linux-kernel - Re: [PATCH Resend] epoll: add EPOLLEXCLUSIVE support

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Message-ID: <4F7E1D23.1080507@mit.edu>
Date:	Thu, 05 Apr 2012 15:30:59 -0700
From:	Andy Lutomirski <luto@....EDU>
To:	Hagen Paul Pfeifer <hagen@...u.net>
CC:	Jason Baron <jbaron@...hat.com>,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	torvalds@...ux-foundation.org, LKML <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH Resend] epoll: add EPOLLEXCLUSIVE support

On 03/29/2012 08:05 AM, Hagen Paul Pfeifer wrote:
> * Jason Baron | 2012-03-29 10:16:53 [-0400]:
> 
>> Right, for level triggered events, they all wait up. However, if you use
>> edge triggered, ie add 'EPOLLET', then the event gets 'consumed' by the
>> first thread that wakes up, and the subseqent waiters wouldn't get woken
>> up. IE you'll get one wakeup.
> 
> I addressed level triggered, right - it match the model. But I don't wanted to
> wake up every every thread anyway. I don't want to abandon level triggered
> functioning.

I think that what you want is a mode in which, once epoll_wait returns,
the bits it returns get cleared from the event mask.  Am I right?

(To get this right, you'd need another flag that disables the automatic
addition of POLLERR and POLLHUP.)

If you do that and add an extra syscall that simultaneously does a bunch
of epoll_ctls, a timerfd_settime, and an epoll_wait, I'll be extra happy.

--Andy
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