Re: Threading Issues (If you can answer this, I'll kiss you.)

From: Stephen Martin (smartin_at_removethis.emsoft.andthis.ca)
Date: 05/19/04 

Date: Wed, 19 May 2004 14:34:21 -0400

When you register for a SystemEvent a window is created to receive the OS
broadcast messages. In your case the window is created on your main thread
but that thread is suspended so when the session ending broadcast message is
sent it is not read from the message queue and your SessionEnding handler is
never called.

On the other hand when you register for the process exit event the system
simply registers a wait on the process handle with the ThreadPool. When the
process exits a threadpool thread then calls your event handler. So the Exit
handler is not blocked by suspending your thread since it is called on a
different thread.

I assume in your case that your app is a console app and you do not want to
use a form on your main thread to provide a message pump for the broadcast
window. If that is the case, I think adding a MTAThread attribute to your
Main function in wrapper.exe might do the trick. The framework assumes that
any STA thread has a UI and so creates the broadcast window on that thread
but if the thread is MTA then no UI is assumed and a thread is created
specifically to handle the broadcast messages. The VB compiler, by default,
makes your Main thread STA unless you add the MTAThread attribute.

"Jerry Camel" <rlrcstr@msn.com> wrote in message
news:OU%23wjFOPEHA.560@TK2MSFTNGP10.phx.gbl...
> Any insight here is greatly appreciated... (Eveything is in VB .NET)
>
> Here's the baisc app flow:
> -------------------------------------
> Launch wrapper.exe:
> wrapper.exe registers for the SessionEnding system event
> wrapper.exe stores a pointer to its thread in MainThread
> wrapper.exe declares, withevents, a process variable: np
> wrapper.exe does some basic maintenance
> wrapper.exe populates np with process info and sets
> fp.EnableRaisingEvents to True
> wrapper.exe launches fp
> wrapper.exe suspends its thread <- Waiting for fp exit
> wrapper.exe does some basic maintenance
> Exit wrapper.exe
>
> SessionEnding Handler: (User is logging off or shutting down without
> exiting fp)
> force fp to exit
> End Handler
>
> fp Exit Handler: (fp has exited either via user interaction or the
> SessionEnding Handler)
> resume MainThread
> End Handler
> ------------------------------------
>
> If the user exits fp then everythign works just fine. If the user tries
to
> shutdown or logoff while fp is still running, then my SessionEnding
handler
> never gets called. The message just waits in the queue and fp is never
> forced to exit and the user gets a dialog box claiming that some .NET
> process isn't ending. (This is the typical dialog seen when a process
> doesn't play nice at shutdown.) While that dialog is on the screen, if
the
> user then shuts down fp, my code will continue to run.
>
> So, here's the basic question. Why does the ExitHandler run while the
> MainThread is suspended, but the SessionEnding Handler does not? (If you
> need more info to provide some advice, please let me know...)
>
> Thanks.
>
> Jerry
>
>

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