137 lines
4.6 KiB
C++
137 lines
4.6 KiB
C++
// 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.
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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 <memory>
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#include "base/logging.h"
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#include "base/macros.h"
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#include "base/threading/thread_local_internal.h"
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#include "base/threading/thread_local_storage.h"
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namespace base {
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template <typename T>
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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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T* Get() const { return static_cast<T*>(slot_.Get()); }
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void Set(T* 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<T>);
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};
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// A ThreadLocalOwnedPointer<T> is like a ThreadLocalPointer<T> except that
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// pointers handed to it are owned and automatically deleted during their
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// associated thread's exit phase (or when replaced if Set() is invoked multiple
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// times on the same thread).
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// The ThreadLocalOwnedPointer instance itself can only be destroyed when no
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// threads, other than the one it is destroyed on, have remaining state set in
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// it. Typically this means that ThreadLocalOwnedPointer instances are held in
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// static storage or at the very least only recycled in the single-threaded
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// phase between tests in the same process.
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#if DCHECK_IS_ON()
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template <typename T>
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using ThreadLocalOwnedPointer = internal::CheckedThreadLocalOwnedPointer<T>;
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#else // DCHECK_IS_ON()
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template <typename T>
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class ThreadLocalOwnedPointer {
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public:
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ThreadLocalOwnedPointer() = default;
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~ThreadLocalOwnedPointer() {
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// Assume that this thread is the only one with potential state left. This
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// is verified in ~CheckedThreadLocalOwnedPointer().
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Set(nullptr);
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}
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T* Get() const { return static_cast<T*>(slot_.Get()); }
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void Set(std::unique_ptr<T> ptr) {
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delete Get();
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slot_.Set(const_cast<void*>(static_cast<const void*>(ptr.release())));
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}
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private:
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static void DeleteTlsPtr(void* ptr) { delete static_cast<T*>(ptr); }
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ThreadLocalStorage::Slot slot_{&DeleteTlsPtr};
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DISALLOW_COPY_AND_ASSIGN(ThreadLocalOwnedPointer<T>);
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};
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#endif // DCHECK_IS_ON()
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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() const { return tlp_.Get() != nullptr; }
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void Set(bool val) { tlp_.Set(val ? this : nullptr); }
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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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