Stop Threads created with ThreadPool.QueueUserWorkItem that have a specific task

Question

Let's say I queue those two methods in a for loop

for (int i = 0; i < 100; i++)
{
    ThreadPool.QueueUserWorkItem(s =>
    {
        Console.WriteLine("Output");
        Thread.Sleep(1000);
    });
}

for (int i = 0; i < 100; i++)
{
    ThreadPool.QueueUserWorkItem(s =>
    {
        Console.WriteLine("Output2");
        Thread.Sleep(1000);
    });
}

Is there a way to stop all the threads that output Console.WriteLine("Output2"); but keep the ones running that output Console.WriteLine("Output"); ?

Answer 1

You could use a CancellationToken:

for (int i = 0; i < 100; i++)
{
    ThreadPool.QueueUserWorkItem(s =>
    {
        Console.WriteLine("Output");
        Thread.Sleep(1000);
    });
}

CancellationTokenSource cts = new CancellationTokenSource();

for (int i = 0; i < 100; i++)
{
    ThreadPool.QueueUserWorkItem(s =>
    {
        CancellationToken token = (CancellationToken) s;
        if (token.IsCancellationRequested)
            return;
        Console.WriteLine("Output2");
        token.WaitHandle.WaitOne(1000);
    }, cts.Token);
}

cts.Cancel();