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);
+
+

@@ -323,11 +538,7 @@ 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.
-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.
@@ -387,6 +598,84 @@ 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
 
@@ -427,6 +716,10 @@ 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
 
@@ -435,17 +728,18 @@ 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)
@@ -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

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.

TIME AND OTHER GLOBAL FUNCTIONS

TIME REPRESENTATION

GLOBAL FUNCTIONS

SUMMARY OF GENERIC WATCHER FUNCTIONS

ASSOCIATING CUSTOM DATA WITH A WATCHER

`ev_io` - is this file descriptor readable or writable

`ev_timer` - relative and optionally recurring timeouts

`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

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 this file descriptor readable or writable

ev_timer - relative and optionally recurring timeouts

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

OTHER FUNCTIONS

LIBEVENT EMULATION

C++ SUPPORT

AUTHOR

`ev_io` - is this file descriptor readable or writable

`ev_timer` - relative and optionally recurring timeouts

`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