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Revision 1.56 by root, Sat Dec 22 05:47:57 2007 UTC vs.
Revision 1.59 by root, Tue Dec 25 07:16:53 2007 UTC

… …
127.\} 127.\}
128.rm #[ #] #H #V #F C 128.rm #[ #] #H #V #F C
129.\" ======================================================================== 129.\" ========================================================================
130.\" 130.\"
131.IX Title "EV 1" 131.IX Title "EV 1"
132.TH EV 1 "2007-12-22" "perl v5.8.8" "User Contributed Perl Documentation" 132.TH EV 1 "2007-12-25" "perl v5.8.8" "User Contributed Perl Documentation"
133.SH "NAME" 133.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 134libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 135.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 136.IX Header "SYNOPSIS"
137.Vb 1 137.Vb 1
138\& #include <ev.h> 138\& #include <ev.h>
139.Ve 139.Ve
140.SH "EXAMPLE PROGRAM" 140.Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
141.IX Header "EXAMPLE PROGRAM" 141.IX Subsection "EXAMPLE PROGRAM"
142.Vb 1 142.Vb 1
143\& #include <ev.h> 143\& #include <ev.h>
144.Ve 144.Ve
145.PP 145.PP
146.Vb 2 146.Vb 2
… …
212.PP 212.PP
213You register interest in certain events by registering so-called \fIevent 213You register interest in certain events by registering so-called \fIevent
214watchers\fR, which are relatively small C structures you initialise with the 214watchers\fR, which are relatively small C structures you initialise with the
215details of the event, and then hand it over to libev by \fIstarting\fR the 215details of the event, and then hand it over to libev by \fIstarting\fR the
216watcher. 216watcher.
217.SH "FEATURES" 217.Sh "\s-1FEATURES\s0"
218.IX Header "FEATURES" 218.IX Subsection "FEATURES"
219Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the 219Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
220BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms 220BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
221for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface 221for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
222(for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers 222(for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers
223with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals 223with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals
… …
228(\f(CW\*(C`ev_fork\*(C'\fR). 228(\f(CW\*(C`ev_fork\*(C'\fR).
229.PP 229.PP
230It also is quite fast (see this 230It also is quite fast (see this
231benchmark comparing it to libevent 231benchmark comparing it to libevent
232for example). 232for example).
233.SH "CONVENTIONS" 233.Sh "\s-1CONVENTIONS\s0"
234.IX Header "CONVENTIONS" 234.IX Subsection "CONVENTIONS"
235Libev is very configurable. In this manual the default configuration will 235Libev is very configurable. In this manual the default configuration will
236be described, which supports multiple event loops. For more info about 236be described, which supports multiple event loops. For more info about
237various configuration options please have a look at \fB\s-1EMBED\s0\fR section in 237various configuration options please have a look at \fB\s-1EMBED\s0\fR section in
238this manual. If libev was configured without support for multiple event 238this manual. If libev was configured without support for multiple event
239loops, then all functions taking an initial argument of name \f(CW\*(C`loop\*(C'\fR 239loops, then all functions taking an initial argument of name \f(CW\*(C`loop\*(C'\fR
240(which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have this argument. 240(which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have this argument.
241.SH "TIME REPRESENTATION" 241.Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"
242.IX Header "TIME REPRESENTATION" 242.IX Subsection "TIME REPRESENTATION"
243Libev represents time as a single floating point number, representing the 243Libev represents time as a single floating point number, representing the
244(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 244(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
245the beginning of 1970, details are complicated, don't ask). This type is 245the beginning of 1970, details are complicated, don't ask). This type is
246called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 246called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
247to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on 247to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on
… …
255.IP "ev_tstamp ev_time ()" 4 255.IP "ev_tstamp ev_time ()" 4
256.IX Item "ev_tstamp ev_time ()" 256.IX Item "ev_tstamp ev_time ()"
257Returns the current time as libev would use it. Please note that the 257Returns the current time as libev would use it. Please note that the
258\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp 258\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
259you actually want to know. 259you actually want to know.
260.IP "void ev_sleep (ev_tstamp interval)" 4 260.IP "ev_sleep (ev_tstamp interval)" 4
261.IX Item "void ev_sleep (ev_tstamp interval)" 261.IX Item "ev_sleep (ev_tstamp interval)"
262Sleep for the given interval: The current thread will be blocked until 262Sleep for the given interval: The current thread will be blocked until
263either it is interrupted or the given time interval has passed. Basically 263either it is interrupted or the given time interval has passed. Basically
264this is a subsecond-resolution \f(CW\*(C`sleep ()\*(C'\fR. 264this is a subsecond-resolution \f(CW\*(C`sleep ()\*(C'\fR.
265.IP "int ev_version_major ()" 4 265.IP "int ev_version_major ()" 4
266.IX Item "int ev_version_major ()" 266.IX Item "int ev_version_major ()"
… …
451.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 451.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
452.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 452.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
453This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 453This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
454libev tries to roll its own fd_set with no limits on the number of fds, 454libev tries to roll its own fd_set with no limits on the number of fds,
455but if that fails, expect a fairly low limit on the number of fds when 455but if that fails, expect a fairly low limit on the number of fds when
456using this backend. It doesn't scale too well (O(highest_fd)), but its usually 456using this backend. It doesn't scale too well (O(highest_fd)), but its
457the fastest backend for a low number of fds. 457usually the fastest backend for a low number of (low\-numbered :) fds.
458.Sp
459To get good performance out of this backend you need a high amount of
460parallelity (most of the file descriptors should be busy). If you are
461writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
462connections as possible during one iteration. You might also want to have
463a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
464readyness notifications you get per iteration.
458.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 465.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
459.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 466.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
460.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 467.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
461And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 468And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
462select, but handles sparse fds better and has no artificial limit on the 469than select, but handles sparse fds better and has no artificial
463number of fds you can use (except it will slow down considerably with a 470limit on the number of fds you can use (except it will slow down
464lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 471considerably with a lot of inactive fds). It scales similarly to select,
472i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
473performance tips.
465.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 474.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
466.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 475.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
467.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 476.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
468For few fds, this backend is a bit little slower than poll and select, 477For few fds, this backend is a bit little slower than poll and select,
469but it scales phenomenally better. While poll and select usually scale 478but it scales phenomenally better. While poll and select usually scale
470like O(total_fds) where n is the total number of fds (or the highest fd), 479like O(total_fds) where n is the total number of fds (or the highest fd),
471epoll scales either O(1) or O(active_fds). The epoll design has a number 480epoll scales either O(1) or O(active_fds). The epoll design has a number
472of shortcomings, such as silently dropping events in some hard-to-detect 481of shortcomings, such as silently dropping events in some hard-to-detect
473cases and rewiring a syscall per fd change, no fork support and bad 482cases and rewiring a syscall per fd change, no fork support and bad
474support for dup: 483support for dup.
475.Sp 484.Sp
476While stopping, setting and starting an I/O watcher in the same iteration 485While stopping, setting and starting an I/O watcher in the same iteration
477will result in some caching, there is still a syscall per such incident 486will result in some caching, there is still a syscall per such incident
478(because the fd could point to a different file description now), so its 487(because the fd could point to a different file description now), so its
479best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work 488best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work
480very well if you register events for both fds. 489very well if you register events for both fds.
481.Sp 490.Sp
482Please note that epoll sometimes generates spurious notifications, so you 491Please note that epoll sometimes generates spurious notifications, so you
483need to use non-blocking I/O or other means to avoid blocking when no data 492need to use non-blocking I/O or other means to avoid blocking when no data
484(or space) is available. 493(or space) is available.
494.Sp
495Best performance from this backend is achieved by not unregistering all
496watchers for a file descriptor until it has been closed, if possible, i.e.
497keep at least one watcher active per fd at all times.
498.Sp
499While nominally embeddeble in other event loops, this feature is broken in
500all kernel versions tested so far.
485.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 501.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
486.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 502.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
487.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 503.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
488Kqueue deserves special mention, as at the time of this writing, it 504Kqueue deserves special mention, as at the time of this writing, it
489was broken on \fIall\fR BSDs (usually it doesn't work with anything but 505was broken on all BSDs except NetBSD (usually it doesn't work reliably
490sockets and pipes, except on Darwin, where of course it's completely 506with anything but sockets and pipes, except on Darwin, where of course
491useless. On NetBSD, it seems to work for all the \s-1FD\s0 types I tested, so it
492is used by default there). For this reason it's not being \*(L"autodetected\*(R" 507it's completely useless). For this reason it's not being \*(L"autodetected\*(R"
493unless you explicitly specify it explicitly in the flags (i.e. using 508unless you explicitly specify it explicitly in the flags (i.e. using
494\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough) 509\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
495system like NetBSD. 510system like NetBSD.
496.Sp 511.Sp
512You still can embed kqueue into a normal poll or select backend and use it
513only for sockets (after having made sure that sockets work with kqueue on
514the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
515.Sp
497It scales in the same way as the epoll backend, but the interface to the 516It scales in the same way as the epoll backend, but the interface to the
498kernel is more efficient (which says nothing about its actual speed, 517kernel is more efficient (which says nothing about its actual speed, of
499of course). While stopping, setting and starting an I/O watcher does 518course). While stopping, setting and starting an I/O watcher does never
500never cause an extra syscall as with epoll, it still adds up to two event 519cause an extra syscall as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
501changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it drops fds 520two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it
502silently in similarly hard-to-detetc cases. 521drops fds silently in similarly hard-to-detect cases.
522.Sp
523This backend usually performs well under most conditions.
524.Sp
525While nominally embeddable in other event loops, this doesn't work
526everywhere, so you might need to test for this. And since it is broken
527almost everywhere, you should only use it when you have a lot of sockets
528(for which it usually works), by embedding it into another event loop
529(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR) and using it only for
530sockets.
503.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 531.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
504.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 532.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
505.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 533.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
506This is not implemented yet (and might never be). 534This is not implemented yet (and might never be, unless you send me an
535implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
536and is not embeddable, which would limit the usefulness of this backend
537immensely.
507.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 538.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
508.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 539.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
509.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 540.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
510This uses the Solaris 10 event port mechanism. As with everything on Solaris, 541This uses the Solaris 10 event port mechanism. As with everything on Solaris,
511it's really slow, but it still scales very well (O(active_fds)). 542it's really slow, but it still scales very well (O(active_fds)).
512.Sp 543.Sp
513Please note that solaris event ports can deliver a lot of spurious 544Please note that solaris event ports can deliver a lot of spurious
514notifications, so you need to use non-blocking I/O or other means to avoid 545notifications, so you need to use non-blocking I/O or other means to avoid
515blocking when no data (or space) is available. 546blocking when no data (or space) is available.
547.Sp
548While this backend scales well, it requires one system call per active
549file descriptor per loop iteration. For small and medium numbers of file
550descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
551might perform better.
516.ie n .IP """EVBACKEND_ALL""" 4 552.ie n .IP """EVBACKEND_ALL""" 4
517.el .IP "\f(CWEVBACKEND_ALL\fR" 4 553.el .IP "\f(CWEVBACKEND_ALL\fR" 4
518.IX Item "EVBACKEND_ALL" 554.IX Item "EVBACKEND_ALL"
519Try all backends (even potentially broken ones that wouldn't be tried 555Try all backends (even potentially broken ones that wouldn't be tried
520with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 556with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
521\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 557\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
558.Sp
559It is definitely not recommended to use this flag.
522.RE 560.RE
523.RS 4 561.RS 4
524.Sp 562.Sp
525If one or more of these are ored into the flags value, then only these 563If one or more of these are ored into the flags value, then only these
526backends will be tried (in the reverse order as given here). If none are 564backends will be tried (in the reverse order as given here). If none are
… …
729.Sp 767.Sp
730.Vb 2 768.Vb 2
731\& ev_ref (loop); 769\& ev_ref (loop);
732\& ev_signal_stop (loop, &exitsig); 770\& ev_signal_stop (loop, &exitsig);
733.Ve 771.Ve
734.IP "ev_set_io_collect_interval (ev_tstamp interval)" 4 772.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
735.IX Item "ev_set_io_collect_interval (ev_tstamp interval)" 773.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
736.PD 0 774.PD 0
737.IP "ev_set_timeout_collect_interval (ev_tstamp interval)" 4 775.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
738.IX Item "ev_set_timeout_collect_interval (ev_tstamp interval)" 776.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
739.PD 777.PD
740These advanced functions influence the time that libev will spend waiting 778These advanced functions influence the time that libev will spend waiting
741for events. Both are by default \f(CW0\fR, meaning that libev will try to 779for events. Both are by default \f(CW0\fR, meaning that libev will try to
742invoke timer/periodic callbacks and I/O callbacks with minimum latency. 780invoke timer/periodic callbacks and I/O callbacks with minimum latency.
743.Sp 781.Sp
… …
752overhead for the actual polling but can deliver many events at once. 790overhead for the actual polling but can deliver many events at once.
753.Sp 791.Sp
754By setting a higher \fIio collect interval\fR you allow libev to spend more 792By setting a higher \fIio collect interval\fR you allow libev to spend more
755time collecting I/O events, so you can handle more events per iteration, 793time collecting I/O events, so you can handle more events per iteration,
756at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and 794at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
757\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. 795\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
796introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
758.Sp 797.Sp
759Likewise, by setting a higher \fItimeout collect interval\fR you allow libev 798Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
760to spend more time collecting timeouts, at the expense of increased 799to spend more time collecting timeouts, at the expense of increased
761latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers 800latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers
762will not be affected. 801will not be affected. Setting this to a non-null value will not introduce
802any overhead in libev.
763.Sp 803.Sp
764Many programs can usually benefit by setting the io collect interval to 804Many (busy) programs can usually benefit by setting the io collect
765a value near \f(CW0.1\fR or so, which is often enough for interactive servers 805interval to a value near \f(CW0.1\fR or so, which is often enough for
766(of course not for games), likewise for timeouts. It usually doesn't make 806interactive servers (of course not for games), likewise for timeouts. It
767much sense to set it to a lower value than \f(CW0.01\fR, as this approsaches 807usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
768the timing granularity of most systems. 808as this approsaches the timing granularity of most systems.
769.SH "ANATOMY OF A WATCHER" 809.SH "ANATOMY OF A WATCHER"
770.IX Header "ANATOMY OF A WATCHER" 810.IX Header "ANATOMY OF A WATCHER"
771A watcher is a structure that you create and register to record your 811A watcher is a structure that you create and register to record your
772interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 812interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
773become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 813become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
… …
1098In general you can register as many read and/or write event watchers per 1138In general you can register as many read and/or write event watchers per
1099fd as you want (as long as you don't confuse yourself). Setting all file 1139fd as you want (as long as you don't confuse yourself). Setting all file
1100descriptors to non-blocking mode is also usually a good idea (but not 1140descriptors to non-blocking mode is also usually a good idea (but not
1101required if you know what you are doing). 1141required if you know what you are doing).
1102.PP 1142.PP
1103You have to be careful with dup'ed file descriptors, though. Some backends
1104(the linux epoll backend is a notable example) cannot handle dup'ed file
1105descriptors correctly if you register interest in two or more fds pointing
1106to the same underlying file/socket/etc. description (that is, they share
1107the same underlying \*(L"file open\*(R").
1108.PP
1109If you must do this, then force the use of a known-to-be-good backend 1143If you must do this, then force the use of a known-to-be-good backend
1110(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and 1144(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
1111\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR). 1145\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
1112.PP 1146.PP
1113Another thing you have to watch out for is that it is quite easy to 1147Another thing you have to watch out for is that it is quite easy to
… …
1149.PP 1183.PP
1150\fIThe special problem of dup'ed file descriptors\fR 1184\fIThe special problem of dup'ed file descriptors\fR
1151.IX Subsection "The special problem of dup'ed file descriptors" 1185.IX Subsection "The special problem of dup'ed file descriptors"
1152.PP 1186.PP
1153Some backends (e.g. epoll), cannot register events for file descriptors, 1187Some backends (e.g. epoll), cannot register events for file descriptors,
1154but only events for the underlying file descriptions. That menas when you 1188but only events for the underlying file descriptions. That means when you
1155have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors and register events for them, only one 1189have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1156file descriptor might actually receive events. 1190events for them, only one file descriptor might actually receive events.
1157.PP 1191.PP
1158There is no workaorund possible except not registering events 1192There is no workaround possible except not registering events
1159for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or to resort to 1193for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1160\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR. 1194\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1161.PP 1195.PP
1162\fIThe special problem of fork\fR 1196\fIThe special problem of fork\fR
1163.IX Subsection "The special problem of fork" 1197.IX Subsection "The special problem of fork"
1164.PP 1198.PP
… …
1619reader). Inotify will be used to give hints only and should not change the 1653reader). Inotify will be used to give hints only and should not change the
1620semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev sometimes needs 1654semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev sometimes needs
1621to fall back to regular polling again even with inotify, but changes are 1655to fall back to regular polling again even with inotify, but changes are
1622usually detected immediately, and if the file exists there will be no 1656usually detected immediately, and if the file exists there will be no
1623polling. 1657polling.
1658.PP
1659\fIInotify\fR
1660.IX Subsection "Inotify"
1661.PP
1662When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev (generally only
1663available on Linux) and present at runtime, it will be used to speed up
1664change detection where possible. The inotify descriptor will be created lazily
1665when the first \f(CW\*(C`ev_stat\*(C'\fR watcher is being started.
1666.PP
1667Inotify presense does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
1668except that changes might be detected earlier, and in some cases, to avoid
1669making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presense of inotify support
1670there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling.
1671.PP
1672(There is no support for kqueue, as apparently it cannot be used to
1673implement this functionality, due to the requirement of having a file
1674descriptor open on the object at all times).
1675.PP
1676\fIThe special problem of stat time resolution\fR
1677.IX Subsection "The special problem of stat time resolution"
1678.PP
1679The \f(CW\*(C`stat ()\*(C'\fR syscall only supports full-second resolution portably, and
1680even on systems where the resolution is higher, many filesystems still
1681only support whole seconds.
1682.PP
1683That means that, if the time is the only thing that changes, you might
1684miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and calls
1685your callback, which does something. When there is another update within
1686the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect it.
1687.PP
1688The solution to this is to delay acting on a change for a second (or till
1689the next second boundary), using a roughly one-second delay \f(CW\*(C`ev_timer\*(C'\fR
1690(\f(CW\*(C`ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)\*(C'\fR). The \f(CW.01\fR
1691is added to work around small timing inconsistencies of some operating
1692systems.
1624.PP 1693.PP
1625\fIWatcher-Specific Functions and Data Members\fR 1694\fIWatcher-Specific Functions and Data Members\fR
1626.IX Subsection "Watcher-Specific Functions and Data Members" 1695.IX Subsection "Watcher-Specific Functions and Data Members"
1627.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 1696.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1628.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 1697.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
… …
1660The specified interval. 1729The specified interval.
1661.IP "const char *path [read\-only]" 4 1730.IP "const char *path [read\-only]" 4
1662.IX Item "const char *path [read-only]" 1731.IX Item "const char *path [read-only]"
1663The filesystem path that is being watched. 1732The filesystem path that is being watched.
1664.PP 1733.PP
1734\fIExamples\fR
1735.IX Subsection "Examples"
1736.PP
1665Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. 1737Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1666.PP 1738.PP
1667.Vb 15 1739.Vb 15
1668\& static void 1740\& static void
1669\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 1741\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
… …
1686\& ... 1758\& ...
1687\& ev_stat passwd; 1759\& ev_stat passwd;
1688.Ve 1760.Ve
1689.PP 1761.PP
1690.Vb 2 1762.Vb 2
1691\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); 1763\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1692\& ev_stat_start (loop, &passwd); 1764\& ev_stat_start (loop, &passwd);
1765.Ve
1766.PP
1767Example: Like above, but additionally use a one-second delay so we do not
1768miss updates (however, frequent updates will delay processing, too, so
1769one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
1770\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1771.PP
1772.Vb 2
1773\& static ev_stat passwd;
1774\& static ev_timer timer;
1775.Ve
1776.PP
1777.Vb 4
1778\& static void
1779\& timer_cb (EV_P_ ev_timer *w, int revents)
1780\& {
1781\& ev_timer_stop (EV_A_ w);
1782.Ve
1783.PP
1784.Vb 2
1785\& /* now it's one second after the most recent passwd change */
1786\& }
1787.Ve
1788.PP
1789.Vb 6
1790\& static void
1791\& stat_cb (EV_P_ ev_stat *w, int revents)
1792\& {
1793\& /* reset the one-second timer */
1794\& ev_timer_again (EV_A_ &timer);
1795\& }
1796.Ve
1797.PP
1798.Vb 4
1799\& ...
1800\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1801\& ev_stat_start (loop, &passwd);
1802\& ev_timer_init (&timer, timer_cb, 0., 1.01);
1693.Ve 1803.Ve
1694.ie n .Sh """ev_idle"" \- when you've got nothing better to do..." 1804.ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
1695.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..." 1805.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
1696.IX Subsection "ev_idle - when you've got nothing better to do..." 1806.IX Subsection "ev_idle - when you've got nothing better to do..."
1697Idle watchers trigger events when no other events of the same or higher 1807Idle watchers trigger events when no other events of the same or higher
… …
1782.PP 1892.PP
1783It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) 1893It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
1784priority, to ensure that they are being run before any other watchers 1894priority, to ensure that they are being run before any other watchers
1785after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, 1895after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers,
1786too) should not activate (\*(L"feed\*(R") events into libev. While libev fully 1896too) should not activate (\*(L"feed\*(R") events into libev. While libev fully
1787supports this, they will be called before other \f(CW\*(C`ev_check\*(C'\fR watchers did 1897supports this, they will be called before other \f(CW\*(C`ev_check\*(C'\fR watchers
1788their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other event 1898did their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other
1789loops those other event loops might be in an unusable state until their 1899(non\-libev) event loops those other event loops might be in an unusable
1790\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with 1900state until their \f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to
1791others). 1901coexist peacefully with others).
1792.PP 1902.PP
1793\fIWatcher-Specific Functions and Data Members\fR 1903\fIWatcher-Specific Functions and Data Members\fR
1794.IX Subsection "Watcher-Specific Functions and Data Members" 1904.IX Subsection "Watcher-Specific Functions and Data Members"
1795.IP "ev_prepare_init (ev_prepare *, callback)" 4 1905.IP "ev_prepare_init (ev_prepare *, callback)" 4
1796.IX Item "ev_prepare_init (ev_prepare *, callback)" 1906.IX Item "ev_prepare_init (ev_prepare *, callback)"
… …
1976.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." 2086.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
1977.IX Subsection "ev_embed - when one backend isn't enough..." 2087.IX Subsection "ev_embed - when one backend isn't enough..."
1978This is a rather advanced watcher type that lets you embed one event loop 2088This is a rather advanced watcher type that lets you embed one event loop
1979into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 2089into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1980loop, other types of watchers might be handled in a delayed or incorrect 2090loop, other types of watchers might be handled in a delayed or incorrect
1981fashion and must not be used). (See portability notes, below). 2091fashion and must not be used).
1982.PP 2092.PP
1983There are primarily two reasons you would want that: work around bugs and 2093There are primarily two reasons you would want that: work around bugs and
1984prioritise I/O. 2094prioritise I/O.
1985.PP 2095.PP
1986As an example for a bug workaround, the kqueue backend might only support 2096As an example for a bug workaround, the kqueue backend might only support
… …
2046\& ev_embed_start (loop_hi, &embed); 2156\& ev_embed_start (loop_hi, &embed);
2047\& } 2157\& }
2048\& else 2158\& else
2049\& loop_lo = loop_hi; 2159\& loop_lo = loop_hi;
2050.Ve 2160.Ve
2051.Sh "Portability notes"
2052.IX Subsection "Portability notes"
2053Kqueue is nominally embeddable, but this is broken on all BSDs that I
2054tried, in various ways. Usually the embedded event loop will simply never
2055receive events, sometimes it will only trigger a few times, sometimes in a
2056loop. Epoll is also nominally embeddable, but many Linux kernel versions
2057will always eport the epoll fd as ready, even when no events are pending.
2058.PP
2059While libev allows embedding these backends (they are contained in
2060\&\f(CW\*(C`ev_embeddable_backends ()\*(C'\fR), take extreme care that it will actually
2061work.
2062.PP
2063When in doubt, create a dynamic event loop forced to use sockets (this
2064usually works) and possibly another thread and a pipe or so to report to
2065your main event loop.
2066.PP 2161.PP
2067\fIWatcher-Specific Functions and Data Members\fR 2162\fIWatcher-Specific Functions and Data Members\fR
2068.IX Subsection "Watcher-Specific Functions and Data Members" 2163.IX Subsection "Watcher-Specific Functions and Data Members"
2069.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 2164.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2070.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 2165.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
… …
2608interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will 2703interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
2609be detected at runtime. 2704be detected at runtime.
2610.IP "\s-1EV_H\s0" 4 2705.IP "\s-1EV_H\s0" 4
2611.IX Item "EV_H" 2706.IX Item "EV_H"
2612The name of the \fIev.h\fR header file used to include it. The default if 2707The name of the \fIev.h\fR header file used to include it. The default if
2613undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 2708undefined is \f(CW"ev.h"\fR in \fIevent.h\fR and \fIev.c\fR. This can be used to
2614can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 2709virtually rename the \fIev.h\fR header file in case of conflicts.
2615.IP "\s-1EV_CONFIG_H\s0" 4 2710.IP "\s-1EV_CONFIG_H\s0" 4
2616.IX Item "EV_CONFIG_H" 2711.IX Item "EV_CONFIG_H"
2617If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 2712If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2618\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 2713\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2619\&\f(CW\*(C`EV_H\*(C'\fR, above. 2714\&\f(CW\*(C`EV_H\*(C'\fR, above.
2620.IP "\s-1EV_EVENT_H\s0" 4 2715.IP "\s-1EV_EVENT_H\s0" 4
2621.IX Item "EV_EVENT_H" 2716.IX Item "EV_EVENT_H"
2622Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 2717Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2623of how the \fIevent.h\fR header can be found. 2718of how the \fIevent.h\fR header can be found, the dfeault is \f(CW"event.h"\fR.
2624.IP "\s-1EV_PROTOTYPES\s0" 4 2719.IP "\s-1EV_PROTOTYPES\s0" 4
2625.IX Item "EV_PROTOTYPES" 2720.IX Item "EV_PROTOTYPES"
2626If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 2721If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2627prototypes, but still define all the structs and other symbols. This is 2722prototypes, but still define all the structs and other symbols. This is
2628occasionally useful if you want to provide your own wrapper functions 2723occasionally useful if you want to provide your own wrapper functions
… …
2685pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more 2780pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
2686than enough. If you need to manage thousands of children you might want to 2781than enough. If you need to manage thousands of children you might want to
2687increase this value (\fImust\fR be a power of two). 2782increase this value (\fImust\fR be a power of two).
2688.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4 2783.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
2689.IX Item "EV_INOTIFY_HASHSIZE" 2784.IX Item "EV_INOTIFY_HASHSIZE"
2690\&\f(CW\*(C`ev_staz\*(C'\fR watchers use a small hash table to distribute workload by 2785\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
2691inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), 2786inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
2692usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR 2787usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
2693watchers you might want to increase this value (\fImust\fR be a power of 2788watchers you might want to increase this value (\fImust\fR be a power of
2694two). 2789two).
2695.IP "\s-1EV_COMMON\s0" 4 2790.IP "\s-1EV_COMMON\s0" 4
… …
2799.RS 4 2894.RS 4
2800.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 2895.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2801.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 2896.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
2802This means that, when you have a watcher that triggers in one hour and 2897This means that, when you have a watcher that triggers in one hour and
2803there are 100 watchers that would trigger before that then inserting will 2898there are 100 watchers that would trigger before that then inserting will
2804have to skip those 100 watchers. 2899have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
2805.IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4 2900.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
2806.IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 2901.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
2807That means that for changing a timer costs less than removing/adding them 2902That means that changing a timer costs less than removing/adding them
2808as only the relative motion in the event queue has to be paid for. 2903as only the relative motion in the event queue has to be paid for.
2809.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4 2904.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4
2810.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)" 2905.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)"
2811These just add the watcher into an array or at the head of a list. 2906These just add the watcher into an array or at the head of a list.
2907.IP "Stopping check/prepare/idle watchers: O(1)" 4
2812=item Stopping check/prepare/idle watchers: O(1) 2908.IX Item "Stopping check/prepare/idle watchers: O(1)"
2909.PD 0
2813.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4 2910.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2814.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))" 2911.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
2912.PD
2815These watchers are stored in lists then need to be walked to find the 2913These watchers are stored in lists then need to be walked to find the
2816correct watcher to remove. The lists are usually short (you don't usually 2914correct watcher to remove. The lists are usually short (you don't usually
2817have many watchers waiting for the same fd or signal). 2915have many watchers waiting for the same fd or signal).
2818.IP "Finding the next timer per loop iteration: O(1)" 4 2916.IP "Finding the next timer in each loop iteration: O(1)" 4
2819.IX Item "Finding the next timer per loop iteration: O(1)" 2917.IX Item "Finding the next timer in each loop iteration: O(1)"
2820.PD 0 2918By virtue of using a binary heap, the next timer is always found at the
2919beginning of the storage array.
2821.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 2920.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2822.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 2921.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2823.PD
2824A change means an I/O watcher gets started or stopped, which requires 2922A change means an I/O watcher gets started or stopped, which requires
2825libev to recalculate its status (and possibly tell the kernel). 2923libev to recalculate its status (and possibly tell the kernel, depending
2826.IP "Activating one watcher: O(1)" 4 2924on backend and wether \f(CW\*(C`ev_io_set\*(C'\fR was used).
2827.IX Item "Activating one watcher: O(1)" 2925.IP "Activating one watcher (putting it into the pending state): O(1)" 4
2926.IX Item "Activating one watcher (putting it into the pending state): O(1)"
2828.PD 0 2927.PD 0
2829.IP "Priority handling: O(number_of_priorities)" 4 2928.IP "Priority handling: O(number_of_priorities)" 4
2830.IX Item "Priority handling: O(number_of_priorities)" 2929.IX Item "Priority handling: O(number_of_priorities)"
2831.PD 2930.PD
2832Priorities are implemented by allocating some space for each 2931Priorities are implemented by allocating some space for each
2833priority. When doing priority-based operations, libev usually has to 2932priority. When doing priority-based operations, libev usually has to
2834linearly search all the priorities. 2933linearly search all the priorities, but starting/stopping and activating
2934watchers becomes O(1) w.r.t. prioritiy handling.
2835.RE 2935.RE
2836.RS 4 2936.RS 4
2837.SH "AUTHOR" 2937.SH "AUTHOR"
2838.IX Header "AUTHOR" 2938.IX Header "AUTHOR"
2839Marc Lehmann <libev@schmorp.de>. 2939Marc Lehmann <libev@schmorp.de>.

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