1 |
=head1 NAME |
2 |
|
3 |
libev - a high performance full-featured event loop written in C |
4 |
|
5 |
=head1 SYNOPSIS |
6 |
|
7 |
#include <ev.h> |
8 |
|
9 |
=head1 DESCRIPTION |
10 |
|
11 |
Libev is an event loop: you register interest in certain events (such as a |
12 |
file descriptor being readable or a timeout occuring), and it will manage |
13 |
these event sources and provide your program with events. |
14 |
|
15 |
To 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 |
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communicate events via a callback mechanism. |
18 |
|
19 |
You register interest in certain events by registering so-called I<event |
20 |
watchers>, which are relatively small C structures you initialise with the |
21 |
details of the event, and then hand it over to libev by I<starting> the |
22 |
watcher. |
23 |
|
24 |
=head1 FEATURES |
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|
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Libev supports select, poll, the linux-specific epoll and the bsd-specific |
27 |
kqueue mechanisms for file descriptor events, relative timers, absolute |
28 |
timers with customised rescheduling, signal events, process status change |
29 |
events (related to SIGCHLD), and event watchers dealing with the event |
30 |
loop mechanism itself (idle, prepare and check watchers). |
31 |
|
32 |
=head1 CONVENTIONS |
33 |
|
34 |
Libev is very configurable. In this manual the default configuration |
35 |
will be described, which supports multiple event loops. For more info |
36 |
about various configuraiton options please have a look at the file |
37 |
F<README.embed> in the libev distribution. If libev was configured without |
38 |
support for multiple event loops, then all functions taking an initial |
39 |
argument of name C<loop> (which is always of type C<struct ev_loop *>) |
40 |
will not have this argument. |
41 |
|
42 |
=head1 TIME AND OTHER GLOBAL FUNCTIONS |
43 |
|
44 |
Libev represents time as a single floating point number, representing the |
45 |
(fractional) number of seconds since the (POSIX) epoch (somewhere near |
46 |
the beginning of 1970, details are complicated, don't ask). This type is |
47 |
called C<ev_tstamp>, which is what you should use too. It usually aliases |
48 |
to the double type in C. |
49 |
|
50 |
=over 4 |
51 |
|
52 |
=item ev_tstamp ev_time () |
53 |
|
54 |
Returns the current time as libev would use it. |
55 |
|
56 |
=item int ev_version_major () |
57 |
|
58 |
=item int ev_version_minor () |
59 |
|
60 |
You can find out the major and minor version numbers of the library |
61 |
you linked against by calling the functions C<ev_version_major> and |
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C<ev_version_minor>. If you want, you can compare against the global |
63 |
symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the |
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version of the library your program was compiled against. |
65 |
|
66 |
Usually, its a good idea to terminate if the major versions mismatch, |
67 |
as this indicates an incompatible change. Minor versions are usually |
68 |
compatible to older versions, so a larger minor version alone is usually |
69 |
not a problem. |
70 |
|
71 |
=item ev_set_allocator (void *(*cb)(void *ptr, long size)) |
72 |
|
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Sets the allocation function to use (the prototype is similar to the |
74 |
realloc function). It is used to allocate and free memory (no surprises |
75 |
here). If it returns zero when memory needs to be allocated, the library |
76 |
might abort or take some potentially destructive action. The default is |
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your system realloc function. |
78 |
|
79 |
You could override this function in high-availability programs to, say, |
80 |
free some memory if it cannot allocate memory, to use a special allocator, |
81 |
or even to sleep a while and retry until some memory is available. |
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|
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=item ev_set_syserr_cb (void (*cb)(const char *msg)); |
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|
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Set the callback function to call on a retryable syscall error (such |
86 |
as failed select, poll, epoll_wait). The message is a printable string |
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indicating the system call or subsystem causing the problem. If this |
88 |
callback is set, then libev will expect it to remedy the sitution, no |
89 |
matter what, when it returns. That is, libev will geenrally retry the |
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requested operation, or, if the condition doesn't go away, do bad stuff |
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(such as abort). |
92 |
|
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=back |
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|
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=head1 FUNCTIONS CONTROLLING THE EVENT LOOP |
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|
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An event loop is described by a C<struct ev_loop *>. The library knows two |
98 |
types of such loops, the I<default> loop, which supports signals and child |
99 |
events, and dynamically created loops which do not. |
100 |
|
101 |
If you use threads, a common model is to run the default event loop |
102 |
in your main thread (or in a separate thrad) and for each thread you |
103 |
create, you also create another event loop. Libev itself does no lockign |
104 |
whatsoever, so if you mix calls to different event loops, make sure you |
105 |
lock (this is usually a bad idea, though, even if done right). |
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|
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=over 4 |
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|
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=item struct ev_loop *ev_default_loop (unsigned int flags) |
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|
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This will initialise the default event loop if it hasn't been initialised |
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yet and return it. If the default loop could not be initialised, returns |
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false. If it already was initialised it simply returns it (and ignores the |
114 |
flags). |
115 |
|
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If you don't know what event loop to use, use the one returned from this |
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function. |
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|
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The flags argument can be used to specify special behaviour or specific |
120 |
backends to use, and is usually specified as 0 (or EVFLAG_AUTO) |
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|
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It supports the following flags: |
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|
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=over 4 |
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|
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=item EVFLAG_AUTO |
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|
128 |
The default flags value. Use this if you have no clue (its the right |
129 |
thing, believe me). |
130 |
|
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=item EVFLAG_NOENV |
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|
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If this flag bit is ored into the flag value then libev will I<not> look |
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at the environment variable C<LIBEV_FLAGS>. Otherwise (the default), this |
135 |
environment variable will override the flags completely. This is useful |
136 |
to try out specific backends to tets their performance, or to work around |
137 |
bugs. |
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|
139 |
=item EVMETHOD_SELECT portable select backend |
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|
141 |
=item EVMETHOD_POLL poll backend (everywhere except windows) |
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|
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=item EVMETHOD_EPOLL linux only |
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|
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=item EVMETHOD_KQUEUE some bsds only |
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|
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=item EVMETHOD_DEVPOLL solaris 8 only |
148 |
|
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=item EVMETHOD_PORT solaris 10 only |
150 |
|
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If one or more of these are ored into the flags value, then only these |
152 |
backends will be tried (in the reverse order as given here). If one are |
153 |
specified, any backend will do. |
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|
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=back |
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|
157 |
=item struct ev_loop *ev_loop_new (unsigned int flags) |
158 |
|
159 |
Similar to C<ev_default_loop>, but always creates a new event loop that is |
160 |
always distinct from the default loop. Unlike the default loop, it cannot |
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handle signal and child watchers, and attempts to do so will be greeted by |
162 |
undefined behaviour (or a failed assertion if assertions are enabled). |
163 |
|
164 |
=item ev_default_destroy () |
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|
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Destroys the default loop again (frees all memory and kernel state |
167 |
etc.). This stops all registered event watchers (by not touching them in |
168 |
any way whatsoever, although you cnanot rely on this :). |
169 |
|
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=item ev_loop_destroy (loop) |
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|
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Like C<ev_default_destroy>, but destroys an event loop created by an |
173 |
earlier call to C<ev_loop_new>. |
174 |
|
175 |
=item ev_default_fork () |
176 |
|
177 |
This function reinitialises the kernel state for backends that have |
178 |
one. Despite the name, you can call it anytime, but it makes most sense |
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after forking, in either the parent or child process (or both, but that |
180 |
again makes little sense). |
181 |
|
182 |
You I<must> call this function after forking if and only if you want to |
183 |
use the event library in both processes. If you just fork+exec, you don't |
184 |
have to call it. |
185 |
|
186 |
The function itself is quite fast and its usually not a problem to call |
187 |
it just in case after a fork. To make this easy, the function will fit in |
188 |
quite nicely into a call to C<pthread_atfork>: |
189 |
|
190 |
pthread_atfork (0, 0, ev_default_fork); |
191 |
|
192 |
=item ev_loop_fork (loop) |
193 |
|
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Like C<ev_default_fork>, but acts on an event loop created by |
195 |
C<ev_loop_new>. Yes, you have to call this on every allocated event loop |
196 |
after fork, and how you do this is entirely your own problem. |
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|
198 |
=item unsigned int ev_method (loop) |
199 |
|
200 |
Returns one of the C<EVMETHOD_*> flags indicating the event backend in |
201 |
use. |
202 |
|
203 |
=item ev_tstamp = ev_now (loop) |
204 |
|
205 |
Returns the current "event loop time", which is the time the event loop |
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got events and started processing them. This timestamp does not change |
207 |
as long as callbacks are being processed, and this is also the base time |
208 |
used for relative timers. You can treat it as the timestamp of the event |
209 |
occuring (or more correctly, the mainloop finding out about it). |
210 |
|
211 |
=item ev_loop (loop, int flags) |
212 |
|
213 |
Finally, this is it, the event handler. This function usually is called |
214 |
after you initialised all your watchers and you want to start handling |
215 |
events. |
216 |
|
217 |
If the flags argument is specified as 0, it will not return until either |
218 |
no event watchers are active anymore or C<ev_unloop> was called. |
219 |
|
220 |
A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle |
221 |
those events and any outstanding ones, but will not block your process in |
222 |
case there are no events. |
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|
224 |
A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if |
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neccessary) and will handle those and any outstanding ones. It will block |
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your process until at least one new event arrives. |
227 |
|
228 |
This flags value could be used to implement alternative looping |
229 |
constructs, but the C<prepare> and C<check> watchers provide a better and |
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more generic mechanism. |
231 |
|
232 |
=item ev_unloop (loop, how) |
233 |
|
234 |
Can be used to make a call to C<ev_loop> return early. The C<how> argument |
235 |
must be either C<EVUNLOOP_ONCE>, which will make the innermost C<ev_loop> |
236 |
call return, or C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> |
237 |
calls return. |
238 |
|
239 |
=item ev_ref (loop) |
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|
241 |
=item ev_unref (loop) |
242 |
|
243 |
Ref/unref can be used to add or remove a refcount on the event loop: Every |
244 |
watcher keeps one reference. If you have a long-runing watcher you never |
245 |
unregister that should not keep ev_loop from running, ev_unref() after |
246 |
starting, and ev_ref() before stopping it. Libev itself uses this for |
247 |
example for its internal signal pipe: It is not visible to you as a user |
248 |
and should not keep C<ev_loop> from exiting if the work is done. It is |
249 |
also an excellent way to do this for generic recurring timers or from |
250 |
within third-party libraries. Just remember to unref after start and ref |
251 |
before stop. |
252 |
|
253 |
=back |
254 |
|
255 |
=head1 ANATOMY OF A WATCHER |
256 |
|
257 |
A watcher is a structure that you create and register to record your |
258 |
interest in some event. For instance, if you want to wait for STDIN to |
259 |
become readable, you would create an ev_io watcher for that: |
260 |
|
261 |
static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
262 |
{ |
263 |
ev_io_stop (w); |
264 |
ev_unloop (loop, EVUNLOOP_ALL); |
265 |
} |
266 |
|
267 |
struct ev_loop *loop = ev_default_loop (0); |
268 |
struct ev_io stdin_watcher; |
269 |
ev_init (&stdin_watcher, my_cb); |
270 |
ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); |
271 |
ev_io_start (loop, &stdin_watcher); |
272 |
ev_loop (loop, 0); |
273 |
|
274 |
As you can see, you are responsible for allocating the memory for your |
275 |
watcher structures (and it is usually a bad idea to do this on the stack, |
276 |
although this can sometimes be quite valid). |
277 |
|
278 |
Each watcher structure must be initialised by a call to C<ev_init |
279 |
(watcher *, callback)>, which expects a callback to be provided. This |
280 |
callback gets invoked each time the event occurs (or, in the case of io |
281 |
watchers, each time the event loop detects that the file descriptor given |
282 |
is readable and/or writable). |
283 |
|
284 |
Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro |
285 |
with arguments specific to this watcher type. There is also a macro |
286 |
to combine initialisation and setting in one call: C<< ev_<type>_init |
287 |
(watcher *, callback, ...) >>. |
288 |
|
289 |
To make the watcher actually watch out for events, you have to start it |
290 |
with a watcher-specific start function (C<< ev_<type>_start (loop, watcher |
291 |
*) >>), and you can stop watching for events at any time by calling the |
292 |
corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>. |
293 |
|
294 |
As long as your watcher is active (has been started but not stopped) you |
295 |
must not touch the values stored in it. Most specifically you must never |
296 |
reinitialise it or call its set method. |
297 |
|
298 |
You cna check whether an event is active by calling the C<ev_is_active |
299 |
(watcher *)> macro. To see whether an event is outstanding (but the |
300 |
callback for it has not been called yet) you cna use the C<ev_is_pending |
301 |
(watcher *)> macro. |
302 |
|
303 |
Each and every callback receives the event loop pointer as first, the |
304 |
registered watcher structure as second, and a bitset of received events as |
305 |
third argument. |
306 |
|
307 |
The rceeived events usually include a single bit per event type received |
308 |
(you can receive multiple events at the same time). The possible bit masks |
309 |
are: |
310 |
|
311 |
=over 4 |
312 |
|
313 |
=item EV_READ |
314 |
|
315 |
=item EV_WRITE |
316 |
|
317 |
The file descriptor in the ev_io watcher has become readable and/or |
318 |
writable. |
319 |
|
320 |
=item EV_TIMEOUT |
321 |
|
322 |
The ev_timer watcher has timed out. |
323 |
|
324 |
=item EV_PERIODIC |
325 |
|
326 |
The ev_periodic watcher has timed out. |
327 |
|
328 |
=item EV_SIGNAL |
329 |
|
330 |
The signal specified in the ev_signal watcher has been received by a thread. |
331 |
|
332 |
=item EV_CHILD |
333 |
|
334 |
The pid specified in the ev_child watcher has received a status change. |
335 |
|
336 |
=item EV_IDLE |
337 |
|
338 |
The ev_idle watcher has determined that you have nothing better to do. |
339 |
|
340 |
=item EV_PREPARE |
341 |
|
342 |
=item EV_CHECK |
343 |
|
344 |
All ev_prepare watchers are invoked just I<before> C<ev_loop> starts |
345 |
to gather new events, and all ev_check watchers are invoked just after |
346 |
C<ev_loop> has gathered them, but before it invokes any callbacks for any |
347 |
received events. Callbacks of both watcher types can start and stop as |
348 |
many watchers as they want, and all of them will be taken into account |
349 |
(for example, a ev_prepare watcher might start an idle watcher to keep |
350 |
C<ev_loop> from blocking). |
351 |
|
352 |
=item EV_ERROR |
353 |
|
354 |
An unspecified error has occured, the watcher has been stopped. This might |
355 |
happen because the watcher could not be properly started because libev |
356 |
ran out of memory, a file descriptor was found to be closed or any other |
357 |
problem. You best act on it by reporting the problem and somehow coping |
358 |
with the watcher being stopped. |
359 |
|
360 |
Libev will usually signal a few "dummy" events together with an error, |
361 |
for example it might indicate that a fd is readable or writable, and if |
362 |
your callbacks is well-written it can just attempt the operation and cope |
363 |
with the error from read() or write(). This will not work in multithreaded |
364 |
programs, though, so beware. |
365 |
|
366 |
=back |
367 |
|
368 |
=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
369 |
|
370 |
Each watcher has, by default, a member C<void *data> that you can change |
371 |
and read at any time, libev will completely ignore it. This cna be used |
372 |
to associate arbitrary data with your watcher. If you need more data and |
373 |
don't want to allocate memory and store a pointer to it in that data |
374 |
member, you can also "subclass" the watcher type and provide your own |
375 |
data: |
376 |
|
377 |
struct my_io |
378 |
{ |
379 |
struct ev_io io; |
380 |
int otherfd; |
381 |
void *somedata; |
382 |
struct whatever *mostinteresting; |
383 |
} |
384 |
|
385 |
And since your callback will be called with a pointer to the watcher, you |
386 |
can cast it back to your own type: |
387 |
|
388 |
static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) |
389 |
{ |
390 |
struct my_io *w = (struct my_io *)w_; |
391 |
... |
392 |
} |
393 |
|
394 |
More interesting and less C-conformant ways of catsing your callback type |
395 |
have been omitted.... |
396 |
|
397 |
|
398 |
=head1 WATCHER TYPES |
399 |
|
400 |
This section describes each watcher in detail, but will not repeat |
401 |
information given in the last section. |
402 |
|
403 |
=head2 struct ev_io - is my file descriptor readable or writable |
404 |
|
405 |
I/O watchers check whether a file descriptor is readable or writable |
406 |
in each iteration of the event loop (This behaviour is called |
407 |
level-triggering because you keep receiving events as long as the |
408 |
condition persists. Remember you cna stop the watcher if you don't want to |
409 |
act on the event and neither want to receive future events). |
410 |
|
411 |
=over 4 |
412 |
|
413 |
=item ev_io_init (ev_io *, callback, int fd, int events) |
414 |
|
415 |
=item ev_io_set (ev_io *, int fd, int events) |
416 |
|
417 |
Configures an ev_io watcher. The fd is the file descriptor to rceeive |
418 |
events for and events is either C<EV_READ>, C<EV_WRITE> or C<EV_READ | |
419 |
EV_WRITE> to receive the given events. |
420 |
|
421 |
=back |
422 |
|
423 |
=head2 struct ev_timer - relative and optionally recurring timeouts |
424 |
|
425 |
Timer watchers are simple relative timers that generate an event after a |
426 |
given time, and optionally repeating in regular intervals after that. |
427 |
|
428 |
The timers are based on real time, that is, if you register an event that |
429 |
times out after an hour and youreset your system clock to last years |
430 |
time, it will still time out after (roughly) and hour. "Roughly" because |
431 |
detecting time jumps is hard, and soem inaccuracies are unavoidable (the |
432 |
monotonic clock option helps a lot here). |
433 |
|
434 |
=over 4 |
435 |
|
436 |
=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) |
437 |
|
438 |
=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat) |
439 |
|
440 |
Configure the timer to trigger after C<after> seconds. If C<repeat> is |
441 |
C<0.>, then it will automatically be stopped. If it is positive, then the |
442 |
timer will automatically be configured to trigger again C<repeat> seconds |
443 |
later, again, and again, until stopped manually. |
444 |
|
445 |
The timer itself will do a best-effort at avoiding drift, that is, if you |
446 |
configure a timer to trigger every 10 seconds, then it will trigger at |
447 |
exactly 10 second intervals. If, however, your program cannot keep up with |
448 |
the timer (ecause it takes longer than those 10 seconds to do stuff) the |
449 |
timer will not fire more than once per event loop iteration. |
450 |
|
451 |
=item ev_timer_again (loop) |
452 |
|
453 |
This will act as if the timer timed out and restart it again if it is |
454 |
repeating. The exact semantics are: |
455 |
|
456 |
If the timer is started but nonrepeating, stop it. |
457 |
|
458 |
If the timer is repeating, either start it if necessary (with the repeat |
459 |
value), or reset the running timer to the repeat value. |
460 |
|
461 |
This sounds a bit complicated, but here is a useful and typical |
462 |
example: Imagine you have a tcp connection and you want a so-called idle |
463 |
timeout, that is, you want to be called when there have been, say, 60 |
464 |
seconds of inactivity on the socket. The easiest way to do this is to |
465 |
configure an ev_timer with after=repeat=60 and calling ev_timer_again each |
466 |
time you successfully read or write some data. If you go into an idle |
467 |
state where you do not expect data to travel on the socket, you can stop |
468 |
the timer, and again will automatically restart it if need be. |
469 |
|
470 |
=back |
471 |
|
472 |
=head2 ev_periodic - to cron or not to cron it |
473 |
|
474 |
Periodic watchers are also timers of a kind, but they are very versatile |
475 |
(and unfortunately a bit complex). |
476 |
|
477 |
Unlike ev_timer's, they are not based on real time (or relative time) |
478 |
but on wallclock time (absolute time). You can tell a periodic watcher |
479 |
to trigger "at" some specific point in time. For example, if you tell a |
480 |
periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () |
481 |
+ 10.>) and then reset your system clock to the last year, then it will |
482 |
take a year to trigger the event (unlike an ev_timer, which would trigger |
483 |
roughly 10 seconds later and of course not if you reset your system time |
484 |
again). |
485 |
|
486 |
They can also be used to implement vastly more complex timers, such as |
487 |
triggering an event on eahc midnight, local time. |
488 |
|
489 |
=over 4 |
490 |
|
491 |
=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb) |
492 |
|
493 |
=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb) |
494 |
|
495 |
Lots of arguments, lets sort it out... There are basically three modes of |
496 |
operation, and we will explain them from simplest to complex: |
497 |
|
498 |
|
499 |
=over 4 |
500 |
|
501 |
=item * absolute timer (interval = reschedule_cb = 0) |
502 |
|
503 |
In this configuration the watcher triggers an event at the wallclock time |
504 |
C<at> and doesn't repeat. It will not adjust when a time jump occurs, |
505 |
that is, if it is to be run at January 1st 2011 then it will run when the |
506 |
system time reaches or surpasses this time. |
507 |
|
508 |
=item * non-repeating interval timer (interval > 0, reschedule_cb = 0) |
509 |
|
510 |
In this mode the watcher will always be scheduled to time out at the next |
511 |
C<at + N * interval> time (for some integer N) and then repeat, regardless |
512 |
of any time jumps. |
513 |
|
514 |
This can be used to create timers that do not drift with respect to system |
515 |
time: |
516 |
|
517 |
ev_periodic_set (&periodic, 0., 3600., 0); |
518 |
|
519 |
This doesn't mean there will always be 3600 seconds in between triggers, |
520 |
but only that the the callback will be called when the system time shows a |
521 |
full hour (UTC), or more correct, when the system time is evenly divisible |
522 |
by 3600. |
523 |
|
524 |
Another way to think about it (for the mathematically inclined) is that |
525 |
ev_periodic will try to run the callback in this mode at the next possible |
526 |
time where C<time = at (mod interval)>, regardless of any time jumps. |
527 |
|
528 |
=item * manual reschedule mode (reschedule_cb = callback) |
529 |
|
530 |
In this mode the values for C<interval> and C<at> are both being |
531 |
ignored. Instead, each time the periodic watcher gets scheduled, the |
532 |
reschedule callback will be called with the watcher as first, and the |
533 |
current time as second argument. |
534 |
|
535 |
NOTE: I<This callback MUST NOT stop or destroy the periodic or any other |
536 |
periodic watcher, ever, or make any event loop modificstions>. If you need |
537 |
to stop it, return 1e30 (or so, fudge fudge) and stop it afterwards. |
538 |
|
539 |
Its prototype is c<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, |
540 |
ev_tstamp now)>, e.g.: |
541 |
|
542 |
static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) |
543 |
{ |
544 |
return now + 60.; |
545 |
} |
546 |
|
547 |
It must return the next time to trigger, based on the passed time value |
548 |
(that is, the lowest time value larger than to the second argument). It |
549 |
will usually be called just before the callback will be triggered, but |
550 |
might be called at other times, too. |
551 |
|
552 |
This can be used to create very complex timers, such as a timer that |
553 |
triggers on each midnight, local time. To do this, you would calculate the |
554 |
next midnight after C<now> and return the timestamp value for this. How you do this |
555 |
is, again, up to you (but it is not trivial). |
556 |
|
557 |
=back |
558 |
|
559 |
=item ev_periodic_again (loop, ev_periodic *) |
560 |
|
561 |
Simply stops and restarts the periodic watcher again. This is only useful |
562 |
when you changed some parameters or the reschedule callback would return |
563 |
a different time than the last time it was called (e.g. in a crond like |
564 |
program when the crontabs have changed). |
565 |
|
566 |
=back |
567 |
|
568 |
=head2 ev_signal - signal me when a signal gets signalled |
569 |
|
570 |
Signal watchers will trigger an event when the process receives a specific |
571 |
signal one or more times. Even though signals are very asynchronous, libev |
572 |
will try its best to deliver signals synchronously, i.e. as part of the |
573 |
normal event processing, like any other event. |
574 |
|
575 |
You cna configure as many watchers as you like per signal. Only when the |
576 |
first watcher gets started will libev actually register a signal watcher |
577 |
with the kernel (thus it coexists with your own signal handlers as long |
578 |
as you don't register any with libev). Similarly, when the last signal |
579 |
watcher for a signal is stopped libev will reset the signal handler to |
580 |
SIG_DFL (regardless of what it was set to before). |
581 |
|
582 |
=over 4 |
583 |
|
584 |
=item ev_signal_init (ev_signal *, callback, int signum) |
585 |
|
586 |
=item ev_signal_set (ev_signal *, int signum) |
587 |
|
588 |
Configures the watcher to trigger on the given signal number (usually one |
589 |
of the C<SIGxxx> constants). |
590 |
|
591 |
=back |
592 |
|
593 |
=head2 ev_child - wait for pid status changes |
594 |
|
595 |
Child watchers trigger when your process receives a SIGCHLD in response to |
596 |
some child status changes (most typically when a child of yours dies). |
597 |
|
598 |
=over 4 |
599 |
|
600 |
=item ev_child_init (ev_child *, callback, int pid) |
601 |
|
602 |
=item ev_child_set (ev_child *, int pid) |
603 |
|
604 |
Configures the watcher to wait for status changes of process C<pid> (or |
605 |
I<any> process if C<pid> is specified as C<0>). The callback can look |
606 |
at the C<rstatus> member of the C<ev_child> watcher structure to see |
607 |
the status word (use the macros from C<sys/wait.h>). The C<rpid> member |
608 |
contains the pid of the process causing the status change. |
609 |
|
610 |
=back |
611 |
|
612 |
=head2 ev_idle - when you've got nothing better to do |
613 |
|
614 |
Idle watchers trigger events when there are no other I/O or timer (or |
615 |
periodic) events pending. That is, as long as your process is busy |
616 |
handling sockets or timeouts it will not be called. But when your process |
617 |
is idle all idle watchers are being called again and again - until |
618 |
stopped, that is, or your process receives more events. |
619 |
|
620 |
The most noteworthy effect is that as long as any idle watchers are |
621 |
active, the process will not block when waiting for new events. |
622 |
|
623 |
Apart from keeping your process non-blocking (which is a useful |
624 |
effect on its own sometimes), idle watchers are a good place to do |
625 |
"pseudo-background processing", or delay processing stuff to after the |
626 |
event loop has handled all outstanding events. |
627 |
|
628 |
=over 4 |
629 |
|
630 |
=item ev_idle_init (ev_signal *, callback) |
631 |
|
632 |
Initialises and configures the idle watcher - it has no parameters of any |
633 |
kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, |
634 |
believe me. |
635 |
|
636 |
=back |
637 |
|
638 |
=head2 prepare and check - your hooks into the event loop |
639 |
|
640 |
Prepare and check watchers usually (but not always) are used in |
641 |
tandom. Prepare watchers get invoked before the process blocks and check |
642 |
watchers afterwards. |
643 |
|
644 |
Their main purpose is to integrate other event mechanisms into libev. This |
645 |
could be used, for example, to track variable changes, implement your own |
646 |
watchers, integrate net-snmp or a coroutine library and lots more. |
647 |
|
648 |
This is done by examining in each prepare call which file descriptors need |
649 |
to be watched by the other library, registering ev_io watchers for them |
650 |
and starting an ev_timer watcher for any timeouts (many libraries provide |
651 |
just this functionality). Then, in the check watcher you check for any |
652 |
events that occured (by making your callbacks set soem flags for example) |
653 |
and call back into the library. |
654 |
|
655 |
As another example, the perl Coro module uses these hooks to integrate |
656 |
coroutines into libev programs, by yielding to other active coroutines |
657 |
during each prepare and only letting the process block if no coroutines |
658 |
are ready to run. |
659 |
|
660 |
=over 4 |
661 |
|
662 |
=item ev_prepare_init (ev_prepare *, callback) |
663 |
|
664 |
=item ev_check_init (ev_check *, callback) |
665 |
|
666 |
Initialises and configures the prepare or check watcher - they have no |
667 |
parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set> |
668 |
macros, but using them is utterly, utterly pointless. |
669 |
|
670 |
=back |
671 |
|
672 |
=head1 OTHER FUNCTIONS |
673 |
|
674 |
There are some other fucntions of possible interest. Described. Here. Now. |
675 |
|
676 |
=over 4 |
677 |
|
678 |
=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) |
679 |
|
680 |
This function combines a simple timer and an I/O watcher, calls your |
681 |
callback on whichever event happens first and automatically stop both |
682 |
watchers. This is useful if you want to wait for a single event on an fd |
683 |
or timeout without havign to allocate/configure/start/stop/free one or |
684 |
more watchers yourself. |
685 |
|
686 |
If C<fd> is less than 0, then no I/O watcher will be started and events is |
687 |
ignored. Otherwise, an ev_io watcher for the given C<fd> and C<events> set |
688 |
will be craeted and started. |
689 |
|
690 |
If C<timeout> is less than 0, then no timeout watcher will be |
691 |
started. Otherwise an ev_timer watcher with after = C<timeout> (and repeat |
692 |
= 0) will be started. |
693 |
|
694 |
The callback has the type C<void (*cb)(int revents, void *arg)> and |
695 |
gets passed an events set (normally a combination of EV_ERROR, EV_READ, |
696 |
EV_WRITE or EV_TIMEOUT) and the C<arg> value passed to C<ev_once>: |
697 |
|
698 |
static void stdin_ready (int revents, void *arg) |
699 |
{ |
700 |
if (revents & EV_TIMEOUT) |
701 |
/* doh, nothing entered */ |
702 |
else if (revents & EV_READ) |
703 |
/* stdin might have data for us, joy! */ |
704 |
} |
705 |
|
706 |
ev_once (STDIN_FILENO, EV_READm 10., stdin_ready, 0); |
707 |
|
708 |
=item ev_feed_event (loop, watcher, int events) |
709 |
|
710 |
Feeds the given event set into the event loop, as if the specified event |
711 |
has happened for the specified watcher (which must be a pointer to an |
712 |
initialised but not necessarily active event watcher). |
713 |
|
714 |
=item ev_feed_fd_event (loop, int fd, int revents) |
715 |
|
716 |
Feed an event on the given fd, as if a file descriptor backend detected it. |
717 |
|
718 |
=item ev_feed_signal_event (loop, int signum) |
719 |
|
720 |
Feed an event as if the given signal occured (loop must be the default loop!). |
721 |
|
722 |
=back |
723 |
|
724 |
=head1 AUTHOR |
725 |
|
726 |
Marc Lehmann <libev@schmorp.de>. |
727 |
|