TIME REPRESENTATION

Top

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.

+ +

GLOBAL FUNCTIONS

Top

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 ()

default

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 @@ -177,19 +188,66 @@ override the flags completely if it is found in the environment. This is useful to try out specific backends to test their performance, or to work around bugs.

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)

EVMETHOD_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.

EVMETHOD_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).

EVMETHOD_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.

EVMETHOD_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 the flags (i.e. you don't use EVFLAG_AUTO).

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.

EVMETHOD_DEVPOLL (value 16, Solaris 8)

This is not implemented yet (and might never be).

EVMETHOD_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)).

EVMETHOD_ALL

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.

Try all backends (even potentially broken ones). Since this is a mask, you +can do stuff like EVMETHOD_ALL & ~EVMETHOD_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 :)

struct ev_loop *ev_loop_new (unsigned int flags)

@@ -261,12 +319,30 @@ one iteration of the loop.

This flags value could be used to implement alternative looping constructs, but the prepare and check watchers provide a better and more generic mechanism.

Here are the gory details of what ev_loop does:

   1. If there are no active watchers (reference count is zero), return.
+   2. Queue and immediately call all prepare watchers.
+   3. If we have been forked, recreate the kernel state.
+   4. Update the kernel state with all outstanding changes.
+   5. Update the "event loop time".
+   6. Calculate for how long to block.
+   7. Block the process, waiting for events.
+   8. Update the "event loop time" and do time jump handling.
+   9. Queue all outstanding timers.
+  10. Queue all outstanding periodics.
+  11. If no events are pending now, queue all idle watchers.
+  12. Queue all check watchers.
+  13. Call all queued watchers in reverse order (i.e. check watchers first).
+  14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
+      was used, return, otherwise continue with step #1.
+
+

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)

@@ -324,14 +400,14 @@ 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 +

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 cna use the ev_is_pending +callback for it has not been called yet) you can use the ev_is_pending (watcher *) 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:
 
@@ -391,7 +467,7 @@ programs, though, so beware.
 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
@@ -428,21 +504,22 @@ have been omitted....
 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).
@@ -462,18 +539,21 @@ 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)
@@ -485,7 +565,7 @@ later, again, and again, until stopped manually.
 		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.
 	
 	ev_timer_again (loop)
@@ -507,7 +587,7 @@ the timer, and again will automatically restart it if need be.
 
 
 
-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 +601,15 @@ 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)
@@ -552,7 +631,7 @@ time:
 
 					This doesn't mean there will always be 3600 seconds in between triggers,
 but only that the the callback will be called when the system time shows a
-full hour (UTC), or more correct, when the system time is evenly divisible
+full hour (UTC), or more correctly, when the system time is evenly divisible
 by 3600.
 					Another way to think about it (for the mathematically inclined) is that
 ev_periodic will try to run the callback in this mode at the next possible
@@ -564,11 +643,12 @@ time where time = at (mod interval), regardless of any time jumps.<
 ignored. Instead, each time the periodic watcher gets scheduled, the
 reschedule callback will be called with the watcher as first, and the
 current time as second argument.
-					NOTE: This callback MUST NOT stop or destroy the periodic or any other
-periodic watcher, ever, or make any event loop modificstions. If you need
-to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards.
-					Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
-ev_tstamp now)>, e.g.:
+					NOTE: This callback MUST NOT stop or destroy any periodic watcher,
+ever, or make any event loop modifications. If you need to stop it,
+return now + 1e30 (or so, fudge fudge) and stop it afterwards (e.g. by
+starting a prepare watcher).
+					Its prototype is ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
+ev_tstamp now), e.g.:
    static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
    {
      return now + 60.;
@@ -579,10 +659,13 @@ ev_tstamp now)>, e.g.:
 (that is, the lowest time value larger than to the second argument). It
 will usually be called just before the callback will be triggered, but
 might be called at other times, too.
+					NOTE: This callback must always return a time that is later than the
+passed now value. Not even now itself will do, it must be larger.
 					This can be used to create very complex timers, such as a timer that
 triggers on each midnight, local time. To do this, you would calculate the
-next midnight after now and return the timestamp value for this. How you do this
-is, again, up to you (but it is not trivial).
+next midnight after now and return the timestamp value for this. How
+you do this is, again, up to you (but it is not trivial, which is the main
+reason I omitted it as an example).
 				
 			
 		
@@ -603,7 +686,7 @@ 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
@@ -630,19 +713,22 @@ some child status changes (most typically when a child of yours dies).
 		Configures the watcher to wait for status changes of process pid (or
 any process if pid is specified as 0). The callback can look
 at the rstatus member of the ev_child watcher structure to see
-the status word (use the macros from sys/wait.h). The rpid member
-contains the pid of the process causing the status change.
+the status word (use the macros from sys/wait.h and see your systems
+waitpid documentation). The rpid member contains the pid of the
+process causing the status change.


 ev_idle - when you've got nothing better to do
 
-Idle watchers trigger events when there are no other I/O or timer (or
-periodic) events pending. That is, as long as your process is busy
-handling sockets or timeouts it will not be called. But when your process
-is idle all idle watchers are being called again and again - until
-stopped, that is, or your process receives more events.
+Idle watchers trigger events when there are no other events are pending
+(prepare, check and other idle watchers do not count). That is, as long
+as your process is busy handling sockets or timeouts (or even signals,
+imagine) it will not be triggered. But when your process is idle all idle
+watchers are being called again and again, once per event loop iteration -
+until stopped, that is, or your process receives more events and becomes
+busy.
 The most noteworthy effect is that as long as any idle watchers are
 active, the process will not block when waiting for new events.
 Apart from keeping your process non-blocking (which is a useful
@@ -659,76 +745,85 @@ believe me.
 
 
 
-prepare and check - your hooks into the event loop
-
-Prepare and check watchers usually (but not always) are used in
-tandom. Prepare watchers get invoked before the process blocks and check
-watchers afterwards.
+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. 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.
 	
 
 
 
 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)
 	
 		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)
 	
-		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)
 	
@@ -736,6 +831,31 @@ initialised but not necessarily active event watcher).
 	
 
 
+
+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

`ev_io` - is this file descriptor readable or writable

`ev_periodic` - to cron or not to cron it

`ev_periodic` - to cron or not to cron

TIME AND OTHER GLOBAL FUNCTIONS

TIME REPRESENTATION

GLOBAL FUNCTIONS

ASSOCIATING CUSTOM DATA WITH A WATCHER

`ev_io` - is my file descriptor readable or writable

`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

OTHER FUNCTIONS

LIBEVENT EMULATION

C++ SUPPORT

AUTHOR