[Freeciv-Dev] Re: (PR#2794) segfault in civclient (1.14.0beta3)

["olafBuddenhagen@xxxxxx via RT" <rt@xxxxxxxxxxxxxx>]

Hi,

I've found the problem.

I realized that the crash actually happens *always* when a new message
is added to the message window while the window isn't open, and the new
message causes scrolling (i.e. there are already >= N_MSG_VIEW
messages). The problem is that scrolling doesn't work unless the message
window is actually visible: The "viewport.child" component of the
viewport widget (normally pointing to the list widget) isn't set
otherwise, thus causing XawViewportSetCoordinates() to crash.

I've no idea whether this is correct behaviour or a bug in Xaw, neither
why the problem didn't occur before. (I'm not aware of having changed
anything in my system configuration.)

I've created the following workaround, which uses a flag to prevent
scrolling before the window is acutally popped up:

--- messagewin.c.orig   2003-01-17 05:11:18.000000000 +0100
+++ messagewin.c        2003-01-17 05:10:10.000000000 +0100
@@ -106,8 +106,13 @@
 /****************************************************************
 ...
 *****************************************************************/
+static bool creating;    /* we are just creating message window, not popped up
+                           yet (don't scroll -- Xaw may crash otherwise!) */
+
 static void create_meswin_dialog(void)
 {
+  creating=1;
+
   meswin_dialog_shell =
     I_IN(I_T(XtCreatePopupShell("meswinpopup", topLevelShellWidgetClass,
                                toplevel, NULL, 0)));
@@ -169,6 +174,7 @@
   XtOverrideTranslations(meswin_dialog_shell,
       XtParseTranslationTable("<Message>WM_PROTOCOLS: msg-close-messages()"));
 
+  creating=0;
 }
 
 /**************************************************************************
@@ -185,7 +191,7 @@
   Dimension height;
   int pos;
   
-  if (!meswin_dialog_shell)
+  if (!meswin_dialog_shell || creating)
     return;
   if (get_num_messages() <= N_MSG_VIEW) {
     return;

I guess there is a more elegant solution, using Xaw functions/data
structures to determine whether the window is visible. However, I'd
rather write a bigger patch, considerably changing the message window
handling, so that such a situation can't occur in the first place.
(While hunting down the bug I realized that the code is quite messy,
causing superfluous actions etc... Seems somewhere between maintaier
changes people lost track what's actually happening there.)

-Olaf-

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