From: michael.cadilhac@lrde.org (Michaël Cadilhac)
Cc: emacs-devel@gnu.org
Subject: Re: delete-process bug
Date: Sat, 27 May 2006 11:19:58 +0200 [thread overview]
Message-ID: <87odxjakox.fsf@lrde.org> (raw)
In-Reply-To: <loom.20060526T191549-416@post.gmane.org> (Michael Mauger's message of "Fri, 26 May 2006 17:27:36 +0000 (UTC)")
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Michael Mauger <mmaug@yahoo.com> writes:
> Stefan Monnier <monnier <at> iro.umontreal.ca> writes:
>
>>
>> > Thanks for working on this. I agree that `live_deleted_processes'
>> > is a good name. ("Zombie process" has a different meaning.)
>>
>> > However, maybe there is still a race condition. Suppose the signal
>> > comes in the middle of the line
>>
>> > + live_deleted_processes = Fcons (make_number (p->pid),
>> > + /* GC previous elements. */
>> > + Fdelq (Qnil,
> live_deleted_processes));
>>
>> > Suppose it comes between there and the call to remove_process?
>>
>> I think it's OK: if the signal handler comes before the assignment to
>> live_deleted_processes, then it'll all behave as if the signal came even
>> before the call to delete-process. If it comes afterwards, the signal will
>> be ignored (as if it came after the call to delete-process).
>>
>> > Does the right thing happen in all these cases?
>>
>> I believe so.
>>
>
> My instinct would be to add the pid to the list prior to causing the event that
> the list is designed to detect. Treating the signal as though it happened
> before the call to delete-process (if we don't add the pid to the list first)
> when we know it was most likely caused by delete-process seems to be asking for
> trouble.
Sounds better, indeed.
However, no race condition could have happened because of a (more)
simple thing (than what I said):
The race condition appears when
1) Emacs got a SIGCHLD
2) and the process has been suppressed from process_list.
But the deletion from process_list is made _after_ the adding to
live_deleted_processes. So no problem here, I think, the process is
always known (so not supposed to be a synchronous one).
If something has to be put in comment to say that no race condition
is triggered, I think something like the following is OK:
``A race condition occurred when the deleted process was no longer in
process_list but still had a SIGCHLD treatment to do. Now, the deleted
process is never thought to be asynchronous.''
Regards
--
| Michaël `Micha' Cadilhac | Le copillage-collage |
| Epita/LRDE Promo 2007 | tue le programmeur. |
| http://www.lrde.org/~cadilh_m | -- Dictons LRDE |
`-- - JID: micha@amessage.be --' - --'
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next prev parent reply other threads:[~2006-05-27 9:19 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 ` 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 [this message]
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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