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Date: Fri, 28 Nov 1997 11:49:24 -0700 (MST)
From: Marc Slemko <marcs@worldgate.com>
To: TLOSAP <new-httpd@apache.org>
Subject: Re: flock() question  (fwd)
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On Fri, 28 Nov 1997, Dean Gaudet wrote:

> You always need locking if there are multiple Listen statements.

Let me rephrase what I said:

"if using a FreeBSD box of recent 2.2 vintage and you don't need accept
locking because you aren't using multiple Listen statements..."

Yes, I mean what you say.  <g>

> Otherwise FreeBSD has broken accept() semantics.  Our select()/accept()
> loop is not designed for multiple tasks when there are multiple sockets.
> You end up starving sockets because children will block on a single
> socket and not wake up until they manage to get a request on that socket;
> meanwhile requests may be ready on other sockets and go unserviced.
> 
> Defining SAFE_UNSERIALIZED_ACCEPT is fine with me, that only affects
> the single socket case.
> 
> Dean
> 
> On Fri, 28 Nov 1997, Marc Slemko wrote:
> 
> > FYI, if using a FreeBSD box of recent 2.2 vintage and you don't need
> > accept locking to handle multiple Listen statements, you may (or may not)
> > get better performance with many children using SAFE_UNSERIALIZED_ACCEPT.
> > 
> > This is because for each accept() only one child is woken up, but whenever
> > a process fights for a flock(), they all wake up.
> > 
> > ---------- Forwarded message ----------
> > Date: Fri, 28 Nov 1997 03:07:25 -0800
> > From: David Greenman <dg@root.com>
> > To: Marc Slemko <marcs@znep.com>
> > Cc: Charles Mott <cmott@srv.net>, hackers@FreeBSD.ORG
> > Subject: Re: flock() question 
> > 
> > >Hmm.  It looks like if you have multiple processes blocked on the
> > >same lock in FreeBSD (well, 2.2 anyway), they are all woken up when
> > >the lock is freed.  Yes, only one will get the lock but they will
> > >all be woken.  Unless I am reading the code wrong...  This is in
> > >contrast to multiple processes blocking in accept(), where only
> > >one will be woken up.
> > 
> >    The optimized wakeup case for accept() is that way because I optimized
> > it. :-) You're probably right about flock(), but I haven't gotten around to
> > looking at that and other potential wakeup optimizations. Changes like that
> > have to be made with great care...what seems obvious often doesn't turn out
> > that way. :-)
> > 
> > -DG
> > 
> > David Greenman
> > Core-team/Principal Architect, The FreeBSD Project
> > 
> > 
>