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