-.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). Since this is a mask, you
+can do stuff like \f(CW\*(C`EVMETHOD_ALL & ~EVMETHOD_KQUEUE\*(C'\fR.
projects / software / libev.git / blobdiff