c# stopwatch.elapsed values innaccurate

Question

I want to time total runtime of a progam I am working on.

Currently the code looks similar to this (sw is a member of the program class):

 void Main(string[] args)
 {
     sw.Start();
     //Code here starts a thread
     //Code here joins the thread
     //Code operates on results of threaded operation
     sw.Stop();
     Console.WrtieLine("Operation took {0}", sw.Elapsed.ToString());
 }

I assume this issue is caused by the thread taking control of the program execution but that's the operation that takes the most time and I'm supposed to avoid changing that code as other projects depend on it as well.

For reference, simple observation shows that the code takes nearly half an hour to run, but the elapsed time according to the stopwatch is only 23 seconds or so. Exact output Operation took 00:00:23.1064841

It is unlikely that multi-threading causes such a big discrepancy. It sounds like the code in the main thread doesn't actually wait for the second thread to end before stopping the stopwatch. — Mike Dinescu, Jan 19 '15 at 18:18
What is the exact output? Are you sure it's not reporting 23 minutes? — Cameron, Jan 19 '15 at 18:19
Is the final line printed after half a hour, or after 23 sec? — Eugene Sh., Jan 19 '15 at 18:19
@MikeDinescu The log file shows all the processing logs from the thread before the logging of the time. (The person I got the code from redirected console out to a log file.) — mgbowe1, Jan 19 '15 at 18:21
Make `sw` a local, just for the heck of it. See if anything changes. — Chris, Jan 19 '15 at 18:31
Then I suggest abandoning `Stopwatch` and going with `Environment.TickCount` or something similar. Would be really interesting to find the cause of this though. — Chris, Jan 19 '15 at 19:15
Yes, nice alternartive, but this doesnt explain why stopwatch behaves like this — Dimitar Tsonev, Jan 19 '15 at 21:04
Tick count can also be inaccurate. Here is another SO answer showing some more information that should be helpful: http://stackoverflow.com/a/8865560/2267817 — Always Learning, Jan 19 '15 at 21:06
possible duplicate of [Environment.TickCount vs DateTime.Now](http://stackoverflow.com/questions/243351/environment-tickcount-vs-datetime-now) — ivan_pozdeev, Jan 20 '15 at 09:14
@ivan_pozdeev not a duplicate, the accepted answer for that question is the problem that created this one. — mgbowe1, Jan 20 '15 at 15:30

score 1 · Accepted Answer · answered Jan 19 '15 at 20:41

In this case, the best solution is to use Environment.TickCount as it measures milliseconds since the system booted and is not processor-core dependent like Stopwatch.

int StartTime = Environment.TickCount;
//Your Code to measure here
int EndTime = Environment.TickCount;
int runningTime = EndTime - StartTIme; //running time in milliseconds
// code to do whatever you want with runningTime

c# stopwatch.elapsed values innaccurate

1 Answers1