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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_SEQUENCE_CHECKER_H_
#define BASE_SEQUENCE_CHECKER_H_
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/sequence_checker_impl.h"
// SequenceChecker is a helper class used to help verify that some methods of a
// class are called sequentially (for thread-safety).
//
// Use the macros below instead of the SequenceChecker directly so that the
// unused member doesn't result in an extra byte (four when padded) per
// instance in production.
//
// This class is much prefered to ThreadChecker for thread-safety checks.
// ThreadChecker should only be used for classes that are truly thread-affine
// (use thread-local-storage or a third-party API that does).
//
// 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
// // sequence.
// DETACH_FROM_SEQUENCE(my_sequence_checker_);
// }
//
// ~MyClass() {
// // SequenceChecker doesn't automatically check it's destroyed on origin
// // sequence for the same reason it's sometimes detached in the
// // constructor. It's okay to destroy off sequence if the owner
// // otherwise knows usage on the associated sequence is done. If you're
// // not detaching in the constructor, you probably want to explicitly
// // check in the destructor.
// DCHECK_CALLED_ON_VALID_SEQUENCE(my_sequence_checker_);
// }
// void MyMethod() {
// DCHECK_CALLED_ON_VALID_SEQUENCE(my_sequence_checker_);
// ... (do stuff) ...
// }
//
// private:
// SEQUENCE_CHECKER(my_sequence_checker_);
// }
#if DCHECK_IS_ON()
#define SEQUENCE_CHECKER(name) base::SequenceChecker name
#define DCHECK_CALLED_ON_VALID_SEQUENCE(name) \
DCHECK((name).CalledOnValidSequence())
#define DETACH_FROM_SEQUENCE(name) (name).DetachFromSequence()
#else // DCHECK_IS_ON()
#define SEQUENCE_CHECKER(name)
#define DCHECK_CALLED_ON_VALID_SEQUENCE(name) EAT_STREAM_PARAMETERS
#define DETACH_FROM_SEQUENCE(name)
#endif // DCHECK_IS_ON()
namespace base {
// Do nothing implementation, for use in release mode.
//
// Note: You should almost always use the SequenceChecker class (through the
// above macros) to get the right version for your build configuration.
class SequenceCheckerDoNothing {
public:
SequenceCheckerDoNothing() = default;
bool CalledOnValidSequence() const WARN_UNUSED_RESULT { return true; }
void DetachFromSequence() {}
private:
DISALLOW_COPY_AND_ASSIGN(SequenceCheckerDoNothing);
};
#if DCHECK_IS_ON()
class SequenceChecker : public SequenceCheckerImpl {
};
#else
class SequenceChecker : public SequenceCheckerDoNothing {
};
#endif // DCHECK_IS_ON()
} // namespace base
#endif // BASE_SEQUENCE_CHECKER_H_
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