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
-\&\f(CW\*(C`EVFLAG_AUTO\*(C'\fR will probe for.
+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
function.
.Sp
The flags argument can be used to specify special behaviour or specific
-backends to use, and is usually specified as \f(CW0\fR (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
(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.
+.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
.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)).
+.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"
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 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)"
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"
projects / software / libev.git / blobdiff