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… …
8 8
9=head1 DESCRIPTION 9=head1 DESCRIPTION
10 10
11Libev is an event loop: you register interest in certain events (such as a 11Libev is an event loop: you register interest in certain events (such as a
12file descriptor being readable or a timeout occuring), and it will manage 12file descriptor being readable or a timeout occuring), and it will manage
13these event sources and provide your program events. 13these event sources and provide your program with events.
14 14
15To do this, it must take more or less complete control over your process 15To do this, it must take more or less complete control over your process
16(or thread) by executing the I<event loop> handler, and will then 16(or thread) by executing the I<event loop> handler, and will then
17communicate events via a callback mechanism. 17communicate events via a callback mechanism.
18 18
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25 25
26Libev supports select, poll, the linux-specific epoll and the bsd-specific 26Libev supports select, poll, the linux-specific epoll and the bsd-specific
27kqueue mechanisms for file descriptor events, relative timers, absolute 27kqueue mechanisms for file descriptor events, relative timers, absolute
28timers with customised rescheduling, signal events, process status change 28timers with customised rescheduling, signal events, process status change
29events (related to SIGCHLD), and event watchers dealing with the event 29events (related to SIGCHLD), and event watchers dealing with the event
30loop mechanism itself (idle, prepare and check watchers). 30loop mechanism itself (idle, prepare and check watchers). It also is quite
31fast (see this L<benchmark|http://libev.schmorp.de/bench.html> comparing
32it to libevent for example).
31 33
32=head1 CONVENTIONS 34=head1 CONVENTIONS
33 35
34Libev is very configurable. In this manual the default configuration 36Libev is very configurable. In this manual the default configuration
35will be described, which supports multiple event loops. For more info 37will be described, which supports multiple event loops. For more info
36about various configuraiton options please have a look at the file 38about various configuration options please have a look at the file
37F<README.embed> in the libev distribution. If libev was configured without 39F<README.embed> in the libev distribution. If libev was configured without
38support for multiple event loops, then all functions taking an initial 40support for multiple event loops, then all functions taking an initial
39argument of name C<loop> (which is always of type C<struct ev_loop *>) 41argument of name C<loop> (which is always of type C<struct ev_loop *>)
40will not have this argument. 42will not have this argument.
41 43
42=head1 TIME AND OTHER GLOBAL FUNCTIONS 44=head1 TIME REPRESENTATION
43 45
44Libev represents time as a single floating point number. This type is 46Libev represents time as a single floating point number, representing the
47(fractional) number of seconds since the (POSIX) epoch (somewhere near
48the beginning of 1970, details are complicated, don't ask). This type is
45called 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
46to the double type in C. 50to the double type in C.
47 51
52=head1 GLOBAL FUNCTIONS
53
54These functions can be called anytime, even before initialising the
55library in any way.
56
48=over 4 57=over 4
49 58
50=item ev_tstamp ev_time () 59=item ev_tstamp ev_time ()
51 60
52Returns 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.
53 64
54=item int ev_version_major () 65=item int ev_version_major ()
55 66
56=item int ev_version_minor () 67=item int ev_version_minor ()
57 68
… …
59you linked against by calling the functions C<ev_version_major> and 70you linked against by calling the functions C<ev_version_major> and
60C<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
61symbols 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
62version of the library your program was compiled against. 73version of the library your program was compiled against.
63 74
64Usually, its a good idea to terminate if the major versions mismatch, 75Usually, it's a good idea to terminate if the major versions mismatch,
65as this indicates an incompatible change. Minor versions are usually 76as this indicates an incompatible change. Minor versions are usually
66compatible to older versions, so a larger minor version alone is usually 77compatible to older versions, so a larger minor version alone is usually
67not a problem. 78not a problem.
68 79
69=item ev_set_allocator (void *(*cb)(void *ptr, long size)) 80=item ev_set_allocator (void *(*cb)(void *ptr, long size))
70 81
71Sets the allocation function to use (the prototype is similar to the 82Sets the allocation function to use (the prototype is similar to the
72realloc function). It is used to allocate and free memory (no surprises 83realloc C function, the semantics are identical). It is used to allocate
73here). If it returns zero when memory needs to be allocated, the library 84and free memory (no surprises here). If it returns zero when memory
74might abort or take some potentially destructive action. The default is 85needs to be allocated, the library might abort or take some potentially
75your system realloc function. 86destructive action. The default is your system realloc function.
76 87
77You could override this function in high-availability programs to, say, 88You could override this function in high-availability programs to, say,
78free 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,
79or 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.
80 91
… …
82 93
83Set the callback function to call on a retryable syscall error (such 94Set the callback function to call on a retryable syscall error (such
84as failed select, poll, epoll_wait). The message is a printable string 95as failed select, poll, epoll_wait). The message is a printable string
85indicating the system call or subsystem causing the problem. If this 96indicating the system call or subsystem causing the problem. If this
86callback 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
87matter what, when it returns. That is, libev will geenrally retry the 98matter what, when it returns. That is, libev will generally retry the
88requested 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
89(such as abort). 100(such as abort).
90 101
91=back 102=back
92 103
… …
95An 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
96types 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
97events, and dynamically created loops which do not. 108events, and dynamically created loops which do not.
98 109
99If 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
100in 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
101create, you also create another event loop. Libev itself does no lockign 112create, you also create another event loop. Libev itself does no locking
102whatsoever, 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
103lock (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).
104 116
105=over 4 117=over 4
106 118
107=item struct ev_loop *ev_default_loop (unsigned int flags) 119=item struct ev_loop *ev_default_loop (unsigned int flags)
108 120
… …
113 125
114If 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
115function. 127function.
116 128
117The flags argument can be used to specify special behaviour or specific 129The flags argument can be used to specify special behaviour or specific
118backends to use, and is usually specified as 0 (or EVFLAG_AUTO) 130backends to use, and is usually specified as 0 (or EVFLAG_AUTO).
119 131
120It supports the following flags: 132It supports the following flags:
121 133
122=over 4 134=over 4
123 135
124=item EVFLAG_AUTO 136=item C<EVFLAG_AUTO>
125 137
126The 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
127thing, believe me). 139thing, believe me).
128 140
129=item EVFLAG_NOENV 141=item C<EVFLAG_NOENV>
130 142
131If 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
132at the environment variable C<LIBEV_FLAGS>. Otherwise (the default), this 144or setgid) then libev will I<not> look at the environment variable
133environment 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
134to 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
135bugs. 148around bugs.
136 149
137=item EVMETHOD_SELECT portable select backend 150=item C<EVMETHOD_SELECT> (portable select backend)
138 151
139=item EVMETHOD_POLL poll backend (everywhere except windows) 152=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)
140 153
141=item EVMETHOD_EPOLL linux only 154=item C<EVMETHOD_EPOLL> (linux only)
142 155
143=item EVMETHOD_KQUEUE some bsds only 156=item C<EVMETHOD_KQUEUE> (some bsds only)
144 157
145=item EVMETHOD_DEVPOLL solaris 8 only 158=item C<EVMETHOD_DEVPOLL> (solaris 8 only)
146 159
147=item EVMETHOD_PORT solaris 10 only 160=item C<EVMETHOD_PORT> (solaris 10 only)
148 161
149If 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
150backends 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
151specified, any backend will do. 164specified, any backend will do.
152 165
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161 174
162=item ev_default_destroy () 175=item ev_default_destroy ()
163 176
164Destroys the default loop again (frees all memory and kernel state 177Destroys the default loop again (frees all memory and kernel state
165etc.). This stops all registered event watchers (by not touching them in 178etc.). This stops all registered event watchers (by not touching them in
166any way whatsoever, although you cnanot rely on this :). 179any way whatsoever, although you cannot rely on this :).
167 180
168=item ev_loop_destroy (loop) 181=item ev_loop_destroy (loop)
169 182
170Like 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
171earlier call to C<ev_loop_new>. 184earlier call to C<ev_loop_new>.
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179 192
180You 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
181use 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
182have to call it. 195have to call it.
183 196
184The 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
185it 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
186quite nicely into a call to C<pthread_atfork>: 199quite nicely into a call to C<pthread_atfork>:
187 200
188 pthread_atfork (0, 0, ev_default_fork); 201 pthread_atfork (0, 0, ev_default_fork);
189 202
… …
196=item unsigned int ev_method (loop) 209=item unsigned int ev_method (loop)
197 210
198Returns one of the C<EVMETHOD_*> flags indicating the event backend in 211Returns one of the C<EVMETHOD_*> flags indicating the event backend in
199use. 212use.
200 213
201=item ev_tstamp = ev_now (loop) 214=item ev_tstamp ev_now (loop)
202 215
203Returns 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
204got events and started processing them. This timestamp does not change 217got events and started processing them. This timestamp does not change
205as 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
206used 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
… …
215If 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
216no event watchers are active anymore or C<ev_unloop> was called. 229no event watchers are active anymore or C<ev_unloop> was called.
217 230
218A 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
219those 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
220case there are no events. 233case there are no events and will return after one iteration of the loop.
221 234
222A 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
223neccessary) and will handle those and any outstanding ones. It will block 236neccessary) and will handle those and any outstanding ones. It will block
224your 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.
225 239
226This flags value could be used to implement alternative looping 240This flags value could be used to implement alternative looping
227constructs, 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
228more generic mechanism. 242more generic mechanism.
229 243
230=item ev_unloop (loop, how) 244=item ev_unloop (loop, how)
231 245
232Can be used to make a call to C<ev_loop> return early. The C<how> argument 246Can be used to make a call to C<ev_loop> return early (but only after it
247has processed all outstanding events). The C<how> argument must be either
233must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> 248C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
234call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> 249C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
235calls return.
236 250
237=item ev_ref (loop) 251=item ev_ref (loop)
238 252
239=item ev_unref (loop) 253=item ev_unref (loop)
240 254
241Ref/unref can be used to add or remove a refcount on the event loop: Every 255Ref/unref can be used to add or remove a reference count on the event
242watcher keeps one reference. If you have a long-runing watcher you never 256loop: Every watcher keeps one reference, and as long as the reference
243unregister that should not keep ev_loop from running, ev_unref() after 257count is nonzero, C<ev_loop> will not return on its own. If you have
244starting, and ev_ref() before stopping it. Libev itself uses this for 258a watcher you never unregister that should not keep C<ev_loop> from
245example for its internal signal pipe: It is not visible to you as a user 259returning, ev_unref() after starting, and ev_ref() before stopping it. For
246and should not keep C<ev_loop> from exiting if the work is done. It is 260example, libev itself uses this for its internal signal pipe: It is not
247also an excellent way to do this for generic recurring timers or from 261visible to the libev user and should not keep C<ev_loop> from exiting if
248within third-party libraries. Just remember to unref after start and ref 262no event watchers registered by it are active. It is also an excellent
249before stop. 263way to do this for generic recurring timers or from within third-party
264libraries. Just remember to I<unref after start> and I<ref before stop>.
250 265
251=back 266=back
252 267
253=head1 ANATOMY OF A WATCHER 268=head1 ANATOMY OF A WATCHER
254 269
255A watcher is a structure that you create and register to record your 270A watcher is a structure that you create and register to record your
256interest in some event. For instance, if you want to wait for STDIN to 271interest in some event. For instance, if you want to wait for STDIN to
257become readable, you would create an ev_io watcher for that: 272become readable, you would create an C<ev_io> watcher for that:
258 273
259 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 274 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
260 { 275 {
261 ev_io_stop (w); 276 ev_io_stop (w);
262 ev_unloop (loop, EVUNLOOP_ALL); 277 ev_unloop (loop, EVUNLOOP_ALL);
… …
291 306
292As long as your watcher is active (has been started but not stopped) you 307As long as your watcher is active (has been started but not stopped) you
293must not touch the values stored in it. Most specifically you must never 308must not touch the values stored in it. Most specifically you must never
294reinitialise it or call its set method. 309reinitialise it or call its set method.
295 310
296You cna check wether an event is active by calling the C<ev_is_active 311You can check whether an event is active by calling the C<ev_is_active
297(watcher *)> macro. To see wether an event is outstanding (but the 312(watcher *)> macro. To see whether an event is outstanding (but the
298callback for it has not been called yet) you cna use the C<ev_is_pending 313callback for it has not been called yet) you can use the C<ev_is_pending
299(watcher *)> macro. 314(watcher *)> macro.
300 315
301Each and every callback receives the event loop pointer as first, the 316Each and every callback receives the event loop pointer as first, the
302registered watcher structure as second, and a bitset of received events as 317registered watcher structure as second, and a bitset of received events as
303third argument. 318third argument.
304 319
305The rceeived events usually include a single bit per event type received 320The received events usually include a single bit per event type received
306(you can receive multiple events at the same time). The possible bit masks 321(you can receive multiple events at the same time). The possible bit masks
307are: 322are:
308 323
309=over 4 324=over 4
310 325
311=item EV_READ 326=item C<EV_READ>
312 327
313=item EV_WRITE 328=item C<EV_WRITE>
314 329
315The file descriptor in the ev_io watcher has become readable and/or 330The file descriptor in the C<ev_io> watcher has become readable and/or
316writable. 331writable.
317 332
318=item EV_TIMEOUT 333=item C<EV_TIMEOUT>
319 334
320The ev_timer watcher has timed out. 335The C<ev_timer> watcher has timed out.
321 336
322=item EV_PERIODIC 337=item C<EV_PERIODIC>
323 338
324The ev_periodic watcher has timed out. 339The C<ev_periodic> watcher has timed out.
325 340
326=item EV_SIGNAL 341=item C<EV_SIGNAL>
327 342
328The signal specified in the ev_signal watcher has been received by a thread. 343The signal specified in the C<ev_signal> watcher has been received by a thread.
329 344
330=item EV_CHILD 345=item C<EV_CHILD>
331 346
332The pid specified in the ev_child watcher has received a status change. 347The pid specified in the C<ev_child> watcher has received a status change.
333 348
334=item EV_IDLE 349=item C<EV_IDLE>
335 350
336The ev_idle watcher has determined that you have nothing better to do. 351The C<ev_idle> watcher has determined that you have nothing better to do.
337 352
338=item EV_PREPARE 353=item C<EV_PREPARE>
339 354
340=item EV_CHECK 355=item C<EV_CHECK>
341 356
342All ev_prepare watchers are invoked just I<before> C<ev_loop> starts 357All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts
343to gather new events, and all ev_check watchers are invoked just after 358to gather new events, and all C<ev_check> watchers are invoked just after
344C<ev_loop> has gathered them, but before it invokes any callbacks for any 359C<ev_loop> has gathered them, but before it invokes any callbacks for any
345received events. Callbacks of both watcher types can start and stop as 360received events. Callbacks of both watcher types can start and stop as
346many watchers as they want, and all of them will be taken into account 361many watchers as they want, and all of them will be taken into account
347(for example, a ev_prepare watcher might start an idle watcher to keep 362(for example, a C<ev_prepare> watcher might start an idle watcher to keep
348C<ev_loop> from blocking). 363C<ev_loop> from blocking).
349 364
350=item EV_ERROR 365=item C<EV_ERROR>
351 366
352An unspecified error has occured, the watcher has been stopped. This might 367An unspecified error has occured, the watcher has been stopped. This might
353happen because the watcher could not be properly started because libev 368happen because the watcher could not be properly started because libev
354ran out of memory, a file descriptor was found to be closed or any other 369ran out of memory, a file descriptor was found to be closed or any other
355problem. You best act on it by reporting the problem and somehow coping 370problem. You best act on it by reporting the problem and somehow coping
… …
364=back 379=back
365 380
366=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER 381=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
367 382
368Each watcher has, by default, a member C<void *data> that you can change 383Each watcher has, by default, a member C<void *data> that you can change
369and read at any time, libev will completely ignore it. This cna be used 384and read at any time, libev will completely ignore it. This can be used
370to associate arbitrary data with your watcher. If you need more data and 385to associate arbitrary data with your watcher. If you need more data and
371don't want to allocate memory and store a pointer to it in that data 386don't want to allocate memory and store a pointer to it in that data
372member, you can also "subclass" the watcher type and provide your own 387member, you can also "subclass" the watcher type and provide your own
373data: 388data:
374 389
… …
396=head1 WATCHER TYPES 411=head1 WATCHER TYPES
397 412
398This section describes each watcher in detail, but will not repeat 413This section describes each watcher in detail, but will not repeat
399information given in the last section. 414information given in the last section.
400 415
401=head2 struct ev_io - is my file descriptor readable or writable 416=head2 C<ev_io> - is this file descriptor readable or writable
402 417
403I/O watchers check wether a file descriptor is readable or writable 418I/O watchers check whether a file descriptor is readable or writable
404in each iteration of the event loop (This behaviour is called 419in each iteration of the event loop (This behaviour is called
405level-triggering because you keep receiving events as long as the 420level-triggering because you keep receiving events as long as the
406condition persists. Remember you cna stop the watcher if you don't want to 421condition persists. Remember you can stop the watcher if you don't want to
407act on the event and neither want to receive future events). 422act on the event and neither want to receive future events).
408 423
424In general you can register as many read and/or write event watchers per
425fd as you want (as long as you don't confuse yourself). Setting all file
426descriptors to non-blocking mode is also usually a good idea (but not
427required if you know what you are doing).
428
429You have to be careful with dup'ed file descriptors, though. Some backends
430(the linux epoll backend is a notable example) cannot handle dup'ed file
431descriptors correctly if you register interest in two or more fds pointing
432to the same underlying file/socket etc. description (that is, they share
433the same underlying "file open").
434
435If you must do this, then force the use of a known-to-be-good backend
436(at the time of this writing, this includes only EVMETHOD_SELECT and
437EVMETHOD_POLL).
438
409=over 4 439=over 4
410 440
411=item ev_io_init (ev_io *, callback, int fd, int events) 441=item ev_io_init (ev_io *, callback, int fd, int events)
412 442
413=item ev_io_set (ev_io *, int fd, int events) 443=item ev_io_set (ev_io *, int fd, int events)
414 444
415Configures an ev_io watcher. The fd is the file descriptor to rceeive 445Configures an C<ev_io> watcher. The fd is the file descriptor to rceeive
416events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ | 446events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
417EV_WRITE> to receive the given events. 447EV_WRITE> to receive the given events.
418 448
419=back 449=back
420 450
421=head2 struct ev_timer - relative and optionally recurring timeouts 451=head2 C<ev_timer> - relative and optionally recurring timeouts
422 452
423Timer watchers are simple relative timers that generate an event after a 453Timer watchers are simple relative timers that generate an event after a
424given time, and optionally repeating in regular intervals after that. 454given time, and optionally repeating in regular intervals after that.
425 455
426The timers are based on real time, that is, if you register an event that 456The timers are based on real time, that is, if you register an event that
427times out after an hour and youreset your system clock to last years 457times out after an hour and you reset your system clock to last years
428time, it will still time out after (roughly) and hour. "Roughly" because 458time, it will still time out after (roughly) and hour. "Roughly" because
429detecting time jumps is hard, and soem inaccuracies are unavoidable (the 459detecting time jumps is hard, and soem inaccuracies are unavoidable (the
430monotonic clock option helps a lot here). 460monotonic clock option helps a lot here).
461
462The relative timeouts are calculated relative to the C<ev_now ()>
463time. This is usually the right thing as this timestamp refers to the time
464of the event triggering whatever timeout you are modifying/starting. If
465you suspect event processing to be delayed and you *need* to base the timeout
466on the current time, use something like this to adjust for this:
467
468 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
431 469
432=over 4 470=over 4
433 471
434=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) 472=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
435 473
… …
441later, again, and again, until stopped manually. 479later, again, and again, until stopped manually.
442 480
443The timer itself will do a best-effort at avoiding drift, that is, if you 481The timer itself will do a best-effort at avoiding drift, that is, if you
444configure a timer to trigger every 10 seconds, then it will trigger at 482configure a timer to trigger every 10 seconds, then it will trigger at
445exactly 10 second intervals. If, however, your program cannot keep up with 483exactly 10 second intervals. If, however, your program cannot keep up with
446the timer (ecause it takes longer than those 10 seconds to do stuff) the 484the timer (because it takes longer than those 10 seconds to do stuff) the
447timer will not fire more than once per event loop iteration. 485timer will not fire more than once per event loop iteration.
448 486
449=item ev_timer_again (loop) 487=item ev_timer_again (loop)
450 488
451This will act as if the timer timed out and restart it again if it is 489This will act as if the timer timed out and restart it again if it is
… …
458 496
459This sounds a bit complicated, but here is a useful and typical 497This sounds a bit complicated, but here is a useful and typical
460example: Imagine you have a tcp connection and you want a so-called idle 498example: Imagine you have a tcp connection and you want a so-called idle
461timeout, that is, you want to be called when there have been, say, 60 499timeout, that is, you want to be called when there have been, say, 60
462seconds of inactivity on the socket. The easiest way to do this is to 500seconds of inactivity on the socket. The easiest way to do this is to
463configure an ev_timer with after=repeat=60 and calling ev_timer_again each 501configure an C<ev_timer> with after=repeat=60 and calling ev_timer_again each
464time you successfully read or write some data. If you go into an idle 502time you successfully read or write some data. If you go into an idle
465state where you do not expect data to travel on the socket, you can stop 503state where you do not expect data to travel on the socket, you can stop
466the timer, and again will automatically restart it if need be. 504the timer, and again will automatically restart it if need be.
467 505
468=back 506=back
469 507
470=head2 ev_periodic 508=head2 C<ev_periodic> - to cron or not to cron
471 509
472Periodic watchers are also timers of a kind, but they are very versatile 510Periodic watchers are also timers of a kind, but they are very versatile
473(and unfortunately a bit complex). 511(and unfortunately a bit complex).
474 512
475Unlike ev_timer's, they are not based on real time (or relative time) 513Unlike C<ev_timer>'s, they are not based on real time (or relative time)
476but on wallclock time (absolute time). You can tell a periodic watcher 514but on wallclock time (absolute time). You can tell a periodic watcher
477to trigger "at" some specific point in time. For example, if you tell a 515to trigger "at" some specific point in time. For example, if you tell a
478periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 516periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
479+ 10.>) and then reset your system clock to the last year, then it will 517+ 10.>) and then reset your system clock to the last year, then it will
480take a year to trigger the event (unlike an ev_timer, which would trigger 518take a year to trigger the event (unlike an C<ev_timer>, which would trigger
481roughly 10 seconds later and of course not if you reset your system time 519roughly 10 seconds later and of course not if you reset your system time
482again). 520again).
483 521
484They can also be used to implement vastly more complex timers, such as 522They can also be used to implement vastly more complex timers, such as
485triggering an event on eahc midnight, local time. 523triggering an event on eahc midnight, local time.
… …
514 552
515 ev_periodic_set (&periodic, 0., 3600., 0); 553 ev_periodic_set (&periodic, 0., 3600., 0);
516 554
517This doesn't mean there will always be 3600 seconds in between triggers, 555This doesn't mean there will always be 3600 seconds in between triggers,
518but only that the the callback will be called when the system time shows a 556but only that the the callback will be called when the system time shows a
519full hour (UTC), or more correct, when the system time is evenly divisible 557full hour (UTC), or more correctly, when the system time is evenly divisible
520by 3600. 558by 3600.
521 559
522Another way to think about it (for the mathematically inclined) is that 560Another way to think about it (for the mathematically inclined) is that
523ev_periodic will try to run the callback in this mode at the next possible 561C<ev_periodic> will try to run the callback in this mode at the next possible
524time where C<time = at (mod interval)>, regardless of any time jumps. 562time where C<time = at (mod interval)>, regardless of any time jumps.
525 563
526=item * manual reschedule mode (reschedule_cb = callback) 564=item * manual reschedule mode (reschedule_cb = callback)
527 565
528In this mode the values for C<interval> and C<at> are both being 566In this mode the values for C<interval> and C<at> are both being
529ignored. Instead, each time the periodic watcher gets scheduled, the 567ignored. Instead, each time the periodic watcher gets scheduled, the
530reschedule callback will be called with the watcher as first, and the 568reschedule callback will be called with the watcher as first, and the
531current time as second argument. 569current time as second argument.
532 570
533NOTE: I<This callback MUST NOT stop or destroy the periodic or any other 571NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
534periodic watcher, ever, or make any event loop modificstions>. If you need 572ever, or make any event loop modifications>. If you need to stop it,
535to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards. 573return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
574starting a prepare watcher).
536 575
537Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 576Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
538ev_tstamp now)>, e.g.: 577ev_tstamp now)>, e.g.:
539 578
540 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 579 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
541 { 580 {
542 return now + 60.; 581 return now + 60.;
… …
545It must return the next time to trigger, based on the passed time value 584It must return the next time to trigger, based on the passed time value
546(that is, the lowest time value larger than to the second argument). It 585(that is, the lowest time value larger than to the second argument). It
547will usually be called just before the callback will be triggered, but 586will usually be called just before the callback will be triggered, but
548might be called at other times, too. 587might be called at other times, too.
549 588
589NOTE: I<< This callback must always return a time that is later than the
590passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
591
550This can be used to create very complex timers, such as a timer that 592This can be used to create very complex timers, such as a timer that
551triggers on each midnight, local time. To do this, you would calculate the 593triggers on each midnight, local time. To do this, you would calculate the
552next midnight after C<now> and return the timestamp value for this. How you do this 594next midnight after C<now> and return the timestamp value for this. How
553is, again, up to you (but it is not trivial). 595you do this is, again, up to you (but it is not trivial, which is the main
596reason I omitted it as an example).
554 597
555=back 598=back
556 599
557=item ev_periodic_again (loop, ev_periodic *) 600=item ev_periodic_again (loop, ev_periodic *)
558 601
… …
561a different time than the last time it was called (e.g. in a crond like 604a different time than the last time it was called (e.g. in a crond like
562program when the crontabs have changed). 605program when the crontabs have changed).
563 606
564=back 607=back
565 608
566=head2 ev_signal - signal me when a signal gets signalled 609=head2 C<ev_signal> - signal me when a signal gets signalled
567 610
568Signal watchers will trigger an event when the process receives a specific 611Signal watchers will trigger an event when the process receives a specific
569signal one or more times. Even though signals are very asynchronous, libev 612signal one or more times. Even though signals are very asynchronous, libev
570will try its best to deliver signals synchronously, i.e. as part of the 613will try it's best to deliver signals synchronously, i.e. as part of the
571normal event processing, like any other event. 614normal event processing, like any other event.
572 615
573You cna configure as many watchers as you like per signal. Only when the 616You can configure as many watchers as you like per signal. Only when the
574first watcher gets started will libev actually register a signal watcher 617first watcher gets started will libev actually register a signal watcher
575with the kernel (thus it coexists with your own signal handlers as long 618with the kernel (thus it coexists with your own signal handlers as long
576as you don't register any with libev). Similarly, when the last signal 619as you don't register any with libev). Similarly, when the last signal
577watcher for a signal is stopped libev will reset the signal handler to 620watcher for a signal is stopped libev will reset the signal handler to
578SIG_DFL (regardless of what it was set to before). 621SIG_DFL (regardless of what it was set to before).
… …
586Configures the watcher to trigger on the given signal number (usually one 629Configures the watcher to trigger on the given signal number (usually one
587of the C<SIGxxx> constants). 630of the C<SIGxxx> constants).
588 631
589=back 632=back
590 633
591=head2 ev_child - wait for pid status changes 634=head2 C<ev_child> - wait for pid status changes
592 635
593Child watchers trigger when your process receives a SIGCHLD in response to 636Child watchers trigger when your process receives a SIGCHLD in response to
594some child status changes (most typically when a child of yours dies). 637some child status changes (most typically when a child of yours dies).
595 638
596=over 4 639=over 4
… …
600=item ev_child_set (ev_child *, int pid) 643=item ev_child_set (ev_child *, int pid)
601 644
602Configures the watcher to wait for status changes of process C<pid> (or 645Configures the watcher to wait for status changes of process C<pid> (or
603I<any> process if C<pid> is specified as C<0>). The callback can look 646I<any> process if C<pid> is specified as C<0>). The callback can look
604at the C<rstatus> member of the C<ev_child> watcher structure to see 647at the C<rstatus> member of the C<ev_child> watcher structure to see
605the status word (use the macros from C<sys/wait.h>). The C<rpid> member 648the status word (use the macros from C<sys/wait.h> and see your systems
606contains the pid of the process causing the status change. 649C<waitpid> documentation). The C<rpid> member contains the pid of the
650process causing the status change.
607 651
608=back 652=back
609 653
610=head2 ev_idle - when you've got nothing better to do 654=head2 C<ev_idle> - when you've got nothing better to do
611 655
612Idle watchers trigger events when there are no other I/O or timer (or 656Idle watchers trigger events when there are no other events are pending
613periodic) events pending. That is, as long as your process is busy 657(prepare, check and other idle watchers do not count). That is, as long
614handling sockets or timeouts it will not be called. But when your process 658as your process is busy handling sockets or timeouts (or even signals,
615is idle all idle watchers are being called again and again - until 659imagine) it will not be triggered. But when your process is idle all idle
660watchers are being called again and again, once per event loop iteration -
616stopped, that is, or your process receives more events. 661until stopped, that is, or your process receives more events and becomes
662busy.
617 663
618The most noteworthy effect is that as long as any idle watchers are 664The most noteworthy effect is that as long as any idle watchers are
619active, the process will not block when waiting for new events. 665active, the process will not block when waiting for new events.
620 666
621Apart from keeping your process non-blocking (which is a useful 667Apart from keeping your process non-blocking (which is a useful
… …
631kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, 677kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
632believe me. 678believe me.
633 679
634=back 680=back
635 681
636=head2 prepare and check - your hooks into the event loop 682=head2 C<ev_prepare> and C<ev_check> - customise your event loop
637 683
638Prepare and check watchers usually (but not always) are used in 684Prepare and check watchers are usually (but not always) used in tandem:
639tandom. Prepare watchers get invoked before the process blocks and check 685prepare watchers get invoked before the process blocks and check watchers
640watchers afterwards. 686afterwards.
641 687
642Their main purpose is to integrate other event mechanisms into libev. This 688Their main purpose is to integrate other event mechanisms into libev. This
643could be used, for example, to track variable changes, implement your own 689could be used, for example, to track variable changes, implement your own
644watchers, integrate net-snmp or a coroutine library and lots more. 690watchers, integrate net-snmp or a coroutine library and lots more.
645 691
646This is done by examining in each prepare call which file descriptors need 692This is done by examining in each prepare call which file descriptors need
647to be watched by the other library, registering ev_io watchers for them 693to be watched by the other library, registering C<ev_io> watchers for
648and starting an ev_timer watcher for any timeouts (many libraries provide 694them and starting an C<ev_timer> watcher for any timeouts (many libraries
649just this functionality). Then, in the check watcher you check for any 695provide just this functionality). Then, in the check watcher you check for
650events that occured (by making your callbacks set soem flags for example) 696any events that occured (by checking the pending status of all watchers
651and call back into the library. 697and stopping them) and call back into the library. The I/O and timer
698callbacks will never actually be called (but must be valid nevertheless,
699because you never know, you know?).
652 700
653As another example, the perl Coro module uses these hooks to integrate 701As another example, the Perl Coro module uses these hooks to integrate
654coroutines into libev programs, by yielding to other active coroutines 702coroutines into libev programs, by yielding to other active coroutines
655during each prepare and only letting the process block if no coroutines 703during each prepare and only letting the process block if no coroutines
656are ready to run. 704are ready to run (it's actually more complicated: it only runs coroutines
705with priority higher than or equal to the event loop and one coroutine
706of lower priority, but only once, using idle watchers to keep the event
707loop from blocking if lower-priority coroutines are active, thus mapping
708low-priority coroutines to idle/background tasks).
657 709
658=over 4 710=over 4
659 711
660=item ev_prepare_init (ev_prepare *, callback) 712=item ev_prepare_init (ev_prepare *, callback)
661 713
662=item ev_check_init (ev_check *, callback) 714=item ev_check_init (ev_check *, callback)
663 715
664Initialises and configures the prepare or check watcher - they have no 716Initialises and configures the prepare or check watcher - they have no
665parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set> 717parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
666macros, but using them is utterly, utterly pointless. 718macros, but using them is utterly, utterly and completely pointless.
667 719
668=back 720=back
669 721
670=head1 OTHER FUNCTIONS 722=head1 OTHER FUNCTIONS
671 723
672There are some other fucntions of possible interest. Described. Here. Now. 724There are some other functions of possible interest. Described. Here. Now.
673 725
674=over 4 726=over 4
675 727
676=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) 728=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
677 729
678This function combines a simple timer and an I/O watcher, calls your 730This function combines a simple timer and an I/O watcher, calls your
679callback on whichever event happens first and automatically stop both 731callback on whichever event happens first and automatically stop both
680watchers. This is useful if you want to wait for a single event on an fd 732watchers. This is useful if you want to wait for a single event on an fd
681or timeout without havign to allocate/configure/start/stop/free one or 733or timeout without having to allocate/configure/start/stop/free one or
682more watchers yourself. 734more watchers yourself.
683 735
684If C<fd> is less than 0, then no I/O watcher will be started and events is 736If C<fd> is less than 0, then no I/O watcher will be started and events
685ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set 737is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
686will be craeted and started. 738C<events> set will be craeted and started.
687 739
688If C<timeout> is less than 0, then no timeout watcher will be 740If C<timeout> is less than 0, then no timeout watcher will be
689started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat 741started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
690= 0) will be started. 742repeat = 0) will be started. While C<0> is a valid timeout, it is of
743dubious value.
691 744
692The callback has the type C<void (*cb)(int revents, void *arg)> and 745The callback has the type C<void (*cb)(int revents, void *arg)> and gets
693gets passed an events set (normally a combination of EV_ERROR, EV_READ, 746passed an C<revents> set like normal event callbacks (a combination of
694EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>: 747C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
748value passed to C<ev_once>:
695 749
696 static void stdin_ready (int revents, void *arg) 750 static void stdin_ready (int revents, void *arg)
697 { 751 {
698 if (revents & EV_TIMEOUT) 752 if (revents & EV_TIMEOUT)
699 /* doh, nothing entered */ 753 /* doh, nothing entered */;
700 else if (revents & EV_READ) 754 else if (revents & EV_READ)
701 /* stdin might have data for us, joy! */ 755 /* stdin might have data for us, joy! */;
702 } 756 }
703 757
704 ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0); 758 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
705 759
706=item ev_feed_event (loop, watcher, int events) 760=item ev_feed_event (loop, watcher, int events)
707 761
708Feeds the given event set into the event loop, as if the specified event 762Feeds the given event set into the event loop, as if the specified event
709has happened for the specified watcher (which must be a pointer to an 763had happened for the specified watcher (which must be a pointer to an
710initialised but not necessarily active event watcher). 764initialised but not necessarily started event watcher).
711 765
712=item ev_feed_fd_event (loop, int fd, int revents) 766=item ev_feed_fd_event (loop, int fd, int revents)
713 767
714Feed an event on the given fd, as if a file descriptor backend detected it. 768Feed an event on the given fd, as if a file descriptor backend detected
769the given events it.
715 770
716=item ev_feed_signal_event (loop, int signum) 771=item ev_feed_signal_event (loop, int signum)
717 772
718Feed an event as if the given signal occured (loop must be the default loop!). 773Feed an event as if the given signal occured (loop must be the default loop!).
719 774
720=back 775=back
721 776
777=head1 LIBEVENT EMULATION
778
779Libev offers a compatibility emulation layer for libevent. It cannot
780emulate the internals of libevent, so here are some usage hints:
781
782=over 4
783
784=item * Use it by including <event.h>, as usual.
785
786=item * The following members are fully supported: ev_base, ev_callback,
787ev_arg, ev_fd, ev_res, ev_events.
788
789=item * Avoid using ev_flags and the EVLIST_*-macros, while it is
790maintained by libev, it does not work exactly the same way as in libevent (consider
791it a private API).
792
793=item * Priorities are not currently supported. Initialising priorities
794will fail and all watchers will have the same priority, even though there
795is an ev_pri field.
796
797=item * Other members are not supported.
798
799=item * The libev emulation is I<not> ABI compatible to libevent, you need
800to use the libev header file and library.
801
802=back
803
804=head1 C++ SUPPORT
805
806TBD.
807
722=head1 AUTHOR 808=head1 AUTHOR
723 809
724Marc Lehmann <libev@schmorp.de>. 810Marc Lehmann <libev@schmorp.de>.
725 811

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