Re: delete-process bug

[Michaël Cadilhac]

Stefan Monnier <address@hidden> writes:

>> In fact, there is already a configuration that would lead to the non
>> deletion of the PID from the list:
>
>> - Call to delete_process,
>> - Interrupted by a signal before inserting  in deleted_processes_list ,
>> - Deletion from  process_alist,
>
> How can this happen?  Are you saying that a signal handler may delete the
> process from process_alist?  Which signal handler can do that?

You're right, it's not its job.

> I do think there's a leak but it goes like this:
>
> - catch the SIGCHLD signal
> - start processing delete-process, which will add the PID to
>   deleted_pid_list even though the signal has already been caught so the pid
>   won't get a chance to be removed.

> I guess we could check the process's status after adding it to
> deleted_pid_list, to catch this case.

I think it would be OK. Here's the new (new new) version of the patch.
The kill_process part is not called if the process is already
terminated.

Index: src/process.c
===================================================================
RCS file: /sources/emacs/emacs/src/process.c,v
retrieving revision 1.481
diff -c -r1.481 process.c
*** src/process.c       8 May 2006 05:19:42 -0000       1.481
--- src/process.c       29 May 2006 11:36:31 -0000
***************
*** 778,783 ****
--- 778,793 ----
    return proc;
  }
  
+ 
+ #ifdef SIGCHLD
+ /* Fdelete_process promises to immediately forget about the process, but in
+    reality, Emacs needs to remember those processes until they have been
+    treated by sigchld_handler; otherwise this handler would consider the
+    process as being synchronous and say that the synchronous process is
+    dead.  */
+ static Lisp_Object deleted_pid_list;
+ #endif
+ 
  DEFUN ("delete-process", Fdelete_process, Sdelete_process, 1, 1, 0,
         doc: /* Delete PROCESS: kill it and forget about it immediately.
  PROCESS may be a process, a buffer, the name of a process or buffer, or
***************
*** 799,810 ****
      }
    else if (XINT (p->infd) >= 0)
      {
!       Fkill_process (process, Qnil);
!       /* Do this now, since remove_process will make sigchld_handler do 
nothing.  */
!       p->status
!       = Fcons (Qsignal, Fcons (make_number (SIGKILL), Qnil));
!       XSETINT (p->tick, ++process_tick);
!       status_notify (p);
      }
    remove_process (process);
    return Qnil;
--- 809,839 ----
      }
    else if (XINT (p->infd) >= 0)
      {
! #ifdef SIGCHLD
!       Lisp_Object symbol;
! 
!       /* No problem storing the pid here, as it is still in Vprocess_alist.  
*/
!       deleted_pid_list = Fcons (make_fixnum_or_float (p->pid),
!                               /* GC treated elements set to nil.  */
!                               Fdelq (Qnil, deleted_pid_list));
!       /* If the process has already signaled, remove it from the list.  */
!       if (p->raw_status_new)
!       update_status (p);
!       symbol = p->status;
!       if (CONSP (p->status))
!       symbol = XCAR (p->status);
!       if (EQ (symbol, Qsignal) || EQ (symbol, Qexit))
!       Fdelete (make_fixnum_or_float (p->pid), deleted_pid_list);
!       else
! #endif
!       {
!         Fkill_process (process, Qnil);
!         /* Do this now, since remove_process will make sigchld_handler do 
nothing.  */
!         p->status
!           = Fcons (Qsignal, Fcons (make_number (SIGKILL), Qnil));
!         XSETINT (p->tick, ++process_tick);
!         status_notify (p);
!       }
      }
    remove_process (process);
    return Qnil;
***************
*** 6373,6378 ****
--- 6402,6418 ----
  
        /* Find the process that signaled us, and record its status.  */
  
+ #ifdef SIGCHLD
+       /* The process can have been deleted by Fdelete_process.  */
+       tail = Fmember (make_fixnum_or_float (pid), deleted_pid_list);
+       if (!NILP (tail))
+       {
+         Fsetcar (tail, Qnil);
+         goto sigchld_end_of_loop;
+       }
+ #endif
+ 
+       /* Otherwise, if it is asynchronous, it is in Vprocess_alist.  */
        p = 0;
        for (tail = Vprocess_alist; GC_CONSP (tail); tail = XCDR (tail))
        {
***************
*** 6424,6431 ****
            EMACS_SET_SECS_USECS (*input_available_clear_time, 0, 0);
        }
  
!       /* There was no asynchronous process found for that id.  Check
!          if we have a synchronous process.  */
        else
        {
          synch_process_alive = 0;
--- 6464,6471 ----
            EMACS_SET_SECS_USECS (*input_available_clear_time, 0, 0);
        }
  
!       /* There was no asynchronous process found for that pid: we have
!        a synchronous process.  */
        else
        {
          synch_process_alive = 0;
***************
*** 6442,6447 ****
--- 6482,6491 ----
            EMACS_SET_SECS_USECS (*input_available_clear_time, 0, 0);
        }
  
+ 
+     sigchld_end_of_loop:
+       ;
+ 
        /* On some systems, we must return right away.
         If any more processes want to signal us, we will
         get another signal.
***************
*** 6843,6848 ****
--- 6887,6895 ----
    FD_SET (0, &input_wait_mask);
  
    Vprocess_alist = Qnil;
+ #ifdef SIGCHLD
+   deleted_pid_list = Qnil;
+ #endif
    for (i = 0; i < MAXDESC; i++)
      {
        chan_process[i] = Qnil;
***************
*** 6981,6986 ****
--- 7028,7036 ----
    staticpro (&Qlast_nonmenu_event);
  
    staticpro (&Vprocess_alist);
+ #ifdef SIGCHLD
+   staticpro (&deleted_pid_list);
+ #endif
  
    DEFVAR_BOOL ("delete-exited-processes", &delete_exited_processes,
               doc: /* *Non-nil means delete processes immediately when they 
exit.

-- 
 |      Michaël `Micha' Cadilhac   |   Un certain Blaise Pascal             |
 |         Epita/LRDE Promo 2007   |     etc... etc...                      |
 | http://www.lrde.org/~cadilh_m   |   -- Prévert (Les paris stupides)      |
 `--  -   JID: address@hidden --'                                   -  --'

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