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: ThreadLocalPointer()86 ThreadLocalPointer() : slot_() { 87 internal::ThreadLocalPlatform::AllocateSlot(&slot_); 88 } 89 ~ThreadLocalPointer()90 ~ThreadLocalPointer() { 91 internal::ThreadLocalPlatform::FreeSlot(slot_); 92 } 93 Get()94 Type* Get() { 95 return static_cast<Type*>( 96 internal::ThreadLocalPlatform::GetValueFromSlot(slot_)); 97 } 98 Set(Type * ptr)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: ThreadLocalBoolean()114 ThreadLocalBoolean() {} ~ThreadLocalBoolean()115 ~ThreadLocalBoolean() {} 116 Get()117 bool Get() { 118 return tlp_.Get() != NULL; 119 } 120 Set(bool val)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_ 134