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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). It also is quite 30loop mechanism itself (idle, prepare and check watchers). It also is quite
31fast (see a L<http://libev.schmorp.de/bench.html|benchmark> comparing it 31fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing
32to libevent). 32it to libevent for example).
33 33
34=head1 CONVENTIONS 34=head1 CONVENTIONS
35 35
36Libev is very configurable. In this manual the default configuration 36Libev is very configurable. In this manual the default configuration
37will be described, which supports multiple event loops. For more info 37will be described, which supports multiple event loops. For more info
38about various configuraiton options please have a look at the file 38about various configuration options please have a look at the file
39F<README.embed> in the libev distribution. If libev was configured without 39F<README.embed> in the libev distribution. If libev was configured without
40support for multiple event loops, then all functions taking an initial 40support for multiple event loops, then all functions taking an initial
41argument 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 *>)
42will not have this argument. 42will not have this argument.
43 43
63you linked against by calling the functions C<ev_version_major> and 63you linked against by calling the functions C<ev_version_major> and
64C<ev_version_minor>. If you want, you can compare against the global 64C<ev_version_minor>. If you want, you can compare against the global
65symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the 65symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
66version of the library your program was compiled against. 66version of the library your program was compiled against.
67 67
68Usually, its a good idea to terminate if the major versions mismatch, 68Usually, it's a good idea to terminate if the major versions mismatch,
69as this indicates an incompatible change. Minor versions are usually 69as this indicates an incompatible change. Minor versions are usually
70compatible to older versions, so a larger minor version alone is usually 70compatible to older versions, so a larger minor version alone is usually
71not a problem. 71not a problem.
72 72
73=item ev_set_allocator (void *(*cb)(void *ptr, long size)) 73=item ev_set_allocator (void *(*cb)(void *ptr, long size))
74 74
75Sets the allocation function to use (the prototype is similar to the 75Sets the allocation function to use (the prototype is similar to the
76realloc function). It is used to allocate and free memory (no surprises 76realloc C function, the semantics are identical). It is used to allocate
77here). If it returns zero when memory needs to be allocated, the library 77and free memory (no surprises here). If it returns zero when memory
78might abort or take some potentially destructive action. The default is 78needs to be allocated, the library might abort or take some potentially
79your system realloc function. 79destructive action. The default is your system realloc function.
80 80
81You could override this function in high-availability programs to, say, 81You could override this function in high-availability programs to, say,
82free some memory if it cannot allocate memory, to use a special allocator, 82free some memory if it cannot allocate memory, to use a special allocator,
83or even to sleep a while and retry until some memory is available. 83or even to sleep a while and retry until some memory is available.
84 84
86 86
87Set the callback function to call on a retryable syscall error (such 87Set the callback function to call on a retryable syscall error (such
88as failed select, poll, epoll_wait). The message is a printable string 88as failed select, poll, epoll_wait). The message is a printable string
89indicating the system call or subsystem causing the problem. If this 89indicating the system call or subsystem causing the problem. If this
90callback is set, then libev will expect it to remedy the sitution, no 90callback is set, then libev will expect it to remedy the sitution, no
91matter what, when it returns. That is, libev will geenrally retry the 91matter what, when it returns. That is, libev will generally retry the
92requested operation, or, if the condition doesn't go away, do bad stuff 92requested operation, or, if the condition doesn't go away, do bad stuff
93(such as abort). 93(such as abort).
94 94
95=back 95=back
96 96
100types of such loops, the I<default> loop, which supports signals and child 100types of such loops, the I<default> loop, which supports signals and child
101events, and dynamically created loops which do not. 101events, and dynamically created loops which do not.
102 102
103If you use threads, a common model is to run the default event loop 103If you use threads, a common model is to run the default event loop
104in your main thread (or in a separate thrad) and for each thread you 104in your main thread (or in a separate thrad) and for each thread you
105create, you also create another event loop. Libev itself does no lockign 105create, you also create another event loop. Libev itself does no locking
106whatsoever, so if you mix calls to different event loops, make sure you 106whatsoever, so if you mix calls to the same event loop in different
107lock (this is usually a bad idea, though, even if done right). 107threads, make sure you lock (this is usually a bad idea, though, even if
108done correctly, because it's hideous and inefficient).
108 109
109=over 4 110=over 4
110 111
111=item struct ev_loop *ev_default_loop (unsigned int flags) 112=item struct ev_loop *ev_default_loop (unsigned int flags)
112 113
117 118
118If you don't know what event loop to use, use the one returned from this 119If you don't know what event loop to use, use the one returned from this
119function. 120function.
120 121
121The flags argument can be used to specify special behaviour or specific 122The flags argument can be used to specify special behaviour or specific
122backends to use, and is usually specified as 0 (or EVFLAG_AUTO) 123backends to use, and is usually specified as 0 (or EVFLAG_AUTO).
123 124
124It supports the following flags: 125It supports the following flags:
125 126
126=over 4 127=over 4
127 128
128=item EVFLAG_AUTO 129=item C<EVFLAG_AUTO>
129 130
130The default flags value. Use this if you have no clue (its the right 131The default flags value. Use this if you have no clue (it's the right
131thing, believe me). 132thing, believe me).
132 133
133=item EVFLAG_NOENV 134=item C<EVFLAG_NOENV>
134 135
135If this flag bit is ored into the flag value then libev will I<not> look 136If this flag bit is ored into the flag value (or the program runs setuid
136at the environment variable C<LIBEV_FLAGS>. Otherwise (the default), this 137or setgid) then libev will I<not> look at the environment variable
137environment variable will override the flags completely. This is useful 138C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
139override the flags completely if it is found in the environment. This is
138to try out specific backends to tets their performance, or to work around 140useful to try out specific backends to test their performance, or to work
139bugs. 141around bugs.
140 142
141=item EVMETHOD_SELECT portable select backend 143=item C<EVMETHOD_SELECT> (portable select backend)
142 144
143=item EVMETHOD_POLL poll backend (everywhere except windows) 145=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)
144 146
145=item EVMETHOD_EPOLL linux only 147=item C<EVMETHOD_EPOLL> (linux only)
146 148
147=item EVMETHOD_KQUEUE some bsds only 149=item C<EVMETHOD_KQUEUE> (some bsds only)
148 150
149=item EVMETHOD_DEVPOLL solaris 8 only 151=item C<EVMETHOD_DEVPOLL> (solaris 8 only)
150 152
151=item EVMETHOD_PORT solaris 10 only 153=item C<EVMETHOD_PORT> (solaris 10 only)
152 154
153If one or more of these are ored into the flags value, then only these 155If one or more of these are ored into the flags value, then only these
154backends will be tried (in the reverse order as given here). If one are 156backends will be tried (in the reverse order as given here). If one are
155specified, any backend will do. 157specified, any backend will do.
156 158
165 167
166=item ev_default_destroy () 168=item ev_default_destroy ()
167 169
168Destroys the default loop again (frees all memory and kernel state 170Destroys the default loop again (frees all memory and kernel state
169etc.). This stops all registered event watchers (by not touching them in 171etc.). This stops all registered event watchers (by not touching them in
170any way whatsoever, although you cnanot rely on this :). 172any way whatsoever, although you cannot rely on this :).
171 173
172=item ev_loop_destroy (loop) 174=item ev_loop_destroy (loop)
173 175
174Like C<ev_default_destroy>, but destroys an event loop created by an 176Like C<ev_default_destroy>, but destroys an event loop created by an
175earlier call to C<ev_loop_new>. 177earlier call to C<ev_loop_new>.
183 185
184You I<must> call this function after forking if and only if you want to 186You I<must> call this function after forking if and only if you want to
185use the event library in both processes. If you just fork+exec, you don't 187use the event library in both processes. If you just fork+exec, you don't
186have to call it. 188have to call it.
187 189
188The function itself is quite fast and its usually not a problem to call 190The function itself is quite fast and it's usually not a problem to call
189it just in case after a fork. To make this easy, the function will fit in 191it just in case after a fork. To make this easy, the function will fit in
190quite nicely into a call to C<pthread_atfork>: 192quite nicely into a call to C<pthread_atfork>:
191 193
192 pthread_atfork (0, 0, ev_default_fork); 194 pthread_atfork (0, 0, ev_default_fork);
193 195
200=item unsigned int ev_method (loop) 202=item unsigned int ev_method (loop)
201 203
202Returns one of the C<EVMETHOD_*> flags indicating the event backend in 204Returns one of the C<EVMETHOD_*> flags indicating the event backend in
203use. 205use.
204 206
205=item ev_tstamp = ev_now (loop) 207=item ev_tstamp ev_now (loop)
206 208
207Returns the current "event loop time", which is the time the event loop 209Returns the current "event loop time", which is the time the event loop
208got events and started processing them. This timestamp does not change 210got events and started processing them. This timestamp does not change
209as long as callbacks are being processed, and this is also the base time 211as long as callbacks are being processed, and this is also the base time
210used for relative timers. You can treat it as the timestamp of the event 212used for relative timers. You can treat it as the timestamp of the event
219If the flags argument is specified as 0, it will not return until either 221If the flags argument is specified as 0, it will not return until either
220no event watchers are active anymore or C<ev_unloop> was called. 222no event watchers are active anymore or C<ev_unloop> was called.
221 223
222A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle 224A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
223those events and any outstanding ones, but will not block your process in 225those events and any outstanding ones, but will not block your process in
224case there are no events. 226case there are no events and will return after one iteration of the loop.
225 227
226A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if 228A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
227neccessary) and will handle those and any outstanding ones. It will block 229neccessary) and will handle those and any outstanding ones. It will block
228your process until at least one new event arrives. 230your process until at least one new event arrives, and will return after
231one iteration of the loop.
229 232
230This flags value could be used to implement alternative looping 233This flags value could be used to implement alternative looping
231constructs, but the C<prepare> and C<check> watchers provide a better and 234constructs, but the C<prepare> and C<check> watchers provide a better and
232more generic mechanism. 235more generic mechanism.
233 236
234=item ev_unloop (loop, how) 237=item ev_unloop (loop, how)
235 238
236Can be used to make a call to C<ev_loop> return early. The C<how> argument 239Can be used to make a call to C<ev_loop> return early (but only after it
240has processed all outstanding events). The C<how> argument must be either
237must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> 241C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> call return, or
238call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> 242C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
239calls return.
240 243
241=item ev_ref (loop) 244=item ev_ref (loop)
242 245
243=item ev_unref (loop) 246=item ev_unref (loop)
244 247
245Ref/unref can be used to add or remove a refcount on the event loop: Every 248Ref/unref can be used to add or remove a reference count on the event
246watcher keeps one reference. If you have a long-runing watcher you never 249loop: Every watcher keeps one reference, and as long as the reference
247unregister that should not keep ev_loop from running, ev_unref() after 250count is nonzero, C<ev_loop> will not return on its own. If you have
248starting, and ev_ref() before stopping it. Libev itself uses this for 251a watcher you never unregister that should not keep C<ev_loop> from
249example for its internal signal pipe: It is not visible to you as a user 252returning, ev_unref() after starting, and ev_ref() before stopping it. For
250and should not keep C<ev_loop> from exiting if the work is done. It is 253example, libev itself uses this for its internal signal pipe: It is not
251also an excellent way to do this for generic recurring timers or from 254visible to the libev user and should not keep C<ev_loop> from exiting if
252within third-party libraries. Just remember to unref after start and ref 255no event watchers registered by it are active. It is also an excellent
253before stop. 256way to do this for generic recurring timers or from within third-party
257libraries. Just remember to I<unref after start> and I<ref before stop>.
254 258
255=back 259=back
256 260
257=head1 ANATOMY OF A WATCHER 261=head1 ANATOMY OF A WATCHER
258 262
259A watcher is a structure that you create and register to record your 263A watcher is a structure that you create and register to record your
260interest in some event. For instance, if you want to wait for STDIN to 264interest in some event. For instance, if you want to wait for STDIN to
261become readable, you would create an ev_io watcher for that: 265become readable, you would create an C<ev_io> watcher for that:
262 266
263 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 267 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
264 { 268 {
265 ev_io_stop (w); 269 ev_io_stop (w);
266 ev_unloop (loop, EVUNLOOP_ALL); 270 ev_unloop (loop, EVUNLOOP_ALL);
295 299
296As long as your watcher is active (has been started but not stopped) you 300As long as your watcher is active (has been started but not stopped) you
297must not touch the values stored in it. Most specifically you must never 301must not touch the values stored in it. Most specifically you must never
298reinitialise it or call its set method. 302reinitialise it or call its set method.
299 303
300You cna check whether an event is active by calling the C<ev_is_active 304You can check whether an event is active by calling the C<ev_is_active
301(watcher *)> macro. To see whether an event is outstanding (but the 305(watcher *)> macro. To see whether an event is outstanding (but the
302callback for it has not been called yet) you cna use the C<ev_is_pending 306callback for it has not been called yet) you can use the C<ev_is_pending
303(watcher *)> macro. 307(watcher *)> macro.
304 308
305Each and every callback receives the event loop pointer as first, the 309Each and every callback receives the event loop pointer as first, the
306registered watcher structure as second, and a bitset of received events as 310registered watcher structure as second, and a bitset of received events as
307third argument. 311third argument.
308 312
309The rceeived events usually include a single bit per event type received 313The received events usually include a single bit per event type received
310(you can receive multiple events at the same time). The possible bit masks 314(you can receive multiple events at the same time). The possible bit masks
311are: 315are:
312 316
313=over 4 317=over 4
314 318
315=item EV_READ 319=item C<EV_READ>
316 320
317=item EV_WRITE 321=item C<EV_WRITE>
318 322
319The file descriptor in the ev_io watcher has become readable and/or 323The file descriptor in the C<ev_io> watcher has become readable and/or
320writable. 324writable.
321 325
322=item EV_TIMEOUT 326=item C<EV_TIMEOUT>
323 327
324The ev_timer watcher has timed out. 328The C<ev_timer> watcher has timed out.
325 329
326=item EV_PERIODIC 330=item C<EV_PERIODIC>
327 331
328The ev_periodic watcher has timed out. 332The C<ev_periodic> watcher has timed out.
329 333
330=item EV_SIGNAL 334=item C<EV_SIGNAL>
331 335
332The signal specified in the ev_signal watcher has been received by a thread. 336The signal specified in the C<ev_signal> watcher has been received by a thread.
333 337
334=item EV_CHILD 338=item C<EV_CHILD>
335 339
336The pid specified in the ev_child watcher has received a status change. 340The pid specified in the C<ev_child> watcher has received a status change.
337 341
338=item EV_IDLE 342=item C<EV_IDLE>
339 343
340The ev_idle watcher has determined that you have nothing better to do. 344The C<ev_idle> watcher has determined that you have nothing better to do.
341 345
342=item EV_PREPARE 346=item C<EV_PREPARE>
343 347
344=item EV_CHECK 348=item C<EV_CHECK>
345 349
346All ev_prepare watchers are invoked just I<before> C<ev_loop> starts 350All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
347to gather new events, and all ev_check watchers are invoked just after 351to gather new events, and all C<ev_check> watchers are invoked just after
348C<ev_loop> has gathered them, but before it invokes any callbacks for any 352C<ev_loop> has gathered them, but before it invokes any callbacks for any
349received events. Callbacks of both watcher types can start and stop as 353received events. Callbacks of both watcher types can start and stop as
350many watchers as they want, and all of them will be taken into account 354many watchers as they want, and all of them will be taken into account
351(for example, a ev_prepare watcher might start an idle watcher to keep 355(for example, a C<ev_prepare> watcher might start an idle watcher to keep
352C<ev_loop> from blocking). 356C<ev_loop> from blocking).
353 357
354=item EV_ERROR 358=item C<EV_ERROR>
355 359
356An unspecified error has occured, the watcher has been stopped. This might 360An unspecified error has occured, the watcher has been stopped. This might
357happen because the watcher could not be properly started because libev 361happen because the watcher could not be properly started because libev
358ran out of memory, a file descriptor was found to be closed or any other 362ran out of memory, a file descriptor was found to be closed or any other
359problem. You best act on it by reporting the problem and somehow coping 363problem. You best act on it by reporting the problem and somehow coping
368=back 372=back
369 373
370=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER 374=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
371 375
372Each watcher has, by default, a member C<void *data> that you can change 376Each watcher has, by default, a member C<void *data> that you can change
373and read at any time, libev will completely ignore it. This cna be used 377and read at any time, libev will completely ignore it. This can be used
374to associate arbitrary data with your watcher. If you need more data and 378to associate arbitrary data with your watcher. If you need more data and
375don't want to allocate memory and store a pointer to it in that data 379don't want to allocate memory and store a pointer to it in that data
376member, you can also "subclass" the watcher type and provide your own 380member, you can also "subclass" the watcher type and provide your own
377data: 381data:
378 382
400=head1 WATCHER TYPES 404=head1 WATCHER TYPES
401 405
402This section describes each watcher in detail, but will not repeat 406This section describes each watcher in detail, but will not repeat
403information given in the last section. 407information given in the last section.
404 408
405=head2 struct ev_io - is my file descriptor readable or writable 409=head2 C<ev_io> - is this file descriptor readable or writable
406 410
407I/O watchers check whether a file descriptor is readable or writable 411I/O watchers check whether a file descriptor is readable or writable
408in each iteration of the event loop (This behaviour is called 412in each iteration of the event loop (This behaviour is called
409level-triggering because you keep receiving events as long as the 413level-triggering because you keep receiving events as long as the
410condition persists. Remember you cna stop the watcher if you don't want to 414condition persists. Remember you can stop the watcher if you don't want to
411act on the event and neither want to receive future events). 415act on the event and neither want to receive future events).
412 416
417In general you can register as many read and/or write event watchers oer
418fd as you want (as long as you don't confuse yourself). Setting all file
419descriptors to non-blocking mode is also usually a good idea (but not
420required if you know what you are doing).
421
422You have to be careful with dup'ed file descriptors, though. Some backends
423(the linux epoll backend is a notable example) cannot handle dup'ed file
424descriptors correctly if you register interest in two or more fds pointing
425to the same file/socket etc. description.
426
427If you must do this, then force the use of a known-to-be-good backend
428(at the time of this writing, this includes only EVMETHOD_SELECT and
429EVMETHOD_POLL).
430
413=over 4 431=over 4
414 432
415=item ev_io_init (ev_io *, callback, int fd, int events) 433=item ev_io_init (ev_io *, callback, int fd, int events)
416 434
417=item ev_io_set (ev_io *, int fd, int events) 435=item ev_io_set (ev_io *, int fd, int events)
418 436
419Configures an ev_io watcher. The fd is the file descriptor to rceeive 437Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive
420events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ | 438events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
421EV_WRITE> to receive the given events. 439EV_WRITE> to receive the given events.
422 440
423=back 441=back
424 442
425=head2 struct ev_timer - relative and optionally recurring timeouts 443=head2 C<ev_timer> - relative and optionally recurring timeouts
426 444
427Timer watchers are simple relative timers that generate an event after a 445Timer watchers are simple relative timers that generate an event after a
428given time, and optionally repeating in regular intervals after that. 446given time, and optionally repeating in regular intervals after that.
429 447
430The timers are based on real time, that is, if you register an event that 448The timers are based on real time, that is, if you register an event that
431times out after an hour and youreset your system clock to last years 449times out after an hour and youreset your system clock to last years
432time, it will still time out after (roughly) and hour. "Roughly" because 450time, it will still time out after (roughly) and hour. "Roughly" because
433detecting time jumps is hard, and soem inaccuracies are unavoidable (the 451detecting time jumps is hard, and soem inaccuracies are unavoidable (the
434monotonic clock option helps a lot here). 452monotonic clock option helps a lot here).
435 453
454The relative timeouts are calculated relative to the C<ev_now ()>
455time. This is usually the right thing as this timestamp refers to the time
456of the event triggering whatever timeout you are modifying/starting. If
457you suspect event processing to be delayed and you *need* to base the timeout
458ion the current time, use something like this to adjust for this:
459
460 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
461
436=over 4 462=over 4
437 463
438=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) 464=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
439 465
440=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat) 466=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
462 488
463This sounds a bit complicated, but here is a useful and typical 489This sounds a bit complicated, but here is a useful and typical
464example: Imagine you have a tcp connection and you want a so-called idle 490example: Imagine you have a tcp connection and you want a so-called idle
465timeout, that is, you want to be called when there have been, say, 60 491timeout, that is, you want to be called when there have been, say, 60
466seconds of inactivity on the socket. The easiest way to do this is to 492seconds of inactivity on the socket. The easiest way to do this is to
467configure an ev_timer with after=repeat=60 and calling ev_timer_again each 493configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each
468time you successfully read or write some data. If you go into an idle 494time you successfully read or write some data. If you go into an idle
469state where you do not expect data to travel on the socket, you can stop 495state where you do not expect data to travel on the socket, you can stop
470the timer, and again will automatically restart it if need be. 496the timer, and again will automatically restart it if need be.
471 497
472=back 498=back
473 499
474=head2 ev_periodic - to cron or not to cron it 500=head2 C<ev_periodic> - to cron or not to cron
475 501
476Periodic watchers are also timers of a kind, but they are very versatile 502Periodic watchers are also timers of a kind, but they are very versatile
477(and unfortunately a bit complex). 503(and unfortunately a bit complex).
478 504
479Unlike ev_timer's, they are not based on real time (or relative time) 505Unlike C<ev_timer>'s, they are not based on real time (or relative time)
480but on wallclock time (absolute time). You can tell a periodic watcher 506but on wallclock time (absolute time). You can tell a periodic watcher
481to trigger "at" some specific point in time. For example, if you tell a 507to trigger "at" some specific point in time. For example, if you tell a
482periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 508periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
483+ 10.>) and then reset your system clock to the last year, then it will 509+ 10.>) and then reset your system clock to the last year, then it will
484take a year to trigger the event (unlike an ev_timer, which would trigger 510take a year to trigger the event (unlike an C<ev_timer>, which would trigger
485roughly 10 seconds later and of course not if you reset your system time 511roughly 10 seconds later and of course not if you reset your system time
486again). 512again).
487 513
488They can also be used to implement vastly more complex timers, such as 514They can also be used to implement vastly more complex timers, such as
489triggering an event on eahc midnight, local time. 515triggering an event on eahc midnight, local time.
518 544
519 ev_periodic_set (&periodic, 0., 3600., 0); 545 ev_periodic_set (&periodic, 0., 3600., 0);
520 546
521This doesn't mean there will always be 3600 seconds in between triggers, 547This doesn't mean there will always be 3600 seconds in between triggers,
522but only that the the callback will be called when the system time shows a 548but only that the the callback will be called when the system time shows a
523full hour (UTC), or more correct, when the system time is evenly divisible 549full hour (UTC), or more correctly, when the system time is evenly divisible
524by 3600. 550by 3600.
525 551
526Another way to think about it (for the mathematically inclined) is that 552Another way to think about it (for the mathematically inclined) is that
527ev_periodic will try to run the callback in this mode at the next possible 553C<ev_periodic> will try to run the callback in this mode at the next possible
528time where C<time = at (mod interval)>, regardless of any time jumps. 554time where C<time = at (mod interval)>, regardless of any time jumps.
529 555
530=item * manual reschedule mode (reschedule_cb = callback) 556=item * manual reschedule mode (reschedule_cb = callback)
531 557
532In this mode the values for C<interval> and C<at> are both being 558In this mode the values for C<interval> and C<at> are both being
533ignored. Instead, each time the periodic watcher gets scheduled, the 559ignored. Instead, each time the periodic watcher gets scheduled, the
534reschedule callback will be called with the watcher as first, and the 560reschedule callback will be called with the watcher as first, and the
535current time as second argument. 561current time as second argument.
536 562
537NOTE: I<This callback MUST NOT stop or destroy the periodic or any other 563NOTE: I<This callback MUST NOT stop or destroy the periodic or any other
538periodic watcher, ever, or make any event loop modificstions>. If you need 564periodic watcher, ever, or make any event loop modifications>. If you need
539to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards. 565to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.
540 566
567Also, I<< this callback must always return a time that is later than the
568passed C<now> value >>. Not even C<now> itself will be ok.
569
541Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 570Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
542ev_tstamp now)>, e.g.: 571ev_tstamp now)>, e.g.:
543 572
544 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 573 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
545 { 574 {
546 return now + 60.; 575 return now + 60.;
565a different time than the last time it was called (e.g. in a crond like 594a different time than the last time it was called (e.g. in a crond like
566program when the crontabs have changed). 595program when the crontabs have changed).
567 596
568=back 597=back
569 598
570=head2 ev_signal - signal me when a signal gets signalled 599=head2 C<ev_signal> - signal me when a signal gets signalled
571 600
572Signal watchers will trigger an event when the process receives a specific 601Signal watchers will trigger an event when the process receives a specific
573signal one or more times. Even though signals are very asynchronous, libev 602signal one or more times. Even though signals are very asynchronous, libev
574will try its best to deliver signals synchronously, i.e. as part of the 603will try it's best to deliver signals synchronously, i.e. as part of the
575normal event processing, like any other event. 604normal event processing, like any other event.
576 605
577You cna configure as many watchers as you like per signal. Only when the 606You can configure as many watchers as you like per signal. Only when the
578first watcher gets started will libev actually register a signal watcher 607first watcher gets started will libev actually register a signal watcher
579with the kernel (thus it coexists with your own signal handlers as long 608with the kernel (thus it coexists with your own signal handlers as long
580as you don't register any with libev). Similarly, when the last signal 609as you don't register any with libev). Similarly, when the last signal
581watcher for a signal is stopped libev will reset the signal handler to 610watcher for a signal is stopped libev will reset the signal handler to
582SIG_DFL (regardless of what it was set to before). 611SIG_DFL (regardless of what it was set to before).
590Configures the watcher to trigger on the given signal number (usually one 619Configures the watcher to trigger on the given signal number (usually one
591of the C<SIGxxx> constants). 620of the C<SIGxxx> constants).
592 621
593=back 622=back
594 623
595=head2 ev_child - wait for pid status changes 624=head2 C<ev_child> - wait for pid status changes
596 625
597Child watchers trigger when your process receives a SIGCHLD in response to 626Child watchers trigger when your process receives a SIGCHLD in response to
598some child status changes (most typically when a child of yours dies). 627some child status changes (most typically when a child of yours dies).
599 628
600=over 4 629=over 4
604=item ev_child_set (ev_child *, int pid) 633=item ev_child_set (ev_child *, int pid)
605 634
606Configures the watcher to wait for status changes of process C<pid> (or 635Configures the watcher to wait for status changes of process C<pid> (or
607I<any> process if C<pid> is specified as C<0>). The callback can look 636I<any> process if C<pid> is specified as C<0>). The callback can look
608at the C<rstatus> member of the C<ev_child> watcher structure to see 637at the C<rstatus> member of the C<ev_child> watcher structure to see
609the status word (use the macros from C<sys/wait.h>). The C<rpid> member 638the status word (use the macros from C<sys/wait.h> and see your systems
610contains the pid of the process causing the status change. 639C<waitpid> documentation). The C<rpid> member contains the pid of the
640process causing the status change.
611 641
612=back 642=back
613 643
614=head2 ev_idle - when you've got nothing better to do 644=head2 C<ev_idle> - when you've got nothing better to do
615 645
616Idle watchers trigger events when there are no other I/O or timer (or 646Idle watchers trigger events when there are no other events are pending
617periodic) events pending. That is, as long as your process is busy 647(prepare, check and other idle watchers do not count). That is, as long
618handling sockets or timeouts it will not be called. But when your process 648as your process is busy handling sockets or timeouts (or even signals,
619is idle all idle watchers are being called again and again - until 649imagine) it will not be triggered. But when your process is idle all idle
650watchers are being called again and again, once per event loop iteration -
620stopped, that is, or your process receives more events. 651until stopped, that is, or your process receives more events and becomes
652busy.
621 653
622The most noteworthy effect is that as long as any idle watchers are 654The most noteworthy effect is that as long as any idle watchers are
623active, the process will not block when waiting for new events. 655active, the process will not block when waiting for new events.
624 656
625Apart from keeping your process non-blocking (which is a useful 657Apart from keeping your process non-blocking (which is a useful
635kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, 667kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
636believe me. 668believe me.
637 669
638=back 670=back
639 671
640=head2 prepare and check - your hooks into the event loop 672=head2 C<ev_prepare> and C<ev_check> - customise your event loop
641 673
642Prepare and check watchers usually (but not always) are used in 674Prepare and check watchers are usually (but not always) used in tandem:
643tandom. Prepare watchers get invoked before the process blocks and check 675Prepare watchers get invoked before the process blocks and check watchers
644watchers afterwards. 676afterwards.
645 677
646Their main purpose is to integrate other event mechanisms into libev. This 678Their main purpose is to integrate other event mechanisms into libev. This
647could be used, for example, to track variable changes, implement your own 679could be used, for example, to track variable changes, implement your own
648watchers, integrate net-snmp or a coroutine library and lots more. 680watchers, integrate net-snmp or a coroutine library and lots more.
649 681
650This is done by examining in each prepare call which file descriptors need 682This is done by examining in each prepare call which file descriptors need
651to be watched by the other library, registering ev_io watchers for them 683to be watched by the other library, registering C<ev_io> watchers for
652and starting an ev_timer watcher for any timeouts (many libraries provide 684them and starting an C<ev_timer> watcher for any timeouts (many libraries
653just this functionality). Then, in the check watcher you check for any 685provide just this functionality). Then, in the check watcher you check for
654events that occured (by making your callbacks set soem flags for example) 686any events that occured (by checking the pending status of all watchers
655and call back into the library. 687and stopping them) and call back into the library. The I/O and timer
688callbacks will never actually be called (but must be valid neverthelles,
689because you never know, you know?).
656 690
657As another example, the perl Coro module uses these hooks to integrate 691As another example, the Perl Coro module uses these hooks to integrate
658coroutines into libev programs, by yielding to other active coroutines 692coroutines into libev programs, by yielding to other active coroutines
659during each prepare and only letting the process block if no coroutines 693during each prepare and only letting the process block if no coroutines
660are ready to run. 694are ready to run (its actually more complicated, it only runs coroutines
695with priority higher than the event loop and one lower priority once,
696using idle watchers to keep the event loop from blocking if lower-priority
697coroutines exist, thus mapping low-priority coroutines to idle/background
698tasks).
661 699
662=over 4 700=over 4
663 701
664=item ev_prepare_init (ev_prepare *, callback) 702=item ev_prepare_init (ev_prepare *, callback)
665 703
666=item ev_check_init (ev_check *, callback) 704=item ev_check_init (ev_check *, callback)
667 705
668Initialises and configures the prepare or check watcher - they have no 706Initialises and configures the prepare or check watcher - they have no
669parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set> 707parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
670macros, but using them is utterly, utterly pointless. 708macros, but using them is utterly, utterly and completely pointless.
671 709
672=back 710=back
673 711
674=head1 OTHER FUNCTIONS 712=head1 OTHER FUNCTIONS
675 713
676There are some other fucntions of possible interest. Described. Here. Now. 714There are some other functions of possible interest. Described. Here. Now.
677 715
678=over 4 716=over 4
679 717
680=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) 718=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
681 719
683callback on whichever event happens first and automatically stop both 721callback on whichever event happens first and automatically stop both
684watchers. This is useful if you want to wait for a single event on an fd 722watchers. This is useful if you want to wait for a single event on an fd
685or timeout without havign to allocate/configure/start/stop/free one or 723or timeout without havign to allocate/configure/start/stop/free one or
686more watchers yourself. 724more watchers yourself.
687 725
688If C<fd> is less than 0, then no I/O watcher will be started and events is 726If C<fd> is less than 0, then no I/O watcher will be started and events
689ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set 727is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
690will be craeted and started. 728C<events> set will be craeted and started.
691 729
692If C<timeout> is less than 0, then no timeout watcher will be 730If C<timeout> is less than 0, then no timeout watcher will be
693started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat 731started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
694= 0) will be started. 732repeat = 0) will be started. While C<0> is a valid timeout, it is of
733dubious value.
695 734
696The callback has the type C<void (*cb)(int revents, void *arg)> and 735The callback has the type C<void (*cb)(int revents, void *arg)> and gets
697gets passed an events set (normally a combination of EV_ERROR, EV_READ, 736passed an events set like normal event callbacks (with a combination of
698EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>: 737C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
738value passed to C<ev_once>:
699 739
700 static void stdin_ready (int revents, void *arg) 740 static void stdin_ready (int revents, void *arg)
701 { 741 {
702 if (revents & EV_TIMEOUT) 742 if (revents & EV_TIMEOUT)
703 /* doh, nothing entered */ 743 /* doh, nothing entered */;
704 else if (revents & EV_READ) 744 else if (revents & EV_READ)
705 /* stdin might have data for us, joy! */ 745 /* stdin might have data for us, joy! */;
706 } 746 }
707 747
708 ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0); 748 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
709 749
710=item ev_feed_event (loop, watcher, int events) 750=item ev_feed_event (loop, watcher, int events)
711 751
712Feeds the given event set into the event loop, as if the specified event 752Feeds the given event set into the event loop, as if the specified event
713has happened for the specified watcher (which must be a pointer to an 753had happened for the specified watcher (which must be a pointer to an
714initialised but not necessarily active event watcher). 754initialised but not necessarily started event watcher).
715 755
716=item ev_feed_fd_event (loop, int fd, int revents) 756=item ev_feed_fd_event (loop, int fd, int revents)
717 757
718Feed an event on the given fd, as if a file descriptor backend detected it. 758Feed an event on the given fd, as if a file descriptor backend detected
759the given events it.
719 760
720=item ev_feed_signal_event (loop, int signum) 761=item ev_feed_signal_event (loop, int signum)
721 762
722Feed an event as if the given signal occured (loop must be the default loop!). 763Feed an event as if the given signal occured (loop must be the default loop!).
723 764

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