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 59namespace base { 60 61namespace internal { 62 63// Helper functions that abstract the cross-platform APIs. Do not use directly. 64struct 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 79template <typename Type> 80class ThreadLocalPointer { 81 public: 82 ThreadLocalPointer() : slot_() { 83 internal::ThreadLocalPlatform::AllocateSlot(slot_); 84 } 85 86 ~ThreadLocalPointer() { 87 internal::ThreadLocalPlatform::FreeSlot(slot_); 88 } 89 90 Type* Get() { 91 return static_cast<Type*>( 92 internal::ThreadLocalPlatform::GetValueFromSlot(slot_)); 93 } 94 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 107class ThreadLocalBoolean { 108 public: 109 ThreadLocalBoolean() { } 110 ~ThreadLocalBoolean() { } 111 112 bool Get() { 113 return tlp_.Get() != NULL; 114 } 115 116 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