Messages in this thread | | | Date | Fri, 14 Feb 2003 20:09:34 -0800 (PST) | From | Davide Libenzi <> | 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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