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Date: Sat, 15 Feb 2003 02:08:38 +0000
From: Jamie Lokier <jamie@shareable.org>
To: Davide Libenzi <davidel@xmailserver.org>
Cc: Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Synchronous signal delivery..
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Davide Libenzi wrote:
> > Then again, it is also extremely common to write this:
> >
> > 	gettimeofday(...)
> > 	// calculate time until next application timer expires.
> > 	// Note also race condition here, if we're preempted.
> > 	read_events(..., next_app_time - timeofday)
> > 	// we need to know the current time.
> > 	gettimeofday(...)
> >
> > So perhaps the current select/poll/epoll timeout method is not
> > particularly optimal as it is?
> 
> What's bad in epoll_wait() to get events from all pollable descriptors ?

Nothing wrong with that.  It's the "relative to now" timeout argument
that is a bit racy, and the fact that you need a gettimeofday() system
call just before - every time - _purely_ to calculate the time until
the next application timer event.

If you must have a separate system call every time round your event
loop, it may as well set up a timerfd and let that be another pollable
descriptor.

In which case, read() is just fine for getting events :)

-- Jamie

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