[RESOLVED] Timing problem in C#

[hatake_kakashi]

Hi guys,

My OS is Windows 7 32-bit, and I'm using Visual Studio 2008.

In my C# program I use function Thread.Sleep(5) to cause my thread to sleep in 5(ms), and then I print the elapsed time to the screen. My code snippet:

for (int i = 0; i < 20; i++)
            {
                myTimer.Start();
                Thread.Sleep(5);
                myTimer.Stop();
                dTime = myTimer.Duration;
                Console.WriteLine("{0}\n", dTime);
                // Thread.Sleep(1000);
            }
            Thread.Sleep(20000);

The strange thing is that: Depending on whether or not I comment the line Thread.Sleep(1000) (as you can see from the above code snippet), the Thread.Sleep(5) function may not work accurately. If I uncomment the line, then the function seems to work more accurately than when I comment it. Please have a look at the two pictures I attached herewith to see the results more clearly.

So, my question is what causes the inaccuracy in the second case? Is there any thing I can do to improve the accuracy in that case?

Thank you for reading my question.

Kakashi

[BigEd781]

You can't really expect these things to be absolutely precise on a non RTOS. Do you really think there is a problem with the accuracy you see here? What are you actually trying to accomplish? The code doesn't look like it is doing anything meaningful.

[Arjay]

If the timer you are using is based on a windows timer, then I believe the thread where it was created needs to remain unblocked.

[[email protected]]

Arjay is correct, deep down on the inside the timer send a WM_TIMER message to your WndProc, and if your thread is blocked then it can not process the message in a timely manner.

[hatake_kakashi]

Hi guys,

Thank you for your answer.

The timer I used to measure the elapsed time is a high performance timer with an accuracy in the microseconds scale. Its source code can be downloaded from the following address:

http://www.codeproject.com/KB/cs/highperformancetimercshar.aspx

So I believe that the results of the measurements are correct.

@BigEd781: This code just does a simple task: start a timer, sleep the thread in 5 (ms) and then stop the timer and then get the elapsed time. Its sole purpose is to measure the period of time during which the thread really 'sleeps', in order to see whether or not Thread.Sleep(5) is accurate.

It doesn't seem that the thread is blocked in the second case, because the sleep time is smaller than 5 (ms). Do you have any idea about this?

Regards,

Kakashi

[Arjay]

Do you have any idea about this?

Yes, Sleep isn't that accurate. When the OS thread scheduler runs, it hands out time slices to threads based on priority. It runs realtime, high, normal, below normal threads all in that order. If any realtime threads need to run, it runs them to completion, then it runs the high priority threads and so on.

When you call Sleep, the thread scheduler knows to skip over that thread until the sleep expires.

Now given how the thread scheduler works with regard to priority, it doesn't mean that just because the sleep has expired on your thread, it will immediately get to run.

Raising your thread priority to High may help, but you would still be sharing time slices with other high pri threads, so there wouldn't be any guarantee that your results would be consistant.

[Mutant_Fruit]

Sleep is accurate to whatever the system clocks accuracy is. Unless there's a bug in the implementation you are guaranteed that your thread will sleep *at the minimum* the time you specify. However it may sleep a bit longer if your system is busy processing other threads.

Of course reading the documentation will get you right into the nitty gritty of it all and tell you the limits of what's possible:
http://msdn.microsoft.com/en-us/libr...8VS.85%29.aspx
http://msdn.microsoft.com/en-us/libr...8VS.85%29.aspx

I'd always recommend reading the docs when you have questions like this. The can sometimes answer the question much better than your average punter

[hatake_kakashi]

Sleep is accurate to whatever the system clocks accuracy is. Unless there's a bug in the implementation you are guaranteed that your thread will sleep *at the minimum* the time you specify. However it may sleep a bit longer if your system is busy processing other threads.

Of course reading the documentation will get you right into the nitty gritty of it all and tell you the limits of what's possible:
http://msdn.microsoft.com/en-us/libr...8VS.85%29.aspx
http://msdn.microsoft.com/en-us/libr...8VS.85%29.aspx

I'd always recommend reading the docs when you have questions like this. The can sometimes answer the question much better than your average punter

The second link you provided answers my question perfectly. Thank you very much.

Regards,

Kakashi