ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/libev/ev.3
Revision: 1.89
Committed: Sat Mar 24 19:38:51 2012 UTC (12 years, 1 month ago) by root
Branch: MAIN
Changes since 1.88: +5 -1 lines
Log Message:
*** empty log message ***

File Contents

# User Rev Content
1 root 1.88 .\" Automatically generated by Pod::Man 2.23 (Pod::Simple 3.14)
2 root 1.1 .\"
3     .\" Standard preamble:
4     .\" ========================================================================
5     .de Sp \" Vertical space (when we can't use .PP)
6     .if t .sp .5v
7     .if n .sp
8     ..
9     .de Vb \" Begin verbatim text
10     .ft CW
11     .nf
12     .ne \\$1
13     ..
14     .de Ve \" End verbatim text
15     .ft R
16     .fi
17     ..
18     .\" Set up some character translations and predefined strings. \*(-- will
19     .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
20 root 1.60 .\" double quote, and \*(R" will give a right double quote. \*(C+ will
21     .\" give a nicer C++. Capital omega is used to do unbreakable dashes and
22     .\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff,
23     .\" nothing in troff, for use with C<>.
24     .tr \(*W-
25 root 1.1 .ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
26     .ie n \{\
27     . ds -- \(*W-
28     . ds PI pi
29     . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
30     . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
31     . ds L" ""
32     . ds R" ""
33     . ds C` ""
34     . ds C' ""
35     'br\}
36     .el\{\
37     . ds -- \|\(em\|
38     . ds PI \(*p
39     . ds L" ``
40     . ds R" ''
41     'br\}
42     .\"
43 root 1.60 .\" Escape single quotes in literal strings from groff's Unicode transform.
44     .ie \n(.g .ds Aq \(aq
45     .el .ds Aq '
46     .\"
47 root 1.1 .\" If the F register is turned on, we'll generate index entries on stderr for
48 root 1.79 .\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
49 root 1.1 .\" entries marked with X<> in POD. Of course, you'll have to process the
50     .\" output yourself in some meaningful fashion.
51 root 1.60 .ie \nF \{\
52 root 1.1 . de IX
53     . tm Index:\\$1\t\\n%\t"\\$2"
54     ..
55     . nr % 0
56     . rr F
57     .\}
58 root 1.60 .el \{\
59     . de IX
60     ..
61     .\}
62 root 1.1 .\"
63     .\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
64     .\" Fear. Run. Save yourself. No user-serviceable parts.
65     . \" fudge factors for nroff and troff
66     .if n \{\
67     . ds #H 0
68     . ds #V .8m
69     . ds #F .3m
70     . ds #[ \f1
71     . ds #] \fP
72     .\}
73     .if t \{\
74     . ds #H ((1u-(\\\\n(.fu%2u))*.13m)
75     . ds #V .6m
76     . ds #F 0
77     . ds #[ \&
78     . ds #] \&
79     .\}
80     . \" simple accents for nroff and troff
81     .if n \{\
82     . ds ' \&
83     . ds ` \&
84     . ds ^ \&
85     . ds , \&
86     . ds ~ ~
87     . ds /
88     .\}
89     .if t \{\
90     . ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
91     . ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
92     . ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
93     . ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
94     . ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
95     . ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
96     .\}
97     . \" troff and (daisy-wheel) nroff accents
98     .ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
99     .ds 8 \h'\*(#H'\(*b\h'-\*(#H'
100     .ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
101     .ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
102     .ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
103     .ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
104     .ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
105     .ds ae a\h'-(\w'a'u*4/10)'e
106     .ds Ae A\h'-(\w'A'u*4/10)'E
107     . \" corrections for vroff
108     .if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
109     .if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
110     . \" for low resolution devices (crt and lpr)
111     .if \n(.H>23 .if \n(.V>19 \
112     \{\
113     . ds : e
114     . ds 8 ss
115     . ds o a
116     . ds d- d\h'-1'\(ga
117     . ds D- D\h'-1'\(hy
118     . ds th \o'bp'
119     . ds Th \o'LP'
120     . ds ae ae
121     . ds Ae AE
122     .\}
123     .rm #[ #] #H #V #F C
124     .\" ========================================================================
125     .\"
126 root 1.65 .IX Title "LIBEV 3"
127 root 1.89 .TH LIBEV 3 "2012-03-23" "libev-4.11" "libev - high performance full featured event loop"
128 root 1.60 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
129     .\" way too many mistakes in technical documents.
130     .if n .ad l
131     .nh
132 root 1.1 .SH "NAME"
133     libev \- a high performance full\-featured event loop written in C
134     .SH "SYNOPSIS"
135     .IX Header "SYNOPSIS"
136 root 1.28 .Vb 1
137 root 1.68 \& #include <ev.h>
138 root 1.28 .Ve
139 root 1.79 .SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
140 root 1.59 .IX Subsection "EXAMPLE PROGRAM"
141 root 1.61 .Vb 2
142 root 1.68 \& // a single header file is required
143     \& #include <ev.h>
144 root 1.60 \&
145 root 1.74 \& #include <stdio.h> // for puts
146     \&
147 root 1.68 \& // every watcher type has its own typedef\*(Aqd struct
148 root 1.73 \& // with the name ev_TYPE
149 root 1.68 \& ev_io stdin_watcher;
150     \& ev_timer timeout_watcher;
151     \&
152     \& // all watcher callbacks have a similar signature
153     \& // this callback is called when data is readable on stdin
154     \& static void
155 root 1.73 \& stdin_cb (EV_P_ ev_io *w, int revents)
156 root 1.68 \& {
157     \& puts ("stdin ready");
158     \& // for one\-shot events, one must manually stop the watcher
159     \& // with its corresponding stop function.
160     \& ev_io_stop (EV_A_ w);
161     \&
162 root 1.82 \& // this causes all nested ev_run\*(Aqs to stop iterating
163     \& ev_break (EV_A_ EVBREAK_ALL);
164 root 1.68 \& }
165     \&
166     \& // another callback, this time for a time\-out
167     \& static void
168 root 1.73 \& timeout_cb (EV_P_ ev_timer *w, int revents)
169 root 1.68 \& {
170     \& puts ("timeout");
171 root 1.82 \& // this causes the innermost ev_run to stop iterating
172     \& ev_break (EV_A_ EVBREAK_ONE);
173 root 1.68 \& }
174     \&
175     \& int
176     \& main (void)
177     \& {
178     \& // use the default event loop unless you have special needs
179 root 1.82 \& struct ev_loop *loop = EV_DEFAULT;
180 root 1.68 \&
181     \& // initialise an io watcher, then start it
182     \& // this one will watch for stdin to become readable
183     \& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
184     \& ev_io_start (loop, &stdin_watcher);
185     \&
186     \& // initialise a timer watcher, then start it
187     \& // simple non\-repeating 5.5 second timeout
188     \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
189     \& ev_timer_start (loop, &timeout_watcher);
190     \&
191     \& // now wait for events to arrive
192 root 1.82 \& ev_run (loop, 0);
193 root 1.68 \&
194 root 1.86 \& // break was called, so exit
195 root 1.68 \& return 0;
196     \& }
197 root 1.27 .Ve
198 root 1.78 .SH "ABOUT THIS DOCUMENT"
199     .IX Header "ABOUT THIS DOCUMENT"
200     This document documents the libev software package.
201     .PP
202 root 1.61 The newest version of this document is also available as an html-formatted
203 root 1.39 web page you might find easier to navigate when reading it for the first
204 root 1.66 time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
205 root 1.39 .PP
206 root 1.78 While this document tries to be as complete as possible in documenting
207     libev, its usage and the rationale behind its design, it is not a tutorial
208     on event-based programming, nor will it introduce event-based programming
209     with libev.
210     .PP
211 root 1.82 Familiarity with event based programming techniques in general is assumed
212 root 1.78 throughout this document.
213 root 1.82 .SH "WHAT TO READ WHEN IN A HURRY"
214     .IX Header "WHAT TO READ WHEN IN A HURRY"
215     This manual tries to be very detailed, but unfortunately, this also makes
216     it very long. If you just want to know the basics of libev, I suggest
217     reading \*(L"\s-1ANATOMY\s0 \s-1OF\s0 A \s-1WATCHER\s0\*(R", then the \*(L"\s-1EXAMPLE\s0 \s-1PROGRAM\s0\*(R" above and
218     look up the missing functions in \*(L"\s-1GLOBAL\s0 \s-1FUNCTIONS\s0\*(R" and the \f(CW\*(C`ev_io\*(C'\fR and
219     \&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER\s0 \s-1TYPES\s0\*(R".
220 root 1.78 .SH "ABOUT LIBEV"
221     .IX Header "ABOUT LIBEV"
222 root 1.1 Libev is an event loop: you register interest in certain events (such as a
223 root 1.54 file descriptor being readable or a timeout occurring), and it will manage
224 root 1.1 these event sources and provide your program with events.
225     .PP
226     To do this, it must take more or less complete control over your process
227     (or thread) by executing the \fIevent loop\fR handler, and will then
228     communicate events via a callback mechanism.
229     .PP
230     You register interest in certain events by registering so-called \fIevent
231     watchers\fR, which are relatively small C structures you initialise with the
232     details of the event, and then hand it over to libev by \fIstarting\fR the
233     watcher.
234 root 1.79 .SS "\s-1FEATURES\s0"
235 root 1.59 .IX Subsection "FEATURES"
236 root 1.31 Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
237     BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
238     for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
239 root 1.80 (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
240     inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
241     timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
242     (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
243     change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
244     loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
245     \&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
246     limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
247 root 1.28 .PP
248     It also is quite fast (see this
249 root 1.88 benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
250 root 1.28 for example).
251 root 1.79 .SS "\s-1CONVENTIONS\s0"
252 root 1.59 .IX Subsection "CONVENTIONS"
253 root 1.61 Libev is very configurable. In this manual the default (and most common)
254     configuration will be described, which supports multiple event loops. For
255     more info about various configuration options please have a look at
256     \&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
257     for multiple event loops, then all functions taking an initial argument of
258 root 1.81 name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
259 root 1.61 this argument.
260 root 1.79 .SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
261 root 1.59 .IX Subsection "TIME REPRESENTATION"
262 root 1.78 Libev represents time as a single floating point number, representing
263 root 1.82 the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
264     somewhere near the beginning of 1970, details are complicated, don't
265     ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
266     too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
267     any calculations on it, you should treat it as some floating point value.
268     .PP
269     Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
270     time differences (e.g. delays) throughout libev.
271 root 1.67 .SH "ERROR HANDLING"
272     .IX Header "ERROR HANDLING"
273     Libev knows three classes of errors: operating system errors, usage errors
274     and internal errors (bugs).
275     .PP
276     When libev catches an operating system error it cannot handle (for example
277 root 1.68 a system call indicating a condition libev cannot fix), it calls the callback
278 root 1.67 set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
279     abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
280     ()\*(C'\fR.
281     .PP
282     When libev detects a usage error such as a negative timer interval, then
283     it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
284     so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
285     the libev caller and need to be fixed there.
286     .PP
287     Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
288     extensive consistency checking code. These do not trigger under normal
289     circumstances, as they indicate either a bug in libev or worse.
290 root 1.1 .SH "GLOBAL FUNCTIONS"
291     .IX Header "GLOBAL FUNCTIONS"
292     These functions can be called anytime, even before initialising the
293     library in any way.
294     .IP "ev_tstamp ev_time ()" 4
295     .IX Item "ev_tstamp ev_time ()"
296 root 1.2 Returns the current time as libev would use it. Please note that the
297     \&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
298 root 1.82 you actually want to know. Also interesting is the combination of
299 root 1.88 \&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
300 root 1.57 .IP "ev_sleep (ev_tstamp interval)" 4
301     .IX Item "ev_sleep (ev_tstamp interval)"
302 root 1.88 Sleep for the given interval: The current thread will be blocked
303     until either it is interrupted or the given time interval has
304     passed (approximately \- it might return a bit earlier even if not
305     interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
306     .Sp
307     Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
308     .Sp
309     The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
310     with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
311 root 1.1 .IP "int ev_version_major ()" 4
312     .IX Item "int ev_version_major ()"
313     .PD 0
314     .IP "int ev_version_minor ()" 4
315     .IX Item "int ev_version_minor ()"
316     .PD
317 root 1.48 You can find out the major and minor \s-1ABI\s0 version numbers of the library
318 root 1.1 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
319     \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
320     symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
321     version of the library your program was compiled against.
322     .Sp
323 root 1.48 These version numbers refer to the \s-1ABI\s0 version of the library, not the
324     release version.
325 root 1.47 .Sp
326 root 1.1 Usually, it's a good idea to terminate if the major versions mismatch,
327 root 1.47 as this indicates an incompatible change. Minor versions are usually
328 root 1.1 compatible to older versions, so a larger minor version alone is usually
329     not a problem.
330 root 1.9 .Sp
331 root 1.28 Example: Make sure we haven't accidentally been linked against the wrong
332 root 1.82 version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
333     such as \s-1LFS\s0 or reentrancy).
334 root 1.9 .Sp
335     .Vb 3
336 root 1.68 \& assert (("libev version mismatch",
337     \& ev_version_major () == EV_VERSION_MAJOR
338     \& && ev_version_minor () >= EV_VERSION_MINOR));
339 root 1.9 .Ve
340 root 1.6 .IP "unsigned int ev_supported_backends ()" 4
341     .IX Item "unsigned int ev_supported_backends ()"
342     Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
343     value) compiled into this binary of libev (independent of their
344     availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
345     a description of the set values.
346 root 1.9 .Sp
347     Example: make sure we have the epoll method, because yeah this is cool and
348     a must have and can we have a torrent of it please!!!11
349     .Sp
350     .Vb 2
351 root 1.68 \& assert (("sorry, no epoll, no sex",
352     \& ev_supported_backends () & EVBACKEND_EPOLL));
353 root 1.9 .Ve
354 root 1.6 .IP "unsigned int ev_recommended_backends ()" 4
355     .IX Item "unsigned int ev_recommended_backends ()"
356 root 1.82 Return the set of all backends compiled into this binary of libev and
357     also recommended for this platform, meaning it will work for most file
358     descriptor types. This set is often smaller than the one returned by
359     \&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
360     and will not be auto-detected unless you explicitly request it (assuming
361     you know what you are doing). This is the set of backends that libev will
362     probe for if you specify no backends explicitly.
363 root 1.10 .IP "unsigned int ev_embeddable_backends ()" 4
364     .IX Item "unsigned int ev_embeddable_backends ()"
365     Returns the set of backends that are embeddable in other event loops. This
366 root 1.82 value is platform-specific but can include backends not available on the
367     current system. To find which embeddable backends might be supported on
368     the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
369     & ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
370 root 1.10 .Sp
371     See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
372 root 1.84 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
373     .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
374 root 1.32 Sets the allocation function to use (the prototype is similar \- the
375 root 1.64 semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
376     used to allocate and free memory (no surprises here). If it returns zero
377     when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
378     or take some potentially destructive action.
379     .Sp
380     Since some systems (at least OpenBSD and Darwin) fail to implement
381     correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
382     \&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
383 root 1.1 .Sp
384     You could override this function in high-availability programs to, say,
385     free some memory if it cannot allocate memory, to use a special allocator,
386     or even to sleep a while and retry until some memory is available.
387 root 1.9 .Sp
388 root 1.28 Example: Replace the libev allocator with one that waits a bit and then
389 root 1.64 retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
390 root 1.9 .Sp
391     .Vb 6
392     \& static void *
393 root 1.26 \& persistent_realloc (void *ptr, size_t size)
394 root 1.9 \& {
395     \& for (;;)
396     \& {
397     \& void *newptr = realloc (ptr, size);
398 root 1.60 \&
399 root 1.9 \& if (newptr)
400     \& return newptr;
401 root 1.60 \&
402 root 1.9 \& sleep (60);
403     \& }
404     \& }
405 root 1.60 \&
406 root 1.9 \& ...
407     \& ev_set_allocator (persistent_realloc);
408     .Ve
409 root 1.84 .IP "ev_set_syserr_cb (void (*cb)(const char *msg))" 4
410     .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg))"
411 root 1.68 Set the callback function to call on a retryable system call error (such
412 root 1.1 as failed select, poll, epoll_wait). The message is a printable string
413     indicating the system call or subsystem causing the problem. If this
414 root 1.68 callback is set, then libev will expect it to remedy the situation, no
415 root 1.1 matter what, when it returns. That is, libev will generally retry the
416     requested operation, or, if the condition doesn't go away, do bad stuff
417     (such as abort).
418 root 1.9 .Sp
419 root 1.28 Example: This is basically the same thing that libev does internally, too.
420 root 1.9 .Sp
421     .Vb 6
422     \& static void
423     \& fatal_error (const char *msg)
424     \& {
425     \& perror (msg);
426     \& abort ();
427     \& }
428 root 1.60 \&
429 root 1.9 \& ...
430     \& ev_set_syserr_cb (fatal_error);
431     .Ve
432 root 1.85 .IP "ev_feed_signal (int signum)" 4
433     .IX Item "ev_feed_signal (int signum)"
434     This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
435     safe to call this function at any time, from any context, including signal
436     handlers or random threads.
437     .Sp
438     Its main use is to customise signal handling in your process, especially
439     in the presence of threads. For example, you could block signals
440     by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
441     creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
442     mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
443     \&\f(CW\*(C`ev_feed_signal\*(C'\fR.
444 root 1.82 .SH "FUNCTIONS CONTROLLING EVENT LOOPS"
445     .IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
446     An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
447     \&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
448     libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
449 root 1.73 .PP
450     The library knows two types of such loops, the \fIdefault\fR loop, which
451 root 1.82 supports child process events, and dynamically created event loops which
452     do not.
453 root 1.1 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
454     .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
455 root 1.82 This returns the \*(L"default\*(R" event loop object, which is what you should
456     normally use when you just need \*(L"the event loop\*(R". Event loop objects and
457     the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
458     \&\f(CW\*(C`ev_loop_new\*(C'\fR.
459     .Sp
460     If the default loop is already initialised then this function simply
461     returns it (and ignores the flags. If that is troubling you, check
462     \&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
463     flags, which should almost always be \f(CW0\fR, unless the caller is also the
464     one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
465 root 1.1 .Sp
466     If you don't know what event loop to use, use the one returned from this
467 root 1.82 function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
468 root 1.1 .Sp
469 root 1.63 Note that this function is \fInot\fR thread-safe, so if you want to use it
470 root 1.82 from multiple threads, you have to employ some kind of mutex (note also
471     that this case is unlikely, as loops cannot be shared easily between
472     threads anyway).
473     .Sp
474     The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
475     and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
476     a problem for your application you can either create a dynamic loop with
477     \&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
478     \&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
479     .Sp
480     Example: This is the most typical usage.
481     .Sp
482     .Vb 2
483     \& if (!ev_default_loop (0))
484     \& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
485     .Ve
486     .Sp
487     Example: Restrict libev to the select and poll backends, and do not allow
488     environment settings to be taken into account:
489     .Sp
490     .Vb 1
491     \& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
492     .Ve
493     .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
494     .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
495     This will create and initialise a new event loop object. If the loop
496     could not be initialised, returns false.
497 root 1.63 .Sp
498 root 1.85 This function is thread-safe, and one common way to use libev with
499     threads is indeed to create one loop per thread, and using the default
500     loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
501 root 1.60 .Sp
502 root 1.1 The flags argument can be used to specify special behaviour or specific
503 root 1.8 backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
504 root 1.1 .Sp
505 root 1.8 The following flags are supported:
506 root 1.1 .RS 4
507     .ie n .IP """EVFLAG_AUTO""" 4
508     .el .IP "\f(CWEVFLAG_AUTO\fR" 4
509     .IX Item "EVFLAG_AUTO"
510     The default flags value. Use this if you have no clue (it's the right
511     thing, believe me).
512     .ie n .IP """EVFLAG_NOENV""" 4
513     .el .IP "\f(CWEVFLAG_NOENV\fR" 4
514     .IX Item "EVFLAG_NOENV"
515 root 1.68 If this flag bit is or'ed into the flag value (or the program runs setuid
516 root 1.1 or setgid) then libev will \fInot\fR look at the environment variable
517     \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
518     override the flags completely if it is found in the environment. This is
519     useful to try out specific backends to test their performance, or to work
520     around bugs.
521 root 1.35 .ie n .IP """EVFLAG_FORKCHECK""" 4
522     .el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
523     .IX Item "EVFLAG_FORKCHECK"
524 root 1.82 Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
525     make libev check for a fork in each iteration by enabling this flag.
526 root 1.35 .Sp
527     This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
528     and thus this might slow down your event loop if you do a lot of loop
529 root 1.37 iterations and little real work, but is usually not noticeable (on my
530 root 1.61 GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
531 root 1.68 without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
532 root 1.35 \&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
533     .Sp
534     The big advantage of this flag is that you can forget about fork (and
535     forget about forgetting to tell libev about forking) when you use this
536     flag.
537     .Sp
538 root 1.68 This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
539 root 1.35 environment variable.
540 root 1.80 .ie n .IP """EVFLAG_NOINOTIFY""" 4
541     .el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
542     .IX Item "EVFLAG_NOINOTIFY"
543     When this flag is specified, then libev will not attempt to use the
544 root 1.84 \&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
545 root 1.80 testing, this flag can be useful to conserve inotify file descriptors, as
546     otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
547 root 1.81 .ie n .IP """EVFLAG_SIGNALFD""" 4
548     .el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
549     .IX Item "EVFLAG_SIGNALFD"
550     When this flag is specified, then libev will attempt to use the
551 root 1.84 \&\fIsignalfd\fR \s-1API\s0 for its \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
552 root 1.81 delivers signals synchronously, which makes it both faster and might make
553     it possible to get the queued signal data. It can also simplify signal
554     handling with threads, as long as you properly block signals in your
555     threads that are not interested in handling them.
556     .Sp
557     Signalfd will not be used by default as this changes your signal mask, and
558     there are a lot of shoddy libraries and programs (glib's threadpool for
559     example) that can't properly initialise their signal masks.
560 root 1.85 .ie n .IP """EVFLAG_NOSIGMASK""" 4
561     .el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
562     .IX Item "EVFLAG_NOSIGMASK"
563     When this flag is specified, then libev will avoid to modify the signal
564 root 1.88 mask. Specifically, this means you have to make sure signals are unblocked
565 root 1.85 when you want to receive them.
566     .Sp
567     This behaviour is useful when you want to do your own signal handling, or
568     want to handle signals only in specific threads and want to avoid libev
569     unblocking the signals.
570     .Sp
571 root 1.86 It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
572     \&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
573     .Sp
574 root 1.85 This flag's behaviour will become the default in future versions of libev.
575 root 1.6 .ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
576     .el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
577     .IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
578 root 1.3 This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
579     libev tries to roll its own fd_set with no limits on the number of fds,
580     but if that fails, expect a fairly low limit on the number of fds when
581 root 1.58 using this backend. It doesn't scale too well (O(highest_fd)), but its
582 root 1.60 usually the fastest backend for a low number of (low-numbered :) fds.
583 root 1.58 .Sp
584     To get good performance out of this backend you need a high amount of
585 root 1.68 parallelism (most of the file descriptors should be busy). If you are
586 root 1.58 writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
587     connections as possible during one iteration. You might also want to have
588     a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
589 root 1.67 readiness notifications you get per iteration.
590 root 1.71 .Sp
591     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
592     \&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
593     \&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
594 root 1.6 .ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
595     .el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
596     .IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
597 root 1.58 And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
598     than select, but handles sparse fds better and has no artificial
599     limit on the number of fds you can use (except it will slow down
600     considerably with a lot of inactive fds). It scales similarly to select,
601     i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
602     performance tips.
603 root 1.71 .Sp
604     This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
605     \&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
606 root 1.6 .ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
607     .el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
608     .IX Item "EVBACKEND_EPOLL (value 4, Linux)"
609 root 1.81 Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
610     kernels).
611     .Sp
612 root 1.88 For few fds, this backend is a bit little slower than poll and select, but
613     it scales phenomenally better. While poll and select usually scale like
614     O(total_fds) where total_fds is the total number of fds (or the highest
615     fd), epoll scales either O(1) or O(active_fds).
616 root 1.73 .Sp
617     The epoll mechanism deserves honorable mention as the most misdesigned
618     of the more advanced event mechanisms: mere annoyances include silently
619     dropping file descriptors, requiring a system call per change per file
620 root 1.84 descriptor (and unnecessary guessing of parameters), problems with dup,
621     returning before the timeout value, resulting in additional iterations
622     (and only giving 5ms accuracy while select on the same platform gives
623     0.1ms) and so on. The biggest issue is fork races, however \- if a program
624     forks then \fIboth\fR parent and child process have to recreate the epoll
625     set, which can take considerable time (one syscall per file descriptor)
626     and is of course hard to detect.
627 root 1.73 .Sp
628 root 1.88 Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
629     but of course \fIdoesn't\fR, and epoll just loves to report events for
630     totally \fIdifferent\fR file descriptors (even already closed ones, so
631     one cannot even remove them from the set) than registered in the set
632     (especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
633     notifications by employing an additional generation counter and comparing
634     that against the events to filter out spurious ones, recreating the set
635     when required. Epoll also erroneously rounds down timeouts, but gives you
636     no way to know when and by how much, so sometimes you have to busy-wait
637     because epoll returns immediately despite a nonzero timeout. And last
638 root 1.82 not least, it also refuses to work with some file descriptors which work
639     perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
640 root 1.3 .Sp
641 root 1.88 Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
642     cobbled together in a hurry, no thought to design or interaction with
643     others. Oh, the pain, will it ever stop...
644 root 1.84 .Sp
645 root 1.54 While stopping, setting and starting an I/O watcher in the same iteration
646 root 1.73 will result in some caching, there is still a system call per such
647     incident (because the same \fIfile descriptor\fR could point to a different
648     \&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
649     file descriptors might not work very well if you register events for both
650     file descriptors.
651 root 1.58 .Sp
652     Best performance from this backend is achieved by not unregistering all
653 root 1.71 watchers for a file descriptor until it has been closed, if possible,
654     i.e. keep at least one watcher active per fd at all times. Stopping and
655     starting a watcher (without re-setting it) also usually doesn't cause
656 root 1.73 extra overhead. A fork can both result in spurious notifications as well
657     as in libev having to destroy and recreate the epoll object, which can
658     take considerable time and thus should be avoided.
659 root 1.58 .Sp
660 root 1.74 All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
661     faster than epoll for maybe up to a hundred file descriptors, depending on
662     the usage. So sad.
663     .Sp
664 root 1.68 While nominally embeddable in other event loops, this feature is broken in
665 root 1.58 all kernel versions tested so far.
666 root 1.71 .Sp
667     This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
668     \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
669 root 1.6 .ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
670     .el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
671     .IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
672 root 1.73 Kqueue deserves special mention, as at the time of this writing, it
673     was broken on all BSDs except NetBSD (usually it doesn't work reliably
674     with anything but sockets and pipes, except on Darwin, where of course
675     it's completely useless). Unlike epoll, however, whose brokenness
676     is by design, these kqueue bugs can (and eventually will) be fixed
677     without \s-1API\s0 changes to existing programs. For this reason it's not being
678     \&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
679     \&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
680     system like NetBSD.
681 root 1.3 .Sp
682 root 1.57 You still can embed kqueue into a normal poll or select backend and use it
683     only for sockets (after having made sure that sockets work with kqueue on
684     the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
685     .Sp
686 root 1.3 It scales in the same way as the epoll backend, but the interface to the
687 root 1.57 kernel is more efficient (which says nothing about its actual speed, of
688     course). While stopping, setting and starting an I/O watcher does never
689 root 1.68 cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
690 root 1.73 two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
691     sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
692     cases
693 root 1.58 .Sp
694     This backend usually performs well under most conditions.
695     .Sp
696     While nominally embeddable in other event loops, this doesn't work
697     everywhere, so you might need to test for this. And since it is broken
698     almost everywhere, you should only use it when you have a lot of sockets
699     (for which it usually works), by embedding it into another event loop
700 root 1.75 (e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR (but \f(CW\*(C`poll\*(C'\fR is of course
701     also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
702 root 1.71 .Sp
703     This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
704     \&\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
705     \&\f(CW\*(C`NOTE_EOF\*(C'\fR.
706 root 1.6 .ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
707     .el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
708     .IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
709 root 1.58 This is not implemented yet (and might never be, unless you send me an
710     implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
711     and is not embeddable, which would limit the usefulness of this backend
712     immensely.
713 root 1.6 .ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
714     .el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
715     .IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
716 root 1.54 This uses the Solaris 10 event port mechanism. As with everything on Solaris,
717 root 1.3 it's really slow, but it still scales very well (O(active_fds)).
718 root 1.7 .Sp
719 root 1.58 While this backend scales well, it requires one system call per active
720     file descriptor per loop iteration. For small and medium numbers of file
721     descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
722     might perform better.
723 root 1.60 .Sp
724 root 1.85 On the positive side, this backend actually performed fully to
725     specification in all tests and is fully embeddable, which is a rare feat
726     among the OS-specific backends (I vastly prefer correctness over speed
727     hacks).
728     .Sp
729     On the negative side, the interface is \fIbizarre\fR \- so bizarre that
730     even sun itself gets it wrong in their code examples: The event polling
731 root 1.88 function sometimes returns events to the caller even though an error
732 root 1.85 occurred, but with no indication whether it has done so or not (yes, it's
733 root 1.88 even documented that way) \- deadly for edge-triggered interfaces where you
734     absolutely have to know whether an event occurred or not because you have
735     to re-arm the watcher.
736 root 1.85 .Sp
737     Fortunately libev seems to be able to work around these idiocies.
738 root 1.71 .Sp
739     This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
740     \&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
741 root 1.6 .ie n .IP """EVBACKEND_ALL""" 4
742     .el .IP "\f(CWEVBACKEND_ALL\fR" 4
743     .IX Item "EVBACKEND_ALL"
744 root 1.4 Try all backends (even potentially broken ones that wouldn't be tried
745     with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
746 root 1.6 \&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
747 root 1.58 .Sp
748 root 1.85 It is definitely not recommended to use this flag, use whatever
749     \&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
750     at all.
751     .ie n .IP """EVBACKEND_MASK""" 4
752     .el .IP "\f(CWEVBACKEND_MASK\fR" 4
753     .IX Item "EVBACKEND_MASK"
754     Not a backend at all, but a mask to select all backend bits from a
755     \&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
756     value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
757 root 1.1 .RE
758     .RS 4
759 root 1.3 .Sp
760 root 1.80 If one or more of the backend flags are or'ed into the flags value,
761     then only these backends will be tried (in the reverse order as listed
762     here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
763     ()\*(C'\fR will be tried.
764 root 1.8 .Sp
765 root 1.82 Example: Try to create a event loop that uses epoll and nothing else.
766 root 1.8 .Sp
767 root 1.82 .Vb 3
768     \& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
769     \& if (!epoller)
770     \& fatal ("no epoll found here, maybe it hides under your chair");
771 root 1.8 .Ve
772     .Sp
773 root 1.71 Example: Use whatever libev has to offer, but make sure that kqueue is
774 root 1.82 used if available.
775 root 1.8 .Sp
776     .Vb 1
777 root 1.82 \& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
778 root 1.8 .Ve
779 root 1.1 .RE
780 root 1.82 .IP "ev_loop_destroy (loop)" 4
781     .IX Item "ev_loop_destroy (loop)"
782     Destroys an event loop object (frees all memory and kernel state
783 root 1.12 etc.). None of the active event watchers will be stopped in the normal
784     sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
785 root 1.68 responsibility to either stop all watchers cleanly yourself \fIbefore\fR
786 root 1.12 calling this function, or cope with the fact afterwards (which is usually
787 root 1.52 the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
788 root 1.12 for example).
789 root 1.52 .Sp
790 root 1.73 Note that certain global state, such as signal state (and installed signal
791     handlers), will not be freed by this function, and related watchers (such
792     as signal and child watchers) would need to be stopped manually.
793 root 1.52 .Sp
794 root 1.82 This function is normally used on loop objects allocated by
795     \&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
796     \&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
797     .Sp
798     Note that it is not advisable to call this function on the default loop
799 root 1.84 except in the rare occasion where you really need to free its resources.
800 root 1.82 If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
801     and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
802     .IP "ev_loop_fork (loop)" 4
803     .IX Item "ev_loop_fork (loop)"
804     This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations to
805     reinitialise the kernel state for backends that have one. Despite the
806 root 1.60 name, you can call it anytime, but it makes most sense after forking, in
807 root 1.82 the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
808     child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
809     .Sp
810     Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
811     a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
812     because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
813     during fork.
814 root 1.60 .Sp
815     On the other hand, you only need to call this function in the child
816 root 1.82 process if and only if you want to use the event loop in the child. If
817     you just fork+exec or create a new loop in the child, you don't have to
818     call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
819     difference, but libev will usually detect this case on its own and do a
820     costly reset of the backend).
821 root 1.1 .Sp
822     The function itself is quite fast and it's usually not a problem to call
823 root 1.82 it just in case after a fork.
824     .Sp
825     Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
826     using pthreads.
827 root 1.1 .Sp
828 root 1.82 .Vb 5
829     \& static void
830     \& post_fork_child (void)
831     \& {
832     \& ev_loop_fork (EV_DEFAULT);
833     \& }
834     \&
835     \& ...
836     \& pthread_atfork (0, 0, post_fork_child);
837 root 1.1 .Ve
838 root 1.61 .IP "int ev_is_default_loop (loop)" 4
839     .IX Item "int ev_is_default_loop (loop)"
840 root 1.71 Returns true when the given loop is, in fact, the default loop, and false
841     otherwise.
842 root 1.82 .IP "unsigned int ev_iteration (loop)" 4
843     .IX Item "unsigned int ev_iteration (loop)"
844     Returns the current iteration count for the event loop, which is identical
845     to the number of times libev did poll for new events. It starts at \f(CW0\fR
846     and happily wraps around with enough iterations.
847 root 1.37 .Sp
848     This value can sometimes be useful as a generation counter of sorts (it
849     \&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
850 root 1.82 \&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
851     prepare and check phases.
852     .IP "unsigned int ev_depth (loop)" 4
853     .IX Item "unsigned int ev_depth (loop)"
854     Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
855 root 1.85 times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
856 root 1.79 .Sp
857 root 1.82 Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
858     \&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
859 root 1.79 in which case it is higher.
860     .Sp
861 root 1.85 Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
862     throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
863     as a hint to avoid such ungentleman-like behaviour unless it's really
864     convenient, in which case it is fully supported.
865 root 1.6 .IP "unsigned int ev_backend (loop)" 4
866     .IX Item "unsigned int ev_backend (loop)"
867     Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
868 root 1.1 use.
869     .IP "ev_tstamp ev_now (loop)" 4
870     .IX Item "ev_tstamp ev_now (loop)"
871     Returns the current \*(L"event loop time\*(R", which is the time the event loop
872 root 1.9 received events and started processing them. This timestamp does not
873     change as long as callbacks are being processed, and this is also the base
874     time used for relative timers. You can treat it as the timestamp of the
875 root 1.54 event occurring (or more correctly, libev finding out about it).
876 root 1.71 .IP "ev_now_update (loop)" 4
877     .IX Item "ev_now_update (loop)"
878     Establishes the current time by querying the kernel, updating the time
879     returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
880 root 1.82 is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
881 root 1.71 .Sp
882     This function is rarely useful, but when some event callback runs for a
883     very long time without entering the event loop, updating libev's idea of
884     the current time is a good idea.
885     .Sp
886     See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
887 root 1.78 .IP "ev_suspend (loop)" 4
888     .IX Item "ev_suspend (loop)"
889     .PD 0
890     .IP "ev_resume (loop)" 4
891     .IX Item "ev_resume (loop)"
892     .PD
893 root 1.82 These two functions suspend and resume an event loop, for use when the
894     loop is not used for a while and timeouts should not be processed.
895 root 1.78 .Sp
896     A typical use case would be an interactive program such as a game: When
897     the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
898     would be best to handle timeouts as if no time had actually passed while
899     the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
900     in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
901     \&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
902     .Sp
903     Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
904     between \f(CW\*(C`ev_suspend\*(C'\fR and \f(CW\*(C`ev_resume\*(C'\fR, and all \f(CW\*(C`ev_periodic\*(C'\fR watchers
905     will be rescheduled (that is, they will lose any events that would have
906 root 1.82 occurred while suspended).
907 root 1.78 .Sp
908     After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
909     given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
910     without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
911     .Sp
912     Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
913     event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
914 root 1.82 .IP "ev_run (loop, int flags)" 4
915     .IX Item "ev_run (loop, int flags)"
916 root 1.1 Finally, this is it, the event handler. This function usually is called
917 root 1.81 after you have initialised all your watchers and you want to start
918 root 1.82 handling events. It will ask the operating system for any new events, call
919     the watcher callbacks, an then repeat the whole process indefinitely: This
920     is why event loops are called \fIloops\fR.
921 root 1.1 .Sp
922 root 1.82 If the flags argument is specified as \f(CW0\fR, it will keep handling events
923     until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
924     called.
925 root 1.1 .Sp
926 root 1.82 Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
927 root 1.9 relying on all watchers to be stopped when deciding when a program has
928 root 1.71 finished (especially in interactive programs), but having a program
929     that automatically loops as long as it has to and no longer by virtue
930     of relying on its watchers stopping correctly, that is truly a thing of
931     beauty.
932 root 1.9 .Sp
933 root 1.85 This function is also \fImostly\fR exception-safe \- you can break out of
934     a \f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
935     exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
936     will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
937     .Sp
938 root 1.82 A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
939     those events and any already outstanding ones, but will not wait and
940     block your process in case there are no events and will return after one
941     iteration of the loop. This is sometimes useful to poll and handle new
942     events while doing lengthy calculations, to keep the program responsive.
943 root 1.1 .Sp
944 root 1.82 A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
945 root 1.71 necessary) and will handle those and any already outstanding ones. It
946     will block your process until at least one new event arrives (which could
947 root 1.73 be an event internal to libev itself, so there is no guarantee that a
948 root 1.71 user-registered callback will be called), and will return after one
949     iteration of the loop.
950     .Sp
951     This is useful if you are waiting for some external event in conjunction
952     with something not expressible using other libev watchers (i.e. "roll your
953 root 1.82 own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
954 root 1.8 usually a better approach for this kind of thing.
955     .Sp
956 root 1.88 Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
957     understanding, not a guarantee that things will work exactly like this in
958     future versions):
959 root 1.8 .Sp
960 root 1.60 .Vb 10
961 root 1.82 \& \- Increment loop depth.
962     \& \- Reset the ev_break status.
963 root 1.60 \& \- Before the first iteration, call any pending watchers.
964 root 1.82 \& LOOP:
965     \& \- If EVFLAG_FORKCHECK was used, check for a fork.
966 root 1.71 \& \- If a fork was detected (by any means), queue and call all fork watchers.
967 root 1.60 \& \- Queue and call all prepare watchers.
968 root 1.82 \& \- If ev_break was called, goto FINISH.
969 root 1.71 \& \- If we have been forked, detach and recreate the kernel state
970     \& as to not disturb the other process.
971 root 1.60 \& \- Update the kernel state with all outstanding changes.
972 root 1.71 \& \- Update the "event loop time" (ev_now ()).
973 root 1.60 \& \- Calculate for how long to sleep or block, if at all
974 root 1.82 \& (active idle watchers, EVRUN_NOWAIT or not having
975 root 1.60 \& any active watchers at all will result in not sleeping).
976     \& \- Sleep if the I/O and timer collect interval say so.
977 root 1.82 \& \- Increment loop iteration counter.
978 root 1.60 \& \- Block the process, waiting for any events.
979     \& \- Queue all outstanding I/O (fd) events.
980 root 1.71 \& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
981     \& \- Queue all expired timers.
982     \& \- Queue all expired periodics.
983 root 1.82 \& \- Queue all idle watchers with priority higher than that of pending events.
984 root 1.60 \& \- Queue all check watchers.
985     \& \- Call all queued watchers in reverse order (i.e. check watchers first).
986 root 1.8 \& Signals and child watchers are implemented as I/O watchers, and will
987     \& be handled here by queueing them when their watcher gets executed.
988 root 1.82 \& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
989     \& were used, or there are no active watchers, goto FINISH, otherwise
990     \& continue with step LOOP.
991     \& FINISH:
992     \& \- Reset the ev_break status iff it was EVBREAK_ONE.
993     \& \- Decrement the loop depth.
994     \& \- Return.
995 root 1.2 .Ve
996 root 1.9 .Sp
997 root 1.60 Example: Queue some jobs and then loop until no events are outstanding
998 root 1.9 anymore.
999     .Sp
1000     .Vb 4
1001     \& ... queue jobs here, make sure they register event watchers as long
1002     \& ... as they still have work to do (even an idle watcher will do..)
1003 root 1.82 \& ev_run (my_loop, 0);
1004 root 1.86 \& ... jobs done or somebody called break. yeah!
1005 root 1.9 .Ve
1006 root 1.82 .IP "ev_break (loop, how)" 4
1007     .IX Item "ev_break (loop, how)"
1008     Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
1009 root 1.1 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
1010 root 1.82 \&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
1011     \&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1012 root 1.60 .Sp
1013 root 1.85 This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1014 root 1.72 .Sp
1015 root 1.85 It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1016     which case it will have no effect.
1017 root 1.1 .IP "ev_ref (loop)" 4
1018     .IX Item "ev_ref (loop)"
1019     .PD 0
1020     .IP "ev_unref (loop)" 4
1021     .IX Item "ev_unref (loop)"
1022     .PD
1023     Ref/unref can be used to add or remove a reference count on the event
1024     loop: Every watcher keeps one reference, and as long as the reference
1025 root 1.82 count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
1026 root 1.71 .Sp
1027 root 1.81 This is useful when you have a watcher that you never intend to
1028 root 1.82 unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1029 root 1.81 returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1030     before stopping it.
1031 root 1.71 .Sp
1032 root 1.78 As an example, libev itself uses this for its internal signal pipe: It
1033 root 1.82 is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
1034 root 1.78 exiting if no event watchers registered by it are active. It is also an
1035     excellent way to do this for generic recurring timers or from within
1036     third-party libraries. Just remember to \fIunref after start\fR and \fIref
1037     before stop\fR (but only if the watcher wasn't active before, or was active
1038     before, respectively. Note also that libev might stop watchers itself
1039     (e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1040     in the callback).
1041 root 1.9 .Sp
1042 root 1.82 Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
1043 root 1.9 running when nothing else is active.
1044     .Sp
1045     .Vb 4
1046 root 1.73 \& ev_signal exitsig;
1047 root 1.68 \& ev_signal_init (&exitsig, sig_cb, SIGINT);
1048     \& ev_signal_start (loop, &exitsig);
1049 root 1.85 \& ev_unref (loop);
1050 root 1.9 .Ve
1051     .Sp
1052 root 1.28 Example: For some weird reason, unregister the above signal handler again.
1053 root 1.9 .Sp
1054     .Vb 2
1055 root 1.68 \& ev_ref (loop);
1056     \& ev_signal_stop (loop, &exitsig);
1057 root 1.9 .Ve
1058 root 1.57 .IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1059     .IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1060 root 1.56 .PD 0
1061 root 1.57 .IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1062     .IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1063 root 1.56 .PD
1064     These advanced functions influence the time that libev will spend waiting
1065 root 1.71 for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1066     will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1067     latency.
1068 root 1.56 .Sp
1069     Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1070 root 1.71 allows libev to delay invocation of I/O and timer/periodic callbacks
1071     to increase efficiency of loop iterations (or to increase power-saving
1072     opportunities).
1073     .Sp
1074     The idea is that sometimes your program runs just fast enough to handle
1075     one (or very few) event(s) per loop iteration. While this makes the
1076     program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1077 root 1.56 events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1078     overhead for the actual polling but can deliver many events at once.
1079     .Sp
1080     By setting a higher \fIio collect interval\fR you allow libev to spend more
1081     time collecting I/O events, so you can handle more events per iteration,
1082     at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1083 root 1.88 \&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1084 root 1.79 introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1085     sleep time ensures that libev will not poll for I/O events more often then
1086 root 1.88 once per this interval, on average (as long as the host time resolution is
1087     good enough).
1088 root 1.56 .Sp
1089     Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1090     to spend more time collecting timeouts, at the expense of increased
1091 root 1.71 latency/jitter/inexactness (the watcher callback will be called
1092     later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1093     value will not introduce any overhead in libev.
1094 root 1.56 .Sp
1095 root 1.68 Many (busy) programs can usually benefit by setting the I/O collect
1096 root 1.57 interval to a value near \f(CW0.1\fR or so, which is often enough for
1097     interactive servers (of course not for games), likewise for timeouts. It
1098     usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1099 root 1.79 as this approaches the timing granularity of most systems. Note that if
1100     you do transactions with the outside world and you can't increase the
1101     parallelity, then this setting will limit your transaction rate (if you
1102     need to poll once per transaction and the I/O collect interval is 0.01,
1103 root 1.82 then you can't do more than 100 transactions per second).
1104 root 1.71 .Sp
1105     Setting the \fItimeout collect interval\fR can improve the opportunity for
1106     saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1107     are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1108     times the process sleeps and wakes up again. Another useful technique to
1109     reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1110     they fire on, say, one-second boundaries only.
1111 root 1.79 .Sp
1112     Example: we only need 0.1s timeout granularity, and we wish not to poll
1113     more often than 100 times per second:
1114     .Sp
1115     .Vb 2
1116     \& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1117     \& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1118     .Ve
1119     .IP "ev_invoke_pending (loop)" 4
1120     .IX Item "ev_invoke_pending (loop)"
1121     This call will simply invoke all pending watchers while resetting their
1122 root 1.82 pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1123     but when overriding the invoke callback this call comes handy. This
1124     function can be invoked from a watcher \- this can be useful for example
1125     when you want to do some lengthy calculation and want to pass further
1126     event handling to another thread (you still have to make sure only one
1127     thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1128 root 1.79 .IP "int ev_pending_count (loop)" 4
1129     .IX Item "int ev_pending_count (loop)"
1130     Returns the number of pending watchers \- zero indicates that no watchers
1131     are pending.
1132     .IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1133     .IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1134     This overrides the invoke pending functionality of the loop: Instead of
1135 root 1.82 invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1136 root 1.79 this callback instead. This is useful, for example, when you want to
1137     invoke the actual watchers inside another context (another thread etc.).
1138     .Sp
1139     If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1140     callback.
1141     .IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
1142     .IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
1143     Sometimes you want to share the same loop between multiple threads. This
1144     can be done relatively simply by putting mutex_lock/unlock calls around
1145     each call to a libev function.
1146     .Sp
1147 root 1.82 However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1148     to wait for it to return. One way around this is to wake up the event
1149 root 1.88 loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1150 root 1.82 \&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1151 root 1.79 .Sp
1152     When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1153     suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1154     afterwards.
1155     .Sp
1156     Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1157     \&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1158     .Sp
1159     While event loop modifications are allowed between invocations of
1160     \&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1161     modifications done will affect the event loop, i.e. adding watchers will
1162     have no effect on the set of file descriptors being watched, or the time
1163 root 1.82 waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1164 root 1.79 to take note of any changes you made.
1165     .Sp
1166 root 1.82 In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1167 root 1.79 invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1168     .Sp
1169     See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1170     document.
1171     .IP "ev_set_userdata (loop, void *data)" 4
1172     .IX Item "ev_set_userdata (loop, void *data)"
1173     .PD 0
1174 root 1.85 .IP "void *ev_userdata (loop)" 4
1175     .IX Item "void *ev_userdata (loop)"
1176 root 1.79 .PD
1177     Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1178     \&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1179 root 1.85 \&\f(CW0\fR.
1180 root 1.79 .Sp
1181     These two functions can be used to associate arbitrary data with a loop,
1182     and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1183     \&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1184     any other purpose as well.
1185 root 1.82 .IP "ev_verify (loop)" 4
1186     .IX Item "ev_verify (loop)"
1187 root 1.67 This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1188 root 1.73 compiled in, which is the default for non-minimal builds. It tries to go
1189 root 1.71 through all internal structures and checks them for validity. If anything
1190     is found to be inconsistent, it will print an error message to standard
1191     error and call \f(CW\*(C`abort ()\*(C'\fR.
1192 root 1.67 .Sp
1193     This can be used to catch bugs inside libev itself: under normal
1194     circumstances, this function will never abort as of course libev keeps its
1195     data structures consistent.
1196 root 1.1 .SH "ANATOMY OF A WATCHER"
1197     .IX Header "ANATOMY OF A WATCHER"
1198 root 1.73 In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1199     watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1200     watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1201     .PP
1202 root 1.82 A watcher is an opaque structure that you allocate and register to record
1203     your interest in some event. To make a concrete example, imagine you want
1204     to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1205     for that:
1206 root 1.1 .PP
1207     .Vb 5
1208 root 1.73 \& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
1209 root 1.68 \& {
1210     \& ev_io_stop (w);
1211 root 1.82 \& ev_break (loop, EVBREAK_ALL);
1212 root 1.68 \& }
1213     \&
1214     \& struct ev_loop *loop = ev_default_loop (0);
1215 root 1.73 \&
1216     \& ev_io stdin_watcher;
1217     \&
1218 root 1.68 \& ev_init (&stdin_watcher, my_cb);
1219     \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
1220     \& ev_io_start (loop, &stdin_watcher);
1221 root 1.73 \&
1222 root 1.82 \& ev_run (loop, 0);
1223 root 1.1 .Ve
1224     .PP
1225     As you can see, you are responsible for allocating the memory for your
1226 root 1.73 watcher structures (and it is \fIusually\fR a bad idea to do this on the
1227     stack).
1228     .PP
1229     Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1230     or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1231 root 1.1 .PP
1232 root 1.82 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
1233     *, callback)\*(C'\fR, which expects a callback to be provided. This callback is
1234     invoked each time the event occurs (or, in the case of I/O watchers, each
1235     time the event loop detects that the file descriptor given is readable
1236     and/or writable).
1237 root 1.1 .PP
1238 root 1.73 Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
1239     macro to configure it, with arguments specific to the watcher type. There
1240     is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
1241 root 1.1 .PP
1242     To make the watcher actually watch out for events, you have to start it
1243 root 1.73 with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
1244 root 1.1 *)\*(C'\fR), and you can stop watching for events at any time by calling the
1245 root 1.73 corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
1246 root 1.1 .PP
1247     As long as your watcher is active (has been started but not stopped) you
1248     must not touch the values stored in it. Most specifically you must never
1249 root 1.73 reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
1250 root 1.1 .PP
1251     Each and every callback receives the event loop pointer as first, the
1252     registered watcher structure as second, and a bitset of received events as
1253     third argument.
1254     .PP
1255     The received events usually include a single bit per event type received
1256     (you can receive multiple events at the same time). The possible bit masks
1257     are:
1258     .ie n .IP """EV_READ""" 4
1259     .el .IP "\f(CWEV_READ\fR" 4
1260     .IX Item "EV_READ"
1261     .PD 0
1262     .ie n .IP """EV_WRITE""" 4
1263     .el .IP "\f(CWEV_WRITE\fR" 4
1264     .IX Item "EV_WRITE"
1265     .PD
1266     The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
1267     writable.
1268 root 1.82 .ie n .IP """EV_TIMER""" 4
1269     .el .IP "\f(CWEV_TIMER\fR" 4
1270     .IX Item "EV_TIMER"
1271 root 1.1 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
1272     .ie n .IP """EV_PERIODIC""" 4
1273     .el .IP "\f(CWEV_PERIODIC\fR" 4
1274     .IX Item "EV_PERIODIC"
1275     The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
1276     .ie n .IP """EV_SIGNAL""" 4
1277     .el .IP "\f(CWEV_SIGNAL\fR" 4
1278     .IX Item "EV_SIGNAL"
1279     The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
1280     .ie n .IP """EV_CHILD""" 4
1281     .el .IP "\f(CWEV_CHILD\fR" 4
1282     .IX Item "EV_CHILD"
1283     The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1284 root 1.22 .ie n .IP """EV_STAT""" 4
1285     .el .IP "\f(CWEV_STAT\fR" 4
1286     .IX Item "EV_STAT"
1287     The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
1288 root 1.1 .ie n .IP """EV_IDLE""" 4
1289     .el .IP "\f(CWEV_IDLE\fR" 4
1290     .IX Item "EV_IDLE"
1291     The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
1292     .ie n .IP """EV_PREPARE""" 4
1293     .el .IP "\f(CWEV_PREPARE\fR" 4
1294     .IX Item "EV_PREPARE"
1295     .PD 0
1296     .ie n .IP """EV_CHECK""" 4
1297     .el .IP "\f(CWEV_CHECK\fR" 4
1298     .IX Item "EV_CHECK"
1299     .PD
1300 root 1.82 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts
1301 root 1.1 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
1302 root 1.82 \&\f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it invokes any callbacks for any
1303 root 1.1 received events. Callbacks of both watcher types can start and stop as
1304     many watchers as they want, and all of them will be taken into account
1305     (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
1306 root 1.82 \&\f(CW\*(C`ev_run\*(C'\fR from blocking).
1307 root 1.24 .ie n .IP """EV_EMBED""" 4
1308     .el .IP "\f(CWEV_EMBED\fR" 4
1309     .IX Item "EV_EMBED"
1310     The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1311     .ie n .IP """EV_FORK""" 4
1312     .el .IP "\f(CWEV_FORK\fR" 4
1313     .IX Item "EV_FORK"
1314     The event loop has been resumed in the child process after fork (see
1315     \&\f(CW\*(C`ev_fork\*(C'\fR).
1316 root 1.82 .ie n .IP """EV_CLEANUP""" 4
1317     .el .IP "\f(CWEV_CLEANUP\fR" 4
1318     .IX Item "EV_CLEANUP"
1319     The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1320 root 1.61 .ie n .IP """EV_ASYNC""" 4
1321     .el .IP "\f(CWEV_ASYNC\fR" 4
1322     .IX Item "EV_ASYNC"
1323     The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1324 root 1.78 .ie n .IP """EV_CUSTOM""" 4
1325     .el .IP "\f(CWEV_CUSTOM\fR" 4
1326     .IX Item "EV_CUSTOM"
1327     Not ever sent (or otherwise used) by libev itself, but can be freely used
1328     by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
1329 root 1.1 .ie n .IP """EV_ERROR""" 4
1330     .el .IP "\f(CWEV_ERROR\fR" 4
1331     .IX Item "EV_ERROR"
1332 root 1.68 An unspecified error has occurred, the watcher has been stopped. This might
1333 root 1.1 happen because the watcher could not be properly started because libev
1334     ran out of memory, a file descriptor was found to be closed or any other
1335 root 1.73 problem. Libev considers these application bugs.
1336     .Sp
1337     You best act on it by reporting the problem and somehow coping with the
1338     watcher being stopped. Note that well-written programs should not receive
1339     an error ever, so when your watcher receives it, this usually indicates a
1340     bug in your program.
1341 root 1.1 .Sp
1342 root 1.71 Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
1343     example it might indicate that a fd is readable or writable, and if your
1344     callbacks is well-written it can just attempt the operation and cope with
1345     the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
1346     programs, though, as the fd could already be closed and reused for another
1347     thing, so beware.
1348 root 1.79 .SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1349 root 1.17 .IX Subsection "GENERIC WATCHER FUNCTIONS"
1350 root 1.11 .ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1351     .el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1352     .IX Item "ev_init (ev_TYPE *watcher, callback)"
1353     This macro initialises the generic portion of a watcher. The contents
1354     of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1355     the generic parts of the watcher are initialised, you \fIneed\fR to call
1356     the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1357     type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1358     which rolls both calls into one.
1359     .Sp
1360     You can reinitialise a watcher at any time as long as it has been stopped
1361     (or never started) and there are no pending events outstanding.
1362     .Sp
1363 root 1.73 The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1364 root 1.11 int revents)\*(C'\fR.
1365 root 1.71 .Sp
1366     Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1367     .Sp
1368     .Vb 3
1369     \& ev_io w;
1370     \& ev_init (&w, my_cb);
1371     \& ev_io_set (&w, STDIN_FILENO, EV_READ);
1372     .Ve
1373 root 1.81 .ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1374     .el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1375     .IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1376 root 1.11 This macro initialises the type-specific parts of a watcher. You need to
1377     call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1378     call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1379     macro on a watcher that is active (it can be pending, however, which is a
1380     difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1381     .Sp
1382     Although some watcher types do not have type-specific arguments
1383     (e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1384 root 1.71 .Sp
1385     See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1386 root 1.11 .ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1387     .el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1388     .IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1389 root 1.68 This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1390     calls into a single call. This is the most convenient method to initialise
1391 root 1.11 a watcher. The same limitations apply, of course.
1392 root 1.71 .Sp
1393     Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1394     .Sp
1395     .Vb 1
1396     \& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1397     .Ve
1398 root 1.81 .ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1399     .el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1400     .IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1401 root 1.11 Starts (activates) the given watcher. Only active watchers will receive
1402     events. If the watcher is already active nothing will happen.
1403 root 1.71 .Sp
1404     Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1405     whole section.
1406     .Sp
1407     .Vb 1
1408     \& ev_io_start (EV_DEFAULT_UC, &w);
1409     .Ve
1410 root 1.81 .ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1411     .el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1412     .IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1413 root 1.72 Stops the given watcher if active, and clears the pending status (whether
1414     the watcher was active or not).
1415     .Sp
1416     It is possible that stopped watchers are pending \- for example,
1417     non-repeating timers are being stopped when they become pending \- but
1418     calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1419     pending. If you want to free or reuse the memory used by the watcher it is
1420     therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1421 root 1.11 .IP "bool ev_is_active (ev_TYPE *watcher)" 4
1422     .IX Item "bool ev_is_active (ev_TYPE *watcher)"
1423     Returns a true value iff the watcher is active (i.e. it has been started
1424     and not yet been stopped). As long as a watcher is active you must not modify
1425     it.
1426     .IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1427     .IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1428     Returns a true value iff the watcher is pending, (i.e. it has outstanding
1429     events but its callback has not yet been invoked). As long as a watcher
1430     is pending (but not active) you must not call an init function on it (but
1431 root 1.43 \&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1432     make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1433     it).
1434 root 1.29 .IP "callback ev_cb (ev_TYPE *watcher)" 4
1435     .IX Item "callback ev_cb (ev_TYPE *watcher)"
1436 root 1.11 Returns the callback currently set on the watcher.
1437     .IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1438     .IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1439     Change the callback. You can change the callback at virtually any time
1440     (modulo threads).
1441 root 1.81 .IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1442     .IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1443 root 1.37 .PD 0
1444     .IP "int ev_priority (ev_TYPE *watcher)" 4
1445     .IX Item "int ev_priority (ev_TYPE *watcher)"
1446     .PD
1447     Set and query the priority of the watcher. The priority is a small
1448     integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1449     (default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1450     before watchers with lower priority, but priority will not keep watchers
1451     from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1452     .Sp
1453     If you need to suppress invocation when higher priority events are pending
1454     you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1455     .Sp
1456 root 1.43 You \fImust not\fR change the priority of a watcher as long as it is active or
1457     pending.
1458     .Sp
1459 root 1.78 Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1460     fine, as long as you do not mind that the priority value you query might
1461     or might not have been clamped to the valid range.
1462     .Sp
1463 root 1.37 The default priority used by watchers when no priority has been set is
1464     always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1465     .Sp
1466 root 1.78 See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1467     priorities.
1468 root 1.43 .IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1469     .IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1470     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
1471     \&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1472 root 1.71 can deal with that fact, as both are simply passed through to the
1473     callback.
1474 root 1.43 .IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1475     .IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1476 root 1.71 If the watcher is pending, this function clears its pending status and
1477     returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1478 root 1.43 watcher isn't pending it does nothing and returns \f(CW0\fR.
1479 root 1.71 .Sp
1480     Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1481     callback to be invoked, which can be accomplished with this function.
1482 root 1.81 .IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1483     .IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1484     Feeds the given event set into the event loop, as if the specified event
1485     had happened for the specified watcher (which must be a pointer to an
1486     initialised but not necessarily started event watcher). Obviously you must
1487     not free the watcher as long as it has pending events.
1488     .Sp
1489     Stopping the watcher, letting libev invoke it, or calling
1490     \&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1491     not started in the first place.
1492     .Sp
1493     See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1494     functions that do not need a watcher.
1495 root 1.1 .PP
1496 root 1.85 See also the \*(L"\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0\*(R" and \*(L"\s-1BUILDING\s0 \s-1YOUR\s0
1497     \&\s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0\*(R" idioms.
1498 root 1.82 .SS "\s-1WATCHER\s0 \s-1STATES\s0"
1499     .IX Subsection "WATCHER STATES"
1500     There are various watcher states mentioned throughout this manual \-
1501     active, pending and so on. In this section these states and the rules to
1502     transition between them will be described in more detail \- and while these
1503     rules might look complicated, they usually do \*(L"the right thing\*(R".
1504     .IP "initialiased" 4
1505     .IX Item "initialiased"
1506 root 1.88 Before a watcher can be registered with the event loop it has to be
1507 root 1.82 initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1508     \&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1509     .Sp
1510 root 1.86 In this state it is simply some block of memory that is suitable for
1511     use in an event loop. It can be moved around, freed, reused etc. at
1512     will \- as long as you either keep the memory contents intact, or call
1513     \&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1514 root 1.82 .IP "started/running/active" 4
1515     .IX Item "started/running/active"
1516     Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1517     property of the event loop, and is actively waiting for events. While in
1518     this state it cannot be accessed (except in a few documented ways), moved,
1519     freed or anything else \- the only legal thing is to keep a pointer to it,
1520     and call libev functions on it that are documented to work on active watchers.
1521     .IP "pending" 4
1522     .IX Item "pending"
1523     If a watcher is active and libev determines that an event it is interested
1524     in has occurred (such as a timer expiring), it will become pending. It will
1525     stay in this pending state until either it is stopped or its callback is
1526     about to be invoked, so it is not normally pending inside the watcher
1527     callback.
1528     .Sp
1529     The watcher might or might not be active while it is pending (for example,
1530     an expired non-repeating timer can be pending but no longer active). If it
1531     is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1532     but it is still property of the event loop at this time, so cannot be
1533     moved, freed or reused. And if it is active the rules described in the
1534     previous item still apply.
1535     .Sp
1536     It is also possible to feed an event on a watcher that is not active (e.g.
1537     via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1538     active.
1539     .IP "stopped" 4
1540     .IX Item "stopped"
1541     A watcher can be stopped implicitly by libev (in which case it might still
1542     be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1543     latter will clear any pending state the watcher might be in, regardless
1544     of whether it was active or not, so stopping a watcher explicitly before
1545     freeing it is often a good idea.
1546     .Sp
1547     While stopped (and not pending) the watcher is essentially in the
1548 root 1.86 initialised state, that is, it can be reused, moved, modified in any way
1549     you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1550     it again).
1551 root 1.79 .SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1552 root 1.78 .IX Subsection "WATCHER PRIORITY MODELS"
1553     Many event loops support \fIwatcher priorities\fR, which are usually small
1554     integers that influence the ordering of event callback invocation
1555     between watchers in some way, all else being equal.
1556     .PP
1557     In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1558     description for the more technical details such as the actual priority
1559     range.
1560     .PP
1561     There are two common ways how these these priorities are being interpreted
1562     by event loops:
1563     .PP
1564     In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1565     of lower priority watchers, which means as long as higher priority
1566     watchers receive events, lower priority watchers are not being invoked.
1567     .PP
1568     The less common only-for-ordering model uses priorities solely to order
1569     callback invocation within a single event loop iteration: Higher priority
1570     watchers are invoked before lower priority ones, but they all get invoked
1571     before polling for new events.
1572     .PP
1573     Libev uses the second (only-for-ordering) model for all its watchers
1574     except for idle watchers (which use the lock-out model).
1575     .PP
1576     The rationale behind this is that implementing the lock-out model for
1577     watchers is not well supported by most kernel interfaces, and most event
1578     libraries will just poll for the same events again and again as long as
1579     their callbacks have not been executed, which is very inefficient in the
1580     common case of one high-priority watcher locking out a mass of lower
1581     priority ones.
1582     .PP
1583     Static (ordering) priorities are most useful when you have two or more
1584     watchers handling the same resource: a typical usage example is having an
1585     \&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1586     timeouts. Under load, data might be received while the program handles
1587     other jobs, but since timers normally get invoked first, the timeout
1588     handler will be executed before checking for data. In that case, giving
1589     the timer a lower priority than the I/O watcher ensures that I/O will be
1590     handled first even under adverse conditions (which is usually, but not
1591     always, what you want).
1592     .PP
1593     Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1594     will only be executed when no same or higher priority watchers have
1595     received events, they can be used to implement the \*(L"lock-out\*(R" model when
1596     required.
1597     .PP
1598     For example, to emulate how many other event libraries handle priorities,
1599     you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1600     the normal watcher callback, you just start the idle watcher. The real
1601     processing is done in the idle watcher callback. This causes libev to
1602 root 1.82 continuously poll and process kernel event data for the watcher, but when
1603 root 1.78 the lock-out case is known to be rare (which in turn is rare :), this is
1604     workable.
1605     .PP
1606     Usually, however, the lock-out model implemented that way will perform
1607     miserably under the type of load it was designed to handle. In that case,
1608     it might be preferable to stop the real watcher before starting the
1609     idle watcher, so the kernel will not have to process the event in case
1610     the actual processing will be delayed for considerable time.
1611     .PP
1612     Here is an example of an I/O watcher that should run at a strictly lower
1613     priority than the default, and which should only process data when no
1614     other events are pending:
1615     .PP
1616     .Vb 2
1617     \& ev_idle idle; // actual processing watcher
1618     \& ev_io io; // actual event watcher
1619     \&
1620     \& static void
1621     \& io_cb (EV_P_ ev_io *w, int revents)
1622     \& {
1623     \& // stop the I/O watcher, we received the event, but
1624     \& // are not yet ready to handle it.
1625     \& ev_io_stop (EV_A_ w);
1626     \&
1627 root 1.82 \& // start the idle watcher to handle the actual event.
1628 root 1.78 \& // it will not be executed as long as other watchers
1629     \& // with the default priority are receiving events.
1630     \& ev_idle_start (EV_A_ &idle);
1631     \& }
1632     \&
1633     \& static void
1634 root 1.79 \& idle_cb (EV_P_ ev_idle *w, int revents)
1635 root 1.78 \& {
1636     \& // actual processing
1637     \& read (STDIN_FILENO, ...);
1638     \&
1639     \& // have to start the I/O watcher again, as
1640     \& // we have handled the event
1641     \& ev_io_start (EV_P_ &io);
1642     \& }
1643     \&
1644     \& // initialisation
1645     \& ev_idle_init (&idle, idle_cb);
1646     \& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1647     \& ev_io_start (EV_DEFAULT_ &io);
1648     .Ve
1649     .PP
1650     In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1651     low-priority connections can not be locked out forever under load. This
1652     enables your program to keep a lower latency for important connections
1653     during short periods of high load, while not completely locking out less
1654     important ones.
1655 root 1.1 .SH "WATCHER TYPES"
1656     .IX Header "WATCHER TYPES"
1657     This section describes each watcher in detail, but will not repeat
1658 root 1.22 information given in the last section. Any initialisation/set macros,
1659     functions and members specific to the watcher type are explained.
1660     .PP
1661     Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1662     while the watcher is active, you can look at the member and expect some
1663     sensible content, but you must not modify it (you can modify it while the
1664     watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1665     means you can expect it to have some sensible content while the watcher
1666     is active, but you can also modify it. Modifying it may not do something
1667     sensible or take immediate effect (or do anything at all), but libev will
1668     not crash or malfunction in any way.
1669 root 1.79 .ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
1670     .el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
1671 root 1.17 .IX Subsection "ev_io - is this file descriptor readable or writable?"
1672 root 1.1 I/O watchers check whether a file descriptor is readable or writable
1673 root 1.17 in each iteration of the event loop, or, more precisely, when reading
1674     would not block the process and writing would at least be able to write
1675     some data. This behaviour is called level-triggering because you keep
1676     receiving events as long as the condition persists. Remember you can stop
1677     the watcher if you don't want to act on the event and neither want to
1678     receive future events.
1679 root 1.1 .PP
1680     In general you can register as many read and/or write event watchers per
1681     fd as you want (as long as you don't confuse yourself). Setting all file
1682     descriptors to non-blocking mode is also usually a good idea (but not
1683     required if you know what you are doing).
1684     .PP
1685 root 1.17 Another thing you have to watch out for is that it is quite easy to
1686 root 1.85 receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
1687 root 1.17 be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1688 root 1.85 because there is no data. It is very easy to get into this situation even
1689     with a relatively standard program structure. Thus it is best to always
1690     use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1691     preferable to a program hanging until some data arrives.
1692 root 1.17 .PP
1693 root 1.71 If you cannot run the fd in non-blocking mode (for example you should
1694     not play around with an Xlib connection), then you have to separately
1695     re-test whether a file descriptor is really ready with a known-to-be good
1696 root 1.85 interface such as poll (fortunately in the case of Xlib, it already does
1697     this on its own, so its quite safe to use). Some people additionally
1698 root 1.71 use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1699     indefinitely.
1700     .PP
1701     But really, best use non-blocking mode.
1702 root 1.49 .PP
1703     \fIThe special problem of disappearing file descriptors\fR
1704     .IX Subsection "The special problem of disappearing file descriptors"
1705     .PP
1706 root 1.54 Some backends (e.g. kqueue, epoll) need to be told about closing a file
1707 root 1.71 descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1708     such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1709 root 1.49 descriptor, but when it goes away, the operating system will silently drop
1710     this interest. If another file descriptor with the same number then is
1711     registered with libev, there is no efficient way to see that this is, in
1712     fact, a different file descriptor.
1713     .PP
1714     To avoid having to explicitly tell libev about such cases, libev follows
1715     the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1716     will assume that this is potentially a new file descriptor, otherwise
1717     it is assumed that the file descriptor stays the same. That means that
1718     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
1719     descriptor even if the file descriptor number itself did not change.
1720     .PP
1721     This is how one would do it normally anyway, the important point is that
1722     the libev application should not optimise around libev but should leave
1723     optimisations to libev.
1724 root 1.50 .PP
1725 root 1.55 \fIThe special problem of dup'ed file descriptors\fR
1726     .IX Subsection "The special problem of dup'ed file descriptors"
1727 root 1.54 .PP
1728     Some backends (e.g. epoll), cannot register events for file descriptors,
1729 root 1.59 but only events for the underlying file descriptions. That means when you
1730     have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1731     events for them, only one file descriptor might actually receive events.
1732 root 1.54 .PP
1733 root 1.59 There is no workaround possible except not registering events
1734     for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1735 root 1.54 \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1736     .PP
1737 root 1.85 \fIThe special problem of files\fR
1738     .IX Subsection "The special problem of files"
1739     .PP
1740     Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1741     representing files, and expect it to become ready when their program
1742     doesn't block on disk accesses (which can take a long time on their own).
1743     .PP
1744     However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1745     notification as soon as the kernel knows whether and how much data is
1746     there, and in the case of open files, that's always the case, so you
1747     always get a readiness notification instantly, and your read (or possibly
1748     write) will still block on the disk I/O.
1749     .PP
1750     Another way to view it is that in the case of sockets, pipes, character
1751     devices and so on, there is another party (the sender) that delivers data
1752     on its own, but in the case of files, there is no such thing: the disk
1753     will not send data on its own, simply because it doesn't know what you
1754     wish to read \- you would first have to request some data.
1755     .PP
1756     Since files are typically not-so-well supported by advanced notification
1757     mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1758     to files, even though you should not use it. The reason for this is
1759     convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT\s0, which is
1760     usually a tty, often a pipe, but also sometimes files or special devices
1761     (for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1762     \&\fI/dev/urandom\fR), and even though the file might better be served with
1763     asynchronous I/O instead of with non-blocking I/O, it is still useful when
1764     it \*(L"just works\*(R" instead of freezing.
1765     .PP
1766     So avoid file descriptors pointing to files when you know it (e.g. use
1767     libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT\s0, or
1768     when you rarely read from a file instead of from a socket, and want to
1769     reuse the same code path.
1770     .PP
1771 root 1.54 \fIThe special problem of fork\fR
1772     .IX Subsection "The special problem of fork"
1773     .PP
1774     Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1775     useless behaviour. Libev fully supports fork, but needs to be told about
1776 root 1.85 it in the child if you want to continue to use it in the child.
1777 root 1.54 .PP
1778 root 1.85 To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1779     ()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1780     \&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1781 root 1.54 .PP
1782 root 1.63 \fIThe special problem of \s-1SIGPIPE\s0\fR
1783     .IX Subsection "The special problem of SIGPIPE"
1784     .PP
1785 root 1.71 While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1786     when writing to a pipe whose other end has been closed, your program gets
1787     sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1788     this is sensible behaviour, for daemons, this is usually undesirable.
1789 root 1.63 .PP
1790     So when you encounter spurious, unexplained daemon exits, make sure you
1791     ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1792     somewhere, as that would have given you a big clue).
1793     .PP
1794 root 1.82 \fIThe special problem of \fIaccept()\fIing when you can't\fR
1795     .IX Subsection "The special problem of accept()ing when you can't"
1796     .PP
1797     Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1798     found in post\-2004 Linux) have the peculiar behaviour of not removing a
1799     connection from the pending queue in all error cases.
1800     .PP
1801     For example, larger servers often run out of file descriptors (because
1802     of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1803     rejecting the connection, leading to libev signalling readiness on
1804     the next iteration again (the connection still exists after all), and
1805     typically causing the program to loop at 100% \s-1CPU\s0 usage.
1806     .PP
1807     Unfortunately, the set of errors that cause this issue differs between
1808     operating systems, there is usually little the app can do to remedy the
1809     situation, and no known thread-safe method of removing the connection to
1810     cope with overload is known (to me).
1811     .PP
1812     One of the easiest ways to handle this situation is to just ignore it
1813     \&\- when the program encounters an overload, it will just loop until the
1814     situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1815     event-based way to handle this situation, so it's the best one can do.
1816     .PP
1817     A better way to handle the situation is to log any errors other than
1818     \&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1819     messages, and continue as usual, which at least gives the user an idea of
1820     what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1821     the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1822     usage.
1823     .PP
1824     If your program is single-threaded, then you could also keep a dummy file
1825     descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1826     when you run into \f(CW\*(C`ENFILE\*(C'\fR or \f(CW\*(C`EMFILE\*(C'\fR, close it, run \f(CW\*(C`accept\*(C'\fR,
1827     close that fd, and create a new dummy fd. This will gracefully refuse
1828     clients under typical overload conditions.
1829     .PP
1830     The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1831     is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1832     opportunity for a DoS attack.
1833     .PP
1834 root 1.50 \fIWatcher-Specific Functions\fR
1835     .IX Subsection "Watcher-Specific Functions"
1836 root 1.1 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
1837     .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
1838     .PD 0
1839     .IP "ev_io_set (ev_io *, int fd, int events)" 4
1840     .IX Item "ev_io_set (ev_io *, int fd, int events)"
1841     .PD
1842 root 1.17 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
1843 root 1.71 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
1844     \&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1845 root 1.22 .IP "int fd [read\-only]" 4
1846     .IX Item "int fd [read-only]"
1847     The file descriptor being watched.
1848     .IP "int events [read\-only]" 4
1849     .IX Item "int events [read-only]"
1850     The events being watched.
1851 root 1.9 .PP
1852 root 1.60 \fIExamples\fR
1853     .IX Subsection "Examples"
1854     .PP
1855 root 1.28 Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1856 root 1.60 readable, but only once. Since it is likely line-buffered, you could
1857 root 1.28 attempt to read a whole line in the callback.
1858 root 1.9 .PP
1859     .Vb 6
1860 root 1.68 \& static void
1861 root 1.73 \& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1862 root 1.68 \& {
1863     \& ev_io_stop (loop, w);
1864 root 1.71 \& .. read from stdin here (or from w\->fd) and handle any I/O errors
1865 root 1.68 \& }
1866     \&
1867     \& ...
1868     \& struct ev_loop *loop = ev_default_init (0);
1869 root 1.73 \& ev_io stdin_readable;
1870 root 1.68 \& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1871     \& ev_io_start (loop, &stdin_readable);
1872 root 1.82 \& ev_run (loop, 0);
1873 root 1.9 .Ve
1874 root 1.79 .ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
1875     .el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
1876 root 1.17 .IX Subsection "ev_timer - relative and optionally repeating timeouts"
1877 root 1.1 Timer watchers are simple relative timers that generate an event after a
1878     given time, and optionally repeating in regular intervals after that.
1879     .PP
1880     The timers are based on real time, that is, if you register an event that
1881 root 1.68 times out after an hour and you reset your system clock to January last
1882 root 1.71 year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
1883 root 1.2 detecting time jumps is hard, and some inaccuracies are unavoidable (the
1884 root 1.1 monotonic clock option helps a lot here).
1885     .PP
1886 root 1.71 The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1887 root 1.78 passed (not \fIat\fR, so on systems with very low-resolution clocks this
1888 root 1.88 might introduce a small delay, see \*(L"the special problem of being too
1889     early\*(R", below). If multiple timers become ready during the same loop
1890     iteration then the ones with earlier time-out values are invoked before
1891     ones of the same priority with later time-out values (but this is no
1892     longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1893 root 1.71 .PP
1894 root 1.73 \fIBe smart about timeouts\fR
1895     .IX Subsection "Be smart about timeouts"
1896     .PP
1897     Many real-world problems involve some kind of timeout, usually for error
1898     recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1899     you want to raise some error after a while.
1900     .PP
1901     What follows are some ways to handle this problem, from obvious and
1902     inefficient to smart and efficient.
1903     .PP
1904     In the following, a 60 second activity timeout is assumed \- a timeout that
1905     gets reset to 60 seconds each time there is activity (e.g. each time some
1906     data or other life sign was received).
1907     .IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1908     .IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1909     This is the most obvious, but not the most simple way: In the beginning,
1910     start the watcher:
1911     .Sp
1912     .Vb 2
1913     \& ev_timer_init (timer, callback, 60., 0.);
1914     \& ev_timer_start (loop, timer);
1915     .Ve
1916     .Sp
1917     Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1918     and start it again:
1919     .Sp
1920     .Vb 3
1921     \& ev_timer_stop (loop, timer);
1922     \& ev_timer_set (timer, 60., 0.);
1923     \& ev_timer_start (loop, timer);
1924     .Ve
1925     .Sp
1926     This is relatively simple to implement, but means that each time there is
1927     some activity, libev will first have to remove the timer from its internal
1928     data structure and then add it again. Libev tries to be fast, but it's
1929     still not a constant-time operation.
1930     .ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1931     .el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1932     .IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1933     This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1934     \&\f(CW\*(C`ev_timer_start\*(C'\fR.
1935     .Sp
1936     To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1937     of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1938     successfully read or write some data. If you go into an idle state where
1939     you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1940     the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1941     .Sp
1942     That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1943     \&\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
1944     member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1945     .Sp
1946     At start:
1947     .Sp
1948     .Vb 3
1949 root 1.79 \& ev_init (timer, callback);
1950 root 1.73 \& timer\->repeat = 60.;
1951     \& ev_timer_again (loop, timer);
1952     .Ve
1953     .Sp
1954     Each time there is some activity:
1955     .Sp
1956     .Vb 1
1957     \& ev_timer_again (loop, timer);
1958     .Ve
1959     .Sp
1960     It is even possible to change the time-out on the fly, regardless of
1961     whether the watcher is active or not:
1962     .Sp
1963     .Vb 2
1964     \& timer\->repeat = 30.;
1965     \& ev_timer_again (loop, timer);
1966     .Ve
1967     .Sp
1968     This is slightly more efficient then stopping/starting the timer each time
1969     you want to modify its timeout value, as libev does not have to completely
1970     remove and re-insert the timer from/into its internal data structure.
1971     .Sp
1972     It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1973     .IP "3. Let the timer time out, but then re-arm it as required." 4
1974     .IX Item "3. Let the timer time out, but then re-arm it as required."
1975     This method is more tricky, but usually most efficient: Most timeouts are
1976     relatively long compared to the intervals between other activity \- in
1977     our example, within 60 seconds, there are usually many I/O events with
1978     associated activity resets.
1979     .Sp
1980     In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1981     but remember the time of last activity, and check for a real timeout only
1982     within the callback:
1983     .Sp
1984 root 1.88 .Vb 3
1985     \& ev_tstamp timeout = 60.;
1986 root 1.73 \& ev_tstamp last_activity; // time of last activity
1987 root 1.88 \& ev_timer timer;
1988 root 1.73 \&
1989     \& static void
1990     \& callback (EV_P_ ev_timer *w, int revents)
1991     \& {
1992 root 1.88 \& // calculate when the timeout would happen
1993     \& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
1994 root 1.73 \&
1995 root 1.88 \& // if negative, it means we the timeout already occured
1996     \& if (after < 0.)
1997 root 1.73 \& {
1998 root 1.82 \& // timeout occurred, take action
1999 root 1.73 \& }
2000     \& else
2001     \& {
2002 root 1.88 \& // callback was invoked, but there was some recent
2003     \& // activity. simply restart the timer to time out
2004     \& // after "after" seconds, which is the earliest time
2005     \& // the timeout can occur.
2006     \& ev_timer_set (w, after, 0.);
2007     \& ev_timer_start (EV_A_ w);
2008 root 1.73 \& }
2009     \& }
2010     .Ve
2011     .Sp
2012 root 1.88 To summarise the callback: first calculate in how many seconds the
2013     timeout will occur (by calculating the absolute time when it would occur,
2014     \&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2015     (EV_A)\*(C'\fR from that).
2016     .Sp
2017     If this value is negative, then we are already past the timeout, i.e. we
2018     timed out, and need to do whatever is needed in this case.
2019     .Sp
2020     Otherwise, we now the earliest time at which the timeout would trigger,
2021     and simply start the timer with this timeout value.
2022     .Sp
2023     In other words, each time the callback is invoked it will check whether
2024     the timeout cocured. If not, it will simply reschedule itself to check
2025     again at the earliest time it could time out. Rinse. Repeat.
2026 root 1.73 .Sp
2027     This scheme causes more callback invocations (about one every 60 seconds
2028     minus half the average time between activity), but virtually no calls to
2029     libev to change the timeout.
2030     .Sp
2031 root 1.88 To start the machinery, simply initialise the watcher and set
2032     \&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2033     now), then call the callback, which will \*(L"do the right thing\*(R" and start
2034     the timer:
2035 root 1.73 .Sp
2036     .Vb 3
2037 root 1.88 \& last_activity = ev_now (EV_A);
2038     \& ev_init (&timer, callback);
2039     \& callback (EV_A_ &timer, 0);
2040 root 1.73 .Ve
2041     .Sp
2042 root 1.88 When there is some activity, simply store the current time in
2043 root 1.73 \&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2044     .Sp
2045 root 1.88 .Vb 2
2046     \& if (activity detected)
2047     \& last_activity = ev_now (EV_A);
2048     .Ve
2049     .Sp
2050     When your timeout value changes, then the timeout can be changed by simply
2051     providing a new value, stopping the timer and calling the callback, which
2052     will agaion do the right thing (for example, time out immediately :).
2053     .Sp
2054     .Vb 3
2055     \& timeout = new_value;
2056     \& ev_timer_stop (EV_A_ &timer);
2057     \& callback (EV_A_ &timer, 0);
2058 root 1.73 .Ve
2059     .Sp
2060     This technique is slightly more complex, but in most cases where the
2061     time-out is unlikely to be triggered, much more efficient.
2062     .IP "4. Wee, just use a double-linked list for your timeouts." 4
2063     .IX Item "4. Wee, just use a double-linked list for your timeouts."
2064     If there is not one request, but many thousands (millions...), all
2065     employing some kind of timeout with the same timeout value, then one can
2066     do even better:
2067     .Sp
2068     When starting the timeout, calculate the timeout value and put the timeout
2069     at the \fIend\fR of the list.
2070     .Sp
2071     Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2072     the list is expected to fire (for example, using the technique #3).
2073     .Sp
2074     When there is some activity, remove the timer from the list, recalculate
2075     the timeout, append it to the end of the list again, and make sure to
2076     update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2077     .Sp
2078     This way, one can manage an unlimited number of timeouts in O(1) time for
2079     starting, stopping and updating the timers, at the expense of a major
2080     complication, and having to use a constant timeout. The constant timeout
2081     ensures that the list stays sorted.
2082     .PP
2083     So which method the best?
2084     .PP
2085     Method #2 is a simple no-brain-required solution that is adequate in most
2086     situations. Method #3 requires a bit more thinking, but handles many cases
2087     better, and isn't very complicated either. In most case, choosing either
2088     one is fine, with #3 being better in typical situations.
2089     .PP
2090     Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2091     rather complicated, but extremely efficient, something that really pays
2092     off after the first million or so of active timers, i.e. it's usually
2093     overkill :)
2094     .PP
2095 root 1.88 \fIThe special problem of being too early\fR
2096     .IX Subsection "The special problem of being too early"
2097     .PP
2098     If you ask a timer to call your callback after three seconds, then
2099     you expect it to be invoked after three seconds \- but of course, this
2100     cannot be guaranteed to infinite precision. Less obviously, it cannot be
2101     guaranteed to any precision by libev \- imagine somebody suspending the
2102     process with a \s-1STOP\s0 signal for a few hours for example.
2103     .PP
2104     So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2105     delay has occurred, but cannot guarantee this.
2106     .PP
2107     A less obvious failure mode is calling your callback too early: many event
2108     loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2109     this can cause your callback to be invoked much earlier than you would
2110     expect.
2111     .PP
2112     To see why, imagine a system with a clock that only offers full second
2113     resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2114     yourself). If you schedule a one-second timer at the time 500.9, then the
2115     event loop will schedule your timeout to elapse at a system time of 500
2116     (500.9 truncated to the resolution) + 1, or 501.
2117     .PP
2118     If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2119     501\*(R" and invoke the callback 0.1s after it was started, even though a
2120     one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2121     intentions.
2122     .PP
2123     This is the reason why libev will never invoke the callback if the elapsed
2124     delay equals the requested delay, but only when the elapsed delay is
2125     larger than the requested delay. In the example above, libev would only invoke
2126     the callback at system time 502, or 1.1s after the timer was started.
2127     .PP
2128     So, while libev cannot guarantee that your callback will be invoked
2129     exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2130     delay has actually elapsed, or in other words, it always errs on the \*(L"too
2131     late\*(R" side of things.
2132     .PP
2133 root 1.71 \fIThe special problem of time updates\fR
2134     .IX Subsection "The special problem of time updates"
2135     .PP
2136 root 1.88 Establishing the current time is a costly operation (it usually takes
2137     at least one system call): \s-1EV\s0 therefore updates its idea of the current
2138 root 1.82 time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2139 root 1.71 growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2140     lots of events in one iteration.
2141     .PP
2142 root 1.1 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
2143     time. This is usually the right thing as this timestamp refers to the time
2144 root 1.2 of the event triggering whatever timeout you are modifying/starting. If
2145 root 1.71 you suspect event processing to be delayed and you \fIneed\fR to base the
2146     timeout on the current time, use something like this to adjust for this:
2147 root 1.1 .PP
2148     .Vb 1
2149 root 1.60 \& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
2150 root 1.1 .Ve
2151 root 1.2 .PP
2152 root 1.71 If the event loop is suspended for a long time, you can also force an
2153     update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
2154     ()\*(C'\fR.
2155 root 1.50 .PP
2156 root 1.88 \fIThe special problem of unsynchronised clocks\fR
2157     .IX Subsection "The special problem of unsynchronised clocks"
2158     .PP
2159     Modern systems have a variety of clocks \- libev itself uses the normal
2160     \&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2161     jumps).
2162     .PP
2163     Neither of these clocks is synchronised with each other or any other clock
2164     on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2165     than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2166     a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2167     than a directly following call to \f(CW\*(C`time\*(C'\fR.
2168     .PP
2169     The moral of this is to only compare libev-related timestamps with
2170     \&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2171     a second or so.
2172     .PP
2173     One more problem arises due to this lack of synchronisation: if libev uses
2174     the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2175     or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2176     invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2177     .PP
2178     This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2179     libev makes sure your callback is not invoked before the delay happened,
2180     \&\fImeasured according to the real time\fR, not the system clock.
2181     .PP
2182     If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2183     connection after 100 seconds\*(R") then this shouldn't bother you as it is
2184     exactly the right behaviour.
2185     .PP
2186     If you want to compare wall clock/system timestamps to your timers, then
2187     you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2188     time, where your comparisons will always generate correct results.
2189     .PP
2190 root 1.79 \fIThe special problems of suspended animation\fR
2191     .IX Subsection "The special problems of suspended animation"
2192     .PP
2193     When you leave the server world it is quite customary to hit machines that
2194     can suspend/hibernate \- what happens to the clocks during such a suspend?
2195     .PP
2196     Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2197     all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2198     to run until the system is suspended, but they will not advance while the
2199     system is suspended. That means, on resume, it will be as if the program
2200     was frozen for a few seconds, but the suspend time will not be counted
2201     towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2202     clock advanced as expected, but if it is used as sole clocksource, then a
2203     long suspend would be detected as a time jump by libev, and timers would
2204     be adjusted accordingly.
2205     .PP
2206     I would not be surprised to see different behaviour in different between
2207     operating systems, \s-1OS\s0 versions or even different hardware.
2208     .PP
2209     The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2210     time jump in the monotonic clocks and the realtime clock. If the program
2211     is suspended for a very long time, and monotonic clock sources are in use,
2212     then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2213     will be counted towards the timers. When no monotonic clock source is in
2214     use, then libev will again assume a timejump and adjust accordingly.
2215     .PP
2216     It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2217     and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2218     deterministic behaviour in this case (you can do nothing against
2219     \&\f(CW\*(C`SIGSTOP\*(C'\fR).
2220     .PP
2221 root 1.50 \fIWatcher-Specific Functions and Data Members\fR
2222     .IX Subsection "Watcher-Specific Functions and Data Members"
2223 root 1.1 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
2224     .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
2225     .PD 0
2226     .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
2227     .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
2228     .PD
2229 root 1.67 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
2230     is \f(CW0.\fR, then it will automatically be stopped once the timeout is
2231     reached. If it is positive, then the timer will automatically be
2232     configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2233     until stopped manually.
2234     .Sp
2235     The timer itself will do a best-effort at avoiding drift, that is, if
2236     you configure a timer to trigger every 10 seconds, then it will normally
2237     trigger at exactly 10 second intervals. If, however, your program cannot
2238     keep up with the timer (because it takes longer than those 10 seconds to
2239     do stuff) the timer will not fire more than once per event loop iteration.
2240 root 1.61 .IP "ev_timer_again (loop, ev_timer *)" 4
2241     .IX Item "ev_timer_again (loop, ev_timer *)"
2242 root 1.88 This will act as if the timer timed out, and restarts it again if it is
2243     repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2244     timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
2245 root 1.1 .Sp
2246 root 1.88 The exact semantics are as in the following rules, all of which will be
2247     applied to the watcher:
2248     .RS 4
2249     .IP "If the timer is pending, the pending status is always cleared." 4
2250     .IX Item "If the timer is pending, the pending status is always cleared."
2251     .PD 0
2252     .IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2253     .IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2254     .ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2255     .el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2256     .IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2257     .RE
2258     .RS 4
2259     .PD
2260 root 1.1 .Sp
2261 root 1.73 This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
2262     usage example.
2263 root 1.88 .RE
2264 root 1.81 .IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2265     .IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2266 root 1.79 Returns the remaining time until a timer fires. If the timer is active,
2267     then this time is relative to the current event loop time, otherwise it's
2268     the timeout value currently configured.
2269     .Sp
2270     That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2271 root 1.82 \&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
2272 root 1.79 will return \f(CW4\fR. When the timer expires and is restarted, it will return
2273     roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2274     too), and so on.
2275 root 1.22 .IP "ev_tstamp repeat [read\-write]" 4
2276     .IX Item "ev_tstamp repeat [read-write]"
2277     The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2278 root 1.71 or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2279 root 1.22 which is also when any modifications are taken into account.
2280 root 1.9 .PP
2281 root 1.60 \fIExamples\fR
2282     .IX Subsection "Examples"
2283     .PP
2284 root 1.28 Example: Create a timer that fires after 60 seconds.
2285 root 1.9 .PP
2286     .Vb 5
2287 root 1.68 \& static void
2288 root 1.73 \& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2289 root 1.68 \& {
2290     \& .. one minute over, w is actually stopped right here
2291     \& }
2292     \&
2293 root 1.73 \& ev_timer mytimer;
2294 root 1.68 \& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2295     \& ev_timer_start (loop, &mytimer);
2296 root 1.9 .Ve
2297     .PP
2298 root 1.28 Example: Create a timeout timer that times out after 10 seconds of
2299 root 1.9 inactivity.
2300     .PP
2301     .Vb 5
2302 root 1.68 \& static void
2303 root 1.73 \& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2304 root 1.68 \& {
2305     \& .. ten seconds without any activity
2306     \& }
2307     \&
2308 root 1.73 \& ev_timer mytimer;
2309 root 1.68 \& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2310     \& ev_timer_again (&mytimer); /* start timer */
2311 root 1.82 \& ev_run (loop, 0);
2312 root 1.68 \&
2313     \& // and in some piece of code that gets executed on any "activity":
2314     \& // reset the timeout to start ticking again at 10 seconds
2315     \& ev_timer_again (&mytimer);
2316 root 1.9 .Ve
2317 root 1.79 .ie n .SS """ev_periodic"" \- to cron or not to cron?"
2318     .el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
2319 root 1.17 .IX Subsection "ev_periodic - to cron or not to cron?"
2320 root 1.1 Periodic watchers are also timers of a kind, but they are very versatile
2321     (and unfortunately a bit complex).
2322     .PP
2323 root 1.78 Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
2324     relative time, the physical time that passes) but on wall clock time
2325     (absolute time, the thing you can read on your calender or clock). The
2326     difference is that wall clock time can run faster or slower than real
2327     time, and time jumps are not uncommon (e.g. when you adjust your
2328     wrist-watch).
2329     .PP
2330     You can tell a periodic watcher to trigger after some specific point
2331     in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2332     seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2333     not a delay) and then reset your system clock to January of the previous
2334     year, then it will take a year or more to trigger the event (unlike an
2335     \&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2336     it, as it uses a relative timeout).
2337     .PP
2338     \&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2339     timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2340     other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2341     those cannot react to time jumps.
2342 root 1.2 .PP
2343 root 1.68 As with timers, the callback is guaranteed to be invoked only when the
2344 root 1.78 point in time where it is supposed to trigger has passed. If multiple
2345     timers become ready during the same loop iteration then the ones with
2346     earlier time-out values are invoked before ones with later time-out values
2347 root 1.82 (but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2348 root 1.50 .PP
2349     \fIWatcher-Specific Functions and Data Members\fR
2350     .IX Subsection "Watcher-Specific Functions and Data Members"
2351 root 1.78 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2352     .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2353 root 1.1 .PD 0
2354 root 1.78 .IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
2355     .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
2356 root 1.1 .PD
2357 root 1.78 Lots of arguments, let's sort it out... There are basically three modes of
2358 root 1.71 operation, and we will explain them from simplest to most complex:
2359 root 1.1 .RS 4
2360 root 1.60 .IP "\(bu" 4
2361 root 1.78 absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2362 root 1.60 .Sp
2363 root 1.68 In this configuration the watcher triggers an event after the wall clock
2364 root 1.78 time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
2365     time jump occurs, that is, if it is to be run at January 1st 2011 then it
2366     will be stopped and invoked when the system clock reaches or surpasses
2367     this point in time.
2368 root 1.60 .IP "\(bu" 4
2369 root 1.78 repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2370 root 1.60 .Sp
2371 root 1.1 In this mode the watcher will always be scheduled to time out at the next
2372 root 1.78 \&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
2373     negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2374     argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
2375 root 1.1 .Sp
2376 root 1.71 This can be used to create timers that do not drift with respect to the
2377 root 1.78 system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2378     hour, on the hour (with respect to \s-1UTC\s0):
2379 root 1.1 .Sp
2380     .Vb 1
2381     \& ev_periodic_set (&periodic, 0., 3600., 0);
2382     .Ve
2383     .Sp
2384     This doesn't mean there will always be 3600 seconds in between triggers,
2385 root 1.68 but only that the callback will be called when the system time shows a
2386 root 1.1 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
2387     by 3600.
2388     .Sp
2389     Another way to think about it (for the mathematically inclined) is that
2390     \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
2391 root 1.78 time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
2392 root 1.46 .Sp
2393 root 1.88 The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2394     interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2395     microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2396     at most a similar magnitude as the current time (say, within a factor of
2397     ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2398     \&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2399 root 1.67 .Sp
2400 root 1.68 Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2401 root 1.67 speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2402 root 1.68 will of course deteriorate. Libev itself tries to be exact to be about one
2403 root 1.67 millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2404 root 1.60 .IP "\(bu" 4
2405 root 1.78 manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2406 root 1.60 .Sp
2407 root 1.78 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
2408 root 1.1 ignored. Instead, each time the periodic watcher gets scheduled, the
2409     reschedule callback will be called with the watcher as first, and the
2410     current time as second argument.
2411     .Sp
2412 root 1.78 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
2413     or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
2414     allowed by documentation here\fR.
2415 root 1.67 .Sp
2416     If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2417     it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2418     only event loop modification you are allowed to do).
2419 root 1.1 .Sp
2420 root 1.73 The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
2421 root 1.67 *w, ev_tstamp now)\*(C'\fR, e.g.:
2422 root 1.1 .Sp
2423 root 1.73 .Vb 5
2424     \& static ev_tstamp
2425     \& my_rescheduler (ev_periodic *w, ev_tstamp now)
2426 root 1.1 \& {
2427     \& return now + 60.;
2428     \& }
2429     .Ve
2430     .Sp
2431     It must return the next time to trigger, based on the passed time value
2432     (that is, the lowest time value larger than to the second argument). It
2433     will usually be called just before the callback will be triggered, but
2434     might be called at other times, too.
2435     .Sp
2436 root 1.67 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
2437     equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
2438 root 1.1 .Sp
2439     This can be used to create very complex timers, such as a timer that
2440 root 1.67 triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
2441 root 1.1 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
2442     you do this is, again, up to you (but it is not trivial, which is the main
2443     reason I omitted it as an example).
2444     .RE
2445     .RS 4
2446     .RE
2447     .IP "ev_periodic_again (loop, ev_periodic *)" 4
2448     .IX Item "ev_periodic_again (loop, ev_periodic *)"
2449     Simply stops and restarts the periodic watcher again. This is only useful
2450     when you changed some parameters or the reschedule callback would return
2451     a different time than the last time it was called (e.g. in a crond like
2452     program when the crontabs have changed).
2453 root 1.65 .IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2454     .IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2455 root 1.78 When active, returns the absolute time that the watcher is supposed
2456     to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2457     \&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2458     rescheduling modes.
2459 root 1.46 .IP "ev_tstamp offset [read\-write]" 4
2460     .IX Item "ev_tstamp offset [read-write]"
2461     When repeating, this contains the offset value, otherwise this is the
2462 root 1.78 absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2463     although libev might modify this value for better numerical stability).
2464 root 1.46 .Sp
2465     Can be modified any time, but changes only take effect when the periodic
2466     timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2467 root 1.22 .IP "ev_tstamp interval [read\-write]" 4
2468     .IX Item "ev_tstamp interval [read-write]"
2469     The current interval value. Can be modified any time, but changes only
2470     take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2471     called.
2472 root 1.73 .IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2473     .IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2474 root 1.22 The current reschedule callback, or \f(CW0\fR, if this functionality is
2475     switched off. Can be changed any time, but changes only take effect when
2476     the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2477 root 1.9 .PP
2478 root 1.60 \fIExamples\fR
2479     .IX Subsection "Examples"
2480     .PP
2481 root 1.28 Example: Call a callback every hour, or, more precisely, whenever the
2482 root 1.71 system time is divisible by 3600. The callback invocation times have
2483 root 1.68 potentially a lot of jitter, but good long-term stability.
2484 root 1.9 .PP
2485     .Vb 5
2486 root 1.68 \& static void
2487 root 1.82 \& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
2488 root 1.68 \& {
2489     \& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2490     \& }
2491     \&
2492 root 1.73 \& ev_periodic hourly_tick;
2493 root 1.68 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2494     \& ev_periodic_start (loop, &hourly_tick);
2495 root 1.9 .Ve
2496     .PP
2497 root 1.28 Example: The same as above, but use a reschedule callback to do it:
2498 root 1.9 .PP
2499     .Vb 1
2500 root 1.68 \& #include <math.h>
2501 root 1.60 \&
2502 root 1.68 \& static ev_tstamp
2503 root 1.73 \& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2504 root 1.68 \& {
2505 root 1.71 \& return now + (3600. \- fmod (now, 3600.));
2506 root 1.68 \& }
2507 root 1.60 \&
2508 root 1.68 \& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2509 root 1.9 .Ve
2510     .PP
2511 root 1.28 Example: Call a callback every hour, starting now:
2512 root 1.9 .PP
2513     .Vb 4
2514 root 1.73 \& ev_periodic hourly_tick;
2515 root 1.68 \& ev_periodic_init (&hourly_tick, clock_cb,
2516     \& fmod (ev_now (loop), 3600.), 3600., 0);
2517     \& ev_periodic_start (loop, &hourly_tick);
2518 root 1.9 .Ve
2519 root 1.79 .ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
2520     .el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
2521 root 1.17 .IX Subsection "ev_signal - signal me when a signal gets signalled!"
2522 root 1.1 Signal watchers will trigger an event when the process receives a specific
2523     signal one or more times. Even though signals are very asynchronous, libev
2524 root 1.84 will try its best to deliver signals synchronously, i.e. as part of the
2525 root 1.1 normal event processing, like any other event.
2526     .PP
2527 root 1.80 If you want signals to be delivered truly asynchronously, just use
2528     \&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2529     the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2530     synchronously wake up an event loop.
2531     .PP
2532     You can configure as many watchers as you like for the same signal, but
2533     only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2534     default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2535     \&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2536     the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2537 root 1.71 .PP
2538 root 1.80 When the first watcher gets started will libev actually register something
2539 root 1.71 with the kernel (thus it coexists with your own signal handlers as long as
2540 root 1.80 you don't register any with libev for the same signal).
2541     .PP
2542 root 1.61 If possible and supported, libev will install its handlers with
2543 root 1.80 \&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2544     not be unduly interrupted. If you have a problem with system calls getting
2545     interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2546     and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2547 root 1.61 .PP
2548 root 1.81 \fIThe special problem of inheritance over fork/execve/pthread_create\fR
2549     .IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2550     .PP
2551     Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2552     (\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2553     stopping it again), that is, libev might or might not block the signal,
2554 root 1.86 and might or might not set or restore the installed signal handler (but
2555     see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2556 root 1.81 .PP
2557     While this does not matter for the signal disposition (libev never
2558     sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2559     \&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2560     certain signals to be blocked.
2561     .PP
2562     This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2563     the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2564     choice usually).
2565     .PP
2566     The simplest way to ensure that the signal mask is reset in the child is
2567     to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2568     catch fork calls done by libraries (such as the libc) as well.
2569     .PP
2570     In current versions of libev, the signal will not be blocked indefinitely
2571     unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2572     the window of opportunity for problems, it will not go away, as libev
2573     \&\fIhas\fR to modify the signal mask, at least temporarily.
2574     .PP
2575     So I can't stress this enough: \fIIf you do not reset your signal mask when
2576     you expect it to be empty, you have a race condition in your code\fR. This
2577     is not a libev-specific thing, this is true for most event libraries.
2578     .PP
2579 root 1.85 \fIThe special problem of threads signal handling\fR
2580     .IX Subsection "The special problem of threads signal handling"
2581     .PP
2582     \&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2583     a lot of functionality (sigfd, sigwait etc.) only really works if all
2584     threads in a process block signals, which is hard to achieve.
2585     .PP
2586     When you want to use sigwait (or mix libev signal handling with your own
2587     for the same signals), you can tackle this problem by globally blocking
2588     all signals before creating any threads (or creating them with a fully set
2589     sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2590     loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2591     these signals. You can pass on any signals that libev might be interested
2592     in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2593     .PP
2594 root 1.50 \fIWatcher-Specific Functions and Data Members\fR
2595     .IX Subsection "Watcher-Specific Functions and Data Members"
2596 root 1.1 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
2597     .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
2598     .PD 0
2599     .IP "ev_signal_set (ev_signal *, int signum)" 4
2600     .IX Item "ev_signal_set (ev_signal *, int signum)"
2601     .PD
2602     Configures the watcher to trigger on the given signal number (usually one
2603     of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2604 root 1.22 .IP "int signum [read\-only]" 4
2605     .IX Item "int signum [read-only]"
2606     The signal the watcher watches out for.
2607 root 1.61 .PP
2608     \fIExamples\fR
2609     .IX Subsection "Examples"
2610     .PP
2611 root 1.72 Example: Try to exit cleanly on \s-1SIGINT\s0.
2612 root 1.61 .PP
2613     .Vb 5
2614 root 1.68 \& static void
2615 root 1.73 \& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2616 root 1.68 \& {
2617 root 1.82 \& ev_break (loop, EVBREAK_ALL);
2618 root 1.68 \& }
2619     \&
2620 root 1.73 \& ev_signal signal_watcher;
2621 root 1.68 \& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2622 root 1.72 \& ev_signal_start (loop, &signal_watcher);
2623 root 1.61 .Ve
2624 root 1.79 .ie n .SS """ev_child"" \- watch out for process status changes"
2625     .el .SS "\f(CWev_child\fP \- watch out for process status changes"
2626 root 1.17 .IX Subsection "ev_child - watch out for process status changes"
2627 root 1.1 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
2628 root 1.71 some child status changes (most typically when a child of yours dies or
2629     exits). It is permissible to install a child watcher \fIafter\fR the child
2630     has been forked (which implies it might have already exited), as long
2631     as the event loop isn't entered (or is continued from a watcher), i.e.,
2632     forking and then immediately registering a watcher for the child is fine,
2633 root 1.79 but forking and registering a watcher a few event loop iterations later or
2634     in the next callback invocation is not.
2635 root 1.61 .PP
2636     Only the default event loop is capable of handling signals, and therefore
2637 root 1.68 you can only register child watchers in the default event loop.
2638 root 1.61 .PP
2639 root 1.79 Due to some design glitches inside libev, child watchers will always be
2640     handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2641     libev)
2642     .PP
2643 root 1.61 \fIProcess Interaction\fR
2644     .IX Subsection "Process Interaction"
2645     .PP
2646     Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2647 root 1.80 initialised. This is necessary to guarantee proper behaviour even if the
2648     first child watcher is started after the child exits. The occurrence
2649 root 1.61 of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2650     synchronously as part of the event loop processing. Libev always reaps all
2651     children, even ones not watched.
2652     .PP
2653     \fIOverriding the Built-In Processing\fR
2654     .IX Subsection "Overriding the Built-In Processing"
2655     .PP
2656     Libev offers no special support for overriding the built-in child
2657     processing, but if your application collides with libev's default child
2658     handler, you can override it easily by installing your own handler for
2659     \&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2660     default loop never gets destroyed. You are encouraged, however, to use an
2661     event-based approach to child reaping and thus use libev's support for
2662     that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2663 root 1.50 .PP
2664 root 1.71 \fIStopping the Child Watcher\fR
2665     .IX Subsection "Stopping the Child Watcher"
2666     .PP
2667     Currently, the child watcher never gets stopped, even when the
2668     child terminates, so normally one needs to stop the watcher in the
2669     callback. Future versions of libev might stop the watcher automatically
2670 root 1.80 when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2671     problem).
2672 root 1.71 .PP
2673 root 1.50 \fIWatcher-Specific Functions and Data Members\fR
2674     .IX Subsection "Watcher-Specific Functions and Data Members"
2675 root 1.60 .IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
2676     .IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
2677 root 1.1 .PD 0
2678 root 1.60 .IP "ev_child_set (ev_child *, int pid, int trace)" 4
2679     .IX Item "ev_child_set (ev_child *, int pid, int trace)"
2680 root 1.1 .PD
2681     Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
2682     \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
2683     at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
2684     the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
2685     \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
2686 root 1.60 process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2687     activate the watcher when the process terminates) or \f(CW1\fR (additionally
2688     activate the watcher when the process is stopped or continued).
2689 root 1.22 .IP "int pid [read\-only]" 4
2690     .IX Item "int pid [read-only]"
2691     The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2692     .IP "int rpid [read\-write]" 4
2693     .IX Item "int rpid [read-write]"
2694     The process id that detected a status change.
2695     .IP "int rstatus [read\-write]" 4
2696     .IX Item "int rstatus [read-write]"
2697     The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2698     \&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2699 root 1.9 .PP
2700 root 1.60 \fIExamples\fR
2701     .IX Subsection "Examples"
2702     .PP
2703 root 1.61 Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2704     its completion.
2705 root 1.9 .PP
2706 root 1.61 .Vb 1
2707 root 1.68 \& ev_child cw;
2708 root 1.61 \&
2709 root 1.68 \& static void
2710 root 1.73 \& child_cb (EV_P_ ev_child *w, int revents)
2711 root 1.68 \& {
2712     \& ev_child_stop (EV_A_ w);
2713     \& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2714     \& }
2715     \&
2716     \& pid_t pid = fork ();
2717     \&
2718     \& if (pid < 0)
2719     \& // error
2720     \& else if (pid == 0)
2721     \& {
2722     \& // the forked child executes here
2723     \& exit (1);
2724     \& }
2725     \& else
2726     \& {
2727     \& ev_child_init (&cw, child_cb, pid, 0);
2728     \& ev_child_start (EV_DEFAULT_ &cw);
2729     \& }
2730 root 1.9 .Ve
2731 root 1.79 .ie n .SS """ev_stat"" \- did the file attributes just change?"
2732     .el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2733 root 1.22 .IX Subsection "ev_stat - did the file attributes just change?"
2734 root 1.68 This watches a file system path for attribute changes. That is, it calls
2735 root 1.73 \&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2736     and sees if it changed compared to the last time, invoking the callback if
2737     it did.
2738 root 1.22 .PP
2739     The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2740 root 1.74 not exist\*(R" is a status change like any other. The condition \*(L"path does not
2741     exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2742     \&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2743     least one) and all the other fields of the stat buffer having unspecified
2744     contents.
2745 root 1.22 .PP
2746 root 1.73 The path \fImust not\fR end in a slash or contain special components such as
2747     \&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2748     your working directory changes, then the behaviour is undefined.
2749     .PP
2750     Since there is no portable change notification interface available, the
2751     portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2752     to see if it changed somehow. You can specify a recommended polling
2753     interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2754     recommended!) then a \fIsuitable, unspecified default\fR value will be used
2755     (which you can expect to be around five seconds, although this might
2756     change dynamically). Libev will also impose a minimum interval which is
2757     currently around \f(CW0.1\fR, but that's usually overkill.
2758 root 1.22 .PP
2759     This watcher type is not meant for massive numbers of stat watchers,
2760     as even with OS-supported change notifications, this can be
2761 root 1.60 resource-intensive.
2762 root 1.22 .PP
2763 root 1.71 At the time of this writing, the only OS-specific interface implemented
2764 root 1.74 is the Linux inotify interface (implementing kqueue support is left as an
2765     exercise for the reader. Note, however, that the author sees no way of
2766     implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2767 root 1.50 .PP
2768 root 1.63 \fI\s-1ABI\s0 Issues (Largefile Support)\fR
2769     .IX Subsection "ABI Issues (Largefile Support)"
2770     .PP
2771     Libev by default (unless the user overrides this) uses the default
2772 root 1.69 compilation environment, which means that on systems with large file
2773     support disabled by default, you get the 32 bit version of the stat
2774 root 1.63 structure. When using the library from programs that change the \s-1ABI\s0 to
2775     use 64 bit file offsets the programs will fail. In that case you have to
2776     compile libev with the same flags to get binary compatibility. This is
2777     obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2778 root 1.73 most noticeably displayed with ev_stat and large file support.
2779 root 1.69 .PP
2780     The solution for this is to lobby your distribution maker to make large
2781     file interfaces available by default (as e.g. FreeBSD does) and not
2782     optional. Libev cannot simply switch on large file support because it has
2783     to exchange stat structures with application programs compiled using the
2784     default compilation environment.
2785 root 1.63 .PP
2786 root 1.71 \fIInotify and Kqueue\fR
2787     .IX Subsection "Inotify and Kqueue"
2788 root 1.59 .PP
2789 root 1.74 When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2790     runtime, it will be used to speed up change detection where possible. The
2791     inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2792     watcher is being started.
2793 root 1.59 .PP
2794 root 1.65 Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2795 root 1.59 except that changes might be detected earlier, and in some cases, to avoid
2796 root 1.65 making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2797 root 1.71 there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2798 root 1.74 but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2799     many bugs), the path exists (i.e. stat succeeds), and the path resides on
2800     a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2801     xfs are fully working) libev usually gets away without polling.
2802 root 1.59 .PP
2803 root 1.71 There is no support for kqueue, as apparently it cannot be used to
2804 root 1.59 implement this functionality, due to the requirement of having a file
2805 root 1.71 descriptor open on the object at all times, and detecting renames, unlinks
2806     etc. is difficult.
2807 root 1.59 .PP
2808 root 1.74 \fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2809     .IX Subsection "stat () is a synchronous operation"
2810     .PP
2811     Libev doesn't normally do any kind of I/O itself, and so is not blocking
2812     the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2813     ()\*(C'\fR, which is a synchronous operation.
2814     .PP
2815     For local paths, this usually doesn't matter: unless the system is very
2816     busy or the intervals between stat's are large, a stat call will be fast,
2817 root 1.75 as the path data is usually in memory already (except when starting the
2818 root 1.74 watcher).
2819     .PP
2820     For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2821     time due to network issues, and even under good conditions, a stat call
2822     often takes multiple milliseconds.
2823     .PP
2824     Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2825     paths, although this is fully supported by libev.
2826     .PP
2827 root 1.59 \fIThe special problem of stat time resolution\fR
2828     .IX Subsection "The special problem of stat time resolution"
2829     .PP
2830 root 1.73 The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2831     and even on systems where the resolution is higher, most file systems
2832     still only support whole seconds.
2833 root 1.59 .PP
2834 root 1.65 That means that, if the time is the only thing that changes, you can
2835     easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2836     calls your callback, which does something. When there is another update
2837 root 1.71 within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2838     stat data does change in other ways (e.g. file size).
2839 root 1.65 .PP
2840     The solution to this is to delay acting on a change for slightly more
2841 root 1.67 than a second (or till slightly after the next full second boundary), using
2842 root 1.65 a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2843     ev_timer_again (loop, w)\*(C'\fR).
2844     .PP
2845     The \f(CW.02\fR offset is added to work around small timing inconsistencies
2846     of some operating systems (where the second counter of the current time
2847     might be be delayed. One such system is the Linux kernel, where a call to
2848     \&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2849     a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2850     update file times then there will be a small window where the kernel uses
2851     the previous second to update file times but libev might already execute
2852     the timer callback).
2853 root 1.59 .PP
2854 root 1.50 \fIWatcher-Specific Functions and Data Members\fR
2855     .IX Subsection "Watcher-Specific Functions and Data Members"
2856 root 1.22 .IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2857     .IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2858     .PD 0
2859     .IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2860     .IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2861     .PD
2862     Configures the watcher to wait for status changes of the given
2863     \&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2864     be detected and should normally be specified as \f(CW0\fR to let libev choose
2865     a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2866     path for as long as the watcher is active.
2867     .Sp
2868 root 1.71 The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2869     relative to the attributes at the time the watcher was started (or the
2870     last change was detected).
2871 root 1.61 .IP "ev_stat_stat (loop, ev_stat *)" 4
2872     .IX Item "ev_stat_stat (loop, ev_stat *)"
2873 root 1.22 Updates the stat buffer immediately with new values. If you change the
2874 root 1.65 watched path in your callback, you could call this function to avoid
2875     detecting this change (while introducing a race condition if you are not
2876     the only one changing the path). Can also be useful simply to find out the
2877     new values.
2878 root 1.22 .IP "ev_statdata attr [read\-only]" 4
2879     .IX Item "ev_statdata attr [read-only]"
2880 root 1.65 The most-recently detected attributes of the file. Although the type is
2881 root 1.22 \&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2882 root 1.65 suitable for your system, but you can only rely on the POSIX-standardised
2883     members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2884     some error while \f(CW\*(C`stat\*(C'\fRing the file.
2885 root 1.22 .IP "ev_statdata prev [read\-only]" 4
2886     .IX Item "ev_statdata prev [read-only]"
2887     The previous attributes of the file. The callback gets invoked whenever
2888 root 1.65 \&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2889     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,
2890     \&\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.
2891 root 1.22 .IP "ev_tstamp interval [read\-only]" 4
2892     .IX Item "ev_tstamp interval [read-only]"
2893     The specified interval.
2894     .IP "const char *path [read\-only]" 4
2895     .IX Item "const char *path [read-only]"
2896 root 1.68 The file system path that is being watched.
2897 root 1.22 .PP
2898 root 1.59 \fIExamples\fR
2899     .IX Subsection "Examples"
2900     .PP
2901 root 1.22 Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2902     .PP
2903 root 1.60 .Vb 10
2904 root 1.68 \& static void
2905     \& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2906     \& {
2907     \& /* /etc/passwd changed in some way */
2908     \& if (w\->attr.st_nlink)
2909     \& {
2910     \& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2911     \& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2912     \& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2913     \& }
2914     \& else
2915     \& /* you shalt not abuse printf for puts */
2916     \& puts ("wow, /etc/passwd is not there, expect problems. "
2917     \& "if this is windows, they already arrived\en");
2918     \& }
2919 root 1.60 \&
2920 root 1.68 \& ...
2921     \& ev_stat passwd;
2922 root 1.60 \&
2923 root 1.68 \& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2924     \& ev_stat_start (loop, &passwd);
2925 root 1.22 .Ve
2926 root 1.59 .PP
2927     Example: Like above, but additionally use a one-second delay so we do not
2928     miss updates (however, frequent updates will delay processing, too, so
2929     one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2930     \&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2931     .PP
2932     .Vb 2
2933 root 1.68 \& static ev_stat passwd;
2934     \& static ev_timer timer;
2935 root 1.60 \&
2936 root 1.68 \& static void
2937     \& timer_cb (EV_P_ ev_timer *w, int revents)
2938     \& {
2939     \& ev_timer_stop (EV_A_ w);
2940     \&
2941     \& /* now it\*(Aqs one second after the most recent passwd change */
2942     \& }
2943     \&
2944     \& static void
2945     \& stat_cb (EV_P_ ev_stat *w, int revents)
2946     \& {
2947     \& /* reset the one\-second timer */
2948     \& ev_timer_again (EV_A_ &timer);
2949     \& }
2950     \&
2951     \& ...
2952     \& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2953     \& ev_stat_start (loop, &passwd);
2954     \& ev_timer_init (&timer, timer_cb, 0., 1.02);
2955 root 1.59 .Ve
2956 root 1.79 .ie n .SS """ev_idle"" \- when you've got nothing better to do..."
2957     .el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
2958 root 1.17 .IX Subsection "ev_idle - when you've got nothing better to do..."
2959 root 1.37 Idle watchers trigger events when no other events of the same or higher
2960 root 1.71 priority are pending (prepare, check and other idle watchers do not count
2961     as receiving \*(L"events\*(R").
2962 root 1.37 .PP
2963     That is, as long as your process is busy handling sockets or timeouts
2964     (or even signals, imagine) of the same or higher priority it will not be
2965     triggered. But when your process is idle (or only lower-priority watchers
2966     are pending), the idle watchers are being called once per event loop
2967     iteration \- until stopped, that is, or your process receives more events
2968     and becomes busy again with higher priority stuff.
2969 root 1.1 .PP
2970     The most noteworthy effect is that as long as any idle watchers are
2971     active, the process will not block when waiting for new events.
2972     .PP
2973     Apart from keeping your process non-blocking (which is a useful
2974     effect on its own sometimes), idle watchers are a good place to do
2975 root 1.60 \&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
2976 root 1.1 event loop has handled all outstanding events.
2977 root 1.50 .PP
2978     \fIWatcher-Specific Functions and Data Members\fR
2979     .IX Subsection "Watcher-Specific Functions and Data Members"
2980 root 1.78 .IP "ev_idle_init (ev_idle *, callback)" 4
2981     .IX Item "ev_idle_init (ev_idle *, callback)"
2982 root 1.1 Initialises and configures the idle watcher \- it has no parameters of any
2983     kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
2984     believe me.
2985 root 1.9 .PP
2986 root 1.60 \fIExamples\fR
2987     .IX Subsection "Examples"
2988     .PP
2989 root 1.28 Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
2990     callback, free it. Also, use no error checking, as usual.
2991 root 1.9 .PP
2992     .Vb 7
2993 root 1.68 \& static void
2994 root 1.73 \& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2995 root 1.68 \& {
2996     \& free (w);
2997     \& // now do something you wanted to do when the program has
2998     \& // no longer anything immediate to do.
2999     \& }
3000     \&
3001 root 1.73 \& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
3002 root 1.68 \& ev_idle_init (idle_watcher, idle_cb);
3003 root 1.79 \& ev_idle_start (loop, idle_watcher);
3004 root 1.9 .Ve
3005 root 1.79 .ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
3006     .el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
3007 root 1.17 .IX Subsection "ev_prepare and ev_check - customise your event loop!"
3008 root 1.71 Prepare and check watchers are usually (but not always) used in pairs:
3009 root 1.1 prepare watchers get invoked before the process blocks and check watchers
3010     afterwards.
3011     .PP
3012 root 1.82 You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
3013 root 1.20 the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
3014     watchers. Other loops than the current one are fine, however. The
3015     rationale behind this is that you do not need to check for recursion in
3016     those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
3017     \&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
3018     called in pairs bracketing the blocking call.
3019     .PP
3020 root 1.10 Their main purpose is to integrate other event mechanisms into libev and
3021 root 1.71 their use is somewhat advanced. They could be used, for example, to track
3022 root 1.10 variable changes, implement your own watchers, integrate net-snmp or a
3023 root 1.20 coroutine library and lots more. They are also occasionally useful if
3024     you cache some data and want to flush it before blocking (for example,
3025     in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
3026     watcher).
3027 root 1.1 .PP
3028 root 1.71 This is done by examining in each prepare call which file descriptors
3029     need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
3030     for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
3031     libraries provide exactly this functionality). Then, in the check watcher,
3032     you check for any events that occurred (by checking the pending status
3033     of all watchers and stopping them) and call back into the library. The
3034     I/O and timer callbacks will never actually be called (but must be valid
3035     nevertheless, because you never know, you know?).
3036 root 1.1 .PP
3037     As another example, the Perl Coro module uses these hooks to integrate
3038     coroutines into libev programs, by yielding to other active coroutines
3039     during each prepare and only letting the process block if no coroutines
3040     are ready to run (it's actually more complicated: it only runs coroutines
3041     with priority higher than or equal to the event loop and one coroutine
3042     of lower priority, but only once, using idle watchers to keep the event
3043     loop from blocking if lower-priority coroutines are active, thus mapping
3044     low-priority coroutines to idle/background tasks).
3045 root 1.45 .PP
3046     It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
3047     priority, to ensure that they are being run before any other watchers
3048 root 1.71 after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
3049     .PP
3050     Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3051     activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3052     might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3053     \&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3054     loops those other event loops might be in an unusable state until their
3055     \&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3056     others).
3057 root 1.50 .PP
3058     \fIWatcher-Specific Functions and Data Members\fR
3059     .IX Subsection "Watcher-Specific Functions and Data Members"
3060 root 1.1 .IP "ev_prepare_init (ev_prepare *, callback)" 4
3061     .IX Item "ev_prepare_init (ev_prepare *, callback)"
3062     .PD 0
3063     .IP "ev_check_init (ev_check *, callback)" 4
3064     .IX Item "ev_check_init (ev_check *, callback)"
3065     .PD
3066     Initialises and configures the prepare or check watcher \- they have no
3067     parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
3068 root 1.71 macros, but using them is utterly, utterly, utterly and completely
3069     pointless.
3070 root 1.9 .PP
3071 root 1.60 \fIExamples\fR
3072     .IX Subsection "Examples"
3073     .PP
3074 root 1.44 There are a number of principal ways to embed other event loops or modules
3075     into libev. Here are some ideas on how to include libadns into libev
3076     (there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3077 root 1.65 use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3078     Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3079     Glib event loop).
3080 root 1.44 .PP
3081     Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
3082     and in a check watcher, destroy them and call into libadns. What follows
3083     is pseudo-code only of course. This requires you to either use a low
3084     priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3085     the callbacks for the IO/timeout watchers might not have been called yet.
3086 root 1.20 .PP
3087     .Vb 2
3088 root 1.68 \& static ev_io iow [nfd];
3089     \& static ev_timer tw;
3090     \&
3091     \& static void
3092 root 1.73 \& io_cb (struct ev_loop *loop, ev_io *w, int revents)
3093 root 1.68 \& {
3094     \& }
3095     \&
3096     \& // create io watchers for each fd and a timer before blocking
3097     \& static void
3098 root 1.73 \& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
3099 root 1.68 \& {
3100     \& int timeout = 3600000;
3101     \& struct pollfd fds [nfd];
3102     \& // actual code will need to loop here and realloc etc.
3103     \& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
3104     \&
3105     \& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
3106 root 1.79 \& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
3107 root 1.68 \& ev_timer_start (loop, &tw);
3108 root 1.60 \&
3109 root 1.68 \& // create one ev_io per pollfd
3110     \& for (int i = 0; i < nfd; ++i)
3111     \& {
3112     \& ev_io_init (iow + i, io_cb, fds [i].fd,
3113     \& ((fds [i].events & POLLIN ? EV_READ : 0)
3114     \& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3115     \&
3116     \& fds [i].revents = 0;
3117     \& ev_io_start (loop, iow + i);
3118     \& }
3119     \& }
3120     \&
3121     \& // stop all watchers after blocking
3122     \& static void
3123 root 1.73 \& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3124 root 1.68 \& {
3125     \& ev_timer_stop (loop, &tw);
3126     \&
3127     \& for (int i = 0; i < nfd; ++i)
3128     \& {
3129     \& // set the relevant poll flags
3130     \& // could also call adns_processreadable etc. here
3131     \& struct pollfd *fd = fds + i;
3132     \& int revents = ev_clear_pending (iow + i);
3133     \& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3134     \& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3135 root 1.60 \&
3136 root 1.68 \& // now stop the watcher
3137     \& ev_io_stop (loop, iow + i);
3138     \& }
3139     \&
3140     \& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3141     \& }
3142 root 1.20 .Ve
3143 root 1.44 .PP
3144     Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3145     in the prepare watcher and would dispose of the check watcher.
3146     .PP
3147     Method 3: If the module to be embedded supports explicit event
3148 root 1.68 notification (libadns does), you can also make use of the actual watcher
3149 root 1.44 callbacks, and only destroy/create the watchers in the prepare watcher.
3150     .PP
3151     .Vb 5
3152 root 1.68 \& static void
3153     \& timer_cb (EV_P_ ev_timer *w, int revents)
3154     \& {
3155     \& adns_state ads = (adns_state)w\->data;
3156     \& update_now (EV_A);
3157     \&
3158     \& adns_processtimeouts (ads, &tv_now);
3159     \& }
3160     \&
3161     \& static void
3162     \& io_cb (EV_P_ ev_io *w, int revents)
3163     \& {
3164     \& adns_state ads = (adns_state)w\->data;
3165     \& update_now (EV_A);
3166 root 1.60 \&
3167 root 1.68 \& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3168     \& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3169     \& }
3170     \&
3171     \& // do not ever call adns_afterpoll
3172 root 1.44 .Ve
3173     .PP
3174     Method 4: Do not use a prepare or check watcher because the module you
3175 root 1.71 want to embed is not flexible enough to support it. Instead, you can
3176     override their poll function. The drawback with this solution is that the
3177     main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3178     this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3179     libglib event loop.
3180 root 1.44 .PP
3181     .Vb 4
3182 root 1.68 \& static gint
3183     \& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3184     \& {
3185     \& int got_events = 0;
3186     \&
3187     \& for (n = 0; n < nfds; ++n)
3188     \& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3189     \&
3190     \& if (timeout >= 0)
3191     \& // create/start timer
3192     \&
3193     \& // poll
3194 root 1.82 \& ev_run (EV_A_ 0);
3195 root 1.68 \&
3196     \& // stop timer again
3197     \& if (timeout >= 0)
3198     \& ev_timer_stop (EV_A_ &to);
3199 root 1.60 \&
3200 root 1.68 \& // stop io watchers again \- their callbacks should have set
3201     \& for (n = 0; n < nfds; ++n)
3202     \& ev_io_stop (EV_A_ iow [n]);
3203     \&
3204     \& return got_events;
3205     \& }
3206 root 1.44 .Ve
3207 root 1.79 .ie n .SS """ev_embed"" \- when one backend isn't enough..."
3208     .el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
3209 root 1.17 .IX Subsection "ev_embed - when one backend isn't enough..."
3210 root 1.10 This is a rather advanced watcher type that lets you embed one event loop
3211 root 1.11 into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
3212     loop, other types of watchers might be handled in a delayed or incorrect
3213 root 1.57 fashion and must not be used).
3214 root 1.10 .PP
3215     There are primarily two reasons you would want that: work around bugs and
3216     prioritise I/O.
3217     .PP
3218     As an example for a bug workaround, the kqueue backend might only support
3219     sockets on some platform, so it is unusable as generic backend, but you
3220     still want to make use of it because you have many sockets and it scales
3221 root 1.71 so nicely. In this case, you would create a kqueue-based loop and embed
3222     it into your default loop (which might use e.g. poll). Overall operation
3223     will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
3224     \&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3225     best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
3226     .PP
3227     As for prioritising I/O: under rare circumstances you have the case where
3228     some fds have to be watched and handled very quickly (with low latency),
3229     and even priorities and idle watchers might have too much overhead. In
3230     this case you would put all the high priority stuff in one loop and all
3231     the rest in a second one, and embed the second one in the first.
3232 root 1.10 .PP
3233 root 1.75 As long as the watcher is active, the callback will be invoked every
3234     time there might be events pending in the embedded loop. The callback
3235     must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
3236     sweep and invoke their callbacks (the callback doesn't need to invoke the
3237     \&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
3238     to give the embedded loop strictly lower priority for example).
3239     .PP
3240     You can also set the callback to \f(CW0\fR, in which case the embed watcher
3241     will automatically execute the embedded loop sweep whenever necessary.
3242     .PP
3243     Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
3244     is active, i.e., the embedded loop will automatically be forked when the
3245     embedding loop forks. In other cases, the user is responsible for calling
3246     \&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
3247 root 1.10 .PP
3248 root 1.71 Unfortunately, not all backends are embeddable: only the ones returned by
3249 root 1.10 \&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
3250     portable one.
3251     .PP
3252     So when you want to use this feature you will always have to be prepared
3253     that you cannot get an embeddable loop. The recommended way to get around
3254     this is to have a separate variables for your embeddable loop, try to
3255 root 1.60 create it, and if that fails, use the normal loop for everything.
3256 root 1.50 .PP
3257 root 1.71 \fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
3258     .IX Subsection "ev_embed and fork"
3259     .PP
3260     While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
3261     automatically be applied to the embedded loop as well, so no special
3262     fork handling is required in that case. When the watcher is not running,
3263     however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
3264     as applicable.
3265     .PP
3266 root 1.50 \fIWatcher-Specific Functions and Data Members\fR
3267     .IX Subsection "Watcher-Specific Functions and Data Members"
3268 root 1.11 .IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3269     .IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
3270 root 1.10 .PD 0
3271 root 1.11 .IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3272     .IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
3273 root 1.10 .PD
3274 root 1.11 Configures the watcher to embed the given loop, which must be
3275     embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
3276     invoked automatically, otherwise it is the responsibility of the callback
3277     to invoke it (it will continue to be called until the sweep has been done,
3278 root 1.68 if you do not want that, you need to temporarily stop the embed watcher).
3279 root 1.11 .IP "ev_embed_sweep (loop, ev_embed *)" 4
3280     .IX Item "ev_embed_sweep (loop, ev_embed *)"
3281     Make a single, non-blocking sweep over the embedded loop. This works
3282 root 1.82 similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
3283 root 1.68 appropriate way for embedded loops.
3284 root 1.54 .IP "struct ev_loop *other [read\-only]" 4
3285     .IX Item "struct ev_loop *other [read-only]"
3286 root 1.22 The embedded event loop.
3287 root 1.60 .PP
3288     \fIExamples\fR
3289     .IX Subsection "Examples"
3290     .PP
3291     Example: Try to get an embeddable event loop and embed it into the default
3292     event loop. If that is not possible, use the default loop. The default
3293 root 1.68 loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3294     \&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3295 root 1.60 used).
3296     .PP
3297     .Vb 3
3298 root 1.68 \& struct ev_loop *loop_hi = ev_default_init (0);
3299     \& struct ev_loop *loop_lo = 0;
3300 root 1.73 \& ev_embed embed;
3301 root 1.68 \&
3302     \& // see if there is a chance of getting one that works
3303     \& // (remember that a flags value of 0 means autodetection)
3304     \& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3305     \& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3306     \& : 0;
3307     \&
3308     \& // if we got one, then embed it, otherwise default to loop_hi
3309     \& if (loop_lo)
3310     \& {
3311     \& ev_embed_init (&embed, 0, loop_lo);
3312     \& ev_embed_start (loop_hi, &embed);
3313     \& }
3314     \& else
3315     \& loop_lo = loop_hi;
3316 root 1.60 .Ve
3317     .PP
3318     Example: Check if kqueue is available but not recommended and create
3319     a kqueue backend for use with sockets (which usually work with any
3320     kqueue implementation). Store the kqueue/socket\-only event loop in
3321     \&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3322     .PP
3323     .Vb 3
3324 root 1.68 \& struct ev_loop *loop = ev_default_init (0);
3325     \& struct ev_loop *loop_socket = 0;
3326 root 1.73 \& ev_embed embed;
3327 root 1.68 \&
3328     \& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3329     \& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3330     \& {
3331     \& ev_embed_init (&embed, 0, loop_socket);
3332     \& ev_embed_start (loop, &embed);
3333     \& }
3334 root 1.60 \&
3335 root 1.68 \& if (!loop_socket)
3336     \& loop_socket = loop;
3337 root 1.60 \&
3338 root 1.68 \& // now use loop_socket for all sockets, and loop for everything else
3339 root 1.60 .Ve
3340 root 1.79 .ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3341     .el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3342 root 1.24 .IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3343     Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3344     whoever is a good citizen cared to tell libev about it by calling
3345     \&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
3346     event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
3347     and only in the child after the fork. If whoever good citizen calling
3348     \&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
3349     handlers will be invoked, too, of course.
3350 root 1.51 .PP
3351 root 1.78 \fIThe special problem of life after fork \- how is it possible?\fR
3352     .IX Subsection "The special problem of life after fork - how is it possible?"
3353     .PP
3354 root 1.82 Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3355 root 1.78 up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3356     sequence should be handled by libev without any problems.
3357     .PP
3358     This changes when the application actually wants to do event handling
3359     in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3360     fork.
3361     .PP
3362     The default mode of operation (for libev, with application help to detect
3363     forks) is to duplicate all the state in the child, as would be expected
3364     when \fIeither\fR the parent \fIor\fR the child process continues.
3365     .PP
3366     When both processes want to continue using libev, then this is usually the
3367     wrong result. In that case, usually one process (typically the parent) is
3368     supposed to continue with all watchers in place as before, while the other
3369     process typically wants to start fresh, i.e. without any active watchers.
3370     .PP
3371     The cleanest and most efficient way to achieve that with libev is to
3372     simply create a new event loop, which of course will be \*(L"empty\*(R", and
3373     use that for new watchers. This has the advantage of not touching more
3374     memory than necessary, and thus avoiding the copy-on-write, and the
3375     disadvantage of having to use multiple event loops (which do not support
3376     signal watchers).
3377     .PP
3378     When this is not possible, or you want to use the default loop for
3379     other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3380 root 1.82 \&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3381     Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3382     watchers, so you have to be careful not to execute code that modifies
3383     those watchers. Note also that in that case, you have to re-register any
3384     signal watchers.
3385 root 1.78 .PP
3386 root 1.51 \fIWatcher-Specific Functions and Data Members\fR
3387     .IX Subsection "Watcher-Specific Functions and Data Members"
3388 root 1.82 .IP "ev_fork_init (ev_fork *, callback)" 4
3389     .IX Item "ev_fork_init (ev_fork *, callback)"
3390 root 1.24 Initialises and configures the fork watcher \- it has no parameters of any
3391     kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3392 root 1.82 really.
3393     .ie n .SS """ev_cleanup"" \- even the best things end"
3394     .el .SS "\f(CWev_cleanup\fP \- even the best things end"
3395     .IX Subsection "ev_cleanup - even the best things end"
3396     Cleanup watchers are called just before the event loop is being destroyed
3397     by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3398     .PP
3399     While there is no guarantee that the event loop gets destroyed, cleanup
3400     watchers provide a convenient method to install cleanup hooks for your
3401     program, worker threads and so on \- you just to make sure to destroy the
3402     loop when you want them to be invoked.
3403     .PP
3404     Cleanup watchers are invoked in the same way as any other watcher. Unlike
3405     all other watchers, they do not keep a reference to the event loop (which
3406     makes a lot of sense if you think about it). Like all other watchers, you
3407     can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3408     .PP
3409     \fIWatcher-Specific Functions and Data Members\fR
3410     .IX Subsection "Watcher-Specific Functions and Data Members"
3411     .IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3412     .IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3413     Initialises and configures the cleanup watcher \- it has no parameters of
3414     any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3415     pointless, I assure you.
3416     .PP
3417     Example: Register an atexit handler to destroy the default loop, so any
3418     cleanup functions are called.
3419     .PP
3420     .Vb 5
3421     \& static void
3422     \& program_exits (void)
3423     \& {
3424     \& ev_loop_destroy (EV_DEFAULT_UC);
3425     \& }
3426     \&
3427     \& ...
3428     \& atexit (program_exits);
3429     .Ve
3430     .ie n .SS """ev_async"" \- how to wake up an event loop"
3431     .el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3432     .IX Subsection "ev_async - how to wake up an event loop"
3433 root 1.86 In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3434 root 1.61 asynchronous sources such as signal handlers (as opposed to multiple event
3435     loops \- those are of course safe to use in different threads).
3436     .PP
3437 root 1.82 Sometimes, however, you need to wake up an event loop you do not control,
3438     for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3439     watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3440     it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3441 root 1.61 .PP
3442     This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3443     too, are asynchronous in nature, and signals, too, will be compressed
3444     (i.e. the number of callback invocations may be less than the number of
3445 root 1.85 \&\f(CW\*(C`ev_async_sent\*(C'\fR calls). In fact, you could use signal watchers as a kind
3446     of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3447     signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3448     even without knowing which loop owns the signal.
3449 root 1.61 .PP
3450     \fIQueueing\fR
3451     .IX Subsection "Queueing"
3452     .PP
3453     \&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3454     is that the author does not know of a simple (or any) algorithm for a
3455     multiple-writer-single-reader queue that works in all cases and doesn't
3456 root 1.81 need elaborate support such as pthreads or unportable memory access
3457     semantics.
3458 root 1.61 .PP
3459     That means that if you want to queue data, you have to provide your own
3460 root 1.71 queue. But at least I can tell you how to implement locking around your
3461 root 1.61 queue:
3462     .IP "queueing from a signal handler context" 4
3463     .IX Item "queueing from a signal handler context"
3464     To implement race-free queueing, you simply add to the queue in the signal
3465 root 1.72 handler but you block the signal handler in the watcher callback. Here is
3466     an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3467 root 1.61 .Sp
3468     .Vb 1
3469     \& static ev_async mysig;
3470     \&
3471     \& static void
3472     \& sigusr1_handler (void)
3473     \& {
3474     \& sometype data;
3475     \&
3476     \& // no locking etc.
3477     \& queue_put (data);
3478     \& ev_async_send (EV_DEFAULT_ &mysig);
3479     \& }
3480     \&
3481     \& static void
3482     \& mysig_cb (EV_P_ ev_async *w, int revents)
3483     \& {
3484     \& sometype data;
3485     \& sigset_t block, prev;
3486     \&
3487     \& sigemptyset (&block);
3488     \& sigaddset (&block, SIGUSR1);
3489     \& sigprocmask (SIG_BLOCK, &block, &prev);
3490     \&
3491     \& while (queue_get (&data))
3492     \& process (data);
3493     \&
3494     \& if (sigismember (&prev, SIGUSR1)
3495     \& sigprocmask (SIG_UNBLOCK, &block, 0);
3496     \& }
3497     .Ve
3498     .Sp
3499     (Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3500     instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3501     either...).
3502     .IP "queueing from a thread context" 4
3503     .IX Item "queueing from a thread context"
3504     The strategy for threads is different, as you cannot (easily) block
3505     threads but you can easily preempt them, so to queue safely you need to
3506     employ a traditional mutex lock, such as in this pthread example:
3507     .Sp
3508     .Vb 2
3509     \& static ev_async mysig;
3510     \& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3511     \&
3512     \& static void
3513     \& otherthread (void)
3514     \& {
3515     \& // only need to lock the actual queueing operation
3516     \& pthread_mutex_lock (&mymutex);
3517     \& queue_put (data);
3518     \& pthread_mutex_unlock (&mymutex);
3519     \&
3520     \& ev_async_send (EV_DEFAULT_ &mysig);
3521     \& }
3522     \&
3523     \& static void
3524     \& mysig_cb (EV_P_ ev_async *w, int revents)
3525     \& {
3526     \& pthread_mutex_lock (&mymutex);
3527     \&
3528     \& while (queue_get (&data))
3529     \& process (data);
3530     \&
3531     \& pthread_mutex_unlock (&mymutex);
3532     \& }
3533     .Ve
3534     .PP
3535     \fIWatcher-Specific Functions and Data Members\fR
3536     .IX Subsection "Watcher-Specific Functions and Data Members"
3537     .IP "ev_async_init (ev_async *, callback)" 4
3538     .IX Item "ev_async_init (ev_async *, callback)"
3539     Initialises and configures the async watcher \- it has no parameters of any
3540 root 1.73 kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3541 root 1.71 trust me.
3542 root 1.61 .IP "ev_async_send (loop, ev_async *)" 4
3543     .IX Item "ev_async_send (loop, ev_async *)"
3544     Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3545 root 1.86 an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3546     returns.
3547     .Sp
3548     Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3549     signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3550     embedding section below on what exactly this means).
3551 root 1.61 .Sp
3552 root 1.78 Note that, as with other watchers in libev, multiple events might get
3553 root 1.88 compressed into a single callback invocation (another way to look at
3554     this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3555     \&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3556     .Sp
3557     This call incurs the overhead of at most one extra system call per event
3558     loop iteration, if the event loop is blocked, and no syscall at all if
3559     the event loop (or your program) is processing events. That means that
3560     repeated calls are basically free (there is no need to avoid calls for
3561     performance reasons) and that the overhead becomes smaller (typically
3562     zero) under load.
3563 root 1.63 .IP "bool = ev_async_pending (ev_async *)" 4
3564     .IX Item "bool = ev_async_pending (ev_async *)"
3565     Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3566     watcher but the event has not yet been processed (or even noted) by the
3567     event loop.
3568     .Sp
3569     \&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3570     the loop iterates next and checks for the watcher to have become active,
3571     it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3572 root 1.68 quickly check whether invoking the loop might be a good idea.
3573 root 1.63 .Sp
3574 root 1.78 Not that this does \fInot\fR check whether the watcher itself is pending,
3575     only whether it has been requested to make this watcher pending: there
3576     is a time window between the event loop checking and resetting the async
3577     notification, and the callback being invoked.
3578 root 1.1 .SH "OTHER FUNCTIONS"
3579     .IX Header "OTHER FUNCTIONS"
3580     There are some other functions of possible interest. Described. Here. Now.
3581     .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
3582     .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
3583     This function combines a simple timer and an I/O watcher, calls your
3584 root 1.72 callback on whichever event happens first and automatically stops both
3585 root 1.1 watchers. This is useful if you want to wait for a single event on an fd
3586     or timeout without having to allocate/configure/start/stop/free one or
3587     more watchers yourself.
3588     .Sp
3589 root 1.72 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
3590     \&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
3591     the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
3592 root 1.1 .Sp
3593     If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
3594     started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
3595 root 1.72 repeat = 0) will be started. \f(CW0\fR is a valid timeout.
3596 root 1.1 .Sp
3597 root 1.82 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
3598 root 1.1 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
3599 root 1.82 \&\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_TIMER\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
3600 root 1.72 value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3601     a timeout and an io event at the same time \- you probably should give io
3602     events precedence.
3603     .Sp
3604     Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
3605 root 1.1 .Sp
3606     .Vb 7
3607 root 1.68 \& static void stdin_ready (int revents, void *arg)
3608     \& {
3609 root 1.72 \& if (revents & EV_READ)
3610     \& /* stdin might have data for us, joy! */;
3611 root 1.82 \& else if (revents & EV_TIMER)
3612 root 1.68 \& /* doh, nothing entered */;
3613     \& }
3614 root 1.60 \&
3615 root 1.68 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3616 root 1.1 .Ve
3617 root 1.81 .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3618     .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3619 root 1.1 Feed an event on the given fd, as if a file descriptor backend detected
3620 root 1.88 the given events.
3621 root 1.81 .IP "ev_feed_signal_event (loop, int signum)" 4
3622     .IX Item "ev_feed_signal_event (loop, int signum)"
3623 root 1.85 Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3624     which is async-safe.
3625     .SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3626     .IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3627     This section explains some common idioms that are not immediately
3628     obvious. Note that examples are sprinkled over the whole manual, and this
3629     section only contains stuff that wouldn't fit anywhere else.
3630     .SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
3631     .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3632     Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3633     or modify at any time: libev will completely ignore it. This can be used
3634     to associate arbitrary data with your watcher. If you need more data and
3635     don't want to allocate memory separately and store a pointer to it in that
3636     data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3637     data:
3638     .PP
3639     .Vb 7
3640     \& struct my_io
3641     \& {
3642     \& ev_io io;
3643     \& int otherfd;
3644     \& void *somedata;
3645     \& struct whatever *mostinteresting;
3646     \& };
3647     \&
3648     \& ...
3649     \& struct my_io w;
3650     \& ev_io_init (&w.io, my_cb, fd, EV_READ);
3651     .Ve
3652     .PP
3653     And since your callback will be called with a pointer to the watcher, you
3654     can cast it back to your own type:
3655     .PP
3656     .Vb 5
3657     \& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3658     \& {
3659     \& struct my_io *w = (struct my_io *)w_;
3660     \& ...
3661     \& }
3662     .Ve
3663     .PP
3664     More interesting and less C\-conformant ways of casting your callback
3665     function type instead have been omitted.
3666     .SS "\s-1BUILDING\s0 \s-1YOUR\s0 \s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0"
3667     .IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3668     Another common scenario is to use some data structure with multiple
3669     embedded watchers, in effect creating your own watcher that combines
3670     multiple libev event sources into one \*(L"super-watcher\*(R":
3671     .PP
3672     .Vb 6
3673     \& struct my_biggy
3674     \& {
3675     \& int some_data;
3676     \& ev_timer t1;
3677     \& ev_timer t2;
3678     \& }
3679     .Ve
3680     .PP
3681     In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3682     complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3683     the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3684     to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3685     real programmers):
3686     .PP
3687     .Vb 1
3688     \& #include <stddef.h>
3689     \&
3690     \& static void
3691     \& t1_cb (EV_P_ ev_timer *w, int revents)
3692     \& {
3693     \& struct my_biggy big = (struct my_biggy *)
3694     \& (((char *)w) \- offsetof (struct my_biggy, t1));
3695     \& }
3696     \&
3697     \& static void
3698     \& t2_cb (EV_P_ ev_timer *w, int revents)
3699     \& {
3700     \& struct my_biggy big = (struct my_biggy *)
3701     \& (((char *)w) \- offsetof (struct my_biggy, t2));
3702     \& }
3703     .Ve
3704 root 1.88 .SS "\s-1AVOIDING\s0 \s-1FINISHING\s0 \s-1BEFORE\s0 \s-1RETURNING\s0"
3705     .IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3706     Often you have structures like this in event-based programs:
3707     .PP
3708     .Vb 4
3709     \& callback ()
3710     \& {
3711     \& free (request);
3712     \& }
3713     \&
3714     \& request = start_new_request (..., callback);
3715     .Ve
3716     .PP
3717     The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3718     used to cancel the operation, or do other things with it.
3719     .PP
3720     It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3721     immediately invoke the callback, for example, to report errors. Or you add
3722     some caching layer that finds that it can skip the lengthy aspects of the
3723     operation and simply invoke the callback with the result.
3724     .PP
3725     The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3726     has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3727     .PP
3728     Even if you pass the request by some safer means to the callback, you
3729     might want to do something to the request after starting it, such as
3730     canceling it, which probably isn't working so well when the callback has
3731     already been invoked.
3732     .PP
3733     A common way around all these issues is to make sure that
3734     \&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3735     \&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3736     delay invoking the callback by e.g. using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher
3737     for example, or more sneakily, by reusing an existing (stopped) watcher
3738     and pushing it into the pending queue:
3739     .PP
3740     .Vb 2
3741     \& ev_set_cb (watcher, callback);
3742     \& ev_feed_event (EV_A_ watcher, 0);
3743     .Ve
3744     .PP
3745     This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
3746     invoked, while not delaying callback invocation too much.
3747 root 1.85 .SS "\s-1MODEL/NESTED\s0 \s-1EVENT\s0 \s-1LOOP\s0 \s-1INVOCATIONS\s0 \s-1AND\s0 \s-1EXIT\s0 \s-1CONDITIONS\s0"
3748     .IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
3749     Often (especially in \s-1GUI\s0 toolkits) there are places where you have
3750     \&\fImodal\fR interaction, which is most easily implemented by recursively
3751     invoking \f(CW\*(C`ev_run\*(C'\fR.
3752     .PP
3753     This brings the problem of exiting \- a callback might want to finish the
3754     main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
3755     a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
3756     and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3757     other combination: In these cases, \f(CW\*(C`ev_break\*(C'\fR will not work alone.
3758     .PP
3759     The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3760     invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3761     triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3762     .PP
3763     .Vb 2
3764     \& // main loop
3765     \& int exit_main_loop = 0;
3766     \&
3767     \& while (!exit_main_loop)
3768     \& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3769     \&
3770 root 1.88 \& // in a modal watcher
3771 root 1.85 \& int exit_nested_loop = 0;
3772     \&
3773     \& while (!exit_nested_loop)
3774     \& ev_run (EV_A_ EVRUN_ONCE);
3775     .Ve
3776     .PP
3777     To exit from any of these loops, just set the corresponding exit variable:
3778     .PP
3779     .Vb 2
3780     \& // exit modal loop
3781     \& exit_nested_loop = 1;
3782     \&
3783     \& // exit main program, after modal loop is finished
3784     \& exit_main_loop = 1;
3785     \&
3786     \& // exit both
3787     \& exit_main_loop = exit_nested_loop = 1;
3788     .Ve
3789     .SS "\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0"
3790     .IX Subsection "THREAD LOCKING EXAMPLE"
3791     Here is a fictitious example of how to run an event loop in a different
3792     thread from where callbacks are being invoked and watchers are
3793     created/added/removed.
3794     .PP
3795     For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3796     which uses exactly this technique (which is suited for many high-level
3797     languages).
3798     .PP
3799     The example uses a pthread mutex to protect the loop data, a condition
3800     variable to wait for callback invocations, an async watcher to notify the
3801     event loop thread and an unspecified mechanism to wake up the main thread.
3802     .PP
3803     First, you need to associate some data with the event loop:
3804     .PP
3805     .Vb 6
3806     \& typedef struct {
3807     \& mutex_t lock; /* global loop lock */
3808     \& ev_async async_w;
3809     \& thread_t tid;
3810     \& cond_t invoke_cv;
3811     \& } userdata;
3812     \&
3813     \& void prepare_loop (EV_P)
3814     \& {
3815     \& // for simplicity, we use a static userdata struct.
3816     \& static userdata u;
3817     \&
3818     \& ev_async_init (&u\->async_w, async_cb);
3819     \& ev_async_start (EV_A_ &u\->async_w);
3820     \&
3821     \& pthread_mutex_init (&u\->lock, 0);
3822     \& pthread_cond_init (&u\->invoke_cv, 0);
3823     \&
3824     \& // now associate this with the loop
3825     \& ev_set_userdata (EV_A_ u);
3826     \& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3827     \& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3828     \&
3829 root 1.86 \& // then create the thread running ev_run
3830 root 1.85 \& pthread_create (&u\->tid, 0, l_run, EV_A);
3831     \& }
3832     .Ve
3833     .PP
3834     The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3835     solely to wake up the event loop so it takes notice of any new watchers
3836     that might have been added:
3837     .PP
3838     .Vb 5
3839     \& static void
3840     \& async_cb (EV_P_ ev_async *w, int revents)
3841     \& {
3842     \& // just used for the side effects
3843     \& }
3844     .Ve
3845     .PP
3846     The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3847     protecting the loop data, respectively.
3848     .PP
3849     .Vb 6
3850     \& static void
3851     \& l_release (EV_P)
3852     \& {
3853     \& userdata *u = ev_userdata (EV_A);
3854     \& pthread_mutex_unlock (&u\->lock);
3855     \& }
3856     \&
3857     \& static void
3858     \& l_acquire (EV_P)
3859     \& {
3860     \& userdata *u = ev_userdata (EV_A);
3861     \& pthread_mutex_lock (&u\->lock);
3862     \& }
3863     .Ve
3864     .PP
3865     The event loop thread first acquires the mutex, and then jumps straight
3866     into \f(CW\*(C`ev_run\*(C'\fR:
3867     .PP
3868     .Vb 4
3869     \& void *
3870     \& l_run (void *thr_arg)
3871     \& {
3872     \& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3873     \&
3874     \& l_acquire (EV_A);
3875     \& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3876     \& ev_run (EV_A_ 0);
3877     \& l_release (EV_A);
3878     \&
3879     \& return 0;
3880     \& }
3881     .Ve
3882     .PP
3883     Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3884     signal the main thread via some unspecified mechanism (signals? pipe
3885     writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3886     have been called (in a while loop because a) spurious wakeups are possible
3887     and b) skipping inter-thread-communication when there are no pending
3888     watchers is very beneficial):
3889     .PP
3890     .Vb 4
3891     \& static void
3892     \& l_invoke (EV_P)
3893     \& {
3894     \& userdata *u = ev_userdata (EV_A);
3895     \&
3896     \& while (ev_pending_count (EV_A))
3897     \& {
3898     \& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3899     \& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3900     \& }
3901     \& }
3902     .Ve
3903     .PP
3904     Now, whenever the main thread gets told to invoke pending watchers, it
3905     will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3906     thread to continue:
3907     .PP
3908     .Vb 4
3909     \& static void
3910     \& real_invoke_pending (EV_P)
3911     \& {
3912     \& userdata *u = ev_userdata (EV_A);
3913     \&
3914     \& pthread_mutex_lock (&u\->lock);
3915     \& ev_invoke_pending (EV_A);
3916     \& pthread_cond_signal (&u\->invoke_cv);
3917     \& pthread_mutex_unlock (&u\->lock);
3918     \& }
3919     .Ve
3920     .PP
3921     Whenever you want to start/stop a watcher or do other modifications to an
3922     event loop, you will now have to lock:
3923     .PP
3924     .Vb 2
3925     \& ev_timer timeout_watcher;
3926     \& userdata *u = ev_userdata (EV_A);
3927     \&
3928     \& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3929     \&
3930     \& pthread_mutex_lock (&u\->lock);
3931     \& ev_timer_start (EV_A_ &timeout_watcher);
3932     \& ev_async_send (EV_A_ &u\->async_w);
3933     \& pthread_mutex_unlock (&u\->lock);
3934     .Ve
3935     .PP
3936     Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
3937     an event loop currently blocking in the kernel will have no knowledge
3938     about the newly added timer. By waking up the loop it will pick up any new
3939     watchers in the next event loop iteration.
3940     .SS "\s-1THREADS\s0, \s-1COROUTINES\s0, \s-1CONTINUATIONS\s0, \s-1QUEUES\s0... \s-1INSTEAD\s0 \s-1OF\s0 \s-1CALLBACKS\s0"
3941     .IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
3942     While the overhead of a callback that e.g. schedules a thread is small, it
3943     is still an overhead. If you embed libev, and your main usage is with some
3944     kind of threads or coroutines, you might want to customise libev so that
3945     doesn't need callbacks anymore.
3946     .PP
3947     Imagine you have coroutines that you can switch to using a function
3948     \&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
3949     and that due to some magic, the currently active coroutine is stored in a
3950     global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
3951     event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
3952     the differing \f(CW\*(C`;\*(C'\fR conventions):
3953     .PP
3954     .Vb 2
3955     \& #define EV_CB_DECLARE(type) struct my_coro *cb;
3956     \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
3957     .Ve
3958     .PP
3959     That means instead of having a C callback function, you store the
3960     coroutine to switch to in each watcher, and instead of having libev call
3961     your callback, you instead have it switch to that coroutine.
3962     .PP
3963     A coroutine might now wait for an event with a function called
3964     \&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
3965     matter when, or whether the watcher is active or not when this function is
3966     called):
3967     .PP
3968     .Vb 6
3969     \& void
3970     \& wait_for_event (ev_watcher *w)
3971     \& {
3972     \& ev_cb_set (w) = current_coro;
3973     \& switch_to (libev_coro);
3974     \& }
3975     .Ve
3976     .PP
3977     That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
3978     continues the libev coroutine, which, when appropriate, switches back to
3979 root 1.88 this or any other coroutine.
3980 root 1.85 .PP
3981     You can do similar tricks if you have, say, threads with an event queue \-
3982     instead of storing a coroutine, you store the queue object and instead of
3983     switching to a coroutine, you push the watcher onto the queue and notify
3984     any waiters.
3985     .PP
3986     To embed libev, see \s-1EMBEDDING\s0, but in short, it's easiest to create two
3987     files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
3988     .PP
3989     .Vb 4
3990     \& // my_ev.h
3991     \& #define EV_CB_DECLARE(type) struct my_coro *cb;
3992     \& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb);
3993     \& #include "../libev/ev.h"
3994     \&
3995     \& // my_ev.c
3996     \& #define EV_H "my_ev.h"
3997     \& #include "../libev/ev.c"
3998     .Ve
3999     .PP
4000     And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4001     \&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4002     can even use \fIev.h\fR as header file name directly.
4003 root 1.1 .SH "LIBEVENT EMULATION"
4004     .IX Header "LIBEVENT EMULATION"
4005     Libev offers a compatibility emulation layer for libevent. It cannot
4006     emulate the internals of libevent, so here are some usage hints:
4007 root 1.60 .IP "\(bu" 4
4008 root 1.85 Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4009     .Sp
4010     This was the newest libevent version available when libev was implemented,
4011     and is still mostly unchanged in 2010.
4012     .IP "\(bu" 4
4013 root 1.60 Use it by including <event.h>, as usual.
4014     .IP "\(bu" 4
4015     The following members are fully supported: ev_base, ev_callback,
4016     ev_arg, ev_fd, ev_res, ev_events.
4017     .IP "\(bu" 4
4018     Avoid using ev_flags and the EVLIST_*\-macros, while it is
4019     maintained by libev, it does not work exactly the same way as in libevent (consider
4020     it a private \s-1API\s0).
4021     .IP "\(bu" 4
4022     Priorities are not currently supported. Initialising priorities
4023     will fail and all watchers will have the same priority, even though there
4024     is an ev_pri field.
4025     .IP "\(bu" 4
4026 root 1.64 In libevent, the last base created gets the signals, in libev, the
4027 root 1.85 base that registered the signal gets the signals.
4028 root 1.64 .IP "\(bu" 4
4029 root 1.60 Other members are not supported.
4030     .IP "\(bu" 4
4031     The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
4032     to use the libev header file and library.
4033 root 1.1 .SH "\*(C+ SUPPORT"
4034     .IX Header " SUPPORT"
4035 root 1.13 Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
4036 root 1.68 you to use some convenience methods to start/stop watchers and also change
4037 root 1.13 the callback model to a model using method callbacks on objects.
4038     .PP
4039     To use it,
4040     .PP
4041     .Vb 1
4042 root 1.68 \& #include <ev++.h>
4043 root 1.13 .Ve
4044     .PP
4045 root 1.41 This automatically includes \fIev.h\fR and puts all of its definitions (many
4046     of them macros) into the global namespace. All \*(C+ specific things are
4047     put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4048     options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
4049     .PP
4050 root 1.42 Care has been taken to keep the overhead low. The only data member the \*(C+
4051     classes add (compared to plain C\-style watchers) is the event loop pointer
4052     that the watcher is associated with (or no additional members at all if
4053     you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4054 root 1.41 .PP
4055 root 1.85 Currently, functions, static and non-static member functions and classes
4056     with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4057     to add as long as they only need one additional pointer for context. If
4058     you need support for other types of functors please contact the author
4059     (preferably after implementing it).
4060 root 1.13 .PP
4061 root 1.89 For all this to work, your \*(C+ compiler either has to use the same calling
4062     conventions as your C compiler (for static member functions), or you have
4063     to embed libev and compile libev itself as \*(C+.
4064     .PP
4065 root 1.13 Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
4066 root 1.79 .ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
4067 root 1.13 .el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
4068     .IX Item "ev::READ, ev::WRITE etc."
4069     These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
4070     macros from \fIev.h\fR.
4071 root 1.79 .ie n .IP """ev::tstamp"", ""ev::now""" 4
4072 root 1.13 .el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
4073     .IX Item "ev::tstamp, ev::now"
4074     Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
4075 root 1.79 .ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
4076 root 1.13 .el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
4077     .IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
4078     For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
4079     the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
4080     which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
4081 root 1.88 defined by many implementations.
4082 root 1.13 .Sp
4083     All of those classes have these methods:
4084     .RS 4
4085 root 1.41 .IP "ev::TYPE::TYPE ()" 4
4086     .IX Item "ev::TYPE::TYPE ()"
4087 root 1.13 .PD 0
4088 root 1.81 .IP "ev::TYPE::TYPE (loop)" 4
4089     .IX Item "ev::TYPE::TYPE (loop)"
4090 root 1.13 .IP "ev::TYPE::~TYPE" 4
4091     .IX Item "ev::TYPE::~TYPE"
4092     .PD
4093 root 1.41 The constructor (optionally) takes an event loop to associate the watcher
4094     with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
4095     .Sp
4096     The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
4097     \&\f(CW\*(C`set\*(C'\fR method before starting it.
4098     .Sp
4099     It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4100     method to set a callback before you can start the watcher.
4101     .Sp
4102     (The reason why you have to use a method is a limitation in \*(C+ which does
4103     not allow explicit template arguments for constructors).
4104 root 1.13 .Sp
4105     The destructor automatically stops the watcher if it is active.
4106 root 1.41 .IP "w\->set<class, &class::method> (object *)" 4
4107     .IX Item "w->set<class, &class::method> (object *)"
4108     This method sets the callback method to call. The method has to have a
4109     signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4110     first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4111     parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4112     .Sp
4113     This method synthesizes efficient thunking code to call your method from
4114     the C callback that libev requires. If your compiler can inline your
4115     callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4116     your compiler is good :), then the method will be fully inlined into the
4117     thunking function, making it as fast as a direct C callback.
4118     .Sp
4119     Example: simple class declaration and watcher initialisation
4120     .Sp
4121     .Vb 4
4122 root 1.68 \& struct myclass
4123     \& {
4124     \& void io_cb (ev::io &w, int revents) { }
4125     \& }
4126     \&
4127     \& myclass obj;
4128     \& ev::io iow;
4129     \& iow.set <myclass, &myclass::io_cb> (&obj);
4130 root 1.41 .Ve
4131 root 1.75 .IP "w\->set (object *)" 4
4132     .IX Item "w->set (object *)"
4133     This is a variation of a method callback \- leaving out the method to call
4134     will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4135     functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4136     the time. Incidentally, you can then also leave out the template argument
4137     list.
4138     .Sp
4139     The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4140     int revents)\*(C'\fR.
4141     .Sp
4142     See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4143     .Sp
4144     Example: use a functor object as callback.
4145     .Sp
4146     .Vb 7
4147     \& struct myfunctor
4148     \& {
4149     \& void operator() (ev::io &w, int revents)
4150     \& {
4151     \& ...
4152     \& }
4153     \& }
4154     \&
4155     \& myfunctor f;
4156     \&
4157     \& ev::io w;
4158     \& w.set (&f);
4159     .Ve
4160 root 1.43 .IP "w\->set<function> (void *data = 0)" 4
4161     .IX Item "w->set<function> (void *data = 0)"
4162 root 1.41 Also sets a callback, but uses a static method or plain function as
4163     callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4164     \&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4165     .Sp
4166 root 1.43 The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4167     .Sp
4168 root 1.41 See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4169 root 1.43 .Sp
4170 root 1.71 Example: Use a plain function as callback.
4171 root 1.43 .Sp
4172     .Vb 2
4173 root 1.68 \& static void io_cb (ev::io &w, int revents) { }
4174     \& iow.set <io_cb> ();
4175 root 1.43 .Ve
4176 root 1.81 .IP "w\->set (loop)" 4
4177     .IX Item "w->set (loop)"
4178 root 1.13 Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
4179     do this when the watcher is inactive (and not pending either).
4180 root 1.68 .IP "w\->set ([arguments])" 4
4181     .IX Item "w->set ([arguments])"
4182 root 1.82 Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Either this
4183     method or a suitable start method must be called at least once. Unlike the
4184     C counterpart, an active watcher gets automatically stopped and restarted
4185     when reconfiguring it with this method.
4186 root 1.13 .IP "w\->start ()" 4
4187     .IX Item "w->start ()"
4188 root 1.41 Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
4189     constructor already stores the event loop.
4190 root 1.82 .IP "w\->start ([arguments])" 4
4191     .IX Item "w->start ([arguments])"
4192     Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4193     convenient to wrap them in one call. Uses the same type of arguments as
4194     the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
4195 root 1.13 .IP "w\->stop ()" 4
4196     .IX Item "w->stop ()"
4197     Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
4198 root 1.79 .ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
4199 root 1.52 .el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
4200     .IX Item "w->again () (ev::timer, ev::periodic only)"
4201 root 1.13 For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
4202     \&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
4203 root 1.52 .ie n .IP "w\->sweep () (""ev::embed"" only)" 4
4204     .el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
4205     .IX Item "w->sweep () (ev::embed only)"
4206 root 1.13 Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4207 root 1.52 .ie n .IP "w\->update () (""ev::stat"" only)" 4
4208     .el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4209     .IX Item "w->update () (ev::stat only)"
4210 root 1.23 Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
4211 root 1.13 .RE
4212     .RS 4
4213     .RE
4214     .PP
4215 root 1.82 Example: Define a class with two I/O and idle watchers, start the I/O
4216     watchers in the constructor.
4217 root 1.13 .PP
4218 root 1.82 .Vb 5
4219 root 1.68 \& class myclass
4220     \& {
4221 root 1.71 \& ev::io io ; void io_cb (ev::io &w, int revents);
4222 root 1.88 \& ev::io io2 ; void io2_cb (ev::io &w, int revents);
4223 root 1.71 \& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4224 root 1.68 \&
4225     \& myclass (int fd)
4226     \& {
4227     \& io .set <myclass, &myclass::io_cb > (this);
4228 root 1.82 \& io2 .set <myclass, &myclass::io2_cb > (this);
4229 root 1.68 \& idle.set <myclass, &myclass::idle_cb> (this);
4230     \&
4231 root 1.82 \& io.set (fd, ev::WRITE); // configure the watcher
4232     \& io.start (); // start it whenever convenient
4233     \&
4234     \& io2.start (fd, ev::READ); // set + start in one call
4235 root 1.68 \& }
4236     \& };
4237 root 1.13 .Ve
4238 root 1.62 .SH "OTHER LANGUAGE BINDINGS"
4239     .IX Header "OTHER LANGUAGE BINDINGS"
4240     Libev does not offer other language bindings itself, but bindings for a
4241 root 1.68 number of languages exist in the form of third-party packages. If you know
4242 root 1.62 any interesting language binding in addition to the ones listed here, drop
4243     me a note.
4244     .IP "Perl" 4
4245     .IX Item "Perl"
4246     The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4247     libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4248     there are additional modules that implement libev-compatible interfaces
4249 root 1.71 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),
4250     \&\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
4251     and \f(CW\*(C`EV::Glib\*(C'\fR).
4252 root 1.62 .Sp
4253 root 1.68 It can be found and installed via \s-1CPAN\s0, its homepage is at
4254 root 1.62 <http://software.schmorp.de/pkg/EV>.
4255 root 1.68 .IP "Python" 4
4256     .IX Item "Python"
4257     Python bindings can be found at <http://code.google.com/p/pyev/>. It
4258 root 1.78 seems to be quite complete and well-documented.
4259 root 1.62 .IP "Ruby" 4
4260     .IX Item "Ruby"
4261     Tony Arcieri has written a ruby extension that offers access to a subset
4262 root 1.68 of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4263 root 1.62 more on top of it. It can be found via gem servers. Its homepage is at
4264     <http://rev.rubyforge.org/>.
4265 root 1.75 .Sp
4266     Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4267     makes rev work even on mingw.
4268 root 1.78 .IP "Haskell" 4
4269     .IX Item "Haskell"
4270     A haskell binding to libev is available at
4271 root 1.88 http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
4272 root 1.62 .IP "D" 4
4273     .IX Item "D"
4274     Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4275 root 1.88 be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4276 root 1.73 .IP "Ocaml" 4
4277     .IX Item "Ocaml"
4278     Erkki Seppala has written Ocaml bindings for libev, to be found at
4279 root 1.88 http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/ <http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
4280 root 1.80 .IP "Lua" 4
4281     .IX Item "Lua"
4282 root 1.82 Brian Maher has written a partial interface to libev for lua (at the
4283     time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4284 root 1.88 http://github.com/brimworks/lua\-ev <http://github.com/brimworks/lua-ev>.
4285 root 1.24 .SH "MACRO MAGIC"
4286     .IX Header "MACRO MAGIC"
4287 root 1.68 Libev can be compiled with a variety of options, the most fundamental
4288 root 1.52 of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4289     functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
4290 root 1.24 .PP
4291     To make it easier to write programs that cope with either variant, the
4292     following macros are defined:
4293 root 1.79 .ie n .IP """EV_A"", ""EV_A_""" 4
4294 root 1.24 .el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4295     .IX Item "EV_A, EV_A_"
4296     This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4297     loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4298     \&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4299     .Sp
4300     .Vb 3
4301 root 1.68 \& ev_unref (EV_A);
4302     \& ev_timer_add (EV_A_ watcher);
4303 root 1.82 \& ev_run (EV_A_ 0);
4304 root 1.24 .Ve
4305     .Sp
4306     It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4307     which is often provided by the following macro.
4308 root 1.79 .ie n .IP """EV_P"", ""EV_P_""" 4
4309 root 1.24 .el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4310     .IX Item "EV_P, EV_P_"
4311     This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4312     loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4313     \&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4314     .Sp
4315     .Vb 2
4316 root 1.68 \& // this is how ev_unref is being declared
4317     \& static void ev_unref (EV_P);
4318 root 1.60 \&
4319 root 1.68 \& // this is how you can declare your typical callback
4320     \& static void cb (EV_P_ ev_timer *w, int revents)
4321 root 1.24 .Ve
4322     .Sp
4323     It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4324     suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4325 root 1.79 .ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4326 root 1.24 .el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4327     .IX Item "EV_DEFAULT, EV_DEFAULT_"
4328     Similar to the other two macros, this gives you the value of the default
4329 root 1.88 loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4330     will be initialised if it isn't already initialised.
4331     .Sp
4332     For non-multiplicity builds, these macros do nothing, so you always have
4333     to initialise the loop somewhere.
4334 root 1.79 .ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4335 root 1.64 .el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4336     .IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4337     Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4338     default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4339     is undefined when the default loop has not been initialised by a previous
4340     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.
4341     .Sp
4342     It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4343     watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
4344 root 1.24 .PP
4345 root 1.36 Example: Declare and initialise a check watcher, utilising the above
4346 root 1.38 macros so it will work regardless of whether multiple loops are supported
4347 root 1.36 or not.
4348 root 1.24 .PP
4349     .Vb 5
4350 root 1.68 \& static void
4351     \& check_cb (EV_P_ ev_timer *w, int revents)
4352     \& {
4353     \& ev_check_stop (EV_A_ w);
4354     \& }
4355     \&
4356     \& ev_check check;
4357     \& ev_check_init (&check, check_cb);
4358     \& ev_check_start (EV_DEFAULT_ &check);
4359 root 1.82 \& ev_run (EV_DEFAULT_ 0);
4360 root 1.24 .Ve
4361 root 1.14 .SH "EMBEDDING"
4362     .IX Header "EMBEDDING"
4363     Libev can (and often is) directly embedded into host
4364     applications. Examples of applications that embed it include the Deliantra
4365     Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
4366 root 1.60 and rxvt-unicode.
4367 root 1.14 .PP
4368 root 1.54 The goal is to enable you to just copy the necessary files into your
4369 root 1.14 source directory without having to change even a single line in them, so
4370     you can easily upgrade by simply copying (or having a checked-out copy of
4371     libev somewhere in your source tree).
4372 root 1.79 .SS "\s-1FILESETS\s0"
4373 root 1.14 .IX Subsection "FILESETS"
4374     Depending on what features you need you need to include one or more sets of files
4375 root 1.68 in your application.
4376 root 1.14 .PP
4377     \fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
4378     .IX Subsection "CORE EVENT LOOP"
4379     .PP
4380     To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
4381     configuration (no autoconf):
4382     .PP
4383     .Vb 2
4384 root 1.68 \& #define EV_STANDALONE 1
4385     \& #include "ev.c"
4386 root 1.14 .Ve
4387     .PP
4388     This will automatically include \fIev.h\fR, too, and should be done in a
4389     single C source file only to provide the function implementations. To use
4390     it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
4391     done by writing a wrapper around \fIev.h\fR that you can include instead and
4392     where you can put other configuration options):
4393     .PP
4394     .Vb 2
4395 root 1.68 \& #define EV_STANDALONE 1
4396     \& #include "ev.h"
4397 root 1.14 .Ve
4398     .PP
4399     Both header files and implementation files can be compiled with a \*(C+
4400 root 1.73 compiler (at least, that's a stated goal, and breakage will be treated
4401 root 1.14 as a bug).
4402     .PP
4403     You need the following files in your source tree, or in a directory
4404     in your include path (e.g. in libev/ when using \-Ilibev):
4405     .PP
4406     .Vb 4
4407 root 1.68 \& ev.h
4408     \& ev.c
4409     \& ev_vars.h
4410     \& ev_wrap.h
4411     \&
4412     \& ev_win32.c required on win32 platforms only
4413     \&
4414     \& ev_select.c only when select backend is enabled (which is enabled by default)
4415     \& ev_poll.c only when poll backend is enabled (disabled by default)
4416     \& ev_epoll.c only when the epoll backend is enabled (disabled by default)
4417     \& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
4418     \& ev_port.c only when the solaris port backend is enabled (disabled by default)
4419 root 1.14 .Ve
4420     .PP
4421     \&\fIev.c\fR includes the backend files directly when enabled, so you only need
4422 root 1.18 to compile this single file.
4423 root 1.14 .PP
4424     \fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
4425     .IX Subsection "LIBEVENT COMPATIBILITY API"
4426     .PP
4427     To include the libevent compatibility \s-1API\s0, also include:
4428     .PP
4429     .Vb 1
4430 root 1.68 \& #include "event.c"
4431 root 1.14 .Ve
4432     .PP
4433     in the file including \fIev.c\fR, and:
4434     .PP
4435     .Vb 1
4436 root 1.68 \& #include "event.h"
4437 root 1.14 .Ve
4438     .PP
4439     in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
4440     .PP
4441     You need the following additional files for this:
4442     .PP
4443     .Vb 2
4444 root 1.68 \& event.h
4445     \& event.c
4446 root 1.14 .Ve
4447     .PP
4448     \fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
4449     .IX Subsection "AUTOCONF SUPPORT"
4450     .PP
4451 root 1.68 Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
4452 root 1.14 whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
4453 root 1.18 \&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
4454     include \fIconfig.h\fR and configure itself accordingly.
4455 root 1.14 .PP
4456     For this of course you need the m4 file:
4457     .PP
4458     .Vb 1
4459 root 1.68 \& libev.m4
4460 root 1.14 .Ve
4461 root 1.79 .SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
4462 root 1.14 .IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
4463 root 1.64 Libev can be configured via a variety of preprocessor symbols you have to
4464 root 1.82 define before including (or compiling) any of its files. The default in
4465     the absence of autoconf is documented for every option.
4466     .PP
4467     Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
4468     values when compiling libev vs. including \fIev.h\fR, so it is permissible
4469     to redefine them before including \fIev.h\fR without breaking compatibility
4470     to a compiled library. All other symbols change the \s-1ABI\s0, which means all
4471     users of libev and the libev code itself must be compiled with compatible
4472     settings.
4473     .IP "\s-1EV_COMPAT3\s0 (h)" 4
4474     .IX Item "EV_COMPAT3 (h)"
4475     Backwards compatibility is a major concern for libev. This is why this
4476     release of libev comes with wrappers for the functions and symbols that
4477     have been renamed between libev version 3 and 4.
4478     .Sp
4479     You can disable these wrappers (to test compatibility with future
4480     versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4481     sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4482     from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4483     typedef in that case.
4484     .Sp
4485     In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4486     and in some even more future version the compatibility code will be
4487     removed completely.
4488     .IP "\s-1EV_STANDALONE\s0 (h)" 4
4489     .IX Item "EV_STANDALONE (h)"
4490 root 1.14 Must always be \f(CW1\fR if you do not use autoconf configuration, which
4491     keeps libev from including \fIconfig.h\fR, and it also defines dummy
4492     implementations for some libevent functions (such as logging, which is not
4493     supported). It will also not define any of the structs usually found in
4494     \&\fIevent.h\fR that are not directly supported by the libev core alone.
4495 root 1.75 .Sp
4496 root 1.80 In standalone mode, libev will still try to automatically deduce the
4497 root 1.75 configuration, but has to be more conservative.
4498 root 1.88 .IP "\s-1EV_USE_FLOOR\s0" 4
4499     .IX Item "EV_USE_FLOOR"
4500     If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4501     periodic reschedule calculations, otherwise libev will fall back on a
4502     portable (slower) implementation. If you enable this, you usually have to
4503     link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4504     function is not available will fail, so the safe default is to not enable
4505     this.
4506 root 1.14 .IP "\s-1EV_USE_MONOTONIC\s0" 4
4507     .IX Item "EV_USE_MONOTONIC"
4508     If defined to be \f(CW1\fR, libev will try to detect the availability of the
4509 root 1.75 monotonic clock option at both compile time and runtime. Otherwise no
4510     use of the monotonic clock option will be attempted. If you enable this,
4511     you usually have to link against librt or something similar. Enabling it
4512     when the functionality isn't available is safe, though, although you have
4513 root 1.14 to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
4514 root 1.75 function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4515 root 1.14 .IP "\s-1EV_USE_REALTIME\s0" 4
4516     .IX Item "EV_USE_REALTIME"
4517     If defined to be \f(CW1\fR, libev will try to detect the availability of the
4518 root 1.77 real-time clock option at compile time (and assume its availability
4519     at runtime if successful). Otherwise no use of the real-time clock
4520     option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
4521     by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
4522     correctness. See the note about libraries in the description of
4523     \&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4524     \&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4525 root 1.75 .IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4526     .IX Item "EV_USE_CLOCK_SYSCALL"
4527     If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4528     of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4529     exists because on GNU/Linux, \f(CW\*(C`clock_gettime\*(C'\fR is in \f(CW\*(C`librt\*(C'\fR, but \f(CW\*(C`librt\*(C'\fR
4530     unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4531     programs needlessly. Using a direct syscall is slightly slower (in
4532     theory), because no optimised vdso implementation can be used, but avoids
4533     the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4534     higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4535 root 1.56 .IP "\s-1EV_USE_NANOSLEEP\s0" 4
4536     .IX Item "EV_USE_NANOSLEEP"
4537     If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4538     and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4539 root 1.64 .IP "\s-1EV_USE_EVENTFD\s0" 4
4540     .IX Item "EV_USE_EVENTFD"
4541     If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4542     available and will probe for kernel support at runtime. This will improve
4543     \&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4544     If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
4545     2.7 or newer, otherwise disabled.
4546 root 1.14 .IP "\s-1EV_USE_SELECT\s0" 4
4547     .IX Item "EV_USE_SELECT"
4548     If undefined or defined to be \f(CW1\fR, libev will compile in support for the
4549 root 1.68 \&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
4550 root 1.14 other method takes over, select will be it. Otherwise the select backend
4551     will not be compiled in.
4552     .IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
4553     .IX Item "EV_SELECT_USE_FD_SET"
4554     If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
4555     structure. This is useful if libev doesn't compile due to a missing
4556 root 1.75 \&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
4557     on exotic systems. This usually limits the range of file descriptors to
4558     some low limit such as 1024 or might have other limitations (winsocket
4559     only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
4560     configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
4561 root 1.14 .IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
4562     .IX Item "EV_SELECT_IS_WINSOCKET"
4563     When defined to \f(CW1\fR, the select backend will assume that
4564     select/socket/connect etc. don't understand file descriptors but
4565     wants osf handles on win32 (this is the case when the select to
4566     be used is the winsock select). This means that it will call
4567     \&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
4568     it is assumed that all these functions actually work on fds, even
4569     on win32. Should not be defined on non\-win32 platforms.
4570 root 1.81 .IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4571     .IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4572 root 1.60 If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4573     file descriptors to socket handles. When not defining this symbol (the
4574     default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4575     correct. In some cases, programs use their own file descriptor management,
4576     in which case they can provide this function to map fds to socket handles.
4577 root 1.81 .IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4578     .IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4579     If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4580     using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4581     their own fd to handle mapping, overwriting this function makes it easier
4582     to do so. This can be done by defining this macro to an appropriate value.
4583     .IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4584     .IX Item "EV_WIN32_CLOSE_FD(fd)"
4585     If programs implement their own fd to handle mapping on win32, then this
4586     macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4587     file descriptors again. Note that the replacement function has to close
4588     the underlying \s-1OS\s0 handle.
4589 root 1.14 .IP "\s-1EV_USE_POLL\s0" 4
4590     .IX Item "EV_USE_POLL"
4591     If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
4592     backend. Otherwise it will be enabled on non\-win32 platforms. It
4593     takes precedence over select.
4594     .IP "\s-1EV_USE_EPOLL\s0" 4
4595     .IX Item "EV_USE_EPOLL"
4596     If defined to be \f(CW1\fR, libev will compile in support for the Linux
4597     \&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
4598 root 1.64 otherwise another method will be used as fallback. This is the preferred
4599     backend for GNU/Linux systems. If undefined, it will be enabled if the
4600     headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4601 root 1.14 .IP "\s-1EV_USE_KQUEUE\s0" 4
4602     .IX Item "EV_USE_KQUEUE"
4603     If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
4604     \&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
4605     otherwise another method will be used as fallback. This is the preferred
4606     backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
4607     supports some types of fds correctly (the only platform we found that
4608     supports ptys for example was NetBSD), so kqueue might be compiled in, but
4609     not be used unless explicitly requested. The best way to use it is to find
4610 root 1.16 out whether kqueue supports your type of fd properly and use an embedded
4611 root 1.14 kqueue loop.
4612     .IP "\s-1EV_USE_PORT\s0" 4
4613     .IX Item "EV_USE_PORT"
4614     If defined to be \f(CW1\fR, libev will compile in support for the Solaris
4615     10 port style backend. Its availability will be detected at runtime,
4616     otherwise another method will be used as fallback. This is the preferred
4617     backend for Solaris 10 systems.
4618     .IP "\s-1EV_USE_DEVPOLL\s0" 4
4619     .IX Item "EV_USE_DEVPOLL"
4620 root 1.68 Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4621 root 1.30 .IP "\s-1EV_USE_INOTIFY\s0" 4
4622     .IX Item "EV_USE_INOTIFY"
4623     If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4624     interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4625 root 1.64 be detected at runtime. If undefined, it will be enabled if the headers
4626     indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4627 root 1.88 .IP "\s-1EV_NO_SMP\s0" 4
4628     .IX Item "EV_NO_SMP"
4629     If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4630     between threads, that is, threads can be used, but threads never run on
4631     different cpus (or different cpu cores). This reduces dependencies
4632     and makes libev faster.
4633     .IP "\s-1EV_NO_THREADS\s0" 4
4634     .IX Item "EV_NO_THREADS"
4635     If defined to be \f(CW1\fR, libev will assume that it will never be called
4636     from different threads, which is a stronger assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR,
4637     above. This reduces dependencies and makes libev faster.
4638 root 1.61 .IP "\s-1EV_ATOMIC_T\s0" 4
4639     .IX Item "EV_ATOMIC_T"
4640     Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4641 root 1.88 access is atomic and serialised with respect to other threads or signal
4642     contexts. No such type is easily found in the C language, so you can
4643     provide your own type that you know is safe for your purposes. It is used
4644     both for signal handler \*(L"locking\*(R" as well as for signal and thread safety
4645     in \f(CW\*(C`ev_async\*(C'\fR watchers.
4646 root 1.61 .Sp
4647 root 1.68 In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4648 root 1.88 (from \fIsignal.h\fR), which is usually good enough on most platforms,
4649     although strictly speaking using a type that also implies a memory fence
4650     is required.
4651 root 1.82 .IP "\s-1EV_H\s0 (h)" 4
4652     .IX Item "EV_H (h)"
4653 root 1.14 The name of the \fIev.h\fR header file used to include it. The default if
4654 root 1.60 undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
4655     used to virtually rename the \fIev.h\fR header file in case of conflicts.
4656 root 1.82 .IP "\s-1EV_CONFIG_H\s0 (h)" 4
4657     .IX Item "EV_CONFIG_H (h)"
4658 root 1.14 If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
4659     \&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
4660     \&\f(CW\*(C`EV_H\*(C'\fR, above.
4661 root 1.82 .IP "\s-1EV_EVENT_H\s0 (h)" 4
4662     .IX Item "EV_EVENT_H (h)"
4663 root 1.14 Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
4664 root 1.60 of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
4665 root 1.82 .IP "\s-1EV_PROTOTYPES\s0 (h)" 4
4666     .IX Item "EV_PROTOTYPES (h)"
4667 root 1.14 If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
4668     prototypes, but still define all the structs and other symbols. This is
4669     occasionally useful if you want to provide your own wrapper functions
4670     around libev functions.
4671     .IP "\s-1EV_MULTIPLICITY\s0" 4
4672     .IX Item "EV_MULTIPLICITY"
4673     If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
4674     will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
4675     additional independent event loops. Otherwise there will be no support
4676     for multiple event loops and there is no first event loop pointer
4677     argument. Instead, all functions act on the single default loop.
4678 root 1.88 .Sp
4679     Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
4680     default loop when multiplicity is switched off \- you always have to
4681     initialise the loop manually in this case.
4682 root 1.39 .IP "\s-1EV_MINPRI\s0" 4
4683     .IX Item "EV_MINPRI"
4684     .PD 0
4685     .IP "\s-1EV_MAXPRI\s0" 4
4686     .IX Item "EV_MAXPRI"
4687     .PD
4688     The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4689     \&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4690     provide for more priorities by overriding those symbols (usually defined
4691     to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4692     .Sp
4693     When doing priority-based operations, libev usually has to linearly search
4694     all the priorities, so having many of them (hundreds) uses a lot of space
4695     and time, so using the defaults of five priorities (\-2 .. +2) is usually
4696     fine.
4697     .Sp
4698 root 1.71 If your embedding application does not need any priorities, defining these
4699     both to \f(CW0\fR will save some memory and \s-1CPU\s0.
4700 root 1.82 .IP "\s-1EV_PERIODIC_ENABLE\s0, \s-1EV_IDLE_ENABLE\s0, \s-1EV_EMBED_ENABLE\s0, \s-1EV_STAT_ENABLE\s0, \s-1EV_PREPARE_ENABLE\s0, \s-1EV_CHECK_ENABLE\s0, \s-1EV_FORK_ENABLE\s0, \s-1EV_SIGNAL_ENABLE\s0, \s-1EV_ASYNC_ENABLE\s0, \s-1EV_CHILD_ENABLE\s0." 4
4701     .IX Item "EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE."
4702     If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4703     the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4704     is not. Disabling watcher types mainly saves code size.
4705     .IP "\s-1EV_FEATURES\s0" 4
4706     .IX Item "EV_FEATURES"
4707 root 1.22 If you need to shave off some kilobytes of code at the expense of some
4708 root 1.82 speed (but with the full \s-1API\s0), you can define this symbol to request
4709     certain subsets of functionality. The default is to enable all features
4710     that can be enabled on the platform.
4711     .Sp
4712     A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4713     with some broad features you want) and then selectively re-enable
4714     additional parts you want, for example if you want everything minimal,
4715     but multiple event loop support, async and child watchers and the poll
4716     backend, use this:
4717     .Sp
4718     .Vb 5
4719     \& #define EV_FEATURES 0
4720     \& #define EV_MULTIPLICITY 1
4721     \& #define EV_USE_POLL 1
4722     \& #define EV_CHILD_ENABLE 1
4723     \& #define EV_ASYNC_ENABLE 1
4724     .Ve
4725     .Sp
4726     The actual value is a bitset, it can be a combination of the following
4727     values:
4728     .RS 4
4729     .ie n .IP "1 \- faster/larger code" 4
4730     .el .IP "\f(CW1\fR \- faster/larger code" 4
4731     .IX Item "1 - faster/larger code"
4732     Use larger code to speed up some operations.
4733     .Sp
4734     Currently this is used to override some inlining decisions (enlarging the
4735     code size by roughly 30% on amd64).
4736     .Sp
4737     When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4738     gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4739     assertions.
4740     .ie n .IP "2 \- faster/larger data structures" 4
4741     .el .IP "\f(CW2\fR \- faster/larger data structures" 4
4742     .IX Item "2 - faster/larger data structures"
4743     Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4744     hash table sizes and so on. This will usually further increase code size
4745     and can additionally have an effect on the size of data structures at
4746     runtime.
4747     .ie n .IP "4 \- full \s-1API\s0 configuration" 4
4748     .el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4749     .IX Item "4 - full API configuration"
4750     This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4751     enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4752     .ie n .IP "8 \- full \s-1API\s0" 4
4753     .el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4754     .IX Item "8 - full API"
4755     This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4756     details on which parts of the \s-1API\s0 are still available without this
4757     feature, and do not complain if this subset changes over time.
4758     .ie n .IP "16 \- enable all optional watcher types" 4
4759     .el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4760     .IX Item "16 - enable all optional watcher types"
4761     Enables all optional watcher types. If you want to selectively enable
4762     only some watcher types other than I/O and timers (e.g. prepare,
4763     embed, async, child...) you can enable them manually by defining
4764     \&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4765     .ie n .IP "32 \- enable all backends" 4
4766     .el .IP "\f(CW32\fR \- enable all backends" 4
4767     .IX Item "32 - enable all backends"
4768     This enables all backends \- without this feature, you need to enable at
4769     least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4770     .ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4771     .el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4772     .IX Item "64 - enable OS-specific helper APIs"
4773     Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4774     default.
4775     .RE
4776     .RS 4
4777     .Sp
4778     Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4779     reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4780     code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4781     watchers, timers and monotonic clock support.
4782     .Sp
4783     With an intelligent-enough linker (gcc+binutils are intelligent enough
4784     when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4785     your program might be left out as well \- a binary starting a timer and an
4786     I/O watcher then might come out at only 5Kb.
4787     .RE
4788 root 1.88 .IP "\s-1EV_API_STATIC\s0" 4
4789     .IX Item "EV_API_STATIC"
4790     If this symbol is defined (by default it is not), then all identifiers
4791     will have static linkage. This means that libev will not export any
4792     identifiers, and you cannot link against libev anymore. This can be useful
4793     when you embed libev, only want to use libev functions in a single file,
4794     and do not want its identifiers to be visible.
4795     .Sp
4796     To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
4797     wants to use libev.
4798     .Sp
4799     This option only works when libev is compiled with a C compiler, as \*(C+
4800     doesn't support the required declaration syntax.
4801 root 1.82 .IP "\s-1EV_AVOID_STDIO\s0" 4
4802     .IX Item "EV_AVOID_STDIO"
4803     If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4804     functions (printf, scanf, perror etc.). This will increase the code size
4805     somewhat, but if your program doesn't otherwise depend on stdio and your
4806     libc allows it, this avoids linking in the stdio library which is quite
4807     big.
4808     .Sp
4809     Note that error messages might become less precise when this option is
4810     enabled.
4811 root 1.80 .IP "\s-1EV_NSIG\s0" 4
4812     .IX Item "EV_NSIG"
4813     The highest supported signal number, +1 (or, the number of
4814     signals): Normally, libev tries to deduce the maximum number of signals
4815     automatically, but sometimes this fails, in which case it can be
4816     specified. Also, using a lower number than detected (\f(CW32\fR should be
4817 root 1.82 good for about any system in existence) can save some memory, as libev
4818 root 1.80 statically allocates some 12\-24 bytes per signal number.
4819 root 1.25 .IP "\s-1EV_PID_HASHSIZE\s0" 4
4820     .IX Item "EV_PID_HASHSIZE"
4821     \&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
4822 root 1.82 pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
4823     usually more than enough. If you need to manage thousands of children you
4824     might want to increase this value (\fImust\fR be a power of two).
4825 root 1.30 .IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
4826     .IX Item "EV_INOTIFY_HASHSIZE"
4827 root 1.59 \&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
4828 root 1.82 inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
4829     disabled), usually more than enough. If you need to manage thousands of
4830     \&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
4831     power of two).
4832 root 1.65 .IP "\s-1EV_USE_4HEAP\s0" 4
4833     .IX Item "EV_USE_4HEAP"
4834     Heaps are not very cache-efficient. To improve the cache-efficiency of the
4835 root 1.71 timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4836     to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4837     faster performance with many (thousands) of watchers.
4838 root 1.65 .Sp
4839 root 1.82 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4840     will be \f(CW0\fR.
4841 root 1.65 .IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4842     .IX Item "EV_HEAP_CACHE_AT"
4843     Heaps are not very cache-efficient. To improve the cache-efficiency of the
4844 root 1.71 timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4845 root 1.65 the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4846     which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4847 root 1.67 but avoids random read accesses on heap changes. This improves performance
4848 root 1.71 noticeably with many (hundreds) of watchers.
4849 root 1.65 .Sp
4850 root 1.82 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4851     will be \f(CW0\fR.
4852 root 1.67 .IP "\s-1EV_VERIFY\s0" 4
4853     .IX Item "EV_VERIFY"
4854 root 1.82 Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4855 root 1.67 be done: If set to \f(CW0\fR, no internal verification code will be compiled
4856     in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4857     called. If set to \f(CW2\fR, then the internal verification code will be
4858     called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4859     verification code will be called very frequently, which will slow down
4860     libev considerably.
4861     .Sp
4862 root 1.82 The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4863     will be \f(CW0\fR.
4864 root 1.14 .IP "\s-1EV_COMMON\s0" 4
4865     .IX Item "EV_COMMON"
4866     By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
4867 root 1.82 this macro to something else you can include more and other types of
4868 root 1.14 members. You have to define it each time you include one of the files,
4869     though, and it must be identical each time.
4870     .Sp
4871     For example, the perl \s-1EV\s0 module uses something like this:
4872     .Sp
4873     .Vb 3
4874 root 1.68 \& #define EV_COMMON \e
4875     \& SV *self; /* contains this struct */ \e
4876     \& SV *cb_sv, *fh /* note no trailing ";" */
4877 root 1.14 .Ve
4878 root 1.19 .IP "\s-1EV_CB_DECLARE\s0 (type)" 4
4879     .IX Item "EV_CB_DECLARE (type)"
4880 root 1.14 .PD 0
4881 root 1.19 .IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
4882     .IX Item "EV_CB_INVOKE (watcher, revents)"
4883     .IP "ev_set_cb (ev, cb)" 4
4884     .IX Item "ev_set_cb (ev, cb)"
4885 root 1.14 .PD
4886     Can be used to change the callback member declaration in each watcher,
4887     and the way callbacks are invoked and set. Must expand to a struct member
4888 root 1.54 definition and a statement, respectively. See the \fIev.h\fR header file for
4889 root 1.14 their default definitions. One possible use for overriding these is to
4890 root 1.19 avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
4891     method calls instead of plain function calls in \*(C+.
4892 root 1.79 .SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4893 root 1.53 .IX Subsection "EXPORTED API SYMBOLS"
4894 root 1.68 If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4895 root 1.53 exported symbols, you can use the provided \fISymbol.*\fR files which list
4896     all public symbols, one per line:
4897 root 1.60 .PP
4898 root 1.53 .Vb 2
4899 root 1.68 \& Symbols.ev for libev proper
4900     \& Symbols.event for the libevent emulation
4901 root 1.53 .Ve
4902 root 1.60 .PP
4903 root 1.53 This can also be used to rename all public symbols to avoid clashes with
4904     multiple versions of libev linked together (which is obviously bad in
4905 root 1.68 itself, but sometimes it is inconvenient to avoid this).
4906 root 1.60 .PP
4907 root 1.54 A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
4908 root 1.53 include before including \fIev.h\fR:
4909 root 1.60 .PP
4910 root 1.53 .Vb 1
4911 root 1.60 \& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
4912 root 1.53 .Ve
4913 root 1.60 .PP
4914 root 1.53 This would create a file \fIwrap.h\fR which essentially looks like this:
4915 root 1.60 .PP
4916 root 1.53 .Vb 4
4917     \& #define ev_backend myprefix_ev_backend
4918     \& #define ev_check_start myprefix_ev_check_start
4919     \& #define ev_check_stop myprefix_ev_check_stop
4920     \& ...
4921     .Ve
4922 root 1.79 .SS "\s-1EXAMPLES\s0"
4923 root 1.14 .IX Subsection "EXAMPLES"
4924     For a real-world example of a program the includes libev
4925     verbatim, you can have a look at the \s-1EV\s0 perl module
4926     (<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
4927     the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
4928     interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
4929     will be compiled. It is pretty complex because it provides its own header
4930     file.
4931 root 1.60 .PP
4932 root 1.14 The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
4933 root 1.36 that everybody includes and which overrides some configure choices:
4934 root 1.60 .PP
4935 root 1.82 .Vb 8
4936     \& #define EV_FEATURES 8
4937     \& #define EV_USE_SELECT 1
4938     \& #define EV_PREPARE_ENABLE 1
4939     \& #define EV_IDLE_ENABLE 1
4940     \& #define EV_SIGNAL_ENABLE 1
4941     \& #define EV_CHILD_ENABLE 1
4942     \& #define EV_USE_STDEXCEPT 0
4943 root 1.68 \& #define EV_CONFIG_H <config.h>
4944 root 1.60 \&
4945 root 1.68 \& #include "ev++.h"
4946 root 1.14 .Ve
4947 root 1.60 .PP
4948 root 1.14 And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
4949 root 1.60 .PP
4950 root 1.14 .Vb 2
4951 root 1.68 \& #include "ev_cpp.h"
4952     \& #include "ev.c"
4953 root 1.14 .Ve
4954 root 1.85 .SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4955     .IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4956 root 1.79 .SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
4957 root 1.72 .IX Subsection "THREADS AND COROUTINES"
4958     \fI\s-1THREADS\s0\fR
4959 root 1.64 .IX Subsection "THREADS"
4960 root 1.72 .PP
4961 root 1.71 All libev functions are reentrant and thread-safe unless explicitly
4962 root 1.72 documented otherwise, but libev implements no locking itself. This means
4963     that you can use as many loops as you want in parallel, as long as there
4964     are no concurrent calls into any libev function with the same loop
4965     parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
4966     of course): libev guarantees that different event loops share no data
4967 root 1.71 structures that need any locking.
4968     .PP
4969     Or to put it differently: calls with different loop parameters can be done
4970     concurrently from multiple threads, calls with the same loop parameter
4971     must be done serially (but can be done from different threads, as long as
4972     only one thread ever is inside a call at any point in time, e.g. by using
4973     a mutex per loop).
4974     .PP
4975     Specifically to support threads (and signal handlers), libev implements
4976     so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
4977     concurrency on the same event loop, namely waking it up \*(L"from the
4978     outside\*(R".
4979 root 1.64 .PP
4980 root 1.70 If you want to know which design (one loop, locking, or multiple loops
4981     without or something else still) is best for your problem, then I cannot
4982 root 1.71 help you, but here is some generic advice:
4983 root 1.64 .IP "\(bu" 4
4984     most applications have a main thread: use the default libev loop
4985 root 1.68 in that thread, or create a separate thread running only the default loop.
4986 root 1.64 .Sp
4987     This helps integrating other libraries or software modules that use libev
4988     themselves and don't care/know about threading.
4989     .IP "\(bu" 4
4990     one loop per thread is usually a good model.
4991     .Sp
4992     Doing this is almost never wrong, sometimes a better-performance model
4993     exists, but it is always a good start.
4994     .IP "\(bu" 4
4995     other models exist, such as the leader/follower pattern, where one
4996 root 1.68 loop is handed through multiple threads in a kind of round-robin fashion.
4997 root 1.64 .Sp
4998 root 1.68 Choosing a model is hard \- look around, learn, know that usually you can do
4999 root 1.64 better than you currently do :\-)
5000     .IP "\(bu" 4
5001     often you need to talk to some other thread which blocks in the
5002 root 1.71 event loop.
5003     .Sp
5004     \&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5005     (or from signal contexts...).
5006     .Sp
5007     An example use would be to communicate signals or other events that only
5008     work in the default loop by registering the signal watcher with the
5009     default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5010     watcher callback into the event loop interested in the signal.
5011 root 1.72 .PP
5012 root 1.85 See also \*(L"\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0\*(R".
5013 root 1.79 .PP
5014 root 1.72 \fI\s-1COROUTINES\s0\fR
5015 root 1.64 .IX Subsection "COROUTINES"
5016 root 1.72 .PP
5017     Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5018     libev fully supports nesting calls to its functions from different
5019 root 1.82 coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5020 root 1.79 different coroutines, and switch freely between both coroutines running
5021     the loop, as long as you don't confuse yourself). The only exception is
5022     that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5023 root 1.64 .PP
5024 root 1.71 Care has been taken to ensure that libev does not keep local state inside
5025 root 1.82 \&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5026 root 1.73 they do not call any callbacks.
5027 root 1.79 .SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
5028 root 1.72 .IX Subsection "COMPILER WARNINGS"
5029     Depending on your compiler and compiler settings, you might get no or a
5030     lot of warnings when compiling libev code. Some people are apparently
5031     scared by this.
5032     .PP
5033     However, these are unavoidable for many reasons. For one, each compiler
5034     has different warnings, and each user has different tastes regarding
5035     warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5036     targeting a specific compiler and compiler-version.
5037     .PP
5038     Another reason is that some compiler warnings require elaborate
5039     workarounds, or other changes to the code that make it less clear and less
5040     maintainable.
5041     .PP
5042     And of course, some compiler warnings are just plain stupid, or simply
5043     wrong (because they don't actually warn about the condition their message
5044     seems to warn about). For example, certain older gcc versions had some
5045 root 1.82 warnings that resulted in an extreme number of false positives. These have
5046 root 1.72 been fixed, but some people still insist on making code warn-free with
5047     such buggy versions.
5048     .PP
5049     While libev is written to generate as few warnings as possible,
5050     \&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5051     with any compiler warnings enabled unless you are prepared to cope with
5052     them (e.g. by ignoring them). Remember that warnings are just that:
5053     warnings, not errors, or proof of bugs.
5054 root 1.79 .SS "\s-1VALGRIND\s0"
5055 root 1.72 .IX Subsection "VALGRIND"
5056     Valgrind has a special section here because it is a popular tool that is
5057     highly useful. Unfortunately, valgrind reports are very hard to interpret.
5058     .PP
5059     If you think you found a bug (memory leak, uninitialised data access etc.)
5060     in libev, then check twice: If valgrind reports something like:
5061     .PP
5062     .Vb 3
5063     \& ==2274== definitely lost: 0 bytes in 0 blocks.
5064     \& ==2274== possibly lost: 0 bytes in 0 blocks.
5065     \& ==2274== still reachable: 256 bytes in 1 blocks.
5066     .Ve
5067     .PP
5068     Then there is no memory leak, just as memory accounted to global variables
5069 root 1.73 is not a memleak \- the memory is still being referenced, and didn't leak.
5070 root 1.72 .PP
5071     Similarly, under some circumstances, valgrind might report kernel bugs
5072     as if it were a bug in libev (e.g. in realloc or in the poll backend,
5073     although an acceptable workaround has been found here), or it might be
5074     confused.
5075     .PP
5076     Keep in mind that valgrind is a very good tool, but only a tool. Don't
5077     make it into some kind of religion.
5078     .PP
5079     If you are unsure about something, feel free to contact the mailing list
5080     with the full valgrind report and an explanation on why you think this
5081     is a bug in libev (best check the archives, too :). However, don't be
5082     annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5083     of learning how to interpret valgrind properly.
5084 root 1.60 .PP
5085 root 1.72 If you need, for some reason, empty reports from valgrind for your project
5086     I suggest using suppression lists.
5087     .SH "PORTABILITY NOTES"
5088     .IX Header "PORTABILITY NOTES"
5089 root 1.82 .SS "\s-1GNU/LINUX\s0 32 \s-1BIT\s0 \s-1LIMITATIONS\s0"
5090     .IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5091     GNU/Linux is the only common platform that supports 64 bit file/large file
5092     interfaces but \fIdisables\fR them by default.
5093     .PP
5094     That means that libev compiled in the default environment doesn't support
5095     files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5096     .PP
5097     Unfortunately, many programs try to work around this GNU/Linux issue
5098     by enabling the large file \s-1API\s0, which makes them incompatible with the
5099     standard libev compiled for their system.
5100     .PP
5101     Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5102     suddenly make it incompatible to the default compile time environment,
5103     i.e. all programs not using special compile switches.
5104     .SS "\s-1OS/X\s0 \s-1AND\s0 \s-1DARWIN\s0 \s-1BUGS\s0"
5105     .IX Subsection "OS/X AND DARWIN BUGS"
5106     The whole thing is a bug if you ask me \- basically any system interface
5107     you touch is broken, whether it is locales, poll, kqueue or even the
5108     OpenGL drivers.
5109     .PP
5110     \fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5111     .IX Subsection "kqueue is buggy"
5112     .PP
5113     The kqueue syscall is broken in all known versions \- most versions support
5114     only sockets, many support pipes.
5115     .PP
5116     Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5117     rotten platform, but of course you can still ask for it when creating a
5118     loop \- embedding a socket-only kqueue loop into a select-based one is
5119     probably going to work well.
5120     .PP
5121     \fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5122     .IX Subsection "poll is buggy"
5123     .PP
5124     Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5125     implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5126     release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5127     .PP
5128     Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5129     this rotten platform, but of course you can still ask for it when creating
5130     a loop.
5131     .PP
5132     \fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5133     .IX Subsection "select is buggy"
5134     .PP
5135     All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5136     one up as well: On \s-1OS/X\s0, \f(CW\*(C`select\*(C'\fR actively limits the number of file
5137     descriptors you can pass in to 1024 \- your program suddenly crashes when
5138     you use more.
5139     .PP
5140     There is an undocumented \*(L"workaround\*(R" for this \- defining
5141     \&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5142     work on \s-1OS/X\s0.
5143     .SS "\s-1SOLARIS\s0 \s-1PROBLEMS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
5144     .IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5145     \fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5146     .IX Subsection "errno reentrancy"
5147     .PP
5148     The default compile environment on Solaris is unfortunately so
5149     thread-unsafe that you can't even use components/libraries compiled
5150     without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5151     defined by default. A valid, if stupid, implementation choice.
5152     .PP
5153     If you want to use libev in threaded environments you have to make sure
5154     it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5155     .PP
5156     \fIEvent port backend\fR
5157     .IX Subsection "Event port backend"
5158     .PP
5159     The scalable event interface for Solaris is called \*(L"event
5160     ports\*(R". Unfortunately, this mechanism is very buggy in all major
5161     releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5162     a large number of spurious wakeups, make sure you have all the relevant
5163     and latest kernel patches applied. No, I don't know which ones, but there
5164     are multiple ones to apply, and afterwards, event ports actually work
5165     great.
5166     .PP
5167     If you can't get it to work, you can try running the program by setting
5168     the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5169     \&\f(CW\*(C`select\*(C'\fR backends.
5170     .SS "\s-1AIX\s0 \s-1POLL\s0 \s-1BUG\s0"
5171     .IX Subsection "AIX POLL BUG"
5172     \&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5173     this by trying to avoid the poll backend altogether (i.e. it's not even
5174     compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5175     with large bitsets on \s-1AIX\s0, and \s-1AIX\s0 is dead anyway.
5176 root 1.79 .SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
5177 root 1.72 .IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5178 root 1.82 \fIGeneral issues\fR
5179     .IX Subsection "General issues"
5180     .PP
5181 root 1.60 Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5182     requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5183     model. Libev still offers limited functionality on this platform in
5184     the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5185     descriptors. This only applies when using Win32 natively, not when using
5186 root 1.82 e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5187 root 1.88 as every compiler comes with a slightly differently broken/incompatible
5188 root 1.82 environment.
5189 root 1.60 .PP
5190 root 1.65 Lifting these limitations would basically require the full
5191 root 1.82 re-implementation of the I/O system. If you are into this kind of thing,
5192     then note that glib does exactly that for you in a very portable way (note
5193     also that glib is the slowest event library known to man).
5194 root 1.65 .PP
5195 root 1.60 There is no supported compilation method available on windows except
5196     embedding it into other applications.
5197     .PP
5198 root 1.78 Sensible signal handling is officially unsupported by Microsoft \- libev
5199     tries its best, but under most conditions, signals will simply not work.
5200     .PP
5201 root 1.68 Not a libev limitation but worth mentioning: windows apparently doesn't
5202     accept large writes: instead of resulting in a partial write, windows will
5203     either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5204     so make sure you only write small amounts into your sockets (less than a
5205 root 1.71 megabyte seems safe, but this apparently depends on the amount of memory
5206 root 1.68 available).
5207     .PP
5208 root 1.65 Due to the many, low, and arbitrary limits on the win32 platform and
5209     the abysmal performance of winsockets, using a large number of sockets
5210     is not recommended (and not reasonable). If your program needs to use
5211     more than a hundred or so sockets, then likely it needs to use a totally
5212 root 1.67 different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5213 root 1.65 notification model, which cannot be implemented efficiently on windows
5214 root 1.78 (due to Microsoft monopoly games).
5215 root 1.68 .PP
5216     A typical way to use libev under windows is to embed it (see the embedding
5217     section for details) and use the following \fIevwrap.h\fR header file instead
5218     of \fIev.h\fR:
5219     .PP
5220     .Vb 2
5221     \& #define EV_STANDALONE /* keeps ev from requiring config.h */
5222     \& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5223     \&
5224     \& #include "ev.h"
5225     .Ve
5226     .PP
5227     And compile the following \fIevwrap.c\fR file into your project (make sure
5228 root 1.71 you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5229 root 1.68 .PP
5230     .Vb 2
5231     \& #include "evwrap.h"
5232     \& #include "ev.c"
5233     .Ve
5234 root 1.82 .PP
5235     \fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5236     .IX Subsection "The winsocket select function"
5237     .PP
5238 root 1.67 The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5239     requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5240     also extremely buggy). This makes select very inefficient, and also
5241 root 1.68 requires a mapping from file descriptors to socket handles (the Microsoft
5242     C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5243 root 1.67 discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5244     \&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5245 root 1.82 .PP
5246 root 1.68 The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5247 root 1.60 libraries and raw winsocket select is:
5248 root 1.82 .PP
5249 root 1.60 .Vb 2
5250 root 1.68 \& #define EV_USE_SELECT 1
5251     \& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5252 root 1.60 .Ve
5253 root 1.82 .PP
5254 root 1.60 Note that winsockets handling of fd sets is O(n), so you can easily get a
5255     complexity in the O(nA\*^X) range when using win32.
5256 root 1.82 .PP
5257     \fILimited number of file descriptors\fR
5258     .IX Subsection "Limited number of file descriptors"
5259     .PP
5260 root 1.65 Windows has numerous arbitrary (and low) limits on things.
5261 root 1.82 .PP
5262 root 1.65 Early versions of winsocket's select only supported waiting for a maximum
5263     of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5264 root 1.68 can only wait for \f(CW64\fR things at the same time internally; Microsoft
5265 root 1.65 recommends spawning a chain of threads and wait for 63 handles and the
5266 root 1.78 previous thread in each. Sounds great!).
5267 root 1.82 .PP
5268 root 1.60 Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5269     to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5270 root 1.78 call (which might be in libev or elsewhere, for example, perl and many
5271     other interpreters do their own select emulation on windows).
5272 root 1.82 .PP
5273 root 1.68 Another limit is the number of file descriptors in the Microsoft runtime
5274 root 1.78 libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5275     fetish or something like this inside Microsoft). You can increase this
5276     by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5277     (another arbitrary limit), but is broken in many versions of the Microsoft
5278     runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5279     (depending on windows version and/or the phase of the moon). To get more,
5280     you need to wrap all I/O functions and provide your own fd management, but
5281     the cost of calling select (O(nA\*^X)) will likely make this unworkable.
5282 root 1.79 .SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
5283 root 1.72 .IX Subsection "PORTABILITY REQUIREMENTS"
5284     In addition to a working ISO-C implementation and of course the
5285     backend-specific APIs, libev relies on a few additional extensions:
5286 root 1.79 .ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5287 root 1.68 .el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5288     .IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5289     Libev assumes not only that all watcher pointers have the same internal
5290     structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
5291     assumes that the same (machine) code can be used to call any watcher
5292     callback: The watcher callbacks have different type signatures, but libev
5293     calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5294 root 1.82 .IP "pointer accesses must be thread-atomic" 4
5295     .IX Item "pointer accesses must be thread-atomic"
5296     Accessing a pointer value must be atomic, it must both be readable and
5297     writable in one piece \- this is the case on all current architectures.
5298 root 1.65 .ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5299     .el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5300     .IX Item "sig_atomic_t volatile must be thread-atomic as well"
5301     The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5302 root 1.71 \&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5303 root 1.65 threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5304     believed to be sufficiently portable.
5305     .ie n .IP """sigprocmask"" must work in a threaded environment" 4
5306     .el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5307     .IX Item "sigprocmask must work in a threaded environment"
5308     Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5309     allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5310     pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5311     thread\*(R" or will block signals process-wide, both behaviours would
5312     be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5313     \&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5314     .Sp
5315     The most portable way to handle signals is to block signals in all threads
5316     except the initial one, and run the default loop in the initial thread as
5317     well.
5318     .ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5319     .el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5320     .IX Item "long must be large enough for common memory allocation sizes"
5321 root 1.72 To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
5322     instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5323     systems (Microsoft...) this might be unexpectedly low, but is still at
5324     least 31 bits everywhere, which is enough for hundreds of millions of
5325     watchers.
5326 root 1.65 .ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5327     .el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5328     .IX Item "double must hold a time value in seconds with enough accuracy"
5329     The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5330 root 1.82 have at least 51 bits of mantissa (and 9 bits of exponent), which is
5331     good enough for at least into the year 4000 with millisecond accuracy
5332     (the design goal for libev). This requirement is overfulfilled by
5333 root 1.88 implementations using \s-1IEEE\s0 754, which is basically all existing ones.
5334     .Sp
5335     With \s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least the
5336     year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5337     is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5338     something like that, just kidding).
5339 root 1.65 .PP
5340     If you know of other additional requirements drop me a note.
5341 root 1.72 .SH "ALGORITHMIC COMPLEXITIES"
5342     .IX Header "ALGORITHMIC COMPLEXITIES"
5343     In this section the complexities of (many of) the algorithms used inside
5344     libev will be documented. For complexity discussions about backends see
5345     the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
5346 root 1.67 .PP
5347 root 1.72 All of the following are about amortised time: If an array needs to be
5348     extended, libev needs to realloc and move the whole array, but this
5349     happens asymptotically rarer with higher number of elements, so O(1) might
5350     mean that libev does a lengthy realloc operation in rare cases, but on
5351     average it is much faster and asymptotically approaches constant time.
5352     .IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
5353     .IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5354     This means that, when you have a watcher that triggers in one hour and
5355     there are 100 watchers that would trigger before that, then inserting will
5356     have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5357     .IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5358     .IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5359     That means that changing a timer costs less than removing/adding them,
5360     as only the relative motion in the event queue has to be paid for.
5361     .IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5362     .IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5363     These just add the watcher into an array or at the head of a list.
5364     .IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5365     .IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5366     .PD 0
5367     .IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
5368     .IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5369     .PD
5370     These watchers are stored in lists, so they need to be walked to find the
5371     correct watcher to remove. The lists are usually short (you don't usually
5372     have many watchers waiting for the same fd or signal: one is typical, two
5373     is rare).
5374     .IP "Finding the next timer in each loop iteration: O(1)" 4
5375     .IX Item "Finding the next timer in each loop iteration: O(1)"
5376     By virtue of using a binary or 4\-heap, the next timer is always found at a
5377     fixed position in the storage array.
5378     .IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
5379     .IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
5380     A change means an I/O watcher gets started or stopped, which requires
5381     libev to recalculate its status (and possibly tell the kernel, depending
5382     on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
5383     .IP "Activating one watcher (putting it into the pending state): O(1)" 4
5384     .IX Item "Activating one watcher (putting it into the pending state): O(1)"
5385     .PD 0
5386     .IP "Priority handling: O(number_of_priorities)" 4
5387     .IX Item "Priority handling: O(number_of_priorities)"
5388     .PD
5389     Priorities are implemented by allocating some space for each
5390     priority. When doing priority-based operations, libev usually has to
5391     linearly search all the priorities, but starting/stopping and activating
5392     watchers becomes O(1) with respect to priority handling.
5393     .IP "Sending an ev_async: O(1)" 4
5394     .IX Item "Sending an ev_async: O(1)"
5395     .PD 0
5396     .IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5397     .IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5398     .IP "Processing signals: O(max_signal_number)" 4
5399     .IX Item "Processing signals: O(max_signal_number)"
5400     .PD
5401     Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5402 root 1.88 calls in the current loop iteration and the loop is currently
5403     blocked. Checking for async and signal events involves iterating over all
5404     running async watchers or all signal numbers.
5405 root 1.82 .SH "PORTING FROM LIBEV 3.X TO 4.X"
5406     .IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5407     The major version 4 introduced some incompatible changes to the \s-1API\s0.
5408     .PP
5409     At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5410     for all changes, so most programs should still compile. The compatibility
5411     layer might be removed in later versions of libev, so better update to the
5412     new \s-1API\s0 early than late.
5413     .ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5414     .el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5415     .IX Item "EV_COMPAT3 backwards compatibility mechanism"
5416     The backward compatibility mechanism can be controlled by
5417     \&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1MACROS\s0\*(R" in \s-1PREPROCESSOR\s0 \s-1SYMBOLS\s0 in the \s-1EMBEDDING\s0
5418     section.
5419     .ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5420     .el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5421     .IX Item "ev_default_destroy and ev_default_fork have been removed"
5422     These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5423     .Sp
5424     .Vb 2
5425     \& ev_loop_destroy (EV_DEFAULT_UC);
5426     \& ev_loop_fork (EV_DEFAULT);
5427     .Ve
5428     .IP "function/symbol renames" 4
5429     .IX Item "function/symbol renames"
5430     A number of functions and symbols have been renamed:
5431     .Sp
5432     .Vb 3
5433     \& ev_loop => ev_run
5434     \& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5435     \& EVLOOP_ONESHOT => EVRUN_ONCE
5436     \&
5437     \& ev_unloop => ev_break
5438     \& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5439     \& EVUNLOOP_ONE => EVBREAK_ONE
5440     \& EVUNLOOP_ALL => EVBREAK_ALL
5441     \&
5442     \& EV_TIMEOUT => EV_TIMER
5443     \&
5444     \& ev_loop_count => ev_iteration
5445     \& ev_loop_depth => ev_depth
5446     \& ev_loop_verify => ev_verify
5447     .Ve
5448     .Sp
5449     Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5450     \&\f(CW\*(C`ev_loop_\*(C'\fR prefix, so it was removed; \f(CW\*(C`ev_loop\*(C'\fR, \f(CW\*(C`ev_unloop\*(C'\fR and
5451     associated constants have been renamed to not collide with the \f(CW\*(C`struct
5452     ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5453     as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5454     \&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5455     typedef.
5456     .ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5457     .el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5458     .IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5459     The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5460     mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5461     and work, but the library code will of course be larger.
5462 root 1.78 .SH "GLOSSARY"
5463     .IX Header "GLOSSARY"
5464     .IP "active" 4
5465     .IX Item "active"
5466 root 1.82 A watcher is active as long as it has been started and not yet stopped.
5467     See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5468 root 1.78 .IP "application" 4
5469     .IX Item "application"
5470     In this document, an application is whatever is using libev.
5471 root 1.82 .IP "backend" 4
5472     .IX Item "backend"
5473     The part of the code dealing with the operating system interfaces.
5474 root 1.78 .IP "callback" 4
5475     .IX Item "callback"
5476     The address of a function that is called when some event has been
5477     detected. Callbacks are being passed the event loop, the watcher that
5478     received the event, and the actual event bitset.
5479 root 1.82 .IP "callback/watcher invocation" 4
5480     .IX Item "callback/watcher invocation"
5481 root 1.78 The act of calling the callback associated with a watcher.
5482     .IP "event" 4
5483     .IX Item "event"
5484     A change of state of some external event, such as data now being available
5485     for reading on a file descriptor, time having passed or simply not having
5486     any other events happening anymore.
5487     .Sp
5488     In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5489 root 1.82 \&\f(CW\*(C`EV_TIMER\*(C'\fR).
5490 root 1.78 .IP "event library" 4
5491     .IX Item "event library"
5492     A software package implementing an event model and loop.
5493     .IP "event loop" 4
5494     .IX Item "event loop"
5495     An entity that handles and processes external events and converts them
5496     into callback invocations.
5497     .IP "event model" 4
5498     .IX Item "event model"
5499     The model used to describe how an event loop handles and processes
5500     watchers and events.
5501     .IP "pending" 4
5502     .IX Item "pending"
5503 root 1.82 A watcher is pending as soon as the corresponding event has been
5504     detected. See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5505 root 1.78 .IP "real time" 4
5506     .IX Item "real time"
5507     The physical time that is observed. It is apparently strictly monotonic :)
5508     .IP "wall-clock time" 4
5509     .IX Item "wall-clock time"
5510     The time and date as shown on clocks. Unlike real time, it can actually
5511 root 1.87 be wrong and jump forwards and backwards, e.g. when you adjust your
5512 root 1.78 clock.
5513     .IP "watcher" 4
5514     .IX Item "watcher"
5515     A data structure that describes interest in certain events. Watchers need
5516     to be started (attached to an event loop) before they can receive events.
5517 root 1.1 .SH "AUTHOR"
5518     .IX Header "AUTHOR"
5519 root 1.82 Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5520 root 1.86 Magnusson and Emanuele Giaquinta, and minor corrections by many others.