Question:
I find that the System.Diagnostics.Stopwatch class has what seems to be measurable inaccuracy, even over a short time period (i.e. 20 seconds). My process is showing an elapsed time of 20.3+ seconds for a process coded to run 20 seconds:
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$elapsed = [System.Diagnostics.Stopwatch]::StartNew() write-host "Started at $(get-date)" for ($t=1; $t -le 20; $t++) { Write-Host "Elapsed Time: $($elapsed.Elapsed.ToString())" sleep 1 } write-host "Ended at $(get-date)" write-host "Total Elapsed Time: $($elapsed.Elapsed.ToString())" Started at 02/02/2013 15:08:43 Elapsed Time: 00:00:00.0329924 Elapsed Time: 00:00:01.0417435 Elapsed Time: 00:00:02.0547547 Elapsed Time: 00:00:03.0689716 Elapsed Time: 00:00:04.0820497 Elapsed Time: 00:00:05.0963413 Elapsed Time: 00:00:06.1113915 Elapsed Time: 00:00:07.1244044 Elapsed Time: 00:00:08.1396105 Elapsed Time: 00:00:09.1528952 Elapsed Time: 00:00:10.1659905 Elapsed Time: 00:00:11.1800884 Elapsed Time: 00:00:12.1940009 Elapsed Time: 00:00:13.2081824 Elapsed Time: 00:00:14.2223585 Elapsed Time: 00:00:15.2375023 Elapsed Time: 00:00:16.2506360 Elapsed Time: 00:00:17.2656845 Elapsed Time: 00:00:18.2790676 Elapsed Time: 00:00:19.2928700 Ended at 02/02/2013 15:09:04 Total Elapsed Time: 00:00:20.3080067 |
Is this kind of accuracy drift to be expected when using the Stopwatch class in PowerShell? It seems to increase disproportional to the time span (i.e. 10 seconds is off by 0.1 and 20 by 0.3). Is my code at fault?
Answer:
The question is, what are you trying to do? If you are trying to determine how long it takes a script to run, exactly, you should use the stopwatch. However, if you are trying to start a new sequence of commands after a specified period, use a [System.Timers.Timer] and register an event for the elapsed event on the timer object. Then specify the action of the registered event to what it you are trying to accomplish.