Re: [MACTCL] [TCLCORE] Commits to improve drawing in Tk-Cocoa after removal of private API's

[Will D. <wi...@wj...>]

On Sep 25, 2014, at 9:48 AM, Lars Hellström <Lar...@re...> wrote:

> Kevan Hashemi skrev 2014-09-25 16.17:
>> Dear Kevin,
>> 
>> Thank you for all the work you are doing to keep Tk going on MacOS.
>> 
>>> Re-engineering either of these foundational parts of Tcl would, as I
>>> understand it, go far beyond adjusting a platform-specific
>>> implementation of the current API
>> 
>> Indeed it would. But the Tcl event loop has one severe limitation, and I
>> believe it's the one Michiel is referring to. I had to build my own
>> event loop on top of Tcl's, because Tcl's would not do the job.
>> 
>> The problem with Tcl's event loop is that pending "vwaits" are resolved
>> strictly in reverse order of initiation, and "after" events are ignored
>> during an active vwait.
> 
> That sounds very much like a misunderstanding, and also like you're using 
> far-from-recommended programming practices.
> 
> [vwait]s are resolved in reverse order of initialisation, because each is a 
> recursive invokation of the event loop. The first advice on using [vwait] 
> tends to be to avoid that. And [after] events are being serviced during a 
> [vwait], since how else could the following terminate?
> 
> % after 500 {incr epoch}; vwait epoch; set epoch
> 1
> % after 500 {incr epoch}; vwait epoch; set epoch
> 2
> 
> Your premises appear to be flawed.
> 

I'm aware of two canonical uses for vwait:

The first is when a non-event-loop program that needs to enter the event loop for short periods of time; in which case the event loop is not being called recursively.  Presumably this case is not a problem.

The second is when popping up modal dialogs such as tk_getOpenFile, where the dialog is truly modal.  I see this case as reasonable, especially given that Tk itself does it.

Will


> 
> Lars Hellström
> 
> 
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