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// Copyright 2011 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef CC_BASE_COMPLETION_EVENT_H_
#define CC_BASE_COMPLETION_EVENT_H_
#include "base/check.h"
#include "base/synchronization/waitable_event.h"
#include "base/threading/thread_restrictions.h"
#include "base/time/time.h"
namespace cc {
// Used for making blocking calls from one thread to another. Use only when
// absolutely certain that doing-so will not lead to a deadlock.
//
// It is safe to destroy this object as soon as Wait() returns.
class CompletionEvent {
public:
explicit CompletionEvent(base::WaitableEvent::ResetPolicy policy =
base::WaitableEvent::ResetPolicy::AUTOMATIC)
: event_(policy, base::WaitableEvent::InitialState::NOT_SIGNALED) {
#if DCHECK_IS_ON()
waited_ = false;
signaled_ = false;
#endif
}
~CompletionEvent() {
#if DCHECK_IS_ON()
DCHECK(waited_);
DCHECK(signaled_);
#endif
}
void Wait() {
#if DCHECK_IS_ON()
DCHECK(!waited_);
waited_ = true;
#endif
if (IsSignaled()) {
// The event has already been signaled and cannot be re-signaled.
// There is a non-trivial amount of machinery in WaitableEvent to quickly
// return if already signaled, which can be short-circuited.
return;
}
// http://crbug.com/902653
base::ScopedAllowBaseSyncPrimitivesOutsideBlockingScope allow_wait;
event_.Wait();
}
bool TimedWait(const base::TimeDelta& max_time) {
#if DCHECK_IS_ON()
DCHECK(!waited_);
waited_ = true;
#endif
// http://crbug.com/902653
base::ScopedAllowBaseSyncPrimitivesOutsideBlockingScope allow_wait;
if (event_.TimedWait(max_time))
return true;
#if DCHECK_IS_ON()
waited_ = false;
#endif
return false;
}
bool IsSignaled() { return event_.IsSignaled(); }
void Signal() {
#if DCHECK_IS_ON()
DCHECK(!signaled_);
signaled_ = true;
#endif
event_.Signal();
}
private:
base::WaitableEvent event_;
#if DCHECK_IS_ON()
// Used to assert that Wait() and Signal() are each called exactly once.
bool waited_;
bool signaled_;
#endif
};
} // namespace cc
#endif // CC_BASE_COMPLETION_EVENT_H_
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