TIME REPRESENTATION

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Libev represents time as a single floating point number, representing the (fractional) number of seconds since the (POSIX) epoch (somewhere near the beginning of 1970, details are complicated, don't ask). This type is called 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.

+ + + + + +

GLOBAL FUNCTIONS

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These functions can be called anytime, even before initialising the +library in any way.

ev_tstamp ev_time ()

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.

int ev_version_major ()

int ev_version_minor ()

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));
+
+

unsigned int ev_supported_backends ()

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));
+
+

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 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.

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 +ev_embeddable_backends () & ev_supported_backends (), likewise for +recommended ones.

See the description of ev_embed watchers for more info.

ev_set_allocator (void *(*cb)(void *ptr, long size))

@@ -124,6 +180,26 @@ destructive action. The default is your system realloc function.

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);
+
+

ev_set_syserr_cb (void (*cb)(const char *msg));

@@ -134,6 +210,18 @@ callback is set, then libev will expect it to remedy the sitution, no matter what, when it returns. That is, libev will generally retry the 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);
+
+

@@ -144,7 +232,7 @@ requested operation, or, if the condition doesn't go away, do bad stuff types of such loops, the default loop, which supports signals and child events, and dynamically created loops which do not.

If you use threads, a common model is to run the default event loop -in your main thread (or in a separate thrad) and for each thread you +in your main thread (or in a separate thread) and for each thread you create, you also create another event loop. Libev itself does no locking whatsoever, so if you mix calls to the same event loop in different threads, make sure you lock (this is usually a bad idea, though, even if @@ -155,12 +243,12 @@ done correctly, because it's hideous and inefficient).

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 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 as 0 (or EVFLAG_AUTO).

The following flags are supported:

EVFLAG_AUTO

EVMETHOD_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)

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.

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)

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_ALL

Try 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);
+
+

struct ev_loop *ev_loop_new (unsigned int flags)

@@ -197,6 +356,12 @@ specified, any backend will do.

always distinct from the default loop. Unlike the default loop, it cannot 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");
+
+

ev_default_destroy ()

@@ -215,15 +380,18 @@ earlier call to 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.

ev_loop_fork (loop)

@@ -231,42 +399,76 @@ quite nicely into a call to 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.

unsigned int ev_method (loop)

unsigned int ev_backend (loop)

Returns one of the EVMETHOD_* flags indicating the event backend in +

Returns one of the EVBACKEND_* flags indicating the event backend in use.

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).

ev_loop (loop, int flags)

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.

+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 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!
+
+

ev_unloop (loop, how)

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_ref (loop)

@@ -282,6 +484,19 @@ visible to the libev user and should not keep 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);
+
+

@@ -323,15 +538,11 @@ 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.
-You cna 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 cna 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.
-The rceeived events usually include a single bit per event type received
+
The received events usually include a single bit per event type received
 (you can receive multiple events at the same time). The possible bit masks
 are:
 
@@ -387,11 +598,89 @@ programs, though, so beware.
 	
 
 
+


+SUMMARY OF GENERIC WATCHER FUNCTIONS
+
+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 callbakc 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.
+	
+	bool ev_is_active (ev_TYPE *watcher)
+	
+		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.
+	
+	bool ev_is_pending (ev_TYPE *watcher)
+	
+		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).
+	
+	callback = ev_cb (ev_TYPE *watcher)
+	
+		Returns the callback currently set on the watcher.
+	
+	ev_cb_set (ev_TYPE *watcher, callback)
+	
+		Change the callback. You can change the callback at virtually any time
+(modulo threads).
+	
+
+
+
+
+
+
 
 ASSOCIATING CUSTOM DATA WITH A WATCHER
 
 Each watcher has, by default, a member void *data that you can change
-and read at any time, libev will completely ignore it. This cna be used
+and read at any time, libev will completely ignore it. This can be used
 to associate arbitrary data with your watcher. If you need more data and
 don't want to allocate memory and store a pointer to it in that data
 member, you can also "subclass" the watcher type and provide your own
@@ -427,25 +716,30 @@ have been omitted....
 This section describes each watcher in detail, but will not repeat
 information given in the last section.
 
+
+
+
+
 
-ev_io - is my file descriptor readable or writable
-


+ev_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 cna stop the watcher if you don't want to
+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)
@@ -453,8 +747,39 @@ 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
@@ -462,18 +787,21 @@ 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:

+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 +on 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.

ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
ev_timer_again (loop)

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 cron it

`ev_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).

@@ -521,16 +882,15 @@ roughly 10 seconds later and of course not if you reset your system time again).

They 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.

ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)

ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)

Lots of arguments, lets sort it out... There are basically three modes of operation, and we will explain them from simplest to complex:

- - - -

* absolute timer (interval = reschedule_cb = 0)

@@ -595,6 +959,42 @@ a different time than the last time it was called (e.g. in a crond like program when the crontabs have changed).

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 signalled

@@ -603,7 +1003,7 @@ program when the crontabs have changed).

signal one or more times. Even though signals are very asynchronous, libev will try it's best to deliver signals synchronously, i.e. as part of the normal event processing, like any other event.

You cna configure as many watchers as you like per signal. Only when the +

You can configure as many watchers as you like per signal. Only when the first watcher gets started will libev actually register a signal watcher with the kernel (thus it coexists with your own signal handlers as long as you don't register any with libev). Similarly, when the last signal @@ -618,6 +1018,10 @@ of the SIGxxx constants).

+ + + +

Prepare and check watchers usually (but not always) are used in -tandom. 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.

`ev_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 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 ev_io watchers for them -and starting an ev_timer watcher for any timeouts (many libraries provide -just this functionality). Then, in the check watcher you check for any -events that occured (by making your callbacks set soem flags for example) -and call back into the library.

As another example, the perl Coro module uses these hooks to integrate +to be watched by the other library, registering ev_io watchers for +them and starting an ev_timer watcher for any timeouts (many libraries +provide just this functionality). Then, in the check watcher you check for +any events that occured (by checking the pending status of all watchers +and stopping them) and call back into the library. The I/O and timer +callbacks will never actually be called (but must be valid nevertheless, +because you never know, you know?).

As another example, the Perl Coro module uses these hooks to integrate coroutines into libev programs, by yielding to other active coroutines during each prepare and only letting the process block if no coroutines -are ready to run.

+are ready to run (it's actually more complicated: it only runs coroutines +with priority higher than or equal to the event loop and one coroutine +of lower priority, but only once, using idle watchers to keep the event +loop from blocking if lower-priority coroutines are active, thus mapping +low-priority coroutines to idle/background tasks).

ev_prepare_init (ev_prepare *, callback)

ev_check_init (ev_check *, callback)

Initialises and configures the prepare or check watcher - they have no parameters of any kind. There are ev_prepare_set and ev_check_set -macros, but using them is utterly, utterly pointless.

+macros, but using them is utterly, utterly and completely pointless.

Example: *TODO*.

+ + + + + +

`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;
+
+

ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)
ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop): +
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).
+
ev_embed_sweep (loop, ev_embed *): +
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.
+

+ + + +

OTHER FUNCTIONS

Top

There are some other fucntions of possible interest. Described. Here. Now.

There are some other functions of possible interest. Described. Here. Now.

ev_once (loop, int fd, int events, ev_tstamp timeout, callback)

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 -ignored. Otherwise, an ev_io watcher for the given fd and events set -will be craeted and started.

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 +events set will be craeted and started.

If timeout is less than 0, then no timeout watcher will be -started. Otherwise an ev_timer watcher with after = timeout (and repeat -= 0) will be started.

The callback has the type void (*cb)(int revents, void *arg) and -gets passed an events set (normally a combination of EV_ERROR, EV_READ, -EV_WRITE or EV_TIMEOUT) and the arg value passed to ev_once:

+started. Otherwise an ev_timer watcher with after = timeout (and +repeat = 0) will be started. While 0 is a valid timeout, it is of +dubious value.

The callback has the type void (*cb)(int revents, void *arg) and gets +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)
   {
     if (revents & EV_TIMEOUT)
-      /* doh, nothing entered */
+      /* doh, nothing entered */;
     else if (revents & EV_READ)
-      /* stdin might have data for us, joy! */
+      /* stdin might have data for us, joy! */;
   }
 
-  ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0);
+  ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);

ev_feed_event (loop, watcher, int events)

ev_feed_event (ev_loop *, watcher *, int revents)

Feeds the given event set into the event loop, as if the specified event -has happened for the specified watcher (which must be a pointer to an -initialised but not necessarily active event watcher).

+had happened for the specified watcher (which must be a pointer to an +initialised but not necessarily started event watcher).

ev_feed_fd_event (loop, int fd, int revents)

ev_feed_fd_event (ev_loop *, int fd, int revents)

Feed an event on the given fd, as if a file descriptor backend detected it.

Feed an event on the given fd, as if a file descriptor backend detected +the given events it.

ev_feed_signal_event (loop, int signum)

ev_feed_signal_event (ev_loop *loop, int signum)

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!).

+ + + + +

LIBEVENT EMULATION

Top

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

Top

TBD.

AUTHOR

Top

TIME AND OTHER GLOBAL FUNCTIONS

TIME REPRESENTATION

GLOBAL FUNCTIONS

SUMMARY OF GENERIC WATCHER FUNCTIONS

ASSOCIATING CUSTOM DATA WITH A WATCHER

`ev_io` - is my file descriptor readable or writable

`ev_io` - is this file descriptor readable or writable

`ev_timer` - relative and optionally recurring timeouts

`ev_periodic` - to cron or not to cron it

`ev_periodic` - to cron or not to cron

`ev_signal` - signal me when a signal gets signalled

`ev_child` - wait for pid status changes

`ev_idle` - when you've got nothing better to do

prepare and check - your hooks into the event loop

`ev_prepare` and `ev_check` - customise your event loop

`ev_embed` - when one backend isn't enough

OTHER FUNCTIONS

LIBEVENT EMULATION

C++ SUPPORT

AUTHOR

TIME AND OTHER GLOBAL FUNCTIONS

TIME REPRESENTATION

GLOBAL FUNCTIONS

SUMMARY OF GENERIC WATCHER FUNCTIONS

ASSOCIATING CUSTOM DATA WITH A WATCHER

ev_io - is my file descriptor readable or writable

ev_io - is this file descriptor readable or writable

ev_timer - relative and optionally recurring timeouts

ev_periodic - to cron or not to cron it

ev_periodic - to cron or not to cron

ev_signal - signal me when a signal gets signalled

ev_child - wait for pid status changes

ev_idle - when you've got nothing better to do

prepare and check - your hooks into the event loop

ev_prepare and ev_check - customise your event loop

ev_embed - when one backend isn't enough

OTHER FUNCTIONS

LIBEVENT EMULATION

C++ SUPPORT

AUTHOR

`ev_io` - is my file descriptor readable or writable

`ev_io` - is this file descriptor readable or writable

`ev_timer` - relative and optionally recurring timeouts

`ev_periodic` - to cron or not to cron it

`ev_periodic` - to cron or not to cron

`ev_signal` - signal me when a signal gets signalled

`ev_child` - wait for pid status changes

`ev_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