thread_local.h revision b8cf94937c52feb53b55c39e3f82094d27de464c
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 62namespace base { 63namespace internal { 64 65// Helper functions that abstract the cross-platform APIs. Do not use directly. 66struct 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 83template <typename Type> 84class 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 112class 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_ 134