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… …
8 8
9=head1 DESCRIPTION 9=head1 DESCRIPTION
10 10
11Libev is an event loop: you register interest in certain events (such as a 11Libev is an event loop: you register interest in certain events (such as a
12file descriptor being readable or a timeout occuring), and it will manage 12file descriptor being readable or a timeout occuring), and it will manage
13these event sources and provide your program events. 13these event sources and provide your program with events.
14 14
15To do this, it must take more or less complete control over your process 15To do this, it must take more or less complete control over your process
16(or thread) by executing the I<event loop> handler, and will then 16(or thread) by executing the I<event loop> handler, and will then
17communicate events via a callback mechanism. 17communicate events via a callback mechanism.
18 18
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25 25
26Libev supports select, poll, the linux-specific epoll and the bsd-specific 26Libev supports select, poll, the linux-specific epoll and the bsd-specific
27kqueue mechanisms for file descriptor events, relative timers, absolute 27kqueue mechanisms for file descriptor events, relative timers, absolute
28timers with customised rescheduling, signal events, process status change 28timers with customised rescheduling, signal events, process status change
29events (related to SIGCHLD), and event watchers dealing with the event 29events (related to SIGCHLD), and event watchers dealing with the event
30loop mechanism itself (idle, prepare and check watchers). 30loop mechanism itself (idle, prepare and check watchers). It also is quite
31fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing
32it to libevent for example).
31 33
32=head1 CONVENTIONS 34=head1 CONVENTIONS
33 35
34Libev is very configurable. In this manual the default configuration 36Libev is very configurable. In this manual the default configuration
35will be described, which supports multiple event loops. For more info 37will be described, which supports multiple event loops. For more info
36about various configuraiton options please have a look at the file 38about various configuration options please have a look at the file
37F<README.embed> in the libev distribution. If libev was configured without 39F<README.embed> in the libev distribution. If libev was configured without
38support for multiple event loops, then all functions taking an initial 40support for multiple event loops, then all functions taking an initial
39argument of name C<loop> (which is always of type C<struct ev_loop *>) 41argument of name C<loop> (which is always of type C<struct ev_loop *>)
40will not have this argument. 42will not have this argument.
41 43
42=head1 TIME AND OTHER GLOBAL FUNCTIONS 44=head1 TIME REPRESENTATION
43 45
44Libev represents time as a single floating point number, representing the 46Libev represents time as a single floating point number, representing the
45(fractional) number of seconds since the (POSIX) epoch (somewhere near 47(fractional) number of seconds since the (POSIX) epoch (somewhere near
46the beginning of 1970, details are complicated, don't ask). This type is 48the beginning of 1970, details are complicated, don't ask). This type is
47called C<ev_tstamp>, which is what you should use too. It usually aliases 49called C<ev_tstamp>, which is what you should use too. It usually aliases
48to the double type in C. 50to the double type in C.
49 51
52=head1 GLOBAL FUNCTIONS
53
54These functions can be called anytime, even before initialising the
55library in any way.
56
50=over 4 57=over 4
51 58
52=item ev_tstamp ev_time () 59=item ev_tstamp ev_time ()
53 60
54Returns the current time as libev would use it. 61Returns the current time as libev would use it. Please note that the
62C<ev_now> function is usually faster and also often returns the timestamp
63you actually want to know.
55 64
56=item int ev_version_major () 65=item int ev_version_major ()
57 66
58=item int ev_version_minor () 67=item int ev_version_minor ()
59 68
… …
61you linked against by calling the functions C<ev_version_major> and 70you linked against by calling the functions C<ev_version_major> and
62C<ev_version_minor>. If you want, you can compare against the global 71C<ev_version_minor>. If you want, you can compare against the global
63symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the 72symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
64version of the library your program was compiled against. 73version of the library your program was compiled against.
65 74
66Usually, its a good idea to terminate if the major versions mismatch, 75Usually, it's a good idea to terminate if the major versions mismatch,
67as this indicates an incompatible change. Minor versions are usually 76as this indicates an incompatible change. Minor versions are usually
68compatible to older versions, so a larger minor version alone is usually 77compatible to older versions, so a larger minor version alone is usually
69not a problem. 78not a problem.
70 79
71=item ev_set_allocator (void *(*cb)(void *ptr, long size)) 80=item ev_set_allocator (void *(*cb)(void *ptr, long size))
72 81
73Sets the allocation function to use (the prototype is similar to the 82Sets the allocation function to use (the prototype is similar to the
74realloc function). It is used to allocate and free memory (no surprises 83realloc C function, the semantics are identical). It is used to allocate
75here). If it returns zero when memory needs to be allocated, the library 84and free memory (no surprises here). If it returns zero when memory
76might abort or take some potentially destructive action. The default is 85needs to be allocated, the library might abort or take some potentially
77your system realloc function. 86destructive action. The default is your system realloc function.
78 87
79You could override this function in high-availability programs to, say, 88You could override this function in high-availability programs to, say,
80free some memory if it cannot allocate memory, to use a special allocator, 89free some memory if it cannot allocate memory, to use a special allocator,
81or even to sleep a while and retry until some memory is available. 90or even to sleep a while and retry until some memory is available.
82 91
… …
84 93
85Set the callback function to call on a retryable syscall error (such 94Set the callback function to call on a retryable syscall error (such
86as failed select, poll, epoll_wait). The message is a printable string 95as failed select, poll, epoll_wait). The message is a printable string
87indicating the system call or subsystem causing the problem. If this 96indicating the system call or subsystem causing the problem. If this
88callback is set, then libev will expect it to remedy the sitution, no 97callback is set, then libev will expect it to remedy the sitution, no
89matter what, when it returns. That is, libev will geenrally retry the 98matter what, when it returns. That is, libev will generally retry the
90requested operation, or, if the condition doesn't go away, do bad stuff 99requested operation, or, if the condition doesn't go away, do bad stuff
91(such as abort). 100(such as abort).
92 101
93=back 102=back
94 103
… …
97An event loop is described by a C<struct ev_loop *>. The library knows two 106An event loop is described by a C<struct ev_loop *>. The library knows two
98types of such loops, the I<default> loop, which supports signals and child 107types of such loops, the I<default> loop, which supports signals and child
99events, and dynamically created loops which do not. 108events, and dynamically created loops which do not.
100 109
101If you use threads, a common model is to run the default event loop 110If you use threads, a common model is to run the default event loop
102in your main thread (or in a separate thrad) and for each thread you 111in your main thread (or in a separate thread) and for each thread you
103create, you also create another event loop. Libev itself does no lockign 112create, you also create another event loop. Libev itself does no locking
104whatsoever, so if you mix calls to different event loops, make sure you 113whatsoever, so if you mix calls to the same event loop in different
105lock (this is usually a bad idea, though, even if done right). 114threads, make sure you lock (this is usually a bad idea, though, even if
115done correctly, because it's hideous and inefficient).
106 116
107=over 4 117=over 4
108 118
109=item struct ev_loop *ev_default_loop (unsigned int flags) 119=item struct ev_loop *ev_default_loop (unsigned int flags)
110 120
… …
115 125
116If you don't know what event loop to use, use the one returned from this 126If you don't know what event loop to use, use the one returned from this
117function. 127function.
118 128
119The flags argument can be used to specify special behaviour or specific 129The flags argument can be used to specify special behaviour or specific
120backends to use, and is usually specified as 0 (or EVFLAG_AUTO) 130backends to use, and is usually specified as 0 (or EVFLAG_AUTO).
121 131
122It supports the following flags: 132It supports the following flags:
123 133
124=over 4 134=over 4
125 135
126=item EVFLAG_AUTO 136=item C<EVFLAG_AUTO>
127 137
128The default flags value. Use this if you have no clue (its the right 138The default flags value. Use this if you have no clue (it's the right
129thing, believe me). 139thing, believe me).
130 140
131=item EVFLAG_NOENV 141=item C<EVFLAG_NOENV>
132 142
133If this flag bit is ored into the flag value then libev will I<not> look 143If this flag bit is ored into the flag value (or the program runs setuid
134at the environment variable C<LIBEV_FLAGS>. Otherwise (the default), this 144or setgid) then libev will I<not> look at the environment variable
135environment variable will override the flags completely. This is useful 145C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
146override the flags completely if it is found in the environment. This is
136to try out specific backends to tets their performance, or to work around 147useful to try out specific backends to test their performance, or to work
137bugs. 148around bugs.
138 149
139=item EVMETHOD_SELECT portable select backend 150=item C<EVMETHOD_SELECT> (portable select backend)
140 151
141=item EVMETHOD_POLL poll backend (everywhere except windows) 152=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)
142 153
143=item EVMETHOD_EPOLL linux only 154=item C<EVMETHOD_EPOLL> (linux only)
144 155
145=item EVMETHOD_KQUEUE some bsds only 156=item C<EVMETHOD_KQUEUE> (some bsds only)
146 157
147=item EVMETHOD_DEVPOLL solaris 8 only 158=item C<EVMETHOD_DEVPOLL> (solaris 8 only)
148 159
149=item EVMETHOD_PORT solaris 10 only 160=item C<EVMETHOD_PORT> (solaris 10 only)
150 161
151If one or more of these are ored into the flags value, then only these 162If one or more of these are ored into the flags value, then only these
152backends will be tried (in the reverse order as given here). If one are 163backends will be tried (in the reverse order as given here). If one are
153specified, any backend will do. 164specified, any backend will do.
154 165
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163 174
164=item ev_default_destroy () 175=item ev_default_destroy ()
165 176
166Destroys the default loop again (frees all memory and kernel state 177Destroys the default loop again (frees all memory and kernel state
167etc.). This stops all registered event watchers (by not touching them in 178etc.). This stops all registered event watchers (by not touching them in
168any way whatsoever, although you cnanot rely on this :). 179any way whatsoever, although you cannot rely on this :).
169 180
170=item ev_loop_destroy (loop) 181=item ev_loop_destroy (loop)
171 182
172Like C<ev_default_destroy>, but destroys an event loop created by an 183Like C<ev_default_destroy>, but destroys an event loop created by an
173earlier call to C<ev_loop_new>. 184earlier call to C<ev_loop_new>.
… …
181 192
182You I<must> call this function after forking if and only if you want to 193You I<must> call this function after forking if and only if you want to
183use the event library in both processes. If you just fork+exec, you don't 194use the event library in both processes. If you just fork+exec, you don't
184have to call it. 195have to call it.
185 196
186The function itself is quite fast and its usually not a problem to call 197The function itself is quite fast and it's usually not a problem to call
187it just in case after a fork. To make this easy, the function will fit in 198it just in case after a fork. To make this easy, the function will fit in
188quite nicely into a call to C<pthread_atfork>: 199quite nicely into a call to C<pthread_atfork>:
189 200
190 pthread_atfork (0, 0, ev_default_fork); 201 pthread_atfork (0, 0, ev_default_fork);
191 202
… …
198=item unsigned int ev_method (loop) 209=item unsigned int ev_method (loop)
199 210
200Returns one of the C<EVMETHOD_*> flags indicating the event backend in 211Returns one of the C<EVMETHOD_*> flags indicating the event backend in
201use. 212use.
202 213
203=item ev_tstamp = ev_now (loop) 214=item ev_tstamp ev_now (loop)
204 215
205Returns the current "event loop time", which is the time the event loop 216Returns the current "event loop time", which is the time the event loop
206got events and started processing them. This timestamp does not change 217got events and started processing them. This timestamp does not change
207as long as callbacks are being processed, and this is also the base time 218as long as callbacks are being processed, and this is also the base time
208used for relative timers. You can treat it as the timestamp of the event 219used for relative timers. You can treat it as the timestamp of the event
… …
217If the flags argument is specified as 0, it will not return until either 228If the flags argument is specified as 0, it will not return until either
218no event watchers are active anymore or C<ev_unloop> was called. 229no event watchers are active anymore or C<ev_unloop> was called.
219 230
220A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle 231A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
221those events and any outstanding ones, but will not block your process in 232those events and any outstanding ones, but will not block your process in
222case there are no events. 233case there are no events and will return after one iteration of the loop.
223 234
224A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if 235A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
225neccessary) and will handle those and any outstanding ones. It will block 236neccessary) and will handle those and any outstanding ones. It will block
226your process until at least one new event arrives. 237your process until at least one new event arrives, and will return after
238one iteration of the loop.
227 239
228This flags value could be used to implement alternative looping 240This flags value could be used to implement alternative looping
229constructs, but the C<prepare> and C<check> watchers provide a better and 241constructs, but the C<prepare> and C<check> watchers provide a better and
230more generic mechanism. 242more generic mechanism.
231 243
232=item ev_unloop (loop, how) 244=item ev_unloop (loop, how)
233 245
234Can be used to make a call to C<ev_loop> return early. The C<how> argument 246Can be used to make a call to C<ev_loop> return early (but only after it
247has processed all outstanding events). The C<how> argument must be either
235must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> 248C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
236call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> 249C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
237calls return.
238 250
239=item ev_ref (loop) 251=item ev_ref (loop)
240 252
241=item ev_unref (loop) 253=item ev_unref (loop)
242 254
243Ref/unref can be used to add or remove a refcount on the event loop: Every 255Ref/unref can be used to add or remove a reference count on the event
244watcher keeps one reference. If you have a long-runing watcher you never 256loop: Every watcher keeps one reference, and as long as the reference
245unregister that should not keep ev_loop from running, ev_unref() after 257count is nonzero, C<ev_loop> will not return on its own. If you have
246starting, and ev_ref() before stopping it. Libev itself uses this for 258a watcher you never unregister that should not keep C<ev_loop> from
247example for its internal signal pipe: It is not visible to you as a user 259returning, ev_unref() after starting, and ev_ref() before stopping it. For
248and should not keep C<ev_loop> from exiting if the work is done. It is 260example, libev itself uses this for its internal signal pipe: It is not
249also an excellent way to do this for generic recurring timers or from 261visible to the libev user and should not keep C<ev_loop> from exiting if
250within third-party libraries. Just remember to unref after start and ref 262no event watchers registered by it are active. It is also an excellent
251before stop. 263way to do this for generic recurring timers or from within third-party
264libraries. Just remember to I<unref after start> and I<ref before stop>.
252 265
253=back 266=back
254 267
255=head1 ANATOMY OF A WATCHER 268=head1 ANATOMY OF A WATCHER
256 269
257A watcher is a structure that you create and register to record your 270A watcher is a structure that you create and register to record your
258interest in some event. For instance, if you want to wait for STDIN to 271interest in some event. For instance, if you want to wait for STDIN to
259become readable, you would create an ev_io watcher for that: 272become readable, you would create an C<ev_io> watcher for that:
260 273
261 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 274 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
262 { 275 {
263 ev_io_stop (w); 276 ev_io_stop (w);
264 ev_unloop (loop, EVUNLOOP_ALL); 277 ev_unloop (loop, EVUNLOOP_ALL);
… …
293 306
294As long as your watcher is active (has been started but not stopped) you 307As long as your watcher is active (has been started but not stopped) you
295must not touch the values stored in it. Most specifically you must never 308must not touch the values stored in it. Most specifically you must never
296reinitialise it or call its set method. 309reinitialise it or call its set method.
297 310
298You cna check wether an event is active by calling the C<ev_is_active 311You can check whether an event is active by calling the C<ev_is_active
299(watcher *)> macro. To see wether an event is outstanding (but the 312(watcher *)> macro. To see whether an event is outstanding (but the
300callback for it has not been called yet) you cna use the C<ev_is_pending 313callback for it has not been called yet) you can use the C<ev_is_pending
301(watcher *)> macro. 314(watcher *)> macro.
302 315
303Each and every callback receives the event loop pointer as first, the 316Each and every callback receives the event loop pointer as first, the
304registered watcher structure as second, and a bitset of received events as 317registered watcher structure as second, and a bitset of received events as
305third argument. 318third argument.
306 319
307The rceeived events usually include a single bit per event type received 320The received events usually include a single bit per event type received
308(you can receive multiple events at the same time). The possible bit masks 321(you can receive multiple events at the same time). The possible bit masks
309are: 322are:
310 323
311=over 4 324=over 4
312 325
313=item EV_READ 326=item C<EV_READ>
314 327
315=item EV_WRITE 328=item C<EV_WRITE>
316 329
317The file descriptor in the ev_io watcher has become readable and/or 330The file descriptor in the C<ev_io> watcher has become readable and/or
318writable. 331writable.
319 332
320=item EV_TIMEOUT 333=item C<EV_TIMEOUT>
321 334
322The ev_timer watcher has timed out. 335The C<ev_timer> watcher has timed out.
323 336
324=item EV_PERIODIC 337=item C<EV_PERIODIC>
325 338
326The ev_periodic watcher has timed out. 339The C<ev_periodic> watcher has timed out.
327 340
328=item EV_SIGNAL 341=item C<EV_SIGNAL>
329 342
330The signal specified in the ev_signal watcher has been received by a thread. 343The signal specified in the C<ev_signal> watcher has been received by a thread.
331 344
332=item EV_CHILD 345=item C<EV_CHILD>
333 346
334The pid specified in the ev_child watcher has received a status change. 347The pid specified in the C<ev_child> watcher has received a status change.
335 348
336=item EV_IDLE 349=item C<EV_IDLE>
337 350
338The ev_idle watcher has determined that you have nothing better to do. 351The C<ev_idle> watcher has determined that you have nothing better to do.
339 352
340=item EV_PREPARE 353=item C<EV_PREPARE>
341 354
342=item EV_CHECK 355=item C<EV_CHECK>
343 356
344All ev_prepare watchers are invoked just I<before> C<ev_loop> starts 357All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
345to gather new events, and all ev_check watchers are invoked just after 358to gather new events, and all C<ev_check> watchers are invoked just after
346C<ev_loop> has gathered them, but before it invokes any callbacks for any 359C<ev_loop> has gathered them, but before it invokes any callbacks for any
347received events. Callbacks of both watcher types can start and stop as 360received events. Callbacks of both watcher types can start and stop as
348many watchers as they want, and all of them will be taken into account 361many watchers as they want, and all of them will be taken into account
349(for example, a ev_prepare watcher might start an idle watcher to keep 362(for example, a C<ev_prepare> watcher might start an idle watcher to keep
350C<ev_loop> from blocking). 363C<ev_loop> from blocking).
351 364
352=item EV_ERROR 365=item C<EV_ERROR>
353 366
354An unspecified error has occured, the watcher has been stopped. This might 367An unspecified error has occured, the watcher has been stopped. This might
355happen because the watcher could not be properly started because libev 368happen because the watcher could not be properly started because libev
356ran out of memory, a file descriptor was found to be closed or any other 369ran out of memory, a file descriptor was found to be closed or any other
357problem. You best act on it by reporting the problem and somehow coping 370problem. You best act on it by reporting the problem and somehow coping
… …
366=back 379=back
367 380
368=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER 381=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
369 382
370Each watcher has, by default, a member C<void *data> that you can change 383Each watcher has, by default, a member C<void *data> that you can change
371and read at any time, libev will completely ignore it. This cna be used 384and read at any time, libev will completely ignore it. This can be used
372to associate arbitrary data with your watcher. If you need more data and 385to associate arbitrary data with your watcher. If you need more data and
373don't want to allocate memory and store a pointer to it in that data 386don't want to allocate memory and store a pointer to it in that data
374member, you can also "subclass" the watcher type and provide your own 387member, you can also "subclass" the watcher type and provide your own
375data: 388data:
376 389
… …
398=head1 WATCHER TYPES 411=head1 WATCHER TYPES
399 412
400This section describes each watcher in detail, but will not repeat 413This section describes each watcher in detail, but will not repeat
401information given in the last section. 414information given in the last section.
402 415
403=head2 struct ev_io - is my file descriptor readable or writable 416=head2 C<ev_io> - is this file descriptor readable or writable
404 417
405I/O watchers check wether a file descriptor is readable or writable 418I/O watchers check whether a file descriptor is readable or writable
406in each iteration of the event loop (This behaviour is called 419in each iteration of the event loop (This behaviour is called
407level-triggering because you keep receiving events as long as the 420level-triggering because you keep receiving events as long as the
408condition persists. Remember you cna stop the watcher if you don't want to 421condition persists. Remember you can stop the watcher if you don't want to
409act on the event and neither want to receive future events). 422act on the event and neither want to receive future events).
410 423
424In general you can register as many read and/or write event watchers per
425fd as you want (as long as you don't confuse yourself). Setting all file
426descriptors to non-blocking mode is also usually a good idea (but not
427required if you know what you are doing).
428
429You have to be careful with dup'ed file descriptors, though. Some backends
430(the linux epoll backend is a notable example) cannot handle dup'ed file
431descriptors correctly if you register interest in two or more fds pointing
432to the same underlying file/socket etc. description (that is, they share
433the same underlying "file open").
434
435If you must do this, then force the use of a known-to-be-good backend
436(at the time of this writing, this includes only EVMETHOD_SELECT and
437EVMETHOD_POLL).
438
411=over 4 439=over 4
412 440
413=item ev_io_init (ev_io *, callback, int fd, int events) 441=item ev_io_init (ev_io *, callback, int fd, int events)
414 442
415=item ev_io_set (ev_io *, int fd, int events) 443=item ev_io_set (ev_io *, int fd, int events)
416 444
417Configures an ev_io watcher. The fd is the file descriptor to rceeive 445Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive
418events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ | 446events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
419EV_WRITE> to receive the given events. 447EV_WRITE> to receive the given events.
420 448
421=back 449=back
422 450
423=head2 struct ev_timer - relative and optionally recurring timeouts 451=head2 C<ev_timer> - relative and optionally recurring timeouts
424 452
425Timer watchers are simple relative timers that generate an event after a 453Timer watchers are simple relative timers that generate an event after a
426given time, and optionally repeating in regular intervals after that. 454given time, and optionally repeating in regular intervals after that.
427 455
428The timers are based on real time, that is, if you register an event that 456The timers are based on real time, that is, if you register an event that
429times out after an hour and youreset your system clock to last years 457times out after an hour and you reset your system clock to last years
430time, it will still time out after (roughly) and hour. "Roughly" because 458time, it will still time out after (roughly) and hour. "Roughly" because
431detecting time jumps is hard, and soem inaccuracies are unavoidable (the 459detecting time jumps is hard, and soem inaccuracies are unavoidable (the
432monotonic clock option helps a lot here). 460monotonic clock option helps a lot here).
461
462The relative timeouts are calculated relative to the C<ev_now ()>
463time. This is usually the right thing as this timestamp refers to the time
464of the event triggering whatever timeout you are modifying/starting. If
465you suspect event processing to be delayed and you *need* to base the timeout
466on the current time, use something like this to adjust for this:
467
468 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
433 469
434=over 4 470=over 4
435 471
436=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) 472=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
437 473
… …
443later, again, and again, until stopped manually. 479later, again, and again, until stopped manually.
444 480
445The timer itself will do a best-effort at avoiding drift, that is, if you 481The timer itself will do a best-effort at avoiding drift, that is, if you
446configure a timer to trigger every 10 seconds, then it will trigger at 482configure a timer to trigger every 10 seconds, then it will trigger at
447exactly 10 second intervals. If, however, your program cannot keep up with 483exactly 10 second intervals. If, however, your program cannot keep up with
448the timer (ecause it takes longer than those 10 seconds to do stuff) the 484the timer (because it takes longer than those 10 seconds to do stuff) the
449timer will not fire more than once per event loop iteration. 485timer will not fire more than once per event loop iteration.
450 486
451=item ev_timer_again (loop) 487=item ev_timer_again (loop)
452 488
453This will act as if the timer timed out and restart it again if it is 489This will act as if the timer timed out and restart it again if it is
… …
460 496
461This sounds a bit complicated, but here is a useful and typical 497This sounds a bit complicated, but here is a useful and typical
462example: Imagine you have a tcp connection and you want a so-called idle 498example: Imagine you have a tcp connection and you want a so-called idle
463timeout, that is, you want to be called when there have been, say, 60 499timeout, that is, you want to be called when there have been, say, 60
464seconds of inactivity on the socket. The easiest way to do this is to 500seconds of inactivity on the socket. The easiest way to do this is to
465configure an ev_timer with after=repeat=60 and calling ev_timer_again each 501configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each
466time you successfully read or write some data. If you go into an idle 502time you successfully read or write some data. If you go into an idle
467state where you do not expect data to travel on the socket, you can stop 503state where you do not expect data to travel on the socket, you can stop
468the timer, and again will automatically restart it if need be. 504the timer, and again will automatically restart it if need be.
469 505
470=back 506=back
471 507
472=head2 ev_periodic - to cron or not to cron it 508=head2 C<ev_periodic> - to cron or not to cron
473 509
474Periodic watchers are also timers of a kind, but they are very versatile 510Periodic watchers are also timers of a kind, but they are very versatile
475(and unfortunately a bit complex). 511(and unfortunately a bit complex).
476 512
477Unlike ev_timer's, they are not based on real time (or relative time) 513Unlike C<ev_timer>'s, they are not based on real time (or relative time)
478but on wallclock time (absolute time). You can tell a periodic watcher 514but on wallclock time (absolute time). You can tell a periodic watcher
479to trigger "at" some specific point in time. For example, if you tell a 515to trigger "at" some specific point in time. For example, if you tell a
480periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 516periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
481+ 10.>) and then reset your system clock to the last year, then it will 517+ 10.>) and then reset your system clock to the last year, then it will
482take a year to trigger the event (unlike an ev_timer, which would trigger 518take a year to trigger the event (unlike an C<ev_timer>, which would trigger
483roughly 10 seconds later and of course not if you reset your system time 519roughly 10 seconds later and of course not if you reset your system time
484again). 520again).
485 521
486They can also be used to implement vastly more complex timers, such as 522They can also be used to implement vastly more complex timers, such as
487triggering an event on eahc midnight, local time. 523triggering an event on eahc midnight, local time.
… …
516 552
517 ev_periodic_set (&periodic, 0., 3600., 0); 553 ev_periodic_set (&periodic, 0., 3600., 0);
518 554
519This doesn't mean there will always be 3600 seconds in between triggers, 555This doesn't mean there will always be 3600 seconds in between triggers,
520but only that the the callback will be called when the system time shows a 556but only that the the callback will be called when the system time shows a
521full hour (UTC), or more correct, when the system time is evenly divisible 557full hour (UTC), or more correctly, when the system time is evenly divisible
522by 3600. 558by 3600.
523 559
524Another way to think about it (for the mathematically inclined) is that 560Another way to think about it (for the mathematically inclined) is that
525ev_periodic will try to run the callback in this mode at the next possible 561C<ev_periodic> will try to run the callback in this mode at the next possible
526time where C<time = at (mod interval)>, regardless of any time jumps. 562time where C<time = at (mod interval)>, regardless of any time jumps.
527 563
528=item * manual reschedule mode (reschedule_cb = callback) 564=item * manual reschedule mode (reschedule_cb = callback)
529 565
530In this mode the values for C<interval> and C<at> are both being 566In this mode the values for C<interval> and C<at> are both being
531ignored. Instead, each time the periodic watcher gets scheduled, the 567ignored. Instead, each time the periodic watcher gets scheduled, the
532reschedule callback will be called with the watcher as first, and the 568reschedule callback will be called with the watcher as first, and the
533current time as second argument. 569current time as second argument.
534 570
535NOTE: I<This callback MUST NOT stop or destroy the periodic or any other 571NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
536periodic watcher, ever, or make any event loop modificstions>. If you need 572ever, or make any event loop modifications>. If you need to stop it,
537to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards. 573return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
574starting a prepare watcher).
538 575
539Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 576Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
540ev_tstamp now)>, e.g.: 577ev_tstamp now)>, e.g.:
541 578
542 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 579 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
543 { 580 {
544 return now + 60.; 581 return now + 60.;
… …
547It must return the next time to trigger, based on the passed time value 584It must return the next time to trigger, based on the passed time value
548(that is, the lowest time value larger than to the second argument). It 585(that is, the lowest time value larger than to the second argument). It
549will usually be called just before the callback will be triggered, but 586will usually be called just before the callback will be triggered, but
550might be called at other times, too. 587might be called at other times, too.
551 588
589NOTE: I<< This callback must always return a time that is later than the
590passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
591
552This can be used to create very complex timers, such as a timer that 592This can be used to create very complex timers, such as a timer that
553triggers on each midnight, local time. To do this, you would calculate the 593triggers on each midnight, local time. To do this, you would calculate the
554next midnight after C<now> and return the timestamp value for this. How you do this 594next midnight after C<now> and return the timestamp value for this. How
555is, again, up to you (but it is not trivial). 595you do this is, again, up to you (but it is not trivial, which is the main
596reason I omitted it as an example).
556 597
557=back 598=back
558 599
559=item ev_periodic_again (loop, ev_periodic *) 600=item ev_periodic_again (loop, ev_periodic *)
560 601
… …
563a different time than the last time it was called (e.g. in a crond like 604a different time than the last time it was called (e.g. in a crond like
564program when the crontabs have changed). 605program when the crontabs have changed).
565 606
566=back 607=back
567 608
568=head2 ev_signal - signal me when a signal gets signalled 609=head2 C<ev_signal> - signal me when a signal gets signalled
569 610
570Signal watchers will trigger an event when the process receives a specific 611Signal watchers will trigger an event when the process receives a specific
571signal one or more times. Even though signals are very asynchronous, libev 612signal one or more times. Even though signals are very asynchronous, libev
572will try its best to deliver signals synchronously, i.e. as part of the 613will try it's best to deliver signals synchronously, i.e. as part of the
573normal event processing, like any other event. 614normal event processing, like any other event.
574 615
575You cna configure as many watchers as you like per signal. Only when the 616You can configure as many watchers as you like per signal. Only when the
576first watcher gets started will libev actually register a signal watcher 617first watcher gets started will libev actually register a signal watcher
577with the kernel (thus it coexists with your own signal handlers as long 618with the kernel (thus it coexists with your own signal handlers as long
578as you don't register any with libev). Similarly, when the last signal 619as you don't register any with libev). Similarly, when the last signal
579watcher for a signal is stopped libev will reset the signal handler to 620watcher for a signal is stopped libev will reset the signal handler to
580SIG_DFL (regardless of what it was set to before). 621SIG_DFL (regardless of what it was set to before).
… …
588Configures the watcher to trigger on the given signal number (usually one 629Configures the watcher to trigger on the given signal number (usually one
589of the C<SIGxxx> constants). 630of the C<SIGxxx> constants).
590 631
591=back 632=back
592 633
593=head2 ev_child - wait for pid status changes 634=head2 C<ev_child> - wait for pid status changes
594 635
595Child watchers trigger when your process receives a SIGCHLD in response to 636Child watchers trigger when your process receives a SIGCHLD in response to
596some child status changes (most typically when a child of yours dies). 637some child status changes (most typically when a child of yours dies).
597 638
598=over 4 639=over 4
… …
602=item ev_child_set (ev_child *, int pid) 643=item ev_child_set (ev_child *, int pid)
603 644
604Configures the watcher to wait for status changes of process C<pid> (or 645Configures the watcher to wait for status changes of process C<pid> (or
605I<any> process if C<pid> is specified as C<0>). The callback can look 646I<any> process if C<pid> is specified as C<0>). The callback can look
606at the C<rstatus> member of the C<ev_child> watcher structure to see 647at the C<rstatus> member of the C<ev_child> watcher structure to see
607the status word (use the macros from C<sys/wait.h>). The C<rpid> member 648the status word (use the macros from C<sys/wait.h> and see your systems
608contains the pid of the process causing the status change. 649C<waitpid> documentation). The C<rpid> member contains the pid of the
650process causing the status change.
609 651
610=back 652=back
611 653
612=head2 ev_idle - when you've got nothing better to do 654=head2 C<ev_idle> - when you've got nothing better to do
613 655
614Idle watchers trigger events when there are no other I/O or timer (or 656Idle watchers trigger events when there are no other events are pending
615periodic) events pending. That is, as long as your process is busy 657(prepare, check and other idle watchers do not count). That is, as long
616handling sockets or timeouts it will not be called. But when your process 658as your process is busy handling sockets or timeouts (or even signals,
617is idle all idle watchers are being called again and again - until 659imagine) it will not be triggered. But when your process is idle all idle
660watchers are being called again and again, once per event loop iteration -
618stopped, that is, or your process receives more events. 661until stopped, that is, or your process receives more events and becomes
662busy.
619 663
620The most noteworthy effect is that as long as any idle watchers are 664The most noteworthy effect is that as long as any idle watchers are
621active, the process will not block when waiting for new events. 665active, the process will not block when waiting for new events.
622 666
623Apart from keeping your process non-blocking (which is a useful 667Apart from keeping your process non-blocking (which is a useful
… …
633kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, 677kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
634believe me. 678believe me.
635 679
636=back 680=back
637 681
638=head2 prepare and check - your hooks into the event loop 682=head2 C<ev_prepare> and C<ev_check> - customise your event loop
639 683
640Prepare and check watchers usually (but not always) are used in 684Prepare and check watchers are usually (but not always) used in tandem:
641tandom. Prepare watchers get invoked before the process blocks and check 685prepare watchers get invoked before the process blocks and check watchers
642watchers afterwards. 686afterwards.
643 687
644Their main purpose is to integrate other event mechanisms into libev. This 688Their main purpose is to integrate other event mechanisms into libev. This
645could be used, for example, to track variable changes, implement your own 689could be used, for example, to track variable changes, implement your own
646watchers, integrate net-snmp or a coroutine library and lots more. 690watchers, integrate net-snmp or a coroutine library and lots more.
647 691
648This is done by examining in each prepare call which file descriptors need 692This is done by examining in each prepare call which file descriptors need
649to be watched by the other library, registering ev_io watchers for them 693to be watched by the other library, registering C<ev_io> watchers for
650and starting an ev_timer watcher for any timeouts (many libraries provide 694them and starting an C<ev_timer> watcher for any timeouts (many libraries
651just this functionality). Then, in the check watcher you check for any 695provide just this functionality). Then, in the check watcher you check for
652events that occured (by making your callbacks set soem flags for example) 696any events that occured (by checking the pending status of all watchers
653and call back into the library. 697and stopping them) and call back into the library. The I/O and timer
698callbacks will never actually be called (but must be valid nevertheless,
699because you never know, you know?).
654 700
655As another example, the perl Coro module uses these hooks to integrate 701As another example, the Perl Coro module uses these hooks to integrate
656coroutines into libev programs, by yielding to other active coroutines 702coroutines into libev programs, by yielding to other active coroutines
657during each prepare and only letting the process block if no coroutines 703during each prepare and only letting the process block if no coroutines
658are ready to run. 704are ready to run (it's actually more complicated: it only runs coroutines
705with priority higher than or equal to the event loop and one coroutine
706of lower priority, but only once, using idle watchers to keep the event
707loop from blocking if lower-priority coroutines are active, thus mapping
708low-priority coroutines to idle/background tasks).
659 709
660=over 4 710=over 4
661 711
662=item ev_prepare_init (ev_prepare *, callback) 712=item ev_prepare_init (ev_prepare *, callback)
663 713
664=item ev_check_init (ev_check *, callback) 714=item ev_check_init (ev_check *, callback)
665 715
666Initialises and configures the prepare or check watcher - they have no 716Initialises and configures the prepare or check watcher - they have no
667parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set> 717parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
668macros, but using them is utterly, utterly pointless. 718macros, but using them is utterly, utterly and completely pointless.
669 719
670=back 720=back
671 721
672=head1 OTHER FUNCTIONS 722=head1 OTHER FUNCTIONS
673 723
674There are some other fucntions of possible interest. Described. Here. Now. 724There are some other functions of possible interest. Described. Here. Now.
675 725
676=over 4 726=over 4
677 727
678=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) 728=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
679 729
680This function combines a simple timer and an I/O watcher, calls your 730This function combines a simple timer and an I/O watcher, calls your
681callback on whichever event happens first and automatically stop both 731callback on whichever event happens first and automatically stop both
682watchers. This is useful if you want to wait for a single event on an fd 732watchers. This is useful if you want to wait for a single event on an fd
683or timeout without havign to allocate/configure/start/stop/free one or 733or timeout without having to allocate/configure/start/stop/free one or
684more watchers yourself. 734more watchers yourself.
685 735
686If C<fd> is less than 0, then no I/O watcher will be started and events is 736If C<fd> is less than 0, then no I/O watcher will be started and events
687ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set 737is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
688will be craeted and started. 738C<events> set will be craeted and started.
689 739
690If C<timeout> is less than 0, then no timeout watcher will be 740If C<timeout> is less than 0, then no timeout watcher will be
691started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat 741started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
692= 0) will be started. 742repeat = 0) will be started. While C<0> is a valid timeout, it is of
743dubious value.
693 744
694The callback has the type C<void (*cb)(int revents, void *arg)> and 745The callback has the type C<void (*cb)(int revents, void *arg)> and gets
695gets passed an events set (normally a combination of EV_ERROR, EV_READ, 746passed an C<revents> set like normal event callbacks (a combination of
696EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>: 747C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
748value passed to C<ev_once>:
697 749
698 static void stdin_ready (int revents, void *arg) 750 static void stdin_ready (int revents, void *arg)
699 { 751 {
700 if (revents & EV_TIMEOUT) 752 if (revents & EV_TIMEOUT)
701 /* doh, nothing entered */ 753 /* doh, nothing entered */;
702 else if (revents & EV_READ) 754 else if (revents & EV_READ)
703 /* stdin might have data for us, joy! */ 755 /* stdin might have data for us, joy! */;
704 } 756 }
705 757
706 ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0); 758 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
707 759
708=item ev_feed_event (loop, watcher, int events) 760=item ev_feed_event (loop, watcher, int events)
709 761
710Feeds the given event set into the event loop, as if the specified event 762Feeds the given event set into the event loop, as if the specified event
711has happened for the specified watcher (which must be a pointer to an 763had happened for the specified watcher (which must be a pointer to an
712initialised but not necessarily active event watcher). 764initialised but not necessarily started event watcher).
713 765
714=item ev_feed_fd_event (loop, int fd, int revents) 766=item ev_feed_fd_event (loop, int fd, int revents)
715 767
716Feed an event on the given fd, as if a file descriptor backend detected it. 768Feed an event on the given fd, as if a file descriptor backend detected
769the given events it.
717 770
718=item ev_feed_signal_event (loop, int signum) 771=item ev_feed_signal_event (loop, int signum)
719 772
720Feed an event as if the given signal occured (loop must be the default loop!). 773Feed an event as if the given signal occured (loop must be the default loop!).
721 774
722=back 775=back
723 776
777=head1 LIBEVENT EMULATION
778
779Libev offers a compatibility emulation layer for libevent. It cannot
780emulate the internals of libevent, so here are some usage hints:
781
782=over 4
783
784=item * Use it by including <event.h>, as usual.
785
786=item * The following members are fully supported: ev_base, ev_callback,
787ev_arg, ev_fd, ev_res, ev_events.
788
789=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
790maintained by libev, it does not work exactly the same way as in libevent (consider
791it a private API).
792
793=item * Priorities are not currently supported. Initialising priorities
794will fail and all watchers will have the same priority, even though there
795is an ev_pri field.
796
797=item * Other members are not supported.
798
799=item * The libev emulation is I<not> ABI compatible to libevent, you need
800to use the libev header file and library.
801
802=back
803
804=head1 C++ SUPPORT
805
806TBD.
807
724=head1 AUTHOR 808=head1 AUTHOR
725 809
726Marc Lehmann <libev@schmorp.de>. 810Marc Lehmann <libev@schmorp.de>.
727 811

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