[Lazarus] Sending messages

Michael Schnell mschnell at lumino.de
Fri Nov 25 10:14:34 CET 2011

On 11/25/2011 09:45 AM, Felipe Monteiro de Carvalho wrote:
> X11 does not send direct events. Direct events are sent by Cocoa and 
> also by Android. I don't know if you can stick non-X11 events into 
> that queue, but this hability by itself is not what defines something 
> as a queue or not. 

The question is what is meant by "send" here. AFAIK, (other than Windows 
that does a "Messages" mechanism) here, we have callbacks. And Callbacks 
result from the main thread of the application calling a function. (i.e. 
the LCL main thread calls it's own subroutine via this mechanism). OTOH, 
the external Widget Set only "runs" while being in this call and thus 
the main thread needs to do it "not-busy" waiting within such a call to 
the Widget set, to have same be responsive to the user. Thus the 
LCL-code of the mainthread is stalled while the WidgetSet function 
(including the Callback) is working. So the results that the LCL code 
produces withing the callback needs to be asynchronously transferred 
back to be handled (later) in a user-code event handler and thus need to 
be re-transferred to be handled withing the main execution loop (that 
calls the user code events). This is why an (additional) event queue fed 
by (results of) GUI events is necessary.


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