From owner-freebsd-stable  Sun Jan 23 16:43:18 2000
Delivered-To: freebsd-stable@freebsd.org
Received: from alcanet.com.au (mail.alcanet.com.au [203.62.196.10])
	by hub.freebsd.org (Postfix) with ESMTP
	id 056B114D5D; Sun, 23 Jan 2000 16:43:12 -0800 (PST)
	(envelope-from jeremyp@gsmx07.alcatel.com.au)
Received: by border.alcanet.com.au id <115214>; Mon, 24 Jan 2000 11:43:42 +1100
Content-return: prohibited
From: Peter Jeremy <peter.jeremy@alcatel.com.au>
Subject: Re: kern/13644
In-reply-to: <200001231636.LAA43285@rtfm.newton>; from mi@kot.ne.mediaone.net
 on Mon, Jan 24, 2000 at 03:37:19AM +1100
To: Mikhail Teterin <mi@kot.ne.mediaone.net>
Cc: stable@FreeBSD.ORG, FreeBSD-gnats-submit@FreeBSD.ORG
Message-Id: <00Jan24.114342est.115214@border.alcanet.com.au>
MIME-version: 1.0
X-Mailer: Mutt 1.0i
Content-type: text/plain; charset=us-ascii
References: <000a01bf655e$314bb6c0$021d85d1@youwant.to>
 <200001231636.LAA43285@rtfm.newton>
Date: Mon, 24 Jan 2000 11:43:41 +1100
Sender: owner-freebsd-stable@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG

On 2000-Jan-24 03:37:19 +1100, Mikhail Teterin <mi@kot.ne.mediaone.net> wrote:
>=> =FreeBSD:
>=> ==> =>  If timeout is a non-nil pointer, it specifies a maximum
>=> ==> =>  interval to wait for the selection to complete.
...
>It  appears, that  you,  as well  as other  developers,  speak from  the
>implementation point of view. I only  look at the man-page. The man page
>says, the time out  is the UPPER limit.

Note that the man page talks about waiting for the _selection_ to
complete.  It does not refer to returning from the select(2) call.
And the behaviour is exactly as documented: when the specified
interval is complete, the process will return to the run queue for
normal scheduling (if it hasn't previously found a ready FD).  Unix
is not a real-time OS, so once a process is in the run queue, an
arbitrary period can expire before the process is actually run.

The only cases where a select(2) (or poll(2)) system call will return
before a specified period are:
1) A signal was received
2) One of the specified file descriptors became ready.

>sorts of  other man-pages from all  sorts of other vendors,  who all say
>(almost) the same thing:
>
>	that the timeout is indeed the UPPER limit, and not the LOWER.

Please provide a test program and results from these other vendors
demonstrating that their select() will return before the specified
time limit in the absence of any other event.

It's probably worthwhile adding a comment to select(2) similar to that
in sleep(3), noting that "system activity may lengthen the sleep by an
indeterminate amount."

Peter


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-stable" in the body of the message