Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!ucsd!helios.ee.lbl.gov!pasteur!ucbvax!bloom-beacon!ATHENA.MIT.EDU!swick
From: swick@ATHENA.MIT.EDU (Ralph R. Swick)
Newsgroups: comp.windows.x
Subject: Re: callbacks
Message-ID: <8912151300.AA14880@LYRE.MIT.EDU>
Date: 15 Dec 89 13:00:27 GMT
References: <8912142136.AA19443@cscsun1.larc.nasa.gov>
Sender: root@athena.mit.edu (Wizard A. Root)
Organization: DEC/MIT Project Athena
Lines: 15

> I am having problems with callbacks. I have a commandWidget that has two
> callback routines. One of these routines enables a popup. Based on an error
> condition in my program, I want to remove the enabling of the popup from the
> callback list. I tried using XtRemoveCallback but it seems to "miss" the first
> time around and still pops up the popup.

You're not, by any chance, calling XtRemoveCallback from a callback
that's on the list you're trying to change, are you?  There is
special code to make sure that any changes to a callback list
do not affect an in-progress evaluation of that list, producing
exactly the symptoms you describe.

Since there is no explicit ordering of invocation of the callbacks
on a list, you could never rely upon an "earlier" callback being
able to disable a "later" one by removing it from the list anyway.