Question

after reading a few articles, I am still not sure I understand Multi-threading to solve my
particular problem.

I have a Main form which will start a background worker thread(worker). The worker thread will doing a While(!Stopping) infinity loop and will sleep at end of each iteration terminate by global Stopping object(Read only lock object). With working fine when user press Stop button, the
worker will stop after current iteration.

Now I want when user close the main form, it will set Stop flag first, let the worker thread
finish its current job. After that the main form will close. Seems simple enough, but I couldn’t make it working.

I tried either worker.Join(), or test woker.IsAlive in a while loop, but both case will lock the application(Main form) after a few seconds for some reason ?

The following is my code inside Form_Closing event handler (not working):

               // Tell the thread to stop the file
                Stop();
                Logger.Info("Stopping the thread by Close the application");
               //Not working as well                    
               //worker.Join();
                while (worker.IsAlive)
                {
                    Thread.Sleep(5000);
                    Logger.Info("After sleep for 5 seconds");
                }
                Logger.Info("worker thread stopped");

One thing interesting is that the worker thread seems always writes log event until the end of each loop iteration, then the rest of the log entry will be main form event inside
the while(worker.IsAlive) loop.

Answer 1

Join will always wait on the thread, using it in the UI thread will make application seem to be locked.
IsAlive do not block anything in the GUI thread, it’s your Thread.Sleep.

do somethnig like this instead:

while (worker.IsAlive)
{
    Thread.sleep(50);
    Application.DoEvents();
}