[MACTCL] Possible fix for event loop issues in Tk-Cocoa

[Kevin W. <kw...@co...>]

Hello all,

I've done some additional work with the old Tk-Cocoa event loop bug 
reported here:

http://core.tcl.tk/tk/tktview/3028676fffffffffffffffffffffffffffffffff

and I have developed what may be a fix, or at least an improvement. 
Please see the entire comment thread at the bug report for context and 
background, as well as some test scripts that illustrate the bug, but 
here is my comment below:

---
I've been doing some additional experimentation with this, and this diff 
of tclMacOSXNotify.c in trunk seems to improve things significantly in 
terms of avoiding hangs:

--- tclMacOSXNotify-current.c    2015-03-07 23:31:56.000000000 -0500
+++ tclMacOSXNotify.c    2015-03-07 23:41:21.000000000 -0500
@@ -1412,7 +1412,8 @@
          (tsdPtr->runLoopNestingLevel > 1
              || !tsdPtr->runLoopRunning)) {
          tsdPtr->runLoopServicingEvents = 1;
-        while (Tcl_ServiceAll() && tsdPtr->waitTime == 0) {}
+            /* This call seems to simply force event processing through 
and prevents hangups that have long been observed with Tk-Cocoa.  */
+        Tcl_ServiceAll();
          tsdPtr->runLoopServicingEvents = 0;
      }
      break;

In brief, swapping out the while loop and replacing it with a direct 
call to Tcl_ServiceAll() just seems to force things through. The demo 
script attached to this bug (beachball-bug.tcl) does not lock up, 
although resizing the window and selecting menus does run a bit 
sluggishly until the events are processed. The shorter script referenced 
elsewhere here does not freeze at all with this change.

I see this as a promising fix for this bug, and a way to further reduce 
the issues with the event loop, but I would like others to test as well 
and see if their experiences match mine.
---

I would be very grateful if others who have had issues with the event 
loop could try this patch (the file is in tcl/macosx) as soon as 
possible and try it out against whatever code you find triggers major 
hangs in Tk-Cocoa. As I understand the notifier code, this particular 
code only runs when the Tcl notifier is in embedded mode, cf. in 
Tk-Cocoa, and not in pure Tcl, so it is not likely to be demonstrated by 
the Tcl test suite. Daniel Steffen advised that any changes to the 
notifier code would need to be exercised in Tk, either via the test 
suite or by running the Tk demo code (my preferred method). Running the 
Wish demo, things seem to work just fine.

If others report that this code seems to remove or reduce the major 
issues with Tk's event loop, I will commit it to trunk,  backport it to 
8.5, and may even want to do an updated release of 8.5.18 (I know this 
is a bit late, but it's so critical that I would want to push it out). 
If others report no improvement, then I'll leave the code as is.

Again, please test this as soon as possible, and if it works for you, 
I'll commit it right away.

Thanks,
Kevin

-- 
Kevin Walzer
Code by Kevin/Mobile Code by Kevin
http://www.codebykevin.com
http://www.wtmobilesoftware.com