 // you. There are no at-thread-exit actions taken by these classes. | 14 // at-thread-exit actions taken by these classes. |
15 // | 15 // |
16 // ThreadLocalPointer<Type> wraps a Type*. It performs no creation or | 16 // ThreadLocalPointer<Type> wraps a Type*. It performs no creation or |
17 // destruction, so memory management must be handled elsewhere. The first call | 17 // destruction, so memory management must be handled elsewhere. The first call |
18 // to Get() on a thread will return NULL. You can update the pointer with a | 18 // to Get() on a thread will return NULL. You can update the pointer with a call |
19 // call to Set(). | 19 // to Set(). |
20 // | 20 // |
21 // ThreadLocalBoolean wraps a bool. It will default to false if it has never | 21 // ThreadLocalBoolean wraps a bool. It will default to false if it has never |
22 // been set otherwise with Set(). | 22 // been set otherwise with Set(). |
23 // | 23 // |
24 // Thread Safety: An instance of ThreadLocalStorage is completely thread safe | 24 // Thread Safety: An instance of ThreadLocalStorage is completely thread safe |
25 // once it has been created. If you want to dynamically create an instance, | 25 // once it has been created. If you want to dynamically create an instance, you |
26 // you must of course properly deal with safety and race conditions. This | 26 // must of course properly deal with safety and race conditions. This means a |
27 // means a function-level static initializer is generally inappropiate. | 27 // function-level static initializer is generally inappropiate. |
28 // | 28 // |
29 // In Android, the system TLS is limited, the implementation is backed with | 29 // In Android, the system TLS is limited. |
30 // ThreadLocalStorage. | |
31 // | 30 // |
32 // Example usage: | 31 // Example usage: |
33 // // My class is logically attached to a single thread. We cache a pointer | 32 // // My class is logically attached to a single thread. We cache a pointer |
34 // // on the thread it was created on, so we can implement current(). | 33 // // on the thread it was created on, so we can implement current(). |
35 // MyClass::MyClass() { | 34 // MyClass::MyClass() { |
36 // DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() == NULL); | 35 // DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() == NULL); |
37 // Singleton<ThreadLocalPointer<MyClass> >::get()->Set(this); | 36 // Singleton<ThreadLocalPointer<MyClass> >::get()->Set(this); |
38 // } | 37 // } |
39 // | 38 // |
40 // MyClass::~MyClass() { | 39 // MyClass::~MyClass() { |
41 // DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() != NULL); | 40 // DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() != NULL); |
42 // Singleton<ThreadLocalPointer<MyClass> >::get()->Set(NULL); | 41 // Singleton<ThreadLocalPointer<MyClass> >::get()->Set(NULL); |
43 // } | 42 // } |
44 // | 43 // |
45 // // Return the current MyClass associated with the calling thread, can be | 44 // // Return the current MyClass associated with the calling thread, can be |
46 // // NULL if there isn't a MyClass associated. | 45 // // NULL if there isn't a MyClass associated. |
47 // MyClass* MyClass::current() { | 46 // MyClass* MyClass::current() { |
48 // return Singleton<ThreadLocalPointer<MyClass> >::get()->Get(); | 47 // return Singleton<ThreadLocalPointer<MyClass> >::get()->Get(); |
49 // } | 48 // } |
50 | 49 |
51 #ifndef BASE_THREADING_THREAD_LOCAL_H_ | 50 #ifndef BASE_THREADING_THREAD_LOCAL_H_ |
52 #define BASE_THREADING_THREAD_LOCAL_H_ | 51 #define BASE_THREADING_THREAD_LOCAL_H_ |
53 | 52 |
54 #include "base/base_export.h" | |
55 #include "base/macros.h" | 53 #include "base/macros.h" |
56 #include "base/threading/thread_local_storage.h" | 54 #include "base/threading/thread_local_storage.h" |
57 #include "build/build_config.h" | |
58 | |
59 #if defined(OS_POSIX) | |
60 #include <pthread.h> | |
61 #endif | |
62 | 55 |
63 namespace base { | 56 namespace base { |
64 namespace internal { | |
65 | |
66 // Helper functions that abstract the cross-platform APIs. Do not use directly. | |
67 struct BASE_EXPORT ThreadLocalPlatform { | |
68 #if defined(OS_WIN) | |
69 typedef unsigned long SlotType; | |
70 #elif defined(OS_ANDROID) | |
71 typedef ThreadLocalStorage::StaticSlot SlotType; | |
72 #elif defined(OS_POSIX) | |
73 typedef pthread_key_t SlotType; | |
74 #endif | |
75 | |
76 static void AllocateSlot(SlotType* slot); | |
77 static void FreeSlot(SlotType slot); | |
78 static void* GetValueFromSlot(SlotType slot); | |
79 static void SetValueInSlot(SlotType slot, void* value); | |
80 }; | |
81 | |
82 } // namespace internal | |
83 | 57 |
84 template <typename Type> | 58 template <typename Type> |
85 class ThreadLocalPointer { | 59 class ThreadLocalPointer { |
86 public: | 60 public: |
87 ThreadLocalPointer() : slot_() { | 61 ThreadLocalPointer() = default; |
88 internal::ThreadLocalPlatform::AllocateSlot(&slot_); | 62 ~ThreadLocalPointer() = default; |
89 } | |
90 | |
91 ~ThreadLocalPointer() { | |
92 internal::ThreadLocalPlatform::FreeSlot(slot_); | |
93 } | |
94 | 63 |
95 Type* Get() { | 64 Type* Get() { |
96 return static_cast<Type*>( | 65 return static_cast<Type*>(slot_.Get()); |
97 internal::ThreadLocalPlatform::GetValueFromSlot(slot_)); | |
98 } | 66 } |
99 | 67 |
100 void Set(Type* ptr) { | 68 void Set(Type* ptr) { |
101 internal::ThreadLocalPlatform::SetValueInSlot( | 69 slot_.Set(const_cast<void*>(static_cast<const void*>(ptr))); |
102 slot_, const_cast<void*>(static_cast<const void*>(ptr))); | |
103 } | 70 } |
104 | 71 |
105 private: | 72 private: |
106 typedef internal::ThreadLocalPlatform::SlotType SlotType; | 73 ThreadLocalStorage::Slot slot_; |
107 | |
108 SlotType slot_; | |
109 | 74 |
110 DISALLOW_COPY_AND_ASSIGN(ThreadLocalPointer<Type>); | 75 DISALLOW_COPY_AND_ASSIGN(ThreadLocalPointer<Type>); |
111 }; | 76 }; |
112 | 77 |
113 class ThreadLocalBoolean { | 78 class ThreadLocalBoolean { |
114 public: | 79 public: |
115 ThreadLocalBoolean() {} | 80 ThreadLocalBoolean() = default; |
116 ~ThreadLocalBoolean() {} | 81 ~ThreadLocalBoolean() = default; |
117 | 82 |
118 bool Get() { | 83 bool Get() { |
119 return tlp_.Get() != NULL; | 84 return tlp_.Get() != nullptr; |
120 } | 85 } |
121 | 86 |
122 void Set(bool val) { | 87 void Set(bool val) { |
123 tlp_.Set(val ? this : NULL); | 88 tlp_.Set(val ? this : nullptr); |
124 } | 89 } |
125 | 90 |
126 private: | 91 private: |
127 ThreadLocalPointer<void> tlp_; | 92 ThreadLocalPointer<void> tlp_; |
128 | 93 |
129 DISALLOW_COPY_AND_ASSIGN(ThreadLocalBoolean); | 94 DISALLOW_COPY_AND_ASSIGN(ThreadLocalBoolean); |
130 }; | 95 }; |
131 | 96 |
132 } // namespace base | 97 } // namespace base |
133 | 98 |
134 #endif // BASE_THREADING_THREAD_LOCAL_H_ | 99 #endif // BASE_THREADING_THREAD_LOCAL_H_ |
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