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 // 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_THREADING_THREAD_LOCAL_H_ 49 #define BASE_THREADING_THREAD_LOCAL_H_ 50 #pragma once 51 52 #include "base/base_api.h" 53 #include "base/basictypes.h" 54 55 #if defined(OS_POSIX) 56 #include <pthread.h> 57 #endif 58 59 namespace base { 60 61 namespace internal { 62 63 // Helper functions that abstract the cross-platform APIs. Do not use directly. 64 struct BASE_API ThreadLocalPlatform { 65 #if defined(OS_WIN) 66 typedef unsigned long SlotType; 67 #elif defined(OS_POSIX) 68 typedef pthread_key_t SlotType; 69 #endif 70 71 static void AllocateSlot(SlotType& slot); 72 static void FreeSlot(SlotType& slot); 73 static void* GetValueFromSlot(SlotType& slot); 74 static void SetValueInSlot(SlotType& slot, void* value); 75 }; 76 77 } // namespace internal 78 79 template <typename Type> 80 class ThreadLocalPointer { 81 public: ThreadLocalPointer()82 ThreadLocalPointer() : slot_() { 83 internal::ThreadLocalPlatform::AllocateSlot(slot_); 84 } 85 ~ThreadLocalPointer()86 ~ThreadLocalPointer() { 87 internal::ThreadLocalPlatform::FreeSlot(slot_); 88 } 89 Get()90 Type* Get() { 91 return static_cast<Type*>( 92 internal::ThreadLocalPlatform::GetValueFromSlot(slot_)); 93 } 94 Set(Type * ptr)95 void Set(Type* ptr) { 96 internal::ThreadLocalPlatform::SetValueInSlot(slot_, ptr); 97 } 98 99 private: 100 typedef internal::ThreadLocalPlatform::SlotType SlotType; 101 102 SlotType slot_; 103 104 DISALLOW_COPY_AND_ASSIGN(ThreadLocalPointer<Type>); 105 }; 106 107 class ThreadLocalBoolean { 108 public: ThreadLocalBoolean()109 ThreadLocalBoolean() { } ~ThreadLocalBoolean()110 ~ThreadLocalBoolean() { } 111 Get()112 bool Get() { 113 return tlp_.Get() != NULL; 114 } 115 Set(bool val)116 void Set(bool val) { 117 tlp_.Set(reinterpret_cast<void*>(val ? 1 : 0)); 118 } 119 120 private: 121 ThreadLocalPointer<void> tlp_; 122 123 DISALLOW_COPY_AND_ASSIGN(ThreadLocalBoolean); 124 }; 125 126 } // namespace base 127 128 #endif // BASE_THREADING_THREAD_LOCAL_H_ 129