[Mono-dev] Threads and X-Windows?

Rob Wilkens robwilkens at gmail.com
Thu May 31 13:07:59 UTC 2012

Incidentally (and this is not a personal reply, this is gereral to 
anyone interested), relating to the below reply, unlike .NET, in mono 
more than one thread can be processing the message loop, and delivering 
the same UI messages to more than one thread.

That is, more than one thread can run Application.Run() in mono, and 
that call will start a message processing and passing loop in each 
thread -- on mono anyway.  If you do this on Windows, the second call to 
Application.Run() will just return without doing anything if one is 
already running.

I've fixed this locally, but i'm trying to debug some semi-related 
issues with code which was previously using two Application.Run() calls 
(one per thread).  I'm trying to debug this from the mono side rather 
than the code side, because this code actually does run in Windows as it 
is written.  Not ready to talk about those specific fixes yet, because 
i'll not be convinced it's a good idea until I'm convinced it's a good 
idea (and until it's bug free; not there yet).

I spent all day yesterday staring at the laptop, I'm tempted to give 
myself the day off today, but i may change my mind after coffee and 


On 05/30/2012 04:02 PM, Patrick Cullen wrote:
> In .NET  there is only one thread that does UI work, this is how you
> access it irrespective of what thread makes the call. I use this for
> event patterns often. The key is "SendOrPostCallback" which determines
> if you are running on the UI thread.
> I use this code often and it works under Mono. I think the behavior is
> very different but the end result is what I am looking for.
> Patrick
> protected SynchronizationContext _uiContext;
> _uiContext = WindowsFormsSynchronizationContext.Current;
> _uiContext.Send(new SendOrPostCallback(
> 	  delegate(object state)
> 	  {
> 		// * Interact with controls here
> 	  }
>     ), null);
> On Wed, May 30, 2012 at 2:56 PM, Rob Wilkens<robwilkens at gmail.com>  wrote:
>> I'm troubleshooting a problem in System.Windows.Forms (or an application
>> which uses it):
>> Does anyone know of problems where messages processed from thread a can't
>> reach a window created in thread b?  That is, if thread a is processing
>> messages, those messages don't reach the windows created in thread b?  By
>> messages, i mean things like WM_CLOSE and WM_PAINT (or invalidate? or
>> whatever the equivalents are)...  (Messages that are processed, in theory,
>> by Application.Run() in thread a)...
>> I'm trying to figure out if this is an X11 issue or a mono issue..  I'm
>> thinking depending on how the day goes i may break from troubleshooting this
>> soon.
>> Before you say this is a bad idea (multiple threads creating windows) keep
>> in mind this was code in a problem report and In windows .net messages
>> processed in thread a reach windows created in thread b without issue.  At
>> least as far as i can tell.
>> _______________________________________________
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