X-Spam-Check-By: sourceware.org
To: cygwin AT cygwin DOT com
From: Eric Blake <ebb9 AT byu DOT net>
Subject:  Re: Cygwin speed
Date: Wed, 7 Mar 2007 21:25:48 +0000 (UTC)
Lines: 34
Message-ID:  <loom.20070307T221839-665@post.gmane.org>
References:  <45E86FFD DOT 7060301 AT princeton DOT edu> <45E876FA DOT 7401B017 AT dessent DOT net> <20070305011713 DOT GG6734 AT ns1 DOT anodized DOT com> <45EF1CED DOT 608 AT t-online DOT de>
Mime-Version:  1.0
Content-Type:  text/plain; charset=us-ascii
Content-Transfer-Encoding:  7bit
User-Agent: Loom/3.14 (http://gmane.org/)
X-IsSubscribed: yes
Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Id: <cygwin.cygwin.com>
List-Subscribe: <mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive: <http://sourceware.org/ml/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender: cygwin-owner AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
Delivered-To: mailing list cygwin AT cygwin DOT com

Christian Franke <Christian.Franke <at> t-online.de> writes:

> Cygwin's sigprocmask() unconditionally calls sig_dispatch_pending().
> This is necessary because POSIX requires that at least one pending 
> signal is dispatched by sigprocmask().

Actually, POSIX requires "If there are any pending unblocked signals after the 
call to sigprocmask(), at least one of those signals shall be delivered before 
the call to sigprocmask() returns."

And the way I see it, if the mask is unchanged, then any signal that was 
unblocked before calling sigprocmask() should have already fired.  In other 
words, the only signals that sigprocmask() HAS to worry about are signals that 
just changed to unmasked; and if the mask isn't changing, then there is no need 
to flush the signal queue.

> 
> With the attached patch, sigprocmask() does nothing if the signal mask 
> is not changed.
> This reduces the context switches to <5000.
> (Patch is only intended for testing, it at least breaks above POSIX rule)

I think your patch is still within the spirit of POSIX - I don't see the rule 
being broken.  I'll defer to cgf's judgment on this; but it sounds like a 
worthwhile patch to apply, even if it doesn't help the common case of non-
builtins.

And if cgf decides not to patch cygwin in this manner, I can at least try to 
patch bash to not call sigprocmask() if it knows the mask is not changing.

-- 
Eric Blake
volunteer cygwin bash maintainer



--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Problem reports:       http://cygwin.com/problems.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/