Spawning a task in c# and knowing when its finished

Question

I have this compress video task that uses an external program to do it in c#. It takes some time for this compression to finish and the file to write out. I don't want to run the next piece of code until I know the external operation has had time to finish.

Do I want to do a simple Thread.sleep(some guess); and then run the next line of code or is there a better way?

this is how I am doing the compressing of the video:

 try
        {
            String finalCommand = "";
            String thePath = System.IO.Path.GetDirectoryName(fileName);
            finalCommand ="-i " + fileName + " -s 320x240 -b 300k -r 30 -f avi " + thePath + "\\C" + System.IO.Path.GetFileName(fileName);
            System.Diagnostics.ProcessStartInfo ffmpegcmd = new System.Diagnostics.ProcessStartInfo(Application.StartupPath + "\\ffmpeg.exe",
                 "-i \""  +  fileName + "\" -s 320x240 -b 300k -r 30 -f avi \"" + thePath + "\\C" + System.IO.Path.GetFileName(fileName) + "\"");

            ffmpegcmd.WindowStyle = System.Diagnostics.ProcessWindowStyle.Hidden;
            System.Diagnostics.Process p = System.Diagnostics.Process.Start(ffmpegcmd);
            LogUtil.writeLog("About to wait for FFMPEGCMD process");
            p.WaitForExit();
            success = true;
            LogUtil.writeLog("FFMPEGCMD process exited perfectly!");
        }
        catch (Exception ex)
        {
            LogUtil.writeLog("ERROR compressing and using FFMPEG");
            success = false;
        }

though I realize I am not sure if this is doing a process/thread on its own hmm.

Answer 1

If you're using a new thread, you can just call Thread.Join:

Thread.Join(otherThread);

... possibly with a timeout.

In .NET 4 you can use the Task Parallel Library (creating a Task or Task<TResult>) and then call Wait. (If you're using .NET 4, the TPL is definitely the way to go in general - you can do lots of stuff with it.)

Both of these approaches are blocking - they will stop the waiting thread from doing anything else until the other task has completed; this isn't something you want to do in the UI thread. So if this is in the context of a user interface, it would be best to use a callback instead - make the other task call back into the UI thread when it's done; that can kick off the next piece of code.

EDIT: The code you've shown is creating a new process, not a new thread. You may also be doing it in a new thread, but you haven't shown that. It's also still unclear whether this is all taking place in a UI such as Windows Forms or WPF, or whether it's just a console app.

Answer 2

Have a look at msdn: Task Parallel Library

Answer 3

   Public void compressVideo(obkect o)
   {
      \\ code
    }

    Thread t = new Thread( new threathStart( \\ pass the method that you want to execute on this thread...
    t.start(parameterYouWishtoPas);
    while(t.IsAlive)
    {
       Thread.sleep(1);
     }
     \\ this line will not execute untill thread t finishes executing...

Answer 4

I wouldn't doing the sleep suggestion that Tano suggested...there is no reason to occupy the CPU just for waiting for another thread (busy wait). Jon's suggestion is what you need.

If the compression thread, for some reason, never ends, than I suggest you try using reset events. Take a look here