Re: Locking Desktop and Threading Issue

On Tue, 01 May 2007 09:35:44 -0700, Jenbo <eamonnjennings@xxxxxxxxxxx> wrote:

Hi, I have an application that displays forms on the users desktop,
what I am doing with it is having a SystemEvents
SessionSwitchEventHandler to capture the lock of the desktop, I would
like to kill the forms when this event is captured, that piece is
fine, but I would like to sleep the app until the
SessionSwitchReason.SessionUnlock happens then I can wake it again and
go the correct part of the code? Can I wake a sleeping thread, or
should I not sleep the thread at all, is there another way to get the
thread to sleep or hibernate and then wake up?

It's not clear to me that there's really any need to do any of the things you want to do. What are your forms doing that you can't just leave them open when the desktop is locked? Windows will take care of hiding them from the user and preventing user input, and when the desktop is unlocked then they will still be there, ready to go. Windows is also smart enough to not dedicate any attention to the user interface of the application while it's essentially inactivated by the desktop being locked (not that the UI component of an application is generally a significant load on the computer in the first place).

That said, it is possible to explicitly get a thread to simply stop doing anything. Under Windows, a thread cannot "sleep" or "hibernate" per se (not in the sense that the computer can do those things), but you can create a waitable event and call the WaitOne() method on that. The thread that calls that method will stop and wait at that call until some other thread sets the event, releasing the thread for further execution.

If you use a ManualResetEvent, and you insert a call to the event's WaitOne() method at some appropriate spot (generally a point in some code's processing loop that is executed often enough that latency for any pausing of the thread will be low, but not so often that calling WaitOne() causes a significant performance problem), then when you want the thread to pause you reset the event and when you want the thread to continue to set the event.

Of course, you still need at least one thread around to process the SessionSwitchEvent and manage any other threads that are blocked. But I suppose if you have a thread that is doing something particularly i/o or CPU intensive and you want it to stop taking system resources when the desktop is locked, you could build in this sort of pausing mechanism without affecting the main GUI thread.

If the above doesn't help you, perhaps you could be more explicit about why it is you believe you need to "put your application to sleep" when the desktop is locked. This isn't something that normally needs to be done, so you should probably be more clear about what abnormal situation exists in your scenario that justifies or demands that sort of behavior.

Pete
.

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