From: michael.cadilhac@lrde.org (Michaël Cadilhac)
Subject: delete-process bug (was: Ispell loads dict twice.)
Date: Thu, 25 May 2006 12:57:18 +0200 [thread overview]
Message-ID: <87bqtmjrsh.fsf_-_@lrde.org> (raw)
In-Reply-To: <20060524112846.GA12046@agmartin.aq.upm.es> (Agustin Martin's message of "Wed, 24 May 2006 13:28:46 +0200")
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Agustin Martin <agustin.martin@hispalinux.es> writes:
> Ispell process killed
> Starting new Ispell process [american] ...
> Error in post-command-hook: (error ispell exited with signal Killed)
This is not really due to my patch. However, it shows a real race
condition in process management of Emacs:
Try the following:
(delete-process (start-process "bug" nil "/tmp/sleep"))
(let ((result (call-process "/tmp/sleep")))
(message "%S" result))
(/tmp/sleep is just "sleep 1")
You'll have, as a result, the message « Killed » ; but the process
called by call-process is _not actually killed_, it's the previous
(deleted) one that was.
The bug is simple:
- The first process is launched asynchronously, then killed
- A synchronous process is created and executed
- HERE, sigchld_handler is called, because of the first process death
- The PID of the first process is searched in:
- The list of asynchronous process, in which it is no more,
- As a fall back, it is considered as a synchronous process.
- Then the synchronous process is said to be killed.
... but it isn't.
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.
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Index: src/ChangeLog
===================================================================
RCS file: /sources/emacs/emacs/src/ChangeLog,v
retrieving revision 1.5087
diff -c -B -b -r1.5087 ChangeLog
*** src/ChangeLog 24 May 2006 16:58:47 -0000 1.5087
--- src/ChangeLog 25 May 2006 10:55:02 -0000
***************
*** 1,3 ****
--- 1,8 ----
+ 2006-05-25 Michaël Cadilhac <michael.cadilhac@lrde.org>
+
+ * process.c (Fdelete_process): Wait for process termination to
+ avoid `sigchld_handler' to consider the process to be synchronous.
+
2006-05-24 Luc Teirlinck <teirllm@auburn.edu>
* puresize.h (BASE_PURESIZE): Increase to 1210000.
Index: src/process.c
===================================================================
RCS file: /sources/emacs/emacs/src/process.c,v
retrieving revision 1.481
diff -c -B -b -r1.481 process.c
*** src/process.c 8 May 2006 05:19:42 -0000 1.481
--- src/process.c 25 May 2006 10:55:02 -0000
***************
*** 800,805 ****
--- 800,806 ----
else if (XINT (p->infd) >= 0)
{
Fkill_process (process, Qnil);
+ wait_for_termination (p->pid);
/* Do this now, since remove_process will make sigchld_handler do nothing. */
p->status
= Fcons (Qsignal, Fcons (make_number (SIGKILL), Qnil));
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Regards,
--
| Michaël `Micha' Cadilhac | Mieux vaut se taire |
| Epita/LRDE Promo 2007 | Que de parler trop fort. |
| http://www.lrde.org/~cadilh_m | -- As de trèfle |
`-- - JID: micha@amessage.be --' - --'
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next prev parent reply other threads:[~2006-05-25 10:57 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 ` Michaël Cadilhac [this message]
2006-05-25 12:19 ` delete-process bug (was: Ispell loads dict twice.) Agustin Martin
2006-05-25 14:55 ` delete-process bug Stefan Monnier
2006-05-25 14:59 ` 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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