.\" ========================================================================
.\"
.IX Title ""<STANDARD INPUT>" 1"
-.TH "<STANDARD INPUT>" 1 "2007-11-13" "perl v5.8.8" "User Contributed Perl Documentation"
+.TH "<STANDARD INPUT>" 1 "2007-11-23" "perl v5.8.8" "User Contributed Perl Documentation"
.SH "NAME"
libev \- a high performance full\-featured event loop written in C
.SH "SYNOPSIS"
library in any way.
.IP "ev_tstamp ev_time ()" 4
.IX Item "ev_tstamp ev_time ()"
-Returns the current time as libev would use it.
+Returns the current time as libev would use it. Please note that the
+\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
+you actually want to know.
.IP "int ev_version_major ()" 4
.IX Item "int ev_version_major ()"
.PD 0
override the flags completely if it is found in the environment. This is
useful to try out specific backends to test their performance, or to work
around bugs.
-.ie n .IP """EVMETHOD_SELECT"" (portable select backend)" 4
-.el .IP "\f(CWEVMETHOD_SELECT\fR (portable select backend)" 4
-.IX Item "EVMETHOD_SELECT (portable select backend)"
-.PD 0
-.ie n .IP """EVMETHOD_POLL"" (poll backend, available everywhere except on windows)" 4
-.el .IP "\f(CWEVMETHOD_POLL\fR (poll backend, available everywhere except on windows)" 4
-.IX Item "EVMETHOD_POLL (poll backend, available everywhere except on windows)"
-.ie n .IP """EVMETHOD_EPOLL"" (linux only)" 4
-.el .IP "\f(CWEVMETHOD_EPOLL\fR (linux only)" 4
-.IX Item "EVMETHOD_EPOLL (linux only)"
-.ie n .IP """EVMETHOD_KQUEUE"" (some bsds only)" 4
-.el .IP "\f(CWEVMETHOD_KQUEUE\fR (some bsds only)" 4
-.IX Item "EVMETHOD_KQUEUE (some bsds only)"
-.ie n .IP """EVMETHOD_DEVPOLL"" (solaris 8 only)" 4
-.el .IP "\f(CWEVMETHOD_DEVPOLL\fR (solaris 8 only)" 4
-.IX Item "EVMETHOD_DEVPOLL (solaris 8 only)"
-.ie n .IP """EVMETHOD_PORT"" (solaris 10 only)" 4
-.el .IP "\f(CWEVMETHOD_PORT\fR (solaris 10 only)" 4
-.IX Item "EVMETHOD_PORT (solaris 10 only)"
-.PD
-If one or more of these are ored into the flags value, then only these
-backends will be tried (in the reverse order as given here). If one are
-specified, any backend will do.
+.ie n .IP """EVMETHOD_SELECT"" (value 1, portable select backend)" 4
+.el .IP "\f(CWEVMETHOD_SELECT\fR (value 1, portable select backend)" 4
+.IX Item "EVMETHOD_SELECT (value 1, portable select backend)"
+This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
+libev tries to roll its own fd_set with no limits on the number of fds,
+but if that fails, expect a fairly low limit on the number of fds when
+using this backend. It doesn't scale too well (O(highest_fd)), but its usually
+the fastest backend for a low number of fds.
+.ie n .IP """EVMETHOD_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
+.el .IP "\f(CWEVMETHOD_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
+.IX Item "EVMETHOD_POLL (value 2, poll backend, available everywhere except on windows)"
+And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than
+select, but handles sparse fds better and has no artificial limit on the
+number of fds you can use (except it will slow down considerably with a
+lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
+.ie n .IP """EVMETHOD_EPOLL"" (value 4, Linux)" 4
+.el .IP "\f(CWEVMETHOD_EPOLL\fR (value 4, Linux)" 4
+.IX Item "EVMETHOD_EPOLL (value 4, Linux)"
+For few fds, this backend is a bit little slower than poll and select,
+but it scales phenomenally better. While poll and select usually scale like
+O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
+either O(1) or O(active_fds).
+.Sp
+While stopping and starting an I/O watcher in the same iteration will
+result in some caching, there is still a syscall per such incident
+(because the fd could point to a different file description now), so its
+best to avoid that. Also, \fIdup()\fRed file descriptors might not work very
+well if you register events for both fds.
+.ie n .IP """EVMETHOD_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
+.el .IP "\f(CWEVMETHOD_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
+.IX Item "EVMETHOD_KQUEUE (value 8, most BSD clones)"
+Kqueue deserves special mention, as at the time of this writing, it
+was broken on all BSDs except NetBSD (usually it doesn't work with
+anything but sockets and pipes, except on Darwin, where of course its
+completely useless). For this reason its not being \*(L"autodetected\*(R" unless
+you explicitly specify the flags (i.e. you don't use \s-1EVFLAG_AUTO\s0).
+.Sp
+It scales in the same way as the epoll backend, but the interface to the
+kernel is more efficient (which says nothing about its actual speed, of
+course). While starting and stopping an I/O watcher does not cause an
+extra syscall as with epoll, it still adds up to four event changes per
+incident, so its best to avoid that.
+.ie n .IP """EVMETHOD_DEVPOLL"" (value 16, Solaris 8)" 4
+.el .IP "\f(CWEVMETHOD_DEVPOLL\fR (value 16, Solaris 8)" 4
+.IX Item "EVMETHOD_DEVPOLL (value 16, Solaris 8)"
+This is not implemented yet (and might never be).
+.ie n .IP """EVMETHOD_PORT"" (value 32, Solaris 10)" 4
+.el .IP "\f(CWEVMETHOD_PORT\fR (value 32, Solaris 10)" 4
+.IX Item "EVMETHOD_PORT (value 32, Solaris 10)"
+This uses the Solaris 10 port mechanism. As with everything on Solaris,
+it's really slow, but it still scales very well (O(active_fds)).
+.ie n .IP """EVMETHOD_ALL""" 4
+.el .IP "\f(CWEVMETHOD_ALL\fR" 4
+.IX Item "EVMETHOD_ALL"
+Try all backends (even potentially broken ones that wouldn't be tried
+with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
+\&\f(CW\*(C`EVMETHOD_ALL & ~EVMETHOD_KQUEUE\*(C'\fR.
.RE
.RS 4
+.Sp
+If one or more of these are ored into the flags value, then only these
+backends will be tried (in the reverse order as given here). If none are
+specified, most compiled-in backend will be tried, usually in reverse
+order of their flag values :)
.RE
.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
after forking, in either the parent or child process (or both, but that
again makes little sense).
.Sp
-You \fImust\fR call this function after forking if and only if you want to
-use the event library in both processes. If you just fork+exec, you don't
-have to call it.
+You \fImust\fR call this function in the child process after forking if and
+only if you want to use the event library in both processes. If you just
+fork+exec, you don't have to call it.
.Sp
The function itself is quite fast and it's usually not a problem to call
it just in case after a fork. To make this easy, the function will fit in
This flags value could be used to implement alternative looping
constructs, but the \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`check\*(C'\fR watchers provide a better and
more generic mechanism.
+.Sp
+Here are the gory details of what ev_loop does:
+.Sp
+.Vb 15
+\& 1. If there are no active watchers (reference count is zero), return.
+\& 2. Queue and immediately call all prepare watchers.
+\& 3. If we have been forked, recreate the kernel state.
+\& 4. Update the kernel state with all outstanding changes.
+\& 5. Update the "event loop time".
+\& 6. Calculate for how long to block.
+\& 7. Block the process, waiting for events.
+\& 8. Update the "event loop time" and do time jump handling.
+\& 9. Queue all outstanding timers.
+\& 10. Queue all outstanding periodics.
+\& 11. If no events are pending now, queue all idle watchers.
+\& 12. Queue all check watchers.
+\& 13. Call all queued watchers in reverse order (i.e. check watchers first).
+\& 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
+\& was used, return, otherwise continue with step #1.
+.Ve
.IP "ev_unloop (loop, how)" 4
.IX Item "ev_unloop (loop, how)"
Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
The timers are based on real time, that is, if you register an event that
times out after an hour and you reset your system clock to last years
time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
-detecting time jumps is hard, and soem inaccuracies are unavoidable (the
+detecting time jumps is hard, and some inaccuracies are unavoidable (the
monotonic clock option helps a lot here).
.PP
The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
time. This is usually the right thing as this timestamp refers to the time
-of the event triggering whatever timeout you are modifying/starting. If
-you suspect event processing to be delayed and you *need* to base the timeout
+of the event triggering whatever timeout you are modifying/starting. If
+you suspect event processing to be delayed and you \fIneed\fR to base the timeout
on the current time, use something like this to adjust for this:
.PP
.Vb 1
\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
.Ve
+.PP
+The callback is guarenteed to be invoked only when its timeout has passed,
+but if multiple timers become ready during the same loop iteration then
+order of execution is undefined.
.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
.PD 0
.PP
They can also be used to implement vastly more complex timers, such as
triggering an event on eahc midnight, local time.
+.PP
+As with timers, the callback is guarenteed to be invoked only when the
+time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
+during the same loop iteration then order of execution is undefined.
.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
.PD 0
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