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// Copyright 2012 The Chromium Authors
// 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/base_export.h"
#include "base/dcheck_is_on.h"
#include "base/macros/uniquify.h"
#include "base/sequence_checker_impl.h"
// SequenceChecker verifies mutual exclusion between calls to its
// `CalledOnValidSequence()` method. Mutual exclusion is guaranteed if all calls
// are made from the same thread, from the same sequence (see
// `SequencedTaskRunner`) or under the same lock acquired with
// `base::subtle::LockTracking::kEnabled`. SequenceChecker supports thread
// safety annotations (see base/thread_annotations.h).
//
// 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).
//
// Debugging:
// If SequenceChecker::EnableStackLogging() is called beforehand, then when
// SequenceChecker fails, in addition to crashing with a stack trace of where
// the violation occurred, it will also dump a stack trace of where the
// checker was bound to a sequence.
//
// Usage:
// class MyClass {
// public:
// MyClass() {
// // Detaching on construction is necessary for objects that are
// // constructed on one sequence and forever after used from another
// // sequence.
// DETACH_FROM_SEQUENCE(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(sequence_checker_);
// }
// void MyMethod() {
// DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
// ... (do stuff) ...
// MyOtherMethod();
// }
//
// void MyOtherMethod() VALID_CONTEXT_REQUIRED(sequence_checker_) {
// foo_ = 42;
// }
//
// private:
// // GUARDED_BY_CONTEXT() enforces that this member is only
// // accessed from a scope that invokes DCHECK_CALLED_ON_VALID_SEQUENCE()
// // or from a function annotated with VALID_CONTEXT_REQUIRED(). A
// // DCHECK build will not compile if the member is accessed and these
// // conditions are not met.
// int foo_ GUARDED_BY_CONTEXT(sequence_checker_);
//
// SEQUENCE_CHECKER(sequence_checker_);
// }
#if DCHECK_IS_ON()
#define SEQUENCE_CHECKER(name) base::SequenceChecker name
#define DCHECK_CALLED_ON_VALID_SEQUENCE(name, ...) \
base::ScopedValidateSequenceChecker BASE_UNIQUIFY( \
scoped_validate_sequence_checker_)(name, ##__VA_ARGS__)
#define DETACH_FROM_SEQUENCE(name) (name).DetachFromSequence()
#else // DCHECK_IS_ON()
// A no-op expansion that can be followed by a semicolon at class level.
#define SEQUENCE_CHECKER(name) static_assert(true, "")
#define DCHECK_CALLED_ON_VALID_SEQUENCE(name, ...) EAT_CHECK_STREAM_PARAMS()
#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.
// Note: This is marked with "context" capability in order to support
// thread_annotations.h.
class THREAD_ANNOTATION_ATTRIBUTE__(capability("context"))
SequenceCheckerDoNothing {
public:
static void EnableStackLogging() {}
SequenceCheckerDoNothing() = default;
// Moving between matching sequences is allowed to help classes with
// SequenceCheckers that want a default move-construct/assign.
SequenceCheckerDoNothing(SequenceCheckerDoNothing&& other) = default;
SequenceCheckerDoNothing& operator=(SequenceCheckerDoNothing&& other) =
default;
SequenceCheckerDoNothing(const SequenceCheckerDoNothing&) = delete;
SequenceCheckerDoNothing& operator=(const SequenceCheckerDoNothing&) = delete;
[[nodiscard]] bool CalledOnValidSequence(void* = nullptr) const {
return true;
}
void DetachFromSequence() {}
};
#if DCHECK_IS_ON()
using SequenceChecker = SequenceCheckerImpl;
#else
using SequenceChecker = SequenceCheckerDoNothing;
#endif // DCHECK_IS_ON()
#if DCHECK_IS_ON()
class BASE_EXPORT SCOPED_LOCKABLE ScopedValidateSequenceChecker {
public:
explicit ScopedValidateSequenceChecker(const SequenceChecker& checker)
EXCLUSIVE_LOCK_FUNCTION(checker);
~ScopedValidateSequenceChecker() UNLOCK_FUNCTION();
};
#endif
} // namespace base
#endif // BASE_SEQUENCE_CHECKER_H_
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