From: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: emacs-devel@gnu.org
Subject: Re: delete-process bug
Date: Thu, 25 May 2006 10:55:08 -0400 [thread overview]
Message-ID: <jwv1wuiqit2.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <87bqtmjrsh.fsf_-_@lrde.org> (Michaël Cadilhac's message of "Thu, 25 May 2006 12:57:18 +0200")
> This is not really due to my patch. However, it shows a real race
> condition in process management of Emacs:
[...]
> After an hour of debugging, I can propose a small change that fixes
> this bug and lets no room for any other race condition of that kind,
> AFAICT.
[...]
> + * process.c (Fdelete_process): Wait for process termination to
> + avoid `sigchld_handler' to consider the process to be synchronous.
I don't think it's a good idea. The process might not die in response to
delete-process, so we would end up waiting "indefinitely".
I think in order to avoid such race-conditions without waiting for the
process's death, we'll need to remember those processes that were deleted
but aren't dead yet. Of course, it goes against the docstring of
`delete-process' which says "forget about it immediately". But we don't
need to keep the whole process around; just the PID should be enough, kept
in a list of "deleted but not dead" PIDs. See sample patch below.
Stefan
--- process.c 12 mai 2006 11:54:58 -0400 1.481
+++ process.c 25 mai 2006 10:51:51 -0400
@@ -778,6 +778,13 @@
return proc;
}
+/* Fdelete_process promises to immediately forget about the process, but in
+ reality Emacs needs to remember those processes until they die, otherwise
+ it doesn't know what to do with the SIGCHLD signal and might be tempted
+ to interpret that signal as applying to some other non-deleted
+ process ;-(. */
+static Lisp_Object live_deleted_processes;
+
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
@@ -800,6 +807,9 @@
else if (XINT (p->infd) >= 0)
{
Fkill_process (process, Qnil);
+ live_deleted_processes = Fcons (make_number (p->pid),
+ /* GC previous elements. */
+ Fdelq (Qnil, live_deleted_processes));
/* Do this now, since remove_process will make sigchld_handler do nothing. */
p->status
= Fcons (Qsignal, Fcons (make_number (SIGKILL), Qnil));
@@ -6373,6 +6383,13 @@
/* Find the process that signaled us, and record its status. */
+ /* Maybe the process was already passed to Fdelete_process. */
+ tail = Fmemq (make_number (pid), live_deleted_processes);
+ if (!NILP (tail)) {
+ Fsetcar (tail, Qnil);
+ return;
+ }
+
p = 0;
for (tail = Vprocess_alist; GC_CONSP (tail); tail = XCDR (tail))
{
@@ -7357,6 +7374,7 @@
void
init_process ()
{
+ live_deleted_processes = Qnil;
}
void
next prev parent reply other threads:[~2006-05-25 14:55 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-04-24 19:36 Ispell loads dict twice Michaël Cadilhac
2006-04-26 10:14 ` Agustin Martin
2006-04-26 21:58 ` Michaël Cadilhac
2006-05-23 18:26 ` Michaël Cadilhac
2006-05-24 11:28 ` Agustin Martin
2006-05-25 10:57 ` delete-process bug (was: Ispell loads dict twice.) Michaël Cadilhac
2006-05-25 12:19 ` Agustin Martin
2006-05-25 14:55 ` Stefan Monnier [this message]
2006-05-25 14:59 ` delete-process bug David Kastrup
2006-05-25 15:17 ` Michaël Cadilhac
2006-05-25 15:26 ` David Kastrup
2006-05-25 19:40 ` Stefan Monnier
2006-05-25 23:51 ` Kim F. Storm
2006-05-26 4:49 ` Richard Stallman
2006-05-26 13:03 ` Stefan Monnier
2006-05-26 2:22 ` Richard Stallman
2006-05-26 11:29 ` Michaël Cadilhac
2006-05-27 3:36 ` Richard Stallman
2006-05-26 13:10 ` Stefan Monnier
2006-05-26 17:27 ` Michael Mauger
2006-05-27 9:19 ` Michaël Cadilhac
2006-05-27 14:16 ` Stefan Monnier
2006-05-27 14:29 ` Michaël Cadilhac
2006-05-28 16:01 ` Michaël Cadilhac
2006-05-28 18:00 ` Stefan Monnier
2006-05-28 18:32 ` Michaël Cadilhac
2006-05-28 19:48 ` Stefan Monnier
2006-05-28 20:26 ` Michaël Cadilhac
2006-05-28 21:15 ` Kim F. Storm
2006-05-28 21:36 ` Michaël Cadilhac
2006-05-28 23:54 ` Stefan Monnier
2006-05-29 11:39 ` Michaël Cadilhac
2006-05-29 8:22 ` Kim F. Storm
2006-05-29 8:50 ` David Kastrup
2006-05-29 19:04 ` Eli Zaretskii
2006-05-29 19:27 ` Eli Zaretskii
2006-05-29 21:42 ` Kim F. Storm
2006-05-29 22:08 ` Eli Zaretskii
2006-05-29 3:32 ` Eli Zaretskii
2006-05-29 8:14 ` Kim F. Storm
2006-05-29 10:59 ` Michaël Cadilhac
2006-05-29 19:25 ` Eli Zaretskii
2006-05-29 20:04 ` Michaël Cadilhac
2006-05-29 21:24 ` Eli Zaretskii
2006-05-29 21:42 ` Michaël Cadilhac
2006-05-29 22:11 ` Eli Zaretskii
2006-05-29 22:32 ` Michaël Cadilhac
2006-05-30 12:11 ` Kim F. Storm
2006-05-30 12:42 ` Michaël Cadilhac
2006-05-30 14:26 ` Kim F. Storm
2006-05-30 15:13 ` Michaël Cadilhac
2006-06-01 14:06 ` Kim F. Storm
2006-06-01 14:20 ` Michaël Cadilhac
2006-06-01 14:29 ` Kim F. Storm
2006-06-01 16:05 ` Michaël Cadilhac
2006-06-02 7:46 ` Kim F. Storm
2006-06-01 16:41 ` Agustin Martin
2006-06-01 16:55 ` Michaël Cadilhac
2006-05-29 23:07 ` Agustin Martin
2006-05-25 23:52 ` delete-process bug (was: Ispell loads dict twice.) Kim F. Storm
2006-06-06 20:45 ` Ispell loads dict twice Michaël Cadilhac
2006-06-09 13:02 ` Kim F. Storm
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