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From: David Kastrup <dak@gnu.org>
To: Andreas Schwab <schwab@suse.de>
Cc: Sam Steingold <sds@gnu.org>, emacs-devel@gnu.org
Subject: Re: busyloop in sigchld_handler
Date: Mon, 12 Mar 2007 20:34:43 +0100	[thread overview]
Message-ID: <85ejnumf1o.fsf@lola.goethe.zz> (raw)
In-Reply-To: <jeejnub6se.fsf@sykes.suse.de> (Andreas Schwab's message of "Mon\, 12 Mar 2007 20\:28\:33 +0100")

Andreas Schwab <schwab@suse.de> writes:

> Sam Steingold <sds@gnu.org> writes:
>
>> I don't know the details, but the kernel obviously has to do SOMETHING
>> when the child process terminates: it has to notice the state change so
>> that wait3 in emacs will return "yes, the child is dead" instead of
>> "nothing for you yet". The busyloop prevents the kernel from doing
>> anything for some time.
>
> But the busyloop does not happen when there is nothing to do, it only
> happens when wait3 is interrupted.  A zero return will cause the handler
> to return immediately.
>
>> Now, it might be better to remove the WNOHANG option instead (except that
>> signal handlers are not supposed to hang),
>
> If you don't use WNOHANG you open up a race where several processes may
> have their status changed, but only one signal is sent (non-realtime
> signals are not queued).

How does WNOHANG protect against that?  It does not prevent
scheduling, and it certainly does not prevent parallel execution on
multi-processor machines.

I should think that we need to prepare against this anyway.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum

  reply	other threads:[~2007-03-12 19:34 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-03-11 18:33 busyloop in sigchld_handler Sam Steingold
2007-03-11 19:39 ` Kim F. Storm
2007-03-11 19:43   ` David Kastrup
2007-03-11 19:51     ` Sam Steingold
2007-03-11 20:42       ` Kim F. Storm
2007-03-11 21:06   ` Sam Steingold
2007-03-11 21:14     ` Eli Zaretskii
2007-03-11 21:17       ` Sam Steingold
2007-03-11 21:51         ` Eli Zaretskii
2007-03-11 22:21           ` Sam Steingold
2007-03-12  4:24             ` Richard Stallman
2007-03-12  7:00               ` David Kastrup
2007-03-13  2:43                 ` Richard Stallman
2007-03-11 22:27     ` Andreas Schwab
2007-03-11 22:30     ` Kim F. Storm
2007-03-12 17:37     ` Andreas Schwab
2007-03-12 17:53       ` Sam Steingold
2007-03-12 18:45         ` Andreas Schwab
2007-03-12 18:57           ` Sam Steingold
2007-03-12 19:28             ` Andreas Schwab
2007-03-12 19:34               ` David Kastrup [this message]
2007-03-12 21:36                 ` Andreas Schwab
2007-03-13  7:29                   ` David Kastrup
2007-03-13  9:29                     ` Andreas Schwab
2007-03-13 22:19                       ` David Kastrup
2007-03-13 22:28                         ` Andreas Schwab
2007-03-13 22:54                           ` David Kastrup
2007-03-13 23:17                             ` Andreas Schwab
2007-03-14  7:06                               ` David Kastrup
2007-03-14  9:24                                 ` Kim F. Storm
2007-03-14 10:00                                   ` David Kastrup
2007-03-14 10:22                                     ` Andreas Schwab
2007-03-14 10:52                                       ` David Kastrup
2007-03-14 11:01                                         ` Andreas Schwab
2007-03-14 11:12                                           ` David Kastrup
2007-03-14 12:29                                             ` Andreas Schwab
2007-03-14 10:01                                   ` Andreas Schwab
2007-03-14 13:15                                     ` Kim F. Storm
2007-03-14 13:41                                       ` Andreas Schwab
2007-03-14 14:10                                         ` Kim F. Storm
2007-03-14 14:12                                           ` Andreas Schwab
2007-03-14 15:02                                             ` Kim F. Storm
2007-03-14 16:34                                               ` Andreas Schwab
2007-03-16  9:34                                                 ` Kim F. Storm
2007-03-16  9:59                                                   ` Andreas Schwab
2007-03-14  3:24                     ` Richard Stallman
2007-03-14 17:34                       ` David Kastrup
2007-03-26  1:47 ` YAMAMOTO Mitsuharu
2007-03-26  2:02   ` Sam Steingold
2007-03-26  2:17     ` YAMAMOTO Mitsuharu
2007-03-28 10:02     ` Kim F. Storm
2007-03-28 15:19       ` Chong Yidong
2007-03-28 15:25         ` Andreas Schwab
2007-03-28 15:33           ` Kim F. Storm
2007-03-28 15:37             ` Andreas Schwab
2007-03-28 20:18               ` Kim F. Storm
2007-03-29 17:59                 ` Richard Stallman
2007-03-28 15:30         ` Alfred M. Szmidt

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