(fractional) number of seconds since the (POSIX) epoch (somewhere near
the beginning of 1970, details are complicated, don't ask). This type is
called C<ev_tstamp>, which is what you should use too. It usually aliases
-to the double type in C.
+to the C<double> type in C, and when you need to do any calculations on
+it, you should treat it as such.
+
=head1 GLOBAL FUNCTIONS
compatible to older versions, so a larger minor version alone is usually
not a problem.
+Example: make sure we haven't accidentally been linked against the wrong
+version:
+
+ assert (("libev version mismatch",
+ ev_version_major () == EV_VERSION_MAJOR
+ && ev_version_minor () >= EV_VERSION_MINOR));
+
=item unsigned int ev_supported_backends ()
Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
availability on the system you are running on). See C<ev_default_loop> for
a description of the set values.
+Example: make sure we have the epoll method, because yeah this is cool and
+a must have and can we have a torrent of it please!!!11
+
+ assert (("sorry, no epoll, no sex",
+ ev_supported_backends () & EVBACKEND_EPOLL));
+
=item unsigned int ev_recommended_backends ()
Return the set of all backends compiled into this binary of libev and also
(assuming you know what you are doing). This is the set of backends that
libev will probe for if you specify no backends explicitly.
+=item unsigned int ev_embeddable_backends ()
+
+Returns the set of backends that are embeddable in other event loops. This
+is the theoretical, all-platform, value. To find which backends
+might be supported on the current system, you would need to look at
+C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
+recommended ones.
+
+See the description of C<ev_embed> watchers for more info.
+
=item ev_set_allocator (void *(*cb)(void *ptr, long size))
Sets the allocation function to use (the prototype is similar to the
free some memory if it cannot allocate memory, to use a special allocator,
or even to sleep a while and retry until some memory is available.
+Example: replace the libev allocator with one that waits a bit and then
+retries: better than mine).
+
+ static void *
+ persistent_realloc (void *ptr, long size)
+ {
+ for (;;)
+ {
+ void *newptr = realloc (ptr, size);
+
+ if (newptr)
+ return newptr;
+
+ sleep (60);
+ }
+ }
+
+ ...
+ ev_set_allocator (persistent_realloc);
+
=item ev_set_syserr_cb (void (*cb)(const char *msg));
Set the callback function to call on a retryable syscall error (such
requested operation, or, if the condition doesn't go away, do bad stuff
(such as abort).
+Example: do the same thing as libev does internally:
+
+ static void
+ fatal_error (const char *msg)
+ {
+ perror (msg);
+ abort ();
+ }
+
+ ...
+ ev_set_syserr_cb (fatal_error);
+
=back
=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
handle signal and child watchers, and attempts to do so will be greeted by
undefined behaviour (or a failed assertion if assertions are enabled).
+Example: try to create a event loop that uses epoll and nothing else.
+
+ struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
+ if (!epoller)
+ fatal ("no epoll found here, maybe it hides under your chair");
+
=item ev_default_destroy ()
Destroys the default loop again (frees all memory and kernel state
=item ev_tstamp ev_now (loop)
Returns the current "event loop time", which is the time the event loop
-got events and started processing them. This timestamp does not change
-as long as callbacks are being processed, and this is also the base time
-used for relative timers. You can treat it as the timestamp of the event
-occuring (or more correctly, the mainloop finding out about it).
+received events and started processing them. This timestamp does not
+change as long as callbacks are being processed, and this is also the base
+time used for relative timers. You can treat it as the timestamp of the
+event occuring (or more correctly, libev finding out about it).
=item ev_loop (loop, int flags)
If the flags argument is specified as C<0>, it will not return until
either no event watchers are active anymore or C<ev_unloop> was called.
+Please note that an explicit C<ev_unloop> is usually better than
+relying on all watchers to be stopped when deciding when a program has
+finished (especially in interactive programs), but having a program that
+automatically loops as long as it has to and no longer by virtue of
+relying on its watchers stopping correctly is a thing of beauty.
+
A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
those events and any outstanding ones, but will not block your process in
case there are no events and will return after one iteration of the loop.
- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
were used, return, otherwise continue with step *.
+Example: queue some jobs and then loop until no events are outsanding
+anymore.
+
+ ... queue jobs here, make sure they register event watchers as long
+ ... as they still have work to do (even an idle watcher will do..)
+ ev_loop (my_loop, 0);
+ ... jobs done. yeah!
+
=item ev_unloop (loop, how)
Can be used to make a call to C<ev_loop> return early (but only after it
way to do this for generic recurring timers or from within third-party
libraries. Just remember to I<unref after start> and I<ref before stop>.
+Example: create a signal watcher, but keep it from keeping C<ev_loop>
+running when nothing else is active.
+
+ struct dv_signal exitsig;
+ ev_signal_init (&exitsig, sig_cb, SIGINT);
+ ev_signal_start (myloop, &exitsig);
+ evf_unref (myloop);
+
+Example: for some weird reason, unregister the above signal handler again.
+
+ ev_ref (myloop);
+ ev_signal_stop (myloop, &exitsig);
+
=back
=head1 ANATOMY OF A WATCHER
This section describes each watcher in detail, but will not repeat
information given in the last section.
+
=head2 C<ev_io> - is this file descriptor readable or writable
I/O watchers check whether a file descriptor is readable or writable
=back
+Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well
+readable, but only once. Since it is likely line-buffered, you could
+attempt to read a whole line in the callback:
+
+ static void
+ stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
+ {
+ ev_io_stop (loop, w);
+ .. read from stdin here (or from w->fd) and haqndle any I/O errors
+ }
+
+ ...
+ struct ev_loop *loop = ev_default_init (0);
+ struct ev_io stdin_readable;
+ ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
+ ev_io_start (loop, &stdin_readable);
+ ev_loop (loop, 0);
+
+
=head2 C<ev_timer> - relative and optionally recurring timeouts
Timer watchers are simple relative timers that generate an event after a
=back
+Example: create a timer that fires after 60 seconds.
+
+ static void
+ one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
+ {
+ .. one minute over, w is actually stopped right here
+ }
+
+ struct ev_timer mytimer;
+ ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
+ ev_timer_start (loop, &mytimer);
+
+Example: create a timeout timer that times out after 10 seconds of
+inactivity.
+
+ static void
+ timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
+ {
+ .. ten seconds without any activity
+ }
+
+ struct ev_timer mytimer;
+ ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
+ ev_timer_again (&mytimer); /* start timer */
+ ev_loop (loop, 0);
+
+ // and in some piece of code that gets executed on any "activity":
+ // reset the timeout to start ticking again at 10 seconds
+ ev_timer_again (&mytimer);
+
+
=head2 C<ev_periodic> - to cron or not to cron
Periodic watchers are also timers of a kind, but they are very versatile
=back
+Example: call a callback every hour, or, more precisely, whenever the
+system clock is divisible by 3600. The callback invocation times have
+potentially a lot of jittering, but good long-term stability.
+
+ static void
+ clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
+ {
+ ... its now a full hour (UTC, or TAI or whatever your clock follows)
+ }
+
+ struct ev_periodic hourly_tick;
+ ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
+ ev_periodic_start (loop, &hourly_tick);
+
+Example: the same as above, but use a reschedule callback to do it:
+
+ #include <math.h>
+
+ static ev_tstamp
+ my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
+ {
+ return fmod (now, 3600.) + 3600.;
+ }
+
+ ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
+
+Example: call a callback every hour, starting now:
+
+ struct ev_periodic hourly_tick;
+ ev_periodic_init (&hourly_tick, clock_cb,
+ fmod (ev_now (loop), 3600.), 3600., 0);
+ ev_periodic_start (loop, &hourly_tick);
+
+
=head2 C<ev_signal> - signal me when a signal gets signalled
Signal watchers will trigger an event when the process receives a specific
=back
+
=head2 C<ev_child> - wait for pid status changes
Child watchers trigger when your process receives a SIGCHLD in response to
=back
+Example: try to exit cleanly on SIGINT and SIGTERM.
+
+ static void
+ sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
+ {
+ ev_unloop (loop, EVUNLOOP_ALL);
+ }
+
+ struct ev_signal signal_watcher;
+ ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
+ ev_signal_start (loop, &sigint_cb);
+
+
=head2 C<ev_idle> - when you've got nothing better to do
Idle watchers trigger events when there are no other events are pending
=back
+Example: dynamically allocate an C<ev_idle>, start it, and in the
+callback, free it. Alos, use no error checking, as usual.
+
+ static void
+ idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
+ {
+ free (w);
+ // now do something you wanted to do when the program has
+ // no longer asnything immediate to do.
+ }
+
+ struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
+ ev_idle_init (idle_watcher, idle_cb);
+ ev_idle_start (loop, idle_cb);
+
+
=head2 C<ev_prepare> and C<ev_check> - customise your event loop
Prepare and check watchers are usually (but not always) used in tandem:
prepare watchers get invoked before the process blocks and check watchers
afterwards.
-Their main purpose is to integrate other event mechanisms into libev. This
-could be used, for example, to track variable changes, implement your own
-watchers, integrate net-snmp or a coroutine library and lots more.
+Their main purpose is to integrate other event mechanisms into libev and
+their use is somewhat advanced. This could be used, for example, to track
+variable changes, implement your own watchers, integrate net-snmp or a
+coroutine library and lots more.
This is done by examining in each prepare call which file descriptors need
to be watched by the other library, registering C<ev_io> watchers for
=back
+Example: *TODO*.
+
+
+=head2 C<ev_embed> - when one backend isn't enough
+
+This is a rather advanced watcher type that lets you embed one event loop
+into another.
+
+There are primarily two reasons you would want that: work around bugs and
+prioritise I/O.
+
+As an example for a bug workaround, the kqueue backend might only support
+sockets on some platform, so it is unusable as generic backend, but you
+still want to make use of it because you have many sockets and it scales
+so nicely. In this case, you would create a kqueue-based loop and embed it
+into your default loop (which might use e.g. poll). Overall operation will
+be a bit slower because first libev has to poll and then call kevent, but
+at least you can use both at what they are best.
+
+As for prioritising I/O: rarely you have the case where some fds have
+to be watched and handled very quickly (with low latency), and even
+priorities and idle watchers might have too much overhead. In this case
+you would put all the high priority stuff in one loop and all the rest in
+a second one, and embed the second one in the first.
+
+As long as the watcher is started it will automatically handle events. The
+callback will be invoked whenever some events have been handled. You can
+set the callback to C<0> to avoid having to specify one if you are not
+interested in that.
+
+Also, there have not currently been made special provisions for forking:
+when you fork, you not only have to call C<ev_loop_fork> on both loops,
+but you will also have to stop and restart any C<ev_embed> watchers
+yourself.
+
+Unfortunately, not all backends are embeddable, only the ones returned by
+C<ev_embeddable_backends> are, which, unfortunately, does not include any
+portable one.
+
+So when you want to use this feature you will always have to be prepared
+that you cannot get an embeddable loop. The recommended way to get around
+this is to have a separate variables for your embeddable loop, try to
+create it, and if that fails, use the normal loop for everything:
+
+ struct ev_loop *loop_hi = ev_default_init (0);
+ struct ev_loop *loop_lo = 0;
+ struct ev_embed embed;
+
+ // see if there is a chance of getting one that works
+ // (remember that a flags value of 0 means autodetection)
+ loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
+ ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
+ : 0;
+
+ // if we got one, then embed it, otherwise default to loop_hi
+ if (loop_lo)
+ {
+ ev_embed_init (&embed, 0, loop_lo);
+ ev_embed_start (loop_hi, &embed);
+ }
+ else
+ loop_lo = loop_hi;
+
+=over 4
+
+=item ev_embed_init (ev_embed *, callback, struct ev_loop *loop)
+
+=item ev_embed_set (ev_embed *, callback, struct ev_loop *loop)
+
+Configures the watcher to embed the given loop, which must be embeddable.
+
+=back
+
+
=head1 OTHER FUNCTIONS
There are some other functions of possible interest. Described. Here. Now.
=back
+
=head1 LIBEVENT EMULATION
Libev offers a compatibility emulation layer for libevent. It cannot
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