Does closing the application stops all active BackgroundWorkers?

Question

Simple question, to repeat the title:

Does closing the WinForms application stops all active BackgroundWorkers?

Answer 1

Yes, it does.

BackgroundWorker.RunWorkerAsync simply calls BeginInvoke on a internal delegate, which in turn queues the request to the ThreadPool. Since all ThreadPool threads are background, yes, it will end when the application ends.

However, keep in mind that:

1. By "closing the WinForms application" I am presuming closing the main Form instance (that's generally the one passed to Application.Run in the Program class autogenerated by Visual Studio). If you have a child window with a background worker, it will not stop its BackgroundWorker automatically.

2. Letting a background thread be aborted on application exit is not the recommended way to end the thread, as you have no guarantees where it will be aborted. A much better way would be to signal the worker before closing, wait for it to finish gracefully, and then exit.

More info: Delegate.BeginInvoke, MSDN on Thread Pooling, Thread.IsBackground

Answer 2

The only way a thread can go on executing after your main (UI) thread has stopped is if it has been created explicitely, by creating a new Thread instance and setting the IsBackground to false. If you don't (or if you use the ThreadPool which spawns background threads - or the BackgroundWorker which also uses the ThreadPool internally) your thread will be a background thread and will be terminated when the main thread ends.