[ViewVC] Diff of: cvs/libev/ev.3

Comparing libev/ev.3 (file contents):
Revision 1.7 by root, Fri Nov 23 08:36:35 2007 UTC vs.
Revision 1.74 by root, Wed Nov 19 10:33:32 2008 UTC

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129	.\" ========================================================================	132	.\" ========================================================================
130	.\"	133	.\"
131	.IX Title ""<STANDARD INPUT>" 1"	134	.IX Title "LIBEV 3"
132	.TH "<STANDARD INPUT>" 1 "2007-11-23" "perl v5.8.8" "User Contributed Perl Documentation"	135	.TH LIBEV 3 "2008-11-17" "libev-3.49" "libev - high performance full featured event loop"
		136	.\" For nroff, turn off justification. Always turn off hyphenation; it makes
		137	.\" way too many mistakes in technical documents.
		138	.if n .ad l
		139	.nh
133	.SH "NAME"	140	.SH "NAME"
134	libev \- a high performance full\-featured event loop written in C	141	libev \- a high performance full\-featured event loop written in C
135	.SH "SYNOPSIS"	142	.SH "SYNOPSIS"
136	.IX Header "SYNOPSIS"	143	.IX Header "SYNOPSIS"
137	.Vb 1	144	.Vb 1
138	\& #include <ev.h>	145	\& #include <ev.h>
		146	.Ve
		147	.Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
		148	.IX Subsection "EXAMPLE PROGRAM"
		149	.Vb 2
		150	\& // a single header file is required
		151	\& #include <ev.h>
		152	\&
		153	\& #include <stdio.h> // for puts
		154	\&
		155	\& // every watcher type has its own typedef\*(Aqd struct
		156	\& // with the name ev_TYPE
		157	\& ev_io stdin_watcher;
		158	\& ev_timer timeout_watcher;
		159	\&
		160	\& // all watcher callbacks have a similar signature
		161	\& // this callback is called when data is readable on stdin
		162	\& static void
		163	\& stdin_cb (EV_P_ ev_io *w, int revents)
		164	\& {
		165	\& puts ("stdin ready");
		166	\& // for one\-shot events, one must manually stop the watcher
		167	\& // with its corresponding stop function.
		168	\& ev_io_stop (EV_A_ w);
		169	\&
		170	\& // this causes all nested ev_loop\*(Aqs to stop iterating
		171	\& ev_unloop (EV_A_ EVUNLOOP_ALL);
		172	\& }
		173	\&
		174	\& // another callback, this time for a time\-out
		175	\& static void
		176	\& timeout_cb (EV_P_ ev_timer *w, int revents)
		177	\& {
		178	\& puts ("timeout");
		179	\& // this causes the innermost ev_loop to stop iterating
		180	\& ev_unloop (EV_A_ EVUNLOOP_ONE);
		181	\& }
		182	\&
		183	\& int
		184	\& main (void)
		185	\& {
		186	\& // use the default event loop unless you have special needs
		187	\& ev_loop *loop = ev_default_loop (0);
		188	\&
		189	\& // initialise an io watcher, then start it
		190	\& // this one will watch for stdin to become readable
		191	\& ev_io_init (&stdin_watcher, stdin_cb, /STDIN_FILENO/ 0, EV_READ);
		192	\& ev_io_start (loop, &stdin_watcher);
		193	\&
		194	\& // initialise a timer watcher, then start it
		195	\& // simple non\-repeating 5.5 second timeout
		196	\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		197	\& ev_timer_start (loop, &timeout_watcher);
		198	\&
		199	\& // now wait for events to arrive
		200	\& ev_loop (loop, 0);
		201	\&
		202	\& // unloop was called, so exit
		203	\& return 0;
		204	\& }
139	.Ve	205	.Ve
140	.SH "DESCRIPTION"	206	.SH "DESCRIPTION"
141	.IX Header "DESCRIPTION"	207	.IX Header "DESCRIPTION"
		208	The newest version of this document is also available as an html-formatted
		209	web page you might find easier to navigate when reading it for the first
		210	time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		211	.PP
142	Libev is an event loop: you register interest in certain events (such as a	212	Libev is an event loop: you register interest in certain events (such as a
143	file descriptor being readable or a timeout occuring), and it will manage	213	file descriptor being readable or a timeout occurring), and it will manage
144	these event sources and provide your program with events.	214	these event sources and provide your program with events.
145	.PP	215	.PP
146	To do this, it must take more or less complete control over your process	216	To do this, it must take more or less complete control over your process
147	(or thread) by executing the \fIevent loop\fR handler, and will then	217	(or thread) by executing the \fIevent loop\fR handler, and will then
148	communicate events via a callback mechanism.	218	communicate events via a callback mechanism.
149	.PP	219	.PP
150	You register interest in certain events by registering so-called \fIevent	220	You register interest in certain events by registering so-called \fIevent
151	watchers\fR, which are relatively small C structures you initialise with the	221	watchers\fR, which are relatively small C structures you initialise with the
152	details of the event, and then hand it over to libev by \fIstarting\fR the	222	details of the event, and then hand it over to libev by \fIstarting\fR the
153	watcher.	223	watcher.
154	.SH "FEATURES"	224	.Sh "\s-1FEATURES\s0"
155	.IX Header "FEATURES"	225	.IX Subsection "FEATURES"
156	Libev supports select, poll, the linux-specific epoll and the bsd-specific	226	Libev supports \f(CW\(C`select\(C'\fR, \f(CW\(C`poll\(C'\fR, the Linux-specific \f(CW\(C`epoll\(C'\fR, the
157	kqueue mechanisms for file descriptor events, relative timers, absolute	227	BSD-specific \f(CW\(C`kqueue\(C'\fR and the Solaris-specific event port mechanisms
158	timers with customised rescheduling, signal events, process status change	228	for file descriptor events (\f(CW\(C`ev_io\(C'\fR), the Linux \f(CW\(C`inotify\(C'\fR interface
159	events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event	229	(for \f(CW\(C`ev_stat\(C'\fR), relative timers (\f(CW\(C`ev_timer\(C'\fR), absolute timers
160	loop mechanism itself (idle, prepare and check watchers). It also is quite	230	with customised rescheduling (\f(CW\(C`ev_periodic\(C'\fR), synchronous signals
161	fast (see this benchmark comparing	231	(\f(CW\(C`ev_signal\(C'\fR), process status change events (\f(CW\(C`ev_child\(C'\fR), and event
162	it to libevent for example).	232	watchers dealing with the event loop mechanism itself (\f(CW\(C`ev_idle\(C'\fR,
		233	\&\f(CW\(C`ev_embed\(C'\fR, \f(CW\(C`ev_prepare\(C'\fR and \f(CW\(C`ev_check\(C'\fR watchers) as well as
		234	file watchers (\f(CW\(C`ev_stat\(C'\fR) and even limited support for fork events
		235	(\f(CW\(C`ev_fork\(C'\fR).
		236	.PP
		237	It also is quite fast (see this
		238	benchmark comparing it to libevent
		239	for example).
163	.SH "CONVENTIONS"	240	.Sh "\s-1CONVENTIONS\s0"
164	.IX Header "CONVENTIONS"	241	.IX Subsection "CONVENTIONS"
165	Libev is very configurable. In this manual the default configuration	242	Libev is very configurable. In this manual the default (and most common)
166	will be described, which supports multiple event loops. For more info	243	configuration will be described, which supports multiple event loops. For
167	about various configuration options please have a look at the file	244	more info about various configuration options please have a look at
168	\&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without	245	\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
169	support for multiple event loops, then all functions taking an initial	246	for multiple event loops, then all functions taking an initial argument of
170	argument of name \f(CW\(C`loop\(C'\fR (which is always of type \f(CW\(C`struct ev_loop \*(C'\fR)	247	name \f(CW\(C`loop\(C'\fR (which is always of type \f(CW\(C`ev_loop \*(C'\fR) will not have
171	will not have this argument.	248	this argument.
172	.SH "TIME REPRESENTATION"	249	.Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"
173	.IX Header "TIME REPRESENTATION"	250	.IX Subsection "TIME REPRESENTATION"
174	Libev represents time as a single floating point number, representing the	251	Libev represents time as a single floating point number, representing the
175	(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near	252	(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
176	the beginning of 1970, details are complicated, don't ask). This type is	253	the beginning of 1970, details are complicated, don't ask). This type is
177	called \f(CW\(C`ev_tstamp\(C'\fR, which is what you should use too. It usually aliases	254	called \f(CW\(C`ev_tstamp\(C'\fR, which is what you should use too. It usually aliases
178	to the double type in C.	255	to the \f(CW\(C`double\(C'\fR type in C, and when you need to do any calculations on
		256	it, you should treat it as some floating point value. Unlike the name
		257	component \f(CW\(C`stamp\(C'\fR might indicate, it is also used for time differences
		258	throughout libev.
		259	.SH "ERROR HANDLING"
		260	.IX Header "ERROR HANDLING"
		261	Libev knows three classes of errors: operating system errors, usage errors
		262	and internal errors (bugs).
		263	.PP
		264	When libev catches an operating system error it cannot handle (for example
		265	a system call indicating a condition libev cannot fix), it calls the callback
		266	set via \f(CW\(C`ev_set_syserr_cb\(C'\fR, which is supposed to fix the problem or
		267	abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
		268	()\*(C'\fR.
		269	.PP
		270	When libev detects a usage error such as a negative timer interval, then
		271	it will print a diagnostic message and abort (via the \f(CW\(C`assert\(C'\fR mechanism,
		272	so \f(CW\(C`NDEBUG\(C'\fR will disable this checking): these are programming errors in
		273	the libev caller and need to be fixed there.
		274	.PP
		275	Libev also has a few internal error-checking \f(CW\(C`assert\(C'\fRions, and also has
		276	extensive consistency checking code. These do not trigger under normal
		277	circumstances, as they indicate either a bug in libev or worse.
179	.SH "GLOBAL FUNCTIONS"	278	.SH "GLOBAL FUNCTIONS"
180	.IX Header "GLOBAL FUNCTIONS"	279	.IX Header "GLOBAL FUNCTIONS"
181	These functions can be called anytime, even before initialising the	280	These functions can be called anytime, even before initialising the
182	library in any way.	281	library in any way.
183	.IP "ev_tstamp ev_time ()" 4	282	.IP "ev_tstamp ev_time ()" 4
184	.IX Item "ev_tstamp ev_time ()"	283	.IX Item "ev_tstamp ev_time ()"
185	Returns the current time as libev would use it. Please note that the	284	Returns the current time as libev would use it. Please note that the
186	\&\f(CW\(C`ev_now\(C'\fR function is usually faster and also often returns the timestamp	285	\&\f(CW\(C`ev_now\(C'\fR function is usually faster and also often returns the timestamp
187	you actually want to know.	286	you actually want to know.
		287	.IP "ev_sleep (ev_tstamp interval)" 4
		288	.IX Item "ev_sleep (ev_tstamp interval)"
		289	Sleep for the given interval: The current thread will be blocked until
		290	either it is interrupted or the given time interval has passed. Basically
		291	this is a sub-second-resolution \f(CW\(C`sleep ()\(C'\fR.
188	.IP "int ev_version_major ()" 4	292	.IP "int ev_version_major ()" 4
189	.IX Item "int ev_version_major ()"	293	.IX Item "int ev_version_major ()"
190	.PD 0	294	.PD 0
191	.IP "int ev_version_minor ()" 4	295	.IP "int ev_version_minor ()" 4
192	.IX Item "int ev_version_minor ()"	296	.IX Item "int ev_version_minor ()"
193	.PD	297	.PD
194	You can find out the major and minor version numbers of the library	298	You can find out the major and minor \s-1ABI\s0 version numbers of the library
195	you linked against by calling the functions \f(CW\(C`ev_version_major\(C'\fR and	299	you linked against by calling the functions \f(CW\(C`ev_version_major\(C'\fR and
196	\&\f(CW\(C`ev_version_minor\(C'\fR. If you want, you can compare against the global	300	\&\f(CW\(C`ev_version_minor\(C'\fR. If you want, you can compare against the global
197	symbols \f(CW\(C`EV_VERSION_MAJOR\(C'\fR and \f(CW\(C`EV_VERSION_MINOR\(C'\fR, which specify the	301	symbols \f(CW\(C`EV_VERSION_MAJOR\(C'\fR and \f(CW\(C`EV_VERSION_MINOR\(C'\fR, which specify the
198	version of the library your program was compiled against.	302	version of the library your program was compiled against.
199	.Sp	303	.Sp
		304	These version numbers refer to the \s-1ABI\s0 version of the library, not the
		305	release version.
		306	.Sp
200	Usually, it's a good idea to terminate if the major versions mismatch,	307	Usually, it's a good idea to terminate if the major versions mismatch,
201	as this indicates an incompatible change. Minor versions are usually	308	as this indicates an incompatible change. Minor versions are usually
202	compatible to older versions, so a larger minor version alone is usually	309	compatible to older versions, so a larger minor version alone is usually
203	not a problem.	310	not a problem.
		311	.Sp
		312	Example: Make sure we haven't accidentally been linked against the wrong
		313	version.
		314	.Sp
		315	.Vb 3
		316	\& assert (("libev version mismatch",
		317	\& ev_version_major () == EV_VERSION_MAJOR
		318	\& && ev_version_minor () >= EV_VERSION_MINOR));
		319	.Ve
204	.IP "unsigned int ev_supported_backends ()" 4	320	.IP "unsigned int ev_supported_backends ()" 4
205	.IX Item "unsigned int ev_supported_backends ()"	321	.IX Item "unsigned int ev_supported_backends ()"
206	Return the set of all backends (i.e. their corresponding \f(CW\(C`EV_BACKEND_\*(C'\fR	322	Return the set of all backends (i.e. their corresponding \f(CW\(C`EV_BACKEND_\*(C'\fR
207	value) compiled into this binary of libev (independent of their	323	value) compiled into this binary of libev (independent of their
208	availability on the system you are running on). See \f(CW\(C`ev_default_loop\(C'\fR for	324	availability on the system you are running on). See \f(CW\(C`ev_default_loop\(C'\fR for
209	a description of the set values.	325	a description of the set values.
		326	.Sp
		327	Example: make sure we have the epoll method, because yeah this is cool and
		328	a must have and can we have a torrent of it please!!!11
		329	.Sp
		330	.Vb 2
		331	\& assert (("sorry, no epoll, no sex",
		332	\& ev_supported_backends () & EVBACKEND_EPOLL));
		333	.Ve
210	.IP "unsigned int ev_recommended_backends ()" 4	334	.IP "unsigned int ev_recommended_backends ()" 4
211	.IX Item "unsigned int ev_recommended_backends ()"	335	.IX Item "unsigned int ev_recommended_backends ()"
212	Return the set of all backends compiled into this binary of libev and also	336	Return the set of all backends compiled into this binary of libev and also
213	recommended for this platform. This set is often smaller than the one	337	recommended for this platform. This set is often smaller than the one
214	returned by \f(CW\(C`ev_supported_backends\(C'\fR, as for example kqueue is broken on	338	returned by \f(CW\(C`ev_supported_backends\(C'\fR, as for example kqueue is broken on
215	most BSDs and will not be autodetected unless you explicitly request it	339	most BSDs and will not be auto-detected unless you explicitly request it
216	(assuming you know what you are doing). This is the set of backends that	340	(assuming you know what you are doing). This is the set of backends that
217	\&\f(CW\(C`EVFLAG_AUTO\(C'\fR will probe for.	341	libev will probe for if you specify no backends explicitly.
		342	.IP "unsigned int ev_embeddable_backends ()" 4
		343	.IX Item "unsigned int ev_embeddable_backends ()"
		344	Returns the set of backends that are embeddable in other event loops. This
		345	is the theoretical, all-platform, value. To find which backends
		346	might be supported on the current system, you would need to look at
		347	\&\f(CW\(C`ev_embeddable_backends () & ev_supported_backends ()\(C'\fR, likewise for
		348	recommended ones.
		349	.Sp
		350	See the description of \f(CW\(C`ev_embed\(C'\fR watchers for more info.
218	.IP "ev_set_allocator (void (cb)(void *ptr, long size))" 4	351	.IP "ev_set_allocator (void (cb)(void *ptr, long size)) [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
219	.IX Item "ev_set_allocator (void (cb)(void *ptr, long size))"	352	.IX Item "ev_set_allocator (void (cb)(void *ptr, long size)) [NOT REENTRANT]"
220	Sets the allocation function to use (the prototype is similar to the	353	Sets the allocation function to use (the prototype is similar \- the
221	realloc C function, the semantics are identical). It is used to allocate	354	semantics are identical to the \f(CW\(C`realloc\(C'\fR C89/SuS/POSIX function). It is
222	and free memory (no surprises here). If it returns zero when memory	355	used to allocate and free memory (no surprises here). If it returns zero
223	needs to be allocated, the library might abort or take some potentially	356	when memory needs to be allocated (\f(CW\(C`size != 0\(C'\fR), the library might abort
224	destructive action. The default is your system realloc function.	357	or take some potentially destructive action.
		358	.Sp
		359	Since some systems (at least OpenBSD and Darwin) fail to implement
		360	correct \f(CW\(C`realloc\(C'\fR semantics, libev will use a wrapper around the system
		361	\&\f(CW\(C`realloc\(C'\fR and \f(CW\(C`free\(C'\fR functions by default.
225	.Sp	362	.Sp
226	You could override this function in high-availability programs to, say,	363	You could override this function in high-availability programs to, say,
227	free some memory if it cannot allocate memory, to use a special allocator,	364	free some memory if it cannot allocate memory, to use a special allocator,
228	or even to sleep a while and retry until some memory is available.	365	or even to sleep a while and retry until some memory is available.
		366	.Sp
		367	Example: Replace the libev allocator with one that waits a bit and then
		368	retries (example requires a standards-compliant \f(CW\(C`realloc\(C'\fR).
		369	.Sp
		370	.Vb 6
		371	\& static void *
		372	\& persistent_realloc (void *ptr, size_t size)
		373	\& {
		374	\& for (;;)
		375	\& {
		376	\& void *newptr = realloc (ptr, size);
		377	\&
		378	\& if (newptr)
		379	\& return newptr;
		380	\&
		381	\& sleep (60);
		382	\& }
		383	\& }
		384	\&
		385	\& ...
		386	\& ev_set_allocator (persistent_realloc);
		387	.Ve
229	.IP "ev_set_syserr_cb (void (cb)(const char msg));" 4	388	.IP "ev_set_syserr_cb (void (cb)(const char msg)); [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
230	.IX Item "ev_set_syserr_cb (void (cb)(const char msg));"	389	.IX Item "ev_set_syserr_cb (void (cb)(const char msg)); [NOT REENTRANT]"
231	Set the callback function to call on a retryable syscall error (such	390	Set the callback function to call on a retryable system call error (such
232	as failed select, poll, epoll_wait). The message is a printable string	391	as failed select, poll, epoll_wait). The message is a printable string
233	indicating the system call or subsystem causing the problem. If this	392	indicating the system call or subsystem causing the problem. If this
234	callback is set, then libev will expect it to remedy the sitution, no	393	callback is set, then libev will expect it to remedy the situation, no
235	matter what, when it returns. That is, libev will generally retry the	394	matter what, when it returns. That is, libev will generally retry the
236	requested operation, or, if the condition doesn't go away, do bad stuff	395	requested operation, or, if the condition doesn't go away, do bad stuff
237	(such as abort).	396	(such as abort).
		397	.Sp
		398	Example: This is basically the same thing that libev does internally, too.
		399	.Sp
		400	.Vb 6
		401	\& static void
		402	\& fatal_error (const char *msg)
		403	\& {
		404	\& perror (msg);
		405	\& abort ();
		406	\& }
		407	\&
		408	\& ...
		409	\& ev_set_syserr_cb (fatal_error);
		410	.Ve
238	.SH "FUNCTIONS CONTROLLING THE EVENT LOOP"	411	.SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
239	.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"	412	.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
240	An event loop is described by a \f(CW\(C`struct ev_loop \*(C'\fR. The library knows two	413	An event loop is described by a \f(CW\(C`struct ev_loop \(C'\fR (the \f(CW\(C`struct\*(C'\fR
241	types of such loops, the \fIdefault\fR loop, which supports signals and child	414	is \fInot\fR optional in this case, as there is also an \f(CW\(C`ev_loop\(C'\fR
242	events, and dynamically created loops which do not.	415	\&\fIfunction\fR).
243	.PP	416	.PP
244	If you use threads, a common model is to run the default event loop	417	The library knows two types of such loops, the \fIdefault\fR loop, which
245	in your main thread (or in a separate thread) and for each thread you	418	supports signals and child events, and dynamically created loops which do
246	create, you also create another event loop. Libev itself does no locking	419	not.
247	whatsoever, so if you mix calls to the same event loop in different
248	threads, make sure you lock (this is usually a bad idea, though, even if
249	done correctly, because it's hideous and inefficient).
250	.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4	420	.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
251	.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"	421	.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
252	This will initialise the default event loop if it hasn't been initialised	422	This will initialise the default event loop if it hasn't been initialised
253	yet and return it. If the default loop could not be initialised, returns	423	yet and return it. If the default loop could not be initialised, returns
254	false. If it already was initialised it simply returns it (and ignores the	424	false. If it already was initialised it simply returns it (and ignores the
255	flags. If that is troubling you, check \f(CW\(C`ev_backend ()\(C'\fR afterwards).	425	flags. If that is troubling you, check \f(CW\(C`ev_backend ()\(C'\fR afterwards).
256	.Sp	426	.Sp
257	If you don't know what event loop to use, use the one returned from this	427	If you don't know what event loop to use, use the one returned from this
258	function.	428	function.
259	.Sp	429	.Sp
		430	Note that this function is \fInot\fR thread-safe, so if you want to use it
		431	from multiple threads, you have to lock (note also that this is unlikely,
		432	as loops cannot be shared easily between threads anyway).
		433	.Sp
		434	The default loop is the only loop that can handle \f(CW\(C`ev_signal\(C'\fR and
		435	\&\f(CW\(C`ev_child\(C'\fR watchers, and to do this, it always registers a handler
		436	for \f(CW\(C`SIGCHLD\(C'\fR. If this is a problem for your application you can either
		437	create a dynamic loop with \f(CW\(C`ev_loop_new\(C'\fR that doesn't do that, or you
		438	can simply overwrite the \f(CW\(C`SIGCHLD\(C'\fR signal handler \fIafter\fR calling
		439	\&\f(CW\(C`ev_default_init\(C'\fR.
		440	.Sp
260	The flags argument can be used to specify special behaviour or specific	441	The flags argument can be used to specify special behaviour or specific
261	backends to use, and is usually specified as \f(CW0\fR (or \s-1EVFLAG_AUTO\s0).	442	backends to use, and is usually specified as \f(CW0\fR (or \f(CW\(C`EVFLAG_AUTO\(C'\fR).
262	.Sp	443	.Sp
263	It supports the following flags:	444	The following flags are supported:
264	.RS 4	445	.RS 4
265	.ie n .IP """EVFLAG_AUTO""" 4	446	.ie n .IP """EVFLAG_AUTO""" 4
266	.el .IP "\f(CWEVFLAG_AUTO\fR" 4	447	.el .IP "\f(CWEVFLAG_AUTO\fR" 4
267	.IX Item "EVFLAG_AUTO"	448	.IX Item "EVFLAG_AUTO"
268	The default flags value. Use this if you have no clue (it's the right	449	The default flags value. Use this if you have no clue (it's the right
269	thing, believe me).	450	thing, believe me).
270	.ie n .IP """EVFLAG_NOENV""" 4	451	.ie n .IP """EVFLAG_NOENV""" 4
271	.el .IP "\f(CWEVFLAG_NOENV\fR" 4	452	.el .IP "\f(CWEVFLAG_NOENV\fR" 4
272	.IX Item "EVFLAG_NOENV"	453	.IX Item "EVFLAG_NOENV"
273	If this flag bit is ored into the flag value (or the program runs setuid	454	If this flag bit is or'ed into the flag value (or the program runs setuid
274	or setgid) then libev will \fInot\fR look at the environment variable	455	or setgid) then libev will \fInot\fR look at the environment variable
275	\&\f(CW\(C`LIBEV_FLAGS\(C'\fR. Otherwise (the default), this environment variable will	456	\&\f(CW\(C`LIBEV_FLAGS\(C'\fR. Otherwise (the default), this environment variable will
276	override the flags completely if it is found in the environment. This is	457	override the flags completely if it is found in the environment. This is
277	useful to try out specific backends to test their performance, or to work	458	useful to try out specific backends to test their performance, or to work
278	around bugs.	459	around bugs.
		460	.ie n .IP """EVFLAG_FORKCHECK""" 4
		461	.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
		462	.IX Item "EVFLAG_FORKCHECK"
		463	Instead of calling \f(CW\(C`ev_default_fork\(C'\fR or \f(CW\(C`ev_loop_fork\(C'\fR manually after
		464	a fork, you can also make libev check for a fork in each iteration by
		465	enabling this flag.
		466	.Sp
		467	This works by calling \f(CW\(C`getpid ()\(C'\fR on every iteration of the loop,
		468	and thus this might slow down your event loop if you do a lot of loop
		469	iterations and little real work, but is usually not noticeable (on my
		470	GNU/Linux system for example, \f(CW\(C`getpid\(C'\fR is actually a simple 5\-insn sequence
		471	without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
		472	\&\f(CW\(C`pthread_atfork\(C'\fR which is even faster).
		473	.Sp
		474	The big advantage of this flag is that you can forget about fork (and
		475	forget about forgetting to tell libev about forking) when you use this
		476	flag.
		477	.Sp
		478	This flag setting cannot be overridden or specified in the \f(CW\(C`LIBEV_FLAGS\(C'\fR
		479	environment variable.
279	.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4	480	.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
280	.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4	481	.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
281	.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"	482	.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
282	This is your standard \fIselect\fR\\|(2) backend. Not \fIcompletely\fR standard, as	483	This is your standard \fIselect\fR\\|(2) backend. Not \fIcompletely\fR standard, as
283	libev tries to roll its own fd_set with no limits on the number of fds,	484	libev tries to roll its own fd_set with no limits on the number of fds,
284	but if that fails, expect a fairly low limit on the number of fds when	485	but if that fails, expect a fairly low limit on the number of fds when
285	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	486	using this backend. It doesn't scale too well (O(highest_fd)), but its
286	the fastest backend for a low number of fds.	487	usually the fastest backend for a low number of (low-numbered :) fds.
		488	.Sp
		489	To get good performance out of this backend you need a high amount of
		490	parallelism (most of the file descriptors should be busy). If you are
		491	writing a server, you should \f(CW\(C`accept ()\(C'\fR in a loop to accept as many
		492	connections as possible during one iteration. You might also want to have
		493	a look at \f(CW\(C`ev_set_io_collect_interval ()\(C'\fR to increase the amount of
		494	readiness notifications you get per iteration.
		495	.Sp
		496	This backend maps \f(CW\(C`EV_READ\(C'\fR to the \f(CW\(C`readfds\(C'\fR set and \f(CW\(C`EV_WRITE\(C'\fR to the
		497	\&\f(CW\(C`writefds\(C'\fR set (and to work around Microsoft Windows bugs, also onto the
		498	\&\f(CW\(C`exceptfds\(C'\fR set on that platform).
287	.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4	499	.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
288	.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4	500	.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
289	.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"	501	.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
290	And this is your standard \fIpoll\fR\\|(2) backend. It's more complicated than	502	And this is your standard \fIpoll\fR\\|(2) backend. It's more complicated
291	select, but handles sparse fds better and has no artificial limit on the	503	than select, but handles sparse fds better and has no artificial
292	number of fds you can use (except it will slow down considerably with a	504	limit on the number of fds you can use (except it will slow down
293	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	505	considerably with a lot of inactive fds). It scales similarly to select,
		506	i.e. O(total_fds). See the entry for \f(CW\(C`EVBACKEND_SELECT\(C'\fR, above, for
		507	performance tips.
		508	.Sp
		509	This backend maps \f(CW\(C`EV_READ\(C'\fR to \f(CW\(C`POLLIN \| POLLERR \| POLLHUP\(C'\fR, and
		510	\&\f(CW\(C`EV_WRITE\(C'\fR to \f(CW\(C`POLLOUT \| POLLERR \| POLLHUP\(C'\fR.
294	.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4	511	.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
295	.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4	512	.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
296	.IX Item "EVBACKEND_EPOLL (value 4, Linux)"	513	.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
297	For few fds, this backend is a bit little slower than poll and select,	514	For few fds, this backend is a bit little slower than poll and select,
298	but it scales phenomenally better. While poll and select usually scale like	515	but it scales phenomenally better. While poll and select usually scale
299	O(total_fds) where n is the total number of fds (or the highest fd), epoll scales	516	like O(total_fds) where n is the total number of fds (or the highest fd),
300	either O(1) or O(active_fds).	517	epoll scales either O(1) or O(active_fds).
301	.Sp	518	.Sp
		519	The epoll mechanism deserves honorable mention as the most misdesigned
		520	of the more advanced event mechanisms: mere annoyances include silently
		521	dropping file descriptors, requiring a system call per change per file
		522	descriptor (and unnecessary guessing of parameters), problems with dup and
		523	so on. The biggest issue is fork races, however \- if a program forks then
		524	\&\fIboth\fR parent and child process have to recreate the epoll set, which can
		525	take considerable time (one syscall per file descriptor) and is of course
		526	hard to detect.
		527	.Sp
		528	Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
		529	of course \fIdoesn't\fR, and epoll just loves to report events for totally
		530	\&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
		531	even remove them from the set) than registered in the set (especially
		532	on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
		533	employing an additional generation counter and comparing that against the
		534	events to filter out spurious ones, recreating the set when required.
		535	.Sp
302	While stopping and starting an I/O watcher in the same iteration will	536	While stopping, setting and starting an I/O watcher in the same iteration
303	result in some caching, there is still a syscall per such incident	537	will result in some caching, there is still a system call per such
304	(because the fd could point to a different file description now), so its	538	incident (because the same \fIfile descriptor\fR could point to a different
305	best to avoid that. Also, \fIdup()\fRed file descriptors might not work very	539	\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\(C`dup ()\(C'\fR'ed
306	well if you register events for both fds.	540	file descriptors might not work very well if you register events for both
		541	file descriptors.
307	.Sp	542	.Sp
308	Please note that epoll sometimes generates spurious notifications, so you	543	Best performance from this backend is achieved by not unregistering all
309	need to use non-blocking I/O or other means to avoid blocking when no data	544	watchers for a file descriptor until it has been closed, if possible,
310	(or space) is available.	545	i.e. keep at least one watcher active per fd at all times. Stopping and
		546	starting a watcher (without re-setting it) also usually doesn't cause
		547	extra overhead. A fork can both result in spurious notifications as well
		548	as in libev having to destroy and recreate the epoll object, which can
		549	take considerable time and thus should be avoided.
		550	.Sp
		551	All this means that, in practice, \f(CW\(C`EVBACKEND_SELECT\(C'\fR can be as fast or
		552	faster than epoll for maybe up to a hundred file descriptors, depending on
		553	the usage. So sad.
		554	.Sp
		555	While nominally embeddable in other event loops, this feature is broken in
		556	all kernel versions tested so far.
		557	.Sp
		558	This backend maps \f(CW\(C`EV_READ\(C'\fR and \f(CW\(C`EV_WRITE\(C'\fR in the same way as
		559	\&\f(CW\(C`EVBACKEND_POLL\(C'\fR.
311	.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4	560	.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
312	.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4	561	.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
313	.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"	562	.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
314	Kqueue deserves special mention, as at the time of this writing, it	563	Kqueue deserves special mention, as at the time of this writing, it
315	was broken on all BSDs except NetBSD (usually it doesn't work with	564	was broken on all BSDs except NetBSD (usually it doesn't work reliably
316	anything but sockets and pipes, except on Darwin, where of course its	565	with anything but sockets and pipes, except on Darwin, where of course
317	completely useless). For this reason its not being \(L"autodetected\(R" unless	566	it's completely useless). Unlike epoll, however, whose brokenness
318	you explicitly specify the flags (i.e. you don't use \s-1EVFLAG_AUTO\s0).	567	is by design, these kqueue bugs can (and eventually will) be fixed
		568	without \s-1API\s0 changes to existing programs. For this reason it's not being
		569	\&\(L"auto-detected\(R" unless you explicitly specify it in the flags (i.e. using
		570	\&\f(CW\(C`EVBACKEND_KQUEUE\(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
		571	system like NetBSD.
		572	.Sp
		573	You still can embed kqueue into a normal poll or select backend and use it
		574	only for sockets (after having made sure that sockets work with kqueue on
		575	the target platform). See \f(CW\(C`ev_embed\(C'\fR watchers for more info.
319	.Sp	576	.Sp
320	It scales in the same way as the epoll backend, but the interface to the	577	It scales in the same way as the epoll backend, but the interface to the
321	kernel is more efficient (which says nothing about its actual speed, of	578	kernel is more efficient (which says nothing about its actual speed, of
322	course). While starting and stopping an I/O watcher does not cause an	579	course). While stopping, setting and starting an I/O watcher does never
323	extra syscall as with epoll, it still adds up to four event changes per	580	cause an extra system call as with \f(CW\(C`EVBACKEND_EPOLL\(C'\fR, it still adds up to
324	incident, so its best to avoid that.	581	two event changes per incident. Support for \f(CW\(C`fork ()\(C'\fR is very bad (but
		582	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		583	cases
		584	.Sp
		585	This backend usually performs well under most conditions.
		586	.Sp
		587	While nominally embeddable in other event loops, this doesn't work
		588	everywhere, so you might need to test for this. And since it is broken
		589	almost everywhere, you should only use it when you have a lot of sockets
		590	(for which it usually works), by embedding it into another event loop
		591	(e.g. \f(CW\(C`EVBACKEND_SELECT\(C'\fR or \f(CW\(C`EVBACKEND_POLL\(C'\fR) and, did I mention it,
		592	using it only for sockets.
		593	.Sp
		594	This backend maps \f(CW\(C`EV_READ\(C'\fR into an \f(CW\(C`EVFILT_READ\(C'\fR kevent with
		595	\&\f(CW\(C`NOTE_EOF\(C'\fR, and \f(CW\(C`EV_WRITE\(C'\fR into an \f(CW\(C`EVFILT_WRITE\(C'\fR kevent with
		596	\&\f(CW\(C`NOTE_EOF\(C'\fR.
325	.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4	597	.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
326	.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4	598	.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
327	.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"	599	.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
328	This is not implemented yet (and might never be).	600	This is not implemented yet (and might never be, unless you send me an
		601	implementation). According to reports, \f(CW\(C`/dev/poll\(C'\fR only supports sockets
		602	and is not embeddable, which would limit the usefulness of this backend
		603	immensely.
329	.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4	604	.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
330	.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4	605	.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
331	.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"	606	.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
332	This uses the Solaris 10 port mechanism. As with everything on Solaris,	607	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
333	it's really slow, but it still scales very well (O(active_fds)).	608	it's really slow, but it still scales very well (O(active_fds)).
334	.Sp	609	.Sp
335	Please note that solaris ports can result in a lot of spurious	610	Please note that Solaris event ports can deliver a lot of spurious
336	notifications, so you need to use non-blocking I/O or other means to avoid	611	notifications, so you need to use non-blocking I/O or other means to avoid
337	blocking when no data (or space) is available.	612	blocking when no data (or space) is available.
		613	.Sp
		614	While this backend scales well, it requires one system call per active
		615	file descriptor per loop iteration. For small and medium numbers of file
		616	descriptors a \(L"slow\(R" \f(CW\(C`EVBACKEND_SELECT\(C'\fR or \f(CW\(C`EVBACKEND_POLL\(C'\fR backend
		617	might perform better.
		618	.Sp
		619	On the positive side, with the exception of the spurious readiness
		620	notifications, this backend actually performed fully to specification
		621	in all tests and is fully embeddable, which is a rare feat among the
		622	OS-specific backends (I vastly prefer correctness over speed hacks).
		623	.Sp
		624	This backend maps \f(CW\(C`EV_READ\(C'\fR and \f(CW\(C`EV_WRITE\(C'\fR in the same way as
		625	\&\f(CW\(C`EVBACKEND_POLL\(C'\fR.
338	.ie n .IP """EVBACKEND_ALL""" 4	626	.ie n .IP """EVBACKEND_ALL""" 4
339	.el .IP "\f(CWEVBACKEND_ALL\fR" 4	627	.el .IP "\f(CWEVBACKEND_ALL\fR" 4
340	.IX Item "EVBACKEND_ALL"	628	.IX Item "EVBACKEND_ALL"
341	Try all backends (even potentially broken ones that wouldn't be tried	629	Try all backends (even potentially broken ones that wouldn't be tried
342	with \f(CW\(C`EVFLAG_AUTO\(C'\fR). Since this is a mask, you can do stuff such as	630	with \f(CW\(C`EVFLAG_AUTO\(C'\fR). Since this is a mask, you can do stuff such as
343	\&\f(CW\(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\(C'\fR.	631	\&\f(CW\(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\(C'\fR.
		632	.Sp
		633	It is definitely not recommended to use this flag.
344	.RE	634	.RE
345	.RS 4	635	.RS 4
346	.Sp	636	.Sp
347	If one or more of these are ored into the flags value, then only these	637	If one or more of these are or'ed into the flags value, then only these
348	backends will be tried (in the reverse order as given here). If none are	638	backends will be tried (in the reverse order as listed here). If none are
349	specified, most compiled-in backend will be tried, usually in reverse	639	specified, all backends in \f(CW\(C`ev_recommended_backends ()\(C'\fR will be tried.
350	order of their flag values :)	640	.Sp
		641	Example: This is the most typical usage.
		642	.Sp
		643	.Vb 2
		644	\& if (!ev_default_loop (0))
		645	\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
		646	.Ve
		647	.Sp
		648	Example: Restrict libev to the select and poll backends, and do not allow
		649	environment settings to be taken into account:
		650	.Sp
		651	.Vb 1
		652	\& ev_default_loop (EVBACKEND_POLL \| EVBACKEND_SELECT \| EVFLAG_NOENV);
		653	.Ve
		654	.Sp
		655	Example: Use whatever libev has to offer, but make sure that kqueue is
		656	used if available (warning, breaks stuff, best use only with your own
		657	private event loop and only if you know the \s-1OS\s0 supports your types of
		658	fds):
		659	.Sp
		660	.Vb 1
		661	\& ev_default_loop (ev_recommended_backends () \| EVBACKEND_KQUEUE);
		662	.Ve
351	.RE	663	.RE
352	.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4	664	.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
353	.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"	665	.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
354	Similar to \f(CW\(C`ev_default_loop\(C'\fR, but always creates a new event loop that is	666	Similar to \f(CW\(C`ev_default_loop\(C'\fR, but always creates a new event loop that is
355	always distinct from the default loop. Unlike the default loop, it cannot	667	always distinct from the default loop. Unlike the default loop, it cannot
356	handle signal and child watchers, and attempts to do so will be greeted by	668	handle signal and child watchers, and attempts to do so will be greeted by
357	undefined behaviour (or a failed assertion if assertions are enabled).	669	undefined behaviour (or a failed assertion if assertions are enabled).
		670	.Sp
		671	Note that this function \fIis\fR thread-safe, and the recommended way to use
		672	libev with threads is indeed to create one loop per thread, and using the
		673	default loop in the \(L"main\(R" or \(L"initial\(R" thread.
		674	.Sp
		675	Example: Try to create a event loop that uses epoll and nothing else.
		676	.Sp
		677	.Vb 3
		678	\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL \| EVFLAG_NOENV);
		679	\& if (!epoller)
		680	\& fatal ("no epoll found here, maybe it hides under your chair");
		681	.Ve
358	.IP "ev_default_destroy ()" 4	682	.IP "ev_default_destroy ()" 4
359	.IX Item "ev_default_destroy ()"	683	.IX Item "ev_default_destroy ()"
360	Destroys the default loop again (frees all memory and kernel state	684	Destroys the default loop again (frees all memory and kernel state
361	etc.). This stops all registered event watchers (by not touching them in	685	etc.). None of the active event watchers will be stopped in the normal
362	any way whatsoever, although you cannot rely on this :).	686	sense, so e.g. \f(CW\(C`ev_is_active\(C'\fR might still return true. It is your
		687	responsibility to either stop all watchers cleanly yourself \fIbefore\fR
		688	calling this function, or cope with the fact afterwards (which is usually
		689	the easiest thing, you can just ignore the watchers and/or \f(CW\(C`free ()\(C'\fR them
		690	for example).
		691	.Sp
		692	Note that certain global state, such as signal state (and installed signal
		693	handlers), will not be freed by this function, and related watchers (such
		694	as signal and child watchers) would need to be stopped manually.
		695	.Sp
		696	In general it is not advisable to call this function except in the
		697	rare occasion where you really need to free e.g. the signal handling
		698	pipe fds. If you need dynamically allocated loops it is better to use
		699	\&\f(CW\(C`ev_loop_new\(C'\fR and \f(CW\(C`ev_loop_destroy\(C'\fR).
363	.IP "ev_loop_destroy (loop)" 4	700	.IP "ev_loop_destroy (loop)" 4
364	.IX Item "ev_loop_destroy (loop)"	701	.IX Item "ev_loop_destroy (loop)"
365	Like \f(CW\(C`ev_default_destroy\(C'\fR, but destroys an event loop created by an	702	Like \f(CW\(C`ev_default_destroy\(C'\fR, but destroys an event loop created by an
366	earlier call to \f(CW\(C`ev_loop_new\(C'\fR.	703	earlier call to \f(CW\(C`ev_loop_new\(C'\fR.
367	.IP "ev_default_fork ()" 4	704	.IP "ev_default_fork ()" 4
368	.IX Item "ev_default_fork ()"	705	.IX Item "ev_default_fork ()"
		706	This function sets a flag that causes subsequent \f(CW\(C`ev_loop\(C'\fR iterations
369	This function reinitialises the kernel state for backends that have	707	to reinitialise the kernel state for backends that have one. Despite the
370	one. Despite the name, you can call it anytime, but it makes most sense	708	name, you can call it anytime, but it makes most sense after forking, in
371	after forking, in either the parent or child process (or both, but that	709	the child process (or both child and parent, but that again makes little
372	again makes little sense).	710	sense). You \fImust\fR call it in the child before using any of the libev
		711	functions, and it will only take effect at the next \f(CW\(C`ev_loop\(C'\fR iteration.
373	.Sp	712	.Sp
374	You \fImust\fR call this function in the child process after forking if and	713	On the other hand, you only need to call this function in the child
375	only if you want to use the event library in both processes. If you just	714	process if and only if you want to use the event library in the child. If
376	fork+exec, you don't have to call it.	715	you just fork+exec, you don't have to call it at all.
377	.Sp	716	.Sp
378	The function itself is quite fast and it's usually not a problem to call	717	The function itself is quite fast and it's usually not a problem to call
379	it just in case after a fork. To make this easy, the function will fit in	718	it just in case after a fork. To make this easy, the function will fit in
380	quite nicely into a call to \f(CW\(C`pthread_atfork\(C'\fR:	719	quite nicely into a call to \f(CW\(C`pthread_atfork\(C'\fR:
381	.Sp	720	.Sp
382	.Vb 1	721	.Vb 1
383	\& pthread_atfork (0, 0, ev_default_fork);	722	\& pthread_atfork (0, 0, ev_default_fork);
384	.Ve	723	.Ve
385	.Sp
386	At the moment, \f(CW\(C`EVBACKEND_SELECT\(C'\fR and \f(CW\(C`EVBACKEND_POLL\(C'\fR are safe to use
387	without calling this function, so if you force one of those backends you
388	do not need to care.
389	.IP "ev_loop_fork (loop)" 4	724	.IP "ev_loop_fork (loop)" 4
390	.IX Item "ev_loop_fork (loop)"	725	.IX Item "ev_loop_fork (loop)"
391	Like \f(CW\(C`ev_default_fork\(C'\fR, but acts on an event loop created by	726	Like \f(CW\(C`ev_default_fork\(C'\fR, but acts on an event loop created by
392	\&\f(CW\(C`ev_loop_new\(C'\fR. Yes, you have to call this on every allocated event loop	727	\&\f(CW\(C`ev_loop_new\(C'\fR. Yes, you have to call this on every allocated event loop
393	after fork, and how you do this is entirely your own problem.	728	after fork that you want to re-use in the child, and how you do this is
		729	entirely your own problem.
		730	.IP "int ev_is_default_loop (loop)" 4
		731	.IX Item "int ev_is_default_loop (loop)"
		732	Returns true when the given loop is, in fact, the default loop, and false
		733	otherwise.
		734	.IP "unsigned int ev_loop_count (loop)" 4
		735	.IX Item "unsigned int ev_loop_count (loop)"
		736	Returns the count of loop iterations for the loop, which is identical to
		737	the number of times libev did poll for new events. It starts at \f(CW0\fR and
		738	happily wraps around with enough iterations.
		739	.Sp
		740	This value can sometimes be useful as a generation counter of sorts (it
		741	\&\(L"ticks\(R" the number of loop iterations), as it roughly corresponds with
		742	\&\f(CW\(C`ev_prepare\(C'\fR and \f(CW\(C`ev_check\(C'\fR calls.
394	.IP "unsigned int ev_backend (loop)" 4	743	.IP "unsigned int ev_backend (loop)" 4
395	.IX Item "unsigned int ev_backend (loop)"	744	.IX Item "unsigned int ev_backend (loop)"
396	Returns one of the \f(CW\(C`EVBACKEND_\*(C'\fR flags indicating the event backend in	745	Returns one of the \f(CW\(C`EVBACKEND_\*(C'\fR flags indicating the event backend in
397	use.	746	use.
398	.IP "ev_tstamp ev_now (loop)" 4	747	.IP "ev_tstamp ev_now (loop)" 4
399	.IX Item "ev_tstamp ev_now (loop)"	748	.IX Item "ev_tstamp ev_now (loop)"
400	Returns the current \(L"event loop time\(R", which is the time the event loop	749	Returns the current \(L"event loop time\(R", which is the time the event loop
401	got events and started processing them. This timestamp does not change	750	received events and started processing them. This timestamp does not
402	as long as callbacks are being processed, and this is also the base time	751	change as long as callbacks are being processed, and this is also the base
403	used for relative timers. You can treat it as the timestamp of the event	752	time used for relative timers. You can treat it as the timestamp of the
404	occuring (or more correctly, the mainloop finding out about it).	753	event occurring (or more correctly, libev finding out about it).
		754	.IP "ev_now_update (loop)" 4
		755	.IX Item "ev_now_update (loop)"
		756	Establishes the current time by querying the kernel, updating the time
		757	returned by \f(CW\(C`ev_now ()\(C'\fR in the progress. This is a costly operation and
		758	is usually done automatically within \f(CW\(C`ev_loop ()\(C'\fR.
		759	.Sp
		760	This function is rarely useful, but when some event callback runs for a
		761	very long time without entering the event loop, updating libev's idea of
		762	the current time is a good idea.
		763	.Sp
		764	See also \(L"The special problem of time updates\(R" in the \f(CW\(C`ev_timer\(C'\fR section.
405	.IP "ev_loop (loop, int flags)" 4	765	.IP "ev_loop (loop, int flags)" 4
406	.IX Item "ev_loop (loop, int flags)"	766	.IX Item "ev_loop (loop, int flags)"
407	Finally, this is it, the event handler. This function usually is called	767	Finally, this is it, the event handler. This function usually is called
408	after you initialised all your watchers and you want to start handling	768	after you initialised all your watchers and you want to start handling
409	events.	769	events.
410	.Sp	770	.Sp
411	If the flags argument is specified as 0, it will not return until either	771	If the flags argument is specified as \f(CW0\fR, it will not return until
412	no event watchers are active anymore or \f(CW\(C`ev_unloop\(C'\fR was called.	772	either no event watchers are active anymore or \f(CW\(C`ev_unloop\(C'\fR was called.
		773	.Sp
		774	Please note that an explicit \f(CW\(C`ev_unloop\(C'\fR is usually better than
		775	relying on all watchers to be stopped when deciding when a program has
		776	finished (especially in interactive programs), but having a program
		777	that automatically loops as long as it has to and no longer by virtue
		778	of relying on its watchers stopping correctly, that is truly a thing of
		779	beauty.
413	.Sp	780	.Sp
414	A flags value of \f(CW\(C`EVLOOP_NONBLOCK\(C'\fR will look for new events, will handle	781	A flags value of \f(CW\(C`EVLOOP_NONBLOCK\(C'\fR will look for new events, will handle
415	those events and any outstanding ones, but will not block your process in	782	those events and any already outstanding ones, but will not block your
416	case there are no events and will return after one iteration of the loop.	783	process in case there are no events and will return after one iteration of
		784	the loop.
417	.Sp	785	.Sp
418	A flags value of \f(CW\(C`EVLOOP_ONESHOT\(C'\fR will look for new events (waiting if	786	A flags value of \f(CW\(C`EVLOOP_ONESHOT\(C'\fR will look for new events (waiting if
419	neccessary) and will handle those and any outstanding ones. It will block	787	necessary) and will handle those and any already outstanding ones. It
420	your process until at least one new event arrives, and will return after	788	will block your process until at least one new event arrives (which could
		789	be an event internal to libev itself, so there is no guarantee that a
		790	user-registered callback will be called), and will return after one
421	one iteration of the loop.	791	iteration of the loop.
422	.Sp	792	.Sp
423	This flags value could be used to implement alternative looping	793	This is useful if you are waiting for some external event in conjunction
424	constructs, but the \f(CW\(C`prepare\(C'\fR and \f(CW\(C`check\(C'\fR watchers provide a better and	794	with something not expressible using other libev watchers (i.e. "roll your
425	more generic mechanism.	795	own \f(CW\(C`ev_loop\(C'\fR"). However, a pair of \f(CW\(C`ev_prepare\(C'\fR/\f(CW\(C`ev_check\(C'\fR watchers is
		796	usually a better approach for this kind of thing.
426	.Sp	797	.Sp
427	Here are the gory details of what ev_loop does:	798	Here are the gory details of what \f(CW\(C`ev_loop\(C'\fR does:
428	.Sp	799	.Sp
429	.Vb 15	800	.Vb 10
430	\& 1. If there are no active watchers (reference count is zero), return.	801	\& \- Before the first iteration, call any pending watchers.
		802	\& * If EVFLAG_FORKCHECK was used, check for a fork.
		803	\& \- If a fork was detected (by any means), queue and call all fork watchers.
431	\& 2. Queue and immediately call all prepare watchers.	804	\& \- Queue and call all prepare watchers.
432	\& 3. If we have been forked, recreate the kernel state.	805	\& \- If we have been forked, detach and recreate the kernel state
		806	\& as to not disturb the other process.
433	\& 4. Update the kernel state with all outstanding changes.	807	\& \- Update the kernel state with all outstanding changes.
434	\& 5. Update the "event loop time".	808	\& \- Update the "event loop time" (ev_now ()).
435	\& 6. Calculate for how long to block.	809	\& \- Calculate for how long to sleep or block, if at all
		810	\& (active idle watchers, EVLOOP_NONBLOCK or not having
		811	\& any active watchers at all will result in not sleeping).
		812	\& \- Sleep if the I/O and timer collect interval say so.
436	\& 7. Block the process, waiting for events.	813	\& \- Block the process, waiting for any events.
		814	\& \- Queue all outstanding I/O (fd) events.
437	\& 8. Update the "event loop time" and do time jump handling.	815	\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
438	\& 9. Queue all outstanding timers.	816	\& \- Queue all expired timers.
439	\& 10. Queue all outstanding periodics.	817	\& \- Queue all expired periodics.
440	\& 11. If no events are pending now, queue all idle watchers.	818	\& \- Unless any events are pending now, queue all idle watchers.
441	\& 12. Queue all check watchers.	819	\& \- Queue all check watchers.
442	\& 13. Call all queued watchers in reverse order (i.e. check watchers first).	820	\& \- Call all queued watchers in reverse order (i.e. check watchers first).
		821	\& Signals and child watchers are implemented as I/O watchers, and will
		822	\& be handled here by queueing them when their watcher gets executed.
443	\& 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	823	\& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
444	\& was used, return, otherwise continue with step #1.	824	\& were used, or there are no active watchers, return, otherwise
		825	\& continue with step *.
		826	.Ve
		827	.Sp
		828	Example: Queue some jobs and then loop until no events are outstanding
		829	anymore.
		830	.Sp
		831	.Vb 4
		832	\& ... queue jobs here, make sure they register event watchers as long
		833	\& ... as they still have work to do (even an idle watcher will do..)
		834	\& ev_loop (my_loop, 0);
		835	\& ... jobs done or somebody called unloop. yeah!
445	.Ve	836	.Ve
446	.IP "ev_unloop (loop, how)" 4	837	.IP "ev_unloop (loop, how)" 4
447	.IX Item "ev_unloop (loop, how)"	838	.IX Item "ev_unloop (loop, how)"
448	Can be used to make a call to \f(CW\(C`ev_loop\(C'\fR return early (but only after it	839	Can be used to make a call to \f(CW\(C`ev_loop\(C'\fR return early (but only after it
449	has processed all outstanding events). The \f(CW\(C`how\(C'\fR argument must be either	840	has processed all outstanding events). The \f(CW\(C`how\(C'\fR argument must be either
450	\&\f(CW\(C`EVUNLOOP_ONE\(C'\fR, which will make the innermost \f(CW\(C`ev_loop\(C'\fR call return, or	841	\&\f(CW\(C`EVUNLOOP_ONE\(C'\fR, which will make the innermost \f(CW\(C`ev_loop\(C'\fR call return, or
451	\&\f(CW\(C`EVUNLOOP_ALL\(C'\fR, which will make all nested \f(CW\(C`ev_loop\(C'\fR calls return.	842	\&\f(CW\(C`EVUNLOOP_ALL\(C'\fR, which will make all nested \f(CW\(C`ev_loop\(C'\fR calls return.
		843	.Sp
		844	This \(L"unloop state\(R" will be cleared when entering \f(CW\(C`ev_loop\(C'\fR again.
		845	.Sp
		846	It is safe to call \f(CW\(C`ev_unloop\(C'\fR from otuside any \f(CW\(C`ev_loop\(C'\fR calls.
452	.IP "ev_ref (loop)" 4	847	.IP "ev_ref (loop)" 4
453	.IX Item "ev_ref (loop)"	848	.IX Item "ev_ref (loop)"
454	.PD 0	849	.PD 0
455	.IP "ev_unref (loop)" 4	850	.IP "ev_unref (loop)" 4
456	.IX Item "ev_unref (loop)"	851	.IX Item "ev_unref (loop)"
457	.PD	852	.PD
458	Ref/unref can be used to add or remove a reference count on the event	853	Ref/unref can be used to add or remove a reference count on the event
459	loop: Every watcher keeps one reference, and as long as the reference	854	loop: Every watcher keeps one reference, and as long as the reference
460	count is nonzero, \f(CW\(C`ev_loop\(C'\fR will not return on its own. If you have	855	count is nonzero, \f(CW\(C`ev_loop\(C'\fR will not return on its own.
		856	.Sp
461	a watcher you never unregister that should not keep \f(CW\(C`ev_loop\(C'\fR from	857	If you have a watcher you never unregister that should not keep \f(CW\(C`ev_loop\(C'\fR
462	returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For	858	from returning, call \fIev_unref()\fR after starting, and \fIev_ref()\fR before
		859	stopping it.
		860	.Sp
463	example, libev itself uses this for its internal signal pipe: It is not	861	As an example, libev itself uses this for its internal signal pipe: It is
464	visible to the libev user and should not keep \f(CW\(C`ev_loop\(C'\fR from exiting if	862	not visible to the libev user and should not keep \f(CW\(C`ev_loop\(C'\fR from exiting
465	no event watchers registered by it are active. It is also an excellent	863	if no event watchers registered by it are active. It is also an excellent
466	way to do this for generic recurring timers or from within third-party	864	way to do this for generic recurring timers or from within third-party
467	libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR.	865	libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR
		866	(but only if the watcher wasn't active before, or was active before,
		867	respectively).
		868	.Sp
		869	Example: Create a signal watcher, but keep it from keeping \f(CW\(C`ev_loop\(C'\fR
		870	running when nothing else is active.
		871	.Sp
		872	.Vb 4
		873	\& ev_signal exitsig;
		874	\& ev_signal_init (&exitsig, sig_cb, SIGINT);
		875	\& ev_signal_start (loop, &exitsig);
		876	\& evf_unref (loop);
		877	.Ve
		878	.Sp
		879	Example: For some weird reason, unregister the above signal handler again.
		880	.Sp
		881	.Vb 2
		882	\& ev_ref (loop);
		883	\& ev_signal_stop (loop, &exitsig);
		884	.Ve
		885	.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
		886	.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
		887	.PD 0
		888	.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
		889	.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
		890	.PD
		891	These advanced functions influence the time that libev will spend waiting
		892	for events. Both time intervals are by default \f(CW0\fR, meaning that libev
		893	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		894	latency.
		895	.Sp
		896	Setting these to a higher value (the \f(CW\(C`interval\(C'\fR \fImust\fR be >= \f(CW0\fR)
		897	allows libev to delay invocation of I/O and timer/periodic callbacks
		898	to increase efficiency of loop iterations (or to increase power-saving
		899	opportunities).
		900	.Sp
		901	The idea is that sometimes your program runs just fast enough to handle
		902	one (or very few) event(s) per loop iteration. While this makes the
		903	program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
		904	events, especially with backends like \f(CW\(C`select ()\(C'\fR which have a high
		905	overhead for the actual polling but can deliver many events at once.
		906	.Sp
		907	By setting a higher \fIio collect interval\fR you allow libev to spend more
		908	time collecting I/O events, so you can handle more events per iteration,
		909	at the cost of increasing latency. Timeouts (both \f(CW\(C`ev_periodic\(C'\fR and
		910	\&\f(CW\(C`ev_timer\(C'\fR) will be not affected. Setting this to a non-null value will
		911	introduce an additional \f(CW\(C`ev_sleep ()\(C'\fR call into most loop iterations.
		912	.Sp
		913	Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
		914	to spend more time collecting timeouts, at the expense of increased
		915	latency/jitter/inexactness (the watcher callback will be called
		916	later). \f(CW\(C`ev_io\(C'\fR watchers will not be affected. Setting this to a non-null
		917	value will not introduce any overhead in libev.
		918	.Sp
		919	Many (busy) programs can usually benefit by setting the I/O collect
		920	interval to a value near \f(CW0.1\fR or so, which is often enough for
		921	interactive servers (of course not for games), likewise for timeouts. It
		922	usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
		923	as this approaches the timing granularity of most systems.
		924	.Sp
		925	Setting the \fItimeout collect interval\fR can improve the opportunity for
		926	saving power, as the program will \(L"bundle\(R" timer callback invocations that
		927	are \(L"near\(R" in time together, by delaying some, thus reducing the number of
		928	times the process sleeps and wakes up again. Another useful technique to
		929	reduce iterations/wake\-ups is to use \f(CW\(C`ev_periodic\(C'\fR watchers and make sure
		930	they fire on, say, one-second boundaries only.
		931	.IP "ev_loop_verify (loop)" 4
		932	.IX Item "ev_loop_verify (loop)"
		933	This function only does something when \f(CW\(C`EV_VERIFY\(C'\fR support has been
		934	compiled in, which is the default for non-minimal builds. It tries to go
		935	through all internal structures and checks them for validity. If anything
		936	is found to be inconsistent, it will print an error message to standard
		937	error and call \f(CW\(C`abort ()\(C'\fR.
		938	.Sp
		939	This can be used to catch bugs inside libev itself: under normal
		940	circumstances, this function will never abort as of course libev keeps its
		941	data structures consistent.
468	.SH "ANATOMY OF A WATCHER"	942	.SH "ANATOMY OF A WATCHER"
469	.IX Header "ANATOMY OF A WATCHER"	943	.IX Header "ANATOMY OF A WATCHER"
		944	In the following description, uppercase \f(CW\(C`TYPE\(C'\fR in names stands for the
		945	watcher type, e.g. \f(CW\(C`ev_TYPE_start\(C'\fR can mean \f(CW\(C`ev_timer_start\(C'\fR for timer
		946	watchers and \f(CW\(C`ev_io_start\(C'\fR for I/O watchers.
		947	.PP
470	A watcher is a structure that you create and register to record your	948	A watcher is a structure that you create and register to record your
471	interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to	949	interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
472	become readable, you would create an \f(CW\(C`ev_io\(C'\fR watcher for that:	950	become readable, you would create an \f(CW\(C`ev_io\(C'\fR watcher for that:
473	.PP	951	.PP
474	.Vb 5	952	.Vb 5
475	\& static void my_cb (struct ev_loop loop, struct ev_io w, int revents)	953	\& static void my_cb (struct ev_loop loop, ev_io w, int revents)
476	\& {	954	\& {
477	\& ev_io_stop (w);	955	\& ev_io_stop (w);
478	\& ev_unloop (loop, EVUNLOOP_ALL);	956	\& ev_unloop (loop, EVUNLOOP_ALL);
479	\& }	957	\& }
480	.Ve	958	\&
481	.PP
482	.Vb 6
483	\& struct ev_loop *loop = ev_default_loop (0);	959	\& struct ev_loop *loop = ev_default_loop (0);
		960	\&
484	\& struct ev_io stdin_watcher;	961	\& ev_io stdin_watcher;
		962	\&
485	\& ev_init (&stdin_watcher, my_cb);	963	\& ev_init (&stdin_watcher, my_cb);
486	\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	964	\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
487	\& ev_io_start (loop, &stdin_watcher);	965	\& ev_io_start (loop, &stdin_watcher);
		966	\&
488	\& ev_loop (loop, 0);	967	\& ev_loop (loop, 0);
489	.Ve	968	.Ve
490	.PP	969	.PP
491	As you can see, you are responsible for allocating the memory for your	970	As you can see, you are responsible for allocating the memory for your
492	watcher structures (and it is usually a bad idea to do this on the stack,	971	watcher structures (and it is \fIusually\fR a bad idea to do this on the
493	although this can sometimes be quite valid).	972	stack).
		973	.PP
		974	Each watcher has an associated watcher structure (called \f(CW\(C`struct ev_TYPE\(C'\fR
		975	or simply \f(CW\(C`ev_TYPE\(C'\fR, as typedefs are provided for all watcher structs).
494	.PP	976	.PP
495	Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init	977	Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
496	(watcher , callback)\(C'\fR, which expects a callback to be provided. This	978	(watcher , callback)\(C'\fR, which expects a callback to be provided. This
497	callback gets invoked each time the event occurs (or, in the case of io	979	callback gets invoked each time the event occurs (or, in the case of I/O
498	watchers, each time the event loop detects that the file descriptor given	980	watchers, each time the event loop detects that the file descriptor given
499	is readable and/or writable).	981	is readable and/or writable).
500	.PP	982	.PP
501	Each watcher type has its own \f(CW\(C`ev_<type>_set (watcher , ...)\*(C'\fR macro	983	Each watcher type further has its own \f(CW\(C`ev_TYPE_set (watcher , ...)\*(C'\fR
502	with arguments specific to this watcher type. There is also a macro	984	macro to configure it, with arguments specific to the watcher type. There
503	to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init	985	is also a macro to combine initialisation and setting in one call: \f(CW\(C`ev_TYPE_init (watcher , callback, ...)\*(C'\fR.
504	(watcher , callback, ...)\(C'\fR.
505	.PP	986	.PP
506	To make the watcher actually watch out for events, you have to start it	987	To make the watcher actually watch out for events, you have to start it
507	with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher	988	with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
508	)\(C'\fR), and you can stop watching for events at any time by calling the	989	)\(C'\fR), and you can stop watching for events at any time by calling the
509	corresponding stop function (\f(CW\(C`ev_<type>_stop (loop, watcher )\*(C'\fR.	990	corresponding stop function (\f(CW\(C`ev_TYPE_stop (loop, watcher )\*(C'\fR.
510	.PP	991	.PP
511	As long as your watcher is active (has been started but not stopped) you	992	As long as your watcher is active (has been started but not stopped) you
512	must not touch the values stored in it. Most specifically you must never	993	must not touch the values stored in it. Most specifically you must never
513	reinitialise it or call its set macro.	994	reinitialise it or call its \f(CW\(C`ev_TYPE_set\(C'\fR macro.
514	.PP
515	You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
516	(watcher )\(C'\fR macro. To see whether an event is outstanding (but the
517	callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
518	(watcher )\(C'\fR macro.
519	.PP	995	.PP
520	Each and every callback receives the event loop pointer as first, the	996	Each and every callback receives the event loop pointer as first, the
521	registered watcher structure as second, and a bitset of received events as	997	registered watcher structure as second, and a bitset of received events as
522	third argument.	998	third argument.
523	.PP	999	.PP
…		…
548	The signal specified in the \f(CW\(C`ev_signal\(C'\fR watcher has been received by a thread.	1024	The signal specified in the \f(CW\(C`ev_signal\(C'\fR watcher has been received by a thread.
549	.ie n .IP """EV_CHILD""" 4	1025	.ie n .IP """EV_CHILD""" 4
550	.el .IP "\f(CWEV_CHILD\fR" 4	1026	.el .IP "\f(CWEV_CHILD\fR" 4
551	.IX Item "EV_CHILD"	1027	.IX Item "EV_CHILD"
552	The pid specified in the \f(CW\(C`ev_child\(C'\fR watcher has received a status change.	1028	The pid specified in the \f(CW\(C`ev_child\(C'\fR watcher has received a status change.
		1029	.ie n .IP """EV_STAT""" 4
		1030	.el .IP "\f(CWEV_STAT\fR" 4
		1031	.IX Item "EV_STAT"
		1032	The path specified in the \f(CW\(C`ev_stat\(C'\fR watcher changed its attributes somehow.
553	.ie n .IP """EV_IDLE""" 4	1033	.ie n .IP """EV_IDLE""" 4
554	.el .IP "\f(CWEV_IDLE\fR" 4	1034	.el .IP "\f(CWEV_IDLE\fR" 4
555	.IX Item "EV_IDLE"	1035	.IX Item "EV_IDLE"
556	The \f(CW\(C`ev_idle\(C'\fR watcher has determined that you have nothing better to do.	1036	The \f(CW\(C`ev_idle\(C'\fR watcher has determined that you have nothing better to do.
557	.ie n .IP """EV_PREPARE""" 4	1037	.ie n .IP """EV_PREPARE""" 4
…		…
567	\&\f(CW\(C`ev_loop\(C'\fR has gathered them, but before it invokes any callbacks for any	1047	\&\f(CW\(C`ev_loop\(C'\fR has gathered them, but before it invokes any callbacks for any
568	received events. Callbacks of both watcher types can start and stop as	1048	received events. Callbacks of both watcher types can start and stop as
569	many watchers as they want, and all of them will be taken into account	1049	many watchers as they want, and all of them will be taken into account
570	(for example, a \f(CW\(C`ev_prepare\(C'\fR watcher might start an idle watcher to keep	1050	(for example, a \f(CW\(C`ev_prepare\(C'\fR watcher might start an idle watcher to keep
571	\&\f(CW\(C`ev_loop\(C'\fR from blocking).	1051	\&\f(CW\(C`ev_loop\(C'\fR from blocking).
		1052	.ie n .IP """EV_EMBED""" 4
		1053	.el .IP "\f(CWEV_EMBED\fR" 4
		1054	.IX Item "EV_EMBED"
		1055	The embedded event loop specified in the \f(CW\(C`ev_embed\(C'\fR watcher needs attention.
		1056	.ie n .IP """EV_FORK""" 4
		1057	.el .IP "\f(CWEV_FORK\fR" 4
		1058	.IX Item "EV_FORK"
		1059	The event loop has been resumed in the child process after fork (see
		1060	\&\f(CW\(C`ev_fork\(C'\fR).
		1061	.ie n .IP """EV_ASYNC""" 4
		1062	.el .IP "\f(CWEV_ASYNC\fR" 4
		1063	.IX Item "EV_ASYNC"
		1064	The given async watcher has been asynchronously notified (see \f(CW\(C`ev_async\(C'\fR).
572	.ie n .IP """EV_ERROR""" 4	1065	.ie n .IP """EV_ERROR""" 4
573	.el .IP "\f(CWEV_ERROR\fR" 4	1066	.el .IP "\f(CWEV_ERROR\fR" 4
574	.IX Item "EV_ERROR"	1067	.IX Item "EV_ERROR"
575	An unspecified error has occured, the watcher has been stopped. This might	1068	An unspecified error has occurred, the watcher has been stopped. This might
576	happen because the watcher could not be properly started because libev	1069	happen because the watcher could not be properly started because libev
577	ran out of memory, a file descriptor was found to be closed or any other	1070	ran out of memory, a file descriptor was found to be closed or any other
		1071	problem. Libev considers these application bugs.
		1072	.Sp
578	problem. You best act on it by reporting the problem and somehow coping	1073	You best act on it by reporting the problem and somehow coping with the
579	with the watcher being stopped.	1074	watcher being stopped. Note that well-written programs should not receive
		1075	an error ever, so when your watcher receives it, this usually indicates a
		1076	bug in your program.
580	.Sp	1077	.Sp
581	Libev will usually signal a few \(L"dummy\(R" events together with an error,	1078	Libev will usually signal a few \(L"dummy\(R" events together with an error, for
582	for example it might indicate that a fd is readable or writable, and if	1079	example it might indicate that a fd is readable or writable, and if your
583	your callbacks is well-written it can just attempt the operation and cope	1080	callbacks is well-written it can just attempt the operation and cope with
584	with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded	1081	the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
585	programs, though, so beware.	1082	programs, though, as the fd could already be closed and reused for another
		1083	thing, so beware.
		1084	.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
		1085	.IX Subsection "GENERIC WATCHER FUNCTIONS"
		1086	.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
		1087	.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
		1088	.IX Item "ev_init (ev_TYPE *watcher, callback)"
		1089	This macro initialises the generic portion of a watcher. The contents
		1090	of the watcher object can be arbitrary (so \f(CW\(C`malloc\(C'\fR will do). Only
		1091	the generic parts of the watcher are initialised, you \fIneed\fR to call
		1092	the type-specific \f(CW\(C`ev_TYPE_set\(C'\fR macro afterwards to initialise the
		1093	type-specific parts. For each type there is also a \f(CW\(C`ev_TYPE_init\(C'\fR macro
		1094	which rolls both calls into one.
		1095	.Sp
		1096	You can reinitialise a watcher at any time as long as it has been stopped
		1097	(or never started) and there are no pending events outstanding.
		1098	.Sp
		1099	The callback is always of type \f(CW\(C`void ()(struct ev_loop loop, ev_TYPE watcher,
		1100	int revents)\*(C'\fR.
		1101	.Sp
		1102	Example: Initialise an \f(CW\(C`ev_io\(C'\fR watcher in two steps.
		1103	.Sp
		1104	.Vb 3
		1105	\& ev_io w;
		1106	\& ev_init (&w, my_cb);
		1107	\& ev_io_set (&w, STDIN_FILENO, EV_READ);
		1108	.Ve
		1109	.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
		1110	.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
		1111	.IX Item "ev_TYPE_set (ev_TYPE *, [args])"
		1112	This macro initialises the type-specific parts of a watcher. You need to
		1113	call \f(CW\(C`ev_init\(C'\fR at least once before you call this macro, but you can
		1114	call \f(CW\(C`ev_TYPE_set\(C'\fR any number of times. You must not, however, call this
		1115	macro on a watcher that is active (it can be pending, however, which is a
		1116	difference to the \f(CW\(C`ev_init\(C'\fR macro).
		1117	.Sp
		1118	Although some watcher types do not have type-specific arguments
		1119	(e.g. \f(CW\(C`ev_prepare\(C'\fR) you still need to call its \f(CW\(C`set\(C'\fR macro.
		1120	.Sp
		1121	See \f(CW\(C`ev_init\(C'\fR, above, for an example.
		1122	.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
		1123	.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
		1124	.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
		1125	This convenience macro rolls both \f(CW\(C`ev_init\(C'\fR and \f(CW\(C`ev_TYPE_set\(C'\fR macro
		1126	calls into a single call. This is the most convenient method to initialise
		1127	a watcher. The same limitations apply, of course.
		1128	.Sp
		1129	Example: Initialise and set an \f(CW\(C`ev_io\(C'\fR watcher in one step.
		1130	.Sp
		1131	.Vb 1
		1132	\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1133	.Ve
		1134	.ie n .IP """ev_TYPE_start"" (loop , ev_TYPE watcher)" 4
		1135	.el .IP "\f(CWev_TYPE_start\fR (loop , ev_TYPE watcher)" 4
		1136	.IX Item "ev_TYPE_start (loop , ev_TYPE watcher)"
		1137	Starts (activates) the given watcher. Only active watchers will receive
		1138	events. If the watcher is already active nothing will happen.
		1139	.Sp
		1140	Example: Start the \f(CW\(C`ev_io\(C'\fR watcher that is being abused as example in this
		1141	whole section.
		1142	.Sp
		1143	.Vb 1
		1144	\& ev_io_start (EV_DEFAULT_UC, &w);
		1145	.Ve
		1146	.ie n .IP """ev_TYPE_stop"" (loop , ev_TYPE watcher)" 4
		1147	.el .IP "\f(CWev_TYPE_stop\fR (loop , ev_TYPE watcher)" 4
		1148	.IX Item "ev_TYPE_stop (loop , ev_TYPE watcher)"
		1149	Stops the given watcher if active, and clears the pending status (whether
		1150	the watcher was active or not).
		1151	.Sp
		1152	It is possible that stopped watchers are pending \- for example,
		1153	non-repeating timers are being stopped when they become pending \- but
		1154	calling \f(CW\(C`ev_TYPE_stop\(C'\fR ensures that the watcher is neither active nor
		1155	pending. If you want to free or reuse the memory used by the watcher it is
		1156	therefore a good idea to always call its \f(CW\(C`ev_TYPE_stop\(C'\fR function.
		1157	.IP "bool ev_is_active (ev_TYPE *watcher)" 4
		1158	.IX Item "bool ev_is_active (ev_TYPE *watcher)"
		1159	Returns a true value iff the watcher is active (i.e. it has been started
		1160	and not yet been stopped). As long as a watcher is active you must not modify
		1161	it.
		1162	.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
		1163	.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
		1164	Returns a true value iff the watcher is pending, (i.e. it has outstanding
		1165	events but its callback has not yet been invoked). As long as a watcher
		1166	is pending (but not active) you must not call an init function on it (but
		1167	\&\f(CW\(C`ev_TYPE_set\(C'\fR is safe), you must not change its priority, and you must
		1168	make sure the watcher is available to libev (e.g. you cannot \f(CW\(C`free ()\(C'\fR
		1169	it).
		1170	.IP "callback ev_cb (ev_TYPE *watcher)" 4
		1171	.IX Item "callback ev_cb (ev_TYPE *watcher)"
		1172	Returns the callback currently set on the watcher.
		1173	.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
		1174	.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
		1175	Change the callback. You can change the callback at virtually any time
		1176	(modulo threads).
		1177	.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
		1178	.IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
		1179	.PD 0
		1180	.IP "int ev_priority (ev_TYPE *watcher)" 4
		1181	.IX Item "int ev_priority (ev_TYPE *watcher)"
		1182	.PD
		1183	Set and query the priority of the watcher. The priority is a small
		1184	integer between \f(CW\(C`EV_MAXPRI\(C'\fR (default: \f(CW2\fR) and \f(CW\(C`EV_MINPRI\(C'\fR
		1185	(default: \f(CW\(C`\-2\(C'\fR). Pending watchers with higher priority will be invoked
		1186	before watchers with lower priority, but priority will not keep watchers
		1187	from being executed (except for \f(CW\(C`ev_idle\(C'\fR watchers).
		1188	.Sp
		1189	This means that priorities are \fIonly\fR used for ordering callback
		1190	invocation after new events have been received. This is useful, for
		1191	example, to reduce latency after idling, or more often, to bind two
		1192	watchers on the same event and make sure one is called first.
		1193	.Sp
		1194	If you need to suppress invocation when higher priority events are pending
		1195	you need to look at \f(CW\(C`ev_idle\(C'\fR watchers, which provide this functionality.
		1196	.Sp
		1197	You \fImust not\fR change the priority of a watcher as long as it is active or
		1198	pending.
		1199	.Sp
		1200	The default priority used by watchers when no priority has been set is
		1201	always \f(CW0\fR, which is supposed to not be too high and not be too low :).
		1202	.Sp
		1203	Setting a priority outside the range of \f(CW\(C`EV_MINPRI\(C'\fR to \f(CW\(C`EV_MAXPRI\(C'\fR is
		1204	fine, as long as you do not mind that the priority value you query might
		1205	or might not have been clamped to the valid range.
		1206	.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
		1207	.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
		1208	Invoke the \f(CW\(C`watcher\(C'\fR with the given \f(CW\(C`loop\(C'\fR and \f(CW\(C`revents\(C'\fR. Neither
		1209	\&\f(CW\(C`loop\(C'\fR nor \f(CW\(C`revents\(C'\fR need to be valid as long as the watcher callback
		1210	can deal with that fact, as both are simply passed through to the
		1211	callback.
		1212	.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
		1213	.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
		1214	If the watcher is pending, this function clears its pending status and
		1215	returns its \f(CW\(C`revents\(C'\fR bitset (as if its callback was invoked). If the
		1216	watcher isn't pending it does nothing and returns \f(CW0\fR.
		1217	.Sp
		1218	Sometimes it can be useful to \(L"poll\(R" a watcher instead of waiting for its
		1219	callback to be invoked, which can be accomplished with this function.
586	.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"	1220	.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
587	.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"	1221	.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
588	Each watcher has, by default, a member \f(CW\(C`void data\*(C'\fR that you can change	1222	Each watcher has, by default, a member \f(CW\(C`void data\*(C'\fR that you can change
589	and read at any time, libev will completely ignore it. This can be used	1223	and read at any time: libev will completely ignore it. This can be used
590	to associate arbitrary data with your watcher. If you need more data and	1224	to associate arbitrary data with your watcher. If you need more data and
591	don't want to allocate memory and store a pointer to it in that data	1225	don't want to allocate memory and store a pointer to it in that data
592	member, you can also \(L"subclass\(R" the watcher type and provide your own	1226	member, you can also \(L"subclass\(R" the watcher type and provide your own
593	data:	1227	data:
594	.PP	1228	.PP
595	.Vb 7	1229	.Vb 7
596	\& struct my_io	1230	\& struct my_io
597	\& {	1231	\& {
598	\& struct ev_io io;	1232	\& ev_io io;
599	\& int otherfd;	1233	\& int otherfd;
600	\& void *somedata;	1234	\& void *somedata;
601	\& struct whatever *mostinteresting;	1235	\& struct whatever *mostinteresting;
602	\& }	1236	\& };
		1237	\&
		1238	\& ...
		1239	\& struct my_io w;
		1240	\& ev_io_init (&w.io, my_cb, fd, EV_READ);
603	.Ve	1241	.Ve
604	.PP	1242	.PP
605	And since your callback will be called with a pointer to the watcher, you	1243	And since your callback will be called with a pointer to the watcher, you
606	can cast it back to your own type:	1244	can cast it back to your own type:
607	.PP	1245	.PP
608	.Vb 5	1246	.Vb 5
609	\& static void my_cb (struct ev_loop loop, struct ev_io w_, int revents)	1247	\& static void my_cb (struct ev_loop loop, ev_io w_, int revents)
610	\& {	1248	\& {
611	\& struct my_io w = (struct my_io )w_;	1249	\& struct my_io w = (struct my_io )w_;
612	\& ...	1250	\& ...
613	\& }	1251	\& }
614	.Ve	1252	.Ve
615	.PP	1253	.PP
616	More interesting and less C\-conformant ways of catsing your callback type	1254	More interesting and less C\-conformant ways of casting your callback type
617	have been omitted....	1255	instead have been omitted.
		1256	.PP
		1257	Another common scenario is to use some data structure with multiple
		1258	embedded watchers:
		1259	.PP
		1260	.Vb 6
		1261	\& struct my_biggy
		1262	\& {
		1263	\& int some_data;
		1264	\& ev_timer t1;
		1265	\& ev_timer t2;
		1266	\& }
		1267	.Ve
		1268	.PP
		1269	In this case getting the pointer to \f(CW\(C`my_biggy\(C'\fR is a bit more
		1270	complicated: Either you store the address of your \f(CW\(C`my_biggy\(C'\fR struct
		1271	in the \f(CW\(C`data\(C'\fR member of the watcher (for woozies), or you need to use
		1272	some pointer arithmetic using \f(CW\(C`offsetof\(C'\fR inside your watchers (for real
		1273	programmers):
		1274	.PP
		1275	.Vb 1
		1276	\& #include <stddef.h>
		1277	\&
		1278	\& static void
		1279	\& t1_cb (EV_P_ ev_timer *w, int revents)
		1280	\& {
		1281	\& struct my_biggy big = (struct my_biggy *
		1282	\& (((char *)w) \- offsetof (struct my_biggy, t1));
		1283	\& }
		1284	\&
		1285	\& static void
		1286	\& t2_cb (EV_P_ ev_timer *w, int revents)
		1287	\& {
		1288	\& struct my_biggy big = (struct my_biggy *
		1289	\& (((char *)w) \- offsetof (struct my_biggy, t2));
		1290	\& }
		1291	.Ve
618	.SH "WATCHER TYPES"	1292	.SH "WATCHER TYPES"
619	.IX Header "WATCHER TYPES"	1293	.IX Header "WATCHER TYPES"
620	This section describes each watcher in detail, but will not repeat	1294	This section describes each watcher in detail, but will not repeat
621	information given in the last section.	1295	information given in the last section. Any initialisation/set macros,
		1296	functions and members specific to the watcher type are explained.
		1297	.PP
		1298	Members are additionally marked with either \fI[read\-only]\fR, meaning that,
		1299	while the watcher is active, you can look at the member and expect some
		1300	sensible content, but you must not modify it (you can modify it while the
		1301	watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
		1302	means you can expect it to have some sensible content while the watcher
		1303	is active, but you can also modify it. Modifying it may not do something
		1304	sensible or take immediate effect (or do anything at all), but libev will
		1305	not crash or malfunction in any way.
622	.ie n .Sh """ev_io"" \- is this file descriptor readable or writable"	1306	.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
623	.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable"	1307	.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
624	.IX Subsection "ev_io - is this file descriptor readable or writable"	1308	.IX Subsection "ev_io - is this file descriptor readable or writable?"
625	I/O watchers check whether a file descriptor is readable or writable	1309	I/O watchers check whether a file descriptor is readable or writable
626	in each iteration of the event loop (This behaviour is called	1310	in each iteration of the event loop, or, more precisely, when reading
627	level-triggering because you keep receiving events as long as the	1311	would not block the process and writing would at least be able to write
628	condition persists. Remember you can stop the watcher if you don't want to	1312	some data. This behaviour is called level-triggering because you keep
629	act on the event and neither want to receive future events).	1313	receiving events as long as the condition persists. Remember you can stop
		1314	the watcher if you don't want to act on the event and neither want to
		1315	receive future events.
630	.PP	1316	.PP
631	In general you can register as many read and/or write event watchers per	1317	In general you can register as many read and/or write event watchers per
632	fd as you want (as long as you don't confuse yourself). Setting all file	1318	fd as you want (as long as you don't confuse yourself). Setting all file
633	descriptors to non-blocking mode is also usually a good idea (but not	1319	descriptors to non-blocking mode is also usually a good idea (but not
634	required if you know what you are doing).	1320	required if you know what you are doing).
635	.PP	1321	.PP
636	You have to be careful with dup'ed file descriptors, though. Some backends	1322	If you cannot use non-blocking mode, then force the use of a
637	(the linux epoll backend is a notable example) cannot handle dup'ed file	1323	known-to-be-good backend (at the time of this writing, this includes only
638	descriptors correctly if you register interest in two or more fds pointing	1324	\&\f(CW\(C`EVBACKEND_SELECT\(C'\fR and \f(CW\(C`EVBACKEND_POLL\(C'\fR).
639	to the same underlying file/socket etc. description (that is, they share
640	the same underlying \(L"file open\(R").
641	.PP	1325	.PP
642	If you must do this, then force the use of a known-to-be-good backend	1326	Another thing you have to watch out for is that it is quite easy to
643	(at the time of this writing, this includes only \f(CW\(C`EVBACKEND_SELECT\(C'\fR and	1327	receive \(L"spurious\(R" readiness notifications, that is your callback might
		1328	be called with \f(CW\(C`EV_READ\(C'\fR but a subsequent \f(CW\(C`read\(C'\fR(2) will actually block
		1329	because there is no data. Not only are some backends known to create a
		1330	lot of those (for example Solaris ports), it is very easy to get into
		1331	this situation even with a relatively standard program structure. Thus
		1332	it is best to always use non-blocking I/O: An extra \f(CW\(C`read\(C'\fR(2) returning
		1333	\&\f(CW\(C`EAGAIN\(C'\fR is far preferable to a program hanging until some data arrives.
		1334	.PP
		1335	If you cannot run the fd in non-blocking mode (for example you should
		1336	not play around with an Xlib connection), then you have to separately
		1337	re-test whether a file descriptor is really ready with a known-to-be good
		1338	interface such as poll (fortunately in our Xlib example, Xlib already
		1339	does this on its own, so its quite safe to use). Some people additionally
		1340	use \f(CW\(C`SIGALRM\(C'\fR and an interval timer, just to be sure you won't block
		1341	indefinitely.
		1342	.PP
		1343	But really, best use non-blocking mode.
		1344	.PP
		1345	\fIThe special problem of disappearing file descriptors\fR
		1346	.IX Subsection "The special problem of disappearing file descriptors"
		1347	.PP
		1348	Some backends (e.g. kqueue, epoll) need to be told about closing a file
		1349	descriptor (either due to calling \f(CW\(C`close\(C'\fR explicitly or any other means,
		1350	such as \f(CW\(C`dup2\(C'\fR). The reason is that you register interest in some file
		1351	descriptor, but when it goes away, the operating system will silently drop
		1352	this interest. If another file descriptor with the same number then is
		1353	registered with libev, there is no efficient way to see that this is, in
		1354	fact, a different file descriptor.
		1355	.PP
		1356	To avoid having to explicitly tell libev about such cases, libev follows
		1357	the following policy: Each time \f(CW\(C`ev_io_set\(C'\fR is being called, libev
		1358	will assume that this is potentially a new file descriptor, otherwise
		1359	it is assumed that the file descriptor stays the same. That means that
		1360	you \fIhave\fR to call \f(CW\(C`ev_io_set\(C'\fR (or \f(CW\(C`ev_io_init\(C'\fR) when you change the
		1361	descriptor even if the file descriptor number itself did not change.
		1362	.PP
		1363	This is how one would do it normally anyway, the important point is that
		1364	the libev application should not optimise around libev but should leave
		1365	optimisations to libev.
		1366	.PP
		1367	\fIThe special problem of dup'ed file descriptors\fR
		1368	.IX Subsection "The special problem of dup'ed file descriptors"
		1369	.PP
		1370	Some backends (e.g. epoll), cannot register events for file descriptors,
		1371	but only events for the underlying file descriptions. That means when you
		1372	have \f(CW\(C`dup ()\(C'\fR'ed file descriptors or weirder constellations, and register
		1373	events for them, only one file descriptor might actually receive events.
		1374	.PP
		1375	There is no workaround possible except not registering events
		1376	for potentially \f(CW\(C`dup ()\(C'\fR'ed file descriptors, or to resort to
		1377	\&\f(CW\(C`EVBACKEND_SELECT\(C'\fR or \f(CW\(C`EVBACKEND_POLL\(C'\fR.
		1378	.PP
		1379	\fIThe special problem of fork\fR
		1380	.IX Subsection "The special problem of fork"
		1381	.PP
		1382	Some backends (epoll, kqueue) do not support \f(CW\(C`fork ()\(C'\fR at all or exhibit
		1383	useless behaviour. Libev fully supports fork, but needs to be told about
		1384	it in the child.
		1385	.PP
		1386	To support fork in your programs, you either have to call
		1387	\&\f(CW\(C`ev_default_fork ()\(C'\fR or \f(CW\(C`ev_loop_fork ()\(C'\fR after a fork in the child,
		1388	enable \f(CW\(C`EVFLAG_FORKCHECK\(C'\fR, or resort to \f(CW\(C`EVBACKEND_SELECT\(C'\fR or
644	\&\f(CW\(C`EVBACKEND_POLL\(C'\fR).	1389	\&\f(CW\(C`EVBACKEND_POLL\(C'\fR.
		1390	.PP
		1391	\fIThe special problem of \s-1SIGPIPE\s0\fR
		1392	.IX Subsection "The special problem of SIGPIPE"
		1393	.PP
		1394	While not really specific to libev, it is easy to forget about \f(CW\(C`SIGPIPE\(C'\fR:
		1395	when writing to a pipe whose other end has been closed, your program gets
		1396	sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
		1397	this is sensible behaviour, for daemons, this is usually undesirable.
		1398	.PP
		1399	So when you encounter spurious, unexplained daemon exits, make sure you
		1400	ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
		1401	somewhere, as that would have given you a big clue).
		1402	.PP
		1403	\fIWatcher-Specific Functions\fR
		1404	.IX Subsection "Watcher-Specific Functions"
645	.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4	1405	.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
646	.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"	1406	.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
647	.PD 0	1407	.PD 0
648	.IP "ev_io_set (ev_io *, int fd, int events)" 4	1408	.IP "ev_io_set (ev_io *, int fd, int events)" 4
649	.IX Item "ev_io_set (ev_io *, int fd, int events)"	1409	.IX Item "ev_io_set (ev_io *, int fd, int events)"
650	.PD	1410	.PD
651	Configures an \f(CW\(C`ev_io\(C'\fR watcher. The fd is the file descriptor to rceeive	1411	Configures an \f(CW\(C`ev_io\(C'\fR watcher. The \f(CW\(C`fd\(C'\fR is the file descriptor to
652	events for and events is either \f(CW\(C`EV_READ\(C'\fR, \f(CW\(C`EV_WRITE\(C'\fR or \f(CW\*(C`EV_READ \|	1412	receive events for and \f(CW\(C`events\(C'\fR is either \f(CW\(C`EV_READ\(C'\fR, \f(CW\(C`EV_WRITE\(C'\fR or
653	EV_WRITE\*(C'\fR to receive the given events.	1413	\&\f(CW\(C`EV_READ \| EV_WRITE\(C'\fR, to express the desire to receive the given events.
654	.Sp	1414	.IP "int fd [read\-only]" 4
655	Please note that most of the more scalable backend mechanisms (for example	1415	.IX Item "int fd [read-only]"
656	epoll and solaris ports) can result in spurious readyness notifications	1416	The file descriptor being watched.
657	for file descriptors, so you practically need to use non-blocking I/O (and	1417	.IP "int events [read\-only]" 4
658	treat callback invocation as hint only), or retest separately with a safe	1418	.IX Item "int events [read-only]"
659	interface before doing I/O (XLib can do this), or force the use of either	1419	The events being watched.
660	\&\f(CW\(C`EVBACKEND_SELECT\(C'\fR or \f(CW\(C`EVBACKEND_POLL\(C'\fR, which don't suffer from this	1420	.PP
661	problem. Also note that it is quite easy to have your callback invoked	1421	\fIExamples\fR
662	when the readyness condition is no longer valid even when employing	1422	.IX Subsection "Examples"
663	typical ways of handling events, so its a good idea to use non-blocking	1423	.PP
664	I/O unconditionally.	1424	Example: Call \f(CW\(C`stdin_readable_cb\(C'\fR when \s-1STDIN_FILENO\s0 has become, well
		1425	readable, but only once. Since it is likely line-buffered, you could
		1426	attempt to read a whole line in the callback.
		1427	.PP
		1428	.Vb 6
		1429	\& static void
		1430	\& stdin_readable_cb (struct ev_loop loop, ev_io w, int revents)
		1431	\& {
		1432	\& ev_io_stop (loop, w);
		1433	\& .. read from stdin here (or from w\->fd) and handle any I/O errors
		1434	\& }
		1435	\&
		1436	\& ...
		1437	\& struct ev_loop *loop = ev_default_init (0);
		1438	\& ev_io stdin_readable;
		1439	\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
		1440	\& ev_io_start (loop, &stdin_readable);
		1441	\& ev_loop (loop, 0);
		1442	.Ve
665	.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts"	1443	.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
666	.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts"	1444	.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
667	.IX Subsection "ev_timer - relative and optionally recurring timeouts"	1445	.IX Subsection "ev_timer - relative and optionally repeating timeouts"
668	Timer watchers are simple relative timers that generate an event after a	1446	Timer watchers are simple relative timers that generate an event after a
669	given time, and optionally repeating in regular intervals after that.	1447	given time, and optionally repeating in regular intervals after that.
670	.PP	1448	.PP
671	The timers are based on real time, that is, if you register an event that	1449	The timers are based on real time, that is, if you register an event that
672	times out after an hour and you reset your system clock to last years	1450	times out after an hour and you reset your system clock to January last
673	time, it will still time out after (roughly) and hour. \(L"Roughly\(R" because	1451	year, it will still time out after (roughly) one hour. \(L"Roughly\(R" because
674	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1452	detecting time jumps is hard, and some inaccuracies are unavoidable (the
675	monotonic clock option helps a lot here).	1453	monotonic clock option helps a lot here).
		1454	.PP
		1455	The callback is guaranteed to be invoked only \fIafter\fR its timeout has
		1456	passed, but if multiple timers become ready during the same loop iteration
		1457	then order of execution is undefined.
		1458	.PP
		1459	\fIBe smart about timeouts\fR
		1460	.IX Subsection "Be smart about timeouts"
		1461	.PP
		1462	Many real-world problems involve some kind of timeout, usually for error
		1463	recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
		1464	you want to raise some error after a while.
		1465	.PP
		1466	What follows are some ways to handle this problem, from obvious and
		1467	inefficient to smart and efficient.
		1468	.PP
		1469	In the following, a 60 second activity timeout is assumed \- a timeout that
		1470	gets reset to 60 seconds each time there is activity (e.g. each time some
		1471	data or other life sign was received).
		1472	.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
		1473	.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
		1474	This is the most obvious, but not the most simple way: In the beginning,
		1475	start the watcher:
		1476	.Sp
		1477	.Vb 2
		1478	\& ev_timer_init (timer, callback, 60., 0.);
		1479	\& ev_timer_start (loop, timer);
		1480	.Ve
		1481	.Sp
		1482	Then, each time there is some activity, \f(CW\(C`ev_timer_stop\(C'\fR it, initialise it
		1483	and start it again:
		1484	.Sp
		1485	.Vb 3
		1486	\& ev_timer_stop (loop, timer);
		1487	\& ev_timer_set (timer, 60., 0.);
		1488	\& ev_timer_start (loop, timer);
		1489	.Ve
		1490	.Sp
		1491	This is relatively simple to implement, but means that each time there is
		1492	some activity, libev will first have to remove the timer from its internal
		1493	data structure and then add it again. Libev tries to be fast, but it's
		1494	still not a constant-time operation.
		1495	.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
		1496	.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
		1497	.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
		1498	This is the easiest way, and involves using \f(CW\(C`ev_timer_again\(C'\fR instead of
		1499	\&\f(CW\(C`ev_timer_start\(C'\fR.
		1500	.Sp
		1501	To implement this, configure an \f(CW\(C`ev_timer\(C'\fR with a \f(CW\(C`repeat\(C'\fR value
		1502	of \f(CW60\fR and then call \f(CW\(C`ev_timer_again\(C'\fR at start and each time you
		1503	successfully read or write some data. If you go into an idle state where
		1504	you do not expect data to travel on the socket, you can \f(CW\(C`ev_timer_stop\(C'\fR
		1505	the timer, and \f(CW\(C`ev_timer_again\(C'\fR will automatically restart it if need be.
		1506	.Sp
		1507	That means you can ignore both the \f(CW\(C`ev_timer_start\(C'\fR function and the
		1508	\&\f(CW\(C`after\(C'\fR argument to \f(CW\(C`ev_timer_set\(C'\fR, and only ever use the \f(CW\(C`repeat\(C'\fR
		1509	member and \f(CW\(C`ev_timer_again\(C'\fR.
		1510	.Sp
		1511	At start:
		1512	.Sp
		1513	.Vb 3
		1514	\& ev_timer_init (timer, callback);
		1515	\& timer\->repeat = 60.;
		1516	\& ev_timer_again (loop, timer);
		1517	.Ve
		1518	.Sp
		1519	Each time there is some activity:
		1520	.Sp
		1521	.Vb 1
		1522	\& ev_timer_again (loop, timer);
		1523	.Ve
		1524	.Sp
		1525	It is even possible to change the time-out on the fly, regardless of
		1526	whether the watcher is active or not:
		1527	.Sp
		1528	.Vb 2
		1529	\& timer\->repeat = 30.;
		1530	\& ev_timer_again (loop, timer);
		1531	.Ve
		1532	.Sp
		1533	This is slightly more efficient then stopping/starting the timer each time
		1534	you want to modify its timeout value, as libev does not have to completely
		1535	remove and re-insert the timer from/into its internal data structure.
		1536	.Sp
		1537	It is, however, even simpler than the \(L"obvious\(R" way to do it.
		1538	.IP "3. Let the timer time out, but then re-arm it as required." 4
		1539	.IX Item "3. Let the timer time out, but then re-arm it as required."
		1540	This method is more tricky, but usually most efficient: Most timeouts are
		1541	relatively long compared to the intervals between other activity \- in
		1542	our example, within 60 seconds, there are usually many I/O events with
		1543	associated activity resets.
		1544	.Sp
		1545	In this case, it would be more efficient to leave the \f(CW\(C`ev_timer\(C'\fR alone,
		1546	but remember the time of last activity, and check for a real timeout only
		1547	within the callback:
		1548	.Sp
		1549	.Vb 1
		1550	\& ev_tstamp last_activity; // time of last activity
		1551	\&
		1552	\& static void
		1553	\& callback (EV_P_ ev_timer *w, int revents)
		1554	\& {
		1555	\& ev_tstamp now = ev_now (EV_A);
		1556	\& ev_tstamp timeout = last_activity + 60.;
		1557	\&
		1558	\& // if last_activity + 60. is older than now, we did time out
		1559	\& if (timeout < now)
		1560	\& {
		1561	\& // timeout occured, take action
		1562	\& }
		1563	\& else
		1564	\& {
		1565	\& // callback was invoked, but there was some activity, re\-arm
		1566	\& // the watcher to fire in last_activity + 60, which is
		1567	\& // guaranteed to be in the future, so "again" is positive:
		1568	\& w\->repeat = timeout \- now;
		1569	\& ev_timer_again (EV_A_ w);
		1570	\& }
		1571	\& }
		1572	.Ve
		1573	.Sp
		1574	To summarise the callback: first calculate the real timeout (defined
		1575	as \(L"60 seconds after the last activity\(R"), then check if that time has
		1576	been reached, which means something \fIdid\fR, in fact, time out. Otherwise
		1577	the callback was invoked too early (\f(CW\(C`timeout\(C'\fR is in the future), so
		1578	re-schedule the timer to fire at that future time, to see if maybe we have
		1579	a timeout then.
		1580	.Sp
		1581	Note how \f(CW\(C`ev_timer_again\(C'\fR is used, taking advantage of the
		1582	\&\f(CW\(C`ev_timer_again\(C'\fR optimisation when the timer is already running.
		1583	.Sp
		1584	This scheme causes more callback invocations (about one every 60 seconds
		1585	minus half the average time between activity), but virtually no calls to
		1586	libev to change the timeout.
		1587	.Sp
		1588	To start the timer, simply initialise the watcher and set \f(CW\(C`last_activity\(C'\fR
		1589	to the current time (meaning we just have some activity :), then call the
		1590	callback, which will \(L"do the right thing\(R" and start the timer:
		1591	.Sp
		1592	.Vb 3
		1593	\& ev_timer_init (timer, callback);
		1594	\& last_activity = ev_now (loop);
		1595	\& callback (loop, timer, EV_TIMEOUT);
		1596	.Ve
		1597	.Sp
		1598	And when there is some activity, simply store the current time in
		1599	\&\f(CW\(C`last_activity\(C'\fR, no libev calls at all:
		1600	.Sp
		1601	.Vb 1
		1602	\& last_actiivty = ev_now (loop);
		1603	.Ve
		1604	.Sp
		1605	This technique is slightly more complex, but in most cases where the
		1606	time-out is unlikely to be triggered, much more efficient.
		1607	.Sp
		1608	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1609	callback :) \- just change the timeout and invoke the callback, which will
		1610	fix things for you.
		1611	.IP "4. Wee, just use a double-linked list for your timeouts." 4
		1612	.IX Item "4. Wee, just use a double-linked list for your timeouts."
		1613	If there is not one request, but many thousands (millions...), all
		1614	employing some kind of timeout with the same timeout value, then one can
		1615	do even better:
		1616	.Sp
		1617	When starting the timeout, calculate the timeout value and put the timeout
		1618	at the \fIend\fR of the list.
		1619	.Sp
		1620	Then use an \f(CW\(C`ev_timer\(C'\fR to fire when the timeout at the \fIbeginning\fR of
		1621	the list is expected to fire (for example, using the technique #3).
		1622	.Sp
		1623	When there is some activity, remove the timer from the list, recalculate
		1624	the timeout, append it to the end of the list again, and make sure to
		1625	update the \f(CW\(C`ev_timer\(C'\fR if it was taken from the beginning of the list.
		1626	.Sp
		1627	This way, one can manage an unlimited number of timeouts in O(1) time for
		1628	starting, stopping and updating the timers, at the expense of a major
		1629	complication, and having to use a constant timeout. The constant timeout
		1630	ensures that the list stays sorted.
		1631	.PP
		1632	So which method the best?
		1633	.PP
		1634	Method #2 is a simple no-brain-required solution that is adequate in most
		1635	situations. Method #3 requires a bit more thinking, but handles many cases
		1636	better, and isn't very complicated either. In most case, choosing either
		1637	one is fine, with #3 being better in typical situations.
		1638	.PP
		1639	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1640	rather complicated, but extremely efficient, something that really pays
		1641	off after the first million or so of active timers, i.e. it's usually
		1642	overkill :)
		1643	.PP
		1644	\fIThe special problem of time updates\fR
		1645	.IX Subsection "The special problem of time updates"
		1646	.PP
		1647	Establishing the current time is a costly operation (it usually takes at
		1648	least two system calls): \s-1EV\s0 therefore updates its idea of the current
		1649	time only before and after \f(CW\(C`ev_loop\(C'\fR collects new events, which causes a
		1650	growing difference between \f(CW\(C`ev_now ()\(C'\fR and \f(CW\(C`ev_time ()\(C'\fR when handling
		1651	lots of events in one iteration.
676	.PP	1652	.PP
677	The relative timeouts are calculated relative to the \f(CW\(C`ev_now ()\(C'\fR	1653	The relative timeouts are calculated relative to the \f(CW\(C`ev_now ()\(C'\fR
678	time. This is usually the right thing as this timestamp refers to the time	1654	time. This is usually the right thing as this timestamp refers to the time
679	of the event triggering whatever timeout you are modifying/starting. If	1655	of the event triggering whatever timeout you are modifying/starting. If
680	you suspect event processing to be delayed and you \fIneed\fR to base the timeout	1656	you suspect event processing to be delayed and you \fIneed\fR to base the
681	on the current time, use something like this to adjust for this:	1657	timeout on the current time, use something like this to adjust for this:
682	.PP	1658	.PP
683	.Vb 1	1659	.Vb 1
684	\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1660	\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
685	.Ve	1661	.Ve
686	.PP	1662	.PP
687	The callback is guarenteed to be invoked only when its timeout has passed,	1663	If the event loop is suspended for a long time, you can also force an
688	but if multiple timers become ready during the same loop iteration then	1664	update of the time returned by \f(CW\(C`ev_now ()\(C'\fR by calling \f(CW\*(C`ev_now_update
689	order of execution is undefined.	1665	()\*(C'\fR.
		1666	.PP
		1667	\fIWatcher-Specific Functions and Data Members\fR
		1668	.IX Subsection "Watcher-Specific Functions and Data Members"
690	.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4	1669	.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
691	.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"	1670	.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
692	.PD 0	1671	.PD 0
693	.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4	1672	.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
694	.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"	1673	.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
695	.PD	1674	.PD
696	Configure the timer to trigger after \f(CW\(C`after\(C'\fR seconds. If \f(CW\(C`repeat\(C'\fR is	1675	Configure the timer to trigger after \f(CW\(C`after\(C'\fR seconds. If \f(CW\(C`repeat\(C'\fR
697	\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the	1676	is \f(CW0.\fR, then it will automatically be stopped once the timeout is
698	timer will automatically be configured to trigger again \f(CW\(C`repeat\(C'\fR seconds	1677	reached. If it is positive, then the timer will automatically be
699	later, again, and again, until stopped manually.	1678	configured to trigger again \f(CW\(C`repeat\(C'\fR seconds later, again, and again,
		1679	until stopped manually.
700	.Sp	1680	.Sp
701	The timer itself will do a best-effort at avoiding drift, that is, if you	1681	The timer itself will do a best-effort at avoiding drift, that is, if
702	configure a timer to trigger every 10 seconds, then it will trigger at	1682	you configure a timer to trigger every 10 seconds, then it will normally
703	exactly 10 second intervals. If, however, your program cannot keep up with	1683	trigger at exactly 10 second intervals. If, however, your program cannot
704	the timer (because it takes longer than those 10 seconds to do stuff) the	1684	keep up with the timer (because it takes longer than those 10 seconds to
705	timer will not fire more than once per event loop iteration.	1685	do stuff) the timer will not fire more than once per event loop iteration.
706	.IP "ev_timer_again (loop)" 4	1686	.IP "ev_timer_again (loop, ev_timer *)" 4
707	.IX Item "ev_timer_again (loop)"	1687	.IX Item "ev_timer_again (loop, ev_timer *)"
708	This will act as if the timer timed out and restart it again if it is	1688	This will act as if the timer timed out and restart it again if it is
709	repeating. The exact semantics are:	1689	repeating. The exact semantics are:
710	.Sp	1690	.Sp
		1691	If the timer is pending, its pending status is cleared.
		1692	.Sp
711	If the timer is started but nonrepeating, stop it.	1693	If the timer is started but non-repeating, stop it (as if it timed out).
712	.Sp	1694	.Sp
713	If the timer is repeating, either start it if necessary (with the repeat	1695	If the timer is repeating, either start it if necessary (with the
714	value), or reset the running timer to the repeat value.	1696	\&\f(CW\(C`repeat\(C'\fR value), or reset the running timer to the \f(CW\(C`repeat\(C'\fR value.
715	.Sp	1697	.Sp
716	This sounds a bit complicated, but here is a useful and typical	1698	This sounds a bit complicated, see \(L"Be smart about timeouts\(R", above, for a
717	example: Imagine you have a tcp connection and you want a so-called idle	1699	usage example.
718	timeout, that is, you want to be called when there have been, say, 60	1700	.IP "ev_tstamp repeat [read\-write]" 4
719	seconds of inactivity on the socket. The easiest way to do this is to	1701	.IX Item "ev_tstamp repeat [read-write]"
720	configure an \f(CW\(C`ev_timer\(C'\fR with after=repeat=60 and calling ev_timer_again each	1702	The current \f(CW\(C`repeat\(C'\fR value. Will be used each time the watcher times out
721	time you successfully read or write some data. If you go into an idle	1703	or \f(CW\(C`ev_timer_again\(C'\fR is called, and determines the next timeout (if any),
722	state where you do not expect data to travel on the socket, you can stop	1704	which is also when any modifications are taken into account.
723	the timer, and again will automatically restart it if need be.	1705	.PP
		1706	\fIExamples\fR
		1707	.IX Subsection "Examples"
		1708	.PP
		1709	Example: Create a timer that fires after 60 seconds.
		1710	.PP
		1711	.Vb 5
		1712	\& static void
		1713	\& one_minute_cb (struct ev_loop loop, ev_timer w, int revents)
		1714	\& {
		1715	\& .. one minute over, w is actually stopped right here
		1716	\& }
		1717	\&
		1718	\& ev_timer mytimer;
		1719	\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
		1720	\& ev_timer_start (loop, &mytimer);
		1721	.Ve
		1722	.PP
		1723	Example: Create a timeout timer that times out after 10 seconds of
		1724	inactivity.
		1725	.PP
		1726	.Vb 5
		1727	\& static void
		1728	\& timeout_cb (struct ev_loop loop, ev_timer w, int revents)
		1729	\& {
		1730	\& .. ten seconds without any activity
		1731	\& }
		1732	\&
		1733	\& ev_timer mytimer;
		1734	\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
		1735	\& ev_timer_again (&mytimer); /* start timer */
		1736	\& ev_loop (loop, 0);
		1737	\&
		1738	\& // and in some piece of code that gets executed on any "activity":
		1739	\& // reset the timeout to start ticking again at 10 seconds
		1740	\& ev_timer_again (&mytimer);
		1741	.Ve
724	.ie n .Sh """ev_periodic"" \- to cron or not to cron"	1742	.ie n .Sh """ev_periodic"" \- to cron or not to cron?"
725	.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron"	1743	.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
726	.IX Subsection "ev_periodic - to cron or not to cron"	1744	.IX Subsection "ev_periodic - to cron or not to cron?"
727	Periodic watchers are also timers of a kind, but they are very versatile	1745	Periodic watchers are also timers of a kind, but they are very versatile
728	(and unfortunately a bit complex).	1746	(and unfortunately a bit complex).
729	.PP	1747	.PP
730	Unlike \f(CW\(C`ev_timer\(C'\fR's, they are not based on real time (or relative time)	1748	Unlike \f(CW\(C`ev_timer\(C'\fR's, they are not based on real time (or relative time)
731	but on wallclock time (absolute time). You can tell a periodic watcher	1749	but on wall clock time (absolute time). You can tell a periodic watcher
732	to trigger \(L"at\(R" some specific point in time. For example, if you tell a	1750	to trigger after some specific point in time. For example, if you tell a
733	periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()	1751	periodic watcher to trigger in 10 seconds (by specifying e.g. \f(CW\*(C`ev_now ()
734	+ 10.>) and then reset your system clock to the last year, then it will	1752	+ 10.\*(C'\fR, that is, an absolute time not a delay) and then reset your system
		1753	clock to January of the previous year, then it will take more than year
735	take a year to trigger the event (unlike an \f(CW\(C`ev_timer\(C'\fR, which would trigger	1754	to trigger the event (unlike an \f(CW\(C`ev_timer\(C'\fR, which would still trigger
736	roughly 10 seconds later and of course not if you reset your system time	1755	roughly 10 seconds later as it uses a relative timeout).
737	again).
738	.PP	1756	.PP
739	They can also be used to implement vastly more complex timers, such as	1757	\&\f(CW\(C`ev_periodic\(C'\fRs can also be used to implement vastly more complex timers,
740	triggering an event on eahc midnight, local time.	1758	such as triggering an event on each \(L"midnight, local time\(R", or other
		1759	complicated rules.
741	.PP	1760	.PP
742	As with timers, the callback is guarenteed to be invoked only when the	1761	As with timers, the callback is guaranteed to be invoked only when the
743	time (\f(CW\(C`at\(C'\fR) has been passed, but if multiple periodic timers become ready	1762	time (\f(CW\(C`at\(C'\fR) has passed, but if multiple periodic timers become ready
744	during the same loop iteration then order of execution is undefined.	1763	during the same loop iteration, then order of execution is undefined.
		1764	.PP
		1765	\fIWatcher-Specific Functions and Data Members\fR
		1766	.IX Subsection "Watcher-Specific Functions and Data Members"
745	.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4	1767	.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
746	.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"	1768	.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
747	.PD 0	1769	.PD 0
748	.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4	1770	.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
749	.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"	1771	.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
750	.PD	1772	.PD
751	Lots of arguments, lets sort it out... There are basically three modes of	1773	Lots of arguments, lets sort it out... There are basically three modes of
752	operation, and we will explain them from simplest to complex:	1774	operation, and we will explain them from simplest to most complex:
753	.RS 4	1775	.RS 4
		1776	.IP "\(bu" 4
754	.IP "* absolute timer (interval = reschedule_cb = 0)" 4	1777	absolute timer (at = time, interval = reschedule_cb = 0)
755	.IX Item "absolute timer (interval = reschedule_cb = 0)"	1778	.Sp
756	In this configuration the watcher triggers an event at the wallclock time	1779	In this configuration the watcher triggers an event after the wall clock
757	\&\f(CW\(C`at\(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,	1780	time \f(CW\(C`at\(C'\fR has passed. It will not repeat and will not adjust when a time
758	that is, if it is to be run at January 1st 2011 then it will run when the	1781	jump occurs, that is, if it is to be run at January 1st 2011 then it will
759	system time reaches or surpasses this time.	1782	only run when the system clock reaches or surpasses this time.
		1783	.IP "\(bu" 4
760	.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4	1784	repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
761	.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)"	1785	.Sp
762	In this mode the watcher will always be scheduled to time out at the next	1786	In this mode the watcher will always be scheduled to time out at the next
763	\&\f(CW\(C`at + N interval\*(C'\fR time (for some integer N) and then repeat, regardless	1787	\&\f(CW\(C`at + N interval\*(C'\fR time (for some integer N, which can also be negative)
764	of any time jumps.	1788	and then repeat, regardless of any time jumps.
765	.Sp	1789	.Sp
766	This can be used to create timers that do not drift with respect to system	1790	This can be used to create timers that do not drift with respect to the
767	time:	1791	system clock, for example, here is a \f(CW\(C`ev_periodic\(C'\fR that triggers each
		1792	hour, on the hour:
768	.Sp	1793	.Sp
769	.Vb 1	1794	.Vb 1
770	\& ev_periodic_set (&periodic, 0., 3600., 0);	1795	\& ev_periodic_set (&periodic, 0., 3600., 0);
771	.Ve	1796	.Ve
772	.Sp	1797	.Sp
773	This doesn't mean there will always be 3600 seconds in between triggers,	1798	This doesn't mean there will always be 3600 seconds in between triggers,
774	but only that the the callback will be called when the system time shows a	1799	but only that the callback will be called when the system time shows a
775	full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible	1800	full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
776	by 3600.	1801	by 3600.
777	.Sp	1802	.Sp
778	Another way to think about it (for the mathematically inclined) is that	1803	Another way to think about it (for the mathematically inclined) is that
779	\&\f(CW\(C`ev_periodic\(C'\fR will try to run the callback in this mode at the next possible	1804	\&\f(CW\(C`ev_periodic\(C'\fR will try to run the callback in this mode at the next possible
780	time where \f(CW\(C`time = at (mod interval)\(C'\fR, regardless of any time jumps.	1805	time where \f(CW\(C`time = at (mod interval)\(C'\fR, regardless of any time jumps.
781	.IP "* manual reschedule mode (reschedule_cb = callback)" 4	1806	.Sp
782	.IX Item "manual reschedule mode (reschedule_cb = callback)"	1807	For numerical stability it is preferable that the \f(CW\(C`at\(C'\fR value is near
		1808	\&\f(CW\(C`ev_now ()\(C'\fR (the current time), but there is no range requirement for
		1809	this value, and in fact is often specified as zero.
		1810	.Sp
		1811	Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
		1812	speed for example), so if \f(CW\(C`interval\(C'\fR is very small then timing stability
		1813	will of course deteriorate. Libev itself tries to be exact to be about one
		1814	millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
		1815	.IP "\(bu" 4
		1816	manual reschedule mode (at and interval ignored, reschedule_cb = callback)
		1817	.Sp
783	In this mode the values for \f(CW\(C`interval\(C'\fR and \f(CW\(C`at\(C'\fR are both being	1818	In this mode the values for \f(CW\(C`interval\(C'\fR and \f(CW\(C`at\(C'\fR are both being
784	ignored. Instead, each time the periodic watcher gets scheduled, the	1819	ignored. Instead, each time the periodic watcher gets scheduled, the
785	reschedule callback will be called with the watcher as first, and the	1820	reschedule callback will be called with the watcher as first, and the
786	current time as second argument.	1821	current time as second argument.
787	.Sp	1822	.Sp
788	\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,	1823	\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
789	ever, or make any event loop modifications\fR. If you need to stop it,	1824	ever, or make \s-1ANY\s0 event loop modifications whatsoever\fR.
790	return \f(CW\(C`now + 1e30\(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
791	starting a prepare watcher).
792	.Sp	1825	.Sp
		1826	If you need to stop it, return \f(CW\(C`now + 1e30\(C'\fR (or so, fudge fudge) and stop
		1827	it afterwards (e.g. by starting an \f(CW\(C`ev_prepare\(C'\fR watcher, which is the
		1828	only event loop modification you are allowed to do).
		1829	.Sp
793	Its prototype is \f(CW\(C`ev_tstamp (reschedule_cb)(struct ev_periodic *w,	1830	The callback prototype is \f(CW\(C`ev_tstamp (reschedule_cb)(ev_periodic
794	ev_tstamp now)\*(C'\fR, e.g.:	1831	w, ev_tstamp now)\(C'\fR, e.g.:
795	.Sp	1832	.Sp
796	.Vb 4	1833	.Vb 5
		1834	\& static ev_tstamp
797	\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1835	\& my_rescheduler (ev_periodic *w, ev_tstamp now)
798	\& {	1836	\& {
799	\& return now + 60.;	1837	\& return now + 60.;
800	\& }	1838	\& }
801	.Ve	1839	.Ve
802	.Sp	1840	.Sp
803	It must return the next time to trigger, based on the passed time value	1841	It must return the next time to trigger, based on the passed time value
804	(that is, the lowest time value larger than to the second argument). It	1842	(that is, the lowest time value larger than to the second argument). It
805	will usually be called just before the callback will be triggered, but	1843	will usually be called just before the callback will be triggered, but
806	might be called at other times, too.	1844	might be called at other times, too.
807	.Sp	1845	.Sp
808	\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the	1846	\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
809	passed \f(CI\(C`now\(C'\fI value\fR. Not even \f(CW\(C`now\(C'\fR itself will do, it \fImust\fR be larger.	1847	equal to the passed \f(CI\(C`now\(C'\fI value\fR.
810	.Sp	1848	.Sp
811	This can be used to create very complex timers, such as a timer that	1849	This can be used to create very complex timers, such as a timer that
812	triggers on each midnight, local time. To do this, you would calculate the	1850	triggers on \(L"next midnight, local time\(R". To do this, you would calculate the
813	next midnight after \f(CW\(C`now\(C'\fR and return the timestamp value for this. How	1851	next midnight after \f(CW\(C`now\(C'\fR and return the timestamp value for this. How
814	you do this is, again, up to you (but it is not trivial, which is the main	1852	you do this is, again, up to you (but it is not trivial, which is the main
815	reason I omitted it as an example).	1853	reason I omitted it as an example).
816	.RE	1854	.RE
817	.RS 4	1855	.RS 4
…		…
820	.IX Item "ev_periodic_again (loop, ev_periodic *)"	1858	.IX Item "ev_periodic_again (loop, ev_periodic *)"
821	Simply stops and restarts the periodic watcher again. This is only useful	1859	Simply stops and restarts the periodic watcher again. This is only useful
822	when you changed some parameters or the reschedule callback would return	1860	when you changed some parameters or the reschedule callback would return
823	a different time than the last time it was called (e.g. in a crond like	1861	a different time than the last time it was called (e.g. in a crond like
824	program when the crontabs have changed).	1862	program when the crontabs have changed).
		1863	.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
		1864	.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
		1865	When active, returns the absolute time that the watcher is supposed to
		1866	trigger next.
		1867	.IP "ev_tstamp offset [read\-write]" 4
		1868	.IX Item "ev_tstamp offset [read-write]"
		1869	When repeating, this contains the offset value, otherwise this is the
		1870	absolute point in time (the \f(CW\(C`at\(C'\fR value passed to \f(CW\(C`ev_periodic_set\(C'\fR).
		1871	.Sp
		1872	Can be modified any time, but changes only take effect when the periodic
		1873	timer fires or \f(CW\(C`ev_periodic_again\(C'\fR is being called.
		1874	.IP "ev_tstamp interval [read\-write]" 4
		1875	.IX Item "ev_tstamp interval [read-write]"
		1876	The current interval value. Can be modified any time, but changes only
		1877	take effect when the periodic timer fires or \f(CW\(C`ev_periodic_again\(C'\fR is being
		1878	called.
		1879	.IP "ev_tstamp (reschedule_cb)(ev_periodic w, ev_tstamp now) [read\-write]" 4
		1880	.IX Item "ev_tstamp (reschedule_cb)(ev_periodic w, ev_tstamp now) [read-write]"
		1881	The current reschedule callback, or \f(CW0\fR, if this functionality is
		1882	switched off. Can be changed any time, but changes only take effect when
		1883	the periodic timer fires or \f(CW\(C`ev_periodic_again\(C'\fR is being called.
		1884	.PP
		1885	\fIExamples\fR
		1886	.IX Subsection "Examples"
		1887	.PP
		1888	Example: Call a callback every hour, or, more precisely, whenever the
		1889	system time is divisible by 3600. The callback invocation times have
		1890	potentially a lot of jitter, but good long-term stability.
		1891	.PP
		1892	.Vb 5
		1893	\& static void
		1894	\& clock_cb (struct ev_loop loop, ev_io w, int revents)
		1895	\& {
		1896	\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
		1897	\& }
		1898	\&
		1899	\& ev_periodic hourly_tick;
		1900	\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
		1901	\& ev_periodic_start (loop, &hourly_tick);
		1902	.Ve
		1903	.PP
		1904	Example: The same as above, but use a reschedule callback to do it:
		1905	.PP
		1906	.Vb 1
		1907	\& #include <math.h>
		1908	\&
		1909	\& static ev_tstamp
		1910	\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
		1911	\& {
		1912	\& return now + (3600. \- fmod (now, 3600.));
		1913	\& }
		1914	\&
		1915	\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
		1916	.Ve
		1917	.PP
		1918	Example: Call a callback every hour, starting now:
		1919	.PP
		1920	.Vb 4
		1921	\& ev_periodic hourly_tick;
		1922	\& ev_periodic_init (&hourly_tick, clock_cb,
		1923	\& fmod (ev_now (loop), 3600.), 3600., 0);
		1924	\& ev_periodic_start (loop, &hourly_tick);
		1925	.Ve
825	.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled"	1926	.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
826	.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled"	1927	.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
827	.IX Subsection "ev_signal - signal me when a signal gets signalled"	1928	.IX Subsection "ev_signal - signal me when a signal gets signalled!"
828	Signal watchers will trigger an event when the process receives a specific	1929	Signal watchers will trigger an event when the process receives a specific
829	signal one or more times. Even though signals are very asynchronous, libev	1930	signal one or more times. Even though signals are very asynchronous, libev
830	will try it's best to deliver signals synchronously, i.e. as part of the	1931	will try it's best to deliver signals synchronously, i.e. as part of the
831	normal event processing, like any other event.	1932	normal event processing, like any other event.
832	.PP	1933	.PP
		1934	If you want signals asynchronously, just use \f(CW\(C`sigaction\(C'\fR as you would
		1935	do without libev and forget about sharing the signal. You can even use
		1936	\&\f(CW\(C`ev_async\(C'\fR from a signal handler to synchronously wake up an event loop.
		1937	.PP
833	You can configure as many watchers as you like per signal. Only when the	1938	You can configure as many watchers as you like per signal. Only when the
834	first watcher gets started will libev actually register a signal watcher	1939	first watcher gets started will libev actually register a signal handler
835	with the kernel (thus it coexists with your own signal handlers as long	1940	with the kernel (thus it coexists with your own signal handlers as long as
836	as you don't register any with libev). Similarly, when the last signal	1941	you don't register any with libev for the same signal). Similarly, when
837	watcher for a signal is stopped libev will reset the signal handler to	1942	the last signal watcher for a signal is stopped, libev will reset the
838	\&\s-1SIG_DFL\s0 (regardless of what it was set to before).	1943	signal handler to \s-1SIG_DFL\s0 (regardless of what it was set to before).
		1944	.PP
		1945	If possible and supported, libev will install its handlers with
		1946	\&\f(CW\(C`SA_RESTART\(C'\fR behaviour enabled, so system calls should not be unduly
		1947	interrupted. If you have a problem with system calls getting interrupted by
		1948	signals you can block all signals in an \f(CW\(C`ev_check\(C'\fR watcher and unblock
		1949	them in an \f(CW\(C`ev_prepare\(C'\fR watcher.
		1950	.PP
		1951	\fIWatcher-Specific Functions and Data Members\fR
		1952	.IX Subsection "Watcher-Specific Functions and Data Members"
839	.IP "ev_signal_init (ev_signal *, callback, int signum)" 4	1953	.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
840	.IX Item "ev_signal_init (ev_signal *, callback, int signum)"	1954	.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
841	.PD 0	1955	.PD 0
842	.IP "ev_signal_set (ev_signal *, int signum)" 4	1956	.IP "ev_signal_set (ev_signal *, int signum)" 4
843	.IX Item "ev_signal_set (ev_signal *, int signum)"	1957	.IX Item "ev_signal_set (ev_signal *, int signum)"
844	.PD	1958	.PD
845	Configures the watcher to trigger on the given signal number (usually one	1959	Configures the watcher to trigger on the given signal number (usually one
846	of the \f(CW\(C`SIGxxx\(C'\fR constants).	1960	of the \f(CW\(C`SIGxxx\(C'\fR constants).
		1961	.IP "int signum [read\-only]" 4
		1962	.IX Item "int signum [read-only]"
		1963	The signal the watcher watches out for.
		1964	.PP
		1965	\fIExamples\fR
		1966	.IX Subsection "Examples"
		1967	.PP
		1968	Example: Try to exit cleanly on \s-1SIGINT\s0.
		1969	.PP
		1970	.Vb 5
		1971	\& static void
		1972	\& sigint_cb (struct ev_loop loop, ev_signal w, int revents)
		1973	\& {
		1974	\& ev_unloop (loop, EVUNLOOP_ALL);
		1975	\& }
		1976	\&
		1977	\& ev_signal signal_watcher;
		1978	\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1979	\& ev_signal_start (loop, &signal_watcher);
		1980	.Ve
847	.ie n .Sh """ev_child"" \- wait for pid status changes"	1981	.ie n .Sh """ev_child"" \- watch out for process status changes"
848	.el .Sh "\f(CWev_child\fP \- wait for pid status changes"	1982	.el .Sh "\f(CWev_child\fP \- watch out for process status changes"
849	.IX Subsection "ev_child - wait for pid status changes"	1983	.IX Subsection "ev_child - watch out for process status changes"
850	Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to	1984	Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
851	some child status changes (most typically when a child of yours dies).	1985	some child status changes (most typically when a child of yours dies or
		1986	exits). It is permissible to install a child watcher \fIafter\fR the child
		1987	has been forked (which implies it might have already exited), as long
		1988	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1989	forking and then immediately registering a watcher for the child is fine,
		1990	but forking and registering a watcher a few event loop iterations later is
		1991	not.
		1992	.PP
		1993	Only the default event loop is capable of handling signals, and therefore
		1994	you can only register child watchers in the default event loop.
		1995	.PP
		1996	\fIProcess Interaction\fR
		1997	.IX Subsection "Process Interaction"
		1998	.PP
		1999	Libev grabs \f(CW\(C`SIGCHLD\(C'\fR as soon as the default event loop is
		2000	initialised. This is necessary to guarantee proper behaviour even if
		2001	the first child watcher is started after the child exits. The occurrence
		2002	of \f(CW\(C`SIGCHLD\(C'\fR is recorded asynchronously, but child reaping is done
		2003	synchronously as part of the event loop processing. Libev always reaps all
		2004	children, even ones not watched.
		2005	.PP
		2006	\fIOverriding the Built-In Processing\fR
		2007	.IX Subsection "Overriding the Built-In Processing"
		2008	.PP
		2009	Libev offers no special support for overriding the built-in child
		2010	processing, but if your application collides with libev's default child
		2011	handler, you can override it easily by installing your own handler for
		2012	\&\f(CW\(C`SIGCHLD\(C'\fR after initialising the default loop, and making sure the
		2013	default loop never gets destroyed. You are encouraged, however, to use an
		2014	event-based approach to child reaping and thus use libev's support for
		2015	that, so other libev users can use \f(CW\(C`ev_child\(C'\fR watchers freely.
		2016	.PP
		2017	\fIStopping the Child Watcher\fR
		2018	.IX Subsection "Stopping the Child Watcher"
		2019	.PP
		2020	Currently, the child watcher never gets stopped, even when the
		2021	child terminates, so normally one needs to stop the watcher in the
		2022	callback. Future versions of libev might stop the watcher automatically
		2023	when a child exit is detected.
		2024	.PP
		2025	\fIWatcher-Specific Functions and Data Members\fR
		2026	.IX Subsection "Watcher-Specific Functions and Data Members"
852	.IP "ev_child_init (ev_child *, callback, int pid)" 4	2027	.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
853	.IX Item "ev_child_init (ev_child *, callback, int pid)"	2028	.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
854	.PD 0	2029	.PD 0
855	.IP "ev_child_set (ev_child *, int pid)" 4	2030	.IP "ev_child_set (ev_child *, int pid, int trace)" 4
856	.IX Item "ev_child_set (ev_child *, int pid)"	2031	.IX Item "ev_child_set (ev_child *, int pid, int trace)"
857	.PD	2032	.PD
858	Configures the watcher to wait for status changes of process \f(CW\(C`pid\(C'\fR (or	2033	Configures the watcher to wait for status changes of process \f(CW\(C`pid\(C'\fR (or
859	\&\fIany\fR process if \f(CW\(C`pid\(C'\fR is specified as \f(CW0\fR). The callback can look	2034	\&\fIany\fR process if \f(CW\(C`pid\(C'\fR is specified as \f(CW0\fR). The callback can look
860	at the \f(CW\(C`rstatus\(C'\fR member of the \f(CW\(C`ev_child\(C'\fR watcher structure to see	2035	at the \f(CW\(C`rstatus\(C'\fR member of the \f(CW\(C`ev_child\(C'\fR watcher structure to see
861	the status word (use the macros from \f(CW\(C`sys/wait.h\(C'\fR and see your systems	2036	the status word (use the macros from \f(CW\(C`sys/wait.h\(C'\fR and see your systems
862	\&\f(CW\(C`waitpid\(C'\fR documentation). The \f(CW\(C`rpid\(C'\fR member contains the pid of the	2037	\&\f(CW\(C`waitpid\(C'\fR documentation). The \f(CW\(C`rpid\(C'\fR member contains the pid of the
863	process causing the status change.	2038	process causing the status change. \f(CW\(C`trace\(C'\fR must be either \f(CW0\fR (only
		2039	activate the watcher when the process terminates) or \f(CW1\fR (additionally
		2040	activate the watcher when the process is stopped or continued).
		2041	.IP "int pid [read\-only]" 4
		2042	.IX Item "int pid [read-only]"
		2043	The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
		2044	.IP "int rpid [read\-write]" 4
		2045	.IX Item "int rpid [read-write]"
		2046	The process id that detected a status change.
		2047	.IP "int rstatus [read\-write]" 4
		2048	.IX Item "int rstatus [read-write]"
		2049	The process exit/trace status caused by \f(CW\(C`rpid\(C'\fR (see your systems
		2050	\&\f(CW\(C`waitpid\(C'\fR and \f(CW\(C`sys/wait.h\(C'\fR documentation for details).
		2051	.PP
		2052	\fIExamples\fR
		2053	.IX Subsection "Examples"
		2054	.PP
		2055	Example: \f(CW\(C`fork()\(C'\fR a new process and install a child handler to wait for
		2056	its completion.
		2057	.PP
		2058	.Vb 1
		2059	\& ev_child cw;
		2060	\&
		2061	\& static void
		2062	\& child_cb (EV_P_ ev_child *w, int revents)
		2063	\& {
		2064	\& ev_child_stop (EV_A_ w);
		2065	\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
		2066	\& }
		2067	\&
		2068	\& pid_t pid = fork ();
		2069	\&
		2070	\& if (pid < 0)
		2071	\& // error
		2072	\& else if (pid == 0)
		2073	\& {
		2074	\& // the forked child executes here
		2075	\& exit (1);
		2076	\& }
		2077	\& else
		2078	\& {
		2079	\& ev_child_init (&cw, child_cb, pid, 0);
		2080	\& ev_child_start (EV_DEFAULT_ &cw);
		2081	\& }
		2082	.Ve
		2083	.ie n .Sh """ev_stat"" \- did the file attributes just change?"
		2084	.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
		2085	.IX Subsection "ev_stat - did the file attributes just change?"
		2086	This watches a file system path for attribute changes. That is, it calls
		2087	\&\f(CW\(C`stat\(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
		2088	and sees if it changed compared to the last time, invoking the callback if
		2089	it did.
		2090	.PP
		2091	The path does not need to exist: changing from \(L"path exists\(R" to \*(L"path does
		2092	not exist\(R" is a status change like any other. The condition \(L"path does not
		2093	exist\(R" (or more correctly \(L"path cannot be stat'ed\*(R") is signified by the
		2094	\&\f(CW\(C`st_nlink\(C'\fR field being zero (which is otherwise always forced to be at
		2095	least one) and all the other fields of the stat buffer having unspecified
		2096	contents.
		2097	.PP
		2098	The path \fImust not\fR end in a slash or contain special components such as
		2099	\&\f(CW\(C`.\(C'\fR or \f(CW\(C`..\(C'\fR. The path \fIshould\fR be absolute: If it is relative and
		2100	your working directory changes, then the behaviour is undefined.
		2101	.PP
		2102	Since there is no portable change notification interface available, the
		2103	portable implementation simply calls \f(CWstat(2)\fR regularly on the path
		2104	to see if it changed somehow. You can specify a recommended polling
		2105	interval for this case. If you specify a polling interval of \f(CW0\fR (highly
		2106	recommended!) then a \fIsuitable, unspecified default\fR value will be used
		2107	(which you can expect to be around five seconds, although this might
		2108	change dynamically). Libev will also impose a minimum interval which is
		2109	currently around \f(CW0.1\fR, but that's usually overkill.
		2110	.PP
		2111	This watcher type is not meant for massive numbers of stat watchers,
		2112	as even with OS-supported change notifications, this can be
		2113	resource-intensive.
		2114	.PP
		2115	At the time of this writing, the only OS-specific interface implemented
		2116	is the Linux inotify interface (implementing kqueue support is left as an
		2117	exercise for the reader. Note, however, that the author sees no way of
		2118	implementing \f(CW\(C`ev_stat\(C'\fR semantics with kqueue, except as a hint).
		2119	.PP
		2120	\fI\s-1ABI\s0 Issues (Largefile Support)\fR
		2121	.IX Subsection "ABI Issues (Largefile Support)"
		2122	.PP
		2123	Libev by default (unless the user overrides this) uses the default
		2124	compilation environment, which means that on systems with large file
		2125	support disabled by default, you get the 32 bit version of the stat
		2126	structure. When using the library from programs that change the \s-1ABI\s0 to
		2127	use 64 bit file offsets the programs will fail. In that case you have to
		2128	compile libev with the same flags to get binary compatibility. This is
		2129	obviously the case with any flags that change the \s-1ABI\s0, but the problem is
		2130	most noticeably displayed with ev_stat and large file support.
		2131	.PP
		2132	The solution for this is to lobby your distribution maker to make large
		2133	file interfaces available by default (as e.g. FreeBSD does) and not
		2134	optional. Libev cannot simply switch on large file support because it has
		2135	to exchange stat structures with application programs compiled using the
		2136	default compilation environment.
		2137	.PP
		2138	\fIInotify and Kqueue\fR
		2139	.IX Subsection "Inotify and Kqueue"
		2140	.PP
		2141	When \f(CW\(C`inotify (7)\(C'\fR support has been compiled into libev and present at
		2142	runtime, it will be used to speed up change detection where possible. The
		2143	inotify descriptor will be created lazily when the first \f(CW\(C`ev_stat\(C'\fR
		2144	watcher is being started.
		2145	.PP
		2146	Inotify presence does not change the semantics of \f(CW\(C`ev_stat\(C'\fR watchers
		2147	except that changes might be detected earlier, and in some cases, to avoid
		2148	making regular \f(CW\(C`stat\(C'\fR calls. Even in the presence of inotify support
		2149	there are many cases where libev has to resort to regular \f(CW\(C`stat\(C'\fR polling,
		2150	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2151	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2152	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2153	xfs are fully working) libev usually gets away without polling.
		2154	.PP
		2155	There is no support for kqueue, as apparently it cannot be used to
		2156	implement this functionality, due to the requirement of having a file
		2157	descriptor open on the object at all times, and detecting renames, unlinks
		2158	etc. is difficult.
		2159	.PP
		2160	\fI\f(CI\(C`stat ()\(C'\fI is a synchronous operation\fR
		2161	.IX Subsection "stat () is a synchronous operation"
		2162	.PP
		2163	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2164	the process. The exception are \f(CW\(C`ev_stat\(C'\fR watchers \- those call \f(CW\*(C`stat
		2165	()\*(C'\fR, which is a synchronous operation.
		2166	.PP
		2167	For local paths, this usually doesn't matter: unless the system is very
		2168	busy or the intervals between stat's are large, a stat call will be fast,
		2169	as the path data is suually in memory already (except when starting the
		2170	watcher).
		2171	.PP
		2172	For networked file systems, calling \f(CW\(C`stat ()\(C'\fR can block an indefinite
		2173	time due to network issues, and even under good conditions, a stat call
		2174	often takes multiple milliseconds.
		2175	.PP
		2176	Therefore, it is best to avoid using \f(CW\(C`ev_stat\(C'\fR watchers on networked
		2177	paths, although this is fully supported by libev.
		2178	.PP
		2179	\fIThe special problem of stat time resolution\fR
		2180	.IX Subsection "The special problem of stat time resolution"
		2181	.PP
		2182	The \f(CW\(C`stat ()\(C'\fR system call only supports full-second resolution portably,
		2183	and even on systems where the resolution is higher, most file systems
		2184	still only support whole seconds.
		2185	.PP
		2186	That means that, if the time is the only thing that changes, you can
		2187	easily miss updates: on the first update, \f(CW\(C`ev_stat\(C'\fR detects a change and
		2188	calls your callback, which does something. When there is another update
		2189	within the same second, \f(CW\(C`ev_stat\(C'\fR will be unable to detect unless the
		2190	stat data does change in other ways (e.g. file size).
		2191	.PP
		2192	The solution to this is to delay acting on a change for slightly more
		2193	than a second (or till slightly after the next full second boundary), using
		2194	a roughly one-second-delay \f(CW\(C`ev_timer\(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
		2195	ev_timer_again (loop, w)\*(C'\fR).
		2196	.PP
		2197	The \f(CW.02\fR offset is added to work around small timing inconsistencies
		2198	of some operating systems (where the second counter of the current time
		2199	might be be delayed. One such system is the Linux kernel, where a call to
		2200	\&\f(CW\(C`gettimeofday\(C'\fR might return a timestamp with a full second later than
		2201	a subsequent \f(CW\(C`time\(C'\fR call \- if the equivalent of \f(CW\(C`time ()\(C'\fR is used to
		2202	update file times then there will be a small window where the kernel uses
		2203	the previous second to update file times but libev might already execute
		2204	the timer callback).
		2205	.PP
		2206	\fIWatcher-Specific Functions and Data Members\fR
		2207	.IX Subsection "Watcher-Specific Functions and Data Members"
		2208	.IP "ev_stat_init (ev_stat , callback, const char path, ev_tstamp interval)" 4
		2209	.IX Item "ev_stat_init (ev_stat , callback, const char path, ev_tstamp interval)"
		2210	.PD 0
		2211	.IP "ev_stat_set (ev_stat , const char path, ev_tstamp interval)" 4
		2212	.IX Item "ev_stat_set (ev_stat , const char path, ev_tstamp interval)"
		2213	.PD
		2214	Configures the watcher to wait for status changes of the given
		2215	\&\f(CW\(C`path\(C'\fR. The \f(CW\(C`interval\(C'\fR is a hint on how quickly a change is expected to
		2216	be detected and should normally be specified as \f(CW0\fR to let libev choose
		2217	a suitable value. The memory pointed to by \f(CW\(C`path\(C'\fR must point to the same
		2218	path for as long as the watcher is active.
		2219	.Sp
		2220	The callback will receive an \f(CW\(C`EV_STAT\(C'\fR event when a change was detected,
		2221	relative to the attributes at the time the watcher was started (or the
		2222	last change was detected).
		2223	.IP "ev_stat_stat (loop, ev_stat *)" 4
		2224	.IX Item "ev_stat_stat (loop, ev_stat *)"
		2225	Updates the stat buffer immediately with new values. If you change the
		2226	watched path in your callback, you could call this function to avoid
		2227	detecting this change (while introducing a race condition if you are not
		2228	the only one changing the path). Can also be useful simply to find out the
		2229	new values.
		2230	.IP "ev_statdata attr [read\-only]" 4
		2231	.IX Item "ev_statdata attr [read-only]"
		2232	The most-recently detected attributes of the file. Although the type is
		2233	\&\f(CW\(C`ev_statdata\(C'\fR, this is usually the (or one of the) \f(CW\(C`struct stat\(C'\fR types
		2234	suitable for your system, but you can only rely on the POSIX-standardised
		2235	members to be present. If the \f(CW\(C`st_nlink\(C'\fR member is \f(CW0\fR, then there was
		2236	some error while \f(CW\(C`stat\(C'\fRing the file.
		2237	.IP "ev_statdata prev [read\-only]" 4
		2238	.IX Item "ev_statdata prev [read-only]"
		2239	The previous attributes of the file. The callback gets invoked whenever
		2240	\&\f(CW\(C`prev\(C'\fR != \f(CW\(C`attr\(C'\fR, or, more precisely, one or more of these members
		2241	differ: \f(CW\(C`st_dev\(C'\fR, \f(CW\(C`st_ino\(C'\fR, \f(CW\(C`st_mode\(C'\fR, \f(CW\(C`st_nlink\(C'\fR, \f(CW\(C`st_uid\(C'\fR,
		2242	\&\f(CW\(C`st_gid\(C'\fR, \f(CW\(C`st_rdev\(C'\fR, \f(CW\(C`st_size\(C'\fR, \f(CW\(C`st_atime\(C'\fR, \f(CW\(C`st_mtime\(C'\fR, \f(CW\(C`st_ctime\(C'\fR.
		2243	.IP "ev_tstamp interval [read\-only]" 4
		2244	.IX Item "ev_tstamp interval [read-only]"
		2245	The specified interval.
		2246	.IP "const char *path [read\-only]" 4
		2247	.IX Item "const char *path [read-only]"
		2248	The file system path that is being watched.
		2249	.PP
		2250	\fIExamples\fR
		2251	.IX Subsection "Examples"
		2252	.PP
		2253	Example: Watch \f(CW\(C`/etc/passwd\(C'\fR for attribute changes.
		2254	.PP
		2255	.Vb 10
		2256	\& static void
		2257	\& passwd_cb (struct ev_loop loop, ev_stat w, int revents)
		2258	\& {
		2259	\& /* /etc/passwd changed in some way */
		2260	\& if (w\->attr.st_nlink)
		2261	\& {
		2262	\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
		2263	\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
		2264	\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
		2265	\& }
		2266	\& else
		2267	\& /* you shalt not abuse printf for puts */
		2268	\& puts ("wow, /etc/passwd is not there, expect problems. "
		2269	\& "if this is windows, they already arrived\en");
		2270	\& }
		2271	\&
		2272	\& ...
		2273	\& ev_stat passwd;
		2274	\&
		2275	\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
		2276	\& ev_stat_start (loop, &passwd);
		2277	.Ve
		2278	.PP
		2279	Example: Like above, but additionally use a one-second delay so we do not
		2280	miss updates (however, frequent updates will delay processing, too, so
		2281	one might do the work both on \f(CW\(C`ev_stat\(C'\fR callback invocation \fIand\fR on
		2282	\&\f(CW\(C`ev_timer\(C'\fR callback invocation).
		2283	.PP
		2284	.Vb 2
		2285	\& static ev_stat passwd;
		2286	\& static ev_timer timer;
		2287	\&
		2288	\& static void
		2289	\& timer_cb (EV_P_ ev_timer *w, int revents)
		2290	\& {
		2291	\& ev_timer_stop (EV_A_ w);
		2292	\&
		2293	\& /* now it\(Aqs one second after the most recent passwd change /
		2294	\& }
		2295	\&
		2296	\& static void
		2297	\& stat_cb (EV_P_ ev_stat *w, int revents)
		2298	\& {
		2299	\& /* reset the one\-second timer */
		2300	\& ev_timer_again (EV_A_ &timer);
		2301	\& }
		2302	\&
		2303	\& ...
		2304	\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2305	\& ev_stat_start (loop, &passwd);
		2306	\& ev_timer_init (&timer, timer_cb, 0., 1.02);
		2307	.Ve
864	.ie n .Sh """ev_idle"" \- when you've got nothing better to do"	2308	.ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
865	.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do"	2309	.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
866	.IX Subsection "ev_idle - when you've got nothing better to do"	2310	.IX Subsection "ev_idle - when you've got nothing better to do..."
867	Idle watchers trigger events when there are no other events are pending	2311	Idle watchers trigger events when no other events of the same or higher
868	(prepare, check and other idle watchers do not count). That is, as long	2312	priority are pending (prepare, check and other idle watchers do not count
869	as your process is busy handling sockets or timeouts (or even signals,	2313	as receiving \(L"events\(R").
870	imagine) it will not be triggered. But when your process is idle all idle	2314	.PP
871	watchers are being called again and again, once per event loop iteration \-	2315	That is, as long as your process is busy handling sockets or timeouts
		2316	(or even signals, imagine) of the same or higher priority it will not be
		2317	triggered. But when your process is idle (or only lower-priority watchers
		2318	are pending), the idle watchers are being called once per event loop
872	until stopped, that is, or your process receives more events and becomes	2319	iteration \- until stopped, that is, or your process receives more events
873	busy.	2320	and becomes busy again with higher priority stuff.
874	.PP	2321	.PP
875	The most noteworthy effect is that as long as any idle watchers are	2322	The most noteworthy effect is that as long as any idle watchers are
876	active, the process will not block when waiting for new events.	2323	active, the process will not block when waiting for new events.
877	.PP	2324	.PP
878	Apart from keeping your process non-blocking (which is a useful	2325	Apart from keeping your process non-blocking (which is a useful
879	effect on its own sometimes), idle watchers are a good place to do	2326	effect on its own sometimes), idle watchers are a good place to do
880	\&\(L"pseudo\-background processing\(R", or delay processing stuff to after the	2327	\&\(L"pseudo-background processing\(R", or delay processing stuff to after the
881	event loop has handled all outstanding events.	2328	event loop has handled all outstanding events.
		2329	.PP
		2330	\fIWatcher-Specific Functions and Data Members\fR
		2331	.IX Subsection "Watcher-Specific Functions and Data Members"
882	.IP "ev_idle_init (ev_signal *, callback)" 4	2332	.IP "ev_idle_init (ev_signal *, callback)" 4
883	.IX Item "ev_idle_init (ev_signal *, callback)"	2333	.IX Item "ev_idle_init (ev_signal *, callback)"
884	Initialises and configures the idle watcher \- it has no parameters of any	2334	Initialises and configures the idle watcher \- it has no parameters of any
885	kind. There is a \f(CW\(C`ev_idle_set\(C'\fR macro, but using it is utterly pointless,	2335	kind. There is a \f(CW\(C`ev_idle_set\(C'\fR macro, but using it is utterly pointless,
886	believe me.	2336	believe me.
		2337	.PP
		2338	\fIExamples\fR
		2339	.IX Subsection "Examples"
		2340	.PP
		2341	Example: Dynamically allocate an \f(CW\(C`ev_idle\(C'\fR watcher, start it, and in the
		2342	callback, free it. Also, use no error checking, as usual.
		2343	.PP
		2344	.Vb 7
		2345	\& static void
		2346	\& idle_cb (struct ev_loop loop, ev_idle w, int revents)
		2347	\& {
		2348	\& free (w);
		2349	\& // now do something you wanted to do when the program has
		2350	\& // no longer anything immediate to do.
		2351	\& }
		2352	\&
		2353	\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
		2354	\& ev_idle_init (idle_watcher, idle_cb);
		2355	\& ev_idle_start (loop, idle_cb);
		2356	.Ve
887	.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop"	2357	.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
888	.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop"	2358	.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
889	.IX Subsection "ev_prepare and ev_check - customise your event loop"	2359	.IX Subsection "ev_prepare and ev_check - customise your event loop!"
890	Prepare and check watchers are usually (but not always) used in tandem:	2360	Prepare and check watchers are usually (but not always) used in pairs:
891	prepare watchers get invoked before the process blocks and check watchers	2361	prepare watchers get invoked before the process blocks and check watchers
892	afterwards.	2362	afterwards.
893	.PP	2363	.PP
		2364	You \fImust not\fR call \f(CW\(C`ev_loop\(C'\fR or similar functions that enter
		2365	the current event loop from either \f(CW\(C`ev_prepare\(C'\fR or \f(CW\(C`ev_check\(C'\fR
		2366	watchers. Other loops than the current one are fine, however. The
		2367	rationale behind this is that you do not need to check for recursion in
		2368	those watchers, i.e. the sequence will always be \f(CW\(C`ev_prepare\(C'\fR, blocking,
		2369	\&\f(CW\(C`ev_check\(C'\fR so if you have one watcher of each kind they will always be
		2370	called in pairs bracketing the blocking call.
		2371	.PP
894	Their main purpose is to integrate other event mechanisms into libev. This	2372	Their main purpose is to integrate other event mechanisms into libev and
895	could be used, for example, to track variable changes, implement your own	2373	their use is somewhat advanced. They could be used, for example, to track
896	watchers, integrate net-snmp or a coroutine library and lots more.	2374	variable changes, implement your own watchers, integrate net-snmp or a
		2375	coroutine library and lots more. They are also occasionally useful if
		2376	you cache some data and want to flush it before blocking (for example,
		2377	in X programs you might want to do an \f(CW\(C`XFlush ()\(C'\fR in an \f(CW\(C`ev_prepare\(C'\fR
		2378	watcher).
897	.PP	2379	.PP
898	This is done by examining in each prepare call which file descriptors need	2380	This is done by examining in each prepare call which file descriptors
899	to be watched by the other library, registering \f(CW\(C`ev_io\(C'\fR watchers for	2381	need to be watched by the other library, registering \f(CW\(C`ev_io\(C'\fR watchers
900	them and starting an \f(CW\(C`ev_timer\(C'\fR watcher for any timeouts (many libraries	2382	for them and starting an \f(CW\(C`ev_timer\(C'\fR watcher for any timeouts (many
901	provide just this functionality). Then, in the check watcher you check for	2383	libraries provide exactly this functionality). Then, in the check watcher,
902	any events that occured (by checking the pending status of all watchers	2384	you check for any events that occurred (by checking the pending status
903	and stopping them) and call back into the library. The I/O and timer	2385	of all watchers and stopping them) and call back into the library. The
904	callbacks will never actually be called (but must be valid nevertheless,	2386	I/O and timer callbacks will never actually be called (but must be valid
905	because you never know, you know?).	2387	nevertheless, because you never know, you know?).
906	.PP	2388	.PP
907	As another example, the Perl Coro module uses these hooks to integrate	2389	As another example, the Perl Coro module uses these hooks to integrate
908	coroutines into libev programs, by yielding to other active coroutines	2390	coroutines into libev programs, by yielding to other active coroutines
909	during each prepare and only letting the process block if no coroutines	2391	during each prepare and only letting the process block if no coroutines
910	are ready to run (it's actually more complicated: it only runs coroutines	2392	are ready to run (it's actually more complicated: it only runs coroutines
911	with priority higher than or equal to the event loop and one coroutine	2393	with priority higher than or equal to the event loop and one coroutine
912	of lower priority, but only once, using idle watchers to keep the event	2394	of lower priority, but only once, using idle watchers to keep the event
913	loop from blocking if lower-priority coroutines are active, thus mapping	2395	loop from blocking if lower-priority coroutines are active, thus mapping
914	low-priority coroutines to idle/background tasks).	2396	low-priority coroutines to idle/background tasks).
		2397	.PP
		2398	It is recommended to give \f(CW\(C`ev_check\(C'\fR watchers highest (\f(CW\(C`EV_MAXPRI\(C'\fR)
		2399	priority, to ensure that they are being run before any other watchers
		2400	after the poll (this doesn't matter for \f(CW\(C`ev_prepare\(C'\fR watchers).
		2401	.PP
		2402	Also, \f(CW\(C`ev_check\(C'\fR watchers (and \f(CW\(C`ev_prepare\(C'\fR watchers, too) should not
		2403	activate (\(L"feed\(R") events into libev. While libev fully supports this, they
		2404	might get executed before other \f(CW\(C`ev_check\(C'\fR watchers did their job. As
		2405	\&\f(CW\(C`ev_check\(C'\fR watchers are often used to embed other (non-libev) event
		2406	loops those other event loops might be in an unusable state until their
		2407	\&\f(CW\(C`ev_check\(C'\fR watcher ran (always remind yourself to coexist peacefully with
		2408	others).
		2409	.PP
		2410	\fIWatcher-Specific Functions and Data Members\fR
		2411	.IX Subsection "Watcher-Specific Functions and Data Members"
915	.IP "ev_prepare_init (ev_prepare *, callback)" 4	2412	.IP "ev_prepare_init (ev_prepare *, callback)" 4
916	.IX Item "ev_prepare_init (ev_prepare *, callback)"	2413	.IX Item "ev_prepare_init (ev_prepare *, callback)"
917	.PD 0	2414	.PD 0
918	.IP "ev_check_init (ev_check *, callback)" 4	2415	.IP "ev_check_init (ev_check *, callback)" 4
919	.IX Item "ev_check_init (ev_check *, callback)"	2416	.IX Item "ev_check_init (ev_check *, callback)"
920	.PD	2417	.PD
921	Initialises and configures the prepare or check watcher \- they have no	2418	Initialises and configures the prepare or check watcher \- they have no
922	parameters of any kind. There are \f(CW\(C`ev_prepare_set\(C'\fR and \f(CW\(C`ev_check_set\(C'\fR	2419	parameters of any kind. There are \f(CW\(C`ev_prepare_set\(C'\fR and \f(CW\(C`ev_check_set\(C'\fR
923	macros, but using them is utterly, utterly and completely pointless.	2420	macros, but using them is utterly, utterly, utterly and completely
		2421	pointless.
		2422	.PP
		2423	\fIExamples\fR
		2424	.IX Subsection "Examples"
		2425	.PP
		2426	There are a number of principal ways to embed other event loops or modules
		2427	into libev. Here are some ideas on how to include libadns into libev
		2428	(there is a Perl module named \f(CW\(C`EV::ADNS\(C'\fR that does this, which you could
		2429	use as a working example. Another Perl module named \f(CW\(C`EV::Glib\(C'\fR embeds a
		2430	Glib main context into libev, and finally, \f(CW\(C`Glib::EV\(C'\fR embeds \s-1EV\s0 into the
		2431	Glib event loop).
		2432	.PP
		2433	Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
		2434	and in a check watcher, destroy them and call into libadns. What follows
		2435	is pseudo-code only of course. This requires you to either use a low
		2436	priority for the check watcher or use \f(CW\(C`ev_clear_pending\(C'\fR explicitly, as
		2437	the callbacks for the IO/timeout watchers might not have been called yet.
		2438	.PP
		2439	.Vb 2
		2440	\& static ev_io iow [nfd];
		2441	\& static ev_timer tw;
		2442	\&
		2443	\& static void
		2444	\& io_cb (struct ev_loop loop, ev_io w, int revents)
		2445	\& {
		2446	\& }
		2447	\&
		2448	\& // create io watchers for each fd and a timer before blocking
		2449	\& static void
		2450	\& adns_prepare_cb (struct ev_loop loop, ev_prepare w, int revents)
		2451	\& {
		2452	\& int timeout = 3600000;
		2453	\& struct pollfd fds [nfd];
		2454	\& // actual code will need to loop here and realloc etc.
		2455	\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
		2456	\&
		2457	\& /* the callback is illegal, but won\(Aqt be called as we stop during check /
		2458	\& ev_timer_init (&tw, 0, timeout * 1e\-3);
		2459	\& ev_timer_start (loop, &tw);
		2460	\&
		2461	\& // create one ev_io per pollfd
		2462	\& for (int i = 0; i < nfd; ++i)
		2463	\& {
		2464	\& ev_io_init (iow + i, io_cb, fds [i].fd,
		2465	\& ((fds [i].events & POLLIN ? EV_READ : 0)
		2466	\& \| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
		2467	\&
		2468	\& fds [i].revents = 0;
		2469	\& ev_io_start (loop, iow + i);
		2470	\& }
		2471	\& }
		2472	\&
		2473	\& // stop all watchers after blocking
		2474	\& static void
		2475	\& adns_check_cb (struct ev_loop loop, ev_check w, int revents)
		2476	\& {
		2477	\& ev_timer_stop (loop, &tw);
		2478	\&
		2479	\& for (int i = 0; i < nfd; ++i)
		2480	\& {
		2481	\& // set the relevant poll flags
		2482	\& // could also call adns_processreadable etc. here
		2483	\& struct pollfd *fd = fds + i;
		2484	\& int revents = ev_clear_pending (iow + i);
		2485	\& if (revents & EV_READ ) fd\->revents \|= fd\->events & POLLIN;
		2486	\& if (revents & EV_WRITE) fd\->revents \|= fd\->events & POLLOUT;
		2487	\&
		2488	\& // now stop the watcher
		2489	\& ev_io_stop (loop, iow + i);
		2490	\& }
		2491	\&
		2492	\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
		2493	\& }
		2494	.Ve
		2495	.PP
		2496	Method 2: This would be just like method 1, but you run \f(CW\(C`adns_afterpoll\(C'\fR
		2497	in the prepare watcher and would dispose of the check watcher.
		2498	.PP
		2499	Method 3: If the module to be embedded supports explicit event
		2500	notification (libadns does), you can also make use of the actual watcher
		2501	callbacks, and only destroy/create the watchers in the prepare watcher.
		2502	.PP
		2503	.Vb 5
		2504	\& static void
		2505	\& timer_cb (EV_P_ ev_timer *w, int revents)
		2506	\& {
		2507	\& adns_state ads = (adns_state)w\->data;
		2508	\& update_now (EV_A);
		2509	\&
		2510	\& adns_processtimeouts (ads, &tv_now);
		2511	\& }
		2512	\&
		2513	\& static void
		2514	\& io_cb (EV_P_ ev_io *w, int revents)
		2515	\& {
		2516	\& adns_state ads = (adns_state)w\->data;
		2517	\& update_now (EV_A);
		2518	\&
		2519	\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
		2520	\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
		2521	\& }
		2522	\&
		2523	\& // do not ever call adns_afterpoll
		2524	.Ve
		2525	.PP
		2526	Method 4: Do not use a prepare or check watcher because the module you
		2527	want to embed is not flexible enough to support it. Instead, you can
		2528	override their poll function. The drawback with this solution is that the
		2529	main loop is now no longer controllable by \s-1EV\s0. The \f(CW\(C`Glib::EV\(C'\fR module uses
		2530	this approach, effectively embedding \s-1EV\s0 as a client into the horrible
		2531	libglib event loop.
		2532	.PP
		2533	.Vb 4
		2534	\& static gint
		2535	\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
		2536	\& {
		2537	\& int got_events = 0;
		2538	\&
		2539	\& for (n = 0; n < nfds; ++n)
		2540	\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
		2541	\&
		2542	\& if (timeout >= 0)
		2543	\& // create/start timer
		2544	\&
		2545	\& // poll
		2546	\& ev_loop (EV_A_ 0);
		2547	\&
		2548	\& // stop timer again
		2549	\& if (timeout >= 0)
		2550	\& ev_timer_stop (EV_A_ &to);
		2551	\&
		2552	\& // stop io watchers again \- their callbacks should have set
		2553	\& for (n = 0; n < nfds; ++n)
		2554	\& ev_io_stop (EV_A_ iow [n]);
		2555	\&
		2556	\& return got_events;
		2557	\& }
		2558	.Ve
		2559	.ie n .Sh """ev_embed"" \- when one backend isn't enough..."
		2560	.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
		2561	.IX Subsection "ev_embed - when one backend isn't enough..."
		2562	This is a rather advanced watcher type that lets you embed one event loop
		2563	into another (currently only \f(CW\(C`ev_io\(C'\fR events are supported in the embedded
		2564	loop, other types of watchers might be handled in a delayed or incorrect
		2565	fashion and must not be used).
		2566	.PP
		2567	There are primarily two reasons you would want that: work around bugs and
		2568	prioritise I/O.
		2569	.PP
		2570	As an example for a bug workaround, the kqueue backend might only support
		2571	sockets on some platform, so it is unusable as generic backend, but you
		2572	still want to make use of it because you have many sockets and it scales
		2573	so nicely. In this case, you would create a kqueue-based loop and embed
		2574	it into your default loop (which might use e.g. poll). Overall operation
		2575	will be a bit slower because first libev has to call \f(CW\(C`poll\(C'\fR and then
		2576	\&\f(CW\(C`kevent\(C'\fR, but at least you can use both mechanisms for what they are
		2577	best: \f(CW\(C`kqueue\(C'\fR for scalable sockets and \f(CW\(C`poll\(C'\fR if you want it to work :)
		2578	.PP
		2579	As for prioritising I/O: under rare circumstances you have the case where
		2580	some fds have to be watched and handled very quickly (with low latency),
		2581	and even priorities and idle watchers might have too much overhead. In
		2582	this case you would put all the high priority stuff in one loop and all
		2583	the rest in a second one, and embed the second one in the first.
		2584	.PP
		2585	As long as the watcher is active, the callback will be invoked every time
		2586	there might be events pending in the embedded loop. The callback must then
		2587	call \f(CW\(C`ev_embed_sweep (mainloop, watcher)\(C'\fR to make a single sweep and invoke
		2588	their callbacks (you could also start an idle watcher to give the embedded
		2589	loop strictly lower priority for example). You can also set the callback
		2590	to \f(CW0\fR, in which case the embed watcher will automatically execute the
		2591	embedded loop sweep.
		2592	.PP
		2593	As long as the watcher is started it will automatically handle events. The
		2594	callback will be invoked whenever some events have been handled. You can
		2595	set the callback to \f(CW0\fR to avoid having to specify one if you are not
		2596	interested in that.
		2597	.PP
		2598	Also, there have not currently been made special provisions for forking:
		2599	when you fork, you not only have to call \f(CW\(C`ev_loop_fork\(C'\fR on both loops,
		2600	but you will also have to stop and restart any \f(CW\(C`ev_embed\(C'\fR watchers
		2601	yourself \- but you can use a fork watcher to handle this automatically,
		2602	and future versions of libev might do just that.
		2603	.PP
		2604	Unfortunately, not all backends are embeddable: only the ones returned by
		2605	\&\f(CW\(C`ev_embeddable_backends\(C'\fR are, which, unfortunately, does not include any
		2606	portable one.
		2607	.PP
		2608	So when you want to use this feature you will always have to be prepared
		2609	that you cannot get an embeddable loop. The recommended way to get around
		2610	this is to have a separate variables for your embeddable loop, try to
		2611	create it, and if that fails, use the normal loop for everything.
		2612	.PP
		2613	\fI\f(CI\(C`ev_embed\(C'\fI and fork\fR
		2614	.IX Subsection "ev_embed and fork"
		2615	.PP
		2616	While the \f(CW\(C`ev_embed\(C'\fR watcher is running, forks in the embedding loop will
		2617	automatically be applied to the embedded loop as well, so no special
		2618	fork handling is required in that case. When the watcher is not running,
		2619	however, it is still the task of the libev user to call \f(CW\(C`ev_loop_fork ()\(C'\fR
		2620	as applicable.
		2621	.PP
		2622	\fIWatcher-Specific Functions and Data Members\fR
		2623	.IX Subsection "Watcher-Specific Functions and Data Members"
		2624	.IP "ev_embed_init (ev_embed , callback, struct ev_loop embedded_loop)" 4
		2625	.IX Item "ev_embed_init (ev_embed , callback, struct ev_loop embedded_loop)"
		2626	.PD 0
		2627	.IP "ev_embed_set (ev_embed , callback, struct ev_loop embedded_loop)" 4
		2628	.IX Item "ev_embed_set (ev_embed , callback, struct ev_loop embedded_loop)"
		2629	.PD
		2630	Configures the watcher to embed the given loop, which must be
		2631	embeddable. If the callback is \f(CW0\fR, then \f(CW\(C`ev_embed_sweep\(C'\fR will be
		2632	invoked automatically, otherwise it is the responsibility of the callback
		2633	to invoke it (it will continue to be called until the sweep has been done,
		2634	if you do not want that, you need to temporarily stop the embed watcher).
		2635	.IP "ev_embed_sweep (loop, ev_embed *)" 4
		2636	.IX Item "ev_embed_sweep (loop, ev_embed *)"
		2637	Make a single, non-blocking sweep over the embedded loop. This works
		2638	similarly to \f(CW\(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\(C'\fR, but in the most
		2639	appropriate way for embedded loops.
		2640	.IP "struct ev_loop *other [read\-only]" 4
		2641	.IX Item "struct ev_loop *other [read-only]"
		2642	The embedded event loop.
		2643	.PP
		2644	\fIExamples\fR
		2645	.IX Subsection "Examples"
		2646	.PP
		2647	Example: Try to get an embeddable event loop and embed it into the default
		2648	event loop. If that is not possible, use the default loop. The default
		2649	loop is stored in \f(CW\(C`loop_hi\(C'\fR, while the embeddable loop is stored in
		2650	\&\f(CW\(C`loop_lo\(C'\fR (which is \f(CW\(C`loop_hi\(C'\fR in the case no embeddable loop can be
		2651	used).
		2652	.PP
		2653	.Vb 3
		2654	\& struct ev_loop *loop_hi = ev_default_init (0);
		2655	\& struct ev_loop *loop_lo = 0;
		2656	\& ev_embed embed;
		2657	\&
		2658	\& // see if there is a chance of getting one that works
		2659	\& // (remember that a flags value of 0 means autodetection)
		2660	\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2661	\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2662	\& : 0;
		2663	\&
		2664	\& // if we got one, then embed it, otherwise default to loop_hi
		2665	\& if (loop_lo)
		2666	\& {
		2667	\& ev_embed_init (&embed, 0, loop_lo);
		2668	\& ev_embed_start (loop_hi, &embed);
		2669	\& }
		2670	\& else
		2671	\& loop_lo = loop_hi;
		2672	.Ve
		2673	.PP
		2674	Example: Check if kqueue is available but not recommended and create
		2675	a kqueue backend for use with sockets (which usually work with any
		2676	kqueue implementation). Store the kqueue/socket\-only event loop in
		2677	\&\f(CW\(C`loop_socket\(C'\fR. (One might optionally use \f(CW\(C`EVFLAG_NOENV\(C'\fR, too).
		2678	.PP
		2679	.Vb 3
		2680	\& struct ev_loop *loop = ev_default_init (0);
		2681	\& struct ev_loop *loop_socket = 0;
		2682	\& ev_embed embed;
		2683	\&
		2684	\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2685	\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2686	\& {
		2687	\& ev_embed_init (&embed, 0, loop_socket);
		2688	\& ev_embed_start (loop, &embed);
		2689	\& }
		2690	\&
		2691	\& if (!loop_socket)
		2692	\& loop_socket = loop;
		2693	\&
		2694	\& // now use loop_socket for all sockets, and loop for everything else
		2695	.Ve
		2696	.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
		2697	.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
		2698	.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
		2699	Fork watchers are called when a \f(CW\(C`fork ()\(C'\fR was detected (usually because
		2700	whoever is a good citizen cared to tell libev about it by calling
		2701	\&\f(CW\(C`ev_default_fork\(C'\fR or \f(CW\(C`ev_loop_fork\(C'\fR). The invocation is done before the
		2702	event loop blocks next and before \f(CW\(C`ev_check\(C'\fR watchers are being called,
		2703	and only in the child after the fork. If whoever good citizen calling
		2704	\&\f(CW\(C`ev_default_fork\(C'\fR cheats and calls it in the wrong process, the fork
		2705	handlers will be invoked, too, of course.
		2706	.PP
		2707	\fIWatcher-Specific Functions and Data Members\fR
		2708	.IX Subsection "Watcher-Specific Functions and Data Members"
		2709	.IP "ev_fork_init (ev_signal *, callback)" 4
		2710	.IX Item "ev_fork_init (ev_signal *, callback)"
		2711	Initialises and configures the fork watcher \- it has no parameters of any
		2712	kind. There is a \f(CW\(C`ev_fork_set\(C'\fR macro, but using it is utterly pointless,
		2713	believe me.
		2714	.ie n .Sh """ev_async"" \- how to wake up another event loop"
		2715	.el .Sh "\f(CWev_async\fP \- how to wake up another event loop"
		2716	.IX Subsection "ev_async - how to wake up another event loop"
		2717	In general, you cannot use an \f(CW\(C`ev_loop\(C'\fR from multiple threads or other
		2718	asynchronous sources such as signal handlers (as opposed to multiple event
		2719	loops \- those are of course safe to use in different threads).
		2720	.PP
		2721	Sometimes, however, you need to wake up another event loop you do not
		2722	control, for example because it belongs to another thread. This is what
		2723	\&\f(CW\(C`ev_async\(C'\fR watchers do: as long as the \f(CW\(C`ev_async\(C'\fR watcher is active, you
		2724	can signal it by calling \f(CW\(C`ev_async_send\(C'\fR, which is thread\- and signal
		2725	safe.
		2726	.PP
		2727	This functionality is very similar to \f(CW\(C`ev_signal\(C'\fR watchers, as signals,
		2728	too, are asynchronous in nature, and signals, too, will be compressed
		2729	(i.e. the number of callback invocations may be less than the number of
		2730	\&\f(CW\(C`ev_async_sent\(C'\fR calls).
		2731	.PP
		2732	Unlike \f(CW\(C`ev_signal\(C'\fR watchers, \f(CW\(C`ev_async\(C'\fR works with any event loop, not
		2733	just the default loop.
		2734	.PP
		2735	\fIQueueing\fR
		2736	.IX Subsection "Queueing"
		2737	.PP
		2738	\&\f(CW\(C`ev_async\(C'\fR does not support queueing of data in any way. The reason
		2739	is that the author does not know of a simple (or any) algorithm for a
		2740	multiple-writer-single-reader queue that works in all cases and doesn't
		2741	need elaborate support such as pthreads.
		2742	.PP
		2743	That means that if you want to queue data, you have to provide your own
		2744	queue. But at least I can tell you how to implement locking around your
		2745	queue:
		2746	.IP "queueing from a signal handler context" 4
		2747	.IX Item "queueing from a signal handler context"
		2748	To implement race-free queueing, you simply add to the queue in the signal
		2749	handler but you block the signal handler in the watcher callback. Here is
		2750	an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
		2751	.Sp
		2752	.Vb 1
		2753	\& static ev_async mysig;
		2754	\&
		2755	\& static void
		2756	\& sigusr1_handler (void)
		2757	\& {
		2758	\& sometype data;
		2759	\&
		2760	\& // no locking etc.
		2761	\& queue_put (data);
		2762	\& ev_async_send (EV_DEFAULT_ &mysig);
		2763	\& }
		2764	\&
		2765	\& static void
		2766	\& mysig_cb (EV_P_ ev_async *w, int revents)
		2767	\& {
		2768	\& sometype data;
		2769	\& sigset_t block, prev;
		2770	\&
		2771	\& sigemptyset (&block);
		2772	\& sigaddset (&block, SIGUSR1);
		2773	\& sigprocmask (SIG_BLOCK, &block, &prev);
		2774	\&
		2775	\& while (queue_get (&data))
		2776	\& process (data);
		2777	\&
		2778	\& if (sigismember (&prev, SIGUSR1)
		2779	\& sigprocmask (SIG_UNBLOCK, &block, 0);
		2780	\& }
		2781	.Ve
		2782	.Sp
		2783	(Note: pthreads in theory requires you to use \f(CW\(C`pthread_setmask\(C'\fR
		2784	instead of \f(CW\(C`sigprocmask\(C'\fR when you use threads, but libev doesn't do it
		2785	either...).
		2786	.IP "queueing from a thread context" 4
		2787	.IX Item "queueing from a thread context"
		2788	The strategy for threads is different, as you cannot (easily) block
		2789	threads but you can easily preempt them, so to queue safely you need to
		2790	employ a traditional mutex lock, such as in this pthread example:
		2791	.Sp
		2792	.Vb 2
		2793	\& static ev_async mysig;
		2794	\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2795	\&
		2796	\& static void
		2797	\& otherthread (void)
		2798	\& {
		2799	\& // only need to lock the actual queueing operation
		2800	\& pthread_mutex_lock (&mymutex);
		2801	\& queue_put (data);
		2802	\& pthread_mutex_unlock (&mymutex);
		2803	\&
		2804	\& ev_async_send (EV_DEFAULT_ &mysig);
		2805	\& }
		2806	\&
		2807	\& static void
		2808	\& mysig_cb (EV_P_ ev_async *w, int revents)
		2809	\& {
		2810	\& pthread_mutex_lock (&mymutex);
		2811	\&
		2812	\& while (queue_get (&data))
		2813	\& process (data);
		2814	\&
		2815	\& pthread_mutex_unlock (&mymutex);
		2816	\& }
		2817	.Ve
		2818	.PP
		2819	\fIWatcher-Specific Functions and Data Members\fR
		2820	.IX Subsection "Watcher-Specific Functions and Data Members"
		2821	.IP "ev_async_init (ev_async *, callback)" 4
		2822	.IX Item "ev_async_init (ev_async *, callback)"
		2823	Initialises and configures the async watcher \- it has no parameters of any
		2824	kind. There is a \f(CW\(C`ev_async_set\(C'\fR macro, but using it is utterly pointless,
		2825	trust me.
		2826	.IP "ev_async_send (loop, ev_async *)" 4
		2827	.IX Item "ev_async_send (loop, ev_async *)"
		2828	Sends/signals/activates the given \f(CW\(C`ev_async\(C'\fR watcher, that is, feeds
		2829	an \f(CW\(C`EV_ASYNC\(C'\fR event on the watcher into the event loop. Unlike
		2830	\&\f(CW\(C`ev_feed_event\(C'\fR, this call is safe to do from other threads, signal or
		2831	similar contexts (see the discussion of \f(CW\(C`EV_ATOMIC_T\(C'\fR in the embedding
		2832	section below on what exactly this means).
		2833	.Sp
		2834	This call incurs the overhead of a system call only once per loop iteration,
		2835	so while the overhead might be noticeable, it doesn't apply to repeated
		2836	calls to \f(CW\(C`ev_async_send\(C'\fR.
		2837	.IP "bool = ev_async_pending (ev_async *)" 4
		2838	.IX Item "bool = ev_async_pending (ev_async *)"
		2839	Returns a non-zero value when \f(CW\(C`ev_async_send\(C'\fR has been called on the
		2840	watcher but the event has not yet been processed (or even noted) by the
		2841	event loop.
		2842	.Sp
		2843	\&\f(CW\(C`ev_async_send\(C'\fR sets a flag in the watcher and wakes up the loop. When
		2844	the loop iterates next and checks for the watcher to have become active,
		2845	it will reset the flag again. \f(CW\(C`ev_async_pending\(C'\fR can be used to very
		2846	quickly check whether invoking the loop might be a good idea.
		2847	.Sp
		2848	Not that this does \fInot\fR check whether the watcher itself is pending, only
		2849	whether it has been requested to make this watcher pending.
924	.SH "OTHER FUNCTIONS"	2850	.SH "OTHER FUNCTIONS"
925	.IX Header "OTHER FUNCTIONS"	2851	.IX Header "OTHER FUNCTIONS"
926	There are some other functions of possible interest. Described. Here. Now.	2852	There are some other functions of possible interest. Described. Here. Now.
927	.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4	2853	.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
928	.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"	2854	.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
929	This function combines a simple timer and an I/O watcher, calls your	2855	This function combines a simple timer and an I/O watcher, calls your
930	callback on whichever event happens first and automatically stop both	2856	callback on whichever event happens first and automatically stops both
931	watchers. This is useful if you want to wait for a single event on an fd	2857	watchers. This is useful if you want to wait for a single event on an fd
932	or timeout without having to allocate/configure/start/stop/free one or	2858	or timeout without having to allocate/configure/start/stop/free one or
933	more watchers yourself.	2859	more watchers yourself.
934	.Sp	2860	.Sp
935	If \f(CW\(C`fd\(C'\fR is less than 0, then no I/O watcher will be started and events	2861	If \f(CW\(C`fd\(C'\fR is less than 0, then no I/O watcher will be started and the
936	is being ignored. Otherwise, an \f(CW\(C`ev_io\(C'\fR watcher for the given \f(CW\(C`fd\(C'\fR and	2862	\&\f(CW\(C`events\(C'\fR argument is being ignored. Otherwise, an \f(CW\(C`ev_io\(C'\fR watcher for
937	\&\f(CW\(C`events\(C'\fR set will be craeted and started.	2863	the given \f(CW\(C`fd\(C'\fR and \f(CW\(C`events\(C'\fR set will be created and started.
938	.Sp	2864	.Sp
939	If \f(CW\(C`timeout\(C'\fR is less than 0, then no timeout watcher will be	2865	If \f(CW\(C`timeout\(C'\fR is less than 0, then no timeout watcher will be
940	started. Otherwise an \f(CW\(C`ev_timer\(C'\fR watcher with after = \f(CW\(C`timeout\(C'\fR (and	2866	started. Otherwise an \f(CW\(C`ev_timer\(C'\fR watcher with after = \f(CW\(C`timeout\(C'\fR (and
941	repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of	2867	repeat = 0) will be started. \f(CW0\fR is a valid timeout.
942	dubious value.
943	.Sp	2868	.Sp
944	The callback has the type \f(CW\(C`void (cb)(int revents, void arg)\(C'\fR and gets	2869	The callback has the type \f(CW\(C`void (cb)(int revents, void arg)\(C'\fR and gets
945	passed an \f(CW\(C`revents\(C'\fR set like normal event callbacks (a combination of	2870	passed an \f(CW\(C`revents\(C'\fR set like normal event callbacks (a combination of
946	\&\f(CW\(C`EV_ERROR\(C'\fR, \f(CW\(C`EV_READ\(C'\fR, \f(CW\(C`EV_WRITE\(C'\fR or \f(CW\(C`EV_TIMEOUT\(C'\fR) and the \f(CW\(C`arg\(C'\fR	2871	\&\f(CW\(C`EV_ERROR\(C'\fR, \f(CW\(C`EV_READ\(C'\fR, \f(CW\(C`EV_WRITE\(C'\fR or \f(CW\(C`EV_TIMEOUT\(C'\fR) and the \f(CW\(C`arg\(C'\fR
947	value passed to \f(CW\(C`ev_once\(C'\fR:	2872	value passed to \f(CW\(C`ev_once\(C'\fR. Note that it is possible to receive \fIboth\fR
		2873	a timeout and an io event at the same time \- you probably should give io
		2874	events precedence.
		2875	.Sp
		2876	Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
948	.Sp	2877	.Sp
949	.Vb 7	2878	.Vb 7
950	\& static void stdin_ready (int revents, void *arg)	2879	\& static void stdin_ready (int revents, void *arg)
951	\& {	2880	\& {
952	\& if (revents & EV_TIMEOUT)
953	\& /* doh, nothing entered */;
954	\& else if (revents & EV_READ)	2881	\& if (revents & EV_READ)
955	\& /* stdin might have data for us, joy! */;	2882	\& /* stdin might have data for us, joy! */;
		2883	\& else if (revents & EV_TIMEOUT)
		2884	\& /* doh, nothing entered */;
956	\& }	2885	\& }
957	.Ve	2886	\&
958	.Sp
959	.Vb 1
960	\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2887	\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
961	.Ve	2888	.Ve
962	.IP "ev_feed_event (loop, watcher, int events)" 4	2889	.IP "ev_feed_event (struct ev_loop , watcher , int revents)" 4
963	.IX Item "ev_feed_event (loop, watcher, int events)"	2890	.IX Item "ev_feed_event (struct ev_loop , watcher , int revents)"
964	Feeds the given event set into the event loop, as if the specified event	2891	Feeds the given event set into the event loop, as if the specified event
965	had happened for the specified watcher (which must be a pointer to an	2892	had happened for the specified watcher (which must be a pointer to an
966	initialised but not necessarily started event watcher).	2893	initialised but not necessarily started event watcher).
967	.IP "ev_feed_fd_event (loop, int fd, int revents)" 4	2894	.IP "ev_feed_fd_event (struct ev_loop *, int fd, int revents)" 4
968	.IX Item "ev_feed_fd_event (loop, int fd, int revents)"	2895	.IX Item "ev_feed_fd_event (struct ev_loop *, int fd, int revents)"
969	Feed an event on the given fd, as if a file descriptor backend detected	2896	Feed an event on the given fd, as if a file descriptor backend detected
970	the given events it.	2897	the given events it.
971	.IP "ev_feed_signal_event (loop, int signum)" 4	2898	.IP "ev_feed_signal_event (struct ev_loop *loop, int signum)" 4
972	.IX Item "ev_feed_signal_event (loop, int signum)"	2899	.IX Item "ev_feed_signal_event (struct ev_loop *loop, int signum)"
973	Feed an event as if the given signal occured (loop must be the default loop!).	2900	Feed an event as if the given signal occurred (\f(CW\(C`loop\(C'\fR must be the default
		2901	loop!).
974	.SH "LIBEVENT EMULATION"	2902	.SH "LIBEVENT EMULATION"
975	.IX Header "LIBEVENT EMULATION"	2903	.IX Header "LIBEVENT EMULATION"
976	Libev offers a compatibility emulation layer for libevent. It cannot	2904	Libev offers a compatibility emulation layer for libevent. It cannot
977	emulate the internals of libevent, so here are some usage hints:	2905	emulate the internals of libevent, so here are some usage hints:
		2906	.IP "\(bu" 4
978	.IP "* Use it by including <event.h>, as usual." 4	2907	Use it by including <event.h>, as usual.
979	.IX Item "Use it by including <event.h>, as usual."	2908	.IP "\(bu" 4
980	.PD 0	2909	The following members are fully supported: ev_base, ev_callback,
981	.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4	2910	ev_arg, ev_fd, ev_res, ev_events.
982	.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events."	2911	.IP "\(bu" 4
983	.IP "* 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 \s-1API\s0)." 4	2912	Avoid using ev_flags and the EVLIST_*\-macros, while it is
984	.IX Item "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)."	2913	maintained by libev, it does not work exactly the same way as in libevent (consider
985	.IP "* 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." 4	2914	it a private \s-1API\s0).
986	.IX Item "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."	2915	.IP "\(bu" 4
		2916	Priorities are not currently supported. Initialising priorities
		2917	will fail and all watchers will have the same priority, even though there
		2918	is an ev_pri field.
		2919	.IP "\(bu" 4
		2920	In libevent, the last base created gets the signals, in libev, the
		2921	first base created (== the default loop) gets the signals.
		2922	.IP "\(bu" 4
987	.IP "* Other members are not supported." 4	2923	Other members are not supported.
988	.IX Item "Other members are not supported."	2924	.IP "\(bu" 4
989	.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4	2925	The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
990	.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library."	2926	to use the libev header file and library.
991	.PD
992	.SH "\*(C+ SUPPORT"	2927	.SH "\*(C+ SUPPORT"
993	.IX Header " SUPPORT"	2928	.IX Header " SUPPORT"
994	\&\s-1TBD\s0.	2929	Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
		2930	you to use some convenience methods to start/stop watchers and also change
		2931	the callback model to a model using method callbacks on objects.
		2932	.PP
		2933	To use it,
		2934	.PP
		2935	.Vb 1
		2936	\& #include <ev++.h>
		2937	.Ve
		2938	.PP
		2939	This automatically includes \fIev.h\fR and puts all of its definitions (many
		2940	of them macros) into the global namespace. All \*(C+ specific things are
		2941	put into the \f(CW\(C`ev\(C'\fR namespace. It should support all the same embedding
		2942	options as \fIev.h\fR, most notably \f(CW\(C`EV_MULTIPLICITY\(C'\fR.
		2943	.PP
		2944	Care has been taken to keep the overhead low. The only data member the \*(C+
		2945	classes add (compared to plain C\-style watchers) is the event loop pointer
		2946	that the watcher is associated with (or no additional members at all if
		2947	you disable \f(CW\(C`EV_MULTIPLICITY\(C'\fR when embedding libev).
		2948	.PP
		2949	Currently, functions, and static and non-static member functions can be
		2950	used as callbacks. Other types should be easy to add as long as they only
		2951	need one additional pointer for context. If you need support for other
		2952	types of functors please contact the author (preferably after implementing
		2953	it).
		2954	.PP
		2955	Here is a list of things available in the \f(CW\(C`ev\(C'\fR namespace:
		2956	.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
		2957	.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
		2958	.IX Item "ev::READ, ev::WRITE etc."
		2959	These are just enum values with the same values as the \f(CW\(C`EV_READ\(C'\fR etc.
		2960	macros from \fIev.h\fR.
		2961	.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
		2962	.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
		2963	.IX Item "ev::tstamp, ev::now"
		2964	Aliases to the same types/functions as with the \f(CW\(C`ev_\(C'\fR prefix.
		2965	.ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4
		2966	.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
		2967	.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
		2968	For each \f(CW\(C`ev_TYPE\(C'\fR watcher in \fIev.h\fR there is a corresponding class of
		2969	the same name in the \f(CW\(C`ev\(C'\fR namespace, with the exception of \f(CW\(C`ev_signal\(C'\fR
		2970	which is called \f(CW\(C`ev::sig\(C'\fR to avoid clashes with the \f(CW\(C`signal\(C'\fR macro
		2971	defines by many implementations.
		2972	.Sp
		2973	All of those classes have these methods:
		2974	.RS 4
		2975	.IP "ev::TYPE::TYPE ()" 4
		2976	.IX Item "ev::TYPE::TYPE ()"
		2977	.PD 0
		2978	.IP "ev::TYPE::TYPE (struct ev_loop *)" 4
		2979	.IX Item "ev::TYPE::TYPE (struct ev_loop *)"
		2980	.IP "ev::TYPE::~TYPE" 4
		2981	.IX Item "ev::TYPE::~TYPE"
		2982	.PD
		2983	The constructor (optionally) takes an event loop to associate the watcher
		2984	with. If it is omitted, it will use \f(CW\(C`EV_DEFAULT\(C'\fR.
		2985	.Sp
		2986	The constructor calls \f(CW\(C`ev_init\(C'\fR for you, which means you have to call the
		2987	\&\f(CW\(C`set\(C'\fR method before starting it.
		2988	.Sp
		2989	It will not set a callback, however: You have to call the templated \f(CW\(C`set\(C'\fR
		2990	method to set a callback before you can start the watcher.
		2991	.Sp
		2992	(The reason why you have to use a method is a limitation in \*(C+ which does
		2993	not allow explicit template arguments for constructors).
		2994	.Sp
		2995	The destructor automatically stops the watcher if it is active.
		2996	.IP "w\->set<class, &class::method> (object *)" 4
		2997	.IX Item "w->set<class, &class::method> (object *)"
		2998	This method sets the callback method to call. The method has to have a
		2999	signature of \f(CW\(C`void ()(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
		3000	first argument and the \f(CW\(C`revents\(C'\fR as second. The object must be given as
		3001	parameter and is stored in the \f(CW\(C`data\(C'\fR member of the watcher.
		3002	.Sp
		3003	This method synthesizes efficient thunking code to call your method from
		3004	the C callback that libev requires. If your compiler can inline your
		3005	callback (i.e. it is visible to it at the place of the \f(CW\(C`set\(C'\fR call and
		3006	your compiler is good :), then the method will be fully inlined into the
		3007	thunking function, making it as fast as a direct C callback.
		3008	.Sp
		3009	Example: simple class declaration and watcher initialisation
		3010	.Sp
		3011	.Vb 4
		3012	\& struct myclass
		3013	\& {
		3014	\& void io_cb (ev::io &w, int revents) { }
		3015	\& }
		3016	\&
		3017	\& myclass obj;
		3018	\& ev::io iow;
		3019	\& iow.set <myclass, &myclass::io_cb> (&obj);
		3020	.Ve
		3021	.IP "w\->set<function> (void *data = 0)" 4
		3022	.IX Item "w->set<function> (void *data = 0)"
		3023	Also sets a callback, but uses a static method or plain function as
		3024	callback. The optional \f(CW\(C`data\(C'\fR argument will be stored in the watcher's
		3025	\&\f(CW\(C`data\(C'\fR member and is free for you to use.
		3026	.Sp
		3027	The prototype of the \f(CW\(C`function\(C'\fR must be \f(CW\(C`void ()(ev::TYPE &w, int)\*(C'\fR.
		3028	.Sp
		3029	See the method\-\f(CW\(C`set\(C'\fR above for more details.
		3030	.Sp
		3031	Example: Use a plain function as callback.
		3032	.Sp
		3033	.Vb 2
		3034	\& static void io_cb (ev::io &w, int revents) { }
		3035	\& iow.set <io_cb> ();
		3036	.Ve
		3037	.IP "w\->set (struct ev_loop *)" 4
		3038	.IX Item "w->set (struct ev_loop *)"
		3039	Associates a different \f(CW\(C`struct ev_loop\(C'\fR with this watcher. You can only
		3040	do this when the watcher is inactive (and not pending either).
		3041	.IP "w\->set ([arguments])" 4
		3042	.IX Item "w->set ([arguments])"
		3043	Basically the same as \f(CW\(C`ev_TYPE_set\(C'\fR, with the same arguments. Must be
		3044	called at least once. Unlike the C counterpart, an active watcher gets
		3045	automatically stopped and restarted when reconfiguring it with this
		3046	method.
		3047	.IP "w\->start ()" 4
		3048	.IX Item "w->start ()"
		3049	Starts the watcher. Note that there is no \f(CW\(C`loop\(C'\fR argument, as the
		3050	constructor already stores the event loop.
		3051	.IP "w\->stop ()" 4
		3052	.IX Item "w->stop ()"
		3053	Stops the watcher if it is active. Again, no \f(CW\(C`loop\(C'\fR argument.
		3054	.ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4
		3055	.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
		3056	.IX Item "w->again () (ev::timer, ev::periodic only)"
		3057	For \f(CW\(C`ev::timer\(C'\fR and \f(CW\(C`ev::periodic\(C'\fR, this invokes the corresponding
		3058	\&\f(CW\(C`ev_TYPE_again\(C'\fR function.
		3059	.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
		3060	.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
		3061	.IX Item "w->sweep () (ev::embed only)"
		3062	Invokes \f(CW\(C`ev_embed_sweep\(C'\fR.
		3063	.ie n .IP "w\->update () (""ev::stat"" only)" 4
		3064	.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
		3065	.IX Item "w->update () (ev::stat only)"
		3066	Invokes \f(CW\(C`ev_stat_stat\(C'\fR.
		3067	.RE
		3068	.RS 4
		3069	.RE
		3070	.PP
		3071	Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
		3072	the constructor.
		3073	.PP
		3074	.Vb 4
		3075	\& class myclass
		3076	\& {
		3077	\& ev::io io ; void io_cb (ev::io &w, int revents);
		3078	\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
		3079	\&
		3080	\& myclass (int fd)
		3081	\& {
		3082	\& io .set <myclass, &myclass::io_cb > (this);
		3083	\& idle.set <myclass, &myclass::idle_cb> (this);
		3084	\&
		3085	\& io.start (fd, ev::READ);
		3086	\& }
		3087	\& };
		3088	.Ve
		3089	.SH "OTHER LANGUAGE BINDINGS"
		3090	.IX Header "OTHER LANGUAGE BINDINGS"
		3091	Libev does not offer other language bindings itself, but bindings for a
		3092	number of languages exist in the form of third-party packages. If you know
		3093	any interesting language binding in addition to the ones listed here, drop
		3094	me a note.
		3095	.IP "Perl" 4
		3096	.IX Item "Perl"
		3097	The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
		3098	libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
		3099	there are additional modules that implement libev-compatible interfaces
		3100	to \f(CW\(C`libadns\(C'\fR (\f(CW\(C`EV::ADNS\(C'\fR, but \f(CW\(C`AnyEvent::DNS\(C'\fR is preferred nowadays),
		3101	\&\f(CW\(C`Net::SNMP\(C'\fR (\f(CW\(C`Net::SNMP::EV\(C'\fR) and the \f(CW\(C`libglib\(C'\fR event core (\f(CW\(C`Glib::EV\(C'\fR
		3102	and \f(CW\(C`EV::Glib\(C'\fR).
		3103	.Sp
		3104	It can be found and installed via \s-1CPAN\s0, its homepage is at
		3105	<http://software.schmorp.de/pkg/EV>.
		3106	.IP "Python" 4
		3107	.IX Item "Python"
		3108	Python bindings can be found at <http://code.google.com/p/pyev/>. It
		3109	seems to be quite complete and well-documented. Note, however, that the
		3110	patch they require for libev is outright dangerous as it breaks the \s-1ABI\s0
		3111	for everybody else, and therefore, should never be applied in an installed
		3112	libev (if python requires an incompatible \s-1ABI\s0 then it needs to embed
		3113	libev).
		3114	.IP "Ruby" 4
		3115	.IX Item "Ruby"
		3116	Tony Arcieri has written a ruby extension that offers access to a subset
		3117	of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
		3118	more on top of it. It can be found via gem servers. Its homepage is at
		3119	<http://rev.rubyforge.org/>.
		3120	.IP "D" 4
		3121	.IX Item "D"
		3122	Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
		3123	be found at <http://proj.llucax.com.ar/wiki/evd>.
		3124	.IP "Ocaml" 4
		3125	.IX Item "Ocaml"
		3126	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3127	<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
		3128	.SH "MACRO MAGIC"
		3129	.IX Header "MACRO MAGIC"
		3130	Libev can be compiled with a variety of options, the most fundamental
		3131	of which is \f(CW\(C`EV_MULTIPLICITY\(C'\fR. This option determines whether (most)
		3132	functions and callbacks have an initial \f(CW\(C`struct ev_loop \*(C'\fR argument.
		3133	.PP
		3134	To make it easier to write programs that cope with either variant, the
		3135	following macros are defined:
		3136	.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
		3137	.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
		3138	.IX Item "EV_A, EV_A_"
		3139	This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
		3140	loop argument\(R"). The \f(CW\(C`EV_A\*(C'\fR form is used when this is the sole argument,
		3141	\&\f(CW\(C`EV_A_\(C'\fR is used when other arguments are following. Example:
		3142	.Sp
		3143	.Vb 3
		3144	\& ev_unref (EV_A);
		3145	\& ev_timer_add (EV_A_ watcher);
		3146	\& ev_loop (EV_A_ 0);
		3147	.Ve
		3148	.Sp
		3149	It assumes the variable \f(CW\(C`loop\(C'\fR of type \f(CW\(C`struct ev_loop \*(C'\fR is in scope,
		3150	which is often provided by the following macro.
		3151	.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
		3152	.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
		3153	.IX Item "EV_P, EV_P_"
		3154	This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
		3155	loop parameter\(R"). The \f(CW\(C`EV_P\*(C'\fR form is used when this is the sole parameter,
		3156	\&\f(CW\(C`EV_P_\(C'\fR is used when other parameters are following. Example:
		3157	.Sp
		3158	.Vb 2
		3159	\& // this is how ev_unref is being declared
		3160	\& static void ev_unref (EV_P);
		3161	\&
		3162	\& // this is how you can declare your typical callback
		3163	\& static void cb (EV_P_ ev_timer *w, int revents)
		3164	.Ve
		3165	.Sp
		3166	It declares a parameter \f(CW\(C`loop\(C'\fR of type \f(CW\(C`struct ev_loop \*(C'\fR, quite
		3167	suitable for use with \f(CW\(C`EV_A\(C'\fR.
		3168	.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
		3169	.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
		3170	.IX Item "EV_DEFAULT, EV_DEFAULT_"
		3171	Similar to the other two macros, this gives you the value of the default
		3172	loop, if multiple loops are supported (\(L"ev loop default\(R").
		3173	.ie n .IP """EV_DEFAULT_UC""\fR, \f(CW""EV_DEFAULT_UC_""" 4
		3174	.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
		3175	.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
		3176	Usage identical to \f(CW\(C`EV_DEFAULT\(C'\fR and \f(CW\(C`EV_DEFAULT_\(C'\fR, but requires that the
		3177	default loop has been initialised (\f(CW\(C`UC\(C'\fR == unchecked). Their behaviour
		3178	is undefined when the default loop has not been initialised by a previous
		3179	execution of \f(CW\(C`EV_DEFAULT\(C'\fR, \f(CW\(C`EV_DEFAULT_\(C'\fR or \f(CW\(C`ev_default_init (...)\(C'\fR.
		3180	.Sp
		3181	It is often prudent to use \f(CW\(C`EV_DEFAULT\(C'\fR when initialising the first
		3182	watcher in a function but use \f(CW\(C`EV_DEFAULT_UC\(C'\fR afterwards.
		3183	.PP
		3184	Example: Declare and initialise a check watcher, utilising the above
		3185	macros so it will work regardless of whether multiple loops are supported
		3186	or not.
		3187	.PP
		3188	.Vb 5
		3189	\& static void
		3190	\& check_cb (EV_P_ ev_timer *w, int revents)
		3191	\& {
		3192	\& ev_check_stop (EV_A_ w);
		3193	\& }
		3194	\&
		3195	\& ev_check check;
		3196	\& ev_check_init (&check, check_cb);
		3197	\& ev_check_start (EV_DEFAULT_ &check);
		3198	\& ev_loop (EV_DEFAULT_ 0);
		3199	.Ve
		3200	.SH "EMBEDDING"
		3201	.IX Header "EMBEDDING"
		3202	Libev can (and often is) directly embedded into host
		3203	applications. Examples of applications that embed it include the Deliantra
		3204	Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
		3205	and rxvt-unicode.
		3206	.PP
		3207	The goal is to enable you to just copy the necessary files into your
		3208	source directory without having to change even a single line in them, so
		3209	you can easily upgrade by simply copying (or having a checked-out copy of
		3210	libev somewhere in your source tree).
		3211	.Sh "\s-1FILESETS\s0"
		3212	.IX Subsection "FILESETS"
		3213	Depending on what features you need you need to include one or more sets of files
		3214	in your application.
		3215	.PP
		3216	\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
		3217	.IX Subsection "CORE EVENT LOOP"
		3218	.PP
		3219	To include only the libev core (all the \f(CW\(C`ev_\*(C'\fR functions), with manual
		3220	configuration (no autoconf):
		3221	.PP
		3222	.Vb 2
		3223	\& #define EV_STANDALONE 1
		3224	\& #include "ev.c"
		3225	.Ve
		3226	.PP
		3227	This will automatically include \fIev.h\fR, too, and should be done in a
		3228	single C source file only to provide the function implementations. To use
		3229	it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
		3230	done by writing a wrapper around \fIev.h\fR that you can include instead and
		3231	where you can put other configuration options):
		3232	.PP
		3233	.Vb 2
		3234	\& #define EV_STANDALONE 1
		3235	\& #include "ev.h"
		3236	.Ve
		3237	.PP
		3238	Both header files and implementation files can be compiled with a \*(C+
		3239	compiler (at least, that's a stated goal, and breakage will be treated
		3240	as a bug).
		3241	.PP
		3242	You need the following files in your source tree, or in a directory
		3243	in your include path (e.g. in libev/ when using \-Ilibev):
		3244	.PP
		3245	.Vb 4
		3246	\& ev.h
		3247	\& ev.c
		3248	\& ev_vars.h
		3249	\& ev_wrap.h
		3250	\&
		3251	\& ev_win32.c required on win32 platforms only
		3252	\&
		3253	\& ev_select.c only when select backend is enabled (which is enabled by default)
		3254	\& ev_poll.c only when poll backend is enabled (disabled by default)
		3255	\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
		3256	\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
		3257	\& ev_port.c only when the solaris port backend is enabled (disabled by default)
		3258	.Ve
		3259	.PP
		3260	\&\fIev.c\fR includes the backend files directly when enabled, so you only need
		3261	to compile this single file.
		3262	.PP
		3263	\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
		3264	.IX Subsection "LIBEVENT COMPATIBILITY API"
		3265	.PP
		3266	To include the libevent compatibility \s-1API\s0, also include:
		3267	.PP
		3268	.Vb 1
		3269	\& #include "event.c"
		3270	.Ve
		3271	.PP
		3272	in the file including \fIev.c\fR, and:
		3273	.PP
		3274	.Vb 1
		3275	\& #include "event.h"
		3276	.Ve
		3277	.PP
		3278	in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
		3279	.PP
		3280	You need the following additional files for this:
		3281	.PP
		3282	.Vb 2
		3283	\& event.h
		3284	\& event.c
		3285	.Ve
		3286	.PP
		3287	\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
		3288	.IX Subsection "AUTOCONF SUPPORT"
		3289	.PP
		3290	Instead of using \f(CW\(C`EV_STANDALONE=1\(C'\fR and providing your configuration in
		3291	whatever way you want, you can also \f(CW\(C`m4_include([libev.m4])\(C'\fR in your
		3292	\&\fIconfigure.ac\fR and leave \f(CW\(C`EV_STANDALONE\(C'\fR undefined. \fIev.c\fR will then
		3293	include \fIconfig.h\fR and configure itself accordingly.
		3294	.PP
		3295	For this of course you need the m4 file:
		3296	.PP
		3297	.Vb 1
		3298	\& libev.m4
		3299	.Ve
		3300	.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
		3301	.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
		3302	Libev can be configured via a variety of preprocessor symbols you have to
		3303	define before including any of its files. The default in the absence of
		3304	autoconf is documented for every option.
		3305	.IP "\s-1EV_STANDALONE\s0" 4
		3306	.IX Item "EV_STANDALONE"
		3307	Must always be \f(CW1\fR if you do not use autoconf configuration, which
		3308	keeps libev from including \fIconfig.h\fR, and it also defines dummy
		3309	implementations for some libevent functions (such as logging, which is not
		3310	supported). It will also not define any of the structs usually found in
		3311	\&\fIevent.h\fR that are not directly supported by the libev core alone.
		3312	.IP "\s-1EV_USE_MONOTONIC\s0" 4
		3313	.IX Item "EV_USE_MONOTONIC"
		3314	If defined to be \f(CW1\fR, libev will try to detect the availability of the
		3315	monotonic clock option at both compile time and runtime. Otherwise no use
		3316	of the monotonic clock option will be attempted. If you enable this, you
		3317	usually have to link against librt or something similar. Enabling it when
		3318	the functionality isn't available is safe, though, although you have
		3319	to make sure you link against any libraries where the \f(CW\(C`clock_gettime\(C'\fR
		3320	function is hiding in (often \fI\-lrt\fR).
		3321	.IP "\s-1EV_USE_REALTIME\s0" 4
		3322	.IX Item "EV_USE_REALTIME"
		3323	If defined to be \f(CW1\fR, libev will try to detect the availability of the
		3324	real-time clock option at compile time (and assume its availability at
		3325	runtime if successful). Otherwise no use of the real-time clock option will
		3326	be attempted. This effectively replaces \f(CW\(C`gettimeofday\(C'\fR by \f(CW\*(C`clock_get
		3327	(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the
		3328	note about libraries in the description of \f(CW\(C`EV_USE_MONOTONIC\(C'\fR, though.
		3329	.IP "\s-1EV_USE_NANOSLEEP\s0" 4
		3330	.IX Item "EV_USE_NANOSLEEP"
		3331	If defined to be \f(CW1\fR, libev will assume that \f(CW\(C`nanosleep ()\(C'\fR is available
		3332	and will use it for delays. Otherwise it will use \f(CW\(C`select ()\(C'\fR.
		3333	.IP "\s-1EV_USE_EVENTFD\s0" 4
		3334	.IX Item "EV_USE_EVENTFD"
		3335	If defined to be \f(CW1\fR, then libev will assume that \f(CW\(C`eventfd ()\(C'\fR is
		3336	available and will probe for kernel support at runtime. This will improve
		3337	\&\f(CW\(C`ev_signal\(C'\fR and \f(CW\(C`ev_async\(C'\fR performance and reduce resource consumption.
		3338	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3339	2.7 or newer, otherwise disabled.
		3340	.IP "\s-1EV_USE_SELECT\s0" 4
		3341	.IX Item "EV_USE_SELECT"
		3342	If undefined or defined to be \f(CW1\fR, libev will compile in support for the
		3343	\&\f(CW\(C`select\(C'\fR(2) backend. No attempt at auto-detection will be done: if no
		3344	other method takes over, select will be it. Otherwise the select backend
		3345	will not be compiled in.
		3346	.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
		3347	.IX Item "EV_SELECT_USE_FD_SET"
		3348	If defined to \f(CW1\fR, then the select backend will use the system \f(CW\(C`fd_set\(C'\fR
		3349	structure. This is useful if libev doesn't compile due to a missing
		3350	\&\f(CW\(C`NFDBITS\(C'\fR or \f(CW\(C`fd_mask\(C'\fR definition or it mis-guesses the bitset layout on
		3351	exotic systems. This usually limits the range of file descriptors to some
		3352	low limit such as 1024 or might have other limitations (winsocket only
		3353	allows 64 sockets). The \f(CW\(C`FD_SETSIZE\(C'\fR macro, set before compilation, might
		3354	influence the size of the \f(CW\(C`fd_set\(C'\fR used.
		3355	.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
		3356	.IX Item "EV_SELECT_IS_WINSOCKET"
		3357	When defined to \f(CW1\fR, the select backend will assume that
		3358	select/socket/connect etc. don't understand file descriptors but
		3359	wants osf handles on win32 (this is the case when the select to
		3360	be used is the winsock select). This means that it will call
		3361	\&\f(CW\(C`_get_osfhandle\(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
		3362	it is assumed that all these functions actually work on fds, even
		3363	on win32. Should not be defined on non\-win32 platforms.
		3364	.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0" 4
		3365	.IX Item "EV_FD_TO_WIN32_HANDLE"
		3366	If \f(CW\(C`EV_SELECT_IS_WINSOCKET\(C'\fR is enabled, then libev needs a way to map
		3367	file descriptors to socket handles. When not defining this symbol (the
		3368	default), then libev will call \f(CW\(C`_get_osfhandle\(C'\fR, which is usually
		3369	correct. In some cases, programs use their own file descriptor management,
		3370	in which case they can provide this function to map fds to socket handles.
		3371	.IP "\s-1EV_USE_POLL\s0" 4
		3372	.IX Item "EV_USE_POLL"
		3373	If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\(C`poll\(C'\fR(2)
		3374	backend. Otherwise it will be enabled on non\-win32 platforms. It
		3375	takes precedence over select.
		3376	.IP "\s-1EV_USE_EPOLL\s0" 4
		3377	.IX Item "EV_USE_EPOLL"
		3378	If defined to be \f(CW1\fR, libev will compile in support for the Linux
		3379	\&\f(CW\(C`epoll\(C'\fR(7) backend. Its availability will be detected at runtime,
		3380	otherwise another method will be used as fallback. This is the preferred
		3381	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3382	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3383	.IP "\s-1EV_USE_KQUEUE\s0" 4
		3384	.IX Item "EV_USE_KQUEUE"
		3385	If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
		3386	\&\f(CW\(C`kqueue\(C'\fR(2) backend. Its actual availability will be detected at runtime,
		3387	otherwise another method will be used as fallback. This is the preferred
		3388	backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
		3389	supports some types of fds correctly (the only platform we found that
		3390	supports ptys for example was NetBSD), so kqueue might be compiled in, but
		3391	not be used unless explicitly requested. The best way to use it is to find
		3392	out whether kqueue supports your type of fd properly and use an embedded
		3393	kqueue loop.
		3394	.IP "\s-1EV_USE_PORT\s0" 4
		3395	.IX Item "EV_USE_PORT"
		3396	If defined to be \f(CW1\fR, libev will compile in support for the Solaris
		3397	10 port style backend. Its availability will be detected at runtime,
		3398	otherwise another method will be used as fallback. This is the preferred
		3399	backend for Solaris 10 systems.
		3400	.IP "\s-1EV_USE_DEVPOLL\s0" 4
		3401	.IX Item "EV_USE_DEVPOLL"
		3402	Reserved for future expansion, works like the \s-1USE\s0 symbols above.
		3403	.IP "\s-1EV_USE_INOTIFY\s0" 4
		3404	.IX Item "EV_USE_INOTIFY"
		3405	If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
		3406	interface to speed up \f(CW\(C`ev_stat\(C'\fR watchers. Its actual availability will
		3407	be detected at runtime. If undefined, it will be enabled if the headers
		3408	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3409	.IP "\s-1EV_ATOMIC_T\s0" 4
		3410	.IX Item "EV_ATOMIC_T"
		3411	Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
		3412	access is atomic with respect to other threads or signal contexts. No such
		3413	type is easily found in the C language, so you can provide your own type
		3414	that you know is safe for your purposes. It is used both for signal handler \(L"locking\(R"
		3415	as well as for signal and thread safety in \f(CW\(C`ev_async\(C'\fR watchers.
		3416	.Sp
		3417	In the absence of this define, libev will use \f(CW\(C`sig_atomic_t volatile\(C'\fR
		3418	(from \fIsignal.h\fR), which is usually good enough on most platforms.
		3419	.IP "\s-1EV_H\s0" 4
		3420	.IX Item "EV_H"
		3421	The name of the \fIev.h\fR header file used to include it. The default if
		3422	undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
		3423	used to virtually rename the \fIev.h\fR header file in case of conflicts.
		3424	.IP "\s-1EV_CONFIG_H\s0" 4
		3425	.IX Item "EV_CONFIG_H"
		3426	If \f(CW\(C`EV_STANDALONE\(C'\fR isn't \f(CW1\fR, this variable can be used to override
		3427	\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
		3428	\&\f(CW\(C`EV_H\(C'\fR, above.
		3429	.IP "\s-1EV_EVENT_H\s0" 4
		3430	.IX Item "EV_EVENT_H"
		3431	Similarly to \f(CW\(C`EV_H\(C'\fR, this macro can be used to override \fIevent.c\fR's idea
		3432	of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
		3433	.IP "\s-1EV_PROTOTYPES\s0" 4
		3434	.IX Item "EV_PROTOTYPES"
		3435	If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
		3436	prototypes, but still define all the structs and other symbols. This is
		3437	occasionally useful if you want to provide your own wrapper functions
		3438	around libev functions.
		3439	.IP "\s-1EV_MULTIPLICITY\s0" 4
		3440	.IX Item "EV_MULTIPLICITY"
		3441	If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
		3442	will have the \f(CW\(C`struct ev_loop \*(C'\fR as first argument, and you can create
		3443	additional independent event loops. Otherwise there will be no support
		3444	for multiple event loops and there is no first event loop pointer
		3445	argument. Instead, all functions act on the single default loop.
		3446	.IP "\s-1EV_MINPRI\s0" 4
		3447	.IX Item "EV_MINPRI"
		3448	.PD 0
		3449	.IP "\s-1EV_MAXPRI\s0" 4
		3450	.IX Item "EV_MAXPRI"
		3451	.PD
		3452	The range of allowed priorities. \f(CW\(C`EV_MINPRI\(C'\fR must be smaller or equal to
		3453	\&\f(CW\(C`EV_MAXPRI\(C'\fR, but otherwise there are no non-obvious limitations. You can
		3454	provide for more priorities by overriding those symbols (usually defined
		3455	to be \f(CW\(C`\-2\(C'\fR and \f(CW2\fR, respectively).
		3456	.Sp
		3457	When doing priority-based operations, libev usually has to linearly search
		3458	all the priorities, so having many of them (hundreds) uses a lot of space
		3459	and time, so using the defaults of five priorities (\-2 .. +2) is usually
		3460	fine.
		3461	.Sp
		3462	If your embedding application does not need any priorities, defining these
		3463	both to \f(CW0\fR will save some memory and \s-1CPU\s0.
		3464	.IP "\s-1EV_PERIODIC_ENABLE\s0" 4
		3465	.IX Item "EV_PERIODIC_ENABLE"
		3466	If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
		3467	defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
		3468	code.
		3469	.IP "\s-1EV_IDLE_ENABLE\s0" 4
		3470	.IX Item "EV_IDLE_ENABLE"
		3471	If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
		3472	defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
		3473	code.
		3474	.IP "\s-1EV_EMBED_ENABLE\s0" 4
		3475	.IX Item "EV_EMBED_ENABLE"
		3476	If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
		3477	defined to be \f(CW0\fR, then they are not. Embed watchers rely on most other
		3478	watcher types, which therefore must not be disabled.
		3479	.IP "\s-1EV_STAT_ENABLE\s0" 4
		3480	.IX Item "EV_STAT_ENABLE"
		3481	If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
		3482	defined to be \f(CW0\fR, then they are not.
		3483	.IP "\s-1EV_FORK_ENABLE\s0" 4
		3484	.IX Item "EV_FORK_ENABLE"
		3485	If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
		3486	defined to be \f(CW0\fR, then they are not.
		3487	.IP "\s-1EV_ASYNC_ENABLE\s0" 4
		3488	.IX Item "EV_ASYNC_ENABLE"
		3489	If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
		3490	defined to be \f(CW0\fR, then they are not.
		3491	.IP "\s-1EV_MINIMAL\s0" 4
		3492	.IX Item "EV_MINIMAL"
		3493	If you need to shave off some kilobytes of code at the expense of some
		3494	speed, define this symbol to \f(CW1\fR. Currently this is used to override some
		3495	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3496	much smaller 2\-heap for timer management over the default 4\-heap.
		3497	.IP "\s-1EV_PID_HASHSIZE\s0" 4
		3498	.IX Item "EV_PID_HASHSIZE"
		3499	\&\f(CW\(C`ev_child\(C'\fR watchers use a small hash table to distribute workload by
		3500	pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\(C`EV_MINIMAL\(C'\fR), usually more
		3501	than enough. If you need to manage thousands of children you might want to
		3502	increase this value (\fImust\fR be a power of two).
		3503	.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
		3504	.IX Item "EV_INOTIFY_HASHSIZE"
		3505	\&\f(CW\(C`ev_stat\(C'\fR watchers use a small hash table to distribute workload by
		3506	inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\(C`EV_MINIMAL\(C'\fR),
		3507	usually more than enough. If you need to manage thousands of \f(CW\(C`ev_stat\(C'\fR
		3508	watchers you might want to increase this value (\fImust\fR be a power of
		3509	two).
		3510	.IP "\s-1EV_USE_4HEAP\s0" 4
		3511	.IX Item "EV_USE_4HEAP"
		3512	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3513	timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
		3514	to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
		3515	faster performance with many (thousands) of watchers.
		3516	.Sp
		3517	The default is \f(CW1\fR unless \f(CW\(C`EV_MINIMAL\(C'\fR is set in which case it is \f(CW0\fR
		3518	(disabled).
		3519	.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
		3520	.IX Item "EV_HEAP_CACHE_AT"
		3521	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3522	timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
		3523	the heap structure (selected by defining \f(CW\(C`EV_HEAP_CACHE_AT\(C'\fR to \f(CW1\fR),
		3524	which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
		3525	but avoids random read accesses on heap changes. This improves performance
		3526	noticeably with many (hundreds) of watchers.
		3527	.Sp
		3528	The default is \f(CW1\fR unless \f(CW\(C`EV_MINIMAL\(C'\fR is set in which case it is \f(CW0\fR
		3529	(disabled).
		3530	.IP "\s-1EV_VERIFY\s0" 4
		3531	.IX Item "EV_VERIFY"
		3532	Controls how much internal verification (see \f(CW\(C`ev_loop_verify ()\(C'\fR) will
		3533	be done: If set to \f(CW0\fR, no internal verification code will be compiled
		3534	in. If set to \f(CW1\fR, then verification code will be compiled in, but not
		3535	called. If set to \f(CW2\fR, then the internal verification code will be
		3536	called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
		3537	verification code will be called very frequently, which will slow down
		3538	libev considerably.
		3539	.Sp
		3540	The default is \f(CW1\fR, unless \f(CW\(C`EV_MINIMAL\(C'\fR is set, in which case it will be
		3541	\&\f(CW0\fR.
		3542	.IP "\s-1EV_COMMON\s0" 4
		3543	.IX Item "EV_COMMON"
		3544	By default, all watchers have a \f(CW\(C`void data\*(C'\fR member. By redefining
		3545	this macro to a something else you can include more and other types of
		3546	members. You have to define it each time you include one of the files,
		3547	though, and it must be identical each time.
		3548	.Sp
		3549	For example, the perl \s-1EV\s0 module uses something like this:
		3550	.Sp
		3551	.Vb 3
		3552	\& #define EV_COMMON \e
		3553	\& SV self; / contains this struct */ \e
		3554	\& SV cb_sv, fh /* note no trailing ";" */
		3555	.Ve
		3556	.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
		3557	.IX Item "EV_CB_DECLARE (type)"
		3558	.PD 0
		3559	.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
		3560	.IX Item "EV_CB_INVOKE (watcher, revents)"
		3561	.IP "ev_set_cb (ev, cb)" 4
		3562	.IX Item "ev_set_cb (ev, cb)"
		3563	.PD
		3564	Can be used to change the callback member declaration in each watcher,
		3565	and the way callbacks are invoked and set. Must expand to a struct member
		3566	definition and a statement, respectively. See the \fIev.h\fR header file for
		3567	their default definitions. One possible use for overriding these is to
		3568	avoid the \f(CW\(C`struct ev_loop \*(C'\fR as first argument in all cases, or to use
		3569	method calls instead of plain function calls in \*(C+.
		3570	.Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
		3571	.IX Subsection "EXPORTED API SYMBOLS"
		3572	If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
		3573	exported symbols, you can use the provided \fISymbol.*\fR files which list
		3574	all public symbols, one per line:
		3575	.PP
		3576	.Vb 2
		3577	\& Symbols.ev for libev proper
		3578	\& Symbols.event for the libevent emulation
		3579	.Ve
		3580	.PP
		3581	This can also be used to rename all public symbols to avoid clashes with
		3582	multiple versions of libev linked together (which is obviously bad in
		3583	itself, but sometimes it is inconvenient to avoid this).
		3584	.PP
		3585	A sed command like this will create wrapper \f(CW\(C`#define\(C'\fR's that you need to
		3586	include before including \fIev.h\fR:
		3587	.PP
		3588	.Vb 1
		3589	\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
		3590	.Ve
		3591	.PP
		3592	This would create a file \fIwrap.h\fR which essentially looks like this:
		3593	.PP
		3594	.Vb 4
		3595	\& #define ev_backend myprefix_ev_backend
		3596	\& #define ev_check_start myprefix_ev_check_start
		3597	\& #define ev_check_stop myprefix_ev_check_stop
		3598	\& ...
		3599	.Ve
		3600	.Sh "\s-1EXAMPLES\s0"
		3601	.IX Subsection "EXAMPLES"
		3602	For a real-world example of a program the includes libev
		3603	verbatim, you can have a look at the \s-1EV\s0 perl module
		3604	(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
		3605	the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
		3606	interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
		3607	will be compiled. It is pretty complex because it provides its own header
		3608	file.
		3609	.PP
		3610	The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
		3611	that everybody includes and which overrides some configure choices:
		3612	.PP
		3613	.Vb 9
		3614	\& #define EV_MINIMAL 1
		3615	\& #define EV_USE_POLL 0
		3616	\& #define EV_MULTIPLICITY 0
		3617	\& #define EV_PERIODIC_ENABLE 0
		3618	\& #define EV_STAT_ENABLE 0
		3619	\& #define EV_FORK_ENABLE 0
		3620	\& #define EV_CONFIG_H <config.h>
		3621	\& #define EV_MINPRI 0
		3622	\& #define EV_MAXPRI 0
		3623	\&
		3624	\& #include "ev++.h"
		3625	.Ve
		3626	.PP
		3627	And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
		3628	.PP
		3629	.Vb 2
		3630	\& #include "ev_cpp.h"
		3631	\& #include "ev.c"
		3632	.Ve
		3633	.SH "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
		3634	.IX Header "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
		3635	.Sh "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
		3636	.IX Subsection "THREADS AND COROUTINES"
		3637	\fI\s-1THREADS\s0\fR
		3638	.IX Subsection "THREADS"
		3639	.PP
		3640	All libev functions are reentrant and thread-safe unless explicitly
		3641	documented otherwise, but libev implements no locking itself. This means
		3642	that you can use as many loops as you want in parallel, as long as there
		3643	are no concurrent calls into any libev function with the same loop
		3644	parameter (\f(CW\(C`ev_default_\*(C'\fR calls have an implicit default loop parameter,
		3645	of course): libev guarantees that different event loops share no data
		3646	structures that need any locking.
		3647	.PP
		3648	Or to put it differently: calls with different loop parameters can be done
		3649	concurrently from multiple threads, calls with the same loop parameter
		3650	must be done serially (but can be done from different threads, as long as
		3651	only one thread ever is inside a call at any point in time, e.g. by using
		3652	a mutex per loop).
		3653	.PP
		3654	Specifically to support threads (and signal handlers), libev implements
		3655	so-called \f(CW\(C`ev_async\(C'\fR watchers, which allow some limited form of
		3656	concurrency on the same event loop, namely waking it up \*(L"from the
		3657	outside\*(R".
		3658	.PP
		3659	If you want to know which design (one loop, locking, or multiple loops
		3660	without or something else still) is best for your problem, then I cannot
		3661	help you, but here is some generic advice:
		3662	.IP "\(bu" 4
		3663	most applications have a main thread: use the default libev loop
		3664	in that thread, or create a separate thread running only the default loop.
		3665	.Sp
		3666	This helps integrating other libraries or software modules that use libev
		3667	themselves and don't care/know about threading.
		3668	.IP "\(bu" 4
		3669	one loop per thread is usually a good model.
		3670	.Sp
		3671	Doing this is almost never wrong, sometimes a better-performance model
		3672	exists, but it is always a good start.
		3673	.IP "\(bu" 4
		3674	other models exist, such as the leader/follower pattern, where one
		3675	loop is handed through multiple threads in a kind of round-robin fashion.
		3676	.Sp
		3677	Choosing a model is hard \- look around, learn, know that usually you can do
		3678	better than you currently do :\-)
		3679	.IP "\(bu" 4
		3680	often you need to talk to some other thread which blocks in the
		3681	event loop.
		3682	.Sp
		3683	\&\f(CW\(C`ev_async\(C'\fR watchers can be used to wake them up from other threads safely
		3684	(or from signal contexts...).
		3685	.Sp
		3686	An example use would be to communicate signals or other events that only
		3687	work in the default loop by registering the signal watcher with the
		3688	default loop and triggering an \f(CW\(C`ev_async\(C'\fR watcher from the default loop
		3689	watcher callback into the event loop interested in the signal.
		3690	.PP
		3691	\fI\s-1COROUTINES\s0\fR
		3692	.IX Subsection "COROUTINES"
		3693	.PP
		3694	Libev is very accommodating to coroutines (\(L"cooperative threads\(R"):
		3695	libev fully supports nesting calls to its functions from different
		3696	coroutines (e.g. you can call \f(CW\(C`ev_loop\(C'\fR on the same loop from two
		3697	different coroutines, and switch freely between both coroutines running the
		3698	loop, as long as you don't confuse yourself). The only exception is that
		3699	you must not do this from \f(CW\(C`ev_periodic\(C'\fR reschedule callbacks.
		3700	.PP
		3701	Care has been taken to ensure that libev does not keep local state inside
		3702	\&\f(CW\(C`ev_loop\(C'\fR, and other calls do not usually allow for coroutine switches as
		3703	they do not call any callbacks.
		3704	.Sh "\s-1COMPILER\s0 \s-1WARNINGS\s0"
		3705	.IX Subsection "COMPILER WARNINGS"
		3706	Depending on your compiler and compiler settings, you might get no or a
		3707	lot of warnings when compiling libev code. Some people are apparently
		3708	scared by this.
		3709	.PP
		3710	However, these are unavoidable for many reasons. For one, each compiler
		3711	has different warnings, and each user has different tastes regarding
		3712	warning options. \(L"Warn-free\(R" code therefore cannot be a goal except when
		3713	targeting a specific compiler and compiler-version.
		3714	.PP
		3715	Another reason is that some compiler warnings require elaborate
		3716	workarounds, or other changes to the code that make it less clear and less
		3717	maintainable.
		3718	.PP
		3719	And of course, some compiler warnings are just plain stupid, or simply
		3720	wrong (because they don't actually warn about the condition their message
		3721	seems to warn about). For example, certain older gcc versions had some
		3722	warnings that resulted an extreme number of false positives. These have
		3723	been fixed, but some people still insist on making code warn-free with
		3724	such buggy versions.
		3725	.PP
		3726	While libev is written to generate as few warnings as possible,
		3727	\&\(L"warn-free\(R" code is not a goal, and it is recommended not to build libev
		3728	with any compiler warnings enabled unless you are prepared to cope with
		3729	them (e.g. by ignoring them). Remember that warnings are just that:
		3730	warnings, not errors, or proof of bugs.
		3731	.Sh "\s-1VALGRIND\s0"
		3732	.IX Subsection "VALGRIND"
		3733	Valgrind has a special section here because it is a popular tool that is
		3734	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3735	.PP
		3736	If you think you found a bug (memory leak, uninitialised data access etc.)
		3737	in libev, then check twice: If valgrind reports something like:
		3738	.PP
		3739	.Vb 3
		3740	\& ==2274== definitely lost: 0 bytes in 0 blocks.
		3741	\& ==2274== possibly lost: 0 bytes in 0 blocks.
		3742	\& ==2274== still reachable: 256 bytes in 1 blocks.
		3743	.Ve
		3744	.PP
		3745	Then there is no memory leak, just as memory accounted to global variables
		3746	is not a memleak \- the memory is still being referenced, and didn't leak.
		3747	.PP
		3748	Similarly, under some circumstances, valgrind might report kernel bugs
		3749	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3750	although an acceptable workaround has been found here), or it might be
		3751	confused.
		3752	.PP
		3753	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3754	make it into some kind of religion.
		3755	.PP
		3756	If you are unsure about something, feel free to contact the mailing list
		3757	with the full valgrind report and an explanation on why you think this
		3758	is a bug in libev (best check the archives, too :). However, don't be
		3759	annoyed when you get a brisk \(L"this is no bug\(R" answer and take the chance
		3760	of learning how to interpret valgrind properly.
		3761	.PP
		3762	If you need, for some reason, empty reports from valgrind for your project
		3763	I suggest using suppression lists.
		3764	.SH "PORTABILITY NOTES"
		3765	.IX Header "PORTABILITY NOTES"
		3766	.Sh "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
		3767	.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
		3768	Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
		3769	requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
		3770	model. Libev still offers limited functionality on this platform in
		3771	the form of the \f(CW\(C`EVBACKEND_SELECT\(C'\fR backend, and only supports socket
		3772	descriptors. This only applies when using Win32 natively, not when using
		3773	e.g. cygwin.
		3774	.PP
		3775	Lifting these limitations would basically require the full
		3776	re-implementation of the I/O system. If you are into these kinds of
		3777	things, then note that glib does exactly that for you in a very portable
		3778	way (note also that glib is the slowest event library known to man).
		3779	.PP
		3780	There is no supported compilation method available on windows except
		3781	embedding it into other applications.
		3782	.PP
		3783	Not a libev limitation but worth mentioning: windows apparently doesn't
		3784	accept large writes: instead of resulting in a partial write, windows will
		3785	either accept everything or return \f(CW\(C`ENOBUFS\(C'\fR if the buffer is too large,
		3786	so make sure you only write small amounts into your sockets (less than a
		3787	megabyte seems safe, but this apparently depends on the amount of memory
		3788	available).
		3789	.PP
		3790	Due to the many, low, and arbitrary limits on the win32 platform and
		3791	the abysmal performance of winsockets, using a large number of sockets
		3792	is not recommended (and not reasonable). If your program needs to use
		3793	more than a hundred or so sockets, then likely it needs to use a totally
		3794	different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
		3795	notification model, which cannot be implemented efficiently on windows
		3796	(Microsoft monopoly games).
		3797	.PP
		3798	A typical way to use libev under windows is to embed it (see the embedding
		3799	section for details) and use the following \fIevwrap.h\fR header file instead
		3800	of \fIev.h\fR:
		3801	.PP
		3802	.Vb 2
		3803	\& #define EV_STANDALONE /* keeps ev from requiring config.h */
		3804	\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3805	\&
		3806	\& #include "ev.h"
		3807	.Ve
		3808	.PP
		3809	And compile the following \fIevwrap.c\fR file into your project (make sure
		3810	you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
		3811	.PP
		3812	.Vb 2
		3813	\& #include "evwrap.h"
		3814	\& #include "ev.c"
		3815	.Ve
		3816	.IP "The winsocket select function" 4
		3817	.IX Item "The winsocket select function"
		3818	The winsocket \f(CW\(C`select\(C'\fR function doesn't follow \s-1POSIX\s0 in that it
		3819	requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
		3820	also extremely buggy). This makes select very inefficient, and also
		3821	requires a mapping from file descriptors to socket handles (the Microsoft
		3822	C runtime provides the function \f(CW\(C`_open_osfhandle\(C'\fR for this). See the
		3823	discussion of the \f(CW\(C`EV_SELECT_USE_FD_SET\(C'\fR, \f(CW\(C`EV_SELECT_IS_WINSOCKET\(C'\fR and
		3824	\&\f(CW\(C`EV_FD_TO_WIN32_HANDLE\(C'\fR preprocessor symbols for more info.
		3825	.Sp
		3826	The configuration for a \(L"naked\(R" win32 using the Microsoft runtime
		3827	libraries and raw winsocket select is:
		3828	.Sp
		3829	.Vb 2
		3830	\& #define EV_USE_SELECT 1
		3831	\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3832	.Ve
		3833	.Sp
		3834	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3835	complexity in the O(nA\*^X) range when using win32.
		3836	.IP "Limited number of file descriptors" 4
		3837	.IX Item "Limited number of file descriptors"
		3838	Windows has numerous arbitrary (and low) limits on things.
		3839	.Sp
		3840	Early versions of winsocket's select only supported waiting for a maximum
		3841	of \f(CW64\fR handles (probably owning to the fact that all windows kernels
		3842	can only wait for \f(CW64\fR things at the same time internally; Microsoft
		3843	recommends spawning a chain of threads and wait for 63 handles and the
		3844	previous thread in each. Great).
		3845	.Sp
		3846	Newer versions support more handles, but you need to define \f(CW\(C`FD_SETSIZE\(C'\fR
		3847	to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
		3848	call (which might be in libev or elsewhere, for example, perl does its own
		3849	select emulation on windows).
		3850	.Sp
		3851	Another limit is the number of file descriptors in the Microsoft runtime
		3852	libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR fetish
		3853	or something like this inside Microsoft). You can increase this by calling
		3854	\&\f(CW\(C`_setmaxstdio\(C'\fR, which can increase this limit to \f(CW2048\fR (another
		3855	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3856	libraries.
		3857	.Sp
		3858	This might get you to about \f(CW512\fR or \f(CW2048\fR sockets (depending on
		3859	windows version and/or the phase of the moon). To get more, you need to
		3860	wrap all I/O functions and provide your own fd management, but the cost of
		3861	calling select (O(nA\*^X)) will likely make this unworkable.
		3862	.Sh "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
		3863	.IX Subsection "PORTABILITY REQUIREMENTS"
		3864	In addition to a working ISO-C implementation and of course the
		3865	backend-specific APIs, libev relies on a few additional extensions:
		3866	.ie n .IP """void ()(ev_watcher_type , int revents)""\fR must have compatible calling conventions regardless of \f(CW""ev_watcher_type *""." 4
		3867	.el .IP "\f(CWvoid ()(ev_watcher_type , int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
		3868	.IX Item "void ()(ev_watcher_type , int revents) must have compatible calling conventions regardless of ev_watcher_type *."
		3869	Libev assumes not only that all watcher pointers have the same internal
		3870	structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
		3871	assumes that the same (machine) code can be used to call any watcher
		3872	callback: The watcher callbacks have different type signatures, but libev
		3873	calls them using an \f(CW\(C`ev_watcher \*(C'\fR internally.
		3874	.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
		3875	.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
		3876	.IX Item "sig_atomic_t volatile must be thread-atomic as well"
		3877	The type \f(CW\(C`sig_atomic_t volatile\(C'\fR (or whatever is defined as
		3878	\&\f(CW\(C`EV_ATOMIC_T\(C'\fR) must be atomic with respect to accesses from different
		3879	threads. This is not part of the specification for \f(CW\(C`sig_atomic_t\(C'\fR, but is
		3880	believed to be sufficiently portable.
		3881	.ie n .IP """sigprocmask"" must work in a threaded environment" 4
		3882	.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
		3883	.IX Item "sigprocmask must work in a threaded environment"
		3884	Libev uses \f(CW\(C`sigprocmask\(C'\fR to temporarily block signals. This is not
		3885	allowed in a threaded program (\f(CW\(C`pthread_sigmask\(C'\fR has to be used). Typical
		3886	pthread implementations will either allow \f(CW\(C`sigprocmask\(C'\fR in the \*(L"main
		3887	thread\*(R" or will block signals process-wide, both behaviours would
		3888	be compatible with libev. Interaction between \f(CW\(C`sigprocmask\(C'\fR and
		3889	\&\f(CW\(C`pthread_sigmask\(C'\fR could complicate things, however.
		3890	.Sp
		3891	The most portable way to handle signals is to block signals in all threads
		3892	except the initial one, and run the default loop in the initial thread as
		3893	well.
		3894	.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
		3895	.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
		3896	.IX Item "long must be large enough for common memory allocation sizes"
		3897	To improve portability and simplify its \s-1API\s0, libev uses \f(CW\(C`long\(C'\fR internally
		3898	instead of \f(CW\(C`size_t\(C'\fR when allocating its data structures. On non-POSIX
		3899	systems (Microsoft...) this might be unexpectedly low, but is still at
		3900	least 31 bits everywhere, which is enough for hundreds of millions of
		3901	watchers.
		3902	.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
		3903	.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
		3904	.IX Item "double must hold a time value in seconds with enough accuracy"
		3905	The type \f(CW\(C`double\(C'\fR is used to represent timestamps. It is required to
		3906	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3907	enough for at least into the year 4000. This requirement is fulfilled by
		3908	implementations implementing \s-1IEEE\s0 754 (basically all existing ones).
		3909	.PP
		3910	If you know of other additional requirements drop me a note.
		3911	.SH "ALGORITHMIC COMPLEXITIES"
		3912	.IX Header "ALGORITHMIC COMPLEXITIES"
		3913	In this section the complexities of (many of) the algorithms used inside
		3914	libev will be documented. For complexity discussions about backends see
		3915	the documentation for \f(CW\(C`ev_default_init\(C'\fR.
		3916	.PP
		3917	All of the following are about amortised time: If an array needs to be
		3918	extended, libev needs to realloc and move the whole array, but this
		3919	happens asymptotically rarer with higher number of elements, so O(1) might
		3920	mean that libev does a lengthy realloc operation in rare cases, but on
		3921	average it is much faster and asymptotically approaches constant time.
		3922	.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
		3923	.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
		3924	This means that, when you have a watcher that triggers in one hour and
		3925	there are 100 watchers that would trigger before that, then inserting will
		3926	have to skip roughly seven (\f(CW\(C`ld 100\(C'\fR) of these watchers.
		3927	.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
		3928	.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
		3929	That means that changing a timer costs less than removing/adding them,
		3930	as only the relative motion in the event queue has to be paid for.
		3931	.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
		3932	.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
		3933	These just add the watcher into an array or at the head of a list.
		3934	.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
		3935	.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
		3936	.PD 0
		3937	.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
		3938	.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
		3939	.PD
		3940	These watchers are stored in lists, so they need to be walked to find the
		3941	correct watcher to remove. The lists are usually short (you don't usually
		3942	have many watchers waiting for the same fd or signal: one is typical, two
		3943	is rare).
		3944	.IP "Finding the next timer in each loop iteration: O(1)" 4
		3945	.IX Item "Finding the next timer in each loop iteration: O(1)"
		3946	By virtue of using a binary or 4\-heap, the next timer is always found at a
		3947	fixed position in the storage array.
		3948	.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
		3949	.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
		3950	A change means an I/O watcher gets started or stopped, which requires
		3951	libev to recalculate its status (and possibly tell the kernel, depending
		3952	on backend and whether \f(CW\(C`ev_io_set\(C'\fR was used).
		3953	.IP "Activating one watcher (putting it into the pending state): O(1)" 4
		3954	.IX Item "Activating one watcher (putting it into the pending state): O(1)"
		3955	.PD 0
		3956	.IP "Priority handling: O(number_of_priorities)" 4
		3957	.IX Item "Priority handling: O(number_of_priorities)"
		3958	.PD
		3959	Priorities are implemented by allocating some space for each
		3960	priority. When doing priority-based operations, libev usually has to
		3961	linearly search all the priorities, but starting/stopping and activating
		3962	watchers becomes O(1) with respect to priority handling.
		3963	.IP "Sending an ev_async: O(1)" 4
		3964	.IX Item "Sending an ev_async: O(1)"
		3965	.PD 0
		3966	.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
		3967	.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
		3968	.IP "Processing signals: O(max_signal_number)" 4
		3969	.IX Item "Processing signals: O(max_signal_number)"
		3970	.PD
		3971	Sending involves a system call \fIiff\fR there were no other \f(CW\(C`ev_async_send\(C'\fR
		3972	calls in the current loop iteration. Checking for async and signal events
		3973	involves iterating over all running async watchers or all signal numbers.
995	.SH "AUTHOR"	3974	.SH "AUTHOR"
996	.IX Header "AUTHOR"	3975	.IX Header "AUTHOR"
997	Marc Lehmann <libev@schmorp.de>.	3976	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.

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Revision 1.74 by root, Wed Nov 19 10:33:32 2008 UTC