blob: cad9add3a9ca344ec03b75a8be150370d509ba1a [file] [log] [blame]
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// WARNING: Thread local storage is a bit tricky to get right. Please make sure
// that this is really the proper solution for what you're trying to achieve.
// Don't prematurely optimize, most likely you can just use a Lock.
// These classes implement a wrapper around ThreadLocalStorage::Slot. On
// construction, they will allocate a TLS slot, and free the TLS slot on
// destruction. No memory management (creation or destruction) is handled. This
// means for uses of ThreadLocalPointer, you must correctly manage the memory
// yourself, these classes will not destroy the pointer for you. There are no
// at-thread-exit actions taken by these classes.
// ThreadLocalPointer<Type> wraps a Type*. It performs no creation or
// destruction, so memory management must be handled elsewhere. The first call
// to Get() on a thread will return NULL. You can update the pointer with a call
// to Set().
// ThreadLocalBoolean wraps a bool. It will default to false if it has never
// been set otherwise with Set().
// Thread Safety: An instance of ThreadLocalStorage is completely thread safe
// once it has been created. If you want to dynamically create an instance, you
// must of course properly deal with safety and race conditions. This means a
// function-level static initializer is generally inappropiate.
// In Android, the system TLS is limited.
// Example usage:
// // My class is logically attached to a single thread. We cache a pointer
// // on the thread it was created on, so we can implement current().
// MyClass::MyClass() {
// DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() == NULL);
// Singleton<ThreadLocalPointer<MyClass> >::get()->Set(this);
// }
// MyClass::~MyClass() {
// DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() != NULL);
// Singleton<ThreadLocalPointer<MyClass> >::get()->Set(NULL);
// }
// // Return the current MyClass associated with the calling thread, can be
// // NULL if there isn't a MyClass associated.
// MyClass* MyClass::current() {
// return Singleton<ThreadLocalPointer<MyClass> >::get()->Get();
// }
#include "base/macros.h"
#include "base/threading/thread_local_storage.h"
namespace base {
template <typename Type>
class ThreadLocalPointer {
ThreadLocalPointer() = default;
~ThreadLocalPointer() = default;
Type* Get() {
return static_cast<Type*>(slot_.Get());
void Set(Type* ptr) {
slot_.Set(const_cast<void*>(static_cast<const void*>(ptr)));
ThreadLocalStorage::Slot slot_;
class ThreadLocalBoolean {
ThreadLocalBoolean() = default;
~ThreadLocalBoolean() = default;
bool Get() {
return tlp_.Get() != nullptr;
void Set(bool val) {
tlp_.Set(val ? this : nullptr);
ThreadLocalPointer<void> tlp_;
} // namespace base