ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/libev/ev.3
(Generate patch)

Comparing libev/ev.3 (file contents):
Revision 1.5 by root, Fri Nov 23 04:36:03 2007 UTC vs.
Revision 1.86 by root, Wed Feb 16 08:07:25 2011 UTC

1.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.35 1.\" Automatically generated by Pod::Man 2.22 (Pod::Simple 3.07)
2.\" 2.\"
3.\" Standard preamble: 3.\" Standard preamble:
4.\" ======================================================================== 4.\" ========================================================================
5.de Sh \" Subsection heading
6.br
7.if t .Sp
8.ne 5
9.PP
10\fB\\$1\fR
11.PP
12..
13.de Sp \" Vertical space (when we can't use .PP) 5.de Sp \" Vertical space (when we can't use .PP)
14.if t .sp .5v 6.if t .sp .5v
15.if n .sp 7.if n .sp
16.. 8..
17.de Vb \" Begin verbatim text 9.de Vb \" Begin verbatim text
… …
23.ft R 15.ft R
24.fi 16.fi
25.. 17..
26.\" Set up some character translations and predefined strings. \*(-- will 18.\" Set up some character translations and predefined strings. \*(-- will
27.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left 19.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
28.\" double quote, and \*(R" will give a right double quote. | will give a 20.\" double quote, and \*(R" will give a right double quote. \*(C+ will
29.\" real vertical bar. \*(C+ will give a nicer C++. Capital omega is used to 21.\" give a nicer C++. Capital omega is used to do unbreakable dashes and
30.\" do unbreakable dashes and therefore won't be available. \*(C` and \*(C' 22.\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff,
31.\" expand to `' in nroff, nothing in troff, for use with C<>. 23.\" nothing in troff, for use with C<>.
32.tr \(*W-|\(bv\*(Tr 24.tr \(*W-
33.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' 25.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
34.ie n \{\ 26.ie n \{\
35. ds -- \(*W- 27. ds -- \(*W-
36. ds PI pi 28. ds PI pi
37. if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch 29. if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
… …
46. ds PI \(*p 38. ds PI \(*p
47. ds L" `` 39. ds L" ``
48. ds R" '' 40. ds R" ''
49'br\} 41'br\}
50.\" 42.\"
43.\" Escape single quotes in literal strings from groff's Unicode transform.
44.ie \n(.g .ds Aq \(aq
45.el .ds Aq '
46.\"
51.\" If the F register is turned on, we'll generate index entries on stderr for 47.\" If the F register is turned on, we'll generate index entries on stderr for
52.\" titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and index 48.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
53.\" entries marked with X<> in POD. Of course, you'll have to process the 49.\" entries marked with X<> in POD. Of course, you'll have to process the
54.\" output yourself in some meaningful fashion. 50.\" output yourself in some meaningful fashion.
55.if \nF \{\ 51.ie \nF \{\
56. de IX 52. de IX
57. tm Index:\\$1\t\\n%\t"\\$2" 53. tm Index:\\$1\t\\n%\t"\\$2"
58.. 54..
59. nr % 0 55. nr % 0
60. rr F 56. rr F
61.\} 57.\}
62.\" 58.el \{\
63.\" For nroff, turn off justification. Always turn off hyphenation; it makes 59. de IX
64.\" way too many mistakes in technical documents. 60..
65.hy 0 61.\}
66.if n .na
67.\" 62.\"
68.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2). 63.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
69.\" Fear. Run. Save yourself. No user-serviceable parts. 64.\" Fear. Run. Save yourself. No user-serviceable parts.
70. \" fudge factors for nroff and troff 65. \" fudge factors for nroff and troff
71.if n \{\ 66.if n \{\
… …
126. ds Ae AE 121. ds Ae AE
127.\} 122.\}
128.rm #[ #] #H #V #F C 123.rm #[ #] #H #V #F C
129.\" ======================================================================== 124.\" ========================================================================
130.\" 125.\"
131.IX Title ""<STANDARD INPUT>" 1" 126.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-23" "perl v5.8.8" "User Contributed Perl Documentation" 127.TH LIBEV 3 "2011-01-31" "libev-4.04" "libev - high performance full featured event loop"
128.\" 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
133.SH "NAME" 132.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 133libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 134.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 135.IX Header "SYNOPSIS"
137.Vb 1 136.Vb 1
138\& #include <ev.h> 137\& #include <ev.h>
139.Ve 138.Ve
140.SH "DESCRIPTION" 139.SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
141.IX Header "DESCRIPTION" 140.IX Subsection "EXAMPLE PROGRAM"
141.Vb 2
142\& // a single header file is required
143\& #include <ev.h>
144\&
145\& #include <stdio.h> // for puts
146\&
147\& // every watcher type has its own typedef\*(Aqd struct
148\& // with the name ev_TYPE
149\& 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\& stdin_cb (EV_P_ ev_io *w, int revents)
156\& {
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\& // this causes all nested ev_run\*(Aqs to stop iterating
163\& ev_break (EV_A_ EVBREAK_ALL);
164\& }
165\&
166\& // another callback, this time for a time\-out
167\& static void
168\& timeout_cb (EV_P_ ev_timer *w, int revents)
169\& {
170\& puts ("timeout");
171\& // this causes the innermost ev_run to stop iterating
172\& ev_break (EV_A_ EVBREAK_ONE);
173\& }
174\&
175\& int
176\& main (void)
177\& {
178\& // use the default event loop unless you have special needs
179\& struct ev_loop *loop = EV_DEFAULT;
180\&
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\& ev_run (loop, 0);
193\&
194\& // break was called, so exit
195\& return 0;
196\& }
197.Ve
198.SH "ABOUT THIS DOCUMENT"
199.IX Header "ABOUT THIS DOCUMENT"
200This document documents the libev software package.
201.PP
202The newest version of this document is also available as an html-formatted
203web page you might find easier to navigate when reading it for the first
204time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
205.PP
206While this document tries to be as complete as possible in documenting
207libev, its usage and the rationale behind its design, it is not a tutorial
208on event-based programming, nor will it introduce event-based programming
209with libev.
210.PP
211Familiarity with event based programming techniques in general is assumed
212throughout this document.
213.SH "WHAT TO READ WHEN IN A HURRY"
214.IX Header "WHAT TO READ WHEN IN A HURRY"
215This manual tries to be very detailed, but unfortunately, this also makes
216it very long. If you just want to know the basics of libev, I suggest
217reading \*(L"\s-1ANATOMY\s0 \s-1OF\s0 A \s-1WATCHER\s0\*(R", then the \*(L"\s-1EXAMPLE\s0 \s-1PROGRAM\s0\*(R" above and
218look 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.SH "ABOUT LIBEV"
221.IX Header "ABOUT LIBEV"
142Libev is an event loop: you register interest in certain events (such as a 222Libev is an event loop: you register interest in certain events (such as a
143file descriptor being readable or a timeout occuring), and it will manage 223file descriptor being readable or a timeout occurring), and it will manage
144these event sources and provide your program with events. 224these event sources and provide your program with events.
145.PP 225.PP
146To do this, it must take more or less complete control over your process 226To do this, it must take more or less complete control over your process
147(or thread) by executing the \fIevent loop\fR handler, and will then 227(or thread) by executing the \fIevent loop\fR handler, and will then
148communicate events via a callback mechanism. 228communicate events via a callback mechanism.
149.PP 229.PP
150You register interest in certain events by registering so-called \fIevent 230You register interest in certain events by registering so-called \fIevent
151watchers\fR, which are relatively small C structures you initialise with the 231watchers\fR, which are relatively small C structures you initialise with the
152details of the event, and then hand it over to libev by \fIstarting\fR the 232details of the event, and then hand it over to libev by \fIstarting\fR the
153watcher. 233watcher.
154.SH "FEATURES" 234.SS "\s-1FEATURES\s0"
155.IX Header "FEATURES" 235.IX Subsection "FEATURES"
156Libev supports select, poll, the linux-specific epoll and the bsd-specific 236Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
157kqueue mechanisms for file descriptor events, relative timers, absolute 237BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
158timers with customised rescheduling, signal events, process status change 238for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
159events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event 239(for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
160loop mechanism itself (idle, prepare and check watchers). It also is quite 240inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
161fast (see this benchmark comparing 241timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
162it to libevent for example). 242(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
243change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
244loop 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
246limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
247.PP
248It also is quite fast (see this
249<benchmark> comparing it to libevent
250for example).
163.SH "CONVENTIONS" 251.SS "\s-1CONVENTIONS\s0"
164.IX Header "CONVENTIONS" 252.IX Subsection "CONVENTIONS"
165Libev is very configurable. In this manual the default configuration 253Libev is very configurable. In this manual the default (and most common)
166will be described, which supports multiple event loops. For more info 254configuration will be described, which supports multiple event loops. For
167about various configuration options please have a look at the file 255more info about various configuration options please have a look at
168\&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without 256\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
169support for multiple event loops, then all functions taking an initial 257for multiple event loops, then all functions taking an initial argument of
170argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) 258name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
171will not have this argument. 259this argument.
172.SH "TIME REPRESENTATION" 260.SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
173.IX Header "TIME REPRESENTATION" 261.IX Subsection "TIME REPRESENTATION"
174Libev represents time as a single floating point number, representing the 262Libev represents time as a single floating point number, representing
175(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 263the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
176the beginning of 1970, details are complicated, don't ask). This type is 264somewhere near the beginning of 1970, details are complicated, don't
177called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 265ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
178to the double type in C. 266too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
267any calculations on it, you should treat it as some floating point value.
268.PP
269Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
270time differences (e.g. delays) throughout libev.
271.SH "ERROR HANDLING"
272.IX Header "ERROR HANDLING"
273Libev knows three classes of errors: operating system errors, usage errors
274and internal errors (bugs).
275.PP
276When libev catches an operating system error it cannot handle (for example
277a system call indicating a condition libev cannot fix), it calls the callback
278set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
279abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
280()\*(C'\fR.
281.PP
282When libev detects a usage error such as a negative timer interval, then
283it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
284so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
285the libev caller and need to be fixed there.
286.PP
287Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
288extensive consistency checking code. These do not trigger under normal
289circumstances, as they indicate either a bug in libev or worse.
179.SH "GLOBAL FUNCTIONS" 290.SH "GLOBAL FUNCTIONS"
180.IX Header "GLOBAL FUNCTIONS" 291.IX Header "GLOBAL FUNCTIONS"
181These functions can be called anytime, even before initialising the 292These functions can be called anytime, even before initialising the
182library in any way. 293library in any way.
183.IP "ev_tstamp ev_time ()" 4 294.IP "ev_tstamp ev_time ()" 4
184.IX Item "ev_tstamp ev_time ()" 295.IX Item "ev_tstamp ev_time ()"
185Returns the current time as libev would use it. Please note that the 296Returns the current time as libev would use it. Please note that the
186\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp 297\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
187you actually want to know. 298you actually want to know. Also interesting is the combination of
299\&\f(CW\*(C`ev_update_now\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
300.IP "ev_sleep (ev_tstamp interval)" 4
301.IX Item "ev_sleep (ev_tstamp interval)"
302Sleep for the given interval: The current thread will be blocked until
303either it is interrupted or the given time interval has passed. Basically
304this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
188.IP "int ev_version_major ()" 4 305.IP "int ev_version_major ()" 4
189.IX Item "int ev_version_major ()" 306.IX Item "int ev_version_major ()"
190.PD 0 307.PD 0
191.IP "int ev_version_minor ()" 4 308.IP "int ev_version_minor ()" 4
192.IX Item "int ev_version_minor ()" 309.IX Item "int ev_version_minor ()"
193.PD 310.PD
194You can find out the major and minor version numbers of the library 311You can find out the major and minor \s-1ABI\s0 version numbers of the library
195you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and 312you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
196\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global 313\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
197symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the 314symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
198version of the library your program was compiled against. 315version of the library your program was compiled against.
199.Sp 316.Sp
317These version numbers refer to the \s-1ABI\s0 version of the library, not the
318release version.
319.Sp
200Usually, it's a good idea to terminate if the major versions mismatch, 320Usually, it's a good idea to terminate if the major versions mismatch,
201as this indicates an incompatible change. Minor versions are usually 321as this indicates an incompatible change. Minor versions are usually
202compatible to older versions, so a larger minor version alone is usually 322compatible to older versions, so a larger minor version alone is usually
203not a problem. 323not a problem.
324.Sp
325Example: Make sure we haven't accidentally been linked against the wrong
326version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
327such as \s-1LFS\s0 or reentrancy).
328.Sp
329.Vb 3
330\& assert (("libev version mismatch",
331\& ev_version_major () == EV_VERSION_MAJOR
332\& && ev_version_minor () >= EV_VERSION_MINOR));
333.Ve
334.IP "unsigned int ev_supported_backends ()" 4
335.IX Item "unsigned int ev_supported_backends ()"
336Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
337value) compiled into this binary of libev (independent of their
338availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
339a description of the set values.
340.Sp
341Example: make sure we have the epoll method, because yeah this is cool and
342a must have and can we have a torrent of it please!!!11
343.Sp
344.Vb 2
345\& assert (("sorry, no epoll, no sex",
346\& ev_supported_backends () & EVBACKEND_EPOLL));
347.Ve
348.IP "unsigned int ev_recommended_backends ()" 4
349.IX Item "unsigned int ev_recommended_backends ()"
350Return the set of all backends compiled into this binary of libev and
351also recommended for this platform, meaning it will work for most file
352descriptor types. This set is often smaller than the one returned by
353\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
354and will not be auto-detected unless you explicitly request it (assuming
355you know what you are doing). This is the set of backends that libev will
356probe for if you specify no backends explicitly.
357.IP "unsigned int ev_embeddable_backends ()" 4
358.IX Item "unsigned int ev_embeddable_backends ()"
359Returns the set of backends that are embeddable in other event loops. This
360value is platform-specific but can include backends not available on the
361current system. To find which embeddable backends might be supported on
362the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
363& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
364.Sp
365See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
204.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 366.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
205.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 367.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
206Sets the allocation function to use (the prototype is similar to the 368Sets the allocation function to use (the prototype is similar \- the
207realloc C function, the semantics are identical). It is used to allocate 369semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
208and free memory (no surprises here). If it returns zero when memory 370used to allocate and free memory (no surprises here). If it returns zero
209needs to be allocated, the library might abort or take some potentially 371when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
210destructive action. The default is your system realloc function. 372or take some potentially destructive action.
373.Sp
374Since some systems (at least OpenBSD and Darwin) fail to implement
375correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
376\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
211.Sp 377.Sp
212You could override this function in high-availability programs to, say, 378You could override this function in high-availability programs to, say,
213free some memory if it cannot allocate memory, to use a special allocator, 379free some memory if it cannot allocate memory, to use a special allocator,
214or even to sleep a while and retry until some memory is available. 380or even to sleep a while and retry until some memory is available.
381.Sp
382Example: Replace the libev allocator with one that waits a bit and then
383retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
384.Sp
385.Vb 6
386\& static void *
387\& persistent_realloc (void *ptr, size_t size)
388\& {
389\& for (;;)
390\& {
391\& void *newptr = realloc (ptr, size);
392\&
393\& if (newptr)
394\& return newptr;
395\&
396\& sleep (60);
397\& }
398\& }
399\&
400\& ...
401\& ev_set_allocator (persistent_realloc);
402.Ve
215.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 403.IP "ev_set_syserr_cb (void (*cb)(const char *msg))" 4
216.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 404.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg))"
217Set the callback function to call on a retryable syscall error (such 405Set the callback function to call on a retryable system call error (such
218as failed select, poll, epoll_wait). The message is a printable string 406as failed select, poll, epoll_wait). The message is a printable string
219indicating the system call or subsystem causing the problem. If this 407indicating the system call or subsystem causing the problem. If this
220callback is set, then libev will expect it to remedy the sitution, no 408callback is set, then libev will expect it to remedy the situation, no
221matter what, when it returns. That is, libev will generally retry the 409matter what, when it returns. That is, libev will generally retry the
222requested operation, or, if the condition doesn't go away, do bad stuff 410requested operation, or, if the condition doesn't go away, do bad stuff
223(such as abort). 411(such as abort).
412.Sp
413Example: This is basically the same thing that libev does internally, too.
414.Sp
415.Vb 6
416\& static void
417\& fatal_error (const char *msg)
418\& {
419\& perror (msg);
420\& abort ();
421\& }
422\&
423\& ...
424\& ev_set_syserr_cb (fatal_error);
425.Ve
426.IP "ev_feed_signal (int signum)" 4
427.IX Item "ev_feed_signal (int signum)"
428This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
429safe to call this function at any time, from any context, including signal
430handlers or random threads.
431.Sp
432Its main use is to customise signal handling in your process, especially
433in the presence of threads. For example, you could block signals
434by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
435creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
436mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
437\&\f(CW\*(C`ev_feed_signal\*(C'\fR.
224.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 438.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
225.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 439.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
226An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 440An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
227types of such loops, the \fIdefault\fR loop, which supports signals and child 441\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
228events, and dynamically created loops which do not. 442libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
229.PP 443.PP
230If you use threads, a common model is to run the default event loop 444The library knows two types of such loops, the \fIdefault\fR loop, which
231in your main thread (or in a separate thread) and for each thread you 445supports child process events, and dynamically created event loops which
232create, you also create another event loop. Libev itself does no locking 446do not.
233whatsoever, so if you mix calls to the same event loop in different
234threads, make sure you lock (this is usually a bad idea, though, even if
235done correctly, because it's hideous and inefficient).
236.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 447.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
237.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 448.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
238This will initialise the default event loop if it hasn't been initialised 449This returns the \*(L"default\*(R" event loop object, which is what you should
239yet and return it. If the default loop could not be initialised, returns 450normally use when you just need \*(L"the event loop\*(R". Event loop objects and
240false. If it already was initialised it simply returns it (and ignores the 451the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
241flags). 452\&\f(CW\*(C`ev_loop_new\*(C'\fR.
453.Sp
454If the default loop is already initialised then this function simply
455returns it (and ignores the flags. If that is troubling you, check
456\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
457flags, which should almost always be \f(CW0\fR, unless the caller is also the
458one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
242.Sp 459.Sp
243If you don't know what event loop to use, use the one returned from this 460If you don't know what event loop to use, use the one returned from this
244function. 461function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
462.Sp
463Note that this function is \fInot\fR thread-safe, so if you want to use it
464from multiple threads, you have to employ some kind of mutex (note also
465that this case is unlikely, as loops cannot be shared easily between
466threads anyway).
467.Sp
468The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
469and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
470a problem for your application you can either create a dynamic loop with
471\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
472\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
473.Sp
474Example: This is the most typical usage.
475.Sp
476.Vb 2
477\& if (!ev_default_loop (0))
478\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
479.Ve
480.Sp
481Example: Restrict libev to the select and poll backends, and do not allow
482environment settings to be taken into account:
483.Sp
484.Vb 1
485\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
486.Ve
487.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
488.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
489This will create and initialise a new event loop object. If the loop
490could not be initialised, returns false.
491.Sp
492This function is thread-safe, and one common way to use libev with
493threads is indeed to create one loop per thread, and using the default
494loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
245.Sp 495.Sp
246The flags argument can be used to specify special behaviour or specific 496The flags argument can be used to specify special behaviour or specific
247backends to use, and is usually specified as 0 (or \s-1EVFLAG_AUTO\s0). 497backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
248.Sp 498.Sp
249It supports the following flags: 499The following flags are supported:
250.RS 4 500.RS 4
251.ie n .IP """EVFLAG_AUTO""" 4 501.ie n .IP """EVFLAG_AUTO""" 4
252.el .IP "\f(CWEVFLAG_AUTO\fR" 4 502.el .IP "\f(CWEVFLAG_AUTO\fR" 4
253.IX Item "EVFLAG_AUTO" 503.IX Item "EVFLAG_AUTO"
254The default flags value. Use this if you have no clue (it's the right 504The default flags value. Use this if you have no clue (it's the right
255thing, believe me). 505thing, believe me).
256.ie n .IP """EVFLAG_NOENV""" 4 506.ie n .IP """EVFLAG_NOENV""" 4
257.el .IP "\f(CWEVFLAG_NOENV\fR" 4 507.el .IP "\f(CWEVFLAG_NOENV\fR" 4
258.IX Item "EVFLAG_NOENV" 508.IX Item "EVFLAG_NOENV"
259If this flag bit is ored into the flag value (or the program runs setuid 509If this flag bit is or'ed into the flag value (or the program runs setuid
260or setgid) then libev will \fInot\fR look at the environment variable 510or setgid) then libev will \fInot\fR look at the environment variable
261\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 511\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
262override the flags completely if it is found in the environment. This is 512override the flags completely if it is found in the environment. This is
263useful to try out specific backends to test their performance, or to work 513useful to try out specific backends to test their performance, or to work
264around bugs. 514around bugs.
515.ie n .IP """EVFLAG_FORKCHECK""" 4
516.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
517.IX Item "EVFLAG_FORKCHECK"
518Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
519make libev check for a fork in each iteration by enabling this flag.
520.Sp
521This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
522and thus this might slow down your event loop if you do a lot of loop
523iterations and little real work, but is usually not noticeable (on my
524GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
525without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
526\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
527.Sp
528The big advantage of this flag is that you can forget about fork (and
529forget about forgetting to tell libev about forking) when you use this
530flag.
531.Sp
532This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
533environment variable.
534.ie n .IP """EVFLAG_NOINOTIFY""" 4
535.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
536.IX Item "EVFLAG_NOINOTIFY"
537When this flag is specified, then libev will not attempt to use the
538\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
539testing, this flag can be useful to conserve inotify file descriptors, as
540otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
541.ie n .IP """EVFLAG_SIGNALFD""" 4
542.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
543.IX Item "EVFLAG_SIGNALFD"
544When this flag is specified, then libev will attempt to use the
545\&\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
546delivers signals synchronously, which makes it both faster and might make
547it possible to get the queued signal data. It can also simplify signal
548handling with threads, as long as you properly block signals in your
549threads that are not interested in handling them.
550.Sp
551Signalfd will not be used by default as this changes your signal mask, and
552there are a lot of shoddy libraries and programs (glib's threadpool for
553example) that can't properly initialise their signal masks.
554.ie n .IP """EVFLAG_NOSIGMASK""" 4
555.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
556.IX Item "EVFLAG_NOSIGMASK"
557When this flag is specified, then libev will avoid to modify the signal
558mask. Specifically, this means you ahve to make sure signals are unblocked
559when you want to receive them.
560.Sp
561This behaviour is useful when you want to do your own signal handling, or
562want to handle signals only in specific threads and want to avoid libev
563unblocking the signals.
564.Sp
565It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
566\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
567.Sp
568This flag's behaviour will become the default in future versions of libev.
265.ie n .IP """EVMETHOD_SELECT"" (value 1, portable select backend)" 4 569.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
266.el .IP "\f(CWEVMETHOD_SELECT\fR (value 1, portable select backend)" 4 570.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
267.IX Item "EVMETHOD_SELECT (value 1, portable select backend)" 571.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
268This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 572This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
269libev tries to roll its own fd_set with no limits on the number of fds, 573libev tries to roll its own fd_set with no limits on the number of fds,
270but if that fails, expect a fairly low limit on the number of fds when 574but if that fails, expect a fairly low limit on the number of fds when
271using this backend. It doesn't scale too well (O(highest_fd)), but its usually 575using this backend. It doesn't scale too well (O(highest_fd)), but its
272the fastest backend for a low number of fds. 576usually the fastest backend for a low number of (low-numbered :) fds.
577.Sp
578To get good performance out of this backend you need a high amount of
579parallelism (most of the file descriptors should be busy). If you are
580writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
581connections as possible during one iteration. You might also want to have
582a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
583readiness notifications you get per iteration.
584.Sp
585This 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
586\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
587\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
273.ie n .IP """EVMETHOD_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 588.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
274.el .IP "\f(CWEVMETHOD_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 589.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
275.IX Item "EVMETHOD_POLL (value 2, poll backend, available everywhere except on windows)" 590.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
276And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 591And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
277select, but handles sparse fds better and has no artificial limit on the 592than select, but handles sparse fds better and has no artificial
278number of fds you can use (except it will slow down considerably with a 593limit on the number of fds you can use (except it will slow down
279lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 594considerably with a lot of inactive fds). It scales similarly to select,
595i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
596performance tips.
597.Sp
598This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
599\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
280.ie n .IP """EVMETHOD_EPOLL"" (value 4, Linux)" 4 600.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
281.el .IP "\f(CWEVMETHOD_EPOLL\fR (value 4, Linux)" 4 601.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
282.IX Item "EVMETHOD_EPOLL (value 4, Linux)" 602.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
603Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
604kernels).
605.Sp
283For few fds, this backend is a bit little slower than poll and select, 606For few fds, this backend is a bit little slower than poll and select,
284but it scales phenomenally better. While poll and select usually scale like 607but it scales phenomenally better. While poll and select usually scale
285O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 608like O(total_fds) where n is the total number of fds (or the highest fd),
286either O(1) or O(active_fds). 609epoll scales either O(1) or O(active_fds).
287.Sp 610.Sp
611The epoll mechanism deserves honorable mention as the most misdesigned
612of the more advanced event mechanisms: mere annoyances include silently
613dropping file descriptors, requiring a system call per change per file
614descriptor (and unnecessary guessing of parameters), problems with dup,
615returning before the timeout value, resulting in additional iterations
616(and only giving 5ms accuracy while select on the same platform gives
6170.1ms) and so on. The biggest issue is fork races, however \- if a program
618forks then \fIboth\fR parent and child process have to recreate the epoll
619set, which can take considerable time (one syscall per file descriptor)
620and is of course hard to detect.
621.Sp
622Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
623of course \fIdoesn't\fR, and epoll just loves to report events for totally
624\&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
625even remove them from the set) than registered in the set (especially
626on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
627employing an additional generation counter and comparing that against the
628events to filter out spurious ones, recreating the set when required. Last
629not least, it also refuses to work with some file descriptors which work
630perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
631.Sp
632Epoll is truly the train wreck analog among event poll mechanisms,
633a frankenpoll, cobbled together in a hurry, no thought to design or
634interaction with others.
635.Sp
288While stopping and starting an I/O watcher in the same iteration will 636While stopping, setting and starting an I/O watcher in the same iteration
289result in some caching, there is still a syscall per such incident 637will result in some caching, there is still a system call per such
290(because the fd could point to a different file description now), so its 638incident (because the same \fIfile descriptor\fR could point to a different
291best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 639\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
292well if you register events for both fds. 640file descriptors might not work very well if you register events for both
641file descriptors.
642.Sp
643Best performance from this backend is achieved by not unregistering all
644watchers for a file descriptor until it has been closed, if possible,
645i.e. keep at least one watcher active per fd at all times. Stopping and
646starting a watcher (without re-setting it) also usually doesn't cause
647extra overhead. A fork can both result in spurious notifications as well
648as in libev having to destroy and recreate the epoll object, which can
649take considerable time and thus should be avoided.
650.Sp
651All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
652faster than epoll for maybe up to a hundred file descriptors, depending on
653the usage. So sad.
654.Sp
655While nominally embeddable in other event loops, this feature is broken in
656all kernel versions tested so far.
657.Sp
658This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
659\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
293.ie n .IP """EVMETHOD_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 660.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
294.el .IP "\f(CWEVMETHOD_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 661.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
295.IX Item "EVMETHOD_KQUEUE (value 8, most BSD clones)" 662.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
296Kqueue deserves special mention, as at the time of this writing, it 663Kqueue deserves special mention, as at the time of this writing, it
297was broken on all BSDs except NetBSD (usually it doesn't work with 664was broken on all BSDs except NetBSD (usually it doesn't work reliably
298anything but sockets and pipes, except on Darwin, where of course its 665with anything but sockets and pipes, except on Darwin, where of course
299completely useless). For this reason its not being \*(L"autodetected\*(R" unless 666it's completely useless). Unlike epoll, however, whose brokenness
300you explicitly specify the flags (i.e. you don't use \s-1EVFLAG_AUTO\s0). 667is by design, these kqueue bugs can (and eventually will) be fixed
668without \s-1API\s0 changes to existing programs. For this reason it's not being
669\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
670\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
671system like NetBSD.
672.Sp
673You still can embed kqueue into a normal poll or select backend and use it
674only for sockets (after having made sure that sockets work with kqueue on
675the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
301.Sp 676.Sp
302It scales in the same way as the epoll backend, but the interface to the 677It scales in the same way as the epoll backend, but the interface to the
303kernel is more efficient (which says nothing about its actual speed, of 678kernel is more efficient (which says nothing about its actual speed, of
304course). While starting and stopping an I/O watcher does not cause an 679course). While stopping, setting and starting an I/O watcher does never
305extra syscall as with epoll, it still adds up to four event changes per 680cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
306incident, so its best to avoid that. 681two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
682sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
683cases
684.Sp
685This backend usually performs well under most conditions.
686.Sp
687While nominally embeddable in other event loops, this doesn't work
688everywhere, so you might need to test for this. And since it is broken
689almost everywhere, you should only use it when you have a lot of sockets
690(for which it usually works), by embedding it into another event loop
691(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
692also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
693.Sp
694This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
695\&\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
696\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
307.ie n .IP """EVMETHOD_DEVPOLL"" (value 16, Solaris 8)" 4 697.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
308.el .IP "\f(CWEVMETHOD_DEVPOLL\fR (value 16, Solaris 8)" 4 698.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
309.IX Item "EVMETHOD_DEVPOLL (value 16, Solaris 8)" 699.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
310This is not implemented yet (and might never be). 700This is not implemented yet (and might never be, unless you send me an
701implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
702and is not embeddable, which would limit the usefulness of this backend
703immensely.
311.ie n .IP """EVMETHOD_PORT"" (value 32, Solaris 10)" 4 704.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
312.el .IP "\f(CWEVMETHOD_PORT\fR (value 32, Solaris 10)" 4 705.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
313.IX Item "EVMETHOD_PORT (value 32, Solaris 10)" 706.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
314This uses the Solaris 10 port mechanism. As with everything on Solaris, 707This uses the Solaris 10 event port mechanism. As with everything on Solaris,
315it's really slow, but it still scales very well (O(active_fds)). 708it's really slow, but it still scales very well (O(active_fds)).
709.Sp
710While this backend scales well, it requires one system call per active
711file descriptor per loop iteration. For small and medium numbers of file
712descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
713might perform better.
714.Sp
715On the positive side, this backend actually performed fully to
716specification in all tests and is fully embeddable, which is a rare feat
717among the OS-specific backends (I vastly prefer correctness over speed
718hacks).
719.Sp
720On the negative side, the interface is \fIbizarre\fR \- so bizarre that
721even sun itself gets it wrong in their code examples: The event polling
722function sometimes returning events to the caller even though an error
723occurred, but with no indication whether it has done so or not (yes, it's
724even documented that way) \- deadly for edge-triggered interfaces where
725you absolutely have to know whether an event occurred or not because you
726have to re-arm the watcher.
727.Sp
728Fortunately libev seems to be able to work around these idiocies.
729.Sp
730This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
731\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
316.ie n .IP """EVMETHOD_ALL""" 4 732.ie n .IP """EVBACKEND_ALL""" 4
317.el .IP "\f(CWEVMETHOD_ALL\fR" 4 733.el .IP "\f(CWEVBACKEND_ALL\fR" 4
318.IX Item "EVMETHOD_ALL" 734.IX Item "EVBACKEND_ALL"
319Try all backends (even potentially broken ones that wouldn't be tried 735Try all backends (even potentially broken ones that wouldn't be tried
320with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 736with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
321\&\f(CW\*(C`EVMETHOD_ALL & ~EVMETHOD_KQUEUE\*(C'\fR. 737\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
738.Sp
739It is definitely not recommended to use this flag, use whatever
740\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
741at all.
742.ie n .IP """EVBACKEND_MASK""" 4
743.el .IP "\f(CWEVBACKEND_MASK\fR" 4
744.IX Item "EVBACKEND_MASK"
745Not a backend at all, but a mask to select all backend bits from a
746\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
747value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
322.RE 748.RE
323.RS 4 749.RS 4
324.Sp 750.Sp
325If one or more of these are ored into the flags value, then only these 751If one or more of the backend flags are or'ed into the flags value,
326backends will be tried (in the reverse order as given here). If none are 752then only these backends will be tried (in the reverse order as listed
327specified, most compiled-in backend will be tried, usually in reverse 753here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
328order of their flag values :) 754()\*(C'\fR will be tried.
755.Sp
756Example: Try to create a event loop that uses epoll and nothing else.
757.Sp
758.Vb 3
759\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
760\& if (!epoller)
761\& fatal ("no epoll found here, maybe it hides under your chair");
762.Ve
763.Sp
764Example: Use whatever libev has to offer, but make sure that kqueue is
765used if available.
766.Sp
767.Vb 1
768\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
769.Ve
329.RE 770.RE
330.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
331.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
332Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
333always distinct from the default loop. Unlike the default loop, it cannot
334handle signal and child watchers, and attempts to do so will be greeted by
335undefined behaviour (or a failed assertion if assertions are enabled).
336.IP "ev_default_destroy ()" 4
337.IX Item "ev_default_destroy ()"
338Destroys the default loop again (frees all memory and kernel state
339etc.). This stops all registered event watchers (by not touching them in
340any way whatsoever, although you cannot rely on this :).
341.IP "ev_loop_destroy (loop)" 4 771.IP "ev_loop_destroy (loop)" 4
342.IX Item "ev_loop_destroy (loop)" 772.IX Item "ev_loop_destroy (loop)"
343Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an 773Destroys an event loop object (frees all memory and kernel state
344earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR. 774etc.). None of the active event watchers will be stopped in the normal
345.IP "ev_default_fork ()" 4 775sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
346.IX Item "ev_default_fork ()" 776responsibility to either stop all watchers cleanly yourself \fIbefore\fR
347This function reinitialises the kernel state for backends that have 777calling this function, or cope with the fact afterwards (which is usually
348one. Despite the name, you can call it anytime, but it makes most sense 778the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
349after forking, in either the parent or child process (or both, but that 779for example).
350again makes little sense).
351.Sp 780.Sp
352You \fImust\fR call this function in the child process after forking if and 781Note that certain global state, such as signal state (and installed signal
353only if you want to use the event library in both processes. If you just 782handlers), will not be freed by this function, and related watchers (such
354fork+exec, you don't have to call it. 783as signal and child watchers) would need to be stopped manually.
355.Sp 784.Sp
356The function itself is quite fast and it's usually not a problem to call 785This function is normally used on loop objects allocated by
357it just in case after a fork. To make this easy, the function will fit in 786\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
358quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 787\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
359.Sp 788.Sp
360.Vb 1 789Note that it is not advisable to call this function on the default loop
361\& pthread_atfork (0, 0, ev_default_fork); 790except in the rare occasion where you really need to free its resources.
362.Ve 791If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
792and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
363.IP "ev_loop_fork (loop)" 4 793.IP "ev_loop_fork (loop)" 4
364.IX Item "ev_loop_fork (loop)" 794.IX Item "ev_loop_fork (loop)"
365Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 795This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations to
366\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 796reinitialise the kernel state for backends that have one. Despite the
367after fork, and how you do this is entirely your own problem. 797name, you can call it anytime, but it makes most sense after forking, in
798the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
799child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
800.Sp
801Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
802a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
803because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
804during fork.
805.Sp
806On the other hand, you only need to call this function in the child
807process if and only if you want to use the event loop in the child. If
808you just fork+exec or create a new loop in the child, you don't have to
809call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
810difference, but libev will usually detect this case on its own and do a
811costly reset of the backend).
812.Sp
813The function itself is quite fast and it's usually not a problem to call
814it just in case after a fork.
815.Sp
816Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
817using pthreads.
818.Sp
819.Vb 5
820\& static void
821\& post_fork_child (void)
822\& {
823\& ev_loop_fork (EV_DEFAULT);
824\& }
825\&
826\& ...
827\& pthread_atfork (0, 0, post_fork_child);
828.Ve
829.IP "int ev_is_default_loop (loop)" 4
830.IX Item "int ev_is_default_loop (loop)"
831Returns true when the given loop is, in fact, the default loop, and false
832otherwise.
833.IP "unsigned int ev_iteration (loop)" 4
834.IX Item "unsigned int ev_iteration (loop)"
835Returns the current iteration count for the event loop, which is identical
836to the number of times libev did poll for new events. It starts at \f(CW0\fR
837and happily wraps around with enough iterations.
838.Sp
839This value can sometimes be useful as a generation counter of sorts (it
840\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
841\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
842prepare and check phases.
368.IP "unsigned int ev_method (loop)" 4 843.IP "unsigned int ev_depth (loop)" 4
369.IX Item "unsigned int ev_method (loop)" 844.IX Item "unsigned int ev_depth (loop)"
845Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
846times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
847.Sp
848Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
849\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
850in which case it is higher.
851.Sp
852Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
853throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
854as a hint to avoid such ungentleman-like behaviour unless it's really
855convenient, in which case it is fully supported.
856.IP "unsigned int ev_backend (loop)" 4
857.IX Item "unsigned int ev_backend (loop)"
370Returns one of the \f(CW\*(C`EVMETHOD_*\*(C'\fR flags indicating the event backend in 858Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
371use. 859use.
372.IP "ev_tstamp ev_now (loop)" 4 860.IP "ev_tstamp ev_now (loop)" 4
373.IX Item "ev_tstamp ev_now (loop)" 861.IX Item "ev_tstamp ev_now (loop)"
374Returns the current \*(L"event loop time\*(R", which is the time the event loop 862Returns the current \*(L"event loop time\*(R", which is the time the event loop
375got events and started processing them. This timestamp does not change 863received events and started processing them. This timestamp does not
376as long as callbacks are being processed, and this is also the base time 864change as long as callbacks are being processed, and this is also the base
377used for relative timers. You can treat it as the timestamp of the event 865time used for relative timers. You can treat it as the timestamp of the
378occuring (or more correctly, the mainloop finding out about it). 866event occurring (or more correctly, libev finding out about it).
867.IP "ev_now_update (loop)" 4
868.IX Item "ev_now_update (loop)"
869Establishes the current time by querying the kernel, updating the time
870returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
871is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
872.Sp
873This function is rarely useful, but when some event callback runs for a
874very long time without entering the event loop, updating libev's idea of
875the current time is a good idea.
876.Sp
877See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
878.IP "ev_suspend (loop)" 4
879.IX Item "ev_suspend (loop)"
880.PD 0
881.IP "ev_resume (loop)" 4
882.IX Item "ev_resume (loop)"
883.PD
884These two functions suspend and resume an event loop, for use when the
885loop is not used for a while and timeouts should not be processed.
886.Sp
887A typical use case would be an interactive program such as a game: When
888the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
889would be best to handle timeouts as if no time had actually passed while
890the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
891in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
892\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
893.Sp
894Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
895between \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
896will be rescheduled (that is, they will lose any events that would have
897occurred while suspended).
898.Sp
899After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
900given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
901without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
902.Sp
903Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
904event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
379.IP "ev_loop (loop, int flags)" 4 905.IP "ev_run (loop, int flags)" 4
380.IX Item "ev_loop (loop, int flags)" 906.IX Item "ev_run (loop, int flags)"
381Finally, this is it, the event handler. This function usually is called 907Finally, this is it, the event handler. This function usually is called
382after you initialised all your watchers and you want to start handling 908after you have initialised all your watchers and you want to start
383events. 909handling events. It will ask the operating system for any new events, call
910the watcher callbacks, an then repeat the whole process indefinitely: This
911is why event loops are called \fIloops\fR.
384.Sp 912.Sp
385If the flags argument is specified as 0, it will not return until either 913If the flags argument is specified as \f(CW0\fR, it will keep handling events
386no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 914until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
915called.
387.Sp 916.Sp
917Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
918relying on all watchers to be stopped when deciding when a program has
919finished (especially in interactive programs), but having a program
920that automatically loops as long as it has to and no longer by virtue
921of relying on its watchers stopping correctly, that is truly a thing of
922beauty.
923.Sp
924This function is also \fImostly\fR exception-safe \- you can break out of
925a \f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
926exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
927will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
928.Sp
388A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 929A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
389those events and any outstanding ones, but will not block your process in 930those events and any already outstanding ones, but will not wait and
390case there are no events and will return after one iteration of the loop. 931block your process in case there are no events and will return after one
932iteration of the loop. This is sometimes useful to poll and handle new
933events while doing lengthy calculations, to keep the program responsive.
391.Sp 934.Sp
392A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 935A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
393neccessary) and will handle those and any outstanding ones. It will block 936necessary) and will handle those and any already outstanding ones. It
394your process until at least one new event arrives, and will return after 937will block your process until at least one new event arrives (which could
938be an event internal to libev itself, so there is no guarantee that a
939user-registered callback will be called), and will return after one
395one iteration of the loop. 940iteration of the loop.
396.Sp 941.Sp
397This flags value could be used to implement alternative looping 942This is useful if you are waiting for some external event in conjunction
398constructs, but the \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`check\*(C'\fR watchers provide a better and 943with something not expressible using other libev watchers (i.e. "roll your
399more generic mechanism. 944own \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
945usually a better approach for this kind of thing.
400.Sp 946.Sp
401Here are the gory details of what ev_loop does: 947Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does:
402.Sp 948.Sp
403.Vb 15 949.Vb 10
404\& 1. If there are no active watchers (reference count is zero), return. 950\& \- Increment loop depth.
951\& \- Reset the ev_break status.
952\& \- Before the first iteration, call any pending watchers.
953\& LOOP:
954\& \- If EVFLAG_FORKCHECK was used, check for a fork.
955\& \- If a fork was detected (by any means), queue and call all fork watchers.
405\& 2. Queue and immediately call all prepare watchers. 956\& \- Queue and call all prepare watchers.
957\& \- If ev_break was called, goto FINISH.
406\& 3. If we have been forked, recreate the kernel state. 958\& \- If we have been forked, detach and recreate the kernel state
959\& as to not disturb the other process.
407\& 4. Update the kernel state with all outstanding changes. 960\& \- Update the kernel state with all outstanding changes.
408\& 5. Update the "event loop time". 961\& \- Update the "event loop time" (ev_now ()).
409\& 6. Calculate for how long to block. 962\& \- Calculate for how long to sleep or block, if at all
963\& (active idle watchers, EVRUN_NOWAIT or not having
964\& any active watchers at all will result in not sleeping).
965\& \- Sleep if the I/O and timer collect interval say so.
966\& \- Increment loop iteration counter.
410\& 7. Block the process, waiting for events. 967\& \- Block the process, waiting for any events.
968\& \- Queue all outstanding I/O (fd) events.
411\& 8. Update the "event loop time" and do time jump handling. 969\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
412\& 9. Queue all outstanding timers. 970\& \- Queue all expired timers.
413\& 10. Queue all outstanding periodics. 971\& \- Queue all expired periodics.
414\& 11. If no events are pending now, queue all idle watchers. 972\& \- Queue all idle watchers with priority higher than that of pending events.
415\& 12. Queue all check watchers. 973\& \- Queue all check watchers.
416\& 13. Call all queued watchers in reverse order (i.e. check watchers first). 974\& \- Call all queued watchers in reverse order (i.e. check watchers first).
417\& 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 975\& Signals and child watchers are implemented as I/O watchers, and will
418\& was used, return, otherwise continue with step #1. 976\& be handled here by queueing them when their watcher gets executed.
977\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
978\& were used, or there are no active watchers, goto FINISH, otherwise
979\& continue with step LOOP.
980\& FINISH:
981\& \- Reset the ev_break status iff it was EVBREAK_ONE.
982\& \- Decrement the loop depth.
983\& \- Return.
419.Ve 984.Ve
985.Sp
986Example: Queue some jobs and then loop until no events are outstanding
987anymore.
988.Sp
989.Vb 4
990\& ... queue jobs here, make sure they register event watchers as long
991\& ... as they still have work to do (even an idle watcher will do..)
992\& ev_run (my_loop, 0);
993\& ... jobs done or somebody called break. yeah!
994.Ve
420.IP "ev_unloop (loop, how)" 4 995.IP "ev_break (loop, how)" 4
421.IX Item "ev_unloop (loop, how)" 996.IX Item "ev_break (loop, how)"
422Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 997Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
423has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 998has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
424\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 999\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
425\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 1000\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1001.Sp
1002This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1003.Sp
1004It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1005which case it will have no effect.
426.IP "ev_ref (loop)" 4 1006.IP "ev_ref (loop)" 4
427.IX Item "ev_ref (loop)" 1007.IX Item "ev_ref (loop)"
428.PD 0 1008.PD 0
429.IP "ev_unref (loop)" 4 1009.IP "ev_unref (loop)" 4
430.IX Item "ev_unref (loop)" 1010.IX Item "ev_unref (loop)"
431.PD 1011.PD
432Ref/unref can be used to add or remove a reference count on the event 1012Ref/unref can be used to add or remove a reference count on the event
433loop: Every watcher keeps one reference, and as long as the reference 1013loop: Every watcher keeps one reference, and as long as the reference
434count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 1014count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
435a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1015.Sp
436returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1016This is useful when you have a watcher that you never intend to
1017unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1018returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1019before stopping it.
1020.Sp
437example, libev itself uses this for its internal signal pipe: It is not 1021As an example, libev itself uses this for its internal signal pipe: It
438visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 1022is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
439no event watchers registered by it are active. It is also an excellent 1023exiting if no event watchers registered by it are active. It is also an
440way to do this for generic recurring timers or from within third-party 1024excellent way to do this for generic recurring timers or from within
441libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1025third-party libraries. Just remember to \fIunref after start\fR and \fIref
1026before stop\fR (but only if the watcher wasn't active before, or was active
1027before, respectively. Note also that libev might stop watchers itself
1028(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1029in the callback).
1030.Sp
1031Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
1032running when nothing else is active.
1033.Sp
1034.Vb 4
1035\& ev_signal exitsig;
1036\& ev_signal_init (&exitsig, sig_cb, SIGINT);
1037\& ev_signal_start (loop, &exitsig);
1038\& ev_unref (loop);
1039.Ve
1040.Sp
1041Example: For some weird reason, unregister the above signal handler again.
1042.Sp
1043.Vb 2
1044\& ev_ref (loop);
1045\& ev_signal_stop (loop, &exitsig);
1046.Ve
1047.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1048.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1049.PD 0
1050.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1051.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1052.PD
1053These advanced functions influence the time that libev will spend waiting
1054for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1055will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1056latency.
1057.Sp
1058Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1059allows libev to delay invocation of I/O and timer/periodic callbacks
1060to increase efficiency of loop iterations (or to increase power-saving
1061opportunities).
1062.Sp
1063The idea is that sometimes your program runs just fast enough to handle
1064one (or very few) event(s) per loop iteration. While this makes the
1065program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1066events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1067overhead for the actual polling but can deliver many events at once.
1068.Sp
1069By setting a higher \fIio collect interval\fR you allow libev to spend more
1070time collecting I/O events, so you can handle more events per iteration,
1071at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1072\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
1073introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1074sleep time ensures that libev will not poll for I/O events more often then
1075once per this interval, on average.
1076.Sp
1077Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1078to spend more time collecting timeouts, at the expense of increased
1079latency/jitter/inexactness (the watcher callback will be called
1080later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1081value will not introduce any overhead in libev.
1082.Sp
1083Many (busy) programs can usually benefit by setting the I/O collect
1084interval to a value near \f(CW0.1\fR or so, which is often enough for
1085interactive servers (of course not for games), likewise for timeouts. It
1086usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1087as this approaches the timing granularity of most systems. Note that if
1088you do transactions with the outside world and you can't increase the
1089parallelity, then this setting will limit your transaction rate (if you
1090need to poll once per transaction and the I/O collect interval is 0.01,
1091then you can't do more than 100 transactions per second).
1092.Sp
1093Setting the \fItimeout collect interval\fR can improve the opportunity for
1094saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1095are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1096times the process sleeps and wakes up again. Another useful technique to
1097reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1098they fire on, say, one-second boundaries only.
1099.Sp
1100Example: we only need 0.1s timeout granularity, and we wish not to poll
1101more often than 100 times per second:
1102.Sp
1103.Vb 2
1104\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1105\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1106.Ve
1107.IP "ev_invoke_pending (loop)" 4
1108.IX Item "ev_invoke_pending (loop)"
1109This call will simply invoke all pending watchers while resetting their
1110pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1111but when overriding the invoke callback this call comes handy. This
1112function can be invoked from a watcher \- this can be useful for example
1113when you want to do some lengthy calculation and want to pass further
1114event handling to another thread (you still have to make sure only one
1115thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1116.IP "int ev_pending_count (loop)" 4
1117.IX Item "int ev_pending_count (loop)"
1118Returns the number of pending watchers \- zero indicates that no watchers
1119are pending.
1120.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1121.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1122This overrides the invoke pending functionality of the loop: Instead of
1123invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1124this callback instead. This is useful, for example, when you want to
1125invoke the actual watchers inside another context (another thread etc.).
1126.Sp
1127If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1128callback.
1129.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
1130.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
1131Sometimes you want to share the same loop between multiple threads. This
1132can be done relatively simply by putting mutex_lock/unlock calls around
1133each call to a libev function.
1134.Sp
1135However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1136to wait for it to return. One way around this is to wake up the event
1137loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`av_async_send\*(C'\fR, another way is to set these
1138\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1139.Sp
1140When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1141suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1142afterwards.
1143.Sp
1144Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1145\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1146.Sp
1147While event loop modifications are allowed between invocations of
1148\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1149modifications done will affect the event loop, i.e. adding watchers will
1150have no effect on the set of file descriptors being watched, or the time
1151waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1152to take note of any changes you made.
1153.Sp
1154In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1155invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1156.Sp
1157See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1158document.
1159.IP "ev_set_userdata (loop, void *data)" 4
1160.IX Item "ev_set_userdata (loop, void *data)"
1161.PD 0
1162.IP "void *ev_userdata (loop)" 4
1163.IX Item "void *ev_userdata (loop)"
1164.PD
1165Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1166\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1167\&\f(CW0\fR.
1168.Sp
1169These two functions can be used to associate arbitrary data with a loop,
1170and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1171\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1172any other purpose as well.
1173.IP "ev_verify (loop)" 4
1174.IX Item "ev_verify (loop)"
1175This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1176compiled in, which is the default for non-minimal builds. It tries to go
1177through all internal structures and checks them for validity. If anything
1178is found to be inconsistent, it will print an error message to standard
1179error and call \f(CW\*(C`abort ()\*(C'\fR.
1180.Sp
1181This can be used to catch bugs inside libev itself: under normal
1182circumstances, this function will never abort as of course libev keeps its
1183data structures consistent.
442.SH "ANATOMY OF A WATCHER" 1184.SH "ANATOMY OF A WATCHER"
443.IX Header "ANATOMY OF A WATCHER" 1185.IX Header "ANATOMY OF A WATCHER"
1186In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1187watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1188watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1189.PP
444A watcher is a structure that you create and register to record your 1190A watcher is an opaque structure that you allocate and register to record
445interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1191your interest in some event. To make a concrete example, imagine you want
446become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1192to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1193for that:
447.PP 1194.PP
448.Vb 5 1195.Vb 5
449\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1196\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
450\& { 1197\& {
451\& ev_io_stop (w); 1198\& ev_io_stop (w);
452\& ev_unloop (loop, EVUNLOOP_ALL); 1199\& ev_break (loop, EVBREAK_ALL);
453\& } 1200\& }
454.Ve 1201\&
455.PP
456.Vb 6
457\& struct ev_loop *loop = ev_default_loop (0); 1202\& struct ev_loop *loop = ev_default_loop (0);
1203\&
458\& struct ev_io stdin_watcher; 1204\& ev_io stdin_watcher;
1205\&
459\& ev_init (&stdin_watcher, my_cb); 1206\& ev_init (&stdin_watcher, my_cb);
460\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1207\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
461\& ev_io_start (loop, &stdin_watcher); 1208\& ev_io_start (loop, &stdin_watcher);
1209\&
462\& ev_loop (loop, 0); 1210\& ev_run (loop, 0);
463.Ve 1211.Ve
464.PP 1212.PP
465As you can see, you are responsible for allocating the memory for your 1213As you can see, you are responsible for allocating the memory for your
466watcher structures (and it is usually a bad idea to do this on the stack, 1214watcher structures (and it is \fIusually\fR a bad idea to do this on the
467although this can sometimes be quite valid). 1215stack).
468.PP 1216.PP
1217Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1218or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1219.PP
469Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1220Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
470(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1221*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
471callback gets invoked each time the event occurs (or, in the case of io 1222invoked each time the event occurs (or, in the case of I/O watchers, each
472watchers, each time the event loop detects that the file descriptor given 1223time the event loop detects that the file descriptor given is readable
473is readable and/or writable). 1224and/or writable).
474.PP 1225.PP
475Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1226Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
476with arguments specific to this watcher type. There is also a macro 1227macro to configure it, with arguments specific to the watcher type. There
477to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1228is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
478(watcher *, callback, ...)\*(C'\fR.
479.PP 1229.PP
480To make the watcher actually watch out for events, you have to start it 1230To make the watcher actually watch out for events, you have to start it
481with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1231with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
482*)\*(C'\fR), and you can stop watching for events at any time by calling the 1232*)\*(C'\fR), and you can stop watching for events at any time by calling the
483corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1233corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
484.PP 1234.PP
485As long as your watcher is active (has been started but not stopped) you 1235As long as your watcher is active (has been started but not stopped) you
486must not touch the values stored in it. Most specifically you must never 1236must not touch the values stored in it. Most specifically you must never
487reinitialise it or call its set method. 1237reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
488.PP
489You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
490(watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
491callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
492(watcher *)\*(C'\fR macro.
493.PP 1238.PP
494Each and every callback receives the event loop pointer as first, the 1239Each and every callback receives the event loop pointer as first, the
495registered watcher structure as second, and a bitset of received events as 1240registered watcher structure as second, and a bitset of received events as
496third argument. 1241third argument.
497.PP 1242.PP
… …
506.el .IP "\f(CWEV_WRITE\fR" 4 1251.el .IP "\f(CWEV_WRITE\fR" 4
507.IX Item "EV_WRITE" 1252.IX Item "EV_WRITE"
508.PD 1253.PD
509The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1254The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
510writable. 1255writable.
511.ie n .IP """EV_TIMEOUT""" 4 1256.ie n .IP """EV_TIMER""" 4
512.el .IP "\f(CWEV_TIMEOUT\fR" 4 1257.el .IP "\f(CWEV_TIMER\fR" 4
513.IX Item "EV_TIMEOUT" 1258.IX Item "EV_TIMER"
514The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1259The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
515.ie n .IP """EV_PERIODIC""" 4 1260.ie n .IP """EV_PERIODIC""" 4
516.el .IP "\f(CWEV_PERIODIC\fR" 4 1261.el .IP "\f(CWEV_PERIODIC\fR" 4
517.IX Item "EV_PERIODIC" 1262.IX Item "EV_PERIODIC"
518The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1263The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
522The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 1267The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
523.ie n .IP """EV_CHILD""" 4 1268.ie n .IP """EV_CHILD""" 4
524.el .IP "\f(CWEV_CHILD\fR" 4 1269.el .IP "\f(CWEV_CHILD\fR" 4
525.IX Item "EV_CHILD" 1270.IX Item "EV_CHILD"
526The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 1271The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1272.ie n .IP """EV_STAT""" 4
1273.el .IP "\f(CWEV_STAT\fR" 4
1274.IX Item "EV_STAT"
1275The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
527.ie n .IP """EV_IDLE""" 4 1276.ie n .IP """EV_IDLE""" 4
528.el .IP "\f(CWEV_IDLE\fR" 4 1277.el .IP "\f(CWEV_IDLE\fR" 4
529.IX Item "EV_IDLE" 1278.IX Item "EV_IDLE"
530The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 1279The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
531.ie n .IP """EV_PREPARE""" 4 1280.ie n .IP """EV_PREPARE""" 4
… …
534.PD 0 1283.PD 0
535.ie n .IP """EV_CHECK""" 4 1284.ie n .IP """EV_CHECK""" 4
536.el .IP "\f(CWEV_CHECK\fR" 4 1285.el .IP "\f(CWEV_CHECK\fR" 4
537.IX Item "EV_CHECK" 1286.IX Item "EV_CHECK"
538.PD 1287.PD
539All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1288All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts
540to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1289to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
541\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1290\&\f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it invokes any callbacks for any
542received events. Callbacks of both watcher types can start and stop as 1291received events. Callbacks of both watcher types can start and stop as
543many watchers as they want, and all of them will be taken into account 1292many watchers as they want, and all of them will be taken into account
544(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1293(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
545\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1294\&\f(CW\*(C`ev_run\*(C'\fR from blocking).
1295.ie n .IP """EV_EMBED""" 4
1296.el .IP "\f(CWEV_EMBED\fR" 4
1297.IX Item "EV_EMBED"
1298The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1299.ie n .IP """EV_FORK""" 4
1300.el .IP "\f(CWEV_FORK\fR" 4
1301.IX Item "EV_FORK"
1302The event loop has been resumed in the child process after fork (see
1303\&\f(CW\*(C`ev_fork\*(C'\fR).
1304.ie n .IP """EV_CLEANUP""" 4
1305.el .IP "\f(CWEV_CLEANUP\fR" 4
1306.IX Item "EV_CLEANUP"
1307The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1308.ie n .IP """EV_ASYNC""" 4
1309.el .IP "\f(CWEV_ASYNC\fR" 4
1310.IX Item "EV_ASYNC"
1311The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1312.ie n .IP """EV_CUSTOM""" 4
1313.el .IP "\f(CWEV_CUSTOM\fR" 4
1314.IX Item "EV_CUSTOM"
1315Not ever sent (or otherwise used) by libev itself, but can be freely used
1316by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
546.ie n .IP """EV_ERROR""" 4 1317.ie n .IP """EV_ERROR""" 4
547.el .IP "\f(CWEV_ERROR\fR" 4 1318.el .IP "\f(CWEV_ERROR\fR" 4
548.IX Item "EV_ERROR" 1319.IX Item "EV_ERROR"
549An unspecified error has occured, the watcher has been stopped. This might 1320An unspecified error has occurred, the watcher has been stopped. This might
550happen because the watcher could not be properly started because libev 1321happen because the watcher could not be properly started because libev
551ran out of memory, a file descriptor was found to be closed or any other 1322ran out of memory, a file descriptor was found to be closed or any other
1323problem. Libev considers these application bugs.
1324.Sp
552problem. You best act on it by reporting the problem and somehow coping 1325You best act on it by reporting the problem and somehow coping with the
553with the watcher being stopped. 1326watcher being stopped. Note that well-written programs should not receive
1327an error ever, so when your watcher receives it, this usually indicates a
1328bug in your program.
554.Sp 1329.Sp
555Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1330Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
556for example it might indicate that a fd is readable or writable, and if 1331example it might indicate that a fd is readable or writable, and if your
557your callbacks is well-written it can just attempt the operation and cope 1332callbacks is well-written it can just attempt the operation and cope with
558with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1333the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
559programs, though, so beware. 1334programs, though, as the fd could already be closed and reused for another
560.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1335thing, so beware.
561.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1336.SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
562Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1337.IX Subsection "GENERIC WATCHER FUNCTIONS"
563and read at any time, libev will completely ignore it. This can be used 1338.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
564to associate arbitrary data with your watcher. If you need more data and 1339.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
565don't want to allocate memory and store a pointer to it in that data 1340.IX Item "ev_init (ev_TYPE *watcher, callback)"
566member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1341This macro initialises the generic portion of a watcher. The contents
567data: 1342of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
568.PP 1343the generic parts of the watcher are initialised, you \fIneed\fR to call
1344the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1345type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1346which rolls both calls into one.
1347.Sp
1348You can reinitialise a watcher at any time as long as it has been stopped
1349(or never started) and there are no pending events outstanding.
1350.Sp
1351The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1352int revents)\*(C'\fR.
1353.Sp
1354Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1355.Sp
569.Vb 7 1356.Vb 3
570\& struct my_io 1357\& ev_io w;
1358\& ev_init (&w, my_cb);
1359\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1360.Ve
1361.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1362.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1363.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1364This macro initialises the type-specific parts of a watcher. You need to
1365call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1366call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1367macro on a watcher that is active (it can be pending, however, which is a
1368difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1369.Sp
1370Although some watcher types do not have type-specific arguments
1371(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1372.Sp
1373See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1374.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1375.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1376.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1377This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1378calls into a single call. This is the most convenient method to initialise
1379a watcher. The same limitations apply, of course.
1380.Sp
1381Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1382.Sp
1383.Vb 1
1384\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1385.Ve
1386.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1387.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1388.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1389Starts (activates) the given watcher. Only active watchers will receive
1390events. If the watcher is already active nothing will happen.
1391.Sp
1392Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1393whole section.
1394.Sp
1395.Vb 1
1396\& ev_io_start (EV_DEFAULT_UC, &w);
1397.Ve
1398.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1399.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1400.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1401Stops the given watcher if active, and clears the pending status (whether
1402the watcher was active or not).
1403.Sp
1404It is possible that stopped watchers are pending \- for example,
1405non-repeating timers are being stopped when they become pending \- but
1406calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1407pending. If you want to free or reuse the memory used by the watcher it is
1408therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1409.IP "bool ev_is_active (ev_TYPE *watcher)" 4
1410.IX Item "bool ev_is_active (ev_TYPE *watcher)"
1411Returns a true value iff the watcher is active (i.e. it has been started
1412and not yet been stopped). As long as a watcher is active you must not modify
1413it.
1414.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1415.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1416Returns a true value iff the watcher is pending, (i.e. it has outstanding
1417events but its callback has not yet been invoked). As long as a watcher
1418is pending (but not active) you must not call an init function on it (but
1419\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1420make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1421it).
1422.IP "callback ev_cb (ev_TYPE *watcher)" 4
1423.IX Item "callback ev_cb (ev_TYPE *watcher)"
1424Returns the callback currently set on the watcher.
1425.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1426.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1427Change the callback. You can change the callback at virtually any time
1428(modulo threads).
1429.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1430.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1431.PD 0
1432.IP "int ev_priority (ev_TYPE *watcher)" 4
1433.IX Item "int ev_priority (ev_TYPE *watcher)"
1434.PD
1435Set and query the priority of the watcher. The priority is a small
1436integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1437(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1438before watchers with lower priority, but priority will not keep watchers
1439from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1440.Sp
1441If you need to suppress invocation when higher priority events are pending
1442you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1443.Sp
1444You \fImust not\fR change the priority of a watcher as long as it is active or
1445pending.
1446.Sp
1447Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1448fine, as long as you do not mind that the priority value you query might
1449or might not have been clamped to the valid range.
1450.Sp
1451The default priority used by watchers when no priority has been set is
1452always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1453.Sp
1454See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1455priorities.
1456.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1457.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1458Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1459\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1460can deal with that fact, as both are simply passed through to the
1461callback.
1462.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1463.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1464If the watcher is pending, this function clears its pending status and
1465returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1466watcher isn't pending it does nothing and returns \f(CW0\fR.
1467.Sp
1468Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1469callback to be invoked, which can be accomplished with this function.
1470.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1471.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1472Feeds the given event set into the event loop, as if the specified event
1473had happened for the specified watcher (which must be a pointer to an
1474initialised but not necessarily started event watcher). Obviously you must
1475not free the watcher as long as it has pending events.
1476.Sp
1477Stopping the watcher, letting libev invoke it, or calling
1478\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1479not started in the first place.
1480.Sp
1481See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1482functions that do not need a watcher.
1483.PP
1484See 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
1485\&\s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0\*(R" idioms.
1486.SS "\s-1WATCHER\s0 \s-1STATES\s0"
1487.IX Subsection "WATCHER STATES"
1488There are various watcher states mentioned throughout this manual \-
1489active, pending and so on. In this section these states and the rules to
1490transition between them will be described in more detail \- and while these
1491rules might look complicated, they usually do \*(L"the right thing\*(R".
1492.IP "initialiased" 4
1493.IX Item "initialiased"
1494Before a watcher can be registered with the event looop it has to be
1495initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1496\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1497.Sp
1498In this state it is simply some block of memory that is suitable for
1499use in an event loop. It can be moved around, freed, reused etc. at
1500will \- as long as you either keep the memory contents intact, or call
1501\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1502.IP "started/running/active" 4
1503.IX Item "started/running/active"
1504Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1505property of the event loop, and is actively waiting for events. While in
1506this state it cannot be accessed (except in a few documented ways), moved,
1507freed or anything else \- the only legal thing is to keep a pointer to it,
1508and call libev functions on it that are documented to work on active watchers.
1509.IP "pending" 4
1510.IX Item "pending"
1511If a watcher is active and libev determines that an event it is interested
1512in has occurred (such as a timer expiring), it will become pending. It will
1513stay in this pending state until either it is stopped or its callback is
1514about to be invoked, so it is not normally pending inside the watcher
1515callback.
1516.Sp
1517The watcher might or might not be active while it is pending (for example,
1518an expired non-repeating timer can be pending but no longer active). If it
1519is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1520but it is still property of the event loop at this time, so cannot be
1521moved, freed or reused. And if it is active the rules described in the
1522previous item still apply.
1523.Sp
1524It is also possible to feed an event on a watcher that is not active (e.g.
1525via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1526active.
1527.IP "stopped" 4
1528.IX Item "stopped"
1529A watcher can be stopped implicitly by libev (in which case it might still
1530be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1531latter will clear any pending state the watcher might be in, regardless
1532of whether it was active or not, so stopping a watcher explicitly before
1533freeing it is often a good idea.
1534.Sp
1535While stopped (and not pending) the watcher is essentially in the
1536initialised state, that is, it can be reused, moved, modified in any way
1537you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1538it again).
1539.SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1540.IX Subsection "WATCHER PRIORITY MODELS"
1541Many event loops support \fIwatcher priorities\fR, which are usually small
1542integers that influence the ordering of event callback invocation
1543between watchers in some way, all else being equal.
1544.PP
1545In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1546description for the more technical details such as the actual priority
1547range.
1548.PP
1549There are two common ways how these these priorities are being interpreted
1550by event loops:
1551.PP
1552In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1553of lower priority watchers, which means as long as higher priority
1554watchers receive events, lower priority watchers are not being invoked.
1555.PP
1556The less common only-for-ordering model uses priorities solely to order
1557callback invocation within a single event loop iteration: Higher priority
1558watchers are invoked before lower priority ones, but they all get invoked
1559before polling for new events.
1560.PP
1561Libev uses the second (only-for-ordering) model for all its watchers
1562except for idle watchers (which use the lock-out model).
1563.PP
1564The rationale behind this is that implementing the lock-out model for
1565watchers is not well supported by most kernel interfaces, and most event
1566libraries will just poll for the same events again and again as long as
1567their callbacks have not been executed, which is very inefficient in the
1568common case of one high-priority watcher locking out a mass of lower
1569priority ones.
1570.PP
1571Static (ordering) priorities are most useful when you have two or more
1572watchers handling the same resource: a typical usage example is having an
1573\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1574timeouts. Under load, data might be received while the program handles
1575other jobs, but since timers normally get invoked first, the timeout
1576handler will be executed before checking for data. In that case, giving
1577the timer a lower priority than the I/O watcher ensures that I/O will be
1578handled first even under adverse conditions (which is usually, but not
1579always, what you want).
1580.PP
1581Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1582will only be executed when no same or higher priority watchers have
1583received events, they can be used to implement the \*(L"lock-out\*(R" model when
1584required.
1585.PP
1586For example, to emulate how many other event libraries handle priorities,
1587you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1588the normal watcher callback, you just start the idle watcher. The real
1589processing is done in the idle watcher callback. This causes libev to
1590continuously poll and process kernel event data for the watcher, but when
1591the lock-out case is known to be rare (which in turn is rare :), this is
1592workable.
1593.PP
1594Usually, however, the lock-out model implemented that way will perform
1595miserably under the type of load it was designed to handle. In that case,
1596it might be preferable to stop the real watcher before starting the
1597idle watcher, so the kernel will not have to process the event in case
1598the actual processing will be delayed for considerable time.
1599.PP
1600Here is an example of an I/O watcher that should run at a strictly lower
1601priority than the default, and which should only process data when no
1602other events are pending:
1603.PP
1604.Vb 2
1605\& ev_idle idle; // actual processing watcher
1606\& ev_io io; // actual event watcher
1607\&
1608\& static void
1609\& io_cb (EV_P_ ev_io *w, int revents)
571\& { 1610\& {
572\& struct ev_io io; 1611\& // stop the I/O watcher, we received the event, but
573\& int otherfd; 1612\& // are not yet ready to handle it.
574\& void *somedata; 1613\& ev_io_stop (EV_A_ w);
575\& struct whatever *mostinteresting; 1614\&
1615\& // start the idle watcher to handle the actual event.
1616\& // it will not be executed as long as other watchers
1617\& // with the default priority are receiving events.
1618\& ev_idle_start (EV_A_ &idle);
576\& } 1619\& }
577.Ve 1620\&
578.PP 1621\& static void
579And since your callback will be called with a pointer to the watcher, you 1622\& idle_cb (EV_P_ ev_idle *w, int revents)
580can cast it back to your own type:
581.PP
582.Vb 5
583\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
584\& { 1623\& {
585\& struct my_io *w = (struct my_io *)w_; 1624\& // actual processing
586\& ... 1625\& read (STDIN_FILENO, ...);
1626\&
1627\& // have to start the I/O watcher again, as
1628\& // we have handled the event
1629\& ev_io_start (EV_P_ &io);
587\& } 1630\& }
1631\&
1632\& // initialisation
1633\& ev_idle_init (&idle, idle_cb);
1634\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1635\& ev_io_start (EV_DEFAULT_ &io);
588.Ve 1636.Ve
589.PP 1637.PP
590More interesting and less C\-conformant ways of catsing your callback type 1638In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
591have been omitted.... 1639low-priority connections can not be locked out forever under load. This
1640enables your program to keep a lower latency for important connections
1641during short periods of high load, while not completely locking out less
1642important ones.
592.SH "WATCHER TYPES" 1643.SH "WATCHER TYPES"
593.IX Header "WATCHER TYPES" 1644.IX Header "WATCHER TYPES"
594This section describes each watcher in detail, but will not repeat 1645This section describes each watcher in detail, but will not repeat
595information given in the last section. 1646information given in the last section. Any initialisation/set macros,
1647functions and members specific to the watcher type are explained.
1648.PP
1649Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1650while the watcher is active, you can look at the member and expect some
1651sensible content, but you must not modify it (you can modify it while the
1652watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1653means you can expect it to have some sensible content while the watcher
1654is active, but you can also modify it. Modifying it may not do something
1655sensible or take immediate effect (or do anything at all), but libev will
1656not crash or malfunction in any way.
596.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1657.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
597.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1658.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
598.IX Subsection "ev_io - is this file descriptor readable or writable" 1659.IX Subsection "ev_io - is this file descriptor readable or writable?"
599I/O watchers check whether a file descriptor is readable or writable 1660I/O watchers check whether a file descriptor is readable or writable
600in each iteration of the event loop (This behaviour is called 1661in each iteration of the event loop, or, more precisely, when reading
601level-triggering because you keep receiving events as long as the 1662would not block the process and writing would at least be able to write
602condition persists. Remember you can stop the watcher if you don't want to 1663some data. This behaviour is called level-triggering because you keep
603act on the event and neither want to receive future events). 1664receiving events as long as the condition persists. Remember you can stop
1665the watcher if you don't want to act on the event and neither want to
1666receive future events.
604.PP 1667.PP
605In general you can register as many read and/or write event watchers per 1668In general you can register as many read and/or write event watchers per
606fd as you want (as long as you don't confuse yourself). Setting all file 1669fd as you want (as long as you don't confuse yourself). Setting all file
607descriptors to non-blocking mode is also usually a good idea (but not 1670descriptors to non-blocking mode is also usually a good idea (but not
608required if you know what you are doing). 1671required if you know what you are doing).
609.PP 1672.PP
610You have to be careful with dup'ed file descriptors, though. Some backends 1673Another thing you have to watch out for is that it is quite easy to
611(the linux epoll backend is a notable example) cannot handle dup'ed file 1674receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
612descriptors correctly if you register interest in two or more fds pointing 1675be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
613to the same underlying file/socket etc. description (that is, they share 1676because there is no data. It is very easy to get into this situation even
614the same underlying \*(L"file open\*(R"). 1677with a relatively standard program structure. Thus it is best to always
1678use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1679preferable to a program hanging until some data arrives.
615.PP 1680.PP
616If you must do this, then force the use of a known-to-be-good backend 1681If you cannot run the fd in non-blocking mode (for example you should
617(at the time of this writing, this includes only \s-1EVMETHOD_SELECT\s0 and 1682not play around with an Xlib connection), then you have to separately
618\&\s-1EVMETHOD_POLL\s0). 1683re-test whether a file descriptor is really ready with a known-to-be good
1684interface such as poll (fortunately in the case of Xlib, it already does
1685this on its own, so its quite safe to use). Some people additionally
1686use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1687indefinitely.
1688.PP
1689But really, best use non-blocking mode.
1690.PP
1691\fIThe special problem of disappearing file descriptors\fR
1692.IX Subsection "The special problem of disappearing file descriptors"
1693.PP
1694Some backends (e.g. kqueue, epoll) need to be told about closing a file
1695descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1696such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1697descriptor, but when it goes away, the operating system will silently drop
1698this interest. If another file descriptor with the same number then is
1699registered with libev, there is no efficient way to see that this is, in
1700fact, a different file descriptor.
1701.PP
1702To avoid having to explicitly tell libev about such cases, libev follows
1703the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1704will assume that this is potentially a new file descriptor, otherwise
1705it is assumed that the file descriptor stays the same. That means that
1706you \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
1707descriptor even if the file descriptor number itself did not change.
1708.PP
1709This is how one would do it normally anyway, the important point is that
1710the libev application should not optimise around libev but should leave
1711optimisations to libev.
1712.PP
1713\fIThe special problem of dup'ed file descriptors\fR
1714.IX Subsection "The special problem of dup'ed file descriptors"
1715.PP
1716Some backends (e.g. epoll), cannot register events for file descriptors,
1717but only events for the underlying file descriptions. That means when you
1718have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1719events for them, only one file descriptor might actually receive events.
1720.PP
1721There is no workaround possible except not registering events
1722for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1723\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1724.PP
1725\fIThe special problem of files\fR
1726.IX Subsection "The special problem of files"
1727.PP
1728Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1729representing files, and expect it to become ready when their program
1730doesn't block on disk accesses (which can take a long time on their own).
1731.PP
1732However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1733notification as soon as the kernel knows whether and how much data is
1734there, and in the case of open files, that's always the case, so you
1735always get a readiness notification instantly, and your read (or possibly
1736write) will still block on the disk I/O.
1737.PP
1738Another way to view it is that in the case of sockets, pipes, character
1739devices and so on, there is another party (the sender) that delivers data
1740on its own, but in the case of files, there is no such thing: the disk
1741will not send data on its own, simply because it doesn't know what you
1742wish to read \- you would first have to request some data.
1743.PP
1744Since files are typically not-so-well supported by advanced notification
1745mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1746to files, even though you should not use it. The reason for this is
1747convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT\s0, which is
1748usually a tty, often a pipe, but also sometimes files or special devices
1749(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1750\&\fI/dev/urandom\fR), and even though the file might better be served with
1751asynchronous I/O instead of with non-blocking I/O, it is still useful when
1752it \*(L"just works\*(R" instead of freezing.
1753.PP
1754So avoid file descriptors pointing to files when you know it (e.g. use
1755libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT\s0, or
1756when you rarely read from a file instead of from a socket, and want to
1757reuse the same code path.
1758.PP
1759\fIThe special problem of fork\fR
1760.IX Subsection "The special problem of fork"
1761.PP
1762Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1763useless behaviour. Libev fully supports fork, but needs to be told about
1764it in the child if you want to continue to use it in the child.
1765.PP
1766To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1767()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1768\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1769.PP
1770\fIThe special problem of \s-1SIGPIPE\s0\fR
1771.IX Subsection "The special problem of SIGPIPE"
1772.PP
1773While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1774when writing to a pipe whose other end has been closed, your program gets
1775sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1776this is sensible behaviour, for daemons, this is usually undesirable.
1777.PP
1778So when you encounter spurious, unexplained daemon exits, make sure you
1779ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1780somewhere, as that would have given you a big clue).
1781.PP
1782\fIThe special problem of \fIaccept()\fIing when you can't\fR
1783.IX Subsection "The special problem of accept()ing when you can't"
1784.PP
1785Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1786found in post\-2004 Linux) have the peculiar behaviour of not removing a
1787connection from the pending queue in all error cases.
1788.PP
1789For example, larger servers often run out of file descriptors (because
1790of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1791rejecting the connection, leading to libev signalling readiness on
1792the next iteration again (the connection still exists after all), and
1793typically causing the program to loop at 100% \s-1CPU\s0 usage.
1794.PP
1795Unfortunately, the set of errors that cause this issue differs between
1796operating systems, there is usually little the app can do to remedy the
1797situation, and no known thread-safe method of removing the connection to
1798cope with overload is known (to me).
1799.PP
1800One of the easiest ways to handle this situation is to just ignore it
1801\&\- when the program encounters an overload, it will just loop until the
1802situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1803event-based way to handle this situation, so it's the best one can do.
1804.PP
1805A better way to handle the situation is to log any errors other than
1806\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1807messages, and continue as usual, which at least gives the user an idea of
1808what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1809the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1810usage.
1811.PP
1812If your program is single-threaded, then you could also keep a dummy file
1813descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1814when 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,
1815close that fd, and create a new dummy fd. This will gracefully refuse
1816clients under typical overload conditions.
1817.PP
1818The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1819is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1820opportunity for a DoS attack.
1821.PP
1822\fIWatcher-Specific Functions\fR
1823.IX Subsection "Watcher-Specific Functions"
619.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1824.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
620.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1825.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
621.PD 0 1826.PD 0
622.IP "ev_io_set (ev_io *, int fd, int events)" 4 1827.IP "ev_io_set (ev_io *, int fd, int events)" 4
623.IX Item "ev_io_set (ev_io *, int fd, int events)" 1828.IX Item "ev_io_set (ev_io *, int fd, int events)"
624.PD 1829.PD
625Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1830Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
626events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_READ | 1831receive 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
627EV_WRITE\*(C'\fR to receive the given events. 1832\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1833.IP "int fd [read\-only]" 4
1834.IX Item "int fd [read-only]"
1835The file descriptor being watched.
1836.IP "int events [read\-only]" 4
1837.IX Item "int events [read-only]"
1838The events being watched.
1839.PP
1840\fIExamples\fR
1841.IX Subsection "Examples"
1842.PP
1843Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1844readable, but only once. Since it is likely line-buffered, you could
1845attempt to read a whole line in the callback.
1846.PP
1847.Vb 6
1848\& static void
1849\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1850\& {
1851\& ev_io_stop (loop, w);
1852\& .. read from stdin here (or from w\->fd) and handle any I/O errors
1853\& }
1854\&
1855\& ...
1856\& struct ev_loop *loop = ev_default_init (0);
1857\& ev_io stdin_readable;
1858\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1859\& ev_io_start (loop, &stdin_readable);
1860\& ev_run (loop, 0);
1861.Ve
628.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1862.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
629.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1863.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
630.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1864.IX Subsection "ev_timer - relative and optionally repeating timeouts"
631Timer watchers are simple relative timers that generate an event after a 1865Timer watchers are simple relative timers that generate an event after a
632given time, and optionally repeating in regular intervals after that. 1866given time, and optionally repeating in regular intervals after that.
633.PP 1867.PP
634The timers are based on real time, that is, if you register an event that 1868The timers are based on real time, that is, if you register an event that
635times out after an hour and you reset your system clock to last years 1869times out after an hour and you reset your system clock to January last
636time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1870year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
637detecting time jumps is hard, and some inaccuracies are unavoidable (the 1871detecting time jumps is hard, and some inaccuracies are unavoidable (the
638monotonic clock option helps a lot here). 1872monotonic clock option helps a lot here).
1873.PP
1874The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1875passed (not \fIat\fR, so on systems with very low-resolution clocks this
1876might introduce a small delay). If multiple timers become ready during the
1877same loop iteration then the ones with earlier time-out values are invoked
1878before ones of the same priority with later time-out values (but this is
1879no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1880.PP
1881\fIBe smart about timeouts\fR
1882.IX Subsection "Be smart about timeouts"
1883.PP
1884Many real-world problems involve some kind of timeout, usually for error
1885recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1886you want to raise some error after a while.
1887.PP
1888What follows are some ways to handle this problem, from obvious and
1889inefficient to smart and efficient.
1890.PP
1891In the following, a 60 second activity timeout is assumed \- a timeout that
1892gets reset to 60 seconds each time there is activity (e.g. each time some
1893data or other life sign was received).
1894.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1895.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1896This is the most obvious, but not the most simple way: In the beginning,
1897start the watcher:
1898.Sp
1899.Vb 2
1900\& ev_timer_init (timer, callback, 60., 0.);
1901\& ev_timer_start (loop, timer);
1902.Ve
1903.Sp
1904Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1905and start it again:
1906.Sp
1907.Vb 3
1908\& ev_timer_stop (loop, timer);
1909\& ev_timer_set (timer, 60., 0.);
1910\& ev_timer_start (loop, timer);
1911.Ve
1912.Sp
1913This is relatively simple to implement, but means that each time there is
1914some activity, libev will first have to remove the timer from its internal
1915data structure and then add it again. Libev tries to be fast, but it's
1916still not a constant-time operation.
1917.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1918.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1919.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1920This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1921\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1922.Sp
1923To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1924of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1925successfully read or write some data. If you go into an idle state where
1926you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1927the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1928.Sp
1929That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1930\&\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
1931member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1932.Sp
1933At start:
1934.Sp
1935.Vb 3
1936\& ev_init (timer, callback);
1937\& timer\->repeat = 60.;
1938\& ev_timer_again (loop, timer);
1939.Ve
1940.Sp
1941Each time there is some activity:
1942.Sp
1943.Vb 1
1944\& ev_timer_again (loop, timer);
1945.Ve
1946.Sp
1947It is even possible to change the time-out on the fly, regardless of
1948whether the watcher is active or not:
1949.Sp
1950.Vb 2
1951\& timer\->repeat = 30.;
1952\& ev_timer_again (loop, timer);
1953.Ve
1954.Sp
1955This is slightly more efficient then stopping/starting the timer each time
1956you want to modify its timeout value, as libev does not have to completely
1957remove and re-insert the timer from/into its internal data structure.
1958.Sp
1959It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1960.IP "3. Let the timer time out, but then re-arm it as required." 4
1961.IX Item "3. Let the timer time out, but then re-arm it as required."
1962This method is more tricky, but usually most efficient: Most timeouts are
1963relatively long compared to the intervals between other activity \- in
1964our example, within 60 seconds, there are usually many I/O events with
1965associated activity resets.
1966.Sp
1967In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1968but remember the time of last activity, and check for a real timeout only
1969within the callback:
1970.Sp
1971.Vb 1
1972\& ev_tstamp last_activity; // time of last activity
1973\&
1974\& static void
1975\& callback (EV_P_ ev_timer *w, int revents)
1976\& {
1977\& ev_tstamp now = ev_now (EV_A);
1978\& ev_tstamp timeout = last_activity + 60.;
1979\&
1980\& // if last_activity + 60. is older than now, we did time out
1981\& if (timeout < now)
1982\& {
1983\& // timeout occurred, take action
1984\& }
1985\& else
1986\& {
1987\& // callback was invoked, but there was some activity, re\-arm
1988\& // the watcher to fire in last_activity + 60, which is
1989\& // guaranteed to be in the future, so "again" is positive:
1990\& w\->repeat = timeout \- now;
1991\& ev_timer_again (EV_A_ w);
1992\& }
1993\& }
1994.Ve
1995.Sp
1996To summarise the callback: first calculate the real timeout (defined
1997as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1998been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1999the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
2000re-schedule the timer to fire at that future time, to see if maybe we have
2001a timeout then.
2002.Sp
2003Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
2004\&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
2005.Sp
2006This scheme causes more callback invocations (about one every 60 seconds
2007minus half the average time between activity), but virtually no calls to
2008libev to change the timeout.
2009.Sp
2010To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
2011to the current time (meaning we just have some activity :), then call the
2012callback, which will \*(L"do the right thing\*(R" and start the timer:
2013.Sp
2014.Vb 3
2015\& ev_init (timer, callback);
2016\& last_activity = ev_now (loop);
2017\& callback (loop, timer, EV_TIMER);
2018.Ve
2019.Sp
2020And when there is some activity, simply store the current time in
2021\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2022.Sp
2023.Vb 1
2024\& last_activity = ev_now (loop);
2025.Ve
2026.Sp
2027This technique is slightly more complex, but in most cases where the
2028time-out is unlikely to be triggered, much more efficient.
2029.Sp
2030Changing the timeout is trivial as well (if it isn't hard-coded in the
2031callback :) \- just change the timeout and invoke the callback, which will
2032fix things for you.
2033.IP "4. Wee, just use a double-linked list for your timeouts." 4
2034.IX Item "4. Wee, just use a double-linked list for your timeouts."
2035If there is not one request, but many thousands (millions...), all
2036employing some kind of timeout with the same timeout value, then one can
2037do even better:
2038.Sp
2039When starting the timeout, calculate the timeout value and put the timeout
2040at the \fIend\fR of the list.
2041.Sp
2042Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2043the list is expected to fire (for example, using the technique #3).
2044.Sp
2045When there is some activity, remove the timer from the list, recalculate
2046the timeout, append it to the end of the list again, and make sure to
2047update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2048.Sp
2049This way, one can manage an unlimited number of timeouts in O(1) time for
2050starting, stopping and updating the timers, at the expense of a major
2051complication, and having to use a constant timeout. The constant timeout
2052ensures that the list stays sorted.
2053.PP
2054So which method the best?
2055.PP
2056Method #2 is a simple no-brain-required solution that is adequate in most
2057situations. Method #3 requires a bit more thinking, but handles many cases
2058better, and isn't very complicated either. In most case, choosing either
2059one is fine, with #3 being better in typical situations.
2060.PP
2061Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2062rather complicated, but extremely efficient, something that really pays
2063off after the first million or so of active timers, i.e. it's usually
2064overkill :)
2065.PP
2066\fIThe special problem of time updates\fR
2067.IX Subsection "The special problem of time updates"
2068.PP
2069Establishing the current time is a costly operation (it usually takes at
2070least two system calls): \s-1EV\s0 therefore updates its idea of the current
2071time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2072growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2073lots of events in one iteration.
639.PP 2074.PP
640The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2075The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
641time. This is usually the right thing as this timestamp refers to the time 2076time. This is usually the right thing as this timestamp refers to the time
642of the event triggering whatever timeout you are modifying/starting. If 2077of the event triggering whatever timeout you are modifying/starting. If
643you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2078you suspect event processing to be delayed and you \fIneed\fR to base the
644on the current time, use something like this to adjust for this: 2079timeout on the current time, use something like this to adjust for this:
645.PP 2080.PP
646.Vb 1 2081.Vb 1
647\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2082\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
648.Ve 2083.Ve
649.PP 2084.PP
650The callback is guarenteed to be invoked only when its timeout has passed, 2085If the event loop is suspended for a long time, you can also force an
651but if multiple timers become ready during the same loop iteration then 2086update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
652order of execution is undefined. 2087()\*(C'\fR.
2088.PP
2089\fIThe special problems of suspended animation\fR
2090.IX Subsection "The special problems of suspended animation"
2091.PP
2092When you leave the server world it is quite customary to hit machines that
2093can suspend/hibernate \- what happens to the clocks during such a suspend?
2094.PP
2095Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2096all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2097to run until the system is suspended, but they will not advance while the
2098system is suspended. That means, on resume, it will be as if the program
2099was frozen for a few seconds, but the suspend time will not be counted
2100towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2101clock advanced as expected, but if it is used as sole clocksource, then a
2102long suspend would be detected as a time jump by libev, and timers would
2103be adjusted accordingly.
2104.PP
2105I would not be surprised to see different behaviour in different between
2106operating systems, \s-1OS\s0 versions or even different hardware.
2107.PP
2108The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2109time jump in the monotonic clocks and the realtime clock. If the program
2110is suspended for a very long time, and monotonic clock sources are in use,
2111then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2112will be counted towards the timers. When no monotonic clock source is in
2113use, then libev will again assume a timejump and adjust accordingly.
2114.PP
2115It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2116and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2117deterministic behaviour in this case (you can do nothing against
2118\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2119.PP
2120\fIWatcher-Specific Functions and Data Members\fR
2121.IX Subsection "Watcher-Specific Functions and Data Members"
653.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2122.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
654.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2123.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
655.PD 0 2124.PD 0
656.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2125.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
657.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2126.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
658.PD 2127.PD
659Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2128Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
660\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2129is \f(CW0.\fR, then it will automatically be stopped once the timeout is
661timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2130reached. If it is positive, then the timer will automatically be
662later, again, and again, until stopped manually. 2131configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2132until stopped manually.
663.Sp 2133.Sp
664The timer itself will do a best-effort at avoiding drift, that is, if you 2134The timer itself will do a best-effort at avoiding drift, that is, if
665configure a timer to trigger every 10 seconds, then it will trigger at 2135you configure a timer to trigger every 10 seconds, then it will normally
666exactly 10 second intervals. If, however, your program cannot keep up with 2136trigger at exactly 10 second intervals. If, however, your program cannot
667the timer (because it takes longer than those 10 seconds to do stuff) the 2137keep up with the timer (because it takes longer than those 10 seconds to
668timer will not fire more than once per event loop iteration. 2138do stuff) the timer will not fire more than once per event loop iteration.
669.IP "ev_timer_again (loop)" 4 2139.IP "ev_timer_again (loop, ev_timer *)" 4
670.IX Item "ev_timer_again (loop)" 2140.IX Item "ev_timer_again (loop, ev_timer *)"
671This will act as if the timer timed out and restart it again if it is 2141This will act as if the timer timed out and restart it again if it is
672repeating. The exact semantics are: 2142repeating. The exact semantics are:
673.Sp 2143.Sp
2144If the timer is pending, its pending status is cleared.
2145.Sp
674If the timer is started but nonrepeating, stop it. 2146If the timer is started but non-repeating, stop it (as if it timed out).
675.Sp 2147.Sp
676If the timer is repeating, either start it if necessary (with the repeat 2148If the timer is repeating, either start it if necessary (with the
677value), or reset the running timer to the repeat value. 2149\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
678.Sp 2150.Sp
679This sounds a bit complicated, but here is a useful and typical 2151This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
680example: Imagine you have a tcp connection and you want a so-called idle 2152usage example.
681timeout, that is, you want to be called when there have been, say, 60 2153.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
682seconds of inactivity on the socket. The easiest way to do this is to 2154.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
683configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 2155Returns the remaining time until a timer fires. If the timer is active,
684time you successfully read or write some data. If you go into an idle 2156then this time is relative to the current event loop time, otherwise it's
685state where you do not expect data to travel on the socket, you can stop 2157the timeout value currently configured.
686the timer, and again will automatically restart it if need be. 2158.Sp
2159That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2160\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
2161will return \f(CW4\fR. When the timer expires and is restarted, it will return
2162roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2163too), and so on.
2164.IP "ev_tstamp repeat [read\-write]" 4
2165.IX Item "ev_tstamp repeat [read-write]"
2166The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2167or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2168which is also when any modifications are taken into account.
2169.PP
2170\fIExamples\fR
2171.IX Subsection "Examples"
2172.PP
2173Example: Create a timer that fires after 60 seconds.
2174.PP
2175.Vb 5
2176\& static void
2177\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2178\& {
2179\& .. one minute over, w is actually stopped right here
2180\& }
2181\&
2182\& ev_timer mytimer;
2183\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2184\& ev_timer_start (loop, &mytimer);
2185.Ve
2186.PP
2187Example: Create a timeout timer that times out after 10 seconds of
2188inactivity.
2189.PP
2190.Vb 5
2191\& static void
2192\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2193\& {
2194\& .. ten seconds without any activity
2195\& }
2196\&
2197\& ev_timer mytimer;
2198\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2199\& ev_timer_again (&mytimer); /* start timer */
2200\& ev_run (loop, 0);
2201\&
2202\& // and in some piece of code that gets executed on any "activity":
2203\& // reset the timeout to start ticking again at 10 seconds
2204\& ev_timer_again (&mytimer);
2205.Ve
687.ie n .Sh """ev_periodic"" \- to cron or not to cron" 2206.ie n .SS """ev_periodic"" \- to cron or not to cron?"
688.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 2207.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
689.IX Subsection "ev_periodic - to cron or not to cron" 2208.IX Subsection "ev_periodic - to cron or not to cron?"
690Periodic watchers are also timers of a kind, but they are very versatile 2209Periodic watchers are also timers of a kind, but they are very versatile
691(and unfortunately a bit complex). 2210(and unfortunately a bit complex).
692.PP 2211.PP
693Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2212Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
694but on wallclock time (absolute time). You can tell a periodic watcher 2213relative time, the physical time that passes) but on wall clock time
695to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2214(absolute time, the thing you can read on your calender or clock). The
696periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 2215difference is that wall clock time can run faster or slower than real
697+ 10.>) and then reset your system clock to the last year, then it will 2216time, and time jumps are not uncommon (e.g. when you adjust your
698take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2217wrist-watch).
699roughly 10 seconds later and of course not if you reset your system time
700again).
701.PP 2218.PP
702They can also be used to implement vastly more complex timers, such as 2219You can tell a periodic watcher to trigger after some specific point
703triggering an event on eahc midnight, local time. 2220in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2221seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2222not a delay) and then reset your system clock to January of the previous
2223year, then it will take a year or more to trigger the event (unlike an
2224\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2225it, as it uses a relative timeout).
704.PP 2226.PP
2227\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2228timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2229other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2230those cannot react to time jumps.
2231.PP
705As with timers, the callback is guarenteed to be invoked only when the 2232As with timers, the callback is guaranteed to be invoked only when the
706time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2233point in time where it is supposed to trigger has passed. If multiple
707during the same loop iteration then order of execution is undefined. 2234timers become ready during the same loop iteration then the ones with
2235earlier time-out values are invoked before ones with later time-out values
2236(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2237.PP
2238\fIWatcher-Specific Functions and Data Members\fR
2239.IX Subsection "Watcher-Specific Functions and Data Members"
708.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2240.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
709.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2241.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
710.PD 0 2242.PD 0
711.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2243.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
712.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2244.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
713.PD 2245.PD
714Lots of arguments, lets sort it out... There are basically three modes of 2246Lots of arguments, let's sort it out... There are basically three modes of
715operation, and we will explain them from simplest to complex: 2247operation, and we will explain them from simplest to most complex:
716.RS 4 2248.RS 4
717.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2249.IP "\(bu" 4
718.IX Item "absolute timer (interval = reschedule_cb = 0)" 2250absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2251.Sp
719In this configuration the watcher triggers an event at the wallclock time 2252In this configuration the watcher triggers an event after the wall clock
720\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2253time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
721that is, if it is to be run at January 1st 2011 then it will run when the 2254time jump occurs, that is, if it is to be run at January 1st 2011 then it
722system time reaches or surpasses this time. 2255will be stopped and invoked when the system clock reaches or surpasses
723.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2256this point in time.
724.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2257.IP "\(bu" 4
2258repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2259.Sp
725In this mode the watcher will always be scheduled to time out at the next 2260In this mode the watcher will always be scheduled to time out at the next
726\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2261\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
727of any time jumps. 2262negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2263argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
728.Sp 2264.Sp
729This can be used to create timers that do not drift with respect to system 2265This can be used to create timers that do not drift with respect to the
730time: 2266system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2267hour, on the hour (with respect to \s-1UTC\s0):
731.Sp 2268.Sp
732.Vb 1 2269.Vb 1
733\& ev_periodic_set (&periodic, 0., 3600., 0); 2270\& ev_periodic_set (&periodic, 0., 3600., 0);
734.Ve 2271.Ve
735.Sp 2272.Sp
736This doesn't mean there will always be 3600 seconds in between triggers, 2273This doesn't mean there will always be 3600 seconds in between triggers,
737but only that the the callback will be called when the system time shows a 2274but only that the callback will be called when the system time shows a
738full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2275full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
739by 3600. 2276by 3600.
740.Sp 2277.Sp
741Another way to think about it (for the mathematically inclined) is that 2278Another way to think about it (for the mathematically inclined) is that
742\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2279\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
743time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2280time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
744.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2281.Sp
745.IX Item "manual reschedule mode (reschedule_cb = callback)" 2282For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
2283\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
2284this value, and in fact is often specified as zero.
2285.Sp
2286Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2287speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2288will of course deteriorate. Libev itself tries to be exact to be about one
2289millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2290.IP "\(bu" 4
2291manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2292.Sp
746In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2293In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
747ignored. Instead, each time the periodic watcher gets scheduled, the 2294ignored. Instead, each time the periodic watcher gets scheduled, the
748reschedule callback will be called with the watcher as first, and the 2295reschedule callback will be called with the watcher as first, and the
749current time as second argument. 2296current time as second argument.
750.Sp 2297.Sp
751\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2298\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
752ever, or make any event loop modifications\fR. If you need to stop it, 2299or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
753return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2300allowed by documentation here\fR.
754starting a prepare watcher).
755.Sp 2301.Sp
2302If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2303it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2304only event loop modification you are allowed to do).
2305.Sp
756Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2306The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
757ev_tstamp now)\*(C'\fR, e.g.: 2307*w, ev_tstamp now)\*(C'\fR, e.g.:
758.Sp 2308.Sp
759.Vb 4 2309.Vb 5
2310\& static ev_tstamp
760\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2311\& my_rescheduler (ev_periodic *w, ev_tstamp now)
761\& { 2312\& {
762\& return now + 60.; 2313\& return now + 60.;
763\& } 2314\& }
764.Ve 2315.Ve
765.Sp 2316.Sp
766It must return the next time to trigger, based on the passed time value 2317It must return the next time to trigger, based on the passed time value
767(that is, the lowest time value larger than to the second argument). It 2318(that is, the lowest time value larger than to the second argument). It
768will usually be called just before the callback will be triggered, but 2319will usually be called just before the callback will be triggered, but
769might be called at other times, too. 2320might be called at other times, too.
770.Sp 2321.Sp
771\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2322\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
772passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2323equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
773.Sp 2324.Sp
774This can be used to create very complex timers, such as a timer that 2325This can be used to create very complex timers, such as a timer that
775triggers on each midnight, local time. To do this, you would calculate the 2326triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
776next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2327next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
777you do this is, again, up to you (but it is not trivial, which is the main 2328you do this is, again, up to you (but it is not trivial, which is the main
778reason I omitted it as an example). 2329reason I omitted it as an example).
779.RE 2330.RE
780.RS 4 2331.RS 4
… …
783.IX Item "ev_periodic_again (loop, ev_periodic *)" 2334.IX Item "ev_periodic_again (loop, ev_periodic *)"
784Simply stops and restarts the periodic watcher again. This is only useful 2335Simply stops and restarts the periodic watcher again. This is only useful
785when you changed some parameters or the reschedule callback would return 2336when you changed some parameters or the reschedule callback would return
786a different time than the last time it was called (e.g. in a crond like 2337a different time than the last time it was called (e.g. in a crond like
787program when the crontabs have changed). 2338program when the crontabs have changed).
2339.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2340.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2341When active, returns the absolute time that the watcher is supposed
2342to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2343\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2344rescheduling modes.
2345.IP "ev_tstamp offset [read\-write]" 4
2346.IX Item "ev_tstamp offset [read-write]"
2347When repeating, this contains the offset value, otherwise this is the
2348absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2349although libev might modify this value for better numerical stability).
2350.Sp
2351Can be modified any time, but changes only take effect when the periodic
2352timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2353.IP "ev_tstamp interval [read\-write]" 4
2354.IX Item "ev_tstamp interval [read-write]"
2355The current interval value. Can be modified any time, but changes only
2356take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2357called.
2358.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2359.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2360The current reschedule callback, or \f(CW0\fR, if this functionality is
2361switched off. Can be changed any time, but changes only take effect when
2362the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2363.PP
2364\fIExamples\fR
2365.IX Subsection "Examples"
2366.PP
2367Example: Call a callback every hour, or, more precisely, whenever the
2368system time is divisible by 3600. The callback invocation times have
2369potentially a lot of jitter, but good long-term stability.
2370.PP
2371.Vb 5
2372\& static void
2373\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
2374\& {
2375\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2376\& }
2377\&
2378\& ev_periodic hourly_tick;
2379\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2380\& ev_periodic_start (loop, &hourly_tick);
2381.Ve
2382.PP
2383Example: The same as above, but use a reschedule callback to do it:
2384.PP
2385.Vb 1
2386\& #include <math.h>
2387\&
2388\& static ev_tstamp
2389\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2390\& {
2391\& return now + (3600. \- fmod (now, 3600.));
2392\& }
2393\&
2394\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2395.Ve
2396.PP
2397Example: Call a callback every hour, starting now:
2398.PP
2399.Vb 4
2400\& ev_periodic hourly_tick;
2401\& ev_periodic_init (&hourly_tick, clock_cb,
2402\& fmod (ev_now (loop), 3600.), 3600., 0);
2403\& ev_periodic_start (loop, &hourly_tick);
2404.Ve
788.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 2405.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
789.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 2406.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
790.IX Subsection "ev_signal - signal me when a signal gets signalled" 2407.IX Subsection "ev_signal - signal me when a signal gets signalled!"
791Signal watchers will trigger an event when the process receives a specific 2408Signal watchers will trigger an event when the process receives a specific
792signal one or more times. Even though signals are very asynchronous, libev 2409signal one or more times. Even though signals are very asynchronous, libev
793will try it's best to deliver signals synchronously, i.e. as part of the 2410will try its best to deliver signals synchronously, i.e. as part of the
794normal event processing, like any other event. 2411normal event processing, like any other event.
795.PP 2412.PP
2413If you want signals to be delivered truly asynchronously, just use
2414\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2415the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2416synchronously wake up an event loop.
2417.PP
796You can configure as many watchers as you like per signal. Only when the 2418You can configure as many watchers as you like for the same signal, but
2419only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2420default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2421\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2422the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2423.PP
797first watcher gets started will libev actually register a signal watcher 2424When the first watcher gets started will libev actually register something
798with the kernel (thus it coexists with your own signal handlers as long 2425with the kernel (thus it coexists with your own signal handlers as long as
799as you don't register any with libev). Similarly, when the last signal 2426you don't register any with libev for the same signal).
800watcher for a signal is stopped libev will reset the signal handler to 2427.PP
801\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2428If possible and supported, libev will install its handlers with
2429\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2430not be unduly interrupted. If you have a problem with system calls getting
2431interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2432and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2433.PP
2434\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2435.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2436.PP
2437Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2438(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2439stopping it again), that is, libev might or might not block the signal,
2440and might or might not set or restore the installed signal handler (but
2441see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2442.PP
2443While this does not matter for the signal disposition (libev never
2444sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2445\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2446certain signals to be blocked.
2447.PP
2448This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2449the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2450choice usually).
2451.PP
2452The simplest way to ensure that the signal mask is reset in the child is
2453to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2454catch fork calls done by libraries (such as the libc) as well.
2455.PP
2456In current versions of libev, the signal will not be blocked indefinitely
2457unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2458the window of opportunity for problems, it will not go away, as libev
2459\&\fIhas\fR to modify the signal mask, at least temporarily.
2460.PP
2461So I can't stress this enough: \fIIf you do not reset your signal mask when
2462you expect it to be empty, you have a race condition in your code\fR. This
2463is not a libev-specific thing, this is true for most event libraries.
2464.PP
2465\fIThe special problem of threads signal handling\fR
2466.IX Subsection "The special problem of threads signal handling"
2467.PP
2468\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2469a lot of functionality (sigfd, sigwait etc.) only really works if all
2470threads in a process block signals, which is hard to achieve.
2471.PP
2472When you want to use sigwait (or mix libev signal handling with your own
2473for the same signals), you can tackle this problem by globally blocking
2474all signals before creating any threads (or creating them with a fully set
2475sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2476loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2477these signals. You can pass on any signals that libev might be interested
2478in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2479.PP
2480\fIWatcher-Specific Functions and Data Members\fR
2481.IX Subsection "Watcher-Specific Functions and Data Members"
802.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2482.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
803.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2483.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
804.PD 0 2484.PD 0
805.IP "ev_signal_set (ev_signal *, int signum)" 4 2485.IP "ev_signal_set (ev_signal *, int signum)" 4
806.IX Item "ev_signal_set (ev_signal *, int signum)" 2486.IX Item "ev_signal_set (ev_signal *, int signum)"
807.PD 2487.PD
808Configures the watcher to trigger on the given signal number (usually one 2488Configures the watcher to trigger on the given signal number (usually one
809of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2489of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2490.IP "int signum [read\-only]" 4
2491.IX Item "int signum [read-only]"
2492The signal the watcher watches out for.
2493.PP
2494\fIExamples\fR
2495.IX Subsection "Examples"
2496.PP
2497Example: Try to exit cleanly on \s-1SIGINT\s0.
2498.PP
2499.Vb 5
2500\& static void
2501\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2502\& {
2503\& ev_break (loop, EVBREAK_ALL);
2504\& }
2505\&
2506\& ev_signal signal_watcher;
2507\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2508\& ev_signal_start (loop, &signal_watcher);
2509.Ve
810.ie n .Sh """ev_child"" \- wait for pid status changes" 2510.ie n .SS """ev_child"" \- watch out for process status changes"
811.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 2511.el .SS "\f(CWev_child\fP \- watch out for process status changes"
812.IX Subsection "ev_child - wait for pid status changes" 2512.IX Subsection "ev_child - watch out for process status changes"
813Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2513Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
814some child status changes (most typically when a child of yours dies). 2514some child status changes (most typically when a child of yours dies or
2515exits). It is permissible to install a child watcher \fIafter\fR the child
2516has been forked (which implies it might have already exited), as long
2517as the event loop isn't entered (or is continued from a watcher), i.e.,
2518forking and then immediately registering a watcher for the child is fine,
2519but forking and registering a watcher a few event loop iterations later or
2520in the next callback invocation is not.
2521.PP
2522Only the default event loop is capable of handling signals, and therefore
2523you can only register child watchers in the default event loop.
2524.PP
2525Due to some design glitches inside libev, child watchers will always be
2526handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2527libev)
2528.PP
2529\fIProcess Interaction\fR
2530.IX Subsection "Process Interaction"
2531.PP
2532Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2533initialised. This is necessary to guarantee proper behaviour even if the
2534first child watcher is started after the child exits. The occurrence
2535of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2536synchronously as part of the event loop processing. Libev always reaps all
2537children, even ones not watched.
2538.PP
2539\fIOverriding the Built-In Processing\fR
2540.IX Subsection "Overriding the Built-In Processing"
2541.PP
2542Libev offers no special support for overriding the built-in child
2543processing, but if your application collides with libev's default child
2544handler, you can override it easily by installing your own handler for
2545\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2546default loop never gets destroyed. You are encouraged, however, to use an
2547event-based approach to child reaping and thus use libev's support for
2548that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2549.PP
2550\fIStopping the Child Watcher\fR
2551.IX Subsection "Stopping the Child Watcher"
2552.PP
2553Currently, the child watcher never gets stopped, even when the
2554child terminates, so normally one needs to stop the watcher in the
2555callback. Future versions of libev might stop the watcher automatically
2556when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2557problem).
2558.PP
2559\fIWatcher-Specific Functions and Data Members\fR
2560.IX Subsection "Watcher-Specific Functions and Data Members"
815.IP "ev_child_init (ev_child *, callback, int pid)" 4 2561.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
816.IX Item "ev_child_init (ev_child *, callback, int pid)" 2562.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
817.PD 0 2563.PD 0
818.IP "ev_child_set (ev_child *, int pid)" 4 2564.IP "ev_child_set (ev_child *, int pid, int trace)" 4
819.IX Item "ev_child_set (ev_child *, int pid)" 2565.IX Item "ev_child_set (ev_child *, int pid, int trace)"
820.PD 2566.PD
821Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2567Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
822\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2568\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
823at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2569at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
824the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2570the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
825\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2571\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
826process causing the status change. 2572process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2573activate the watcher when the process terminates) or \f(CW1\fR (additionally
2574activate the watcher when the process is stopped or continued).
2575.IP "int pid [read\-only]" 4
2576.IX Item "int pid [read-only]"
2577The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2578.IP "int rpid [read\-write]" 4
2579.IX Item "int rpid [read-write]"
2580The process id that detected a status change.
2581.IP "int rstatus [read\-write]" 4
2582.IX Item "int rstatus [read-write]"
2583The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2584\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2585.PP
2586\fIExamples\fR
2587.IX Subsection "Examples"
2588.PP
2589Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2590its completion.
2591.PP
2592.Vb 1
2593\& ev_child cw;
2594\&
2595\& static void
2596\& child_cb (EV_P_ ev_child *w, int revents)
2597\& {
2598\& ev_child_stop (EV_A_ w);
2599\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2600\& }
2601\&
2602\& pid_t pid = fork ();
2603\&
2604\& if (pid < 0)
2605\& // error
2606\& else if (pid == 0)
2607\& {
2608\& // the forked child executes here
2609\& exit (1);
2610\& }
2611\& else
2612\& {
2613\& ev_child_init (&cw, child_cb, pid, 0);
2614\& ev_child_start (EV_DEFAULT_ &cw);
2615\& }
2616.Ve
2617.ie n .SS """ev_stat"" \- did the file attributes just change?"
2618.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2619.IX Subsection "ev_stat - did the file attributes just change?"
2620This watches a file system path for attribute changes. That is, it calls
2621\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2622and sees if it changed compared to the last time, invoking the callback if
2623it did.
2624.PP
2625The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2626not exist\*(R" is a status change like any other. The condition \*(L"path does not
2627exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2628\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2629least one) and all the other fields of the stat buffer having unspecified
2630contents.
2631.PP
2632The path \fImust not\fR end in a slash or contain special components such as
2633\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2634your working directory changes, then the behaviour is undefined.
2635.PP
2636Since there is no portable change notification interface available, the
2637portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2638to see if it changed somehow. You can specify a recommended polling
2639interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2640recommended!) then a \fIsuitable, unspecified default\fR value will be used
2641(which you can expect to be around five seconds, although this might
2642change dynamically). Libev will also impose a minimum interval which is
2643currently around \f(CW0.1\fR, but that's usually overkill.
2644.PP
2645This watcher type is not meant for massive numbers of stat watchers,
2646as even with OS-supported change notifications, this can be
2647resource-intensive.
2648.PP
2649At the time of this writing, the only OS-specific interface implemented
2650is the Linux inotify interface (implementing kqueue support is left as an
2651exercise for the reader. Note, however, that the author sees no way of
2652implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2653.PP
2654\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2655.IX Subsection "ABI Issues (Largefile Support)"
2656.PP
2657Libev by default (unless the user overrides this) uses the default
2658compilation environment, which means that on systems with large file
2659support disabled by default, you get the 32 bit version of the stat
2660structure. When using the library from programs that change the \s-1ABI\s0 to
2661use 64 bit file offsets the programs will fail. In that case you have to
2662compile libev with the same flags to get binary compatibility. This is
2663obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2664most noticeably displayed with ev_stat and large file support.
2665.PP
2666The solution for this is to lobby your distribution maker to make large
2667file interfaces available by default (as e.g. FreeBSD does) and not
2668optional. Libev cannot simply switch on large file support because it has
2669to exchange stat structures with application programs compiled using the
2670default compilation environment.
2671.PP
2672\fIInotify and Kqueue\fR
2673.IX Subsection "Inotify and Kqueue"
2674.PP
2675When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2676runtime, it will be used to speed up change detection where possible. The
2677inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2678watcher is being started.
2679.PP
2680Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2681except that changes might be detected earlier, and in some cases, to avoid
2682making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2683there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2684but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2685many bugs), the path exists (i.e. stat succeeds), and the path resides on
2686a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2687xfs are fully working) libev usually gets away without polling.
2688.PP
2689There is no support for kqueue, as apparently it cannot be used to
2690implement this functionality, due to the requirement of having a file
2691descriptor open on the object at all times, and detecting renames, unlinks
2692etc. is difficult.
2693.PP
2694\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2695.IX Subsection "stat () is a synchronous operation"
2696.PP
2697Libev doesn't normally do any kind of I/O itself, and so is not blocking
2698the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2699()\*(C'\fR, which is a synchronous operation.
2700.PP
2701For local paths, this usually doesn't matter: unless the system is very
2702busy or the intervals between stat's are large, a stat call will be fast,
2703as the path data is usually in memory already (except when starting the
2704watcher).
2705.PP
2706For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2707time due to network issues, and even under good conditions, a stat call
2708often takes multiple milliseconds.
2709.PP
2710Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2711paths, although this is fully supported by libev.
2712.PP
2713\fIThe special problem of stat time resolution\fR
2714.IX Subsection "The special problem of stat time resolution"
2715.PP
2716The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2717and even on systems where the resolution is higher, most file systems
2718still only support whole seconds.
2719.PP
2720That means that, if the time is the only thing that changes, you can
2721easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2722calls your callback, which does something. When there is another update
2723within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2724stat data does change in other ways (e.g. file size).
2725.PP
2726The solution to this is to delay acting on a change for slightly more
2727than a second (or till slightly after the next full second boundary), using
2728a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2729ev_timer_again (loop, w)\*(C'\fR).
2730.PP
2731The \f(CW.02\fR offset is added to work around small timing inconsistencies
2732of some operating systems (where the second counter of the current time
2733might be be delayed. One such system is the Linux kernel, where a call to
2734\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2735a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2736update file times then there will be a small window where the kernel uses
2737the previous second to update file times but libev might already execute
2738the timer callback).
2739.PP
2740\fIWatcher-Specific Functions and Data Members\fR
2741.IX Subsection "Watcher-Specific Functions and Data Members"
2742.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2743.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2744.PD 0
2745.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2746.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2747.PD
2748Configures the watcher to wait for status changes of the given
2749\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2750be detected and should normally be specified as \f(CW0\fR to let libev choose
2751a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2752path for as long as the watcher is active.
2753.Sp
2754The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2755relative to the attributes at the time the watcher was started (or the
2756last change was detected).
2757.IP "ev_stat_stat (loop, ev_stat *)" 4
2758.IX Item "ev_stat_stat (loop, ev_stat *)"
2759Updates the stat buffer immediately with new values. If you change the
2760watched path in your callback, you could call this function to avoid
2761detecting this change (while introducing a race condition if you are not
2762the only one changing the path). Can also be useful simply to find out the
2763new values.
2764.IP "ev_statdata attr [read\-only]" 4
2765.IX Item "ev_statdata attr [read-only]"
2766The most-recently detected attributes of the file. Although the type is
2767\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2768suitable for your system, but you can only rely on the POSIX-standardised
2769members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2770some error while \f(CW\*(C`stat\*(C'\fRing the file.
2771.IP "ev_statdata prev [read\-only]" 4
2772.IX Item "ev_statdata prev [read-only]"
2773The previous attributes of the file. The callback gets invoked whenever
2774\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2775differ: \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,
2776\&\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.
2777.IP "ev_tstamp interval [read\-only]" 4
2778.IX Item "ev_tstamp interval [read-only]"
2779The specified interval.
2780.IP "const char *path [read\-only]" 4
2781.IX Item "const char *path [read-only]"
2782The file system path that is being watched.
2783.PP
2784\fIExamples\fR
2785.IX Subsection "Examples"
2786.PP
2787Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2788.PP
2789.Vb 10
2790\& static void
2791\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2792\& {
2793\& /* /etc/passwd changed in some way */
2794\& if (w\->attr.st_nlink)
2795\& {
2796\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2797\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2798\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2799\& }
2800\& else
2801\& /* you shalt not abuse printf for puts */
2802\& puts ("wow, /etc/passwd is not there, expect problems. "
2803\& "if this is windows, they already arrived\en");
2804\& }
2805\&
2806\& ...
2807\& ev_stat passwd;
2808\&
2809\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2810\& ev_stat_start (loop, &passwd);
2811.Ve
2812.PP
2813Example: Like above, but additionally use a one-second delay so we do not
2814miss updates (however, frequent updates will delay processing, too, so
2815one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2816\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2817.PP
2818.Vb 2
2819\& static ev_stat passwd;
2820\& static ev_timer timer;
2821\&
2822\& static void
2823\& timer_cb (EV_P_ ev_timer *w, int revents)
2824\& {
2825\& ev_timer_stop (EV_A_ w);
2826\&
2827\& /* now it\*(Aqs one second after the most recent passwd change */
2828\& }
2829\&
2830\& static void
2831\& stat_cb (EV_P_ ev_stat *w, int revents)
2832\& {
2833\& /* reset the one\-second timer */
2834\& ev_timer_again (EV_A_ &timer);
2835\& }
2836\&
2837\& ...
2838\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2839\& ev_stat_start (loop, &passwd);
2840\& ev_timer_init (&timer, timer_cb, 0., 1.02);
2841.Ve
827.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 2842.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
828.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 2843.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
829.IX Subsection "ev_idle - when you've got nothing better to do" 2844.IX Subsection "ev_idle - when you've got nothing better to do..."
830Idle watchers trigger events when there are no other events are pending 2845Idle watchers trigger events when no other events of the same or higher
831(prepare, check and other idle watchers do not count). That is, as long 2846priority are pending (prepare, check and other idle watchers do not count
832as your process is busy handling sockets or timeouts (or even signals, 2847as receiving \*(L"events\*(R").
833imagine) it will not be triggered. But when your process is idle all idle 2848.PP
834watchers are being called again and again, once per event loop iteration \- 2849That is, as long as your process is busy handling sockets or timeouts
2850(or even signals, imagine) of the same or higher priority it will not be
2851triggered. But when your process is idle (or only lower-priority watchers
2852are pending), the idle watchers are being called once per event loop
835until stopped, that is, or your process receives more events and becomes 2853iteration \- until stopped, that is, or your process receives more events
836busy. 2854and becomes busy again with higher priority stuff.
837.PP 2855.PP
838The most noteworthy effect is that as long as any idle watchers are 2856The most noteworthy effect is that as long as any idle watchers are
839active, the process will not block when waiting for new events. 2857active, the process will not block when waiting for new events.
840.PP 2858.PP
841Apart from keeping your process non-blocking (which is a useful 2859Apart from keeping your process non-blocking (which is a useful
842effect on its own sometimes), idle watchers are a good place to do 2860effect on its own sometimes), idle watchers are a good place to do
843\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 2861\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
844event loop has handled all outstanding events. 2862event loop has handled all outstanding events.
2863.PP
2864\fIWatcher-Specific Functions and Data Members\fR
2865.IX Subsection "Watcher-Specific Functions and Data Members"
845.IP "ev_idle_init (ev_signal *, callback)" 4 2866.IP "ev_idle_init (ev_idle *, callback)" 4
846.IX Item "ev_idle_init (ev_signal *, callback)" 2867.IX Item "ev_idle_init (ev_idle *, callback)"
847Initialises and configures the idle watcher \- it has no parameters of any 2868Initialises and configures the idle watcher \- it has no parameters of any
848kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 2869kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
849believe me. 2870believe me.
2871.PP
2872\fIExamples\fR
2873.IX Subsection "Examples"
2874.PP
2875Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
2876callback, free it. Also, use no error checking, as usual.
2877.PP
2878.Vb 7
2879\& static void
2880\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2881\& {
2882\& free (w);
2883\& // now do something you wanted to do when the program has
2884\& // no longer anything immediate to do.
2885\& }
2886\&
2887\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2888\& ev_idle_init (idle_watcher, idle_cb);
2889\& ev_idle_start (loop, idle_watcher);
2890.Ve
850.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 2891.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
851.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 2892.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
852.IX Subsection "ev_prepare and ev_check - customise your event loop" 2893.IX Subsection "ev_prepare and ev_check - customise your event loop!"
853Prepare and check watchers are usually (but not always) used in tandem: 2894Prepare and check watchers are usually (but not always) used in pairs:
854prepare watchers get invoked before the process blocks and check watchers 2895prepare watchers get invoked before the process blocks and check watchers
855afterwards. 2896afterwards.
856.PP 2897.PP
2898You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
2899the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2900watchers. Other loops than the current one are fine, however. The
2901rationale behind this is that you do not need to check for recursion in
2902those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2903\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2904called in pairs bracketing the blocking call.
2905.PP
857Their main purpose is to integrate other event mechanisms into libev. This 2906Their main purpose is to integrate other event mechanisms into libev and
858could be used, for example, to track variable changes, implement your own 2907their use is somewhat advanced. They could be used, for example, to track
859watchers, integrate net-snmp or a coroutine library and lots more. 2908variable changes, implement your own watchers, integrate net-snmp or a
2909coroutine library and lots more. They are also occasionally useful if
2910you cache some data and want to flush it before blocking (for example,
2911in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2912watcher).
860.PP 2913.PP
861This is done by examining in each prepare call which file descriptors need 2914This is done by examining in each prepare call which file descriptors
862to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 2915need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
863them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 2916for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
864provide just this functionality). Then, in the check watcher you check for 2917libraries provide exactly this functionality). Then, in the check watcher,
865any events that occured (by checking the pending status of all watchers 2918you check for any events that occurred (by checking the pending status
866and stopping them) and call back into the library. The I/O and timer 2919of all watchers and stopping them) and call back into the library. The
867callbacks will never actually be called (but must be valid nevertheless, 2920I/O and timer callbacks will never actually be called (but must be valid
868because you never know, you know?). 2921nevertheless, because you never know, you know?).
869.PP 2922.PP
870As another example, the Perl Coro module uses these hooks to integrate 2923As another example, the Perl Coro module uses these hooks to integrate
871coroutines into libev programs, by yielding to other active coroutines 2924coroutines into libev programs, by yielding to other active coroutines
872during each prepare and only letting the process block if no coroutines 2925during each prepare and only letting the process block if no coroutines
873are ready to run (it's actually more complicated: it only runs coroutines 2926are ready to run (it's actually more complicated: it only runs coroutines
874with priority higher than or equal to the event loop and one coroutine 2927with priority higher than or equal to the event loop and one coroutine
875of lower priority, but only once, using idle watchers to keep the event 2928of lower priority, but only once, using idle watchers to keep the event
876loop from blocking if lower-priority coroutines are active, thus mapping 2929loop from blocking if lower-priority coroutines are active, thus mapping
877low-priority coroutines to idle/background tasks). 2930low-priority coroutines to idle/background tasks).
2931.PP
2932It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2933priority, to ensure that they are being run before any other watchers
2934after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2935.PP
2936Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2937activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2938might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2939\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2940loops those other event loops might be in an unusable state until their
2941\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2942others).
2943.PP
2944\fIWatcher-Specific Functions and Data Members\fR
2945.IX Subsection "Watcher-Specific Functions and Data Members"
878.IP "ev_prepare_init (ev_prepare *, callback)" 4 2946.IP "ev_prepare_init (ev_prepare *, callback)" 4
879.IX Item "ev_prepare_init (ev_prepare *, callback)" 2947.IX Item "ev_prepare_init (ev_prepare *, callback)"
880.PD 0 2948.PD 0
881.IP "ev_check_init (ev_check *, callback)" 4 2949.IP "ev_check_init (ev_check *, callback)" 4
882.IX Item "ev_check_init (ev_check *, callback)" 2950.IX Item "ev_check_init (ev_check *, callback)"
883.PD 2951.PD
884Initialises and configures the prepare or check watcher \- they have no 2952Initialises and configures the prepare or check watcher \- they have no
885parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 2953parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
886macros, but using them is utterly, utterly and completely pointless. 2954macros, but using them is utterly, utterly, utterly and completely
2955pointless.
2956.PP
2957\fIExamples\fR
2958.IX Subsection "Examples"
2959.PP
2960There are a number of principal ways to embed other event loops or modules
2961into libev. Here are some ideas on how to include libadns into libev
2962(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2963use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2964Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2965Glib event loop).
2966.PP
2967Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2968and in a check watcher, destroy them and call into libadns. What follows
2969is pseudo-code only of course. This requires you to either use a low
2970priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2971the callbacks for the IO/timeout watchers might not have been called yet.
2972.PP
2973.Vb 2
2974\& static ev_io iow [nfd];
2975\& static ev_timer tw;
2976\&
2977\& static void
2978\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2979\& {
2980\& }
2981\&
2982\& // create io watchers for each fd and a timer before blocking
2983\& static void
2984\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2985\& {
2986\& int timeout = 3600000;
2987\& struct pollfd fds [nfd];
2988\& // actual code will need to loop here and realloc etc.
2989\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2990\&
2991\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2992\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
2993\& ev_timer_start (loop, &tw);
2994\&
2995\& // create one ev_io per pollfd
2996\& for (int i = 0; i < nfd; ++i)
2997\& {
2998\& ev_io_init (iow + i, io_cb, fds [i].fd,
2999\& ((fds [i].events & POLLIN ? EV_READ : 0)
3000\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3001\&
3002\& fds [i].revents = 0;
3003\& ev_io_start (loop, iow + i);
3004\& }
3005\& }
3006\&
3007\& // stop all watchers after blocking
3008\& static void
3009\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3010\& {
3011\& ev_timer_stop (loop, &tw);
3012\&
3013\& for (int i = 0; i < nfd; ++i)
3014\& {
3015\& // set the relevant poll flags
3016\& // could also call adns_processreadable etc. here
3017\& struct pollfd *fd = fds + i;
3018\& int revents = ev_clear_pending (iow + i);
3019\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3020\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3021\&
3022\& // now stop the watcher
3023\& ev_io_stop (loop, iow + i);
3024\& }
3025\&
3026\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3027\& }
3028.Ve
3029.PP
3030Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3031in the prepare watcher and would dispose of the check watcher.
3032.PP
3033Method 3: If the module to be embedded supports explicit event
3034notification (libadns does), you can also make use of the actual watcher
3035callbacks, and only destroy/create the watchers in the prepare watcher.
3036.PP
3037.Vb 5
3038\& static void
3039\& timer_cb (EV_P_ ev_timer *w, int revents)
3040\& {
3041\& adns_state ads = (adns_state)w\->data;
3042\& update_now (EV_A);
3043\&
3044\& adns_processtimeouts (ads, &tv_now);
3045\& }
3046\&
3047\& static void
3048\& io_cb (EV_P_ ev_io *w, int revents)
3049\& {
3050\& adns_state ads = (adns_state)w\->data;
3051\& update_now (EV_A);
3052\&
3053\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3054\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3055\& }
3056\&
3057\& // do not ever call adns_afterpoll
3058.Ve
3059.PP
3060Method 4: Do not use a prepare or check watcher because the module you
3061want to embed is not flexible enough to support it. Instead, you can
3062override their poll function. The drawback with this solution is that the
3063main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3064this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3065libglib event loop.
3066.PP
3067.Vb 4
3068\& static gint
3069\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3070\& {
3071\& int got_events = 0;
3072\&
3073\& for (n = 0; n < nfds; ++n)
3074\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3075\&
3076\& if (timeout >= 0)
3077\& // create/start timer
3078\&
3079\& // poll
3080\& ev_run (EV_A_ 0);
3081\&
3082\& // stop timer again
3083\& if (timeout >= 0)
3084\& ev_timer_stop (EV_A_ &to);
3085\&
3086\& // stop io watchers again \- their callbacks should have set
3087\& for (n = 0; n < nfds; ++n)
3088\& ev_io_stop (EV_A_ iow [n]);
3089\&
3090\& return got_events;
3091\& }
3092.Ve
3093.ie n .SS """ev_embed"" \- when one backend isn't enough..."
3094.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
3095.IX Subsection "ev_embed - when one backend isn't enough..."
3096This is a rather advanced watcher type that lets you embed one event loop
3097into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
3098loop, other types of watchers might be handled in a delayed or incorrect
3099fashion and must not be used).
3100.PP
3101There are primarily two reasons you would want that: work around bugs and
3102prioritise I/O.
3103.PP
3104As an example for a bug workaround, the kqueue backend might only support
3105sockets on some platform, so it is unusable as generic backend, but you
3106still want to make use of it because you have many sockets and it scales
3107so nicely. In this case, you would create a kqueue-based loop and embed
3108it into your default loop (which might use e.g. poll). Overall operation
3109will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
3110\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3111best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
3112.PP
3113As for prioritising I/O: under rare circumstances you have the case where
3114some fds have to be watched and handled very quickly (with low latency),
3115and even priorities and idle watchers might have too much overhead. In
3116this case you would put all the high priority stuff in one loop and all
3117the rest in a second one, and embed the second one in the first.
3118.PP
3119As long as the watcher is active, the callback will be invoked every
3120time there might be events pending in the embedded loop. The callback
3121must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
3122sweep and invoke their callbacks (the callback doesn't need to invoke the
3123\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
3124to give the embedded loop strictly lower priority for example).
3125.PP
3126You can also set the callback to \f(CW0\fR, in which case the embed watcher
3127will automatically execute the embedded loop sweep whenever necessary.
3128.PP
3129Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
3130is active, i.e., the embedded loop will automatically be forked when the
3131embedding loop forks. In other cases, the user is responsible for calling
3132\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
3133.PP
3134Unfortunately, not all backends are embeddable: only the ones returned by
3135\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
3136portable one.
3137.PP
3138So when you want to use this feature you will always have to be prepared
3139that you cannot get an embeddable loop. The recommended way to get around
3140this is to have a separate variables for your embeddable loop, try to
3141create it, and if that fails, use the normal loop for everything.
3142.PP
3143\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
3144.IX Subsection "ev_embed and fork"
3145.PP
3146While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
3147automatically be applied to the embedded loop as well, so no special
3148fork handling is required in that case. When the watcher is not running,
3149however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
3150as applicable.
3151.PP
3152\fIWatcher-Specific Functions and Data Members\fR
3153.IX Subsection "Watcher-Specific Functions and Data Members"
3154.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3155.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
3156.PD 0
3157.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3158.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
3159.PD
3160Configures the watcher to embed the given loop, which must be
3161embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
3162invoked automatically, otherwise it is the responsibility of the callback
3163to invoke it (it will continue to be called until the sweep has been done,
3164if you do not want that, you need to temporarily stop the embed watcher).
3165.IP "ev_embed_sweep (loop, ev_embed *)" 4
3166.IX Item "ev_embed_sweep (loop, ev_embed *)"
3167Make a single, non-blocking sweep over the embedded loop. This works
3168similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
3169appropriate way for embedded loops.
3170.IP "struct ev_loop *other [read\-only]" 4
3171.IX Item "struct ev_loop *other [read-only]"
3172The embedded event loop.
3173.PP
3174\fIExamples\fR
3175.IX Subsection "Examples"
3176.PP
3177Example: Try to get an embeddable event loop and embed it into the default
3178event loop. If that is not possible, use the default loop. The default
3179loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3180\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3181used).
3182.PP
3183.Vb 3
3184\& struct ev_loop *loop_hi = ev_default_init (0);
3185\& struct ev_loop *loop_lo = 0;
3186\& ev_embed embed;
3187\&
3188\& // see if there is a chance of getting one that works
3189\& // (remember that a flags value of 0 means autodetection)
3190\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3191\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3192\& : 0;
3193\&
3194\& // if we got one, then embed it, otherwise default to loop_hi
3195\& if (loop_lo)
3196\& {
3197\& ev_embed_init (&embed, 0, loop_lo);
3198\& ev_embed_start (loop_hi, &embed);
3199\& }
3200\& else
3201\& loop_lo = loop_hi;
3202.Ve
3203.PP
3204Example: Check if kqueue is available but not recommended and create
3205a kqueue backend for use with sockets (which usually work with any
3206kqueue implementation). Store the kqueue/socket\-only event loop in
3207\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3208.PP
3209.Vb 3
3210\& struct ev_loop *loop = ev_default_init (0);
3211\& struct ev_loop *loop_socket = 0;
3212\& ev_embed embed;
3213\&
3214\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3215\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3216\& {
3217\& ev_embed_init (&embed, 0, loop_socket);
3218\& ev_embed_start (loop, &embed);
3219\& }
3220\&
3221\& if (!loop_socket)
3222\& loop_socket = loop;
3223\&
3224\& // now use loop_socket for all sockets, and loop for everything else
3225.Ve
3226.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3227.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3228.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3229Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3230whoever is a good citizen cared to tell libev about it by calling
3231\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
3232event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
3233and only in the child after the fork. If whoever good citizen calling
3234\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
3235handlers will be invoked, too, of course.
3236.PP
3237\fIThe special problem of life after fork \- how is it possible?\fR
3238.IX Subsection "The special problem of life after fork - how is it possible?"
3239.PP
3240Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3241up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3242sequence should be handled by libev without any problems.
3243.PP
3244This changes when the application actually wants to do event handling
3245in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3246fork.
3247.PP
3248The default mode of operation (for libev, with application help to detect
3249forks) is to duplicate all the state in the child, as would be expected
3250when \fIeither\fR the parent \fIor\fR the child process continues.
3251.PP
3252When both processes want to continue using libev, then this is usually the
3253wrong result. In that case, usually one process (typically the parent) is
3254supposed to continue with all watchers in place as before, while the other
3255process typically wants to start fresh, i.e. without any active watchers.
3256.PP
3257The cleanest and most efficient way to achieve that with libev is to
3258simply create a new event loop, which of course will be \*(L"empty\*(R", and
3259use that for new watchers. This has the advantage of not touching more
3260memory than necessary, and thus avoiding the copy-on-write, and the
3261disadvantage of having to use multiple event loops (which do not support
3262signal watchers).
3263.PP
3264When this is not possible, or you want to use the default loop for
3265other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3266\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3267Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3268watchers, so you have to be careful not to execute code that modifies
3269those watchers. Note also that in that case, you have to re-register any
3270signal watchers.
3271.PP
3272\fIWatcher-Specific Functions and Data Members\fR
3273.IX Subsection "Watcher-Specific Functions and Data Members"
3274.IP "ev_fork_init (ev_fork *, callback)" 4
3275.IX Item "ev_fork_init (ev_fork *, callback)"
3276Initialises and configures the fork watcher \- it has no parameters of any
3277kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3278really.
3279.ie n .SS """ev_cleanup"" \- even the best things end"
3280.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3281.IX Subsection "ev_cleanup - even the best things end"
3282Cleanup watchers are called just before the event loop is being destroyed
3283by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3284.PP
3285While there is no guarantee that the event loop gets destroyed, cleanup
3286watchers provide a convenient method to install cleanup hooks for your
3287program, worker threads and so on \- you just to make sure to destroy the
3288loop when you want them to be invoked.
3289.PP
3290Cleanup watchers are invoked in the same way as any other watcher. Unlike
3291all other watchers, they do not keep a reference to the event loop (which
3292makes a lot of sense if you think about it). Like all other watchers, you
3293can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3294.PP
3295\fIWatcher-Specific Functions and Data Members\fR
3296.IX Subsection "Watcher-Specific Functions and Data Members"
3297.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3298.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3299Initialises and configures the cleanup watcher \- it has no parameters of
3300any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3301pointless, I assure you.
3302.PP
3303Example: Register an atexit handler to destroy the default loop, so any
3304cleanup functions are called.
3305.PP
3306.Vb 5
3307\& static void
3308\& program_exits (void)
3309\& {
3310\& ev_loop_destroy (EV_DEFAULT_UC);
3311\& }
3312\&
3313\& ...
3314\& atexit (program_exits);
3315.Ve
3316.ie n .SS """ev_async"" \- how to wake up an event loop"
3317.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3318.IX Subsection "ev_async - how to wake up an event loop"
3319In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3320asynchronous sources such as signal handlers (as opposed to multiple event
3321loops \- those are of course safe to use in different threads).
3322.PP
3323Sometimes, however, you need to wake up an event loop you do not control,
3324for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3325watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3326it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3327.PP
3328This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3329too, are asynchronous in nature, and signals, too, will be compressed
3330(i.e. the number of callback invocations may be less than the number of
3331\&\f(CW\*(C`ev_async_sent\*(C'\fR calls). In fact, you could use signal watchers as a kind
3332of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3333signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3334even without knowing which loop owns the signal.
3335.PP
3336Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
3337just the default loop.
3338.PP
3339\fIQueueing\fR
3340.IX Subsection "Queueing"
3341.PP
3342\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3343is that the author does not know of a simple (or any) algorithm for a
3344multiple-writer-single-reader queue that works in all cases and doesn't
3345need elaborate support such as pthreads or unportable memory access
3346semantics.
3347.PP
3348That means that if you want to queue data, you have to provide your own
3349queue. But at least I can tell you how to implement locking around your
3350queue:
3351.IP "queueing from a signal handler context" 4
3352.IX Item "queueing from a signal handler context"
3353To implement race-free queueing, you simply add to the queue in the signal
3354handler but you block the signal handler in the watcher callback. Here is
3355an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3356.Sp
3357.Vb 1
3358\& static ev_async mysig;
3359\&
3360\& static void
3361\& sigusr1_handler (void)
3362\& {
3363\& sometype data;
3364\&
3365\& // no locking etc.
3366\& queue_put (data);
3367\& ev_async_send (EV_DEFAULT_ &mysig);
3368\& }
3369\&
3370\& static void
3371\& mysig_cb (EV_P_ ev_async *w, int revents)
3372\& {
3373\& sometype data;
3374\& sigset_t block, prev;
3375\&
3376\& sigemptyset (&block);
3377\& sigaddset (&block, SIGUSR1);
3378\& sigprocmask (SIG_BLOCK, &block, &prev);
3379\&
3380\& while (queue_get (&data))
3381\& process (data);
3382\&
3383\& if (sigismember (&prev, SIGUSR1)
3384\& sigprocmask (SIG_UNBLOCK, &block, 0);
3385\& }
3386.Ve
3387.Sp
3388(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3389instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3390either...).
3391.IP "queueing from a thread context" 4
3392.IX Item "queueing from a thread context"
3393The strategy for threads is different, as you cannot (easily) block
3394threads but you can easily preempt them, so to queue safely you need to
3395employ a traditional mutex lock, such as in this pthread example:
3396.Sp
3397.Vb 2
3398\& static ev_async mysig;
3399\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3400\&
3401\& static void
3402\& otherthread (void)
3403\& {
3404\& // only need to lock the actual queueing operation
3405\& pthread_mutex_lock (&mymutex);
3406\& queue_put (data);
3407\& pthread_mutex_unlock (&mymutex);
3408\&
3409\& ev_async_send (EV_DEFAULT_ &mysig);
3410\& }
3411\&
3412\& static void
3413\& mysig_cb (EV_P_ ev_async *w, int revents)
3414\& {
3415\& pthread_mutex_lock (&mymutex);
3416\&
3417\& while (queue_get (&data))
3418\& process (data);
3419\&
3420\& pthread_mutex_unlock (&mymutex);
3421\& }
3422.Ve
3423.PP
3424\fIWatcher-Specific Functions and Data Members\fR
3425.IX Subsection "Watcher-Specific Functions and Data Members"
3426.IP "ev_async_init (ev_async *, callback)" 4
3427.IX Item "ev_async_init (ev_async *, callback)"
3428Initialises and configures the async watcher \- it has no parameters of any
3429kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3430trust me.
3431.IP "ev_async_send (loop, ev_async *)" 4
3432.IX Item "ev_async_send (loop, ev_async *)"
3433Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3434an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3435returns.
3436.Sp
3437Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3438signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3439embedding section below on what exactly this means).
3440.Sp
3441Note that, as with other watchers in libev, multiple events might get
3442compressed into a single callback invocation (another way to look at this
3443is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
3444reset when the event loop detects that).
3445.Sp
3446This call incurs the overhead of a system call only once per event loop
3447iteration, so while the overhead might be noticeable, it doesn't apply to
3448repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
3449.IP "bool = ev_async_pending (ev_async *)" 4
3450.IX Item "bool = ev_async_pending (ev_async *)"
3451Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3452watcher but the event has not yet been processed (or even noted) by the
3453event loop.
3454.Sp
3455\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3456the loop iterates next and checks for the watcher to have become active,
3457it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3458quickly check whether invoking the loop might be a good idea.
3459.Sp
3460Not that this does \fInot\fR check whether the watcher itself is pending,
3461only whether it has been requested to make this watcher pending: there
3462is a time window between the event loop checking and resetting the async
3463notification, and the callback being invoked.
887.SH "OTHER FUNCTIONS" 3464.SH "OTHER FUNCTIONS"
888.IX Header "OTHER FUNCTIONS" 3465.IX Header "OTHER FUNCTIONS"
889There are some other functions of possible interest. Described. Here. Now. 3466There are some other functions of possible interest. Described. Here. Now.
890.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3467.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
891.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3468.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
892This function combines a simple timer and an I/O watcher, calls your 3469This function combines a simple timer and an I/O watcher, calls your
893callback on whichever event happens first and automatically stop both 3470callback on whichever event happens first and automatically stops both
894watchers. This is useful if you want to wait for a single event on an fd 3471watchers. This is useful if you want to wait for a single event on an fd
895or timeout without having to allocate/configure/start/stop/free one or 3472or timeout without having to allocate/configure/start/stop/free one or
896more watchers yourself. 3473more watchers yourself.
897.Sp 3474.Sp
898If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3475If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
899is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3476\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
900\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3477the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
901.Sp 3478.Sp
902If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3479If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
903started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3480started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
904repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3481repeat = 0) will be started. \f(CW0\fR is a valid timeout.
905dubious value.
906.Sp 3482.Sp
907The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3483The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
908passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3484passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
909\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR 3485\&\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
910value passed to \f(CW\*(C`ev_once\*(C'\fR: 3486value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3487a timeout and an io event at the same time \- you probably should give io
3488events precedence.
3489.Sp
3490Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
911.Sp 3491.Sp
912.Vb 7 3492.Vb 7
913\& static void stdin_ready (int revents, void *arg) 3493\& static void stdin_ready (int revents, void *arg)
914\& { 3494\& {
915\& if (revents & EV_TIMEOUT)
916\& /* doh, nothing entered */;
917\& else if (revents & EV_READ) 3495\& if (revents & EV_READ)
918\& /* stdin might have data for us, joy! */; 3496\& /* stdin might have data for us, joy! */;
3497\& else if (revents & EV_TIMER)
3498\& /* doh, nothing entered */;
919\& } 3499\& }
920.Ve 3500\&
921.Sp
922.Vb 1
923\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3501\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
924.Ve 3502.Ve
925.IP "ev_feed_event (loop, watcher, int events)" 4
926.IX Item "ev_feed_event (loop, watcher, int events)"
927Feeds the given event set into the event loop, as if the specified event
928had happened for the specified watcher (which must be a pointer to an
929initialised but not necessarily started event watcher).
930.IP "ev_feed_fd_event (loop, int fd, int revents)" 4 3503.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
931.IX Item "ev_feed_fd_event (loop, int fd, int revents)" 3504.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
932Feed an event on the given fd, as if a file descriptor backend detected 3505Feed an event on the given fd, as if a file descriptor backend detected
933the given events it. 3506the given events it.
934.IP "ev_feed_signal_event (loop, int signum)" 4 3507.IP "ev_feed_signal_event (loop, int signum)" 4
935.IX Item "ev_feed_signal_event (loop, int signum)" 3508.IX Item "ev_feed_signal_event (loop, int signum)"
936Feed an event as if the given signal occured (loop must be the default loop!). 3509Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3510which is async-safe.
3511.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3512.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3513This section explains some common idioms that are not immediately
3514obvious. Note that examples are sprinkled over the whole manual, and this
3515section only contains stuff that wouldn't fit anywhere else.
3516.SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
3517.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3518Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3519or modify at any time: libev will completely ignore it. This can be used
3520to associate arbitrary data with your watcher. If you need more data and
3521don't want to allocate memory separately and store a pointer to it in that
3522data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3523data:
3524.PP
3525.Vb 7
3526\& struct my_io
3527\& {
3528\& ev_io io;
3529\& int otherfd;
3530\& void *somedata;
3531\& struct whatever *mostinteresting;
3532\& };
3533\&
3534\& ...
3535\& struct my_io w;
3536\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3537.Ve
3538.PP
3539And since your callback will be called with a pointer to the watcher, you
3540can cast it back to your own type:
3541.PP
3542.Vb 5
3543\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3544\& {
3545\& struct my_io *w = (struct my_io *)w_;
3546\& ...
3547\& }
3548.Ve
3549.PP
3550More interesting and less C\-conformant ways of casting your callback
3551function type instead have been omitted.
3552.SS "\s-1BUILDING\s0 \s-1YOUR\s0 \s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0"
3553.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3554Another common scenario is to use some data structure with multiple
3555embedded watchers, in effect creating your own watcher that combines
3556multiple libev event sources into one \*(L"super-watcher\*(R":
3557.PP
3558.Vb 6
3559\& struct my_biggy
3560\& {
3561\& int some_data;
3562\& ev_timer t1;
3563\& ev_timer t2;
3564\& }
3565.Ve
3566.PP
3567In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3568complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3569the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3570to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3571real programmers):
3572.PP
3573.Vb 1
3574\& #include <stddef.h>
3575\&
3576\& static void
3577\& t1_cb (EV_P_ ev_timer *w, int revents)
3578\& {
3579\& struct my_biggy big = (struct my_biggy *)
3580\& (((char *)w) \- offsetof (struct my_biggy, t1));
3581\& }
3582\&
3583\& static void
3584\& t2_cb (EV_P_ ev_timer *w, int revents)
3585\& {
3586\& struct my_biggy big = (struct my_biggy *)
3587\& (((char *)w) \- offsetof (struct my_biggy, t2));
3588\& }
3589.Ve
3590.SS "\s-1MODEL/NESTED\s0 \s-1EVENT\s0 \s-1LOOP\s0 \s-1INVOCATIONS\s0 \s-1AND\s0 \s-1EXIT\s0 \s-1CONDITIONS\s0"
3591.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
3592Often (especially in \s-1GUI\s0 toolkits) there are places where you have
3593\&\fImodal\fR interaction, which is most easily implemented by recursively
3594invoking \f(CW\*(C`ev_run\*(C'\fR.
3595.PP
3596This brings the problem of exiting \- a callback might want to finish the
3597main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
3598a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
3599and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3600other combination: In these cases, \f(CW\*(C`ev_break\*(C'\fR will not work alone.
3601.PP
3602The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3603invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3604triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3605.PP
3606.Vb 2
3607\& // main loop
3608\& int exit_main_loop = 0;
3609\&
3610\& while (!exit_main_loop)
3611\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3612\&
3613\& // in a model watcher
3614\& int exit_nested_loop = 0;
3615\&
3616\& while (!exit_nested_loop)
3617\& ev_run (EV_A_ EVRUN_ONCE);
3618.Ve
3619.PP
3620To exit from any of these loops, just set the corresponding exit variable:
3621.PP
3622.Vb 2
3623\& // exit modal loop
3624\& exit_nested_loop = 1;
3625\&
3626\& // exit main program, after modal loop is finished
3627\& exit_main_loop = 1;
3628\&
3629\& // exit both
3630\& exit_main_loop = exit_nested_loop = 1;
3631.Ve
3632.SS "\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0"
3633.IX Subsection "THREAD LOCKING EXAMPLE"
3634Here is a fictitious example of how to run an event loop in a different
3635thread from where callbacks are being invoked and watchers are
3636created/added/removed.
3637.PP
3638For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3639which uses exactly this technique (which is suited for many high-level
3640languages).
3641.PP
3642The example uses a pthread mutex to protect the loop data, a condition
3643variable to wait for callback invocations, an async watcher to notify the
3644event loop thread and an unspecified mechanism to wake up the main thread.
3645.PP
3646First, you need to associate some data with the event loop:
3647.PP
3648.Vb 6
3649\& typedef struct {
3650\& mutex_t lock; /* global loop lock */
3651\& ev_async async_w;
3652\& thread_t tid;
3653\& cond_t invoke_cv;
3654\& } userdata;
3655\&
3656\& void prepare_loop (EV_P)
3657\& {
3658\& // for simplicity, we use a static userdata struct.
3659\& static userdata u;
3660\&
3661\& ev_async_init (&u\->async_w, async_cb);
3662\& ev_async_start (EV_A_ &u\->async_w);
3663\&
3664\& pthread_mutex_init (&u\->lock, 0);
3665\& pthread_cond_init (&u\->invoke_cv, 0);
3666\&
3667\& // now associate this with the loop
3668\& ev_set_userdata (EV_A_ u);
3669\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3670\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3671\&
3672\& // then create the thread running ev_run
3673\& pthread_create (&u\->tid, 0, l_run, EV_A);
3674\& }
3675.Ve
3676.PP
3677The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3678solely to wake up the event loop so it takes notice of any new watchers
3679that might have been added:
3680.PP
3681.Vb 5
3682\& static void
3683\& async_cb (EV_P_ ev_async *w, int revents)
3684\& {
3685\& // just used for the side effects
3686\& }
3687.Ve
3688.PP
3689The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3690protecting the loop data, respectively.
3691.PP
3692.Vb 6
3693\& static void
3694\& l_release (EV_P)
3695\& {
3696\& userdata *u = ev_userdata (EV_A);
3697\& pthread_mutex_unlock (&u\->lock);
3698\& }
3699\&
3700\& static void
3701\& l_acquire (EV_P)
3702\& {
3703\& userdata *u = ev_userdata (EV_A);
3704\& pthread_mutex_lock (&u\->lock);
3705\& }
3706.Ve
3707.PP
3708The event loop thread first acquires the mutex, and then jumps straight
3709into \f(CW\*(C`ev_run\*(C'\fR:
3710.PP
3711.Vb 4
3712\& void *
3713\& l_run (void *thr_arg)
3714\& {
3715\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3716\&
3717\& l_acquire (EV_A);
3718\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3719\& ev_run (EV_A_ 0);
3720\& l_release (EV_A);
3721\&
3722\& return 0;
3723\& }
3724.Ve
3725.PP
3726Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3727signal the main thread via some unspecified mechanism (signals? pipe
3728writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3729have been called (in a while loop because a) spurious wakeups are possible
3730and b) skipping inter-thread-communication when there are no pending
3731watchers is very beneficial):
3732.PP
3733.Vb 4
3734\& static void
3735\& l_invoke (EV_P)
3736\& {
3737\& userdata *u = ev_userdata (EV_A);
3738\&
3739\& while (ev_pending_count (EV_A))
3740\& {
3741\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3742\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3743\& }
3744\& }
3745.Ve
3746.PP
3747Now, whenever the main thread gets told to invoke pending watchers, it
3748will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3749thread to continue:
3750.PP
3751.Vb 4
3752\& static void
3753\& real_invoke_pending (EV_P)
3754\& {
3755\& userdata *u = ev_userdata (EV_A);
3756\&
3757\& pthread_mutex_lock (&u\->lock);
3758\& ev_invoke_pending (EV_A);
3759\& pthread_cond_signal (&u\->invoke_cv);
3760\& pthread_mutex_unlock (&u\->lock);
3761\& }
3762.Ve
3763.PP
3764Whenever you want to start/stop a watcher or do other modifications to an
3765event loop, you will now have to lock:
3766.PP
3767.Vb 2
3768\& ev_timer timeout_watcher;
3769\& userdata *u = ev_userdata (EV_A);
3770\&
3771\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3772\&
3773\& pthread_mutex_lock (&u\->lock);
3774\& ev_timer_start (EV_A_ &timeout_watcher);
3775\& ev_async_send (EV_A_ &u\->async_w);
3776\& pthread_mutex_unlock (&u\->lock);
3777.Ve
3778.PP
3779Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
3780an event loop currently blocking in the kernel will have no knowledge
3781about the newly added timer. By waking up the loop it will pick up any new
3782watchers in the next event loop iteration.
3783.SS "\s-1THREADS\s0, \s-1COROUTINES\s0, \s-1CONTINUATIONS\s0, \s-1QUEUES\s0... \s-1INSTEAD\s0 \s-1OF\s0 \s-1CALLBACKS\s0"
3784.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
3785While the overhead of a callback that e.g. schedules a thread is small, it
3786is still an overhead. If you embed libev, and your main usage is with some
3787kind of threads or coroutines, you might want to customise libev so that
3788doesn't need callbacks anymore.
3789.PP
3790Imagine you have coroutines that you can switch to using a function
3791\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
3792and that due to some magic, the currently active coroutine is stored in a
3793global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
3794event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
3795the differing \f(CW\*(C`;\*(C'\fR conventions):
3796.PP
3797.Vb 2
3798\& #define EV_CB_DECLARE(type) struct my_coro *cb;
3799\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
3800.Ve
3801.PP
3802That means instead of having a C callback function, you store the
3803coroutine to switch to in each watcher, and instead of having libev call
3804your callback, you instead have it switch to that coroutine.
3805.PP
3806A coroutine might now wait for an event with a function called
3807\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
3808matter when, or whether the watcher is active or not when this function is
3809called):
3810.PP
3811.Vb 6
3812\& void
3813\& wait_for_event (ev_watcher *w)
3814\& {
3815\& ev_cb_set (w) = current_coro;
3816\& switch_to (libev_coro);
3817\& }
3818.Ve
3819.PP
3820That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
3821continues the libev coroutine, which, when appropriate, switches back to
3822this or any other coroutine. I am sure if you sue this your own :)
3823.PP
3824You can do similar tricks if you have, say, threads with an event queue \-
3825instead of storing a coroutine, you store the queue object and instead of
3826switching to a coroutine, you push the watcher onto the queue and notify
3827any waiters.
3828.PP
3829To embed libev, see \s-1EMBEDDING\s0, but in short, it's easiest to create two
3830files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
3831.PP
3832.Vb 4
3833\& // my_ev.h
3834\& #define EV_CB_DECLARE(type) struct my_coro *cb;
3835\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb);
3836\& #include "../libev/ev.h"
3837\&
3838\& // my_ev.c
3839\& #define EV_H "my_ev.h"
3840\& #include "../libev/ev.c"
3841.Ve
3842.PP
3843And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
3844\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
3845can even use \fIev.h\fR as header file name directly.
937.SH "LIBEVENT EMULATION" 3846.SH "LIBEVENT EMULATION"
938.IX Header "LIBEVENT EMULATION" 3847.IX Header "LIBEVENT EMULATION"
939Libev offers a compatibility emulation layer for libevent. It cannot 3848Libev offers a compatibility emulation layer for libevent. It cannot
940emulate the internals of libevent, so here are some usage hints: 3849emulate the internals of libevent, so here are some usage hints:
3850.IP "\(bu" 4
3851Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
3852.Sp
3853This was the newest libevent version available when libev was implemented,
3854and is still mostly unchanged in 2010.
3855.IP "\(bu" 4
941.IP "* Use it by including <event.h>, as usual." 4 3856Use it by including <event.h>, as usual.
942.IX Item "Use it by including <event.h>, as usual." 3857.IP "\(bu" 4
943.PD 0 3858The following members are fully supported: ev_base, ev_callback,
944.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 3859ev_arg, ev_fd, ev_res, ev_events.
945.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 3860.IP "\(bu" 4
946.IP "* Avoid using ev_flags and the EVLIST_*\-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private \s-1API\s0)." 4 3861Avoid using ev_flags and the EVLIST_*\-macros, while it is
947.IX Item "Avoid using ev_flags and the EVLIST_*-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private API)." 3862maintained by libev, it does not work exactly the same way as in libevent (consider
948.IP "* Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4 3863it a private \s-1API\s0).
949.IX Item "Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 3864.IP "\(bu" 4
3865Priorities are not currently supported. Initialising priorities
3866will fail and all watchers will have the same priority, even though there
3867is an ev_pri field.
3868.IP "\(bu" 4
3869In libevent, the last base created gets the signals, in libev, the
3870base that registered the signal gets the signals.
3871.IP "\(bu" 4
950.IP "* Other members are not supported." 4 3872Other members are not supported.
951.IX Item "Other members are not supported." 3873.IP "\(bu" 4
952.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 3874The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
953.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 3875to use the libev header file and library.
954.PD
955.SH "\*(C+ SUPPORT" 3876.SH "\*(C+ SUPPORT"
956.IX Header " SUPPORT" 3877.IX Header " SUPPORT"
957\&\s-1TBD\s0. 3878Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
3879you to use some convenience methods to start/stop watchers and also change
3880the callback model to a model using method callbacks on objects.
3881.PP
3882To use it,
3883.PP
3884.Vb 1
3885\& #include <ev++.h>
3886.Ve
3887.PP
3888This automatically includes \fIev.h\fR and puts all of its definitions (many
3889of them macros) into the global namespace. All \*(C+ specific things are
3890put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
3891options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
3892.PP
3893Care has been taken to keep the overhead low. The only data member the \*(C+
3894classes add (compared to plain C\-style watchers) is the event loop pointer
3895that the watcher is associated with (or no additional members at all if
3896you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
3897.PP
3898Currently, functions, static and non-static member functions and classes
3899with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
3900to add as long as they only need one additional pointer for context. If
3901you need support for other types of functors please contact the author
3902(preferably after implementing it).
3903.PP
3904Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
3905.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
3906.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
3907.IX Item "ev::READ, ev::WRITE etc."
3908These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
3909macros from \fIev.h\fR.
3910.ie n .IP """ev::tstamp"", ""ev::now""" 4
3911.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
3912.IX Item "ev::tstamp, ev::now"
3913Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
3914.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
3915.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
3916.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
3917For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
3918the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
3919which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
3920defines by many implementations.
3921.Sp
3922All of those classes have these methods:
3923.RS 4
3924.IP "ev::TYPE::TYPE ()" 4
3925.IX Item "ev::TYPE::TYPE ()"
3926.PD 0
3927.IP "ev::TYPE::TYPE (loop)" 4
3928.IX Item "ev::TYPE::TYPE (loop)"
3929.IP "ev::TYPE::~TYPE" 4
3930.IX Item "ev::TYPE::~TYPE"
3931.PD
3932The constructor (optionally) takes an event loop to associate the watcher
3933with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
3934.Sp
3935The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
3936\&\f(CW\*(C`set\*(C'\fR method before starting it.
3937.Sp
3938It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
3939method to set a callback before you can start the watcher.
3940.Sp
3941(The reason why you have to use a method is a limitation in \*(C+ which does
3942not allow explicit template arguments for constructors).
3943.Sp
3944The destructor automatically stops the watcher if it is active.
3945.IP "w\->set<class, &class::method> (object *)" 4
3946.IX Item "w->set<class, &class::method> (object *)"
3947This method sets the callback method to call. The method has to have a
3948signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3949first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3950parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3951.Sp
3952This method synthesizes efficient thunking code to call your method from
3953the C callback that libev requires. If your compiler can inline your
3954callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3955your compiler is good :), then the method will be fully inlined into the
3956thunking function, making it as fast as a direct C callback.
3957.Sp
3958Example: simple class declaration and watcher initialisation
3959.Sp
3960.Vb 4
3961\& struct myclass
3962\& {
3963\& void io_cb (ev::io &w, int revents) { }
3964\& }
3965\&
3966\& myclass obj;
3967\& ev::io iow;
3968\& iow.set <myclass, &myclass::io_cb> (&obj);
3969.Ve
3970.IP "w\->set (object *)" 4
3971.IX Item "w->set (object *)"
3972This is a variation of a method callback \- leaving out the method to call
3973will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
3974functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
3975the time. Incidentally, you can then also leave out the template argument
3976list.
3977.Sp
3978The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
3979int revents)\*(C'\fR.
3980.Sp
3981See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3982.Sp
3983Example: use a functor object as callback.
3984.Sp
3985.Vb 7
3986\& struct myfunctor
3987\& {
3988\& void operator() (ev::io &w, int revents)
3989\& {
3990\& ...
3991\& }
3992\& }
3993\&
3994\& myfunctor f;
3995\&
3996\& ev::io w;
3997\& w.set (&f);
3998.Ve
3999.IP "w\->set<function> (void *data = 0)" 4
4000.IX Item "w->set<function> (void *data = 0)"
4001Also sets a callback, but uses a static method or plain function as
4002callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4003\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4004.Sp
4005The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4006.Sp
4007See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4008.Sp
4009Example: Use a plain function as callback.
4010.Sp
4011.Vb 2
4012\& static void io_cb (ev::io &w, int revents) { }
4013\& iow.set <io_cb> ();
4014.Ve
4015.IP "w\->set (loop)" 4
4016.IX Item "w->set (loop)"
4017Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
4018do this when the watcher is inactive (and not pending either).
4019.IP "w\->set ([arguments])" 4
4020.IX Item "w->set ([arguments])"
4021Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Either this
4022method or a suitable start method must be called at least once. Unlike the
4023C counterpart, an active watcher gets automatically stopped and restarted
4024when reconfiguring it with this method.
4025.IP "w\->start ()" 4
4026.IX Item "w->start ()"
4027Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
4028constructor already stores the event loop.
4029.IP "w\->start ([arguments])" 4
4030.IX Item "w->start ([arguments])"
4031Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4032convenient to wrap them in one call. Uses the same type of arguments as
4033the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
4034.IP "w\->stop ()" 4
4035.IX Item "w->stop ()"
4036Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
4037.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
4038.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
4039.IX Item "w->again () (ev::timer, ev::periodic only)"
4040For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
4041\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
4042.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
4043.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
4044.IX Item "w->sweep () (ev::embed only)"
4045Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4046.ie n .IP "w\->update () (""ev::stat"" only)" 4
4047.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4048.IX Item "w->update () (ev::stat only)"
4049Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
4050.RE
4051.RS 4
4052.RE
4053.PP
4054Example: Define a class with two I/O and idle watchers, start the I/O
4055watchers in the constructor.
4056.PP
4057.Vb 5
4058\& class myclass
4059\& {
4060\& ev::io io ; void io_cb (ev::io &w, int revents);
4061\& ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
4062\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4063\&
4064\& myclass (int fd)
4065\& {
4066\& io .set <myclass, &myclass::io_cb > (this);
4067\& io2 .set <myclass, &myclass::io2_cb > (this);
4068\& idle.set <myclass, &myclass::idle_cb> (this);
4069\&
4070\& io.set (fd, ev::WRITE); // configure the watcher
4071\& io.start (); // start it whenever convenient
4072\&
4073\& io2.start (fd, ev::READ); // set + start in one call
4074\& }
4075\& };
4076.Ve
4077.SH "OTHER LANGUAGE BINDINGS"
4078.IX Header "OTHER LANGUAGE BINDINGS"
4079Libev does not offer other language bindings itself, but bindings for a
4080number of languages exist in the form of third-party packages. If you know
4081any interesting language binding in addition to the ones listed here, drop
4082me a note.
4083.IP "Perl" 4
4084.IX Item "Perl"
4085The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4086libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4087there are additional modules that implement libev-compatible interfaces
4088to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4089\&\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
4090and \f(CW\*(C`EV::Glib\*(C'\fR).
4091.Sp
4092It can be found and installed via \s-1CPAN\s0, its homepage is at
4093<http://software.schmorp.de/pkg/EV>.
4094.IP "Python" 4
4095.IX Item "Python"
4096Python bindings can be found at <http://code.google.com/p/pyev/>. It
4097seems to be quite complete and well-documented.
4098.IP "Ruby" 4
4099.IX Item "Ruby"
4100Tony Arcieri has written a ruby extension that offers access to a subset
4101of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4102more on top of it. It can be found via gem servers. Its homepage is at
4103<http://rev.rubyforge.org/>.
4104.Sp
4105Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4106makes rev work even on mingw.
4107.IP "Haskell" 4
4108.IX Item "Haskell"
4109A haskell binding to libev is available at
4110<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4111.IP "D" 4
4112.IX Item "D"
4113Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4114be found at <http://proj.llucax.com.ar/wiki/evd>.
4115.IP "Ocaml" 4
4116.IX Item "Ocaml"
4117Erkki Seppala has written Ocaml bindings for libev, to be found at
4118<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4119.IP "Lua" 4
4120.IX Item "Lua"
4121Brian Maher has written a partial interface to libev for lua (at the
4122time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4123<http://github.com/brimworks/lua\-ev>.
4124.SH "MACRO MAGIC"
4125.IX Header "MACRO MAGIC"
4126Libev can be compiled with a variety of options, the most fundamental
4127of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4128functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
4129.PP
4130To make it easier to write programs that cope with either variant, the
4131following macros are defined:
4132.ie n .IP """EV_A"", ""EV_A_""" 4
4133.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4134.IX Item "EV_A, EV_A_"
4135This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4136loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4137\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4138.Sp
4139.Vb 3
4140\& ev_unref (EV_A);
4141\& ev_timer_add (EV_A_ watcher);
4142\& ev_run (EV_A_ 0);
4143.Ve
4144.Sp
4145It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4146which is often provided by the following macro.
4147.ie n .IP """EV_P"", ""EV_P_""" 4
4148.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4149.IX Item "EV_P, EV_P_"
4150This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4151loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4152\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4153.Sp
4154.Vb 2
4155\& // this is how ev_unref is being declared
4156\& static void ev_unref (EV_P);
4157\&
4158\& // this is how you can declare your typical callback
4159\& static void cb (EV_P_ ev_timer *w, int revents)
4160.Ve
4161.Sp
4162It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4163suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4164.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4165.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4166.IX Item "EV_DEFAULT, EV_DEFAULT_"
4167Similar to the other two macros, this gives you the value of the default
4168loop, if multiple loops are supported (\*(L"ev loop default\*(R").
4169.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4170.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4171.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4172Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4173default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4174is undefined when the default loop has not been initialised by a previous
4175execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4176.Sp
4177It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4178watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
4179.PP
4180Example: Declare and initialise a check watcher, utilising the above
4181macros so it will work regardless of whether multiple loops are supported
4182or not.
4183.PP
4184.Vb 5
4185\& static void
4186\& check_cb (EV_P_ ev_timer *w, int revents)
4187\& {
4188\& ev_check_stop (EV_A_ w);
4189\& }
4190\&
4191\& ev_check check;
4192\& ev_check_init (&check, check_cb);
4193\& ev_check_start (EV_DEFAULT_ &check);
4194\& ev_run (EV_DEFAULT_ 0);
4195.Ve
4196.SH "EMBEDDING"
4197.IX Header "EMBEDDING"
4198Libev can (and often is) directly embedded into host
4199applications. Examples of applications that embed it include the Deliantra
4200Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
4201and rxvt-unicode.
4202.PP
4203The goal is to enable you to just copy the necessary files into your
4204source directory without having to change even a single line in them, so
4205you can easily upgrade by simply copying (or having a checked-out copy of
4206libev somewhere in your source tree).
4207.SS "\s-1FILESETS\s0"
4208.IX Subsection "FILESETS"
4209Depending on what features you need you need to include one or more sets of files
4210in your application.
4211.PP
4212\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
4213.IX Subsection "CORE EVENT LOOP"
4214.PP
4215To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
4216configuration (no autoconf):
4217.PP
4218.Vb 2
4219\& #define EV_STANDALONE 1
4220\& #include "ev.c"
4221.Ve
4222.PP
4223This will automatically include \fIev.h\fR, too, and should be done in a
4224single C source file only to provide the function implementations. To use
4225it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
4226done by writing a wrapper around \fIev.h\fR that you can include instead and
4227where you can put other configuration options):
4228.PP
4229.Vb 2
4230\& #define EV_STANDALONE 1
4231\& #include "ev.h"
4232.Ve
4233.PP
4234Both header files and implementation files can be compiled with a \*(C+
4235compiler (at least, that's a stated goal, and breakage will be treated
4236as a bug).
4237.PP
4238You need the following files in your source tree, or in a directory
4239in your include path (e.g. in libev/ when using \-Ilibev):
4240.PP
4241.Vb 4
4242\& ev.h
4243\& ev.c
4244\& ev_vars.h
4245\& ev_wrap.h
4246\&
4247\& ev_win32.c required on win32 platforms only
4248\&
4249\& ev_select.c only when select backend is enabled (which is enabled by default)
4250\& ev_poll.c only when poll backend is enabled (disabled by default)
4251\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
4252\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
4253\& ev_port.c only when the solaris port backend is enabled (disabled by default)
4254.Ve
4255.PP
4256\&\fIev.c\fR includes the backend files directly when enabled, so you only need
4257to compile this single file.
4258.PP
4259\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
4260.IX Subsection "LIBEVENT COMPATIBILITY API"
4261.PP
4262To include the libevent compatibility \s-1API\s0, also include:
4263.PP
4264.Vb 1
4265\& #include "event.c"
4266.Ve
4267.PP
4268in the file including \fIev.c\fR, and:
4269.PP
4270.Vb 1
4271\& #include "event.h"
4272.Ve
4273.PP
4274in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
4275.PP
4276You need the following additional files for this:
4277.PP
4278.Vb 2
4279\& event.h
4280\& event.c
4281.Ve
4282.PP
4283\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
4284.IX Subsection "AUTOCONF SUPPORT"
4285.PP
4286Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
4287whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
4288\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
4289include \fIconfig.h\fR and configure itself accordingly.
4290.PP
4291For this of course you need the m4 file:
4292.PP
4293.Vb 1
4294\& libev.m4
4295.Ve
4296.SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
4297.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
4298Libev can be configured via a variety of preprocessor symbols you have to
4299define before including (or compiling) any of its files. The default in
4300the absence of autoconf is documented for every option.
4301.PP
4302Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
4303values when compiling libev vs. including \fIev.h\fR, so it is permissible
4304to redefine them before including \fIev.h\fR without breaking compatibility
4305to a compiled library. All other symbols change the \s-1ABI\s0, which means all
4306users of libev and the libev code itself must be compiled with compatible
4307settings.
4308.IP "\s-1EV_COMPAT3\s0 (h)" 4
4309.IX Item "EV_COMPAT3 (h)"
4310Backwards compatibility is a major concern for libev. This is why this
4311release of libev comes with wrappers for the functions and symbols that
4312have been renamed between libev version 3 and 4.
4313.Sp
4314You can disable these wrappers (to test compatibility with future
4315versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4316sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4317from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4318typedef in that case.
4319.Sp
4320In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4321and in some even more future version the compatibility code will be
4322removed completely.
4323.IP "\s-1EV_STANDALONE\s0 (h)" 4
4324.IX Item "EV_STANDALONE (h)"
4325Must always be \f(CW1\fR if you do not use autoconf configuration, which
4326keeps libev from including \fIconfig.h\fR, and it also defines dummy
4327implementations for some libevent functions (such as logging, which is not
4328supported). It will also not define any of the structs usually found in
4329\&\fIevent.h\fR that are not directly supported by the libev core alone.
4330.Sp
4331In standalone mode, libev will still try to automatically deduce the
4332configuration, but has to be more conservative.
4333.IP "\s-1EV_USE_MONOTONIC\s0" 4
4334.IX Item "EV_USE_MONOTONIC"
4335If defined to be \f(CW1\fR, libev will try to detect the availability of the
4336monotonic clock option at both compile time and runtime. Otherwise no
4337use of the monotonic clock option will be attempted. If you enable this,
4338you usually have to link against librt or something similar. Enabling it
4339when the functionality isn't available is safe, though, although you have
4340to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
4341function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4342.IP "\s-1EV_USE_REALTIME\s0" 4
4343.IX Item "EV_USE_REALTIME"
4344If defined to be \f(CW1\fR, libev will try to detect the availability of the
4345real-time clock option at compile time (and assume its availability
4346at runtime if successful). Otherwise no use of the real-time clock
4347option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
4348by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
4349correctness. See the note about libraries in the description of
4350\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4351\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4352.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4353.IX Item "EV_USE_CLOCK_SYSCALL"
4354If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4355of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4356exists 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
4357unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4358programs needlessly. Using a direct syscall is slightly slower (in
4359theory), because no optimised vdso implementation can be used, but avoids
4360the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4361higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4362.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4363.IX Item "EV_USE_NANOSLEEP"
4364If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4365and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4366.IP "\s-1EV_USE_EVENTFD\s0" 4
4367.IX Item "EV_USE_EVENTFD"
4368If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4369available and will probe for kernel support at runtime. This will improve
4370\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4371If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
43722.7 or newer, otherwise disabled.
4373.IP "\s-1EV_USE_SELECT\s0" 4
4374.IX Item "EV_USE_SELECT"
4375If undefined or defined to be \f(CW1\fR, libev will compile in support for the
4376\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
4377other method takes over, select will be it. Otherwise the select backend
4378will not be compiled in.
4379.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
4380.IX Item "EV_SELECT_USE_FD_SET"
4381If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
4382structure. This is useful if libev doesn't compile due to a missing
4383\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
4384on exotic systems. This usually limits the range of file descriptors to
4385some low limit such as 1024 or might have other limitations (winsocket
4386only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
4387configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
4388.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
4389.IX Item "EV_SELECT_IS_WINSOCKET"
4390When defined to \f(CW1\fR, the select backend will assume that
4391select/socket/connect etc. don't understand file descriptors but
4392wants osf handles on win32 (this is the case when the select to
4393be used is the winsock select). This means that it will call
4394\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
4395it is assumed that all these functions actually work on fds, even
4396on win32. Should not be defined on non\-win32 platforms.
4397.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4398.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4399If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4400file descriptors to socket handles. When not defining this symbol (the
4401default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4402correct. In some cases, programs use their own file descriptor management,
4403in which case they can provide this function to map fds to socket handles.
4404.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4405.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4406If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4407using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4408their own fd to handle mapping, overwriting this function makes it easier
4409to do so. This can be done by defining this macro to an appropriate value.
4410.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4411.IX Item "EV_WIN32_CLOSE_FD(fd)"
4412If programs implement their own fd to handle mapping on win32, then this
4413macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4414file descriptors again. Note that the replacement function has to close
4415the underlying \s-1OS\s0 handle.
4416.IP "\s-1EV_USE_POLL\s0" 4
4417.IX Item "EV_USE_POLL"
4418If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
4419backend. Otherwise it will be enabled on non\-win32 platforms. It
4420takes precedence over select.
4421.IP "\s-1EV_USE_EPOLL\s0" 4
4422.IX Item "EV_USE_EPOLL"
4423If defined to be \f(CW1\fR, libev will compile in support for the Linux
4424\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
4425otherwise another method will be used as fallback. This is the preferred
4426backend for GNU/Linux systems. If undefined, it will be enabled if the
4427headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4428.IP "\s-1EV_USE_KQUEUE\s0" 4
4429.IX Item "EV_USE_KQUEUE"
4430If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
4431\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
4432otherwise another method will be used as fallback. This is the preferred
4433backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
4434supports some types of fds correctly (the only platform we found that
4435supports ptys for example was NetBSD), so kqueue might be compiled in, but
4436not be used unless explicitly requested. The best way to use it is to find
4437out whether kqueue supports your type of fd properly and use an embedded
4438kqueue loop.
4439.IP "\s-1EV_USE_PORT\s0" 4
4440.IX Item "EV_USE_PORT"
4441If defined to be \f(CW1\fR, libev will compile in support for the Solaris
444210 port style backend. Its availability will be detected at runtime,
4443otherwise another method will be used as fallback. This is the preferred
4444backend for Solaris 10 systems.
4445.IP "\s-1EV_USE_DEVPOLL\s0" 4
4446.IX Item "EV_USE_DEVPOLL"
4447Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4448.IP "\s-1EV_USE_INOTIFY\s0" 4
4449.IX Item "EV_USE_INOTIFY"
4450If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4451interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4452be detected at runtime. If undefined, it will be enabled if the headers
4453indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4454.IP "\s-1EV_ATOMIC_T\s0" 4
4455.IX Item "EV_ATOMIC_T"
4456Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4457access is atomic with respect to other threads or signal contexts. No such
4458type is easily found in the C language, so you can provide your own type
4459that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
4460as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
4461.Sp
4462In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4463(from \fIsignal.h\fR), which is usually good enough on most platforms.
4464.IP "\s-1EV_H\s0 (h)" 4
4465.IX Item "EV_H (h)"
4466The name of the \fIev.h\fR header file used to include it. The default if
4467undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
4468used to virtually rename the \fIev.h\fR header file in case of conflicts.
4469.IP "\s-1EV_CONFIG_H\s0 (h)" 4
4470.IX Item "EV_CONFIG_H (h)"
4471If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
4472\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
4473\&\f(CW\*(C`EV_H\*(C'\fR, above.
4474.IP "\s-1EV_EVENT_H\s0 (h)" 4
4475.IX Item "EV_EVENT_H (h)"
4476Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
4477of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
4478.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
4479.IX Item "EV_PROTOTYPES (h)"
4480If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
4481prototypes, but still define all the structs and other symbols. This is
4482occasionally useful if you want to provide your own wrapper functions
4483around libev functions.
4484.IP "\s-1EV_MULTIPLICITY\s0" 4
4485.IX Item "EV_MULTIPLICITY"
4486If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
4487will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
4488additional independent event loops. Otherwise there will be no support
4489for multiple event loops and there is no first event loop pointer
4490argument. Instead, all functions act on the single default loop.
4491.IP "\s-1EV_MINPRI\s0" 4
4492.IX Item "EV_MINPRI"
4493.PD 0
4494.IP "\s-1EV_MAXPRI\s0" 4
4495.IX Item "EV_MAXPRI"
4496.PD
4497The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4498\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4499provide for more priorities by overriding those symbols (usually defined
4500to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4501.Sp
4502When doing priority-based operations, libev usually has to linearly search
4503all the priorities, so having many of them (hundreds) uses a lot of space
4504and time, so using the defaults of five priorities (\-2 .. +2) is usually
4505fine.
4506.Sp
4507If your embedding application does not need any priorities, defining these
4508both to \f(CW0\fR will save some memory and \s-1CPU\s0.
4509.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
4510.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."
4511If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4512the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4513is not. Disabling watcher types mainly saves code size.
4514.IP "\s-1EV_FEATURES\s0" 4
4515.IX Item "EV_FEATURES"
4516If you need to shave off some kilobytes of code at the expense of some
4517speed (but with the full \s-1API\s0), you can define this symbol to request
4518certain subsets of functionality. The default is to enable all features
4519that can be enabled on the platform.
4520.Sp
4521A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4522with some broad features you want) and then selectively re-enable
4523additional parts you want, for example if you want everything minimal,
4524but multiple event loop support, async and child watchers and the poll
4525backend, use this:
4526.Sp
4527.Vb 5
4528\& #define EV_FEATURES 0
4529\& #define EV_MULTIPLICITY 1
4530\& #define EV_USE_POLL 1
4531\& #define EV_CHILD_ENABLE 1
4532\& #define EV_ASYNC_ENABLE 1
4533.Ve
4534.Sp
4535The actual value is a bitset, it can be a combination of the following
4536values:
4537.RS 4
4538.ie n .IP "1 \- faster/larger code" 4
4539.el .IP "\f(CW1\fR \- faster/larger code" 4
4540.IX Item "1 - faster/larger code"
4541Use larger code to speed up some operations.
4542.Sp
4543Currently this is used to override some inlining decisions (enlarging the
4544code size by roughly 30% on amd64).
4545.Sp
4546When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4547gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4548assertions.
4549.ie n .IP "2 \- faster/larger data structures" 4
4550.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4551.IX Item "2 - faster/larger data structures"
4552Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4553hash table sizes and so on. This will usually further increase code size
4554and can additionally have an effect on the size of data structures at
4555runtime.
4556.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4557.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4558.IX Item "4 - full API configuration"
4559This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4560enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4561.ie n .IP "8 \- full \s-1API\s0" 4
4562.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4563.IX Item "8 - full API"
4564This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4565details on which parts of the \s-1API\s0 are still available without this
4566feature, and do not complain if this subset changes over time.
4567.ie n .IP "16 \- enable all optional watcher types" 4
4568.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4569.IX Item "16 - enable all optional watcher types"
4570Enables all optional watcher types. If you want to selectively enable
4571only some watcher types other than I/O and timers (e.g. prepare,
4572embed, async, child...) you can enable them manually by defining
4573\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4574.ie n .IP "32 \- enable all backends" 4
4575.el .IP "\f(CW32\fR \- enable all backends" 4
4576.IX Item "32 - enable all backends"
4577This enables all backends \- without this feature, you need to enable at
4578least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4579.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4580.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4581.IX Item "64 - enable OS-specific helper APIs"
4582Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4583default.
4584.RE
4585.RS 4
4586.Sp
4587Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4588reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4589code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4590watchers, timers and monotonic clock support.
4591.Sp
4592With an intelligent-enough linker (gcc+binutils are intelligent enough
4593when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4594your program might be left out as well \- a binary starting a timer and an
4595I/O watcher then might come out at only 5Kb.
4596.RE
4597.IP "\s-1EV_AVOID_STDIO\s0" 4
4598.IX Item "EV_AVOID_STDIO"
4599If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4600functions (printf, scanf, perror etc.). This will increase the code size
4601somewhat, but if your program doesn't otherwise depend on stdio and your
4602libc allows it, this avoids linking in the stdio library which is quite
4603big.
4604.Sp
4605Note that error messages might become less precise when this option is
4606enabled.
4607.IP "\s-1EV_NSIG\s0" 4
4608.IX Item "EV_NSIG"
4609The highest supported signal number, +1 (or, the number of
4610signals): Normally, libev tries to deduce the maximum number of signals
4611automatically, but sometimes this fails, in which case it can be
4612specified. Also, using a lower number than detected (\f(CW32\fR should be
4613good for about any system in existence) can save some memory, as libev
4614statically allocates some 12\-24 bytes per signal number.
4615.IP "\s-1EV_PID_HASHSIZE\s0" 4
4616.IX Item "EV_PID_HASHSIZE"
4617\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
4618pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
4619usually more than enough. If you need to manage thousands of children you
4620might want to increase this value (\fImust\fR be a power of two).
4621.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
4622.IX Item "EV_INOTIFY_HASHSIZE"
4623\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
4624inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
4625disabled), usually more than enough. If you need to manage thousands of
4626\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
4627power of two).
4628.IP "\s-1EV_USE_4HEAP\s0" 4
4629.IX Item "EV_USE_4HEAP"
4630Heaps are not very cache-efficient. To improve the cache-efficiency of the
4631timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4632to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4633faster performance with many (thousands) of watchers.
4634.Sp
4635The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4636will be \f(CW0\fR.
4637.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4638.IX Item "EV_HEAP_CACHE_AT"
4639Heaps are not very cache-efficient. To improve the cache-efficiency of the
4640timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4641the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4642which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4643but avoids random read accesses on heap changes. This improves performance
4644noticeably with many (hundreds) of watchers.
4645.Sp
4646The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4647will be \f(CW0\fR.
4648.IP "\s-1EV_VERIFY\s0" 4
4649.IX Item "EV_VERIFY"
4650Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4651be done: If set to \f(CW0\fR, no internal verification code will be compiled
4652in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4653called. If set to \f(CW2\fR, then the internal verification code will be
4654called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4655verification code will be called very frequently, which will slow down
4656libev considerably.
4657.Sp
4658The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4659will be \f(CW0\fR.
4660.IP "\s-1EV_COMMON\s0" 4
4661.IX Item "EV_COMMON"
4662By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
4663this macro to something else you can include more and other types of
4664members. You have to define it each time you include one of the files,
4665though, and it must be identical each time.
4666.Sp
4667For example, the perl \s-1EV\s0 module uses something like this:
4668.Sp
4669.Vb 3
4670\& #define EV_COMMON \e
4671\& SV *self; /* contains this struct */ \e
4672\& SV *cb_sv, *fh /* note no trailing ";" */
4673.Ve
4674.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
4675.IX Item "EV_CB_DECLARE (type)"
4676.PD 0
4677.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
4678.IX Item "EV_CB_INVOKE (watcher, revents)"
4679.IP "ev_set_cb (ev, cb)" 4
4680.IX Item "ev_set_cb (ev, cb)"
4681.PD
4682Can be used to change the callback member declaration in each watcher,
4683and the way callbacks are invoked and set. Must expand to a struct member
4684definition and a statement, respectively. See the \fIev.h\fR header file for
4685their default definitions. One possible use for overriding these is to
4686avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
4687method calls instead of plain function calls in \*(C+.
4688.SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4689.IX Subsection "EXPORTED API SYMBOLS"
4690If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4691exported symbols, you can use the provided \fISymbol.*\fR files which list
4692all public symbols, one per line:
4693.PP
4694.Vb 2
4695\& Symbols.ev for libev proper
4696\& Symbols.event for the libevent emulation
4697.Ve
4698.PP
4699This can also be used to rename all public symbols to avoid clashes with
4700multiple versions of libev linked together (which is obviously bad in
4701itself, but sometimes it is inconvenient to avoid this).
4702.PP
4703A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
4704include before including \fIev.h\fR:
4705.PP
4706.Vb 1
4707\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
4708.Ve
4709.PP
4710This would create a file \fIwrap.h\fR which essentially looks like this:
4711.PP
4712.Vb 4
4713\& #define ev_backend myprefix_ev_backend
4714\& #define ev_check_start myprefix_ev_check_start
4715\& #define ev_check_stop myprefix_ev_check_stop
4716\& ...
4717.Ve
4718.SS "\s-1EXAMPLES\s0"
4719.IX Subsection "EXAMPLES"
4720For a real-world example of a program the includes libev
4721verbatim, you can have a look at the \s-1EV\s0 perl module
4722(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
4723the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
4724interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
4725will be compiled. It is pretty complex because it provides its own header
4726file.
4727.PP
4728The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
4729that everybody includes and which overrides some configure choices:
4730.PP
4731.Vb 8
4732\& #define EV_FEATURES 8
4733\& #define EV_USE_SELECT 1
4734\& #define EV_PREPARE_ENABLE 1
4735\& #define EV_IDLE_ENABLE 1
4736\& #define EV_SIGNAL_ENABLE 1
4737\& #define EV_CHILD_ENABLE 1
4738\& #define EV_USE_STDEXCEPT 0
4739\& #define EV_CONFIG_H <config.h>
4740\&
4741\& #include "ev++.h"
4742.Ve
4743.PP
4744And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
4745.PP
4746.Vb 2
4747\& #include "ev_cpp.h"
4748\& #include "ev.c"
4749.Ve
4750.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4751.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4752.SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
4753.IX Subsection "THREADS AND COROUTINES"
4754\fI\s-1THREADS\s0\fR
4755.IX Subsection "THREADS"
4756.PP
4757All libev functions are reentrant and thread-safe unless explicitly
4758documented otherwise, but libev implements no locking itself. This means
4759that you can use as many loops as you want in parallel, as long as there
4760are no concurrent calls into any libev function with the same loop
4761parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
4762of course): libev guarantees that different event loops share no data
4763structures that need any locking.
4764.PP
4765Or to put it differently: calls with different loop parameters can be done
4766concurrently from multiple threads, calls with the same loop parameter
4767must be done serially (but can be done from different threads, as long as
4768only one thread ever is inside a call at any point in time, e.g. by using
4769a mutex per loop).
4770.PP
4771Specifically to support threads (and signal handlers), libev implements
4772so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
4773concurrency on the same event loop, namely waking it up \*(L"from the
4774outside\*(R".
4775.PP
4776If you want to know which design (one loop, locking, or multiple loops
4777without or something else still) is best for your problem, then I cannot
4778help you, but here is some generic advice:
4779.IP "\(bu" 4
4780most applications have a main thread: use the default libev loop
4781in that thread, or create a separate thread running only the default loop.
4782.Sp
4783This helps integrating other libraries or software modules that use libev
4784themselves and don't care/know about threading.
4785.IP "\(bu" 4
4786one loop per thread is usually a good model.
4787.Sp
4788Doing this is almost never wrong, sometimes a better-performance model
4789exists, but it is always a good start.
4790.IP "\(bu" 4
4791other models exist, such as the leader/follower pattern, where one
4792loop is handed through multiple threads in a kind of round-robin fashion.
4793.Sp
4794Choosing a model is hard \- look around, learn, know that usually you can do
4795better than you currently do :\-)
4796.IP "\(bu" 4
4797often you need to talk to some other thread which blocks in the
4798event loop.
4799.Sp
4800\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
4801(or from signal contexts...).
4802.Sp
4803An example use would be to communicate signals or other events that only
4804work in the default loop by registering the signal watcher with the
4805default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
4806watcher callback into the event loop interested in the signal.
4807.PP
4808See also \*(L"\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0\*(R".
4809.PP
4810\fI\s-1COROUTINES\s0\fR
4811.IX Subsection "COROUTINES"
4812.PP
4813Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
4814libev fully supports nesting calls to its functions from different
4815coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
4816different coroutines, and switch freely between both coroutines running
4817the loop, as long as you don't confuse yourself). The only exception is
4818that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
4819.PP
4820Care has been taken to ensure that libev does not keep local state inside
4821\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
4822they do not call any callbacks.
4823.SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
4824.IX Subsection "COMPILER WARNINGS"
4825Depending on your compiler and compiler settings, you might get no or a
4826lot of warnings when compiling libev code. Some people are apparently
4827scared by this.
4828.PP
4829However, these are unavoidable for many reasons. For one, each compiler
4830has different warnings, and each user has different tastes regarding
4831warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
4832targeting a specific compiler and compiler-version.
4833.PP
4834Another reason is that some compiler warnings require elaborate
4835workarounds, or other changes to the code that make it less clear and less
4836maintainable.
4837.PP
4838And of course, some compiler warnings are just plain stupid, or simply
4839wrong (because they don't actually warn about the condition their message
4840seems to warn about). For example, certain older gcc versions had some
4841warnings that resulted in an extreme number of false positives. These have
4842been fixed, but some people still insist on making code warn-free with
4843such buggy versions.
4844.PP
4845While libev is written to generate as few warnings as possible,
4846\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
4847with any compiler warnings enabled unless you are prepared to cope with
4848them (e.g. by ignoring them). Remember that warnings are just that:
4849warnings, not errors, or proof of bugs.
4850.SS "\s-1VALGRIND\s0"
4851.IX Subsection "VALGRIND"
4852Valgrind has a special section here because it is a popular tool that is
4853highly useful. Unfortunately, valgrind reports are very hard to interpret.
4854.PP
4855If you think you found a bug (memory leak, uninitialised data access etc.)
4856in libev, then check twice: If valgrind reports something like:
4857.PP
4858.Vb 3
4859\& ==2274== definitely lost: 0 bytes in 0 blocks.
4860\& ==2274== possibly lost: 0 bytes in 0 blocks.
4861\& ==2274== still reachable: 256 bytes in 1 blocks.
4862.Ve
4863.PP
4864Then there is no memory leak, just as memory accounted to global variables
4865is not a memleak \- the memory is still being referenced, and didn't leak.
4866.PP
4867Similarly, under some circumstances, valgrind might report kernel bugs
4868as if it were a bug in libev (e.g. in realloc or in the poll backend,
4869although an acceptable workaround has been found here), or it might be
4870confused.
4871.PP
4872Keep in mind that valgrind is a very good tool, but only a tool. Don't
4873make it into some kind of religion.
4874.PP
4875If you are unsure about something, feel free to contact the mailing list
4876with the full valgrind report and an explanation on why you think this
4877is a bug in libev (best check the archives, too :). However, don't be
4878annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
4879of learning how to interpret valgrind properly.
4880.PP
4881If you need, for some reason, empty reports from valgrind for your project
4882I suggest using suppression lists.
4883.SH "PORTABILITY NOTES"
4884.IX Header "PORTABILITY NOTES"
4885.SS "\s-1GNU/LINUX\s0 32 \s-1BIT\s0 \s-1LIMITATIONS\s0"
4886.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
4887GNU/Linux is the only common platform that supports 64 bit file/large file
4888interfaces but \fIdisables\fR them by default.
4889.PP
4890That means that libev compiled in the default environment doesn't support
4891files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
4892.PP
4893Unfortunately, many programs try to work around this GNU/Linux issue
4894by enabling the large file \s-1API\s0, which makes them incompatible with the
4895standard libev compiled for their system.
4896.PP
4897Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
4898suddenly make it incompatible to the default compile time environment,
4899i.e. all programs not using special compile switches.
4900.SS "\s-1OS/X\s0 \s-1AND\s0 \s-1DARWIN\s0 \s-1BUGS\s0"
4901.IX Subsection "OS/X AND DARWIN BUGS"
4902The whole thing is a bug if you ask me \- basically any system interface
4903you touch is broken, whether it is locales, poll, kqueue or even the
4904OpenGL drivers.
4905.PP
4906\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
4907.IX Subsection "kqueue is buggy"
4908.PP
4909The kqueue syscall is broken in all known versions \- most versions support
4910only sockets, many support pipes.
4911.PP
4912Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
4913rotten platform, but of course you can still ask for it when creating a
4914loop \- embedding a socket-only kqueue loop into a select-based one is
4915probably going to work well.
4916.PP
4917\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
4918.IX Subsection "poll is buggy"
4919.PP
4920Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
4921implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
4922release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
4923.PP
4924Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
4925this rotten platform, but of course you can still ask for it when creating
4926a loop.
4927.PP
4928\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
4929.IX Subsection "select is buggy"
4930.PP
4931All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
4932one up as well: On \s-1OS/X\s0, \f(CW\*(C`select\*(C'\fR actively limits the number of file
4933descriptors you can pass in to 1024 \- your program suddenly crashes when
4934you use more.
4935.PP
4936There is an undocumented \*(L"workaround\*(R" for this \- defining
4937\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
4938work on \s-1OS/X\s0.
4939.SS "\s-1SOLARIS\s0 \s-1PROBLEMS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4940.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
4941\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
4942.IX Subsection "errno reentrancy"
4943.PP
4944The default compile environment on Solaris is unfortunately so
4945thread-unsafe that you can't even use components/libraries compiled
4946without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
4947defined by default. A valid, if stupid, implementation choice.
4948.PP
4949If you want to use libev in threaded environments you have to make sure
4950it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
4951.PP
4952\fIEvent port backend\fR
4953.IX Subsection "Event port backend"
4954.PP
4955The scalable event interface for Solaris is called \*(L"event
4956ports\*(R". Unfortunately, this mechanism is very buggy in all major
4957releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
4958a large number of spurious wakeups, make sure you have all the relevant
4959and latest kernel patches applied. No, I don't know which ones, but there
4960are multiple ones to apply, and afterwards, event ports actually work
4961great.
4962.PP
4963If you can't get it to work, you can try running the program by setting
4964the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
4965\&\f(CW\*(C`select\*(C'\fR backends.
4966.SS "\s-1AIX\s0 \s-1POLL\s0 \s-1BUG\s0"
4967.IX Subsection "AIX POLL BUG"
4968\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
4969this by trying to avoid the poll backend altogether (i.e. it's not even
4970compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
4971with large bitsets on \s-1AIX\s0, and \s-1AIX\s0 is dead anyway.
4972.SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4973.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
4974\fIGeneral issues\fR
4975.IX Subsection "General issues"
4976.PP
4977Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
4978requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
4979model. Libev still offers limited functionality on this platform in
4980the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
4981descriptors. This only applies when using Win32 natively, not when using
4982e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4983as every compielr comes with a slightly differently broken/incompatible
4984environment.
4985.PP
4986Lifting these limitations would basically require the full
4987re-implementation of the I/O system. If you are into this kind of thing,
4988then note that glib does exactly that for you in a very portable way (note
4989also that glib is the slowest event library known to man).
4990.PP
4991There is no supported compilation method available on windows except
4992embedding it into other applications.
4993.PP
4994Sensible signal handling is officially unsupported by Microsoft \- libev
4995tries its best, but under most conditions, signals will simply not work.
4996.PP
4997Not a libev limitation but worth mentioning: windows apparently doesn't
4998accept large writes: instead of resulting in a partial write, windows will
4999either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5000so make sure you only write small amounts into your sockets (less than a
5001megabyte seems safe, but this apparently depends on the amount of memory
5002available).
5003.PP
5004Due to the many, low, and arbitrary limits on the win32 platform and
5005the abysmal performance of winsockets, using a large number of sockets
5006is not recommended (and not reasonable). If your program needs to use
5007more than a hundred or so sockets, then likely it needs to use a totally
5008different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5009notification model, which cannot be implemented efficiently on windows
5010(due to Microsoft monopoly games).
5011.PP
5012A typical way to use libev under windows is to embed it (see the embedding
5013section for details) and use the following \fIevwrap.h\fR header file instead
5014of \fIev.h\fR:
5015.PP
5016.Vb 2
5017\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5018\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5019\&
5020\& #include "ev.h"
5021.Ve
5022.PP
5023And compile the following \fIevwrap.c\fR file into your project (make sure
5024you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5025.PP
5026.Vb 2
5027\& #include "evwrap.h"
5028\& #include "ev.c"
5029.Ve
5030.PP
5031\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5032.IX Subsection "The winsocket select function"
5033.PP
5034The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5035requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5036also extremely buggy). This makes select very inefficient, and also
5037requires a mapping from file descriptors to socket handles (the Microsoft
5038C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5039discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5040\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5041.PP
5042The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5043libraries and raw winsocket select is:
5044.PP
5045.Vb 2
5046\& #define EV_USE_SELECT 1
5047\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5048.Ve
5049.PP
5050Note that winsockets handling of fd sets is O(n), so you can easily get a
5051complexity in the O(nA\*^X) range when using win32.
5052.PP
5053\fILimited number of file descriptors\fR
5054.IX Subsection "Limited number of file descriptors"
5055.PP
5056Windows has numerous arbitrary (and low) limits on things.
5057.PP
5058Early versions of winsocket's select only supported waiting for a maximum
5059of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5060can only wait for \f(CW64\fR things at the same time internally; Microsoft
5061recommends spawning a chain of threads and wait for 63 handles and the
5062previous thread in each. Sounds great!).
5063.PP
5064Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5065to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5066call (which might be in libev or elsewhere, for example, perl and many
5067other interpreters do their own select emulation on windows).
5068.PP
5069Another limit is the number of file descriptors in the Microsoft runtime
5070libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5071fetish or something like this inside Microsoft). You can increase this
5072by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5073(another arbitrary limit), but is broken in many versions of the Microsoft
5074runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5075(depending on windows version and/or the phase of the moon). To get more,
5076you need to wrap all I/O functions and provide your own fd management, but
5077the cost of calling select (O(nA\*^X)) will likely make this unworkable.
5078.SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
5079.IX Subsection "PORTABILITY REQUIREMENTS"
5080In addition to a working ISO-C implementation and of course the
5081backend-specific APIs, libev relies on a few additional extensions:
5082.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5083.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5084.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5085Libev assumes not only that all watcher pointers have the same internal
5086structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
5087assumes that the same (machine) code can be used to call any watcher
5088callback: The watcher callbacks have different type signatures, but libev
5089calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5090.IP "pointer accesses must be thread-atomic" 4
5091.IX Item "pointer accesses must be thread-atomic"
5092Accessing a pointer value must be atomic, it must both be readable and
5093writable in one piece \- this is the case on all current architectures.
5094.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5095.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5096.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5097The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5098\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5099threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5100believed to be sufficiently portable.
5101.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5102.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5103.IX Item "sigprocmask must work in a threaded environment"
5104Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5105allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5106pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5107thread\*(R" or will block signals process-wide, both behaviours would
5108be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5109\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5110.Sp
5111The most portable way to handle signals is to block signals in all threads
5112except the initial one, and run the default loop in the initial thread as
5113well.
5114.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5115.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5116.IX Item "long must be large enough for common memory allocation sizes"
5117To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
5118instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5119systems (Microsoft...) this might be unexpectedly low, but is still at
5120least 31 bits everywhere, which is enough for hundreds of millions of
5121watchers.
5122.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5123.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5124.IX Item "double must hold a time value in seconds with enough accuracy"
5125The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5126have at least 51 bits of mantissa (and 9 bits of exponent), which is
5127good enough for at least into the year 4000 with millisecond accuracy
5128(the design goal for libev). This requirement is overfulfilled by
5129implementations using \s-1IEEE\s0 754, which is basically all existing ones. With
5130\&\s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least 2200.
5131.PP
5132If you know of other additional requirements drop me a note.
5133.SH "ALGORITHMIC COMPLEXITIES"
5134.IX Header "ALGORITHMIC COMPLEXITIES"
5135In this section the complexities of (many of) the algorithms used inside
5136libev will be documented. For complexity discussions about backends see
5137the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
5138.PP
5139All of the following are about amortised time: If an array needs to be
5140extended, libev needs to realloc and move the whole array, but this
5141happens asymptotically rarer with higher number of elements, so O(1) might
5142mean that libev does a lengthy realloc operation in rare cases, but on
5143average it is much faster and asymptotically approaches constant time.
5144.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
5145.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5146This means that, when you have a watcher that triggers in one hour and
5147there are 100 watchers that would trigger before that, then inserting will
5148have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5149.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5150.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5151That means that changing a timer costs less than removing/adding them,
5152as only the relative motion in the event queue has to be paid for.
5153.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5154.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5155These just add the watcher into an array or at the head of a list.
5156.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5157.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5158.PD 0
5159.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
5160.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5161.PD
5162These watchers are stored in lists, so they need to be walked to find the
5163correct watcher to remove. The lists are usually short (you don't usually
5164have many watchers waiting for the same fd or signal: one is typical, two
5165is rare).
5166.IP "Finding the next timer in each loop iteration: O(1)" 4
5167.IX Item "Finding the next timer in each loop iteration: O(1)"
5168By virtue of using a binary or 4\-heap, the next timer is always found at a
5169fixed position in the storage array.
5170.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
5171.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
5172A change means an I/O watcher gets started or stopped, which requires
5173libev to recalculate its status (and possibly tell the kernel, depending
5174on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
5175.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5176.IX Item "Activating one watcher (putting it into the pending state): O(1)"
5177.PD 0
5178.IP "Priority handling: O(number_of_priorities)" 4
5179.IX Item "Priority handling: O(number_of_priorities)"
5180.PD
5181Priorities are implemented by allocating some space for each
5182priority. When doing priority-based operations, libev usually has to
5183linearly search all the priorities, but starting/stopping and activating
5184watchers becomes O(1) with respect to priority handling.
5185.IP "Sending an ev_async: O(1)" 4
5186.IX Item "Sending an ev_async: O(1)"
5187.PD 0
5188.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5189.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5190.IP "Processing signals: O(max_signal_number)" 4
5191.IX Item "Processing signals: O(max_signal_number)"
5192.PD
5193Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5194calls in the current loop iteration. Checking for async and signal events
5195involves iterating over all running async watchers or all signal numbers.
5196.SH "PORTING FROM LIBEV 3.X TO 4.X"
5197.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5198The major version 4 introduced some incompatible changes to the \s-1API\s0.
5199.PP
5200At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5201for all changes, so most programs should still compile. The compatibility
5202layer might be removed in later versions of libev, so better update to the
5203new \s-1API\s0 early than late.
5204.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5205.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5206.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5207The backward compatibility mechanism can be controlled by
5208\&\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
5209section.
5210.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5211.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5212.IX Item "ev_default_destroy and ev_default_fork have been removed"
5213These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5214.Sp
5215.Vb 2
5216\& ev_loop_destroy (EV_DEFAULT_UC);
5217\& ev_loop_fork (EV_DEFAULT);
5218.Ve
5219.IP "function/symbol renames" 4
5220.IX Item "function/symbol renames"
5221A number of functions and symbols have been renamed:
5222.Sp
5223.Vb 3
5224\& ev_loop => ev_run
5225\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5226\& EVLOOP_ONESHOT => EVRUN_ONCE
5227\&
5228\& ev_unloop => ev_break
5229\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5230\& EVUNLOOP_ONE => EVBREAK_ONE
5231\& EVUNLOOP_ALL => EVBREAK_ALL
5232\&
5233\& EV_TIMEOUT => EV_TIMER
5234\&
5235\& ev_loop_count => ev_iteration
5236\& ev_loop_depth => ev_depth
5237\& ev_loop_verify => ev_verify
5238.Ve
5239.Sp
5240Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5241\&\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
5242associated constants have been renamed to not collide with the \f(CW\*(C`struct
5243ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5244as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5245\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5246typedef.
5247.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5248.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5249.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5250The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5251mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5252and work, but the library code will of course be larger.
5253.SH "GLOSSARY"
5254.IX Header "GLOSSARY"
5255.IP "active" 4
5256.IX Item "active"
5257A watcher is active as long as it has been started and not yet stopped.
5258See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5259.IP "application" 4
5260.IX Item "application"
5261In this document, an application is whatever is using libev.
5262.IP "backend" 4
5263.IX Item "backend"
5264The part of the code dealing with the operating system interfaces.
5265.IP "callback" 4
5266.IX Item "callback"
5267The address of a function that is called when some event has been
5268detected. Callbacks are being passed the event loop, the watcher that
5269received the event, and the actual event bitset.
5270.IP "callback/watcher invocation" 4
5271.IX Item "callback/watcher invocation"
5272The act of calling the callback associated with a watcher.
5273.IP "event" 4
5274.IX Item "event"
5275A change of state of some external event, such as data now being available
5276for reading on a file descriptor, time having passed or simply not having
5277any other events happening anymore.
5278.Sp
5279In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5280\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5281.IP "event library" 4
5282.IX Item "event library"
5283A software package implementing an event model and loop.
5284.IP "event loop" 4
5285.IX Item "event loop"
5286An entity that handles and processes external events and converts them
5287into callback invocations.
5288.IP "event model" 4
5289.IX Item "event model"
5290The model used to describe how an event loop handles and processes
5291watchers and events.
5292.IP "pending" 4
5293.IX Item "pending"
5294A watcher is pending as soon as the corresponding event has been
5295detected. See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5296.IP "real time" 4
5297.IX Item "real time"
5298The physical time that is observed. It is apparently strictly monotonic :)
5299.IP "wall-clock time" 4
5300.IX Item "wall-clock time"
5301The time and date as shown on clocks. Unlike real time, it can actually
5302be wrong and jump forwards and backwards, e.g. when the you adjust your
5303clock.
5304.IP "watcher" 4
5305.IX Item "watcher"
5306A data structure that describes interest in certain events. Watchers need
5307to be started (attached to an event loop) before they can receive events.
958.SH "AUTHOR" 5308.SH "AUTHOR"
959.IX Header "AUTHOR" 5309.IX Header "AUTHOR"
960Marc Lehmann <libev@schmorp.de>. 5310Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5311Magnusson and Emanuele Giaquinta, and minor corrections by many others.

Diff Legend

– Removed lines
+ Added lines
< Changed lines
> Changed lines