On Mar 15, 2009, at 9:37 PM, YAMAMOTO Mitsuharu wrote:

> [Revisiting an old change]
>
>>>>>> On Wed, 25 Apr 2007 20:30:08 +0200, Jan Djärv  
>>>>>> <jan.h.d@swipnet.se> said:
>
>> After some experimenting it seems that this patch fixes it.  Note
>> that a call to redisplay() does not fix the bug.  I don't know why.
>> But a full redisplay before every dialog maybe is too much?
>
>> diff -w -c src/xmenu.c.~1.317.~ src/xmenu.c
>> Index: src/xmenu.c
>> *** src/xmenu.c.~1.317.~        2007-01-21 11:33:57.000000000 +0100
>> --- src/xmenu.c 2007-04-25 20:27:02.000000000 +0200
>> ***************
>> *** 3333,3338 ****
>> --- 3333,3340 ----
>>     /* No selection has been chosen yet.  */
>>     menu_item_selection = 0;
>
>> +   Fredisplay (Qt);
>> +
>>     /* Actually create and show the dialog.  */
>>     create_and_show_dialog (f, first_wv);
>
> Fredisplay runs timers and may cause string data relocation by GC.
> Just before the call to Fredisplay, a widget value is created and it
> points to some string data, which are to be used as button labels
> after the Fredisplay call.  So this may cause corruption of dialog
> button labels.  I've never seen such corruption actually, but I think
> that may happen in principle unless I'm missing something.


I absolutely see such corruption in the Carbon port, which creates the  
dialog in a similar fashion.  This was in connection with a header  
line that uses an :eval expression, and a modified map-y-or-n-p that  
switches buffers to show the right one.  As you say, the strings get  
destroyed, but that was relatively easy to fix by doing the redisplay  
a bit earlier.



*** src/macmenu.c	30 Aug 2008 00:10:18 -0400	1.56.2.7
--- src/macmenu.c	09 Feb 2009 13:21:20 -0500	
***************
*** 1882,1888 ****
         return Qnil;
       }

!   /* Create a tree of widget_value objects
        representing the text label and buttons.  */
     {
       Lisp_Object pane_name, prefix;
--- 1882,1893 ----
         return Qnil;
       }

!   /* Force a redisplay before showing the dialog.  If a frame is  
created
!      just before showing the dialog, its contents may not have been  
fully
!      drawn.  */
!   Fredisplay (Qt);
!
!  /* Create a tree of widget_value objects
        representing the text label and buttons.  */
     {
       Lisp_Object pane_name, prefix;
***************
*** 1985,1994 ****
     /* No selection has been chosen yet.  */
     menu_item_selection = 0;

-   /* Force a redisplay before showing the dialog.  If a frame is  
created
-      just before showing the dialog, its contents may not have been  
fully
-      drawn.  */
-   Fredisplay (Qt);

     /* Actually create the dialog.  */
   #if TARGET_API_MAC_CARBON
--- 1990,1995 ----