C# Waiting for multiple threads to finish

Question

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

Answer 1

You can use a CountDownLatch:

public class CountDownLatch
{
    private int m_remain;
    private EventWaitHandle m_event;

    public CountDownLatch(int count)
    {
        Reset(count);
    }

    public void Reset(int count)
    {
        if (count < 0)
            throw new ArgumentOutOfRangeException();
        m_remain = count;
        m_event = new ManualResetEvent(false);
        if (m_remain == 0)
        {
            m_event.Set();
        }
    }

    public void Signal()
    {
        // The last thread to signal also sets the event.
        if (Interlocked.Decrement(ref m_remain) == 0)
            m_event.Set();
    }

    public void Wait()
    {
        m_event.WaitOne();
    }
}

Example how to use it:

void StartThreads
{
    CountDownLatch latch = new CountDownLatch(availPorts.Count);

    foreach (cpsComms.cpsSerial ser in availPorts)
    {
        Thread t = new Thread(new ParameterizedThreadStart(lookForValidDev));

        //start thread and pass it the port and the latch
        t.Start((object)new Pair(ser, latch));

    }

    DoSomeWork();

    // wait for all the threads to signal
    latch.Wait();

    DoSomeMoreWork();
}

// In each thread
void NameOfRunMethod
{
    while(running)
    {
        // do work
    }

    // Signal that the thread is done running
    latch.Signal();
}