C# Waiting for multiple threads to finish

Asked 2010-02-17T15:28:57.850

I have a windows forms app that I am checking all the serial ports to see if a particular device is connected.

This is how I spin off each thread. The below code is already spun off the main gui thread.

foreach (cpsComms.cpsSerial ser in availPorts)
{
    Thread t = new Thread(new ParameterizedThreadStart(lookForValidDev));
    t.Start((object)ser);//start thread and pass it the port
}

I want the next line of code to wait until all the threads have finished. I've tried using a t.join in there, but that just processes them linearly.

c# multithreading

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2 Answers

Use the AutoResetEvent and ManualResetEvent Classes:

private ManualResetEvent manual = new ManualResetEvent(false);
void Main(string[] args)
{
    AutoResetEvent[] autos = new AutoResetEvent[availPorts.Count];

    manual.Set();

    for (int i = 0; i < availPorts.Count - 1; i++)
        {

        AutoResetEvent Auto = new AutoResetEvent(false);
        autos[i] = Auto;

        Thread t = new Thread(() => lookForValidDev(Auto, (object)availPorts[i]));
        t.Start();//start thread and pass it the port  

    }
    WaitHandle.WaitAll(autos);
    manual.Reset();

}


void lookForValidDev(AutoResetEvent auto, object obj)
{
    try
    {
         manual.WaitOne();
         // do something with obj 
    }
    catch (Exception)
    {

    }
    finally
    {
        auto.Set();
    }


}

answered 2010-02-17T17:34:29.940

Store the Thread results in a list after they were spawned and iterate the list - during iteration call join then. You still join linearly, but it should do what you want.

answered 2010-02-17T15:31:49.203

C# Waiting for multiple threads to finish

2 Answers

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