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// Copyright 2013 the V8 project 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 V8_BASE_PLATFORM_ELAPSED_TIMER_H_
#define V8_BASE_PLATFORM_ELAPSED_TIMER_H_
#include "src/base/logging.h"
#include "src/base/platform/time.h"
namespace v8 {
namespace base {
class ElapsedTimer final {
public:
#ifdef DEBUG
ElapsedTimer() : started_(false) {}
#endif
// Starts this timer. Once started a timer can be checked with
// |Elapsed()| or |HasExpired()|, and may be restarted using |Restart()|.
// This method must not be called on an already started timer.
void Start() {
DCHECK(!IsStarted());
start_ticks_ = Now();
#ifdef DEBUG
started_ = true;
#endif
DCHECK(IsStarted());
}
// Stops this timer. Must not be called on a timer that was not
// started before.
void Stop() {
DCHECK(IsStarted());
start_ticks_ = TimeTicks();
#ifdef DEBUG
started_ = false;
#endif
DCHECK(!IsStarted());
}
// Returns |true| if this timer was started previously.
bool IsStarted() const {
DCHECK(started_ || start_ticks_.IsNull());
DCHECK(!started_ || !start_ticks_.IsNull());
return !start_ticks_.IsNull();
}
// Restarts the timer and returns the time elapsed since the previous start.
// This method is equivalent to obtaining the elapsed time with |Elapsed()|
// and then starting the timer again, but does so in one single operation,
// avoiding the need to obtain the clock value twice. It may only be called
// on a previously started timer.
TimeDelta Restart() {
DCHECK(IsStarted());
TimeTicks ticks = Now();
TimeDelta elapsed = ticks - start_ticks_;
DCHECK_GE(elapsed.InMicroseconds(), 0);
start_ticks_ = ticks;
DCHECK(IsStarted());
return elapsed;
}
// Returns the time elapsed since the previous start. This method may only
// be called on a previously started timer.
TimeDelta Elapsed() const {
DCHECK(IsStarted());
TimeDelta elapsed = Now() - start_ticks_;
DCHECK_GE(elapsed.InMicroseconds(), 0);
return elapsed;
}
// Returns |true| if the specified |time_delta| has elapsed since the
// previous start, or |false| if not. This method may only be called on
// a previously started timer.
bool HasExpired(TimeDelta time_delta) const {
DCHECK(IsStarted());
return Elapsed() >= time_delta;
}
private:
static V8_INLINE TimeTicks Now() {
TimeTicks now = TimeTicks::HighResolutionNow();
DCHECK(!now.IsNull());
return now;
}
TimeTicks start_ticks_;
#ifdef DEBUG
bool started_;
#endif
};
} // namespace base
} // namespace v8
#endif // V8_BASE_PLATFORM_ELAPSED_TIMER_H_
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