.\" ========================================================================
.\"
.IX Title ""<STANDARD INPUT>" 1"
-.TH "<STANDARD INPUT>" 1 "2007-11-22" "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"
as this indicates an incompatible change. Minor versions are usually
compatible to older versions, so a larger minor version alone is usually
not a problem.
+.IP "unsigned int ev_supported_backends ()" 4
+.IX Item "unsigned int ev_supported_backends ()"
+Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
+value) compiled into this binary of libev (independent of their
+availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
+a description of the set values.
+.IP "unsigned int ev_recommended_backends ()" 4
+.IX Item "unsigned int ev_recommended_backends ()"
+Return the set of all backends compiled into this binary of libev and also
+recommended for this platform. This set is often smaller than the one
+returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
+most BSDs and will not be autodetected unless you explicitly request it
+(assuming you know what you are doing). This is the set of backends that
+libev will probe for if you specify no backends explicitly.
.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
Sets the allocation function to use (the prototype is similar to the
This will initialise the default event loop if it hasn't been initialised
yet and return it. If the default loop could not be initialised, returns
false. If it already was initialised it simply returns it (and ignores the
-flags).
+flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
.Sp
If you don't know what event loop to use, use the one returned from this
function.
.Sp
The flags argument can be used to specify special behaviour or specific
-backends to use, and is usually specified as 0 (or \s-1EVFLAG_AUTO\s0).
+backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
.Sp
-It supports the following flags:
+The following flags are supported:
.RS 4
.ie n .IP """EVFLAG_AUTO""" 4
.el .IP "\f(CWEVFLAG_AUTO\fR" 4
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"" (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)"
+.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
+.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
+.IX Item "EVBACKEND_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)"
+.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
+.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
+.IX Item "EVBACKEND_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)"
+.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
+.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
+.IX Item "EVBACKEND_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
(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)"
+.Sp
+Please note that epoll sometimes generates spurious notifications, so you
+need to use non-blocking I/O or other means to avoid blocking when no data
+(or space) is available.
+.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
+.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
+.IX Item "EVBACKEND_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).
+completely useless). For this reason its not being \*(L"autodetected\*(R"
+unless you explicitly specify it explicitly in the flags (i.e. using
+\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR).
.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)"
+.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
+.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
+.IX Item "EVBACKEND_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)"
+.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
+.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
+.IX Item "EVBACKEND_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"
+.Sp
+Please note that solaris ports can result in a lot of spurious
+notifications, so you need to use non-blocking I/O or other means to avoid
+blocking when no data (or space) is available.
+.ie n .IP """EVBACKEND_ALL""" 4
+.el .IP "\f(CWEVBACKEND_ALL\fR" 4
+.IX Item "EVBACKEND_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.
+\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
.RE
.RS 4
.Sp
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 :)
+.Sp
+The most typical usage is like this:
+.Sp
+.Vb 2
+\& if (!ev_default_loop (0))
+\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
+.Ve
+.Sp
+Restrict libev to the select and poll backends, and do not allow
+environment settings to be taken into account:
+.Sp
+.Vb 1
+\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
+.Ve
+.Sp
+Use whatever libev has to offer, but make sure that kqueue is used if
+available (warning, breaks stuff, best use only with your own private
+event loop and only if you know the \s-1OS\s0 supports your types of fds):
+.Sp
+.Vb 1
+\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
+.Ve
.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
.Vb 1
\& pthread_atfork (0, 0, ev_default_fork);
.Ve
+.Sp
+At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
+without calling this function, so if you force one of those backends you
+do not need to care.
.IP "ev_loop_fork (loop)" 4
.IX Item "ev_loop_fork (loop)"
Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
after fork, and how you do this is entirely your own problem.
-.IP "unsigned int ev_method (loop)" 4
-.IX Item "unsigned int ev_method (loop)"
-Returns one of the \f(CW\*(C`EVMETHOD_*\*(C'\fR flags indicating the event backend in
+.IP "unsigned int ev_backend (loop)" 4
+.IX Item "unsigned int ev_backend (loop)"
+Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
use.
.IP "ev_tstamp ev_now (loop)" 4
.IX Item "ev_tstamp ev_now (loop)"
after you initialised all your watchers and you want to start handling
events.
.Sp
-If the flags argument is specified as 0, it will not return until either
-no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
+If the flags argument is specified as \f(CW0\fR, it will not return until
+either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
.Sp
A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
those events and any outstanding ones, but will not block your process in
A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
neccessary) and will handle those and any outstanding ones. It will block
your process until at least one new event arrives, and will return after
-one iteration of the loop.
-.Sp
-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.
+one iteration of the loop. This is useful if you are waiting for some
+external event in conjunction with something not expressible using other
+libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
+usually a better approach for this kind of thing.
+.Sp
+Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
+.Sp
+.Vb 18
+\& * If there are no active watchers (reference count is zero), return.
+\& - Queue prepare watchers and then call all outstanding watchers.
+\& - If we have been forked, recreate the kernel state.
+\& - Update the kernel state with all outstanding changes.
+\& - Update the "event loop time".
+\& - Calculate for how long to block.
+\& - Block the process, waiting for any events.
+\& - Queue all outstanding I/O (fd) events.
+\& - Update the "event loop time" and do time jump handling.
+\& - Queue all outstanding timers.
+\& - Queue all outstanding periodics.
+\& - If no events are pending now, queue all idle watchers.
+\& - Queue all check watchers.
+\& - Call all queued watchers in reverse order (i.e. check watchers first).
+\& Signals and child watchers are implemented as I/O watchers, and will
+\& be handled here by queueing them when their watcher gets executed.
+\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
+\& were used, return, otherwise continue with step *.
.Ve
.IP "ev_unloop (loop, how)" 4
.IX Item "ev_unloop (loop, how)"
.PP
As long as your watcher is active (has been started but not stopped) you
must not touch the values stored in it. Most specifically you must never
-reinitialise it or call its set method.
+reinitialise it or call its set macro.
.PP
You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
(watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
the same underlying \*(L"file open\*(R").
.PP
If you must do this, then force the use of a known-to-be-good backend
-(at the time of this writing, this includes only \s-1EVMETHOD_SELECT\s0 and
-\&\s-1EVMETHOD_POLL\s0).
+(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
+\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
.PD 0
Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive
events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_READ |
EV_WRITE\*(C'\fR to receive the given events.
+.Sp
+Please note that most of the more scalable backend mechanisms (for example
+epoll and solaris ports) can result in spurious readyness notifications
+for file descriptors, so you practically need to use non-blocking I/O (and
+treat callback invocation as hint only), or retest separately with a safe
+interface before doing I/O (XLib can do this), or force the use of either
+\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this
+problem. Also note that it is quite easy to have your callback invoked
+when the readyness condition is no longer valid even when employing
+typical ways of handling events, so its a good idea to use non-blocking
+I/O unconditionally.
.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts"
.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts"
.IX Subsection "ev_timer - relative and optionally recurring timeouts"
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