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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.
51
52=head1 GLOBAL FUNCTIONS
47 53
48=over 4 54=over 4
49 55
50=item ev_tstamp ev_time () 56=item ev_tstamp ev_time ()
51 57
… …
59you linked against by calling the functions C<ev_version_major> and 65you linked against by calling the functions C<ev_version_major> and
60C<ev_version_minor>. If you want, you can compare against the global 66C<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 67symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
62version of the library your program was compiled against. 68version of the library your program was compiled against.
63 69
64Usually, its a good idea to terminate if the major versions mismatch, 70Usually, it's a good idea to terminate if the major versions mismatch,
65as this indicates an incompatible change. Minor versions are usually 71as this indicates an incompatible change. Minor versions are usually
66compatible to older versions, so a larger minor version alone is usually 72compatible to older versions, so a larger minor version alone is usually
67not a problem. 73not a problem.
68 74
69=item ev_set_allocator (void *(*cb)(void *ptr, long size)) 75=item ev_set_allocator (void *(*cb)(void *ptr, long size))
70 76
71Sets the allocation function to use (the prototype is similar to the 77Sets the allocation function to use (the prototype is similar to the
72realloc function). It is used to allocate and free memory (no surprises 78realloc C function, the semantics are identical). It is used to allocate
73here). If it returns zero when memory needs to be allocated, the library 79and free memory (no surprises here). If it returns zero when memory
74might abort or take some potentially destructive action. The default is 80needs to be allocated, the library might abort or take some potentially
75your system realloc function. 81destructive action. The default is your system realloc function.
76 82
77You could override this function in high-availability programs to, say, 83You could override this function in high-availability programs to, say,
78free some memory if it cannot allocate memory, to use a special allocator, 84free 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. 85or even to sleep a while and retry until some memory is available.
80 86
… …
82 88
83Set the callback function to call on a retryable syscall error (such 89Set the callback function to call on a retryable syscall error (such
84as failed select, poll, epoll_wait). The message is a printable string 90as failed select, poll, epoll_wait). The message is a printable string
85indicating the system call or subsystem causing the problem. If this 91indicating the system call or subsystem causing the problem. If this
86callback is set, then libev will expect it to remedy the sitution, no 92callback is set, then libev will expect it to remedy the sitution, no
87matter what, when it returns. That is, libev will geenrally retry the 93matter what, when it returns. That is, libev will generally retry the
88requested operation, or, if the condition doesn't go away, do bad stuff 94requested operation, or, if the condition doesn't go away, do bad stuff
89(such as abort). 95(such as abort).
90 96
91=back 97=back
92 98
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95An event loop is described by a C<struct ev_loop *>. The library knows two 101An 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 102types of such loops, the I<default> loop, which supports signals and child
97events, and dynamically created loops which do not. 103events, and dynamically created loops which do not.
98 104
99If you use threads, a common model is to run the default event loop 105If 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 106in 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 107create, you also create another event loop. Libev itself does no locking
102whatsoever, so if you mix calls to different event loops, make sure you 108whatsoever, so if you mix calls to the same event loop in different
103lock (this is usually a bad idea, though, even if done right). 109threads, make sure you lock (this is usually a bad idea, though, even if
110done correctly, because it's hideous and inefficient).
104 111
105=over 4 112=over 4
106 113
107=item struct ev_loop *ev_default_loop (unsigned int flags) 114=item struct ev_loop *ev_default_loop (unsigned int flags)
108 115
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113 120
114If you don't know what event loop to use, use the one returned from this 121If you don't know what event loop to use, use the one returned from this
115function. 122function.
116 123
117The flags argument can be used to specify special behaviour or specific 124The flags argument can be used to specify special behaviour or specific
118backends to use, and is usually specified as 0 (or EVFLAG_AUTO) 125backends to use, and is usually specified as 0 (or EVFLAG_AUTO).
119 126
120It supports the following flags: 127It supports the following flags:
121 128
122=over 4 129=over 4
123 130
124=item EVFLAG_AUTO 131=item C<EVFLAG_AUTO>
125 132
126The default flags value. Use this if you have no clue (its the right 133The default flags value. Use this if you have no clue (it's the right
127thing, believe me). 134thing, believe me).
128 135
129=item EVFLAG_NOENV 136=item C<EVFLAG_NOENV>
130 137
131If this flag bit is ored into the flag value then libev will I<not> look 138If 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 139or setgid) then libev will I<not> look at the environment variable
133environment variable will override the flags completely. This is useful 140C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
141override 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 142useful to try out specific backends to test their performance, or to work
135bugs. 143around bugs.
136 144
137=item EVMETHOD_SELECT portable select backend 145=item C<EVMETHOD_SELECT> (portable select backend)
138 146
139=item EVMETHOD_POLL poll backend (everywhere except windows) 147=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)
140 148
141=item EVMETHOD_EPOLL linux only 149=item C<EVMETHOD_EPOLL> (linux only)
142 150
143=item EVMETHOD_KQUEUE some bsds only 151=item C<EVMETHOD_KQUEUE> (some bsds only)
144 152
145=item EVMETHOD_DEVPOLL solaris 8 only 153=item C<EVMETHOD_DEVPOLL> (solaris 8 only)
146 154
147=item EVMETHOD_PORT solaris 10 only 155=item C<EVMETHOD_PORT> (solaris 10 only)
148 156
149If one or more of these are ored into the flags value, then only these 157If 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 158backends will be tried (in the reverse order as given here). If one are
151specified, any backend will do. 159specified, any backend will do.
152 160
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161 169
162=item ev_default_destroy () 170=item ev_default_destroy ()
163 171
164Destroys the default loop again (frees all memory and kernel state 172Destroys the default loop again (frees all memory and kernel state
165etc.). This stops all registered event watchers (by not touching them in 173etc.). This stops all registered event watchers (by not touching them in
166any way whatsoever, although you cnanot rely on this :). 174any way whatsoever, although you cannot rely on this :).
167 175
168=item ev_loop_destroy (loop) 176=item ev_loop_destroy (loop)
169 177
170Like C<ev_default_destroy>, but destroys an event loop created by an 178Like C<ev_default_destroy>, but destroys an event loop created by an
171earlier call to C<ev_loop_new>. 179earlier call to C<ev_loop_new>.
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179 187
180You I<must> call this function after forking if and only if you want to 188You 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 189use the event library in both processes. If you just fork+exec, you don't
182have to call it. 190have to call it.
183 191
184The function itself is quite fast and its usually not a problem to call 192The 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 193it just in case after a fork. To make this easy, the function will fit in
186quite nicely into a call to C<pthread_atfork>: 194quite nicely into a call to C<pthread_atfork>:
187 195
188 pthread_atfork (0, 0, ev_default_fork); 196 pthread_atfork (0, 0, ev_default_fork);
189 197
… …
196=item unsigned int ev_method (loop) 204=item unsigned int ev_method (loop)
197 205
198Returns one of the C<EVMETHOD_*> flags indicating the event backend in 206Returns one of the C<EVMETHOD_*> flags indicating the event backend in
199use. 207use.
200 208
201=item ev_tstamp = ev_now (loop) 209=item ev_tstamp ev_now (loop)
202 210
203Returns the current "event loop time", which is the time the event loop 211Returns the current "event loop time", which is the time the event loop
204got events and started processing them. This timestamp does not change 212got events and started processing them. This timestamp does not change
205as long as callbacks are being processed, and this is also the base time 213as 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 214used 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 223If 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. 224no event watchers are active anymore or C<ev_unloop> was called.
217 225
218A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle 226A 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 227those events and any outstanding ones, but will not block your process in
220case there are no events. 228case there are no events and will return after one iteration of the loop.
221 229
222A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if 230A 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 231neccessary) and will handle those and any outstanding ones. It will block
224your process until at least one new event arrives. 232your process until at least one new event arrives, and will return after
233one iteration of the loop.
225 234
226This flags value could be used to implement alternative looping 235This flags value could be used to implement alternative looping
227constructs, but the C<prepare> and C<check> watchers provide a better and 236constructs, but the C<prepare> and C<check> watchers provide a better and
228more generic mechanism. 237more generic mechanism.
229 238
230=item ev_unloop (loop, how) 239=item ev_unloop (loop, how)
231 240
232Can be used to make a call to C<ev_loop> return early. The C<how> argument 241Can be used to make a call to C<ev_loop> return early (but only after it
242has 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> 243C<EVUNLOOP_ONCE>, 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> 244C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
235calls return.
236 245
237=item ev_ref (loop) 246=item ev_ref (loop)
238 247
239=item ev_unref (loop) 248=item ev_unref (loop)
240 249
241Ref/unref can be used to add or remove a refcount on the event loop: Every 250Ref/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 251loop: Every watcher keeps one reference, and as long as the reference
243unregister that should not keep ev_loop from running, ev_unref() after 252count 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 253a 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 254returning, 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 255example, 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 256visible 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 257no event watchers registered by it are active. It is also an excellent
249before stop. 258way to do this for generic recurring timers or from within third-party
259libraries. Just remember to I<unref after start> and I<ref before stop>.
250 260
251=back 261=back
252 262
253=head1 ANATOMY OF A WATCHER 263=head1 ANATOMY OF A WATCHER
254 264
255A watcher is a structure that you create and register to record your 265A 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 266interest in some event. For instance, if you want to wait for STDIN to
257become readable, you would create an ev_io watcher for that: 267become readable, you would create an C<ev_io> watcher for that:
258 268
259 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 269 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
260 { 270 {
261 ev_io_stop (w); 271 ev_io_stop (w);
262 ev_unloop (loop, EVUNLOOP_ALL); 272 ev_unloop (loop, EVUNLOOP_ALL);
… …
291 301
292As long as your watcher is active (has been started but not stopped) you 302As 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 303must not touch the values stored in it. Most specifically you must never
294reinitialise it or call its set method. 304reinitialise it or call its set method.
295 305
296You cna check wether an event is active by calling the C<ev_is_active 306You 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 307(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 308callback for it has not been called yet) you can use the C<ev_is_pending
299(watcher *)> macro. 309(watcher *)> macro.
300 310
301Each and every callback receives the event loop pointer as first, the 311Each and every callback receives the event loop pointer as first, the
302registered watcher structure as second, and a bitset of received events as 312registered watcher structure as second, and a bitset of received events as
303third argument. 313third argument.
304 314
305The rceeived events usually include a single bit per event type received 315The 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 316(you can receive multiple events at the same time). The possible bit masks
307are: 317are:
308 318
309=over 4 319=over 4
310 320
311=item EV_READ 321=item C<EV_READ>
312 322
313=item EV_WRITE 323=item C<EV_WRITE>
314 324
315The file descriptor in the ev_io watcher has become readable and/or 325The file descriptor in the C<ev_io> watcher has become readable and/or
316writable. 326writable.
317 327
318=item EV_TIMEOUT 328=item C<EV_TIMEOUT>
319 329
320The ev_timer watcher has timed out. 330The C<ev_timer> watcher has timed out.
321 331
322=item EV_PERIODIC 332=item C<EV_PERIODIC>
323 333
324The ev_periodic watcher has timed out. 334The C<ev_periodic> watcher has timed out.
325 335
326=item EV_SIGNAL 336=item C<EV_SIGNAL>
327 337
328The signal specified in the ev_signal watcher has been received by a thread. 338The signal specified in the C<ev_signal> watcher has been received by a thread.
329 339
330=item EV_CHILD 340=item C<EV_CHILD>
331 341
332The pid specified in the ev_child watcher has received a status change. 342The pid specified in the C<ev_child> watcher has received a status change.
333 343
334=item EV_IDLE 344=item C<EV_IDLE>
335 345
336The ev_idle watcher has determined that you have nothing better to do. 346The C<ev_idle> watcher has determined that you have nothing better to do.
337 347
338=item EV_PREPARE 348=item C<EV_PREPARE>
339 349
340=item EV_CHECK 350=item C<EV_CHECK>
341 351
342All ev_prepare watchers are invoked just I<before> C<ev_loop> starts 352All 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 353to 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 354C<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 355received 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 356many 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 357(for example, a C<ev_prepare> watcher might start an idle watcher to keep
348C<ev_loop> from blocking). 358C<ev_loop> from blocking).
349 359
350=item EV_ERROR 360=item C<EV_ERROR>
351 361
352An unspecified error has occured, the watcher has been stopped. This might 362An unspecified error has occured, the watcher has been stopped. This might
353happen because the watcher could not be properly started because libev 363happen 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 364ran 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 365problem. You best act on it by reporting the problem and somehow coping
… …
364=back 374=back
365 375
366=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER 376=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
367 377
368Each watcher has, by default, a member C<void *data> that you can change 378Each 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 379and 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 380to 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 381don'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 382member, you can also "subclass" the watcher type and provide your own
373data: 383data:
374 384
… …
396=head1 WATCHER TYPES 406=head1 WATCHER TYPES
397 407
398This section describes each watcher in detail, but will not repeat 408This section describes each watcher in detail, but will not repeat
399information given in the last section. 409information given in the last section.
400 410
401=head2 struct ev_io - is my file descriptor readable or writable 411=head2 C<ev_io> - is this file descriptor readable or writable
402 412
403I/O watchers check wether a file descriptor is readable or writable 413I/O watchers check whether a file descriptor is readable or writable
404in each iteration of the event loop (This behaviour is called 414in each iteration of the event loop (This behaviour is called
405level-triggering because you keep receiving events as long as the 415level-triggering because you keep receiving events as long as the
406condition persists. Remember you cna stop the watcher if you don't want to 416condition persists. Remember you can stop the watcher if you don't want to
407act on the event and neither want to receive future events). 417act on the event and neither want to receive future events).
408 418
419In general you can register as many read and/or write event watchers oer
420fd as you want (as long as you don't confuse yourself). Setting all file
421descriptors to non-blocking mode is also usually a good idea (but not
422required if you know what you are doing).
423
424You have to be careful with dup'ed file descriptors, though. Some backends
425(the linux epoll backend is a notable example) cannot handle dup'ed file
426descriptors correctly if you register interest in two or more fds pointing
427to the same file/socket etc. description.
428
429If you must do this, then force the use of a known-to-be-good backend
430(at the time of this writing, this includes only EVMETHOD_SELECT and
431EVMETHOD_POLL).
432
409=over 4 433=over 4
410 434
411=item ev_io_init (ev_io *, callback, int fd, int events) 435=item ev_io_init (ev_io *, callback, int fd, int events)
412 436
413=item ev_io_set (ev_io *, int fd, int events) 437=item ev_io_set (ev_io *, int fd, int events)
414 438
415Configures an ev_io watcher. The fd is the file descriptor to rceeive 439Configures 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 | 440events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
417EV_WRITE> to receive the given events. 441EV_WRITE> to receive the given events.
418 442
419=back 443=back
420 444
421=head2 struct ev_timer - relative and optionally recurring timeouts 445=head2 C<ev_timer> - relative and optionally recurring timeouts
422 446
423Timer watchers are simple relative timers that generate an event after a 447Timer watchers are simple relative timers that generate an event after a
424given time, and optionally repeating in regular intervals after that. 448given time, and optionally repeating in regular intervals after that.
425 449
426The timers are based on real time, that is, if you register an event that 450The 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 451times out after an hour and youreset your system clock to last years
428time, it will still time out after (roughly) and hour. "Roughly" because 452time, it will still time out after (roughly) and hour. "Roughly" because
429detecting time jumps is hard, and soem inaccuracies are unavoidable (the 453detecting time jumps is hard, and soem inaccuracies are unavoidable (the
430monotonic clock option helps a lot here). 454monotonic clock option helps a lot here).
431 455
456The relative timeouts are calculated relative to the C<ev_now ()>
457time. This is usually the right thing as this timestamp refers to the time
458of the event triggering whatever timeout you are modifying/starting. If
459you suspect event processing to be delayed and you *need* to base the timeout
460ion the current time, use something like this to adjust for this:
461
462 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
463
432=over 4 464=over 4
433 465
434=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) 466=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
435 467
436=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat) 468=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
… …
458 490
459This sounds a bit complicated, but here is a useful and typical 491This 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 492example: 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 493timeout, 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 494seconds 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 495configure 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 496time 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 497state 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. 498the timer, and again will automatically restart it if need be.
467 499
468=back 500=back
469 501
470=head2 ev_periodic 502=head2 C<ev_periodic> - to cron or not to cron
471 503
472Periodic watchers are also timers of a kind, but they are very versatile 504Periodic watchers are also timers of a kind, but they are very versatile
473(and unfortunately a bit complex). 505(and unfortunately a bit complex).
474 506
475Unlike ev_timer's, they are not based on real time (or relative time) 507Unlike 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 508but 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 509to 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 () 510periodic 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 511+ 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 512take 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 513roughly 10 seconds later and of course not if you reset your system time
482again). 514again).
483 515
484They can also be used to implement vastly more complex timers, such as 516They can also be used to implement vastly more complex timers, such as
485triggering an event on eahc midnight, local time. 517triggering an event on eahc midnight, local time.
… …
514 546
515 ev_periodic_set (&periodic, 0., 3600., 0); 547 ev_periodic_set (&periodic, 0., 3600., 0);
516 548
517This doesn't mean there will always be 3600 seconds in between triggers, 549This 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 550but 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 551full hour (UTC), or more correctly, when the system time is evenly divisible
520by 3600. 552by 3600.
521 553
522Another way to think about it (for the mathematically inclined) is that 554Another 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 555C<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. 556time where C<time = at (mod interval)>, regardless of any time jumps.
525 557
526=item * manual reschedule mode (reschedule_cb = callback) 558=item * manual reschedule mode (reschedule_cb = callback)
527 559
528In this mode the values for C<interval> and C<at> are both being 560In this mode the values for C<interval> and C<at> are both being
529ignored. Instead, each time the periodic watcher gets scheduled, the 561ignored. Instead, each time the periodic watcher gets scheduled, the
530reschedule callback will be called with the watcher as first, and the 562reschedule callback will be called with the watcher as first, and the
531current time as second argument. 563current time as second argument.
532 564
533NOTE: I<This callback MUST NOT stop or destroy the periodic or any other 565NOTE: I<This callback MUST NOT stop or destroy the periodic or any other
534periodic watcher, ever, or make any event loop modificstions>. If you need 566periodic watcher, ever, or make any event loop modifications>. If you need
535to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards. 567to stop it, return C<now + 1e30> (or so, fudge fudge) and stop it afterwards.
536 568
569Also, I<< this callback must always return a time that is later than the
570passed C<now> value >>. Not even C<now> itself will be ok.
571
537Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 572Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
538ev_tstamp now)>, e.g.: 573ev_tstamp now)>, e.g.:
539 574
540 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 575 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
541 { 576 {
542 return now + 60.; 577 return now + 60.;
… …
561a different time than the last time it was called (e.g. in a crond like 596a different time than the last time it was called (e.g. in a crond like
562program when the crontabs have changed). 597program when the crontabs have changed).
563 598
564=back 599=back
565 600
566=head2 ev_signal - signal me when a signal gets signalled 601=head2 C<ev_signal> - signal me when a signal gets signalled
567 602
568Signal watchers will trigger an event when the process receives a specific 603Signal watchers will trigger an event when the process receives a specific
569signal one or more times. Even though signals are very asynchronous, libev 604signal 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 605will try it's best to deliver signals synchronously, i.e. as part of the
571normal event processing, like any other event. 606normal event processing, like any other event.
572 607
573You cna configure as many watchers as you like per signal. Only when the 608You can configure as many watchers as you like per signal. Only when the
574first watcher gets started will libev actually register a signal watcher 609first watcher gets started will libev actually register a signal watcher
575with the kernel (thus it coexists with your own signal handlers as long 610with 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 611as 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 612watcher for a signal is stopped libev will reset the signal handler to
578SIG_DFL (regardless of what it was set to before). 613SIG_DFL (regardless of what it was set to before).
… …
586Configures the watcher to trigger on the given signal number (usually one 621Configures the watcher to trigger on the given signal number (usually one
587of the C<SIGxxx> constants). 622of the C<SIGxxx> constants).
588 623
589=back 624=back
590 625
591=head2 ev_child - wait for pid status changes 626=head2 C<ev_child> - wait for pid status changes
592 627
593Child watchers trigger when your process receives a SIGCHLD in response to 628Child watchers trigger when your process receives a SIGCHLD in response to
594some child status changes (most typically when a child of yours dies). 629some child status changes (most typically when a child of yours dies).
595 630
596=over 4 631=over 4
… …
600=item ev_child_set (ev_child *, int pid) 635=item ev_child_set (ev_child *, int pid)
601 636
602Configures the watcher to wait for status changes of process C<pid> (or 637Configures 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 638I<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 639at 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 640the status word (use the macros from C<sys/wait.h> and see your systems
606contains the pid of the process causing the status change. 641C<waitpid> documentation). The C<rpid> member contains the pid of the
642process causing the status change.
607 643
608=back 644=back
609 645
610=head2 ev_idle - when you've got nothing better to do 646=head2 C<ev_idle> - when you've got nothing better to do
611 647
612Idle watchers trigger events when there are no other I/O or timer (or 648Idle watchers trigger events when there are no other events are pending
613periodic) events pending. That is, as long as your process is busy 649(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 650as your process is busy handling sockets or timeouts (or even signals,
615is idle all idle watchers are being called again and again - until 651imagine) it will not be triggered. But when your process is idle all idle
652watchers are being called again and again, once per event loop iteration -
616stopped, that is, or your process receives more events. 653until stopped, that is, or your process receives more events and becomes
654busy.
617 655
618The most noteworthy effect is that as long as any idle watchers are 656The most noteworthy effect is that as long as any idle watchers are
619active, the process will not block when waiting for new events. 657active, the process will not block when waiting for new events.
620 658
621Apart from keeping your process non-blocking (which is a useful 659Apart 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, 669kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
632believe me. 670believe me.
633 671
634=back 672=back
635 673
636=head2 prepare and check - your hooks into the event loop 674=head2 C<ev_prepare> and C<ev_check> - customise your event loop
637 675
638Prepare and check watchers usually (but not always) are used in 676Prepare and check watchers are usually (but not always) used in tandem:
639tandom. Prepare watchers get invoked before the process blocks and check 677Prepare watchers get invoked before the process blocks and check watchers
640watchers afterwards. 678afterwards.
641 679
642Their main purpose is to integrate other event mechanisms into libev. This 680Their main purpose is to integrate other event mechanisms into libev. This
643could be used, for example, to track variable changes, implement your own 681could be used, for example, to track variable changes, implement your own
644watchers, integrate net-snmp or a coroutine library and lots more. 682watchers, integrate net-snmp or a coroutine library and lots more.
645 683
646This is done by examining in each prepare call which file descriptors need 684This 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 685to be watched by the other library, registering C<ev_io> watchers for
648and starting an ev_timer watcher for any timeouts (many libraries provide 686them and starting an C<ev_timer> watcher for any timeouts (many libraries
649just this functionality). Then, in the check watcher you check for any 687provide just this functionality). Then, in the check watcher you check for
650events that occured (by making your callbacks set soem flags for example) 688any events that occured (by checking the pending status of all watchers
651and call back into the library. 689and stopping them) and call back into the library. The I/O and timer
690callbacks will never actually be called (but must be valid neverthelles,
691because you never know, you know?).
652 692
653As another example, the perl Coro module uses these hooks to integrate 693As another example, the Perl Coro module uses these hooks to integrate
654coroutines into libev programs, by yielding to other active coroutines 694coroutines into libev programs, by yielding to other active coroutines
655during each prepare and only letting the process block if no coroutines 695during each prepare and only letting the process block if no coroutines
656are ready to run. 696are ready to run (its actually more complicated, it only runs coroutines
697with priority higher than the event loop and one lower priority once,
698using idle watchers to keep the event loop from blocking if lower-priority
699coroutines exist, thus mapping low-priority coroutines to idle/background
700tasks).
657 701
658=over 4 702=over 4
659 703
660=item ev_prepare_init (ev_prepare *, callback) 704=item ev_prepare_init (ev_prepare *, callback)
661 705
662=item ev_check_init (ev_check *, callback) 706=item ev_check_init (ev_check *, callback)
663 707
664Initialises and configures the prepare or check watcher - they have no 708Initialises 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> 709parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
666macros, but using them is utterly, utterly pointless. 710macros, but using them is utterly, utterly and completely pointless.
667 711
668=back 712=back
669 713
670=head1 OTHER FUNCTIONS 714=head1 OTHER FUNCTIONS
671 715
672There are some other fucntions of possible interest. Described. Here. Now. 716There are some other functions of possible interest. Described. Here. Now.
673 717
674=over 4 718=over 4
675 719
676=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) 720=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
677 721
… …
679callback on whichever event happens first and automatically stop both 723callback 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 724watchers. 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 725or timeout without havign to allocate/configure/start/stop/free one or
682more watchers yourself. 726more watchers yourself.
683 727
684If C<fd> is less than 0, then no I/O watcher will be started and events is 728If 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 729is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
686will be craeted and started. 730C<events> set will be craeted and started.
687 731
688If C<timeout> is less than 0, then no timeout watcher will be 732If C<timeout> is less than 0, then no timeout watcher will be
689started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat 733started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
690= 0) will be started. 734repeat = 0) will be started. While C<0> is a valid timeout, it is of
735dubious value.
691 736
692The callback has the type C<void (*cb)(int revents, void *arg)> and 737The 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, 738passed an events set like normal event callbacks (with a combination of
694EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>: 739C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
740value passed to C<ev_once>:
695 741
696 static void stdin_ready (int revents, void *arg) 742 static void stdin_ready (int revents, void *arg)
697 { 743 {
698 if (revents & EV_TIMEOUT) 744 if (revents & EV_TIMEOUT)
699 /* doh, nothing entered */ 745 /* doh, nothing entered */;
700 else if (revents & EV_READ) 746 else if (revents & EV_READ)
701 /* stdin might have data for us, joy! */ 747 /* stdin might have data for us, joy! */;
702 } 748 }
703 749
704 ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0); 750 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
705 751
706=item ev_feed_event (loop, watcher, int events) 752=item ev_feed_event (loop, watcher, int events)
707 753
708Feeds the given event set into the event loop, as if the specified event 754Feeds 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 755had happened for the specified watcher (which must be a pointer to an
710initialised but not necessarily active event watcher). 756initialised but not necessarily started event watcher).
711 757
712=item ev_feed_fd_event (loop, int fd, int revents) 758=item ev_feed_fd_event (loop, int fd, int revents)
713 759
714Feed an event on the given fd, as if a file descriptor backend detected it. 760Feed an event on the given fd, as if a file descriptor backend detected
761the given events it.
715 762
716=item ev_feed_signal_event (loop, int signum) 763=item ev_feed_signal_event (loop, int signum)
717 764
718Feed an event as if the given signal occured (loop must be the default loop!). 765Feed an event as if the given signal occured (loop must be the default loop!).
719 766

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