ev_io - is this file descriptor readable or writableev_timer - relative and optionally recurring timeoutsev_periodic - to cron or not to cronev_signal - signal me when a signal gets signalledev_child - wait for pid status changesev_idle - when you've got nothing better to doev_prepare and ev_check - customise your event loopev_io - is this file descriptor readable or writable?ev_timer - relative and optionally repeating timeoutsev_periodic - to cron or not to cron?ev_signal - signal me when a signal gets signalled!ev_child - watch out for process status changesev_idle - when you've got nothing better to do...ev_prepare and ev_check - customise your event loop!ev_embed - when one backend isn't enough...ev_tstamp, which is what you should use too. It usually aliases
-to the double type in C.
+to the double type in C, and when you need to do any calculations on
+it, you should treat it as such.
+
+
+
+
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));
+
+
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));
+
+
ev_supported_backends, 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
-EVFLAG_AUTO will probe for.
+libev will probe for if you specify no backends explicitly.
+ 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
+ev_embeddable_backends () & ev_supported_backends (), likewise for
+recommended ones.
See the description of ev_embed watchers for more info.
You could override this function in high-availability programs to, say, 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);
+
+
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);
+
+
ev_backend () afterwards).If you don't know what event loop to use, use the one returned from this
function.
The flags argument can be used to specify special behaviour or specific
-backends to use, and is usually specified as 0 (or EVFLAG_AUTO).
It supports the following flags:
+backends to use, and is usually specified as0 (or EVFLAG_AUTO).
+ The following flags are supported:
EVFLAG_AUTOKqueue 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 "autodetected" unless -you explicitly specify the flags (i.e. you don't use EVFLAG_AUTO).
+completely useless). For this reason its not being "autodetected" +unless you explicitly specify it explicitly in the flags (i.e. using +EVBACKEND_KQUEUE).
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
@@ -271,6 +345,22 @@ with EVFLAG_AUTO). Since this is a mask, you can do stuff such as
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 :)
The most typical usage is like this:
+ if (!ev_default_loop (0))
+ fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
+
+
+ Restrict libev to the select and poll backends, and do not allow +environment settings to be taken into account:
+ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); + ++
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 OS supports your types of fds):
+ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); + +
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");
+
+
Destroys the default loop again (frees all memory and kernel state -etc.). This stops all registered event watchers (by not touching them in -any way whatsoever, although you cannot rely on this :).
+etc.). None of the active event watchers will be stopped in the normal +sense, so e.g.ev_is_active might still return true. It is your
+responsibility to either stop all watchers cleanly yoursef before
+calling this function, or cope with the fact afterwards (which is usually
+the easiest thing, youc na just ignore the watchers and/or free () them
+for example).
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).Finally, this is it, the event handler. This function usually is called after you initialised all your watchers and you want to start handling events.
-If the flags argument is specified as 0, it will not return until either
-no event watchers are active anymore or ev_unloop was called.
If the flags argument is specified as 0, it will not return until
+either no event watchers are active anymore or ev_unloop was called.
Please note that an explicit 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 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.
A flags value of EVLOOP_ONESHOT 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.
This flags value could be used to implement alternative looping
-constructs, but the prepare and check watchers provide a better and
-more generic mechanism.
Here are the gory details of what ev_loop does:
-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 ofev_prepare/ev_checkwatchers is +usually a better approach for this kind of thing. +Here are the gory details of what
+ev_loopdoes:* 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 *. + ++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!
ev_loop from exiting
no event watchers registered by it are active. It is also an excellent
way to do this for generic recurring timers or from within third-party
libraries. Just remember to unref after start and ref before stop.
+ Example: create a signal watcher, but keep it from keeping 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); + +
ev_<type>_start (loop, watch
corresponding stop function (ev_<type>_stop (loop, watcher *).
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 macro.
-You can check whether an event is active by calling the ev_is_active
-(watcher *) macro. To see whether an event is outstanding (but the
-callback for it has not been called yet) you can use the ev_is_pending
-(watcher *) macro.
+reinitialise it or call its set macro.
Each and every callback receives the event loop pointer as first, the
registered watcher structure as second, and a bitset of received events as
third argument.
@@ -489,6 +618,84 @@ programs, though, so beware.
+In the following description, TYPE stands for the watcher type,
+e.g. timer for ev_timer watchers and io for ev_io watchers.
ev_init (ev_TYPE *watcher, callback)This macro initialises the generic portion of a watcher. The contents
+of the watcher object can be arbitrary (so malloc will do). Only
+the generic parts of the watcher are initialised, you need to call
+the type-specific ev_TYPE_set macro afterwards to initialise the
+type-specific parts. For each type there is also a ev_TYPE_init macro
+which rolls both calls into one.
You can reinitialise a watcher at any time as long as it has been stopped +(or never started) and there are no pending events outstanding.
+The callback is always of type void (*)(ev_loop *loop, ev_TYPE *watcher,
+int revents).
ev_TYPE_set (ev_TYPE *, [args])This macro initialises the type-specific parts of a watcher. You need to
+call ev_init at least once before you call this macro, but you can
+call ev_TYPE_set any number of times. You must not, however, call this
+macro on a watcher that is active (it can be pending, however, which is a
+difference to the ev_init macro).
Although some watcher types do not have type-specific arguments
+(e.g. ev_prepare) you still need to call its set macro.
ev_TYPE_init (ev_TYPE *watcher, callback, [args])This convinience macro rolls both ev_init and ev_TYPE_set macro
+calls into a single call. This is the most convinient method to initialise
+a watcher. The same limitations apply, of course.
ev_TYPE_start (loop *, ev_TYPE *watcher)Starts (activates) the given watcher. Only active watchers will receive +events. If the watcher is already active nothing will happen.
+ev_TYPE_stop (loop *, ev_TYPE *watcher)Stops the given watcher again (if active) and clears the pending
+status. It is possible that stopped watchers are pending (for example,
+non-repeating timers are being stopped when they become pending), but
+ev_TYPE_stop ensures that the watcher is neither active nor pending. If
+you want to free or reuse the memory used by the watcher it is therefore a
+good idea to always call its ev_TYPE_stop function.
Returns a true value iff the watcher is active (i.e. it has been started +and not yet been stopped). As long as a watcher is active you must not modify +it.
+Returns a true value iff the watcher is pending, (i.e. it has outstanding
+events but its callback has not yet been invoked). As long as a watcher
+is pending (but not active) you must not call an init function on it (but
+ev_TYPE_set is safe) and you must make sure the watcher is available to
+libev (e.g. you cnanot free () it).
Returns the callback currently set on the watcher.
+Change the callback. You can change the callback at virtually any time +(modulo threads).
+This section describes each watcher in detail, but will not repeat information given in the last section.
+ + + +ev_io - is this file descriptor readable or writableev_io - is this file descriptor readable or writable?I/O watchers check whether a file descriptor is readable or writable -in each iteration of the event loop (This behaviour is called -level-triggering because you keep receiving events as long as the -condition persists. Remember you can stop the watcher if you don't want to -act on the event and neither want to receive future events).
+in each iteration of the event loop, or, more precisely, when reading +would not block the process and writing would at least be able to write +some data. This behaviour is called level-triggering because you keep +receiving events as long as the condition persists. Remember you can stop +the watcher if you don't want to act on the event and neither want to +receive future events.In general you can register as many read and/or write event watchers per fd as you want (as long as you don't confuse yourself). Setting all file descriptors to non-blocking mode is also usually a good idea (but not @@ -544,33 +757,57 @@ required if you know what you are doing).
You have to be careful with dup'ed file descriptors, though. Some backends (the linux epoll backend is a notable example) cannot handle dup'ed file descriptors correctly if you register interest in two or more fds pointing -to the same underlying file/socket etc. description (that is, they share +to the same underlying file/socket/etc. description (that is, they share the same underlying "file open").
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 EVBACKEND_SELECT and
EVBACKEND_POLL).
Another thing you have to watch out for is that it is quite easy to
+receive "spurious" readyness notifications, that is your callback might
+be called with EV_READ but a subsequent read(2) will actually block
+because there is no data. Not only are some backends known to create a
+lot of those (for example solaris ports), it is very easy to get into
+this situation even with a relatively standard program structure. Thus
+it is best to always use non-blocking I/O: An extra read(2) returning
+EAGAIN is far preferable to a program hanging until some data arrives.
If you cannot run the fd in non-blocking mode (for example you should not +play around with an Xlib connection), then you have to seperately re-test +wether a file descriptor is really ready with a known-to-be good interface +such as poll (fortunately in our Xlib example, Xlib already does this on +its own, so its quite safe to use).
Configures an ev_io watcher. The fd is the file descriptor to rceeive
-events for and events is either EV_READ, EV_WRITE or EV_READ |
-EV_WRITE to receive the given events.
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
-EVBACKEND_SELECT or EVBACKEND_POLL, 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.
Configures an ev_io watcher. The fd is the file descriptor to
+rceeive events for and events is either EV_READ, EV_WRITE or
+EV_READ | EV_WRITE to receive the given events.
Example: call 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);
+
+
+
+
+
ev_timer - relative and optionally recurring timeoutsev_timer - relative and optionally repeating timeoutsTimer watchers are simple relative timers that generate an event after a given time, and optionally repeating in regular intervals after that.
@@ -621,17 +858,50 @@ state where you do not expect data to travel on the socket, you can stop the timer, and again will automatically restart it if need be. +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);
+
+
+
+
+
ev_periodic - to cron or not to cronev_periodic - to cron or not to cron?Periodic watchers are also timers of a kind, but they are very versatile (and unfortunately a bit complex).
Unlike ev_timer's, they are not based on real time (or relative time)
but on wallclock time (absolute time). You can tell a periodic watcher
to trigger "at" some specific point in time. For example, if you tell a
-periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
-+ 10.>) and then reset your system clock to the last year, then it will
+periodic watcher to trigger in 10 seconds (by specifiying e.g. ev_now ()
++ 10.) and then reset your system clock to the last year, then it will
take a year to trigger the event (unlike an ev_timer, which would trigger
roughly 10 seconds later and of course not if you reset your system time
again).
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); + + + + +
ev_signal - signal me when a signal gets signalledev_signal - signal me when a signal gets signalled!Signal watchers will trigger an event when the process receives a specific
signal one or more times. Even though signals are very asynchronous, libev
@@ -737,9 +1043,13 @@ of the SIGxxx constants).
ev_child - wait for pid status changesev_child - watch out for process status changesChild watchers trigger when your process receives a SIGCHLD in response to some child status changes (most typically when a child of yours dies).
sys/wait.h and see your system
process causing the status change.
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);
+
+
+
+
+
ev_idle - when you've got nothing better to doev_idle - when you've got nothing better to do...Idle watchers trigger events when there are no other events are pending
(prepare, check and other idle watchers do not count). That is, as long
@@ -779,16 +1104,45 @@ kind. There is a ev_idle_set macro, but using it is utterly pointle
believe me.
Example: dynamically allocate an 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);
+
+
+
+
+
ev_prepare and ev_check - customise your event loopev_prepare and 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.
+You must not call ev_loop or similar functions that enter
+the current event loop from either ev_prepare or ev_check
+watchers. Other loops than the current one are fine, however. The
+rationale behind this is that you do not need to check for recursion in
+those watchers, i.e. the sequence will always be ev_prepare, blocking,
+ev_check so if you have one watcher of each kind they will always be
+called in pairs bracketing the blocking call.
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. They are also occasionally useful if
+you cache some data and want to flush it before blocking (for example,
+in X programs you might want to do an XFlush () in an ev_prepare
+watcher).
This is done by examining in each prepare call which file descriptors need
to be watched by the other library, registering ev_io watchers for
them and starting an ev_timer watcher for any timeouts (many libraries
@@ -814,6 +1168,149 @@ parameters of any kind. There are ev_prepare_set and ev_check
macros, but using them is utterly, utterly and completely pointless.
Example: To include a library such as adns, you would add IO watchers +and a timeout watcher in a prepare handler, as required by libadns, and +in a check watcher, destroy them and call into libadns. What follows is +pseudo-code only of course:
+ static ev_io iow [nfd];
+ static ev_timer tw;
+
+ static void
+ io_cb (ev_loop *loop, ev_io *w, int revents)
+ {
+ // set the relevant poll flags
+ // could also call adns_processreadable etc. here
+ struct pollfd *fd = (struct pollfd *)w->data;
+ if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
+ if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
+ }
+
+ // create io watchers for each fd and a timer before blocking
+ static void
+ adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
+ {
+ int timeout = 3600000;truct pollfd fds [nfd];
+ // actual code will need to loop here and realloc etc.
+ adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
+
+ /* the callback is illegal, but won't be called as we stop during check */
+ ev_timer_init (&tw, 0, timeout * 1e-3);
+ ev_timer_start (loop, &tw);
+
+ // create on ev_io per pollfd
+ for (int i = 0; i < nfd; ++i)
+ {
+ ev_io_init (iow + i, io_cb, fds [i].fd,
+ ((fds [i].events & POLLIN ? EV_READ : 0)
+ | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
+
+ fds [i].revents = 0;
+ iow [i].data = fds + i;
+ ev_io_start (loop, iow + i);
+ }
+ }
+
+ // stop all watchers after blocking
+ static void
+ adns_check_cb (ev_loop *loop, ev_check *w, int revents)
+ {
+ ev_timer_stop (loop, &tw);
+
+ for (int i = 0; i < nfd; ++i)
+ ev_io_stop (loop, iow + i);
+
+ adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
+ }
+
+
+
+
+
+
+ev_embed - when one backend isn't enough...This is a rather advanced watcher type that lets you embed one event loop
+into another (currently only ev_io events are supported in the embedded
+loop, other types of watchers might be handled in a delayed or incorrect
+fashion and must not be used).
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 active, the callback will be invoked every time
+there might be events pending in the embedded loop. The callback must then
+call ev_embed_sweep (mainloop, watcher) to make a single sweep and invoke
+their callbacks (you could also start an idle watcher to give the embedded
+loop strictly lower priority for example). You can also set the callback
+to 0, in which case the embed watcher will automatically execute the
+embedded loop sweep.
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 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 ev_loop_fork on both loops,
+but you will also have to stop and restart any ev_embed watchers
+yourself.
Unfortunately, not all backends are embeddable, only the ones returned by
+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;
+
+
+Configures the watcher to embed the given loop, which must be
+embeddable. If the callback is 0, then ev_embed_sweep will be
+invoked automatically, otherwise it is the responsibility of the callback
+to invoke it (it will continue to be called until the sweep has been done,
+if you do not want thta, you need to temporarily stop the embed watcher).
Make a single, non-blocking sweep over the embedded loop. This works
+similarly to ev_loop (embedded_loop, EVLOOP_NONBLOCK), but in the most
+apropriate way for embedded loops.
ev_once:
- Feeds the given event set into the event loop, as if the specified event had happened for the specified watcher (which must be a pointer to an initialised but not necessarily started event watcher).
Feed an event on the given fd, as if a file descriptor backend detected the given events it.
Feed an event as if the given signal occured (loop must be the default loop!).
+Feed an event as if the given signal occured (loop must be the default
+loop!).
TBD.
+Libev comes with some simplistic wrapper classes for C++ that mainly allow +you to use some convinience methods to start/stop watchers and also change +the callback model to a model using method callbacks on objects.
+To use it,
+#include <ev++.h> + ++
(it is not installed by default). This automatically includes ev.h
+and puts all of its definitions (many of them macros) into the global
+namespace. All C++ specific things are put into the ev namespace.
It should support all the same embedding options as ev.h, most notably
+EV_MULTIPLICITY.
Here is a list of things available in the ev namespace:
ev::READ, ev::WRITE etc.These are just enum values with the same values as the EV_READ etc.
+macros from ev.h.
ev::tstamp, ev::nowAliases to the same types/functions as with the ev_ prefix.
ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc.For each ev_TYPE watcher in ev.h there is a corresponding class of
+the same name in the ev namespace, with the exception of ev_signal
+which is called ev::sig to avoid clashes with the signal macro
+defines by many implementations.
All of those classes have these methods:
++
The constructor takes a pointer to an object and a method pointer to
+the event handler callback to call in this class. The constructor calls
+ev_init for you, which means you have to call the set method
+before starting it. If you do not specify a loop then the constructor
+automatically associates the default loop with this watcher.
The destructor automatically stops the watcher if it is active.
+Associates a different struct ev_loop with this watcher. You can only
+do this when the watcher is inactive (and not pending either).
Basically the same as ev_TYPE_set, with the same args. Must be
+called at least once. Unlike the C counterpart, an active watcher gets
+automatically stopped and restarted.
Starts the watcher. Note that there is no loop argument as the
+constructor already takes the loop.
Stops the watcher if it is active. Again, no loop argument.
ev::timer, ev::periodic onlyFor ev::timer and ev::periodic, this invokes the corresponding
+ev_TYPE_again function.
ev::embed onlyInvokes ev_embed_sweep.
Example: Define a class with an IO and idle watcher, start one of them in +the constructor.
+ class myclass
+ {
+ ev_io io; void io_cb (ev::io &w, int revents);
+ ev_idle idle void idle_cb (ev::idle &w, int revents);
+
+ myclass ();
+ }
+
+ myclass::myclass (int fd)
+ : io (this, &myclass::io_cb),
+ idle (this, &myclass::idle_cb)
+ {
+ io.start (fd, ev::READ);
+ }
+
+
+
+Libev can (and often is) directly embedded into host +applications. Examples of applications that embed it include the Deliantra +Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe) +and rxvt-unicode.
+The goal is to enable you to just copy the neecssary files into your +source directory without having to change even a single line in them, so +you can easily upgrade by simply copying (or having a checked-out copy of +libev somewhere in your source tree).
+ +Depending on what features you need you need to include one or more sets of files +in your app.
+ +To include only the libev core (all the ev_* functions), with manual
+configuration (no autoconf):
#define EV_STANDALONE 1 + #include "ev.c" + ++
This will automatically include ev.h, too, and should be done in a +single C source file only to provide the function implementations. To use +it, do the same for ev.h in all files wishing to use this API (best +done by writing a wrapper around ev.h that you can include instead and +where you can put other configuration options):
+#define EV_STANDALONE 1 + #include "ev.h" + ++
Both header files and implementation files can be compiled with a C++ +compiler (at least, thats a stated goal, and breakage will be treated +as a bug).
+You need the following files in your source tree, or in a directory +in your include path (e.g. in libev/ when using -Ilibev):
+ev.h + ev.c + ev_vars.h + ev_wrap.h + + ev_win32.c required on win32 platforms only + + ev_select.c only when select backend is enabled (which is by default) + ev_poll.c only when poll backend is enabled (disabled by default) + ev_epoll.c only when the epoll backend is enabled (disabled by default) + ev_kqueue.c only when the kqueue backend is enabled (disabled by default) + ev_port.c only when the solaris port backend is enabled (disabled by default) + ++
ev.c includes the backend files directly when enabled, so you only need +to compile this single file.
+ +To include the libevent compatibility API, also include:
+#include "event.c" + ++
in the file including ev.c, and:
+#include "event.h" + ++
in the files that want to use the libevent API. This also includes ev.h.
+You need the following additional files for this:
+event.h + event.c + ++ +
Instead of using EV_STANDALONE=1 and providing your config in
+whatever way you want, you can also m4_include([libev.m4]) in your
+configure.ac and leave EV_STANDALONE undefined. ev.c will then
+include config.h and configure itself accordingly.
For this of course you need the m4 file:
+libev.m4 + ++ +
Libev can be configured via a variety of preprocessor symbols you have to define +before including any of its files. The default is not to build for multiplicity +and only include the select backend.
+Must always be 1 if you do not use autoconf configuration, which
+keeps libev from including config.h, and it also defines dummy
+implementations for some libevent functions (such as logging, which is not
+supported). It will also not define any of the structs usually found in
+event.h that are not directly supported by the libev core alone.
If defined to be 1, libev will try to detect the availability of the
+monotonic clock option at both compiletime and runtime. Otherwise no use
+of the monotonic clock option will be attempted. If you enable this, you
+usually have to link against librt or something similar. Enabling it when
+the functionality isn't available is safe, though, althoguh you have
+to make sure you link against any libraries where the clock_gettime
+function is hiding in (often -lrt).
If defined to be 1, libev will try to detect the availability of the
+realtime clock option at compiletime (and assume its availability at
+runtime if successful). Otherwise no use of the realtime clock option will
+be attempted. This effectively replaces gettimeofday by clock_get
+(CLOCK_REALTIME, ...) and will not normally affect correctness. See tzhe note about libraries
+in the description of EV_USE_MONOTONIC, though.
If undefined or defined to be 1, libev will compile in support for the
+select(2) backend. No attempt at autodetection will be done: if no
+other method takes over, select will be it. Otherwise the select backend
+will not be compiled in.
If defined to 1, then the select backend will use the system fd_set
+structure. This is useful if libev doesn't compile due to a missing
+NFDBITS or fd_mask definition or it misguesses the bitset layout on
+exotic systems. This usually limits the range of file descriptors to some
+low limit such as 1024 or might have other limitations (winsocket only
+allows 64 sockets). The FD_SETSIZE macro, set before compilation, might
+influence the size of the fd_set used.
When defined to 1, the select backend will assume that
+select/socket/connect etc. don't understand file descriptors but
+wants osf handles on win32 (this is the case when the select to
+be used is the winsock select). This means that it will call
+_get_osfhandle on the fd to convert it to an OS handle. Otherwise,
+it is assumed that all these functions actually work on fds, even
+on win32. Should not be defined on non-win32 platforms.
If defined to be 1, libev will compile in support for the poll(2)
+backend. Otherwise it will be enabled on non-win32 platforms. It
+takes precedence over select.
If defined to be 1, libev will compile in support for the Linux
+epoll(7) backend. Its availability will be detected at runtime,
+otherwise another method will be used as fallback. This is the
+preferred backend for GNU/Linux systems.
If defined to be 1, libev will compile in support for the BSD style
+kqueue(2) backend. Its actual availability will be detected at runtime,
+otherwise another method will be used as fallback. This is the preferred
+backend for BSD and BSD-like systems, although on most BSDs kqueue only
+supports some types of fds correctly (the only platform we found that
+supports ptys for example was NetBSD), so kqueue might be compiled in, but
+not be used unless explicitly requested. The best way to use it is to find
+out whether kqueue supports your type of fd properly and use an embedded
+kqueue loop.
If defined to be 1, libev will compile in support for the Solaris
+10 port style backend. Its availability will be detected at runtime,
+otherwise another method will be used as fallback. This is the preferred
+backend for Solaris 10 systems.
reserved for future expansion, works like the USE symbols above.
+The name of the ev.h header file used to include it. The default if
+undefined is <ev.h> in event.h and "ev.h" in ev.c. This
+can be used to virtually rename the ev.h header file in case of conflicts.
If EV_STANDALONE isn't 1, this variable can be used to override
+ev.c's idea of where to find the config.h file, similarly to
+EV_H, above.
Similarly to EV_H, this macro can be used to override event.c's idea
+of how the event.h header can be found.
If defined to be 0, then ev.h will not define any function
+prototypes, but still define all the structs and other symbols. This is
+occasionally useful if you want to provide your own wrapper functions
+around libev functions.
If undefined or defined to 1, then all event-loop-specific functions
+will have the struct ev_loop * as first argument, and you can create
+additional independent event loops. Otherwise there will be no support
+for multiple event loops and there is no first event loop pointer
+argument. Instead, all functions act on the single default loop.
If undefined or defined to be 1, then periodic timers are supported,
+otherwise not. This saves a few kb of code.
By default, all watchers have a void *data member. By redefining
+this macro to a something else you can include more and other types of
+members. You have to define it each time you include one of the files,
+though, and it must be identical each time.
For example, the perl EV module uses something like this:
+#define EV_COMMON \ + SV *self; /* contains this struct */ \ + SV *cb_sv, *fh /* note no trailing ";" */ + ++
Can be used to change the callback member declaration in each watcher,
+and the way callbacks are invoked and set. Must expand to a struct member
+definition and a statement, respectively. See the ev.v header file for
+their default definitions. One possible use for overriding these is to
+avoid the struct ev_loop * as first argument in all cases, or to use
+method calls instead of plain function calls in C++.
For a real-world example of a program the includes libev +verbatim, you can have a look at the EV perl module +(http://software.schmorp.de/pkg/EV.html). It has the libev files in +the libev/ subdirectory and includes them in the EV/EVAPI.h (public +interface) and EV.xs (implementation) files. Only the EV.xs file +will be compiled. It is pretty complex because it provides its own header +file.
+The usage in rxvt-unicode is simpler. It has a ev_cpp.h header file +that everybody includes and which overrides some autoconf choices:
+#define EV_USE_POLL 0 + #define EV_MULTIPLICITY 0 + #define EV_PERIODICS 0 + #define EV_CONFIG_H <config.h> + + #include "ev++.h" + ++
And a ev_cpp.C implementation file that contains libev proper and is compiled:
+#include "ev_cpp.h" + #include "ev.c" + + + + ++ +
In this section the complexities of (many of) the algorithms used inside
+libev will be explained. For complexity discussions about backends see the
+documentation for ev_default_init.
+
Marc Lehmann <libev@schmorp.de>.
+Marc Lehmann <libev@schmorp.de>.