timerfd() and system call review
Posted Aug 15, 2007 19:01 UTC (Wed) by njs
In reply to: timerfd() and system call review
Parent article: timerfd() and system call review
You, uh, want to have one thread per pending timer?
The real solution avoiding timerfd is to write a proper main loop like the ones in glib, Qt, Twisted Python, libevent, etc., that puts timers on a heap and uses the delay from timer at the head of the heap to set the timeout on one's blocking syscall (select, epoll, kqueue, whatever).
This is all a truly fantastic pain in the butt, though, esp. once you bring in other events like signals, process handling (waitpid), etc. Even worse, it's not composable -- if you have libraries that need to do IO, getting them integrated with each other and with your main loop is almost impossible. Again there are pure-userspace solutions possible in principle (e.g. abstracted wrappers over multiple event loops like liboop), but in practice it remains a huge issue. This is one of the reasons we still don't have a really decent async dns resolver library, for instance.
I don't know how much of a help these Linux-specific solutions will be in the long run, but being able to wrap all event sources into fds via timerfd and signalfd and so on, and combine multiple fds into a single fd (for purposes of event selection) via epoll, certainly has the *potential* to simplify all these messes significantly. Maybe we'll even figure out eventually whether this or kqueue is better.
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