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