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Date: Fri, 14 Feb 2003 20:09:34 -0800 (PST)
From: Davide Libenzi <davidel@xmailserver.org>
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To: Jamie Lokier <jamie@shareable.org>
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Subject: Re: Synchronous signal delivery..
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On Sat, 15 Feb 2003, Jamie Lokier wrote:

> 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 :)

Many ( many ) times, when you're going to wait for events, you want to
specify a maximum wait time ( reletive time ) and not an absolute time.
This is how ppl think about "timeouts". Different beast is the absolute
timer, that you can easily achieve with POSIX timers ( TIMER_ABSTIME ) and
a sigfd() dropped inside an event retrieval interface.




- Davide

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