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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
… …
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
53
54These functions can be called anytime, even before initialising the
55library in any way.
47 56
48=over 4 57=over 4
49 58
50=item ev_tstamp ev_time () 59=item ev_tstamp ev_time ()
51 60
… …
59you linked against by calling the functions C<ev_version_major> and 68you linked against by calling the functions C<ev_version_major> and
60C<ev_version_minor>. If you want, you can compare against the global 69C<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 70symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the
62version of the library your program was compiled against. 71version of the library your program was compiled against.
63 72
64Usually, its a good idea to terminate if the major versions mismatch, 73Usually, it's a good idea to terminate if the major versions mismatch,
65as this indicates an incompatible change. Minor versions are usually 74as this indicates an incompatible change. Minor versions are usually
66compatible to older versions, so a larger minor version alone is usually 75compatible to older versions, so a larger minor version alone is usually
67not a problem. 76not a problem.
68 77
69=item ev_set_allocator (void *(*cb)(void *ptr, long size)) 78=item ev_set_allocator (void *(*cb)(void *ptr, long size))
70 79
71Sets the allocation function to use (the prototype is similar to the 80Sets the allocation function to use (the prototype is similar to the
72realloc function). It is used to allocate and free memory (no surprises 81realloc C function, the semantics are identical). It is used to allocate
73here). If it returns zero when memory needs to be allocated, the library 82and free memory (no surprises here). If it returns zero when memory
74might abort or take some potentially destructive action. The default is 83needs to be allocated, the library might abort or take some potentially
75your system realloc function. 84destructive action. The default is your system realloc function.
76 85
77You could override this function in high-availability programs to, say, 86You could override this function in high-availability programs to, say,
78free some memory if it cannot allocate memory, to use a special allocator, 87free 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. 88or even to sleep a while and retry until some memory is available.
80 89
… …
82 91
83Set the callback function to call on a retryable syscall error (such 92Set the callback function to call on a retryable syscall error (such
84as failed select, poll, epoll_wait). The message is a printable string 93as failed select, poll, epoll_wait). The message is a printable string
85indicating the system call or subsystem causing the problem. If this 94indicating the system call or subsystem causing the problem. If this
86callback is set, then libev will expect it to remedy the sitution, no 95callback is set, then libev will expect it to remedy the sitution, no
87matter what, when it returns. That is, libev will geenrally retry the 96matter what, when it returns. That is, libev will generally retry the
88requested operation, or, if the condition doesn't go away, do bad stuff 97requested operation, or, if the condition doesn't go away, do bad stuff
89(such as abort). 98(such as abort).
90 99
91=back 100=back
92 101
… …
95An event loop is described by a C<struct ev_loop *>. The library knows two 104An 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 105types of such loops, the I<default> loop, which supports signals and child
97events, and dynamically created loops which do not. 106events, and dynamically created loops which do not.
98 107
99If you use threads, a common model is to run the default event loop 108If 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 109in 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 110create, you also create another event loop. Libev itself does no locking
102whatsoever, so if you mix calls to different event loops, make sure you 111whatsoever, so if you mix calls to the same event loop in different
103lock (this is usually a bad idea, though, even if done right). 112threads, make sure you lock (this is usually a bad idea, though, even if
113done correctly, because it's hideous and inefficient).
104 114
105=over 4 115=over 4
106 116
107=item struct ev_loop *ev_default_loop (unsigned int flags) 117=item struct ev_loop *ev_default_loop (unsigned int flags)
108 118
… …
113 123
114If you don't know what event loop to use, use the one returned from this 124If you don't know what event loop to use, use the one returned from this
115function. 125function.
116 126
117The flags argument can be used to specify special behaviour or specific 127The flags argument can be used to specify special behaviour or specific
118backends to use, and is usually specified as 0 (or EVFLAG_AUTO) 128backends to use, and is usually specified as 0 (or EVFLAG_AUTO).
119 129
120It supports the following flags: 130It supports the following flags:
121 131
122=over 4 132=over 4
123 133
124=item EVFLAG_AUTO 134=item C<EVFLAG_AUTO>
125 135
126The default flags value. Use this if you have no clue (its the right 136The default flags value. Use this if you have no clue (it's the right
127thing, believe me). 137thing, believe me).
128 138
129=item EVFLAG_NOENV 139=item C<EVFLAG_NOENV>
130 140
131If this flag bit is ored into the flag value then libev will I<not> look 141If 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 142or setgid) then libev will I<not> look at the environment variable
133environment variable will override the flags completely. This is useful 143C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
144override 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 145useful to try out specific backends to test their performance, or to work
135bugs. 146around bugs.
136 147
137=item EVMETHOD_SELECT portable select backend 148=item C<EVMETHOD_SELECT> (portable select backend)
138 149
139=item EVMETHOD_POLL poll backend (everywhere except windows) 150=item C<EVMETHOD_POLL> (poll backend, available everywhere except on windows)
140 151
141=item EVMETHOD_EPOLL linux only 152=item C<EVMETHOD_EPOLL> (linux only)
142 153
143=item EVMETHOD_KQUEUE some bsds only 154=item C<EVMETHOD_KQUEUE> (some bsds only)
144 155
145=item EVMETHOD_DEVPOLL solaris 8 only 156=item C<EVMETHOD_DEVPOLL> (solaris 8 only)
146 157
147=item EVMETHOD_PORT solaris 10 only 158=item C<EVMETHOD_PORT> (solaris 10 only)
148 159
149If one or more of these are ored into the flags value, then only these 160If 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 161backends will be tried (in the reverse order as given here). If one are
151specified, any backend will do. 162specified, any backend will do.
152 163
… …
161 172
162=item ev_default_destroy () 173=item ev_default_destroy ()
163 174
164Destroys the default loop again (frees all memory and kernel state 175Destroys the default loop again (frees all memory and kernel state
165etc.). This stops all registered event watchers (by not touching them in 176etc.). This stops all registered event watchers (by not touching them in
166any way whatsoever, although you cnanot rely on this :). 177any way whatsoever, although you cannot rely on this :).
167 178
168=item ev_loop_destroy (loop) 179=item ev_loop_destroy (loop)
169 180
170Like C<ev_default_destroy>, but destroys an event loop created by an 181Like C<ev_default_destroy>, but destroys an event loop created by an
171earlier call to C<ev_loop_new>. 182earlier call to C<ev_loop_new>.
… …
179 190
180You I<must> call this function after forking if and only if you want to 191You 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 192use the event library in both processes. If you just fork+exec, you don't
182have to call it. 193have to call it.
183 194
184The function itself is quite fast and its usually not a problem to call 195The 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 196it just in case after a fork. To make this easy, the function will fit in
186quite nicely into a call to C<pthread_atfork>: 197quite nicely into a call to C<pthread_atfork>:
187 198
188 pthread_atfork (0, 0, ev_default_fork); 199 pthread_atfork (0, 0, ev_default_fork);
189 200
… …
196=item unsigned int ev_method (loop) 207=item unsigned int ev_method (loop)
197 208
198Returns one of the C<EVMETHOD_*> flags indicating the event backend in 209Returns one of the C<EVMETHOD_*> flags indicating the event backend in
199use. 210use.
200 211
201=item ev_tstamp = ev_now (loop) 212=item ev_tstamp ev_now (loop)
202 213
203Returns the current "event loop time", which is the time the event loop 214Returns the current "event loop time", which is the time the event loop
204got events and started processing them. This timestamp does not change 215got events and started processing them. This timestamp does not change
205as long as callbacks are being processed, and this is also the base time 216as 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 217used 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 226If 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. 227no event watchers are active anymore or C<ev_unloop> was called.
217 228
218A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle 229A 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 230those events and any outstanding ones, but will not block your process in
220case there are no events. 231case there are no events and will return after one iteration of the loop.
221 232
222A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if 233A 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 234neccessary) and will handle those and any outstanding ones. It will block
224your process until at least one new event arrives. 235your process until at least one new event arrives, and will return after
236one iteration of the loop.
225 237
226This flags value could be used to implement alternative looping 238This flags value could be used to implement alternative looping
227constructs, but the C<prepare> and C<check> watchers provide a better and 239constructs, but the C<prepare> and C<check> watchers provide a better and
228more generic mechanism. 240more generic mechanism.
229 241
230=item ev_unloop (loop, how) 242=item ev_unloop (loop, how)
231 243
232Can be used to make a call to C<ev_loop> return early. The C<how> argument 244Can be used to make a call to C<ev_loop> return early (but only after it
245has 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> 246C<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> 247C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
235calls return.
236 248
237=item ev_ref (loop) 249=item ev_ref (loop)
238 250
239=item ev_unref (loop) 251=item ev_unref (loop)
240 252
241Ref/unref can be used to add or remove a refcount on the event loop: Every 253Ref/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 254loop: Every watcher keeps one reference, and as long as the reference
243unregister that should not keep ev_loop from running, ev_unref() after 255count 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 256a 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 257returning, 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 258example, 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 259visible 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 260no event watchers registered by it are active. It is also an excellent
249before stop. 261way to do this for generic recurring timers or from within third-party
262libraries. Just remember to I<unref after start> and I<ref before stop>.
250 263
251=back 264=back
252 265
253=head1 ANATOMY OF A WATCHER 266=head1 ANATOMY OF A WATCHER
254 267
255A watcher is a structure that you create and register to record your 268A 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 269interest in some event. For instance, if you want to wait for STDIN to
257become readable, you would create an ev_io watcher for that: 270become readable, you would create an C<ev_io> watcher for that:
258 271
259 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 272 static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
260 { 273 {
261 ev_io_stop (w); 274 ev_io_stop (w);
262 ev_unloop (loop, EVUNLOOP_ALL); 275 ev_unloop (loop, EVUNLOOP_ALL);
… …
291 304
292As long as your watcher is active (has been started but not stopped) you 305As 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 306must not touch the values stored in it. Most specifically you must never
294reinitialise it or call its set method. 307reinitialise it or call its set method.
295 308
296You cna check wether an event is active by calling the C<ev_is_active 309You 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 310(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 311callback for it has not been called yet) you can use the C<ev_is_pending
299(watcher *)> macro. 312(watcher *)> macro.
300 313
301Each and every callback receives the event loop pointer as first, the 314Each and every callback receives the event loop pointer as first, the
302registered watcher structure as second, and a bitset of received events as 315registered watcher structure as second, and a bitset of received events as
303third argument. 316third argument.
304 317
305The rceeived events usually include a single bit per event type received 318The 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 319(you can receive multiple events at the same time). The possible bit masks
307are: 320are:
308 321
309=over 4 322=over 4
310 323
311=item EV_READ 324=item C<EV_READ>
312 325
313=item EV_WRITE 326=item C<EV_WRITE>
314 327
315The file descriptor in the ev_io watcher has become readable and/or 328The file descriptor in the C<ev_io> watcher has become readable and/or
316writable. 329writable.
317 330
318=item EV_TIMEOUT 331=item C<EV_TIMEOUT>
319 332
320The ev_timer watcher has timed out. 333The C<ev_timer> watcher has timed out.
321 334
322=item EV_PERIODIC 335=item C<EV_PERIODIC>
323 336
324The ev_periodic watcher has timed out. 337The C<ev_periodic> watcher has timed out.
325 338
326=item EV_SIGNAL 339=item C<EV_SIGNAL>
327 340
328The signal specified in the ev_signal watcher has been received by a thread. 341The signal specified in the C<ev_signal> watcher has been received by a thread.
329 342
330=item EV_CHILD 343=item C<EV_CHILD>
331 344
332The pid specified in the ev_child watcher has received a status change. 345The pid specified in the C<ev_child> watcher has received a status change.
333 346
334=item EV_IDLE 347=item C<EV_IDLE>
335 348
336The ev_idle watcher has determined that you have nothing better to do. 349The C<ev_idle> watcher has determined that you have nothing better to do.
337 350
338=item EV_PREPARE 351=item C<EV_PREPARE>
339 352
340=item EV_CHECK 353=item C<EV_CHECK>
341 354
342All ev_prepare watchers are invoked just I<before> C<ev_loop> starts 355All 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 356to 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 357C<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 358received 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 359many 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 360(for example, a C<ev_prepare> watcher might start an idle watcher to keep
348C<ev_loop> from blocking). 361C<ev_loop> from blocking).
349 362
350=item EV_ERROR 363=item C<EV_ERROR>
351 364
352An unspecified error has occured, the watcher has been stopped. This might 365An unspecified error has occured, the watcher has been stopped. This might
353happen because the watcher could not be properly started because libev 366happen 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 367ran 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 368problem. You best act on it by reporting the problem and somehow coping
… …
364=back 377=back
365 378
366=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER 379=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
367 380
368Each watcher has, by default, a member C<void *data> that you can change 381Each 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 382and 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 383to 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 384don'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 385member, you can also "subclass" the watcher type and provide your own
373data: 386data:
374 387
… …
396=head1 WATCHER TYPES 409=head1 WATCHER TYPES
397 410
398This section describes each watcher in detail, but will not repeat 411This section describes each watcher in detail, but will not repeat
399information given in the last section. 412information given in the last section.
400 413
401=head2 struct ev_io - is my file descriptor readable or writable 414=head2 C<ev_io> - is this file descriptor readable or writable
402 415
403I/O watchers check wether a file descriptor is readable or writable 416I/O watchers check whether a file descriptor is readable or writable
404in each iteration of the event loop (This behaviour is called 417in each iteration of the event loop (This behaviour is called
405level-triggering because you keep receiving events as long as the 418level-triggering because you keep receiving events as long as the
406condition persists. Remember you cna stop the watcher if you don't want to 419condition persists. Remember you can stop the watcher if you don't want to
407act on the event and neither want to receive future events). 420act on the event and neither want to receive future events).
408 421
422In general you can register as many read and/or write event watchers oer
423fd as you want (as long as you don't confuse yourself). Setting all file
424descriptors to non-blocking mode is also usually a good idea (but not
425required if you know what you are doing).
426
427You have to be careful with dup'ed file descriptors, though. Some backends
428(the linux epoll backend is a notable example) cannot handle dup'ed file
429descriptors correctly if you register interest in two or more fds pointing
430to the same file/socket etc. description.
431
432If you must do this, then force the use of a known-to-be-good backend
433(at the time of this writing, this includes only EVMETHOD_SELECT and
434EVMETHOD_POLL).
435
409=over 4 436=over 4
410 437
411=item ev_io_init (ev_io *, callback, int fd, int events) 438=item ev_io_init (ev_io *, callback, int fd, int events)
412 439
413=item ev_io_set (ev_io *, int fd, int events) 440=item ev_io_set (ev_io *, int fd, int events)
414 441
415Configures an ev_io watcher. The fd is the file descriptor to rceeive 442Configures 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 | 443events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ |
417EV_WRITE> to receive the given events. 444EV_WRITE> to receive the given events.
418 445
419=back 446=back
420 447
421=head2 struct ev_timer - relative and optionally recurring timeouts 448=head2 C<ev_timer> - relative and optionally recurring timeouts
422 449
423Timer watchers are simple relative timers that generate an event after a 450Timer watchers are simple relative timers that generate an event after a
424given time, and optionally repeating in regular intervals after that. 451given time, and optionally repeating in regular intervals after that.
425 452
426The timers are based on real time, that is, if you register an event that 453The 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 454times out after an hour and youreset your system clock to last years
428time, it will still time out after (roughly) and hour. "Roughly" because 455time, it will still time out after (roughly) and hour. "Roughly" because
429detecting time jumps is hard, and soem inaccuracies are unavoidable (the 456detecting time jumps is hard, and soem inaccuracies are unavoidable (the
430monotonic clock option helps a lot here). 457monotonic clock option helps a lot here).
431 458
459The relative timeouts are calculated relative to the C<ev_now ()>
460time. This is usually the right thing as this timestamp refers to the time
461of the event triggering whatever timeout you are modifying/starting. If
462you suspect event processing to be delayed and you *need* to base the timeout
463ion the current time, use something like this to adjust for this:
464
465 ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
466
432=over 4 467=over 4
433 468
434=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) 469=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
435 470
436=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat) 471=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
… …
458 493
459This sounds a bit complicated, but here is a useful and typical 494This 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 495example: 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 496timeout, 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 497seconds 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 498configure 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 499time 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 500state 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. 501the timer, and again will automatically restart it if need be.
467 502
468=back 503=back
469 504
470=head2 ev_periodic 505=head2 C<ev_periodic> - to cron or not to cron
471 506
472Periodic watchers are also timers of a kind, but they are very versatile 507Periodic watchers are also timers of a kind, but they are very versatile
473(and unfortunately a bit complex). 508(and unfortunately a bit complex).
474 509
475Unlike ev_timer's, they are not based on real time (or relative time) 510Unlike 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 511but 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 512to 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 () 513periodic 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 514+ 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 515take 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 516roughly 10 seconds later and of course not if you reset your system time
482again). 517again).
483 518
484They can also be used to implement vastly more complex timers, such as 519They can also be used to implement vastly more complex timers, such as
485triggering an event on eahc midnight, local time. 520triggering an event on eahc midnight, local time.
… …
514 549
515 ev_periodic_set (&periodic, 0., 3600., 0); 550 ev_periodic_set (&periodic, 0., 3600., 0);
516 551
517This doesn't mean there will always be 3600 seconds in between triggers, 552This 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 553but 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 554full hour (UTC), or more correctly, when the system time is evenly divisible
520by 3600. 555by 3600.
521 556
522Another way to think about it (for the mathematically inclined) is that 557Another 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 558C<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. 559time where C<time = at (mod interval)>, regardless of any time jumps.
525 560
526=item * manual reschedule mode (reschedule_cb = callback) 561=item * manual reschedule mode (reschedule_cb = callback)
527 562
528In this mode the values for C<interval> and C<at> are both being 563In this mode the values for C<interval> and C<at> are both being
529ignored. Instead, each time the periodic watcher gets scheduled, the 564ignored. Instead, each time the periodic watcher gets scheduled, the
530reschedule callback will be called with the watcher as first, and the 565reschedule callback will be called with the watcher as first, and the
531current time as second argument. 566current time as second argument.
532 567
533NOTE: I<This callback MUST NOT stop or destroy the periodic or any other 568NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,
534periodic watcher, ever, or make any event loop modificstions>. If you need 569ever, 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. 570return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by
571starting a prepare watcher).
536 572
537Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 573Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
538ev_tstamp now)>, e.g.: 574ev_tstamp now)>, e.g.:
539 575
540 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 576 static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
541 { 577 {
542 return now + 60.; 578 return now + 60.;
… …
545It must return the next time to trigger, based on the passed time value 581It 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 582(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 583will usually be called just before the callback will be triggered, but
548might be called at other times, too. 584might be called at other times, too.
549 585
586NOTE: I<< This callback must always return a time that is later than the
587passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.
588
550This can be used to create very complex timers, such as a timer that 589This 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 590triggers 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 591next midnight after C<now> and return the timestamp value for this. How
553is, again, up to you (but it is not trivial). 592you do this is, again, up to you (but it is not trivial, which is the main
593reason I omitted it as an example).
554 594
555=back 595=back
556 596
557=item ev_periodic_again (loop, ev_periodic *) 597=item ev_periodic_again (loop, ev_periodic *)
558 598
… …
561a different time than the last time it was called (e.g. in a crond like 601a different time than the last time it was called (e.g. in a crond like
562program when the crontabs have changed). 602program when the crontabs have changed).
563 603
564=back 604=back
565 605
566=head2 ev_signal - signal me when a signal gets signalled 606=head2 C<ev_signal> - signal me when a signal gets signalled
567 607
568Signal watchers will trigger an event when the process receives a specific 608Signal watchers will trigger an event when the process receives a specific
569signal one or more times. Even though signals are very asynchronous, libev 609signal 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 610will try it's best to deliver signals synchronously, i.e. as part of the
571normal event processing, like any other event. 611normal event processing, like any other event.
572 612
573You cna configure as many watchers as you like per signal. Only when the 613You can configure as many watchers as you like per signal. Only when the
574first watcher gets started will libev actually register a signal watcher 614first watcher gets started will libev actually register a signal watcher
575with the kernel (thus it coexists with your own signal handlers as long 615with 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 616as 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 617watcher for a signal is stopped libev will reset the signal handler to
578SIG_DFL (regardless of what it was set to before). 618SIG_DFL (regardless of what it was set to before).
… …
586Configures the watcher to trigger on the given signal number (usually one 626Configures the watcher to trigger on the given signal number (usually one
587of the C<SIGxxx> constants). 627of the C<SIGxxx> constants).
588 628
589=back 629=back
590 630
591=head2 ev_child - wait for pid status changes 631=head2 C<ev_child> - wait for pid status changes
592 632
593Child watchers trigger when your process receives a SIGCHLD in response to 633Child watchers trigger when your process receives a SIGCHLD in response to
594some child status changes (most typically when a child of yours dies). 634some child status changes (most typically when a child of yours dies).
595 635
596=over 4 636=over 4
… …
600=item ev_child_set (ev_child *, int pid) 640=item ev_child_set (ev_child *, int pid)
601 641
602Configures the watcher to wait for status changes of process C<pid> (or 642Configures 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 643I<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 644at 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 645the status word (use the macros from C<sys/wait.h> and see your systems
606contains the pid of the process causing the status change. 646C<waitpid> documentation). The C<rpid> member contains the pid of the
647process causing the status change.
607 648
608=back 649=back
609 650
610=head2 ev_idle - when you've got nothing better to do 651=head2 C<ev_idle> - when you've got nothing better to do
611 652
612Idle watchers trigger events when there are no other I/O or timer (or 653Idle watchers trigger events when there are no other events are pending
613periodic) events pending. That is, as long as your process is busy 654(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 655as your process is busy handling sockets or timeouts (or even signals,
615is idle all idle watchers are being called again and again - until 656imagine) it will not be triggered. But when your process is idle all idle
657watchers are being called again and again, once per event loop iteration -
616stopped, that is, or your process receives more events. 658until stopped, that is, or your process receives more events and becomes
659busy.
617 660
618The most noteworthy effect is that as long as any idle watchers are 661The most noteworthy effect is that as long as any idle watchers are
619active, the process will not block when waiting for new events. 662active, the process will not block when waiting for new events.
620 663
621Apart from keeping your process non-blocking (which is a useful 664Apart 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, 674kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
632believe me. 675believe me.
633 676
634=back 677=back
635 678
636=head2 prepare and check - your hooks into the event loop 679=head2 C<ev_prepare> and C<ev_check> - customise your event loop
637 680
638Prepare and check watchers usually (but not always) are used in 681Prepare and check watchers are usually (but not always) used in tandem:
639tandom. Prepare watchers get invoked before the process blocks and check 682prepare watchers get invoked before the process blocks and check watchers
640watchers afterwards. 683afterwards.
641 684
642Their main purpose is to integrate other event mechanisms into libev. This 685Their main purpose is to integrate other event mechanisms into libev. This
643could be used, for example, to track variable changes, implement your own 686could be used, for example, to track variable changes, implement your own
644watchers, integrate net-snmp or a coroutine library and lots more. 687watchers, integrate net-snmp or a coroutine library and lots more.
645 688
646This is done by examining in each prepare call which file descriptors need 689This 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 690to be watched by the other library, registering C<ev_io> watchers for
648and starting an ev_timer watcher for any timeouts (many libraries provide 691them and starting an C<ev_timer> watcher for any timeouts (many libraries
649just this functionality). Then, in the check watcher you check for any 692provide just this functionality). Then, in the check watcher you check for
650events that occured (by making your callbacks set soem flags for example) 693any events that occured (by checking the pending status of all watchers
651and call back into the library. 694and stopping them) and call back into the library. The I/O and timer
695callbacks will never actually be called (but must be valid nevertheless,
696because you never know, you know?).
652 697
653As another example, the perl Coro module uses these hooks to integrate 698As another example, the Perl Coro module uses these hooks to integrate
654coroutines into libev programs, by yielding to other active coroutines 699coroutines into libev programs, by yielding to other active coroutines
655during each prepare and only letting the process block if no coroutines 700during each prepare and only letting the process block if no coroutines
656are ready to run. 701are ready to run (it's actually more complicated: it only runs coroutines
702with priority higher than or equal to the event loop and one coroutine
703of lower priority, but only once, using idle watchers to keep the event
704loop from blocking if lower-priority coroutines are active, thus mapping
705low-priority coroutines to idle/background tasks).
657 706
658=over 4 707=over 4
659 708
660=item ev_prepare_init (ev_prepare *, callback) 709=item ev_prepare_init (ev_prepare *, callback)
661 710
662=item ev_check_init (ev_check *, callback) 711=item ev_check_init (ev_check *, callback)
663 712
664Initialises and configures the prepare or check watcher - they have no 713Initialises 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> 714parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
666macros, but using them is utterly, utterly pointless. 715macros, but using them is utterly, utterly and completely pointless.
667 716
668=back 717=back
669 718
670=head1 OTHER FUNCTIONS 719=head1 OTHER FUNCTIONS
671 720
672There are some other fucntions of possible interest. Described. Here. Now. 721There are some other functions of possible interest. Described. Here. Now.
673 722
674=over 4 723=over 4
675 724
676=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) 725=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
677 726
… …
679callback on whichever event happens first and automatically stop both 728callback 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 729watchers. 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 730or timeout without havign to allocate/configure/start/stop/free one or
682more watchers yourself. 731more watchers yourself.
683 732
684If C<fd> is less than 0, then no I/O watcher will be started and events is 733If 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 734is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and
686will be craeted and started. 735C<events> set will be craeted and started.
687 736
688If C<timeout> is less than 0, then no timeout watcher will be 737If C<timeout> is less than 0, then no timeout watcher will be
689started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat 738started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
690= 0) will be started. 739repeat = 0) will be started. While C<0> is a valid timeout, it is of
740dubious value.
691 741
692The callback has the type C<void (*cb)(int revents, void *arg)> and 742The 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, 743passed 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>: 744C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
745value passed to C<ev_once>:
695 746
696 static void stdin_ready (int revents, void *arg) 747 static void stdin_ready (int revents, void *arg)
697 { 748 {
698 if (revents & EV_TIMEOUT) 749 if (revents & EV_TIMEOUT)
699 /* doh, nothing entered */ 750 /* doh, nothing entered */;
700 else if (revents & EV_READ) 751 else if (revents & EV_READ)
701 /* stdin might have data for us, joy! */ 752 /* stdin might have data for us, joy! */;
702 } 753 }
703 754
704 ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0); 755 ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
705 756
706=item ev_feed_event (loop, watcher, int events) 757=item ev_feed_event (loop, watcher, int events)
707 758
708Feeds the given event set into the event loop, as if the specified event 759Feeds 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 760had happened for the specified watcher (which must be a pointer to an
710initialised but not necessarily active event watcher). 761initialised but not necessarily started event watcher).
711 762
712=item ev_feed_fd_event (loop, int fd, int revents) 763=item ev_feed_fd_event (loop, int fd, int revents)
713 764
714Feed an event on the given fd, as if a file descriptor backend detected it. 765Feed an event on the given fd, as if a file descriptor backend detected
766the given events it.
715 767
716=item ev_feed_signal_event (loop, int signum) 768=item ev_feed_signal_event (loop, int signum)
717 769
718Feed an event as if the given signal occured (loop must be the default loop!). 770Feed an event as if the given signal occured (loop must be the default loop!).
719 771
720=back 772=back
721 773
774=head1 LIBEVENT EMULATION
775
776TBD.
777
778=head1 C++ SUPPORT
779
780TBD.
781
722=head1 AUTHOR 782=head1 AUTHOR
723 783
724Marc Lehmann <libev@schmorp.de>. 784Marc Lehmann <libev@schmorp.de>.
725 785

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