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.
+
+
+
+
Returns the current time as libev would use it.
+Returns the current time as libev would use it. Please note that the
+ev_now function is usually faster and also often returns the timestamp
+you actually want to know.
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));
+
+
+
+ Return the set of all backends (i.e. their corresponding EV_BACKEND_*
+value) compiled into this binary of libev (independent of their
+availability on the system you are running on). See 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));
+
+
+ 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 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
+libev will probe for if you specify no backends explicitly.
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);
+
+
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, checkev_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_AUTOEVMETHOD_SELECT (portable select backend)EVMETHOD_POLL (poll backend, available everywhere except on windows)EVMETHOD_EPOLL (linux only)EVMETHOD_KQUEUE (some bsds only)EVMETHOD_DEVPOLL (solaris 8 only)EVMETHOD_PORT (solaris 10 only)EVBACKEND_SELECT (value 1, portable select backend)This is your standard select(2) backend. Not completely 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.
+EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)And this is your standard poll(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).
+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 +either O(1) or O(active_fds).
+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, dup()ed file descriptors might not work very +well if you register events for both fds.
+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.
+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 "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 +extra syscall as with epoll, it still adds up to four event changes per +incident, so its best to avoid that.
+EVBACKEND_DEVPOLL (value 16, Solaris 8)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.
+This is not implemented yet (and might never be).
+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)).
+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.
+EVBACKEND_ALLTry all backends (even potentially broken ones that wouldn't be tried
+with EVFLAG_AUTO). Since this is a mask, you can do stuff such as
+EVBACKEND_ALL & ~EVBACKEND_KQUEUE.
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 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");
+
+
ev_loop_new.
one. Despite the name, you can call it anytime, but it makes most sense
after forking, in either the parent or child process (or both, but that
again makes little sense).
- You must 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 must 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.
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
quite nicely into a call to pthread_atfork:
pthread_atfork (0, 0, ev_default_fork);+
At the moment, EVBACKEND_SELECT and EVBACKEND_POLL are safe to use
+without calling this function, so if you force one of those backends you
+do not need to care.
pthread_atfork:
ev_loop_new. Yes, you have to call this on every allocated event loop
after fork, and how you do this is entirely your own problem.
Returns one of the EVMETHOD_* flags indicating the event backend in
+
Returns one of the EVBACKEND_* flags indicating the event backend in
use.
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.
ev_prepare/ev_check watchers is
+usually a better approach for this kind of thing.
+ Here are the gory details of what ev_loop does:
* 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! + +
Can be used to make a call to ev_loop return early (but only after it
has processed all outstanding events). The how argument must be either
-EVUNLOOP_ONCE, which will make the innermost ev_loop call return, or
+EVUNLOOP_ONE, which will make the innermost ev_loop call return, or
EVUNLOOP_ALL, which will make all nested ev_loop calls return.
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); + +@@ -332,7 +527,7 @@ with a watcher-specific start function (
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 method.
+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
@@ -436,6 +631,10 @@ have been omitted....
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 writable
@@ -444,17 +643,18 @@ 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 general you can register as many read and/or write event watchers oer
+
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
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 file/socket etc. description.
+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 EVMETHOD_SELECT and
-EVMETHOD_POLL).
+(at the time of this writing, this includes only EVBACKEND_SELECT and
+EVBACKEND_POLL).
- ev_io_init (ev_io *, callback, int fd, int events)
- ev_io_set (ev_io *, int fd, int events)
@@ -462,8 +662,39 @@ EVMETHOD_POLL).
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.
+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 timeouts
@@ -471,18 +702,21 @@ EV_WRITE to receive the given events.
Timer watchers are simple relative timers that generate an event after a given time, and optionally repeating in regular intervals after that.
The timers are based on real time, that is, if you register an event that -times out after an hour and youreset your system clock to last years +times out after an hour and you reset your system clock to last years time, it will still time out after (roughly) and hour. "Roughly" because -detecting time jumps is hard, and soem inaccuracies are unavoidable (the +detecting time jumps is hard, and some inaccuracies are unavoidable (the monotonic clock option helps a lot here).
The relative timeouts are calculated relative to the ev_now ()
time. This is usually the right thing as this timestamp refers to the time
-of the event triggering whatever timeout you are modifying/starting. If
-you suspect event processing to be delayed and you *need* to base the timeout
-ion the current time, use something like this to adjust for this:
ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);+
The callback is guarenteed to be invoked only when its timeout has passed, +but if multiple timers become ready during the same loop iteration then +order of execution is undefined.
The timer itself will do a best-effort at avoiding drift, that is, if you configure a timer to trigger every 10 seconds, then it will trigger at exactly 10 second intervals. If, however, your program cannot keep up with -the timer (ecause it takes longer than those 10 seconds to do stuff) the +the timer (because it takes longer than those 10 seconds to do stuff) the timer will not fire more than once per event loop iteration.
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 cronThey can also be used to implement vastly more complex timers, such as triggering an event on eahc midnight, local time.
+As with timers, the callback is guarenteed to be invoked only when the
+time (at) has been passed, but if multiple periodic timers become ready
+during the same loop iteration then order of execution is undefined.
Lots of arguments, lets sort it out... There are basically three modes of operation, and we will explain them from simplest to complex:
- - - -
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 signalledsys/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_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_set and ev_check
macros, but using them is utterly, utterly and completely pointless.
+Example: *TODO*.
+
+
+
+
OTHER FUNCTIONS
@@ -719,7 +1059,7 @@ macros, but using them is utterly, utterly and completely pointless.
This function combines a simple timer and an I/O watcher, calls your
callback on whichever event happens first and automatically stop both
watchers. This is useful if you want to wait for a single event on an fd
-or timeout without havign to allocate/configure/start/stop/free one or
+or timeout without having to allocate/configure/start/stop/free one or
more watchers yourself.
If fd is less than 0, then no I/O watcher will be started and events
is being ignored. Otherwise, an ev_io watcher for the given fd and
@@ -729,7 +1069,7 @@ started. Otherwise an ev_timer watcher with after = timeout0 is a valid timeout, it is of
dubious value.
The callback has the type void (*cb)(int revents, void *arg) and gets
-passed an events set like normal event callbacks (with a combination of
+passed an revents set like normal event callbacks (a combination of
EV_ERROR, EV_READ, EV_WRITE or EV_TIMEOUT) and the arg
value passed to ev_once:
static void stdin_ready (int revents, void *arg)
@@ -761,10 +1101,29 @@ the given events it.
+
+
+
+
LIBEVENT EMULATION
-TBD.
+Libev offers a compatibility emulation layer for libevent. It cannot
+emulate the internals of libevent, so here are some usage hints:
+
+ - * Use it by including <event.h>, as usual.
+ - * The following members are fully supported: ev_base, ev_callback,
+ev_arg, ev_fd, ev_res, ev_events.
+ - * Avoid using ev_flags and the EVLIST_*-macros, while it is
+maintained by libev, it does not work exactly the same way as in libevent (consider
+it a private API).
+ - * Priorities are not currently supported. Initialising priorities
+will fail and all watchers will have the same priority, even though there
+is an ev_pri field.
+ - * Other members are not supported.
+ - * The libev emulation is not ABI compatible to libevent, you need
+to use the libev header file and library.
+
C++ SUPPORT