Raising events so that they are handled on a the same thread as original subscriber

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Raising events so that they are handled on a the same thread as original subscriber

In dotNET with C# 4.0, How can I ensure that event that happens on an arbitrary thread X will call handlers in the same thread (or synchronization context) as the subscribing thread A, B, or C.

I am trying to avoid having to put in threading-related code into handler method or event site.

It would be really great if I wouldn't have to change += and -= subscription, as well as "public event EventHandler myevent;" code.

I don't think you can directly do this. The best you can do is register handlers which will run on some arbitrary thread, but which will pass the data to the original thread.

Steven Sudit 2010-09-10 22:09:28

It's the sort of thing I believe could make a programmer slightly more productive... oh just slightly.

GregC 2010-09-14 02:51:50

Perhaps, but I'm not convinced it's particularly helpful. The one place it's useful is for dealing with GUI's, which need their controls modified only from the UI thread. However, both WinForms and WPF have solutions for this. Otherwise, it shouldn't matter which thread the event is executed in.

Steven Sudit 2010-09-14 04:21:11

Wanna show code for the GUI interaction?

GregC 2010-09-14 05:10:37

I actually have a continually-running orchestrator in a form of a complex state machine running in the background. I would like back-end logic and GUI to provide events that will drive the state machine. State machine runs on thread X, GUI on thread Y, and communications on thread Z.

GregC 2010-09-14 05:12:45

No need to reinvent the wheel. Look at http://stackoverflow.com/questions/1203909/how-to-invoke-on-background-thread, http://stackoverflow.com/questions/670503/what-should-i-avoid-doing-on-background-thread-in-winforms, http://stackoverflow.com/questions/2526725/winforms-how-do-i-access-call-methods-in-ui-thread-from-a-separate-thread-witho

Steven Sudit 2010-09-14 06:06:41

Ok, the only thing you need to worry about, other than the usual locking of shared resources, is updating controls from X or Z. To do that, use the `Control.Invoke` technique you'll find in the links above. These will ensure that your delegate is executed in Y, which has access to the message pump.

Steven Sudit 2010-09-14 06:08:18

I am sure that with some reflection on this subject, you might note that it would be worthwhile to invest in providing a cleaner, crisper, and more direct user syntax.

GregC 2010-09-17 23:04:37

Nope, I've reflected on it but I still disagree. Sorry.

Steven Sudit 2010-09-18 01:02:03

ansaurus

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Raising events so that they are handled on a the same thread as original subscriber

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