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Revision 1.6 by root, Mon Nov 12 08:12:14 2007 UTC vs.
Revision 1.27 by root, Wed Nov 14 05:02:07 2007 UTC

… …
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<benchmark|http://libev.schmorp.de/bench.html> 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
44=head1 TIME AND OTHER GLOBAL FUNCTIONS 44=head1 TIME REPRESENTATION
45 45
46Libev represents time as a single floating point number, representing the 46Libev represents time as a single floating point number, representing the
47(fractional) number of seconds since the (POSIX) epoch (somewhere near 47(fractional) number of seconds since the (POSIX) epoch (somewhere near
48the 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
49called 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
50to the double type in C. 50to the double type in C.
51 51
52=head1 GLOBAL FUNCTIONS
53
54These functions can be called anytime, even before initialising the
55library in any way.
56
52=over 4 57=over 4
53 58
54=item ev_tstamp ev_time () 59=item ev_tstamp ev_time ()
55 60
56Returns 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.
57 64
58=item int ev_version_major () 65=item int ev_version_major ()
59 66
60=item int ev_version_minor () 67=item int ev_version_minor ()
61 68
… …
63you linked against by calling the functions C<ev_version_major> and 70you linked against by calling the functions C<ev_version_major> and
64C<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
65symbols 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
66version of the library your program was compiled against. 73version of the library your program was compiled against.
67 74
68Usually, its a good idea to terminate if the major versions mismatch, 75Usually, it's a good idea to terminate if the major versions mismatch,
69as this indicates an incompatible change. Minor versions are usually 76as this indicates an incompatible change. Minor versions are usually
70compatible to older versions, so a larger minor version alone is usually 77compatible to older versions, so a larger minor version alone is usually
71not a problem. 78not a problem.
72 79
73=item ev_set_allocator (void *(*cb)(void *ptr, long size)) 80=item ev_set_allocator (void *(*cb)(void *ptr, long size))
74 81
75Sets the allocation function to use (the prototype is similar to the 82Sets the allocation function to use (the prototype is similar to the
76realloc function). It is used to allocate and free memory (no surprises 83realloc C function, the semantics are identical). It is used to allocate
77here). If it returns zero when memory needs to be allocated, the library 84and free memory (no surprises here). If it returns zero when memory
78might abort or take some potentially destructive action. The default is 85needs to be allocated, the library might abort or take some potentially
79your system realloc function. 86destructive action. The default is your system realloc function.
80 87
81You could override this function in high-availability programs to, say, 88You could override this function in high-availability programs to, say,
82free 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,
83or 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.
84 91
… …
86 93
87Set the callback function to call on a retryable syscall error (such 94Set the callback function to call on a retryable syscall error (such
88as failed select, poll, epoll_wait). The message is a printable string 95as failed select, poll, epoll_wait). The message is a printable string
89indicating the system call or subsystem causing the problem. If this 96indicating the system call or subsystem causing the problem. If this
90callback 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
91matter what, when it returns. That is, libev will geenrally retry the 98matter what, when it returns. That is, libev will generally retry the
92requested 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
93(such as abort). 100(such as abort).
94 101
95=back 102=back
96 103
… …
99An 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
100types 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
101events, and dynamically created loops which do not. 108events, and dynamically created loops which do not.
102 109
103If 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
104in 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
105create, you also create another event loop. Libev itself does no lockign 112create, you also create another event loop. Libev itself does no locking
106whatsoever, 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
107lock (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).
108 116
109=over 4 117=over 4
110 118
111=item struct ev_loop *ev_default_loop (unsigned int flags) 119=item struct ev_loop *ev_default_loop (unsigned int flags)
112 120
… …
117 125
118If 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
119function. 127function.
120 128
121The flags argument can be used to specify special behaviour or specific 129The flags argument can be used to specify special behaviour or specific
122backends to use, and is usually specified as 0 (or EVFLAG_AUTO) 130backends to use, and is usually specified as 0 (or EVFLAG_AUTO).
123 131
124It supports the following flags: 132It supports the following flags:
125 133
126=over 4 134=over 4
127 135
128=item EVFLAG_AUTO 136=item C<EVFLAG_AUTO>
129 137
130The 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
131thing, believe me). 139thing, believe me).
132 140
133=item EVFLAG_NOENV 141=item C<EVFLAG_NOENV>
134 142
135If 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
136at the environment variable C<LIBEV_FLAGS>. Otherwise (the default), this 144or setgid) then libev will I<not> look at the environment variable
137environment 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
138to 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
139bugs. 148around bugs.
140 149
141=item EVMETHOD_SELECT portable select backend 150=item C<EVMETHOD_SELECT> (portable select backend)
142 151
143=item EVMETHOD_POLL poll backend (everywhere except windows) 152=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)
144 153
145=item EVMETHOD_EPOLL linux only 154=item C<EVMETHOD_EPOLL> (linux only)
146 155
147=item EVMETHOD_KQUEUE some bsds only 156=item C<EVMETHOD_KQUEUE> (some bsds only)
148 157
149=item EVMETHOD_DEVPOLL solaris 8 only 158=item C<EVMETHOD_DEVPOLL> (solaris 8 only)
150 159
151=item EVMETHOD_PORT solaris 10 only 160=item C<EVMETHOD_PORT> (solaris 10 only)
152 161
153If 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
154backends 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
155specified, any backend will do. 164specified, any backend will do.
156 165
… …
165 174
166=item ev_default_destroy () 175=item ev_default_destroy ()
167 176
168Destroys the default loop again (frees all memory and kernel state 177Destroys the default loop again (frees all memory and kernel state
169etc.). This stops all registered event watchers (by not touching them in 178etc.). This stops all registered event watchers (by not touching them in
170any way whatsoever, although you cnanot rely on this :). 179any way whatsoever, although you cannot rely on this :).
171 180
172=item ev_loop_destroy (loop) 181=item ev_loop_destroy (loop)
173 182
174Like 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
175earlier call to C<ev_loop_new>. 184earlier call to C<ev_loop_new>.
… …
183 192
184You 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
185use 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
186have to call it. 195have to call it.
187 196
188The 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
189it 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
190quite nicely into a call to C<pthread_atfork>: 199quite nicely into a call to C<pthread_atfork>:
191 200
192 pthread_atfork (0, 0, ev_default_fork); 201 pthread_atfork (0, 0, ev_default_fork);
193 202
… …
200=item unsigned int ev_method (loop) 209=item unsigned int ev_method (loop)
201 210
202Returns one of the C<EVMETHOD_*> flags indicating the event backend in 211Returns one of the C<EVMETHOD_*> flags indicating the event backend in
203use. 212use.
204 213
205=item ev_tstamp = ev_now (loop) 214=item ev_tstamp ev_now (loop)
206 215
207Returns 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
208got events and started processing them. This timestamp does not change 217got events and started processing them. This timestamp does not change
209as 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
210used 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
… …
219If 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
220no event watchers are active anymore or C<ev_unloop> was called. 229no event watchers are active anymore or C<ev_unloop> was called.
221 230
222A 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
223those 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
224case there are no events. 233case there are no events and will return after one iteration of the loop.
225 234
226A 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
227neccessary) and will handle those and any outstanding ones. It will block 236neccessary) and will handle those and any outstanding ones. It will block
228your 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.
229 239
230This flags value could be used to implement alternative looping 240This flags value could be used to implement alternative looping
231constructs, 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
232more generic mechanism. 242more generic mechanism.
233 243
244Here are the gory details of what ev_loop does:
245
246 1. If there are no active watchers (reference count is zero), return.
247 2. Queue and immediately call all prepare watchers.
248 3. If we have been forked, recreate the kernel state.
249 4. Update the kernel state with all outstanding changes.
250 5. Update the "event loop time".
251 6. Calculate for how long to block.
252 7. Block the process, waiting for events.
253 8. Update the "event loop time" and do time jump handling.
254 9. Queue all outstanding timers.
255 10. Queue all outstanding periodics.
256 11. If no events are pending now, queue all idle watchers.
257 12. Queue all check watchers.
258 13. Call all queued watchers in reverse order (i.e. check watchers first).
259 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
260 was used, return, otherwise continue with step #1.
261
234=item ev_unloop (loop, how) 262=item ev_unloop (loop, how)
235 263
236Can be used to make a call to C<ev_loop> return early. The C<how> argument 264Can be used to make a call to C<ev_loop> return early (but only after it
265has 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> 266C<EVUNLOOP_ONE>, 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> 267C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
239calls return.
240 268
241=item ev_ref (loop) 269=item ev_ref (loop)
242 270
243=item ev_unref (loop) 271=item ev_unref (loop)
244 272
245Ref/unref can be used to add or remove a refcount on the event loop: Every 273Ref/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 274loop: Every watcher keeps one reference, and as long as the reference
247unregister that should not keep ev_loop from running, ev_unref() after 275count 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 276a 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 277returning, 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 278example, 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 279visible 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 280no event watchers registered by it are active. It is also an excellent
253before stop. 281way to do this for generic recurring timers or from within third-party
282libraries. Just remember to I<unref after start> and I<ref before stop>.
254 283
255=back 284=back
256 285
257=head1 ANATOMY OF A WATCHER 286=head1 ANATOMY OF A WATCHER
258 287
259A watcher is a structure that you create and register to record your 288A 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 289interest in some event. For instance, if you want to wait for STDIN to
261become readable, you would create an ev_io watcher for that: 290become readable, you would create an C<ev_io> watcher for that:
262 291
263 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 292 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
264 { 293 {
265 ev_io_stop (w); 294 ev_io_stop (w);
266 ev_unloop (loop, EVUNLOOP_ALL); 295 ev_unloop (loop, EVUNLOOP_ALL);
… …
295 324
296As long as your watcher is active (has been started but not stopped) you 325As 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 326must not touch the values stored in it. Most specifically you must never
298reinitialise it or call its set method. 327reinitialise it or call its set method.
299 328
300You cna check whether an event is active by calling the C<ev_is_active 329You 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 330(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 331callback for it has not been called yet) you can use the C<ev_is_pending
303(watcher *)> macro. 332(watcher *)> macro.
304 333
305Each and every callback receives the event loop pointer as first, the 334Each and every callback receives the event loop pointer as first, the
306registered watcher structure as second, and a bitset of received events as 335registered watcher structure as second, and a bitset of received events as
307third argument. 336third argument.
308 337
309The rceeived events usually include a single bit per event type received 338The 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 339(you can receive multiple events at the same time). The possible bit masks
311are: 340are:
312 341
313=over 4 342=over 4
314 343
315=item EV_READ 344=item C<EV_READ>
316 345
317=item EV_WRITE 346=item C<EV_WRITE>
318 347
319The file descriptor in the ev_io watcher has become readable and/or 348The file descriptor in the C<ev_io> watcher has become readable and/or
320writable. 349writable.
321 350
322=item EV_TIMEOUT 351=item C<EV_TIMEOUT>
323 352
324The ev_timer watcher has timed out. 353The C<ev_timer> watcher has timed out.
325 354
326=item EV_PERIODIC 355=item C<EV_PERIODIC>
327 356
328The ev_periodic watcher has timed out. 357The C<ev_periodic> watcher has timed out.
329 358
330=item EV_SIGNAL 359=item C<EV_SIGNAL>
331 360
332The signal specified in the ev_signal watcher has been received by a thread. 361The signal specified in the C<ev_signal> watcher has been received by a thread.
333 362
334=item EV_CHILD 363=item C<EV_CHILD>
335 364
336The pid specified in the ev_child watcher has received a status change. 365The pid specified in the C<ev_child> watcher has received a status change.
337 366
338=item EV_IDLE 367=item C<EV_IDLE>
339 368
340The ev_idle watcher has determined that you have nothing better to do. 369The C<ev_idle> watcher has determined that you have nothing better to do.
341 370
342=item EV_PREPARE 371=item C<EV_PREPARE>
343 372
344=item EV_CHECK 373=item C<EV_CHECK>
345 374
346All ev_prepare watchers are invoked just I<before> C<ev_loop> starts 375All 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 376to 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 377C<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 378received 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 379many 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 380(for example, a C<ev_prepare> watcher might start an idle watcher to keep
352C<ev_loop> from blocking). 381C<ev_loop> from blocking).
353 382
354=item EV_ERROR 383=item C<EV_ERROR>
355 384
356An unspecified error has occured, the watcher has been stopped. This might 385An unspecified error has occured, the watcher has been stopped. This might
357happen because the watcher could not be properly started because libev 386happen 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 387ran 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 388problem. You best act on it by reporting the problem and somehow coping
… …
368=back 397=back
369 398
370=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER 399=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
371 400
372Each watcher has, by default, a member C<void *data> that you can change 401Each 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 402and 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 403to 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 404don'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 405member, you can also "subclass" the watcher type and provide your own
377data: 406data:
378 407
… …
400=head1 WATCHER TYPES 429=head1 WATCHER TYPES
401 430
402This section describes each watcher in detail, but will not repeat 431This section describes each watcher in detail, but will not repeat
403information given in the last section. 432information given in the last section.
404 433
405=head2 struct ev_io - is my file descriptor readable or writable 434=head2 C<ev_io> - is this file descriptor readable or writable
406 435
407I/O watchers check whether a file descriptor is readable or writable 436I/O watchers check whether a file descriptor is readable or writable
408in each iteration of the event loop (This behaviour is called 437in each iteration of the event loop (This behaviour is called
409level-triggering because you keep receiving events as long as the 438level-triggering because you keep receiving events as long as the
410condition persists. Remember you cna stop the watcher if you don't want to 439condition persists. Remember you can stop the watcher if you don't want to
411act on the event and neither want to receive future events). 440act on the event and neither want to receive future events).
412 441
442In general you can register as many read and/or write event watchers per
443fd as you want (as long as you don't confuse yourself). Setting all file
444descriptors to non-blocking mode is also usually a good idea (but not
445required if you know what you are doing).
446
447You have to be careful with dup'ed file descriptors, though. Some backends
448(the linux epoll backend is a notable example) cannot handle dup'ed file
449descriptors correctly if you register interest in two or more fds pointing
450to the same underlying file/socket etc. description (that is, they share
451the same underlying "file open").
452
453If you must do this, then force the use of a known-to-be-good backend
454(at the time of this writing, this includes only EVMETHOD_SELECT and
455EVMETHOD_POLL).
456
413=over 4 457=over 4
414 458
415=item ev_io_init (ev_io *, callback, int fd, int events) 459=item ev_io_init (ev_io *, callback, int fd, int events)
416 460
417=item ev_io_set (ev_io *, int fd, int events) 461=item ev_io_set (ev_io *, int fd, int events)
418 462
419Configures an ev_io watcher. The fd is the file descriptor to rceeive 463Configures 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 | 464events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
421EV_WRITE> to receive the given events. 465EV_WRITE> to receive the given events.
422 466
423=back 467=back
424 468
425=head2 struct ev_timer - relative and optionally recurring timeouts 469=head2 C<ev_timer> - relative and optionally recurring timeouts
426 470
427Timer watchers are simple relative timers that generate an event after a 471Timer watchers are simple relative timers that generate an event after a
428given time, and optionally repeating in regular intervals after that. 472given time, and optionally repeating in regular intervals after that.
429 473
430The timers are based on real time, that is, if you register an event that 474The 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 475times out after an hour and you reset your system clock to last years
432time, it will still time out after (roughly) and hour. "Roughly" because 476time, it will still time out after (roughly) and hour. "Roughly" because
433detecting time jumps is hard, and soem inaccuracies are unavoidable (the 477detecting time jumps is hard, and soem inaccuracies are unavoidable (the
434monotonic clock option helps a lot here). 478monotonic clock option helps a lot here).
479
480The relative timeouts are calculated relative to the C<ev_now ()>
481time. This is usually the right thing as this timestamp refers to the time
482of the event triggering whatever timeout you are modifying/starting. If
483you suspect event processing to be delayed and you *need* to base the timeout
484on the current time, use something like this to adjust for this:
485
486 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
435 487
436=over 4 488=over 4
437 489
438=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) 490=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
439 491
… …
445later, again, and again, until stopped manually. 497later, again, and again, until stopped manually.
446 498
447The timer itself will do a best-effort at avoiding drift, that is, if you 499The timer itself will do a best-effort at avoiding drift, that is, if you
448configure a timer to trigger every 10 seconds, then it will trigger at 500configure a timer to trigger every 10 seconds, then it will trigger at
449exactly 10 second intervals. If, however, your program cannot keep up with 501exactly 10 second intervals. If, however, your program cannot keep up with
450the timer (ecause it takes longer than those 10 seconds to do stuff) the 502the timer (because it takes longer than those 10 seconds to do stuff) the
451timer will not fire more than once per event loop iteration. 503timer will not fire more than once per event loop iteration.
452 504
453=item ev_timer_again (loop) 505=item ev_timer_again (loop)
454 506
455This will act as if the timer timed out and restart it again if it is 507This will act as if the timer timed out and restart it again if it is
… …
462 514
463This sounds a bit complicated, but here is a useful and typical 515This 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 516example: 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 517timeout, 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 518seconds 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 519configure 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 520time 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 521state 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. 522the timer, and again will automatically restart it if need be.
471 523
472=back 524=back
473 525
474=head2 ev_periodic - to cron or not to cron it 526=head2 C<ev_periodic> - to cron or not to cron
475 527
476Periodic watchers are also timers of a kind, but they are very versatile 528Periodic watchers are also timers of a kind, but they are very versatile
477(and unfortunately a bit complex). 529(and unfortunately a bit complex).
478 530
479Unlike ev_timer's, they are not based on real time (or relative time) 531Unlike 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 532but 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 533to 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 () 534periodic 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 535+ 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 536take 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 537roughly 10 seconds later and of course not if you reset your system time
486again). 538again).
487 539
488They can also be used to implement vastly more complex timers, such as 540They can also be used to implement vastly more complex timers, such as
489triggering an event on eahc midnight, local time. 541triggering an event on eahc midnight, local time.
… …
518 570
519 ev_periodic_set (&periodic, 0., 3600., 0); 571 ev_periodic_set (&periodic, 0., 3600., 0);
520 572
521This doesn't mean there will always be 3600 seconds in between triggers, 573This 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 574but 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 575full hour (UTC), or more correctly, when the system time is evenly divisible
524by 3600. 576by 3600.
525 577
526Another way to think about it (for the mathematically inclined) is that 578Another 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 579C<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. 580time where C<time = at (mod interval)>, regardless of any time jumps.
529 581
530=item * manual reschedule mode (reschedule_cb = callback) 582=item * manual reschedule mode (reschedule_cb = callback)
531 583
532In this mode the values for C<interval> and C<at> are both being 584In this mode the values for C<interval> and C<at> are both being
533ignored. Instead, each time the periodic watcher gets scheduled, the 585ignored. Instead, each time the periodic watcher gets scheduled, the
534reschedule callback will be called with the watcher as first, and the 586reschedule callback will be called with the watcher as first, and the
535current time as second argument. 587current time as second argument.
536 588
537NOTE: I<This callback MUST NOT stop or destroy the periodic or any other 589NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
538periodic watcher, ever, or make any event loop modificstions>. If you need 590ever, or make any event loop modifications>. If you need to stop it,
539to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards. 591return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
592starting a prepare watcher).
540 593
541Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 594Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
542ev_tstamp now)>, e.g.: 595ev_tstamp now)>, e.g.:
543 596
544 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 597 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
545 { 598 {
546 return now + 60.; 599 return now + 60.;
… …
549It must return the next time to trigger, based on the passed time value 602It must return the next time to trigger, based on the passed time value
550(that is, the lowest time value larger than to the second argument). It 603(that is, the lowest time value larger than to the second argument). It
551will usually be called just before the callback will be triggered, but 604will usually be called just before the callback will be triggered, but
552might be called at other times, too. 605might be called at other times, too.
553 606
607NOTE: I<< This callback must always return a time that is later than the
608passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
609
554This can be used to create very complex timers, such as a timer that 610This can be used to create very complex timers, such as a timer that
555triggers on each midnight, local time. To do this, you would calculate the 611triggers on each midnight, local time. To do this, you would calculate the
556next midnight after C<now> and return the timestamp value for this. How you do this 612next midnight after C<now> and return the timestamp value for this. How
557is, again, up to you (but it is not trivial). 613you do this is, again, up to you (but it is not trivial, which is the main
614reason I omitted it as an example).
558 615
559=back 616=back
560 617
561=item ev_periodic_again (loop, ev_periodic *) 618=item ev_periodic_again (loop, ev_periodic *)
562 619
… …
565a different time than the last time it was called (e.g. in a crond like 622a different time than the last time it was called (e.g. in a crond like
566program when the crontabs have changed). 623program when the crontabs have changed).
567 624
568=back 625=back
569 626
570=head2 ev_signal - signal me when a signal gets signalled 627=head2 C<ev_signal> - signal me when a signal gets signalled
571 628
572Signal watchers will trigger an event when the process receives a specific 629Signal watchers will trigger an event when the process receives a specific
573signal one or more times. Even though signals are very asynchronous, libev 630signal 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 631will try it's best to deliver signals synchronously, i.e. as part of the
575normal event processing, like any other event. 632normal event processing, like any other event.
576 633
577You cna configure as many watchers as you like per signal. Only when the 634You can configure as many watchers as you like per signal. Only when the
578first watcher gets started will libev actually register a signal watcher 635first watcher gets started will libev actually register a signal watcher
579with the kernel (thus it coexists with your own signal handlers as long 636with 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 637as 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 638watcher for a signal is stopped libev will reset the signal handler to
582SIG_DFL (regardless of what it was set to before). 639SIG_DFL (regardless of what it was set to before).
… …
590Configures the watcher to trigger on the given signal number (usually one 647Configures the watcher to trigger on the given signal number (usually one
591of the C<SIGxxx> constants). 648of the C<SIGxxx> constants).
592 649
593=back 650=back
594 651
595=head2 ev_child - wait for pid status changes 652=head2 C<ev_child> - wait for pid status changes
596 653
597Child watchers trigger when your process receives a SIGCHLD in response to 654Child watchers trigger when your process receives a SIGCHLD in response to
598some child status changes (most typically when a child of yours dies). 655some child status changes (most typically when a child of yours dies).
599 656
600=over 4 657=over 4
… …
604=item ev_child_set (ev_child *, int pid) 661=item ev_child_set (ev_child *, int pid)
605 662
606Configures the watcher to wait for status changes of process C<pid> (or 663Configures 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 664I<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 665at 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 666the status word (use the macros from C<sys/wait.h> and see your systems
610contains the pid of the process causing the status change. 667C<waitpid> documentation). The C<rpid> member contains the pid of the
668process causing the status change.
611 669
612=back 670=back
613 671
614=head2 ev_idle - when you've got nothing better to do 672=head2 C<ev_idle> - when you've got nothing better to do
615 673
616Idle watchers trigger events when there are no other I/O or timer (or 674Idle watchers trigger events when there are no other events are pending
617periodic) events pending. That is, as long as your process is busy 675(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 676as your process is busy handling sockets or timeouts (or even signals,
619is idle all idle watchers are being called again and again - until 677imagine) it will not be triggered. But when your process is idle all idle
678watchers are being called again and again, once per event loop iteration -
620stopped, that is, or your process receives more events. 679until stopped, that is, or your process receives more events and becomes
680busy.
621 681
622The most noteworthy effect is that as long as any idle watchers are 682The most noteworthy effect is that as long as any idle watchers are
623active, the process will not block when waiting for new events. 683active, the process will not block when waiting for new events.
624 684
625Apart from keeping your process non-blocking (which is a useful 685Apart 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, 695kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
636believe me. 696believe me.
637 697
638=back 698=back
639 699
640=head2 prepare and check - your hooks into the event loop 700=head2 C<ev_prepare> and C<ev_check> - customise your event loop
641 701
642Prepare and check watchers usually (but not always) are used in 702Prepare and check watchers are usually (but not always) used in tandem:
643tandom. Prepare watchers get invoked before the process blocks and check 703prepare watchers get invoked before the process blocks and check watchers
644watchers afterwards. 704afterwards.
645 705
646Their main purpose is to integrate other event mechanisms into libev. This 706Their main purpose is to integrate other event mechanisms into libev. This
647could be used, for example, to track variable changes, implement your own 707could be used, for example, to track variable changes, implement your own
648watchers, integrate net-snmp or a coroutine library and lots more. 708watchers, integrate net-snmp or a coroutine library and lots more.
649 709
650This is done by examining in each prepare call which file descriptors need 710This 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 711to be watched by the other library, registering C<ev_io> watchers for
652and starting an ev_timer watcher for any timeouts (many libraries provide 712them and starting an C<ev_timer> watcher for any timeouts (many libraries
653just this functionality). Then, in the check watcher you check for any 713provide just this functionality). Then, in the check watcher you check for
654events that occured (by making your callbacks set soem flags for example) 714any events that occured (by checking the pending status of all watchers
655and call back into the library. 715and stopping them) and call back into the library. The I/O and timer
716callbacks will never actually be called (but must be valid nevertheless,
717because you never know, you know?).
656 718
657As another example, the perl Coro module uses these hooks to integrate 719As another example, the Perl Coro module uses these hooks to integrate
658coroutines into libev programs, by yielding to other active coroutines 720coroutines into libev programs, by yielding to other active coroutines
659during each prepare and only letting the process block if no coroutines 721during each prepare and only letting the process block if no coroutines
660are ready to run. 722are ready to run (it's actually more complicated: it only runs coroutines
723with priority higher than or equal to the event loop and one coroutine
724of lower priority, but only once, using idle watchers to keep the event
725loop from blocking if lower-priority coroutines are active, thus mapping
726low-priority coroutines to idle/background tasks).
661 727
662=over 4 728=over 4
663 729
664=item ev_prepare_init (ev_prepare *, callback) 730=item ev_prepare_init (ev_prepare *, callback)
665 731
666=item ev_check_init (ev_check *, callback) 732=item ev_check_init (ev_check *, callback)
667 733
668Initialises and configures the prepare or check watcher - they have no 734Initialises 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> 735parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
670macros, but using them is utterly, utterly pointless. 736macros, but using them is utterly, utterly and completely pointless.
671 737
672=back 738=back
673 739
674=head1 OTHER FUNCTIONS 740=head1 OTHER FUNCTIONS
675 741
676There are some other fucntions of possible interest. Described. Here. Now. 742There are some other functions of possible interest. Described. Here. Now.
677 743
678=over 4 744=over 4
679 745
680=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) 746=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
681 747
682This function combines a simple timer and an I/O watcher, calls your 748This function combines a simple timer and an I/O watcher, calls your
683callback on whichever event happens first and automatically stop both 749callback 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 750watchers. 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 751or timeout without having to allocate/configure/start/stop/free one or
686more watchers yourself. 752more watchers yourself.
687 753
688If C<fd> is less than 0, then no I/O watcher will be started and events is 754If 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 755is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
690will be craeted and started. 756C<events> set will be craeted and started.
691 757
692If C<timeout> is less than 0, then no timeout watcher will be 758If C<timeout> is less than 0, then no timeout watcher will be
693started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat 759started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
694= 0) will be started. 760repeat = 0) will be started. While C<0> is a valid timeout, it is of
761dubious value.
695 762
696The callback has the type C<void (*cb)(int revents, void *arg)> and 763The 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, 764passed an C<revents> set like normal event callbacks (a combination of
698EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>: 765C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
766value passed to C<ev_once>:
699 767
700 static void stdin_ready (int revents, void *arg) 768 static void stdin_ready (int revents, void *arg)
701 { 769 {
702 if (revents & EV_TIMEOUT) 770 if (revents & EV_TIMEOUT)
703 /* doh, nothing entered */ 771 /* doh, nothing entered */;
704 else if (revents & EV_READ) 772 else if (revents & EV_READ)
705 /* stdin might have data for us, joy! */ 773 /* stdin might have data for us, joy! */;
706 } 774 }
707 775
708 ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0); 776 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
709 777
710=item ev_feed_event (loop, watcher, int events) 778=item ev_feed_event (loop, watcher, int events)
711 779
712Feeds the given event set into the event loop, as if the specified event 780Feeds 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 781had happened for the specified watcher (which must be a pointer to an
714initialised but not necessarily active event watcher). 782initialised but not necessarily started event watcher).
715 783
716=item ev_feed_fd_event (loop, int fd, int revents) 784=item ev_feed_fd_event (loop, int fd, int revents)
717 785
718Feed an event on the given fd, as if a file descriptor backend detected it. 786Feed an event on the given fd, as if a file descriptor backend detected
787the given events it.
719 788
720=item ev_feed_signal_event (loop, int signum) 789=item ev_feed_signal_event (loop, int signum)
721 790
722Feed an event as if the given signal occured (loop must be the default loop!). 791Feed an event as if the given signal occured (loop must be the default loop!).
723 792
724=back 793=back
725 794
795=head1 LIBEVENT EMULATION
796
797Libev offers a compatibility emulation layer for libevent. It cannot
798emulate the internals of libevent, so here are some usage hints:
799
800=over 4
801
802=item * Use it by including <event.h>, as usual.
803
804=item * The following members are fully supported: ev_base, ev_callback,
805ev_arg, ev_fd, ev_res, ev_events.
806
807=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
808maintained by libev, it does not work exactly the same way as in libevent (consider
809it a private API).
810
811=item * Priorities are not currently supported. Initialising priorities
812will fail and all watchers will have the same priority, even though there
813is an ev_pri field.
814
815=item * Other members are not supported.
816
817=item * The libev emulation is I<not> ABI compatible to libevent, you need
818to use the libev header file and library.
819
820=back
821
822=head1 C++ SUPPORT
823
824TBD.
825
726=head1 AUTHOR 826=head1 AUTHOR
727 827
728Marc Lehmann <libev@schmorp.de>. 828Marc Lehmann <libev@schmorp.de>.
729 829

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