1 // Copyright (c) 2006-2008 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 warpper 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 // Example usage: 30 // // My class is logically attached to a single thread. We cache a pointer 31 // // on the thread it was created on, so we can implement current(). 32 // MyClass::MyClass() { 33 // DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() == NULL); 34 // Singleton<ThreadLocalPointer<MyClass> >::get()->Set(this); 35 // } 36 // 37 // MyClass::~MyClass() { 38 // DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() != NULL); 39 // Singleton<ThreadLocalPointer<MyClass> >::get()->Set(NULL); 40 // } 41 // 42 // // Return the current MyClass associated with the calling thread, can be 43 // // NULL if there isn't a MyClass associated. 44 // MyClass* MyClass::current() { 45 // return Singleton<ThreadLocalPointer<MyClass> >::get()->Get(); 46 // } 47 48 #ifndef BASE_THREAD_LOCAL_H_ 49 #define BASE_THREAD_LOCAL_H_ 50 51 #include "base/basictypes.h" 52 53 #if defined(OS_POSIX) 54 #include <pthread.h> 55 #endif 56 57 namespace base { 58 59 // Helper functions that abstract the cross-platform APIs. Do not use directly. 60 struct ThreadLocalPlatform { 61 #if defined(OS_WIN) 62 typedef int SlotType; 63 #elif defined(OS_POSIX) 64 typedef pthread_key_t SlotType; 65 #endif 66 67 static void AllocateSlot(SlotType& slot); 68 static void FreeSlot(SlotType& slot); 69 static void* GetValueFromSlot(SlotType& slot); 70 static void SetValueInSlot(SlotType& slot, void* value); 71 }; 72 73 template <typename Type> 74 class ThreadLocalPointer { 75 public: ThreadLocalPointer()76 ThreadLocalPointer() : slot_() { 77 ThreadLocalPlatform::AllocateSlot(slot_); 78 } 79 ~ThreadLocalPointer()80 ~ThreadLocalPointer() { 81 ThreadLocalPlatform::FreeSlot(slot_); 82 } 83 Get()84 Type* Get() { 85 return static_cast<Type*>(ThreadLocalPlatform::GetValueFromSlot(slot_)); 86 } 87 Set(Type * ptr)88 void Set(Type* ptr) { 89 ThreadLocalPlatform::SetValueInSlot(slot_, ptr); 90 } 91 92 private: 93 typedef ThreadLocalPlatform::SlotType SlotType; 94 95 SlotType slot_; 96 97 DISALLOW_COPY_AND_ASSIGN(ThreadLocalPointer<Type>); 98 }; 99 100 class ThreadLocalBoolean { 101 public: ThreadLocalBoolean()102 ThreadLocalBoolean() { } ~ThreadLocalBoolean()103 ~ThreadLocalBoolean() { } 104 Get()105 bool Get() { 106 return tlp_.Get() != NULL; 107 } 108 Set(bool val)109 void Set(bool val) { 110 tlp_.Set(reinterpret_cast<void*>(val ? 1 : 0)); 111 } 112 113 private: 114 ThreadLocalPointer<void> tlp_; 115 116 DISALLOW_COPY_AND_ASSIGN(ThreadLocalBoolean); 117 }; 118 119 } // namespace base 120 121 #endif // BASE_THREAD_LOCAL_H_ 122