be notified when all background threadpool threads are finished

Question

I have a scenario when I start 3..10 threads with ThreadPool. Each thread does its job and returns to the ThreadPool. What are possible options to be notified in main thread

Answer 1

Try this: https://bitbucket.org/nevdelap/poolguard

using (var poolGuard = new PoolGuard())
{
    for (int i = 0; i < ...
    {
        ThreadPool.QueueUserWorkItem(ChildThread, poolGuard);
    }
    // Do stuff.
    poolGuard.WaitOne();
    // Do stuff that required the child threads to have ended.

void ChildThread(object state)
{
    var poolGuard = state as PoolGuard;
    if (poolGuard.TryEnter())
    {
        try
        {
            // Do stuff.
        }
        finally
        {
            poolGuard.Exit();
        }
    }
}

Multiple PoolGuards can be used in different ways to track when threads have ended, and handles threads that haven't started when the pool is already closed.