[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.20 by root, Mon Nov 12 09:06:09 2007 UTC vs.
Revision 1.35 by root, Fri Nov 23 19:35:09 2007 UTC

…		…
45		45
46	Libev represents time as a single floating point number, representing the	46	Libev represents time as a single floating point number, representing the
47	(fractional) number of seconds since the (POSIX) epoch (somewhere near	47	(fractional) number of seconds since the (POSIX) epoch (somewhere near
48	the beginning of 1970, details are complicated, don't ask). This type is	48	the beginning of 1970, details are complicated, don't ask). This type is
49	called C<ev_tstamp>, which is what you should use too. It usually aliases	49	called C<ev_tstamp>, which is what you should use too. It usually aliases
50	to the double type in C.	50	to the C<double> type in C, and when you need to do any calculations on
		51	it, you should treat it as such.
		52
51		53
52	=head1 GLOBAL FUNCTIONS	54	=head1 GLOBAL FUNCTIONS
53		55
54	These functions can be called anytime, even before initialising the	56	These functions can be called anytime, even before initialising the
55	library in any way.	57	library in any way.
56		58
57	=over 4	59	=over 4
58		60
59	=item ev_tstamp ev_time ()	61	=item ev_tstamp ev_time ()
60		62
61	Returns the current time as libev would use it.	63	Returns the current time as libev would use it. Please note that the
		64	C<ev_now> function is usually faster and also often returns the timestamp
		65	you actually want to know.
62		66
63	=item int ev_version_major ()	67	=item int ev_version_major ()
64		68
65	=item int ev_version_minor ()	69	=item int ev_version_minor ()
66		70
…		…
73	Usually, it's a good idea to terminate if the major versions mismatch,	77	Usually, it's a good idea to terminate if the major versions mismatch,
74	as this indicates an incompatible change. Minor versions are usually	78	as this indicates an incompatible change. Minor versions are usually
75	compatible to older versions, so a larger minor version alone is usually	79	compatible to older versions, so a larger minor version alone is usually
76	not a problem.	80	not a problem.
77		81
		82	Example: make sure we haven't accidentally been linked against the wrong
		83	version:
		84
		85	assert (("libev version mismatch",
		86	ev_version_major () == EV_VERSION_MAJOR
		87	&& ev_version_minor () >= EV_VERSION_MINOR));
		88
		89	=item unsigned int ev_supported_backends ()
		90
		91	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
		92	value) compiled into this binary of libev (independent of their
		93	availability on the system you are running on). See C<ev_default_loop> for
		94	a description of the set values.
		95
		96	Example: make sure we have the epoll method, because yeah this is cool and
		97	a must have and can we have a torrent of it please!!!11
		98
		99	assert (("sorry, no epoll, no sex",
		100	ev_supported_backends () & EVBACKEND_EPOLL));
		101
		102	=item unsigned int ev_recommended_backends ()
		103
		104	Return the set of all backends compiled into this binary of libev and also
		105	recommended for this platform. This set is often smaller than the one
		106	returned by C<ev_supported_backends>, as for example kqueue is broken on
		107	most BSDs and will not be autodetected unless you explicitly request it
		108	(assuming you know what you are doing). This is the set of backends that
		109	libev will probe for if you specify no backends explicitly.
		110
		111	=item unsigned int ev_embeddable_backends ()
		112
		113	Returns the set of backends that are embeddable in other event loops. This
		114	is the theoretical, all-platform, value. To find which backends
		115	might be supported on the current system, you would need to look at
		116	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
		117	recommended ones.
		118
		119	See the description of C<ev_embed> watchers for more info.
		120
78	=item ev_set_allocator (void (cb)(void *ptr, long size))	121	=item ev_set_allocator (void (cb)(void *ptr, long size))
79		122
80	Sets the allocation function to use (the prototype is similar to the	123	Sets the allocation function to use (the prototype is similar to the
81	realloc C function, the semantics are identical). It is used to allocate	124	realloc C function, the semantics are identical). It is used to allocate
82	and free memory (no surprises here). If it returns zero when memory	125	and free memory (no surprises here). If it returns zero when memory
…		…
84	destructive action. The default is your system realloc function.	127	destructive action. The default is your system realloc function.
85		128
86	You could override this function in high-availability programs to, say,	129	You could override this function in high-availability programs to, say,
87	free some memory if it cannot allocate memory, to use a special allocator,	130	free some memory if it cannot allocate memory, to use a special allocator,
88	or even to sleep a while and retry until some memory is available.	131	or even to sleep a while and retry until some memory is available.
		132
		133	Example: replace the libev allocator with one that waits a bit and then
		134	retries: better than mine).
		135
		136	static void *
		137	persistent_realloc (void *ptr, long size)
		138	{
		139	for (;;)
		140	{
		141	void *newptr = realloc (ptr, size);
		142
		143	if (newptr)
		144	return newptr;
		145
		146	sleep (60);
		147	}
		148	}
		149
		150	...
		151	ev_set_allocator (persistent_realloc);
89		152
90	=item ev_set_syserr_cb (void (cb)(const char msg));	153	=item ev_set_syserr_cb (void (cb)(const char msg));
91		154
92	Set the callback function to call on a retryable syscall error (such	155	Set the callback function to call on a retryable syscall error (such
93	as failed select, poll, epoll_wait). The message is a printable string	156	as failed select, poll, epoll_wait). The message is a printable string
…		…
95	callback is set, then libev will expect it to remedy the sitution, no	158	callback is set, then libev will expect it to remedy the sitution, no
96	matter what, when it returns. That is, libev will generally retry the	159	matter what, when it returns. That is, libev will generally retry the
97	requested operation, or, if the condition doesn't go away, do bad stuff	160	requested operation, or, if the condition doesn't go away, do bad stuff
98	(such as abort).	161	(such as abort).
99		162
		163	Example: do the same thing as libev does internally:
		164
		165	static void
		166	fatal_error (const char *msg)
		167	{
		168	perror (msg);
		169	abort ();
		170	}
		171
		172	...
		173	ev_set_syserr_cb (fatal_error);
		174
100	=back	175	=back
101		176
102	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	177	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
103		178
104	An event loop is described by a C<struct ev_loop *>. The library knows two	179	An event loop is described by a C<struct ev_loop *>. The library knows two
…		…
117	=item struct ev_loop *ev_default_loop (unsigned int flags)	192	=item struct ev_loop *ev_default_loop (unsigned int flags)
118		193
119	This will initialise the default event loop if it hasn't been initialised	194	This will initialise the default event loop if it hasn't been initialised
120	yet and return it. If the default loop could not be initialised, returns	195	yet and return it. If the default loop could not be initialised, returns
121	false. If it already was initialised it simply returns it (and ignores the	196	false. If it already was initialised it simply returns it (and ignores the
122	flags).	197	flags. If that is troubling you, check C<ev_backend ()> afterwards).
123		198
124	If you don't know what event loop to use, use the one returned from this	199	If you don't know what event loop to use, use the one returned from this
125	function.	200	function.
126		201
127	The flags argument can be used to specify special behaviour or specific	202	The flags argument can be used to specify special behaviour or specific
128	backends to use, and is usually specified as 0 (or EVFLAG_AUTO).	203	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
129		204
130	It supports the following flags:	205	The following flags are supported:
131		206
132	=over 4	207	=over 4
133		208
134	=item C<EVFLAG_AUTO>	209	=item C<EVFLAG_AUTO>
135		210
…		…
143	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	218	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
144	override the flags completely if it is found in the environment. This is	219	override the flags completely if it is found in the environment. This is
145	useful to try out specific backends to test their performance, or to work	220	useful to try out specific backends to test their performance, or to work
146	around bugs.	221	around bugs.
147		222
148	=item C<EVMETHOD_SELECT> (portable select backend)	223	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
149		224
		225	This is your standard select(2) backend. Not I<completely> standard, as
		226	libev tries to roll its own fd_set with no limits on the number of fds,
		227	but if that fails, expect a fairly low limit on the number of fds when
		228	using this backend. It doesn't scale too well (O(highest_fd)), but its usually
		229	the fastest backend for a low number of fds.
		230
150	=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)	231	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
151		232
152	=item C<EVMETHOD_EPOLL> (linux only)	233	And this is your standard poll(2) backend. It's more complicated than
		234	select, but handles sparse fds better and has no artificial limit on the
		235	number of fds you can use (except it will slow down considerably with a
		236	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
153		237
154	=item C<EVMETHOD_KQUEUE> (some bsds only)	238	=item C<EVBACKEND_EPOLL> (value 4, Linux)
155		239
156	=item C<EVMETHOD_DEVPOLL> (solaris 8 only)	240	For few fds, this backend is a bit little slower than poll and select,
		241	but it scales phenomenally better. While poll and select usually scale like
		242	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales
		243	either O(1) or O(active_fds).
157		244
158	=item C<EVMETHOD_PORT> (solaris 10 only)	245	While stopping and starting an I/O watcher in the same iteration will
		246	result in some caching, there is still a syscall per such incident
		247	(because the fd could point to a different file description now), so its
		248	best to avoid that. Also, dup()ed file descriptors might not work very
		249	well if you register events for both fds.
		250
		251	Please note that epoll sometimes generates spurious notifications, so you
		252	need to use non-blocking I/O or other means to avoid blocking when no data
		253	(or space) is available.
		254
		255	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
		256
		257	Kqueue deserves special mention, as at the time of this writing, it
		258	was broken on all BSDs except NetBSD (usually it doesn't work with
		259	anything but sockets and pipes, except on Darwin, where of course its
		260	completely useless). For this reason its not being "autodetected"
		261	unless you explicitly specify it explicitly in the flags (i.e. using
		262	C<EVBACKEND_KQUEUE>).
		263
		264	It scales in the same way as the epoll backend, but the interface to the
		265	kernel is more efficient (which says nothing about its actual speed, of
		266	course). While starting and stopping an I/O watcher does not cause an
		267	extra syscall as with epoll, it still adds up to four event changes per
		268	incident, so its best to avoid that.
		269
		270	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
		271
		272	This is not implemented yet (and might never be).
		273
		274	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
		275
		276	This uses the Solaris 10 port mechanism. As with everything on Solaris,
		277	it's really slow, but it still scales very well (O(active_fds)).
		278
		279	Please note that solaris ports can result in a lot of spurious
		280	notifications, so you need to use non-blocking I/O or other means to avoid
		281	blocking when no data (or space) is available.
		282
		283	=item C<EVBACKEND_ALL>
		284
		285	Try all backends (even potentially broken ones that wouldn't be tried
		286	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
		287	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
		288
		289	=back
159		290
160	If one or more of these are ored into the flags value, then only these	291	If one or more of these are ored into the flags value, then only these
161	backends will be tried (in the reverse order as given here). If one are	292	backends will be tried (in the reverse order as given here). If none are
162	specified, any backend will do.	293	specified, most compiled-in backend will be tried, usually in reverse
		294	order of their flag values :)
163		295
164	=back	296	The most typical usage is like this:
		297
		298	if (!ev_default_loop (0))
		299	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		300
		301	Restrict libev to the select and poll backends, and do not allow
		302	environment settings to be taken into account:
		303
		304	ev_default_loop (EVBACKEND_POLL \| EVBACKEND_SELECT \| EVFLAG_NOENV);
		305
		306	Use whatever libev has to offer, but make sure that kqueue is used if
		307	available (warning, breaks stuff, best use only with your own private
		308	event loop and only if you know the OS supports your types of fds):
		309
		310	ev_default_loop (ev_recommended_backends () \| EVBACKEND_KQUEUE);
165		311
166	=item struct ev_loop *ev_loop_new (unsigned int flags)	312	=item struct ev_loop *ev_loop_new (unsigned int flags)
167		313
168	Similar to C<ev_default_loop>, but always creates a new event loop that is	314	Similar to C<ev_default_loop>, but always creates a new event loop that is
169	always distinct from the default loop. Unlike the default loop, it cannot	315	always distinct from the default loop. Unlike the default loop, it cannot
170	handle signal and child watchers, and attempts to do so will be greeted by	316	handle signal and child watchers, and attempts to do so will be greeted by
171	undefined behaviour (or a failed assertion if assertions are enabled).	317	undefined behaviour (or a failed assertion if assertions are enabled).
172		318
		319	Example: try to create a event loop that uses epoll and nothing else.
		320
		321	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL \| EVFLAG_NOENV);
		322	if (!epoller)
		323	fatal ("no epoll found here, maybe it hides under your chair");
		324
173	=item ev_default_destroy ()	325	=item ev_default_destroy ()
174		326
175	Destroys the default loop again (frees all memory and kernel state	327	Destroys the default loop again (frees all memory and kernel state
176	etc.). This stops all registered event watchers (by not touching them in	328	etc.). This stops all registered event watchers (by not touching them in
177	any way whatsoever, although you cannot rely on this :).	329	any way whatsoever, although you cannot rely on this :).
…		…
186	This function reinitialises the kernel state for backends that have	338	This function reinitialises the kernel state for backends that have
187	one. Despite the name, you can call it anytime, but it makes most sense	339	one. Despite the name, you can call it anytime, but it makes most sense
188	after forking, in either the parent or child process (or both, but that	340	after forking, in either the parent or child process (or both, but that
189	again makes little sense).	341	again makes little sense).
190		342
191	You I<must> call this function after forking if and only if you want to	343	You I<must> call this function in the child process after forking if and
192	use the event library in both processes. If you just fork+exec, you don't	344	only if you want to use the event library in both processes. If you just
193	have to call it.	345	fork+exec, you don't have to call it.
194		346
195	The function itself is quite fast and it's usually not a problem to call	347	The function itself is quite fast and it's usually not a problem to call
196	it just in case after a fork. To make this easy, the function will fit in	348	it just in case after a fork. To make this easy, the function will fit in
197	quite nicely into a call to C<pthread_atfork>:	349	quite nicely into a call to C<pthread_atfork>:
198		350
199	pthread_atfork (0, 0, ev_default_fork);	351	pthread_atfork (0, 0, ev_default_fork);
200		352
		353	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
		354	without calling this function, so if you force one of those backends you
		355	do not need to care.
		356
201	=item ev_loop_fork (loop)	357	=item ev_loop_fork (loop)
202		358
203	Like C<ev_default_fork>, but acts on an event loop created by	359	Like C<ev_default_fork>, but acts on an event loop created by
204	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	360	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
205	after fork, and how you do this is entirely your own problem.	361	after fork, and how you do this is entirely your own problem.
206		362
207	=item unsigned int ev_method (loop)	363	=item unsigned int ev_backend (loop)
208		364
209	Returns one of the C<EVMETHOD_*> flags indicating the event backend in	365	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
210	use.	366	use.
211		367
212	=item ev_tstamp ev_now (loop)	368	=item ev_tstamp ev_now (loop)
213		369
214	Returns the current "event loop time", which is the time the event loop	370	Returns the current "event loop time", which is the time the event loop
215	got events and started processing them. This timestamp does not change	371	received events and started processing them. This timestamp does not
216	as long as callbacks are being processed, and this is also the base time	372	change as long as callbacks are being processed, and this is also the base
217	used for relative timers. You can treat it as the timestamp of the event	373	time used for relative timers. You can treat it as the timestamp of the
218	occuring (or more correctly, the mainloop finding out about it).	374	event occuring (or more correctly, libev finding out about it).
219		375
220	=item ev_loop (loop, int flags)	376	=item ev_loop (loop, int flags)
221		377
222	Finally, this is it, the event handler. This function usually is called	378	Finally, this is it, the event handler. This function usually is called
223	after you initialised all your watchers and you want to start handling	379	after you initialised all your watchers and you want to start handling
224	events.	380	events.
225		381
226	If the flags argument is specified as 0, it will not return until either	382	If the flags argument is specified as C<0>, it will not return until
227	no event watchers are active anymore or C<ev_unloop> was called.	383	either no event watchers are active anymore or C<ev_unloop> was called.
		384
		385	Please note that an explicit C<ev_unloop> is usually better than
		386	relying on all watchers to be stopped when deciding when a program has
		387	finished (especially in interactive programs), but having a program that
		388	automatically loops as long as it has to and no longer by virtue of
		389	relying on its watchers stopping correctly is a thing of beauty.
228		390
229	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	391	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
230	those events and any outstanding ones, but will not block your process in	392	those events and any outstanding ones, but will not block your process in
231	case there are no events and will return after one iteration of the loop.	393	case there are no events and will return after one iteration of the loop.
232		394
233	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	395	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
234	neccessary) and will handle those and any outstanding ones. It will block	396	neccessary) and will handle those and any outstanding ones. It will block
235	your process until at least one new event arrives, and will return after	397	your process until at least one new event arrives, and will return after
236	one iteration of the loop.	398	one iteration of the loop. This is useful if you are waiting for some
		399	external event in conjunction with something not expressible using other
		400	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
		401	usually a better approach for this kind of thing.
237		402
238	This flags value could be used to implement alternative looping	403	Here are the gory details of what C<ev_loop> does:
239	constructs, but the C<prepare> and C<check> watchers provide a better and	404
240	more generic mechanism.	405	* If there are no active watchers (reference count is zero), return.
		406	- Queue prepare watchers and then call all outstanding watchers.
		407	- If we have been forked, recreate the kernel state.
		408	- Update the kernel state with all outstanding changes.
		409	- Update the "event loop time".
		410	- Calculate for how long to block.
		411	- Block the process, waiting for any events.
		412	- Queue all outstanding I/O (fd) events.
		413	- Update the "event loop time" and do time jump handling.
		414	- Queue all outstanding timers.
		415	- Queue all outstanding periodics.
		416	- If no events are pending now, queue all idle watchers.
		417	- Queue all check watchers.
		418	- Call all queued watchers in reverse order (i.e. check watchers first).
		419	Signals and child watchers are implemented as I/O watchers, and will
		420	be handled here by queueing them when their watcher gets executed.
		421	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
		422	were used, return, otherwise continue with step *.
		423
		424	Example: queue some jobs and then loop until no events are outsanding
		425	anymore.
		426
		427	... queue jobs here, make sure they register event watchers as long
		428	... as they still have work to do (even an idle watcher will do..)
		429	ev_loop (my_loop, 0);
		430	... jobs done. yeah!
241		431
242	=item ev_unloop (loop, how)	432	=item ev_unloop (loop, how)
243		433
244	Can be used to make a call to C<ev_loop> return early (but only after it	434	Can be used to make a call to C<ev_loop> return early (but only after it
245	has processed all outstanding events). The C<how> argument must be either	435	has processed all outstanding events). The C<how> argument must be either
246	C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or	436	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
247	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	437	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
248		438
249	=item ev_ref (loop)	439	=item ev_ref (loop)
250		440
251	=item ev_unref (loop)	441	=item ev_unref (loop)
…		…
259	visible to the libev user and should not keep C<ev_loop> from exiting if	449	visible to the libev user and should not keep C<ev_loop> from exiting if
260	no event watchers registered by it are active. It is also an excellent	450	no event watchers registered by it are active. It is also an excellent
261	way to do this for generic recurring timers or from within third-party	451	way to do this for generic recurring timers or from within third-party
262	libraries. Just remember to I<unref after start> and I<ref before stop>.	452	libraries. Just remember to I<unref after start> and I<ref before stop>.
263		453
		454	Example: create a signal watcher, but keep it from keeping C<ev_loop>
		455	running when nothing else is active.
		456
		457	struct dv_signal exitsig;
		458	ev_signal_init (&exitsig, sig_cb, SIGINT);
		459	ev_signal_start (myloop, &exitsig);
		460	evf_unref (myloop);
		461
		462	Example: for some weird reason, unregister the above signal handler again.
		463
		464	ev_ref (myloop);
		465	ev_signal_stop (myloop, &exitsig);
		466
264	=back	467	=back
265		468
266	=head1 ANATOMY OF A WATCHER	469	=head1 ANATOMY OF A WATCHER
267		470
268	A watcher is a structure that you create and register to record your	471	A watcher is a structure that you create and register to record your
…		…
302	*) >>), and you can stop watching for events at any time by calling the	505	*) >>), and you can stop watching for events at any time by calling the
303	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	506	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.
304		507
305	As long as your watcher is active (has been started but not stopped) you	508	As long as your watcher is active (has been started but not stopped) you
306	must not touch the values stored in it. Most specifically you must never	509	must not touch the values stored in it. Most specifically you must never
307	reinitialise it or call its set method.	510	reinitialise it or call its set macro.
308		511
309	You can check whether an event is active by calling the C<ev_is_active	512	You can check whether an event is active by calling the C<ev_is_active
310	(watcher *)> macro. To see whether an event is outstanding (but the	513	(watcher *)> macro. To see whether an event is outstanding (but the
311	callback for it has not been called yet) you can use the C<ev_is_pending	514	callback for it has not been called yet) you can use the C<ev_is_pending
312	(watcher *)> macro.	515	(watcher *)> macro.
…		…
409	=head1 WATCHER TYPES	612	=head1 WATCHER TYPES
410		613
411	This section describes each watcher in detail, but will not repeat	614	This section describes each watcher in detail, but will not repeat
412	information given in the last section.	615	information given in the last section.
413		616
		617
414	=head2 C<ev_io> - is this file descriptor readable or writable	618	=head2 C<ev_io> - is this file descriptor readable or writable
415		619
416	I/O watchers check whether a file descriptor is readable or writable	620	I/O watchers check whether a file descriptor is readable or writable
417	in each iteration of the event loop (This behaviour is called	621	in each iteration of the event loop (This behaviour is called
418	level-triggering because you keep receiving events as long as the	622	level-triggering because you keep receiving events as long as the
419	condition persists. Remember you can stop the watcher if you don't want to	623	condition persists. Remember you can stop the watcher if you don't want to
420	act on the event and neither want to receive future events).	624	act on the event and neither want to receive future events).
421		625
422	In general you can register as many read and/or write event watchers oer	626	In general you can register as many read and/or write event watchers per
423	fd as you want (as long as you don't confuse yourself). Setting all file	627	fd as you want (as long as you don't confuse yourself). Setting all file
424	descriptors to non-blocking mode is also usually a good idea (but not	628	descriptors to non-blocking mode is also usually a good idea (but not
425	required if you know what you are doing).	629	required if you know what you are doing).
426		630
427	You have to be careful with dup'ed file descriptors, though. Some backends	631	You have to be careful with dup'ed file descriptors, though. Some backends
428	(the linux epoll backend is a notable example) cannot handle dup'ed file	632	(the linux epoll backend is a notable example) cannot handle dup'ed file
429	descriptors correctly if you register interest in two or more fds pointing	633	descriptors correctly if you register interest in two or more fds pointing
430	to the same file/socket etc. description.	634	to the same underlying file/socket etc. description (that is, they share
		635	the same underlying "file open").
431		636
432	If you must do this, then force the use of a known-to-be-good backend	637	If you must do this, then force the use of a known-to-be-good backend
433	(at the time of this writing, this includes only EVMETHOD_SELECT and	638	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
434	EVMETHOD_POLL).	639	C<EVBACKEND_POLL>).
435		640
436	=over 4	641	=over 4
437		642
438	=item ev_io_init (ev_io *, callback, int fd, int events)	643	=item ev_io_init (ev_io *, callback, int fd, int events)
439		644
…		…
441		646
442	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive	647	Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive
443	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ \|	648	events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ \|
444	EV_WRITE> to receive the given events.	649	EV_WRITE> to receive the given events.
445		650
		651	Please note that most of the more scalable backend mechanisms (for example
		652	epoll and solaris ports) can result in spurious readyness notifications
		653	for file descriptors, so you practically need to use non-blocking I/O (and
		654	treat callback invocation as hint only), or retest separately with a safe
		655	interface before doing I/O (XLib can do this), or force the use of either
		656	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>, which don't suffer from this
		657	problem. Also note that it is quite easy to have your callback invoked
		658	when the readyness condition is no longer valid even when employing
		659	typical ways of handling events, so its a good idea to use non-blocking
		660	I/O unconditionally.
		661
446	=back	662	=back
		663
		664	Example: call C<stdin_readable_cb> when STDIN_FILENO has become, well
		665	readable, but only once. Since it is likely line-buffered, you could
		666	attempt to read a whole line in the callback:
		667
		668	static void
		669	stdin_readable_cb (struct ev_loop loop, struct ev_io w, int revents)
		670	{
		671	ev_io_stop (loop, w);
		672	.. read from stdin here (or from w->fd) and haqndle any I/O errors
		673	}
		674
		675	...
		676	struct ev_loop *loop = ev_default_init (0);
		677	struct ev_io stdin_readable;
		678	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		679	ev_io_start (loop, &stdin_readable);
		680	ev_loop (loop, 0);
		681
447		682
448	=head2 C<ev_timer> - relative and optionally recurring timeouts	683	=head2 C<ev_timer> - relative and optionally recurring timeouts
449		684
450	Timer watchers are simple relative timers that generate an event after a	685	Timer watchers are simple relative timers that generate an event after a
451	given time, and optionally repeating in regular intervals after that.	686	given time, and optionally repeating in regular intervals after that.
452		687
453	The timers are based on real time, that is, if you register an event that	688	The timers are based on real time, that is, if you register an event that
454	times out after an hour and youreset your system clock to last years	689	times out after an hour and you reset your system clock to last years
455	time, it will still time out after (roughly) and hour. "Roughly" because	690	time, it will still time out after (roughly) and hour. "Roughly" because
456	detecting time jumps is hard, and soem inaccuracies are unavoidable (the	691	detecting time jumps is hard, and some inaccuracies are unavoidable (the
457	monotonic clock option helps a lot here).	692	monotonic clock option helps a lot here).
458		693
459	The relative timeouts are calculated relative to the C<ev_now ()>	694	The relative timeouts are calculated relative to the C<ev_now ()>
460	time. This is usually the right thing as this timestamp refers to the time	695	time. This is usually the right thing as this timestamp refers to the time
461	of the event triggering whatever timeout you are modifying/starting. If	696	of the event triggering whatever timeout you are modifying/starting. If
462	you suspect event processing to be delayed and you need to base the timeout	697	you suspect event processing to be delayed and you I<need> to base the timeout
463	ion the current time, use something like this to adjust for this:	698	on the current time, use something like this to adjust for this:
464		699
465	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	700	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
		701
		702	The callback is guarenteed to be invoked only when its timeout has passed,
		703	but if multiple timers become ready during the same loop iteration then
		704	order of execution is undefined.
466		705
467	=over 4	706	=over 4
468		707
469	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	708	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
470		709
…		…
476	later, again, and again, until stopped manually.	715	later, again, and again, until stopped manually.
477		716
478	The timer itself will do a best-effort at avoiding drift, that is, if you	717	The timer itself will do a best-effort at avoiding drift, that is, if you
479	configure a timer to trigger every 10 seconds, then it will trigger at	718	configure a timer to trigger every 10 seconds, then it will trigger at
480	exactly 10 second intervals. If, however, your program cannot keep up with	719	exactly 10 second intervals. If, however, your program cannot keep up with
481	the timer (ecause it takes longer than those 10 seconds to do stuff) the	720	the timer (because it takes longer than those 10 seconds to do stuff) the
482	timer will not fire more than once per event loop iteration.	721	timer will not fire more than once per event loop iteration.
483		722
484	=item ev_timer_again (loop)	723	=item ev_timer_again (loop)
485		724
486	This will act as if the timer timed out and restart it again if it is	725	This will act as if the timer timed out and restart it again if it is
…		…
500	state where you do not expect data to travel on the socket, you can stop	739	state where you do not expect data to travel on the socket, you can stop
501	the timer, and again will automatically restart it if need be.	740	the timer, and again will automatically restart it if need be.
502		741
503	=back	742	=back
504		743
		744	Example: create a timer that fires after 60 seconds.
		745
		746	static void
		747	one_minute_cb (struct ev_loop loop, struct ev_timer w, int revents)
		748	{
		749	.. one minute over, w is actually stopped right here
		750	}
		751
		752	struct ev_timer mytimer;
		753	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		754	ev_timer_start (loop, &mytimer);
		755
		756	Example: create a timeout timer that times out after 10 seconds of
		757	inactivity.
		758
		759	static void
		760	timeout_cb (struct ev_loop loop, struct ev_timer w, int revents)
		761	{
		762	.. ten seconds without any activity
		763	}
		764
		765	struct ev_timer mytimer;
		766	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		767	ev_timer_again (&mytimer); /* start timer */
		768	ev_loop (loop, 0);
		769
		770	// and in some piece of code that gets executed on any "activity":
		771	// reset the timeout to start ticking again at 10 seconds
		772	ev_timer_again (&mytimer);
		773
		774
505	=head2 C<ev_periodic> - to cron or not to cron	775	=head2 C<ev_periodic> - to cron or not to cron
506		776
507	Periodic watchers are also timers of a kind, but they are very versatile	777	Periodic watchers are also timers of a kind, but they are very versatile
508	(and unfortunately a bit complex).	778	(and unfortunately a bit complex).
509		779
…		…
517	again).	787	again).
518		788
519	They can also be used to implement vastly more complex timers, such as	789	They can also be used to implement vastly more complex timers, such as
520	triggering an event on eahc midnight, local time.	790	triggering an event on eahc midnight, local time.
521		791
		792	As with timers, the callback is guarenteed to be invoked only when the
		793	time (C<at>) has been passed, but if multiple periodic timers become ready
		794	during the same loop iteration then order of execution is undefined.
		795
522	=over 4	796	=over 4
523		797
524	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	798	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)
525		799
526	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	800	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)
527		801
528	Lots of arguments, lets sort it out... There are basically three modes of	802	Lots of arguments, lets sort it out... There are basically three modes of
529	operation, and we will explain them from simplest to complex:	803	operation, and we will explain them from simplest to complex:
530
531		804
532	=over 4	805	=over 4
533		806
534	=item * absolute timer (interval = reschedule_cb = 0)	807	=item * absolute timer (interval = reschedule_cb = 0)
535		808
…		…
600	when you changed some parameters or the reschedule callback would return	873	when you changed some parameters or the reschedule callback would return
601	a different time than the last time it was called (e.g. in a crond like	874	a different time than the last time it was called (e.g. in a crond like
602	program when the crontabs have changed).	875	program when the crontabs have changed).
603		876
604	=back	877	=back
		878
		879	Example: call a callback every hour, or, more precisely, whenever the
		880	system clock is divisible by 3600. The callback invocation times have
		881	potentially a lot of jittering, but good long-term stability.
		882
		883	static void
		884	clock_cb (struct ev_loop loop, struct ev_io w, int revents)
		885	{
		886	... its now a full hour (UTC, or TAI or whatever your clock follows)
		887	}
		888
		889	struct ev_periodic hourly_tick;
		890	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		891	ev_periodic_start (loop, &hourly_tick);
		892
		893	Example: the same as above, but use a reschedule callback to do it:
		894
		895	#include <math.h>
		896
		897	static ev_tstamp
		898	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
		899	{
		900	return fmod (now, 3600.) + 3600.;
		901	}
		902
		903	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		904
		905	Example: call a callback every hour, starting now:
		906
		907	struct ev_periodic hourly_tick;
		908	ev_periodic_init (&hourly_tick, clock_cb,
		909	fmod (ev_now (loop), 3600.), 3600., 0);
		910	ev_periodic_start (loop, &hourly_tick);
		911
605		912
606	=head2 C<ev_signal> - signal me when a signal gets signalled	913	=head2 C<ev_signal> - signal me when a signal gets signalled
607		914
608	Signal watchers will trigger an event when the process receives a specific	915	Signal watchers will trigger an event when the process receives a specific
609	signal one or more times. Even though signals are very asynchronous, libev	916	signal one or more times. Even though signals are very asynchronous, libev
…		…
626	Configures the watcher to trigger on the given signal number (usually one	933	Configures the watcher to trigger on the given signal number (usually one
627	of the C<SIGxxx> constants).	934	of the C<SIGxxx> constants).
628		935
629	=back	936	=back
630		937
		938
631	=head2 C<ev_child> - wait for pid status changes	939	=head2 C<ev_child> - wait for pid status changes
632		940
633	Child watchers trigger when your process receives a SIGCHLD in response to	941	Child watchers trigger when your process receives a SIGCHLD in response to
634	some child status changes (most typically when a child of yours dies).	942	some child status changes (most typically when a child of yours dies).
635		943
…		…
645	the status word (use the macros from C<sys/wait.h> and see your systems	953	the status word (use the macros from C<sys/wait.h> and see your systems
646	C<waitpid> documentation). The C<rpid> member contains the pid of the	954	C<waitpid> documentation). The C<rpid> member contains the pid of the
647	process causing the status change.	955	process causing the status change.
648		956
649	=back	957	=back
		958
		959	Example: try to exit cleanly on SIGINT and SIGTERM.
		960
		961	static void
		962	sigint_cb (struct ev_loop loop, struct ev_signal w, int revents)
		963	{
		964	ev_unloop (loop, EVUNLOOP_ALL);
		965	}
		966
		967	struct ev_signal signal_watcher;
		968	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		969	ev_signal_start (loop, &sigint_cb);
		970
650		971
651	=head2 C<ev_idle> - when you've got nothing better to do	972	=head2 C<ev_idle> - when you've got nothing better to do
652		973
653	Idle watchers trigger events when there are no other events are pending	974	Idle watchers trigger events when there are no other events are pending
654	(prepare, check and other idle watchers do not count). That is, as long	975	(prepare, check and other idle watchers do not count). That is, as long
…		…
674	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	995	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
675	believe me.	996	believe me.
676		997
677	=back	998	=back
678		999
		1000	Example: dynamically allocate an C<ev_idle>, start it, and in the
		1001	callback, free it. Alos, use no error checking, as usual.
		1002
		1003	static void
		1004	idle_cb (struct ev_loop loop, struct ev_idle w, int revents)
		1005	{
		1006	free (w);
		1007	// now do something you wanted to do when the program has
		1008	// no longer asnything immediate to do.
		1009	}
		1010
		1011	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
		1012	ev_idle_init (idle_watcher, idle_cb);
		1013	ev_idle_start (loop, idle_cb);
		1014
		1015
679	=head2 C<ev_prepare> and C<ev_check> - customise your event loop	1016	=head2 C<ev_prepare> and C<ev_check> - customise your event loop
680		1017
681	Prepare and check watchers are usually (but not always) used in tandem:	1018	Prepare and check watchers are usually (but not always) used in tandem:
682	prepare watchers get invoked before the process blocks and check watchers	1019	prepare watchers get invoked before the process blocks and check watchers
683	afterwards.	1020	afterwards.
684		1021
685	Their main purpose is to integrate other event mechanisms into libev. This	1022	Their main purpose is to integrate other event mechanisms into libev and
686	could be used, for example, to track variable changes, implement your own	1023	their use is somewhat advanced. This could be used, for example, to track
687	watchers, integrate net-snmp or a coroutine library and lots more.	1024	variable changes, implement your own watchers, integrate net-snmp or a
		1025	coroutine library and lots more.
688		1026
689	This is done by examining in each prepare call which file descriptors need	1027	This is done by examining in each prepare call which file descriptors need
690	to be watched by the other library, registering C<ev_io> watchers for	1028	to be watched by the other library, registering C<ev_io> watchers for
691	them and starting an C<ev_timer> watcher for any timeouts (many libraries	1029	them and starting an C<ev_timer> watcher for any timeouts (many libraries
692	provide just this functionality). Then, in the check watcher you check for	1030	provide just this functionality). Then, in the check watcher you check for
…		…
714	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	1052	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
715	macros, but using them is utterly, utterly and completely pointless.	1053	macros, but using them is utterly, utterly and completely pointless.
716		1054
717	=back	1055	=back
718		1056
		1057	Example: TODO.
		1058
		1059
		1060	=head2 C<ev_embed> - when one backend isn't enough
		1061
		1062	This is a rather advanced watcher type that lets you embed one event loop
		1063	into another.
		1064
		1065	There are primarily two reasons you would want that: work around bugs and
		1066	prioritise I/O.
		1067
		1068	As an example for a bug workaround, the kqueue backend might only support
		1069	sockets on some platform, so it is unusable as generic backend, but you
		1070	still want to make use of it because you have many sockets and it scales
		1071	so nicely. In this case, you would create a kqueue-based loop and embed it
		1072	into your default loop (which might use e.g. poll). Overall operation will
		1073	be a bit slower because first libev has to poll and then call kevent, but
		1074	at least you can use both at what they are best.
		1075
		1076	As for prioritising I/O: rarely you have the case where some fds have
		1077	to be watched and handled very quickly (with low latency), and even
		1078	priorities and idle watchers might have too much overhead. In this case
		1079	you would put all the high priority stuff in one loop and all the rest in
		1080	a second one, and embed the second one in the first.
		1081
		1082	As long as the watcher is started it will automatically handle events. The
		1083	callback will be invoked whenever some events have been handled. You can
		1084	set the callback to C<0> to avoid having to specify one if you are not
		1085	interested in that.
		1086
		1087	Also, there have not currently been made special provisions for forking:
		1088	when you fork, you not only have to call C<ev_loop_fork> on both loops,
		1089	but you will also have to stop and restart any C<ev_embed> watchers
		1090	yourself.
		1091
		1092	Unfortunately, not all backends are embeddable, only the ones returned by
		1093	C<ev_embeddable_backends> are, which, unfortunately, does not include any
		1094	portable one.
		1095
		1096	So when you want to use this feature you will always have to be prepared
		1097	that you cannot get an embeddable loop. The recommended way to get around
		1098	this is to have a separate variables for your embeddable loop, try to
		1099	create it, and if that fails, use the normal loop for everything:
		1100
		1101	struct ev_loop *loop_hi = ev_default_init (0);
		1102	struct ev_loop *loop_lo = 0;
		1103	struct ev_embed embed;
		1104
		1105	// see if there is a chance of getting one that works
		1106	// (remember that a flags value of 0 means autodetection)
		1107	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		1108	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		1109	: 0;
		1110
		1111	// if we got one, then embed it, otherwise default to loop_hi
		1112	if (loop_lo)
		1113	{
		1114	ev_embed_init (&embed, 0, loop_lo);
		1115	ev_embed_start (loop_hi, &embed);
		1116	}
		1117	else
		1118	loop_lo = loop_hi;
		1119
		1120	=over 4
		1121
		1122	=item ev_embed_init (ev_embed , callback, struct ev_loop loop)
		1123
		1124	=item ev_embed_set (ev_embed , callback, struct ev_loop loop)
		1125
		1126	Configures the watcher to embed the given loop, which must be embeddable.
		1127
		1128	=back
		1129
		1130
719	=head1 OTHER FUNCTIONS	1131	=head1 OTHER FUNCTIONS
720		1132
721	There are some other functions of possible interest. Described. Here. Now.	1133	There are some other functions of possible interest. Described. Here. Now.
722		1134
723	=over 4	1135	=over 4
…		…
725	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	1137	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
726		1138
727	This function combines a simple timer and an I/O watcher, calls your	1139	This function combines a simple timer and an I/O watcher, calls your
728	callback on whichever event happens first and automatically stop both	1140	callback on whichever event happens first and automatically stop both
729	watchers. This is useful if you want to wait for a single event on an fd	1141	watchers. This is useful if you want to wait for a single event on an fd
730	or timeout without havign to allocate/configure/start/stop/free one or	1142	or timeout without having to allocate/configure/start/stop/free one or
731	more watchers yourself.	1143	more watchers yourself.
732		1144
733	If C<fd> is less than 0, then no I/O watcher will be started and events	1145	If C<fd> is less than 0, then no I/O watcher will be started and events
734	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	1146	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
735	C<events> set will be craeted and started.	1147	C<events> set will be craeted and started.
…		…
738	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	1150	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
739	repeat = 0) will be started. While C<0> is a valid timeout, it is of	1151	repeat = 0) will be started. While C<0> is a valid timeout, it is of
740	dubious value.	1152	dubious value.
741		1153
742	The callback has the type C<void (cb)(int revents, void arg)> and gets	1154	The callback has the type C<void (cb)(int revents, void arg)> and gets
743	passed an events set like normal event callbacks (with a combination of	1155	passed an C<revents> set like normal event callbacks (a combination of
744	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	1156	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
745	value passed to C<ev_once>:	1157	value passed to C<ev_once>:
746		1158
747	static void stdin_ready (int revents, void *arg)	1159	static void stdin_ready (int revents, void *arg)
748	{	1160	{
…		…
769		1181
770	Feed an event as if the given signal occured (loop must be the default loop!).	1182	Feed an event as if the given signal occured (loop must be the default loop!).
771		1183
772	=back	1184	=back
773		1185
		1186
774	=head1 LIBEVENT EMULATION	1187	=head1 LIBEVENT EMULATION
775		1188
		1189	Libev offers a compatibility emulation layer for libevent. It cannot
		1190	emulate the internals of libevent, so here are some usage hints:
		1191
		1192	=over 4
		1193
		1194	=item * Use it by including <event.h>, as usual.
		1195
		1196	=item * The following members are fully supported: ev_base, ev_callback,
		1197	ev_arg, ev_fd, ev_res, ev_events.
		1198
		1199	=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
		1200	maintained by libev, it does not work exactly the same way as in libevent (consider
		1201	it a private API).
		1202
		1203	=item * Priorities are not currently supported. Initialising priorities
		1204	will fail and all watchers will have the same priority, even though there
		1205	is an ev_pri field.
		1206
		1207	=item * Other members are not supported.
		1208
		1209	=item * The libev emulation is I<not> ABI compatible to libevent, you need
		1210	to use the libev header file and library.
		1211
		1212	=back
		1213
		1214	=head1 C++ SUPPORT
		1215
776	TBD.	1216	TBD.
777		1217
778	=head1 C++ SUPPORT
779
780	TBD.
781
782	=head1 AUTHOR	1218	=head1 AUTHOR
783		1219
784	Marc Lehmann <libev@schmorp.de>.	1220	Marc Lehmann <libev@schmorp.de>.
785		1221

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Comparing libev/ev.pod (file contents): Revision 1.20 by root, Mon Nov 12 09:06:09 2007 UTC vs. Revision 1.35 by root, Fri Nov 23 19:35:09 2007 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.20 by root, Mon Nov 12 09:06:09 2007 UTC vs.
Revision 1.35 by root, Fri Nov 23 19:35:09 2007 UTC