Re: [Stephen.Berman@gmx.net: Emacs hangs while edebugging recentf.el]

[Chong Yidong <cyd@stupidchicken.com>]

"Richard M. Stallman" <rms@gnu.org> writes:

>     I reproduced the error and also found that Emacs hangs in the built-in
>     function `prin1-to-string' when it tries to print the value the
>     function `widget-create' returns, which contains a lot of circular
>     references in a deeply nested list.  If I don't interrupt the hang,
>     after some time, the function fails with a "Memory exhausted" message.
>     Notice that the widgets are correctly created in the "*Open Recent*"
>     buffer.  This is only the edebug prin1 function that hangs.
>
>     When I set the value of `edebug-print-level' to 10 instead of the
>     default value of 50, Emacs no more hangs.
>
>     Maybe there is a bug in the prin1-to-string function?  Unfortunately I
>     don't know how to fix it.
>
> Can someone investigate that bug?  David Ponce said he can't.

I think the trouble is that the way print_preprocess "follows" nested
lists, while handling print_depth, is slightly different from the way
print_object does it.  Because of this, it is possible for
print_preprocess to give up sooner than print_object would.  An object
could thus fail to be put into Vprint_number_table, even though
print_object later is later called for it.

There is a quick but inelegant way to cover up this bug:

*** emacs/src/print.c.~1.214.~	2005-11-10 08:45:06.000000000 -0500
--- emacs/src/print.c	2005-12-13 17:17:49.000000000 -0500
***************
*** 1313,1319 ****
  
    /* Give up if we go so deep that print_object will get an error.  */
    /* See similar code in print_object.  */
!   if (print_depth >= PRINT_CIRCLE)
      return;
  
    /* Avoid infinite recursion for circular nested structure
--- 1313,1319 ----
  
    /* Give up if we go so deep that print_object will get an error.  */
    /* See similar code in print_object.  */
!   if (print_depth > 2 * PRINT_CIRCLE)
      return;
  
    /* Avoid infinite recursion for circular nested structure