vb.net - If Background Worker is a background thread how come I can executed this code? -

researching found out background worker background thread, when run following code background worker still runs until end when main procedure exited. isn't feature reserved foreground threads?

code:

public class form1     private sub form1_load(sender object, e eventargs) handles mybase.load         'run background worker         backgroundworker1.runworkerasync()         'display exit message         msgbox("main procedure exited")     end sub      private sub backgroundworker1_dowork(sender object, e system.componentmodel.doworkeventargs) handles backgroundworker1.dowork         'wait 10 seconds         threading.thread.sleep(10000)         'modify numbers         dim variable = 3         variable -= 1         'display exit message         msgbox("background thread " & variable & " exited")     end sub end class 

the form1_load method not "main procedure", message box you're displaying @ end of lie. that's event handler method form.load event, raised when form being displayed first time.

the "main procedure" named main , defined in separate file (actually, in vb.net, it's automatically generated compiler , not visible default). can find more information on main method in microsoft's vb programming guide.

the main method still running long program still running. after form1_load event handler method finishes, form1 still on screen, program hasn't closed yet. , since program's main thread still running, backgroundworker object's background thread still running, asynchronously, told to.