C#: Waiting for all threads to complete

Question

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.

Answer 1

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();

Answer 2

With .NET 4.0 I find System.Threading.Tasks a lot easier to work with. Here's spin-wait loop which works reliably for me. It blocks the main thread until all the tasks complete. There's also Task.WaitAll , but that hasn't always worked for me.

        for (int i = 0; i < N; i++)
        {
            tasks[i] = Task.Factory.StartNew(() =>
            {               
                 DoThreadStuff(localData);
            });
        }
        while (tasks.Any(t => !t.IsCompleted)) { } //spin wait

Answer 3

Since the question got bumped I will go ahead and post my solution.

using (var finished = new CountdownEvent(1)) 
{ 
  for (DataObject data in dataList) 
  {   
    finished.AddCount();
    var localData = (DataObject)data.Clone(); 
    var thread = new Thread( 
        delegate() 
        {
          try
          {
            DoThreadStuff(localData); 
            threadFinish.Set();
          }
          finally
          {
            finished.Signal();
          }
        } 
    ); 
    thread.Start(); 
  }  
  finished.Signal(); 
  finished.Wait(YOUR_TIMEOUT); 
} 

Answer 4

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.

Answer 5

This doesn't answer the question (no timeout), but I've made a very simple extension method to wait all threads of a collection:

using System.Collections.Generic;
using System.Threading;
namespace Extensions
{
    public static class ThreadExtension
    {
        public static void WaitAll(this IEnumerable<Thread> threads)
        {
            if(threads!=null)
            {
                foreach(Thread thread in threads)
                { thread.Join(); }
            }
        }
    }
}

Then you simply call:

List<Thread> threads=new List<Thread>();
//Add your threads to this collection
threads.WaitAll();

Answer 6

这可能不是您的选择，但如果您可以使用.NET的并行扩展，那么您可以使用Task而不是原始线程，然后使用Task.WaitAll()等待它们完成。

Answer 7

I read the book C# 4.0: The Complete Reference of Herbert Schildt. The author use join to give a solution :

class MyThread
    {
        public int Count;
        public Thread Thrd;
        public MyThread(string name)
        {
            Count = 0;
            Thrd = new Thread(this.Run);
            Thrd.Name = name;
            Thrd.Start();
        }
        // Entry point of thread.
        void Run()
        {
            Console.WriteLine(Thrd.Name + " starting.");
            do
            {
                Thread.Sleep(500);
                Console.WriteLine("In " + Thrd.Name +
                ", Count is " + Count);
                Count++;
            } while (Count < 10);
            Console.WriteLine(Thrd.Name + " terminating.");
        }
    }
    // Use Join() to wait for threads to end.
    class JoinThreads
    {
        static void Main()
        {
            Console.WriteLine("Main thread starting.");
            // Construct three threads.
            MyThread mt1 = new MyThread("Child #1");
            MyThread mt2 = new MyThread("Child #2");
            MyThread mt3 = new MyThread("Child #3");
            mt1.Thrd.Join();
            Console.WriteLine("Child #1 joined.");
            mt2.Thrd.Join();
            Console.WriteLine("Child #2 joined.");
            mt3.Thrd.Join();
            Console.WriteLine("Child #3 joined.");
            Console.WriteLine("Main thread ending.");
            Console.ReadKey();
        }
    }

Answer 8

I was tying to figure out how to do this but i could not get any answers from google. I know this is an old thread but here was my solution:

Use the following class:

class ThreadWaiter
    {
        private int _numThreads = 0;
        private int _spinTime;

        public ThreadWaiter(int SpinTime)
        {
            this._spinTime = SpinTime;
        }

        public void AddThreads(int numThreads)
        {
            _numThreads += numThreads;
        }

        public void RemoveThread()
        {
            if (_numThreads > 0)
            {
                _numThreads--;
            }
        }

        public void Wait()
        {
            while (_numThreads != 0)
            {
                System.Threading.Thread.Sleep(_spinTime);
            }
        }
    }

1. Call Addthreads(int numThreads) before executing a thread(s).
2. Call RemoveThread() after each one has completed.
3. Use Wait() at the point that you want to wait for all the threads to complete before continuing

Answer 9

Possible solution:

var tasks = dataList
    .Select(data => Task.Factory.StartNew(arg => DoThreadStuff(data), TaskContinuationOptions.LongRunning | TaskContinuationOptions.PreferFairness))
    .ToArray();

var timeout = TimeSpan.FromMinutes(1);
Task.WaitAll(tasks, timeout);

Assuming dataList is the list of items and each item needs to be processed in a separate thread.