Question

I am using

System.Threading.ThreadPool.QueueUserWorkItem(x => MyMethod(param1, param2, param3, param4, param5));

I want to call the following method from the main thread every time the call to MyMethod is completed:

UpdateGui()
{

}

How do I do that?

Thanks!

Answer 1

Keep a global counter of work items queued and an object to protect it:

int runningTasks = 0;
object locker = new object();

Every time a task is added increment the counter:

lock(locker) runningTasks++;
System.Threading.ThreadPool.QueueUserWorkItem(x => MyMethod(param1, param2, param3, param4, param5));

At the end of MyMethod decrement the counter and signal the main thread:

lock(locker) 
{
    runningTasks--;
    Monitor.Pulse(locker);
}

In the main thread (assuming this is not the GUI thread!):

lock(locker)
{
    while(runningTasks > 0)
    {
        Monitor.Wait(locker);            
        UpdateGUI();
    }
}

This way you also have a barrier to wait for all pending tasks to finish.

In case you don’t want to wait, just skip the main thread completely and call UpdateGUI to forward updates to the GUI thread when MyMethod finishes.

Note that inside MyMethod you should have some form of Dispatcher.BeginInvoke (WPF) or Control.BeginInvoke (WinForms) otherwise you cannot update the GUI safely!