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// Copyright (c) 2012 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.
#ifndef BASE_THREADING_THREAD_CHECKER_H_
#define BASE_THREADING_THREAD_CHECKER_H_
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/threading/thread_checker_impl.h"
// ThreadChecker is a helper class used to help verify that some methods of a
// class are called from the same thread (for thread-affinity).
//
// Use the macros below instead of the ThreadChecker directly so that the unused
// member doesn't result in an extra byte (four when padded) per instance in
// production.
//
// Usage of this class should be *rare* as most classes require thread-safety
// but not thread-affinity. Prefer base::SequenceChecker to verify thread-safe
// access.
//
// Thread-affinity checks should only be required in classes that use thread-
// local-storage or a third-party API that does.
//
// Prefer to encode the minimum requirements of each class instead of the
// environment it happens to run in today. e.g. if a class requires thread-
// safety but not thread-affinity, use a SequenceChecker even if it happens to
// run on a SingleThreadTaskRunner today. That makes it easier to understand
// what would need to change to turn that SingleThreadTaskRunner into a
// SequencedTaskRunner for ease of scheduling as well as minimizes side-effects
// if that change is made.
//
// Usage:
// class MyClass {
// public:
// MyClass() {
// // It's sometimes useful to detach on construction for objects that are
// // constructed in one place and forever after used from another
// // thread.
// DETACH_FROM_THREAD(thread_checker_);
// }
//
// ~MyClass() {
// // ThreadChecker doesn't automatically check it's destroyed on origin
// // thread for the same reason it's sometimes detached in the
// // constructor. It's okay to destroy off thread if the owner otherwise
// // knows usage on the associated thread is done. If you're not
// // detaching in the constructor, you probably want to explicitly check
// // in the destructor.
// DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
// }
//
// void MyMethod() {
// DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
// ... (do stuff) ...
// }
//
// private:
// THREAD_CHECKER(thread_checker_);
// }
#if DCHECK_IS_ON()
#define THREAD_CHECKER(name) base::ThreadChecker name
#define DCHECK_CALLED_ON_VALID_THREAD(name) DCHECK((name).CalledOnValidThread())
#define DETACH_FROM_THREAD(name) (name).DetachFromThread()
#else // DCHECK_IS_ON()
#define THREAD_CHECKER(name) static_assert(true, "")
#define DCHECK_CALLED_ON_VALID_THREAD(name) EAT_STREAM_PARAMETERS
#define DETACH_FROM_THREAD(name)
#endif // DCHECK_IS_ON()
namespace base {
// Do nothing implementation, for use in release mode.
//
// Note: You should almost always use the ThreadChecker class (through the above
// macros) to get the right version for your build configuration.
class ThreadCheckerDoNothing {
public:
ThreadCheckerDoNothing() = default;
// Moving between matching threads is allowed to help classes with
// ThreadCheckers that want a default move-construct/assign.
ThreadCheckerDoNothing(ThreadCheckerDoNothing&& other) = default;
ThreadCheckerDoNothing& operator=(ThreadCheckerDoNothing&& other) = default;
bool CalledOnValidThread() const WARN_UNUSED_RESULT { return true; }
void DetachFromThread() {}
private:
DISALLOW_COPY_AND_ASSIGN(ThreadCheckerDoNothing);
};
// Note that ThreadCheckerImpl::CalledOnValidThread() returns false when called
// from tasks posted to SingleThreadTaskRunners bound to different sequences,
// even if the tasks happen to run on the same thread (e.g. two independent
// SingleThreadTaskRunners on the ThreadPool that happen to share a thread).
#if DCHECK_IS_ON()
class ThreadChecker : public ThreadCheckerImpl {
};
#else
class ThreadChecker : public ThreadCheckerDoNothing {
};
#endif // DCHECK_IS_ON()
} // namespace base
#endif // BASE_THREADING_THREAD_CHECKER_H_
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