C#: Waiting for all threads to complete

user_8078 0
Viewed 115210

I'm running into a common pattern in the code that I'm writing, where I need to wait for all threads in a group to complete, with a timeout. The timeout is supposed to be the time required for all threads to complete, so simply doing thread.Join(timeout) for each thread won't work, since the possible timeout is then timeout * numThreads.

Right now I do something like the following:

var threadFinishEvents = new List<EventWaitHandle>();

foreach (DataObject data in dataList)
{
    // Create local variables for the thread delegate
    var threadFinish = new EventWaitHandle(false, EventResetMode.ManualReset);
    threadFinishEvents.Add(threadFinish);

    var localData = (DataObject) data.Clone();
    var thread = new Thread(
        delegate()
        {
            DoThreadStuff(localData);
            threadFinish.Set();
        }
    );
    thread.Start();
}

Mutex.WaitAll(threadFinishEvents.ToArray(), timeout);

However, it seems like there should be a simpler idiom for this sort of thing.

multithreading c#
9 Answers

I still think using Join is simpler. Record the expected completion time (as Now+timeout), then, in a loop, do 

if(!thread.Join(End-now))
    throw new NotFinishedInTime();
user_330060

Off the top of my head, why don't you just Thread.Join(timeout) and remove the time it took to join from the total timeout?

// pseudo-c#:

TimeSpan timeout = timeoutPerThread * threads.Count();

foreach (Thread thread in threads)
{
    DateTime start = DateTime.Now;

    if (!thread.Join(timeout))
        throw new TimeoutException();

    timeout -= (DateTime.Now - start);
}

Edit: code is now less pseudo. don't understand why you would mod an answer -2 when the answer you modded +4 is exactly the same, only less detailed.

Omer_van_Kloeten_49790

This may not be an option for you, but if you can use the Parallel Extension for .NET then you could use Tasks instead of raw threads and then use Task.WaitAll() to wait for them to complete.

Jon_Norton_47970
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