System.Diagnostics.Stopwatch When measuring small time periods #90788
Description
Description
The GetRawElapsedTicks() method dose not handle possebility of negative values.
// Get the elapsed ticks.
private long GetRawElapsedTicks()
{
long timeElapsed = _elapsed;
if (_isRunning)
{
// If the Stopwatch is running, add elapsed time since
// the Stopwatch is started last time.
long currentTimeStamp = GetTimestamp();
long elapsedUntilNow = currentTimeStamp - _startTimeStamp;
timeElapsed += elapsedUntilNow;
}
return timeElapsed;
}
Simple fix:
private long GetRawElapsedTicks()
{
long timeElapsed = _elapsed;
if (_isRunning)
{
// If the Stopwatch is running, add elapsed time since
// the Stopwatch is started last time.
long currentTimeStamp = GetTimestamp();
long elapsedUntilNow = currentTimeStamp - _startTimeStamp;
if (elapsedUntilNow > 0)
{
timeElapsed += elapsedUntilNow;
}
}
return timeElapsed;
}
I would like to suggest a little restructuring of the StopMethod on the System.Diagnostics.Stopwatch.
The current implementation allows negativ values in elapsedThisPeriod to be added to _elapsed and resets _elapsed if the total is a negativ value.
public void Stop()
{
// Calling stop on a stopped Stopwatch is a no-op.
if (_isRunning)
{
long endTimeStamp = GetTimestamp();
long elapsedThisPeriod = endTimeStamp - _startTimeStamp;
_elapsed += elapsedThisPeriod;
_isRunning = false;
if (_elapsed < 0)
{
// When measuring small time periods the Stopwatch.Elapsed*
// properties can return negative values. This is due to
// bugs in the basic input/output system (BIOS) or the hardware
// abstraction layer (HAL) on machines with variable-speed CPUs
// (e.g. Intel SpeedStep).
_elapsed = 0;
}
}
}
Would it not make more sens to skip adding negativ values to _elapsed?
public void Stop()
{
// Calling stop on a stopped Stopwatch is a no-op.
if (_isRunning)
{
long endTimeStamp = GetTimestamp();
long elapsedThisPeriod = endTimeStamp - _startTimeStamp;
_isRunning = false;
if (elapsedThisPeriod > 0)
{
// When measuring small time periods the Stopwatch.Elapsed*
// properties can return negative values. This is due to
// bugs in the basic input/output system (BIOS) or the hardware
// abstraction layer (HAL) on machines with variable-speed CPUs
// (e.g. Intel SpeedStep).
_elapsed += elapsedThisPeriod;
}
}
}
Or is the rationell due to some performance consideration in regards to the if-statement?