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