How to signal threads to stop in c# in any one has exception

Question

Suppose that there are 5 threads, T1, T2, T3, T4 and T5 and 5 of them are currently running. My requirement is to stop all 4 threads in case any one of the 5 threads has any exceptions. How can this be achieved. I am using c# 4.0

Answer 1

This can be achieved by using CancellationTokens. CancellationTokenSource can be shared between your threads.

Here is an example with Tasks, but you can use Threads\ThreadPool

        CancellationTokenSource cts = new CancellationTokenSource();

        Task.Factory.StartNew(() =>
            {
                while (1 == 1)
                {
                    Thread.Sleep(1000);
                    Console.WriteLine("Thread1 in progress...");
                    if (cts.Token.IsCancellationRequested)
                    {
                        Console.WriteLine("Thread1 exiting...");
                        break;
                    }
                }
            }, cts.Token);

        Task.Factory.StartNew(() =>
            {
                while (1 == 1)
                {
                    Thread.Sleep(1000);
                    Console.WriteLine("Thread2 in progress...");
                    if (cts.Token.IsCancellationRequested)
                    {
                        Console.WriteLine("Thread2 exiting...");
                        break;
                    }
                }
            }, cts.Token);

        Task.Factory.StartNew(() =>
        {
            while (1 == 1)
            {
                Thread.Sleep(1000);
                Console.WriteLine("Thread3 in progress...");
                if (cts.Token.IsCancellationRequested)
                {
                    Console.WriteLine("Thread3 exiting...");
                    break;
                }
            }
        }, cts.Token);

        Task.Factory.StartNew(() =>
        {

            Thread.Sleep(5000);
            try
            {
                Console.WriteLine("Thread5 in progress...");
                int y = 0;
                int x = 1 / y;
            }
            catch 
            {
                Console.WriteLine("Thread5 requesting cancellation...");
                cts.Cancel();
            }
        }, cts.Token);

and check this link which has quite a few CalcellationTokenSource examples (including shared CancellationCancellationTokenSources):

EDIT: I should probably mention that instead of "breaking" the loop when calcellation is requested, you could just call ThrowIfCancellationRequested method of the Token. The outcome will be different though - the task will not "run to completion", it will be in "Cancelled" state. You need to consider this when adding task continuations.