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