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 |
=head2 EXAMPLE PROGRAM |
10 |
|
11 |
// a single header file is required |
12 |
#include <ev.h> |
13 |
|
14 |
// every watcher type has its own typedef'd struct |
15 |
// with the name ev_<type> |
16 |
ev_io stdin_watcher; |
17 |
ev_timer timeout_watcher; |
18 |
|
19 |
// all watcher callbacks have a similar signature |
20 |
// this callback is called when data is readable on stdin |
21 |
static void |
22 |
stdin_cb (EV_P_ struct ev_io *w, int revents) |
23 |
{ |
24 |
puts ("stdin ready"); |
25 |
// for one-shot events, one must manually stop the watcher |
26 |
// with its corresponding stop function. |
27 |
ev_io_stop (EV_A_ w); |
28 |
|
29 |
// this causes all nested ev_loop's to stop iterating |
30 |
ev_unloop (EV_A_ EVUNLOOP_ALL); |
31 |
} |
32 |
|
33 |
// another callback, this time for a time-out |
34 |
static void |
35 |
timeout_cb (EV_P_ struct ev_timer *w, int revents) |
36 |
{ |
37 |
puts ("timeout"); |
38 |
// this causes the innermost ev_loop to stop iterating |
39 |
ev_unloop (EV_A_ EVUNLOOP_ONE); |
40 |
} |
41 |
|
42 |
int |
43 |
main (void) |
44 |
{ |
45 |
// use the default event loop unless you have special needs |
46 |
struct ev_loop *loop = ev_default_loop (0); |
47 |
|
48 |
// initialise an io watcher, then start it |
49 |
// this one will watch for stdin to become readable |
50 |
ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); |
51 |
ev_io_start (loop, &stdin_watcher); |
52 |
|
53 |
// initialise a timer watcher, then start it |
54 |
// simple non-repeating 5.5 second timeout |
55 |
ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); |
56 |
ev_timer_start (loop, &timeout_watcher); |
57 |
|
58 |
// now wait for events to arrive |
59 |
ev_loop (loop, 0); |
60 |
|
61 |
// unloop was called, so exit |
62 |
return 0; |
63 |
} |
64 |
|
65 |
=head1 DESCRIPTION |
66 |
|
67 |
The newest version of this document is also available as an html-formatted |
68 |
web page you might find easier to navigate when reading it for the first |
69 |
time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>. |
70 |
|
71 |
Libev is an event loop: you register interest in certain events (such as a |
72 |
file descriptor being readable or a timeout occurring), and it will manage |
73 |
these event sources and provide your program with events. |
74 |
|
75 |
To do this, it must take more or less complete control over your process |
76 |
(or thread) by executing the I<event loop> handler, and will then |
77 |
communicate events via a callback mechanism. |
78 |
|
79 |
You register interest in certain events by registering so-called I<event |
80 |
watchers>, which are relatively small C structures you initialise with the |
81 |
details of the event, and then hand it over to libev by I<starting> the |
82 |
watcher. |
83 |
|
84 |
=head2 FEATURES |
85 |
|
86 |
Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the |
87 |
BSD-specific C<kqueue> and the Solaris-specific event port mechanisms |
88 |
for file descriptor events (C<ev_io>), the Linux C<inotify> interface |
89 |
(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers |
90 |
with customised rescheduling (C<ev_periodic>), synchronous signals |
91 |
(C<ev_signal>), process status change events (C<ev_child>), and event |
92 |
watchers dealing with the event loop mechanism itself (C<ev_idle>, |
93 |
C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as |
94 |
file watchers (C<ev_stat>) and even limited support for fork events |
95 |
(C<ev_fork>). |
96 |
|
97 |
It also is quite fast (see this |
98 |
L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent |
99 |
for example). |
100 |
|
101 |
=head2 CONVENTIONS |
102 |
|
103 |
Libev is very configurable. In this manual the default (and most common) |
104 |
configuration will be described, which supports multiple event loops. For |
105 |
more info about various configuration options please have a look at |
106 |
B<EMBED> section in this manual. If libev was configured without support |
107 |
for multiple event loops, then all functions taking an initial argument of |
108 |
name C<loop> (which is always of type C<struct ev_loop *>) will not have |
109 |
this argument. |
110 |
|
111 |
=head2 TIME REPRESENTATION |
112 |
|
113 |
Libev represents time as a single floating point number, representing the |
114 |
(fractional) number of seconds since the (POSIX) epoch (somewhere near |
115 |
the beginning of 1970, details are complicated, don't ask). This type is |
116 |
called C<ev_tstamp>, which is what you should use too. It usually aliases |
117 |
to the C<double> type in C, and when you need to do any calculations on |
118 |
it, you should treat it as some floatingpoint value. Unlike the name |
119 |
component C<stamp> might indicate, it is also used for time differences |
120 |
throughout libev. |
121 |
|
122 |
=head1 GLOBAL FUNCTIONS |
123 |
|
124 |
These functions can be called anytime, even before initialising the |
125 |
library in any way. |
126 |
|
127 |
=over 4 |
128 |
|
129 |
=item ev_tstamp ev_time () |
130 |
|
131 |
Returns the current time as libev would use it. Please note that the |
132 |
C<ev_now> function is usually faster and also often returns the timestamp |
133 |
you actually want to know. |
134 |
|
135 |
=item ev_sleep (ev_tstamp interval) |
136 |
|
137 |
Sleep for the given interval: The current thread will be blocked until |
138 |
either it is interrupted or the given time interval has passed. Basically |
139 |
this is a subsecond-resolution C<sleep ()>. |
140 |
|
141 |
=item int ev_version_major () |
142 |
|
143 |
=item int ev_version_minor () |
144 |
|
145 |
You can find out the major and minor ABI version numbers of the library |
146 |
you linked against by calling the functions C<ev_version_major> and |
147 |
C<ev_version_minor>. If you want, you can compare against the global |
148 |
symbols C<EV_VERSION_MAJOR> and C<EV_VERSION_MINOR>, which specify the |
149 |
version of the library your program was compiled against. |
150 |
|
151 |
These version numbers refer to the ABI version of the library, not the |
152 |
release version. |
153 |
|
154 |
Usually, it's a good idea to terminate if the major versions mismatch, |
155 |
as this indicates an incompatible change. Minor versions are usually |
156 |
compatible to older versions, so a larger minor version alone is usually |
157 |
not a problem. |
158 |
|
159 |
Example: Make sure we haven't accidentally been linked against the wrong |
160 |
version. |
161 |
|
162 |
assert (("libev version mismatch", |
163 |
ev_version_major () == EV_VERSION_MAJOR |
164 |
&& ev_version_minor () >= EV_VERSION_MINOR)); |
165 |
|
166 |
=item unsigned int ev_supported_backends () |
167 |
|
168 |
Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*> |
169 |
value) compiled into this binary of libev (independent of their |
170 |
availability on the system you are running on). See C<ev_default_loop> for |
171 |
a description of the set values. |
172 |
|
173 |
Example: make sure we have the epoll method, because yeah this is cool and |
174 |
a must have and can we have a torrent of it please!!!11 |
175 |
|
176 |
assert (("sorry, no epoll, no sex", |
177 |
ev_supported_backends () & EVBACKEND_EPOLL)); |
178 |
|
179 |
=item unsigned int ev_recommended_backends () |
180 |
|
181 |
Return the set of all backends compiled into this binary of libev and also |
182 |
recommended for this platform. This set is often smaller than the one |
183 |
returned by C<ev_supported_backends>, as for example kqueue is broken on |
184 |
most BSDs and will not be autodetected unless you explicitly request it |
185 |
(assuming you know what you are doing). This is the set of backends that |
186 |
libev will probe for if you specify no backends explicitly. |
187 |
|
188 |
=item unsigned int ev_embeddable_backends () |
189 |
|
190 |
Returns the set of backends that are embeddable in other event loops. This |
191 |
is the theoretical, all-platform, value. To find which backends |
192 |
might be supported on the current system, you would need to look at |
193 |
C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for |
194 |
recommended ones. |
195 |
|
196 |
See the description of C<ev_embed> watchers for more info. |
197 |
|
198 |
=item ev_set_allocator (void *(*cb)(void *ptr, long size)) |
199 |
|
200 |
Sets the allocation function to use (the prototype is similar - the |
201 |
semantics are identical to the C<realloc> C89/SuS/POSIX function). It is |
202 |
used to allocate and free memory (no surprises here). If it returns zero |
203 |
when memory needs to be allocated (C<size != 0>), the library might abort |
204 |
or take some potentially destructive action. |
205 |
|
206 |
Since some systems (at least OpenBSD and Darwin) fail to implement |
207 |
correct C<realloc> semantics, libev will use a wrapper around the system |
208 |
C<realloc> and C<free> functions by default. |
209 |
|
210 |
You could override this function in high-availability programs to, say, |
211 |
free some memory if it cannot allocate memory, to use a special allocator, |
212 |
or even to sleep a while and retry until some memory is available. |
213 |
|
214 |
Example: Replace the libev allocator with one that waits a bit and then |
215 |
retries (example requires a standards-compliant C<realloc>). |
216 |
|
217 |
static void * |
218 |
persistent_realloc (void *ptr, size_t size) |
219 |
{ |
220 |
for (;;) |
221 |
{ |
222 |
void *newptr = realloc (ptr, size); |
223 |
|
224 |
if (newptr) |
225 |
return newptr; |
226 |
|
227 |
sleep (60); |
228 |
} |
229 |
} |
230 |
|
231 |
... |
232 |
ev_set_allocator (persistent_realloc); |
233 |
|
234 |
=item ev_set_syserr_cb (void (*cb)(const char *msg)); |
235 |
|
236 |
Set the callback function to call on a retryable syscall error (such |
237 |
as failed select, poll, epoll_wait). The message is a printable string |
238 |
indicating the system call or subsystem causing the problem. If this |
239 |
callback is set, then libev will expect it to remedy the sitution, no |
240 |
matter what, when it returns. That is, libev will generally retry the |
241 |
requested operation, or, if the condition doesn't go away, do bad stuff |
242 |
(such as abort). |
243 |
|
244 |
Example: This is basically the same thing that libev does internally, too. |
245 |
|
246 |
static void |
247 |
fatal_error (const char *msg) |
248 |
{ |
249 |
perror (msg); |
250 |
abort (); |
251 |
} |
252 |
|
253 |
... |
254 |
ev_set_syserr_cb (fatal_error); |
255 |
|
256 |
=back |
257 |
|
258 |
=head1 FUNCTIONS CONTROLLING THE EVENT LOOP |
259 |
|
260 |
An event loop is described by a C<struct ev_loop *>. The library knows two |
261 |
types of such loops, the I<default> loop, which supports signals and child |
262 |
events, and dynamically created loops which do not. |
263 |
|
264 |
=over 4 |
265 |
|
266 |
=item struct ev_loop *ev_default_loop (unsigned int flags) |
267 |
|
268 |
This will initialise the default event loop if it hasn't been initialised |
269 |
yet and return it. If the default loop could not be initialised, returns |
270 |
false. If it already was initialised it simply returns it (and ignores the |
271 |
flags. If that is troubling you, check C<ev_backend ()> afterwards). |
272 |
|
273 |
If you don't know what event loop to use, use the one returned from this |
274 |
function. |
275 |
|
276 |
Note that this function is I<not> thread-safe, so if you want to use it |
277 |
from multiple threads, you have to lock (note also that this is unlikely, |
278 |
as loops cannot bes hared easily between threads anyway). |
279 |
|
280 |
The default loop is the only loop that can handle C<ev_signal> and |
281 |
C<ev_child> watchers, and to do this, it always registers a handler |
282 |
for C<SIGCHLD>. If this is a problem for your app you can either |
283 |
create a dynamic loop with C<ev_loop_new> that doesn't do that, or you |
284 |
can simply overwrite the C<SIGCHLD> signal handler I<after> calling |
285 |
C<ev_default_init>. |
286 |
|
287 |
The flags argument can be used to specify special behaviour or specific |
288 |
backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>). |
289 |
|
290 |
The following flags are supported: |
291 |
|
292 |
=over 4 |
293 |
|
294 |
=item C<EVFLAG_AUTO> |
295 |
|
296 |
The default flags value. Use this if you have no clue (it's the right |
297 |
thing, believe me). |
298 |
|
299 |
=item C<EVFLAG_NOENV> |
300 |
|
301 |
If this flag bit is ored into the flag value (or the program runs setuid |
302 |
or setgid) then libev will I<not> look at the environment variable |
303 |
C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will |
304 |
override the flags completely if it is found in the environment. This is |
305 |
useful to try out specific backends to test their performance, or to work |
306 |
around bugs. |
307 |
|
308 |
=item C<EVFLAG_FORKCHECK> |
309 |
|
310 |
Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after |
311 |
a fork, you can also make libev check for a fork in each iteration by |
312 |
enabling this flag. |
313 |
|
314 |
This works by calling C<getpid ()> on every iteration of the loop, |
315 |
and thus this might slow down your event loop if you do a lot of loop |
316 |
iterations and little real work, but is usually not noticeable (on my |
317 |
GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence |
318 |
without a syscall and thus I<very> fast, but my GNU/Linux system also has |
319 |
C<pthread_atfork> which is even faster). |
320 |
|
321 |
The big advantage of this flag is that you can forget about fork (and |
322 |
forget about forgetting to tell libev about forking) when you use this |
323 |
flag. |
324 |
|
325 |
This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS> |
326 |
environment variable. |
327 |
|
328 |
=item C<EVBACKEND_SELECT> (value 1, portable select backend) |
329 |
|
330 |
This is your standard select(2) backend. Not I<completely> standard, as |
331 |
libev tries to roll its own fd_set with no limits on the number of fds, |
332 |
but if that fails, expect a fairly low limit on the number of fds when |
333 |
using this backend. It doesn't scale too well (O(highest_fd)), but its |
334 |
usually the fastest backend for a low number of (low-numbered :) fds. |
335 |
|
336 |
To get good performance out of this backend you need a high amount of |
337 |
parallelity (most of the file descriptors should be busy). If you are |
338 |
writing a server, you should C<accept ()> in a loop to accept as many |
339 |
connections as possible during one iteration. You might also want to have |
340 |
a look at C<ev_set_io_collect_interval ()> to increase the amount of |
341 |
readiness notifications you get per iteration. |
342 |
|
343 |
=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows) |
344 |
|
345 |
And this is your standard poll(2) backend. It's more complicated |
346 |
than select, but handles sparse fds better and has no artificial |
347 |
limit on the number of fds you can use (except it will slow down |
348 |
considerably with a lot of inactive fds). It scales similarly to select, |
349 |
i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for |
350 |
performance tips. |
351 |
|
352 |
=item C<EVBACKEND_EPOLL> (value 4, Linux) |
353 |
|
354 |
For few fds, this backend is a bit little slower than poll and select, |
355 |
but it scales phenomenally better. While poll and select usually scale |
356 |
like O(total_fds) where n is the total number of fds (or the highest fd), |
357 |
epoll scales either O(1) or O(active_fds). The epoll design has a number |
358 |
of shortcomings, such as silently dropping events in some hard-to-detect |
359 |
cases and requiring a syscall per fd change, no fork support and bad |
360 |
support for dup. |
361 |
|
362 |
While stopping, setting and starting an I/O watcher in the same iteration |
363 |
will result in some caching, there is still a syscall per such incident |
364 |
(because the fd could point to a different file description now), so its |
365 |
best to avoid that. Also, C<dup ()>'ed file descriptors might not work |
366 |
very well if you register events for both fds. |
367 |
|
368 |
Please note that epoll sometimes generates spurious notifications, so you |
369 |
need to use non-blocking I/O or other means to avoid blocking when no data |
370 |
(or space) is available. |
371 |
|
372 |
Best performance from this backend is achieved by not unregistering all |
373 |
watchers for a file descriptor until it has been closed, if possible, i.e. |
374 |
keep at least one watcher active per fd at all times. |
375 |
|
376 |
While nominally embeddeble in other event loops, this feature is broken in |
377 |
all kernel versions tested so far. |
378 |
|
379 |
=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones) |
380 |
|
381 |
Kqueue deserves special mention, as at the time of this writing, it |
382 |
was broken on all BSDs except NetBSD (usually it doesn't work reliably |
383 |
with anything but sockets and pipes, except on Darwin, where of course |
384 |
it's completely useless). For this reason it's not being "autodetected" |
385 |
unless you explicitly specify it explicitly in the flags (i.e. using |
386 |
C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough) |
387 |
system like NetBSD. |
388 |
|
389 |
You still can embed kqueue into a normal poll or select backend and use it |
390 |
only for sockets (after having made sure that sockets work with kqueue on |
391 |
the target platform). See C<ev_embed> watchers for more info. |
392 |
|
393 |
It scales in the same way as the epoll backend, but the interface to the |
394 |
kernel is more efficient (which says nothing about its actual speed, of |
395 |
course). While stopping, setting and starting an I/O watcher does never |
396 |
cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to |
397 |
two event changes per incident, support for C<fork ()> is very bad and it |
398 |
drops fds silently in similarly hard-to-detect cases. |
399 |
|
400 |
This backend usually performs well under most conditions. |
401 |
|
402 |
While nominally embeddable in other event loops, this doesn't work |
403 |
everywhere, so you might need to test for this. And since it is broken |
404 |
almost everywhere, you should only use it when you have a lot of sockets |
405 |
(for which it usually works), by embedding it into another event loop |
406 |
(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for |
407 |
sockets. |
408 |
|
409 |
=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8) |
410 |
|
411 |
This is not implemented yet (and might never be, unless you send me an |
412 |
implementation). According to reports, C</dev/poll> only supports sockets |
413 |
and is not embeddable, which would limit the usefulness of this backend |
414 |
immensely. |
415 |
|
416 |
=item C<EVBACKEND_PORT> (value 32, Solaris 10) |
417 |
|
418 |
This uses the Solaris 10 event port mechanism. As with everything on Solaris, |
419 |
it's really slow, but it still scales very well (O(active_fds)). |
420 |
|
421 |
Please note that solaris event ports can deliver a lot of spurious |
422 |
notifications, so you need to use non-blocking I/O or other means to avoid |
423 |
blocking when no data (or space) is available. |
424 |
|
425 |
While this backend scales well, it requires one system call per active |
426 |
file descriptor per loop iteration. For small and medium numbers of file |
427 |
descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend |
428 |
might perform better. |
429 |
|
430 |
On the positive side, ignoring the spurious readiness notifications, this |
431 |
backend actually performed to specification in all tests and is fully |
432 |
embeddable, which is a rare feat among the OS-specific backends. |
433 |
|
434 |
=item C<EVBACKEND_ALL> |
435 |
|
436 |
Try all backends (even potentially broken ones that wouldn't be tried |
437 |
with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as |
438 |
C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>. |
439 |
|
440 |
It is definitely not recommended to use this flag. |
441 |
|
442 |
=back |
443 |
|
444 |
If one or more of these are ored into the flags value, then only these |
445 |
backends will be tried (in the reverse order as listed here). If none are |
446 |
specified, all backends in C<ev_recommended_backends ()> will be tried. |
447 |
|
448 |
The most typical usage is like this: |
449 |
|
450 |
if (!ev_default_loop (0)) |
451 |
fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); |
452 |
|
453 |
Restrict libev to the select and poll backends, and do not allow |
454 |
environment settings to be taken into account: |
455 |
|
456 |
ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); |
457 |
|
458 |
Use whatever libev has to offer, but make sure that kqueue is used if |
459 |
available (warning, breaks stuff, best use only with your own private |
460 |
event loop and only if you know the OS supports your types of fds): |
461 |
|
462 |
ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); |
463 |
|
464 |
=item struct ev_loop *ev_loop_new (unsigned int flags) |
465 |
|
466 |
Similar to C<ev_default_loop>, but always creates a new event loop that is |
467 |
always distinct from the default loop. Unlike the default loop, it cannot |
468 |
handle signal and child watchers, and attempts to do so will be greeted by |
469 |
undefined behaviour (or a failed assertion if assertions are enabled). |
470 |
|
471 |
Note that this function I<is> thread-safe, and the recommended way to use |
472 |
libev with threads is indeed to create one loop per thread, and using the |
473 |
default loop in the "main" or "initial" thread. |
474 |
|
475 |
Example: Try to create a event loop that uses epoll and nothing else. |
476 |
|
477 |
struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); |
478 |
if (!epoller) |
479 |
fatal ("no epoll found here, maybe it hides under your chair"); |
480 |
|
481 |
=item ev_default_destroy () |
482 |
|
483 |
Destroys the default loop again (frees all memory and kernel state |
484 |
etc.). None of the active event watchers will be stopped in the normal |
485 |
sense, so e.g. C<ev_is_active> might still return true. It is your |
486 |
responsibility to either stop all watchers cleanly yoursef I<before> |
487 |
calling this function, or cope with the fact afterwards (which is usually |
488 |
the easiest thing, you can just ignore the watchers and/or C<free ()> them |
489 |
for example). |
490 |
|
491 |
Note that certain global state, such as signal state, will not be freed by |
492 |
this function, and related watchers (such as signal and child watchers) |
493 |
would need to be stopped manually. |
494 |
|
495 |
In general it is not advisable to call this function except in the |
496 |
rare occasion where you really need to free e.g. the signal handling |
497 |
pipe fds. If you need dynamically allocated loops it is better to use |
498 |
C<ev_loop_new> and C<ev_loop_destroy>). |
499 |
|
500 |
=item ev_loop_destroy (loop) |
501 |
|
502 |
Like C<ev_default_destroy>, but destroys an event loop created by an |
503 |
earlier call to C<ev_loop_new>. |
504 |
|
505 |
=item ev_default_fork () |
506 |
|
507 |
This function sets a flag that causes subsequent C<ev_loop> iterations |
508 |
to reinitialise the kernel state for backends that have one. Despite the |
509 |
name, you can call it anytime, but it makes most sense after forking, in |
510 |
the child process (or both child and parent, but that again makes little |
511 |
sense). You I<must> call it in the child before using any of the libev |
512 |
functions, and it will only take effect at the next C<ev_loop> iteration. |
513 |
|
514 |
On the other hand, you only need to call this function in the child |
515 |
process if and only if you want to use the event library in the child. If |
516 |
you just fork+exec, you don't have to call it at all. |
517 |
|
518 |
The function itself is quite fast and it's usually not a problem to call |
519 |
it just in case after a fork. To make this easy, the function will fit in |
520 |
quite nicely into a call to C<pthread_atfork>: |
521 |
|
522 |
pthread_atfork (0, 0, ev_default_fork); |
523 |
|
524 |
=item ev_loop_fork (loop) |
525 |
|
526 |
Like C<ev_default_fork>, but acts on an event loop created by |
527 |
C<ev_loop_new>. Yes, you have to call this on every allocated event loop |
528 |
after fork, and how you do this is entirely your own problem. |
529 |
|
530 |
=item int ev_is_default_loop (loop) |
531 |
|
532 |
Returns true when the given loop actually is the default loop, false otherwise. |
533 |
|
534 |
=item unsigned int ev_loop_count (loop) |
535 |
|
536 |
Returns the count of loop iterations for the loop, which is identical to |
537 |
the number of times libev did poll for new events. It starts at C<0> and |
538 |
happily wraps around with enough iterations. |
539 |
|
540 |
This value can sometimes be useful as a generation counter of sorts (it |
541 |
"ticks" the number of loop iterations), as it roughly corresponds with |
542 |
C<ev_prepare> and C<ev_check> calls. |
543 |
|
544 |
=item unsigned int ev_backend (loop) |
545 |
|
546 |
Returns one of the C<EVBACKEND_*> flags indicating the event backend in |
547 |
use. |
548 |
|
549 |
=item ev_tstamp ev_now (loop) |
550 |
|
551 |
Returns the current "event loop time", which is the time the event loop |
552 |
received events and started processing them. This timestamp does not |
553 |
change as long as callbacks are being processed, and this is also the base |
554 |
time used for relative timers. You can treat it as the timestamp of the |
555 |
event occurring (or more correctly, libev finding out about it). |
556 |
|
557 |
=item ev_loop (loop, int flags) |
558 |
|
559 |
Finally, this is it, the event handler. This function usually is called |
560 |
after you initialised all your watchers and you want to start handling |
561 |
events. |
562 |
|
563 |
If the flags argument is specified as C<0>, it will not return until |
564 |
either no event watchers are active anymore or C<ev_unloop> was called. |
565 |
|
566 |
Please note that an explicit C<ev_unloop> is usually better than |
567 |
relying on all watchers to be stopped when deciding when a program has |
568 |
finished (especially in interactive programs), but having a program that |
569 |
automatically loops as long as it has to and no longer by virtue of |
570 |
relying on its watchers stopping correctly is a thing of beauty. |
571 |
|
572 |
A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle |
573 |
those events and any outstanding ones, but will not block your process in |
574 |
case there are no events and will return after one iteration of the loop. |
575 |
|
576 |
A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if |
577 |
neccessary) and will handle those and any outstanding ones. It will block |
578 |
your process until at least one new event arrives, and will return after |
579 |
one iteration of the loop. This is useful if you are waiting for some |
580 |
external event in conjunction with something not expressible using other |
581 |
libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is |
582 |
usually a better approach for this kind of thing. |
583 |
|
584 |
Here are the gory details of what C<ev_loop> does: |
585 |
|
586 |
- Before the first iteration, call any pending watchers. |
587 |
* If EVFLAG_FORKCHECK was used, check for a fork. |
588 |
- If a fork was detected, queue and call all fork watchers. |
589 |
- Queue and call all prepare watchers. |
590 |
- If we have been forked, recreate the kernel state. |
591 |
- Update the kernel state with all outstanding changes. |
592 |
- Update the "event loop time". |
593 |
- Calculate for how long to sleep or block, if at all |
594 |
(active idle watchers, EVLOOP_NONBLOCK or not having |
595 |
any active watchers at all will result in not sleeping). |
596 |
- Sleep if the I/O and timer collect interval say so. |
597 |
- Block the process, waiting for any events. |
598 |
- Queue all outstanding I/O (fd) events. |
599 |
- Update the "event loop time" and do time jump handling. |
600 |
- Queue all outstanding timers. |
601 |
- Queue all outstanding periodics. |
602 |
- If no events are pending now, queue all idle watchers. |
603 |
- Queue all check watchers. |
604 |
- Call all queued watchers in reverse order (i.e. check watchers first). |
605 |
Signals and child watchers are implemented as I/O watchers, and will |
606 |
be handled here by queueing them when their watcher gets executed. |
607 |
- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK |
608 |
were used, or there are no active watchers, return, otherwise |
609 |
continue with step *. |
610 |
|
611 |
Example: Queue some jobs and then loop until no events are outstanding |
612 |
anymore. |
613 |
|
614 |
... queue jobs here, make sure they register event watchers as long |
615 |
... as they still have work to do (even an idle watcher will do..) |
616 |
ev_loop (my_loop, 0); |
617 |
... jobs done. yeah! |
618 |
|
619 |
=item ev_unloop (loop, how) |
620 |
|
621 |
Can be used to make a call to C<ev_loop> return early (but only after it |
622 |
has processed all outstanding events). The C<how> argument must be either |
623 |
C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or |
624 |
C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return. |
625 |
|
626 |
This "unloop state" will be cleared when entering C<ev_loop> again. |
627 |
|
628 |
=item ev_ref (loop) |
629 |
|
630 |
=item ev_unref (loop) |
631 |
|
632 |
Ref/unref can be used to add or remove a reference count on the event |
633 |
loop: Every watcher keeps one reference, and as long as the reference |
634 |
count is nonzero, C<ev_loop> will not return on its own. If you have |
635 |
a watcher you never unregister that should not keep C<ev_loop> from |
636 |
returning, ev_unref() after starting, and ev_ref() before stopping it. For |
637 |
example, libev itself uses this for its internal signal pipe: It is not |
638 |
visible to the libev user and should not keep C<ev_loop> from exiting if |
639 |
no event watchers registered by it are active. It is also an excellent |
640 |
way to do this for generic recurring timers or from within third-party |
641 |
libraries. Just remember to I<unref after start> and I<ref before stop> |
642 |
(but only if the watcher wasn't active before, or was active before, |
643 |
respectively). |
644 |
|
645 |
Example: Create a signal watcher, but keep it from keeping C<ev_loop> |
646 |
running when nothing else is active. |
647 |
|
648 |
struct ev_signal exitsig; |
649 |
ev_signal_init (&exitsig, sig_cb, SIGINT); |
650 |
ev_signal_start (loop, &exitsig); |
651 |
evf_unref (loop); |
652 |
|
653 |
Example: For some weird reason, unregister the above signal handler again. |
654 |
|
655 |
ev_ref (loop); |
656 |
ev_signal_stop (loop, &exitsig); |
657 |
|
658 |
=item ev_set_io_collect_interval (loop, ev_tstamp interval) |
659 |
|
660 |
=item ev_set_timeout_collect_interval (loop, ev_tstamp interval) |
661 |
|
662 |
These advanced functions influence the time that libev will spend waiting |
663 |
for events. Both are by default C<0>, meaning that libev will try to |
664 |
invoke timer/periodic callbacks and I/O callbacks with minimum latency. |
665 |
|
666 |
Setting these to a higher value (the C<interval> I<must> be >= C<0>) |
667 |
allows libev to delay invocation of I/O and timer/periodic callbacks to |
668 |
increase efficiency of loop iterations. |
669 |
|
670 |
The background is that sometimes your program runs just fast enough to |
671 |
handle one (or very few) event(s) per loop iteration. While this makes |
672 |
the program responsive, it also wastes a lot of CPU time to poll for new |
673 |
events, especially with backends like C<select ()> which have a high |
674 |
overhead for the actual polling but can deliver many events at once. |
675 |
|
676 |
By setting a higher I<io collect interval> you allow libev to spend more |
677 |
time collecting I/O events, so you can handle more events per iteration, |
678 |
at the cost of increasing latency. Timeouts (both C<ev_periodic> and |
679 |
C<ev_timer>) will be not affected. Setting this to a non-null value will |
680 |
introduce an additional C<ev_sleep ()> call into most loop iterations. |
681 |
|
682 |
Likewise, by setting a higher I<timeout collect interval> you allow libev |
683 |
to spend more time collecting timeouts, at the expense of increased |
684 |
latency (the watcher callback will be called later). C<ev_io> watchers |
685 |
will not be affected. Setting this to a non-null value will not introduce |
686 |
any overhead in libev. |
687 |
|
688 |
Many (busy) programs can usually benefit by setting the io collect |
689 |
interval to a value near C<0.1> or so, which is often enough for |
690 |
interactive servers (of course not for games), likewise for timeouts. It |
691 |
usually doesn't make much sense to set it to a lower value than C<0.01>, |
692 |
as this approsaches the timing granularity of most systems. |
693 |
|
694 |
=back |
695 |
|
696 |
|
697 |
=head1 ANATOMY OF A WATCHER |
698 |
|
699 |
A watcher is a structure that you create and register to record your |
700 |
interest in some event. For instance, if you want to wait for STDIN to |
701 |
become readable, you would create an C<ev_io> watcher for that: |
702 |
|
703 |
static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
704 |
{ |
705 |
ev_io_stop (w); |
706 |
ev_unloop (loop, EVUNLOOP_ALL); |
707 |
} |
708 |
|
709 |
struct ev_loop *loop = ev_default_loop (0); |
710 |
struct ev_io stdin_watcher; |
711 |
ev_init (&stdin_watcher, my_cb); |
712 |
ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); |
713 |
ev_io_start (loop, &stdin_watcher); |
714 |
ev_loop (loop, 0); |
715 |
|
716 |
As you can see, you are responsible for allocating the memory for your |
717 |
watcher structures (and it is usually a bad idea to do this on the stack, |
718 |
although this can sometimes be quite valid). |
719 |
|
720 |
Each watcher structure must be initialised by a call to C<ev_init |
721 |
(watcher *, callback)>, which expects a callback to be provided. This |
722 |
callback gets invoked each time the event occurs (or, in the case of io |
723 |
watchers, each time the event loop detects that the file descriptor given |
724 |
is readable and/or writable). |
725 |
|
726 |
Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro |
727 |
with arguments specific to this watcher type. There is also a macro |
728 |
to combine initialisation and setting in one call: C<< ev_<type>_init |
729 |
(watcher *, callback, ...) >>. |
730 |
|
731 |
To make the watcher actually watch out for events, you have to start it |
732 |
with a watcher-specific start function (C<< ev_<type>_start (loop, watcher |
733 |
*) >>), and you can stop watching for events at any time by calling the |
734 |
corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>. |
735 |
|
736 |
As long as your watcher is active (has been started but not stopped) you |
737 |
must not touch the values stored in it. Most specifically you must never |
738 |
reinitialise it or call its C<set> macro. |
739 |
|
740 |
Each and every callback receives the event loop pointer as first, the |
741 |
registered watcher structure as second, and a bitset of received events as |
742 |
third argument. |
743 |
|
744 |
The received events usually include a single bit per event type received |
745 |
(you can receive multiple events at the same time). The possible bit masks |
746 |
are: |
747 |
|
748 |
=over 4 |
749 |
|
750 |
=item C<EV_READ> |
751 |
|
752 |
=item C<EV_WRITE> |
753 |
|
754 |
The file descriptor in the C<ev_io> watcher has become readable and/or |
755 |
writable. |
756 |
|
757 |
=item C<EV_TIMEOUT> |
758 |
|
759 |
The C<ev_timer> watcher has timed out. |
760 |
|
761 |
=item C<EV_PERIODIC> |
762 |
|
763 |
The C<ev_periodic> watcher has timed out. |
764 |
|
765 |
=item C<EV_SIGNAL> |
766 |
|
767 |
The signal specified in the C<ev_signal> watcher has been received by a thread. |
768 |
|
769 |
=item C<EV_CHILD> |
770 |
|
771 |
The pid specified in the C<ev_child> watcher has received a status change. |
772 |
|
773 |
=item C<EV_STAT> |
774 |
|
775 |
The path specified in the C<ev_stat> watcher changed its attributes somehow. |
776 |
|
777 |
=item C<EV_IDLE> |
778 |
|
779 |
The C<ev_idle> watcher has determined that you have nothing better to do. |
780 |
|
781 |
=item C<EV_PREPARE> |
782 |
|
783 |
=item C<EV_CHECK> |
784 |
|
785 |
All C<ev_prepare> watchers are invoked just I<before> C<ev_loop> starts |
786 |
to gather new events, and all C<ev_check> watchers are invoked just after |
787 |
C<ev_loop> has gathered them, but before it invokes any callbacks for any |
788 |
received events. Callbacks of both watcher types can start and stop as |
789 |
many watchers as they want, and all of them will be taken into account |
790 |
(for example, a C<ev_prepare> watcher might start an idle watcher to keep |
791 |
C<ev_loop> from blocking). |
792 |
|
793 |
=item C<EV_EMBED> |
794 |
|
795 |
The embedded event loop specified in the C<ev_embed> watcher needs attention. |
796 |
|
797 |
=item C<EV_FORK> |
798 |
|
799 |
The event loop has been resumed in the child process after fork (see |
800 |
C<ev_fork>). |
801 |
|
802 |
=item C<EV_ASYNC> |
803 |
|
804 |
The given async watcher has been asynchronously notified (see C<ev_async>). |
805 |
|
806 |
=item C<EV_ERROR> |
807 |
|
808 |
An unspecified error has occured, the watcher has been stopped. This might |
809 |
happen because the watcher could not be properly started because libev |
810 |
ran out of memory, a file descriptor was found to be closed or any other |
811 |
problem. You best act on it by reporting the problem and somehow coping |
812 |
with the watcher being stopped. |
813 |
|
814 |
Libev will usually signal a few "dummy" events together with an error, |
815 |
for example it might indicate that a fd is readable or writable, and if |
816 |
your callbacks is well-written it can just attempt the operation and cope |
817 |
with the error from read() or write(). This will not work in multithreaded |
818 |
programs, though, so beware. |
819 |
|
820 |
=back |
821 |
|
822 |
=head2 GENERIC WATCHER FUNCTIONS |
823 |
|
824 |
In the following description, C<TYPE> stands for the watcher type, |
825 |
e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers. |
826 |
|
827 |
=over 4 |
828 |
|
829 |
=item C<ev_init> (ev_TYPE *watcher, callback) |
830 |
|
831 |
This macro initialises the generic portion of a watcher. The contents |
832 |
of the watcher object can be arbitrary (so C<malloc> will do). Only |
833 |
the generic parts of the watcher are initialised, you I<need> to call |
834 |
the type-specific C<ev_TYPE_set> macro afterwards to initialise the |
835 |
type-specific parts. For each type there is also a C<ev_TYPE_init> macro |
836 |
which rolls both calls into one. |
837 |
|
838 |
You can reinitialise a watcher at any time as long as it has been stopped |
839 |
(or never started) and there are no pending events outstanding. |
840 |
|
841 |
The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher, |
842 |
int revents)>. |
843 |
|
844 |
=item C<ev_TYPE_set> (ev_TYPE *, [args]) |
845 |
|
846 |
This macro initialises the type-specific parts of a watcher. You need to |
847 |
call C<ev_init> at least once before you call this macro, but you can |
848 |
call C<ev_TYPE_set> any number of times. You must not, however, call this |
849 |
macro on a watcher that is active (it can be pending, however, which is a |
850 |
difference to the C<ev_init> macro). |
851 |
|
852 |
Although some watcher types do not have type-specific arguments |
853 |
(e.g. C<ev_prepare>) you still need to call its C<set> macro. |
854 |
|
855 |
=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args]) |
856 |
|
857 |
This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro |
858 |
calls into a single call. This is the most convinient method to initialise |
859 |
a watcher. The same limitations apply, of course. |
860 |
|
861 |
=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher) |
862 |
|
863 |
Starts (activates) the given watcher. Only active watchers will receive |
864 |
events. If the watcher is already active nothing will happen. |
865 |
|
866 |
=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher) |
867 |
|
868 |
Stops the given watcher again (if active) and clears the pending |
869 |
status. It is possible that stopped watchers are pending (for example, |
870 |
non-repeating timers are being stopped when they become pending), but |
871 |
C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If |
872 |
you want to free or reuse the memory used by the watcher it is therefore a |
873 |
good idea to always call its C<ev_TYPE_stop> function. |
874 |
|
875 |
=item bool ev_is_active (ev_TYPE *watcher) |
876 |
|
877 |
Returns a true value iff the watcher is active (i.e. it has been started |
878 |
and not yet been stopped). As long as a watcher is active you must not modify |
879 |
it. |
880 |
|
881 |
=item bool ev_is_pending (ev_TYPE *watcher) |
882 |
|
883 |
Returns a true value iff the watcher is pending, (i.e. it has outstanding |
884 |
events but its callback has not yet been invoked). As long as a watcher |
885 |
is pending (but not active) you must not call an init function on it (but |
886 |
C<ev_TYPE_set> is safe), you must not change its priority, and you must |
887 |
make sure the watcher is available to libev (e.g. you cannot C<free ()> |
888 |
it). |
889 |
|
890 |
=item callback ev_cb (ev_TYPE *watcher) |
891 |
|
892 |
Returns the callback currently set on the watcher. |
893 |
|
894 |
=item ev_cb_set (ev_TYPE *watcher, callback) |
895 |
|
896 |
Change the callback. You can change the callback at virtually any time |
897 |
(modulo threads). |
898 |
|
899 |
=item ev_set_priority (ev_TYPE *watcher, priority) |
900 |
|
901 |
=item int ev_priority (ev_TYPE *watcher) |
902 |
|
903 |
Set and query the priority of the watcher. The priority is a small |
904 |
integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI> |
905 |
(default: C<-2>). Pending watchers with higher priority will be invoked |
906 |
before watchers with lower priority, but priority will not keep watchers |
907 |
from being executed (except for C<ev_idle> watchers). |
908 |
|
909 |
This means that priorities are I<only> used for ordering callback |
910 |
invocation after new events have been received. This is useful, for |
911 |
example, to reduce latency after idling, or more often, to bind two |
912 |
watchers on the same event and make sure one is called first. |
913 |
|
914 |
If you need to suppress invocation when higher priority events are pending |
915 |
you need to look at C<ev_idle> watchers, which provide this functionality. |
916 |
|
917 |
You I<must not> change the priority of a watcher as long as it is active or |
918 |
pending. |
919 |
|
920 |
The default priority used by watchers when no priority has been set is |
921 |
always C<0>, which is supposed to not be too high and not be too low :). |
922 |
|
923 |
Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is |
924 |
fine, as long as you do not mind that the priority value you query might |
925 |
or might not have been adjusted to be within valid range. |
926 |
|
927 |
=item ev_invoke (loop, ev_TYPE *watcher, int revents) |
928 |
|
929 |
Invoke the C<watcher> with the given C<loop> and C<revents>. Neither |
930 |
C<loop> nor C<revents> need to be valid as long as the watcher callback |
931 |
can deal with that fact. |
932 |
|
933 |
=item int ev_clear_pending (loop, ev_TYPE *watcher) |
934 |
|
935 |
If the watcher is pending, this function returns clears its pending status |
936 |
and returns its C<revents> bitset (as if its callback was invoked). If the |
937 |
watcher isn't pending it does nothing and returns C<0>. |
938 |
|
939 |
=back |
940 |
|
941 |
|
942 |
=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER |
943 |
|
944 |
Each watcher has, by default, a member C<void *data> that you can change |
945 |
and read at any time, libev will completely ignore it. This can be used |
946 |
to associate arbitrary data with your watcher. If you need more data and |
947 |
don't want to allocate memory and store a pointer to it in that data |
948 |
member, you can also "subclass" the watcher type and provide your own |
949 |
data: |
950 |
|
951 |
struct my_io |
952 |
{ |
953 |
struct ev_io io; |
954 |
int otherfd; |
955 |
void *somedata; |
956 |
struct whatever *mostinteresting; |
957 |
} |
958 |
|
959 |
And since your callback will be called with a pointer to the watcher, you |
960 |
can cast it back to your own type: |
961 |
|
962 |
static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) |
963 |
{ |
964 |
struct my_io *w = (struct my_io *)w_; |
965 |
... |
966 |
} |
967 |
|
968 |
More interesting and less C-conformant ways of casting your callback type |
969 |
instead have been omitted. |
970 |
|
971 |
Another common scenario is having some data structure with multiple |
972 |
watchers: |
973 |
|
974 |
struct my_biggy |
975 |
{ |
976 |
int some_data; |
977 |
ev_timer t1; |
978 |
ev_timer t2; |
979 |
} |
980 |
|
981 |
In this case getting the pointer to C<my_biggy> is a bit more complicated, |
982 |
you need to use C<offsetof>: |
983 |
|
984 |
#include <stddef.h> |
985 |
|
986 |
static void |
987 |
t1_cb (EV_P_ struct ev_timer *w, int revents) |
988 |
{ |
989 |
struct my_biggy big = (struct my_biggy * |
990 |
(((char *)w) - offsetof (struct my_biggy, t1)); |
991 |
} |
992 |
|
993 |
static void |
994 |
t2_cb (EV_P_ struct ev_timer *w, int revents) |
995 |
{ |
996 |
struct my_biggy big = (struct my_biggy * |
997 |
(((char *)w) - offsetof (struct my_biggy, t2)); |
998 |
} |
999 |
|
1000 |
|
1001 |
=head1 WATCHER TYPES |
1002 |
|
1003 |
This section describes each watcher in detail, but will not repeat |
1004 |
information given in the last section. Any initialisation/set macros, |
1005 |
functions and members specific to the watcher type are explained. |
1006 |
|
1007 |
Members are additionally marked with either I<[read-only]>, meaning that, |
1008 |
while the watcher is active, you can look at the member and expect some |
1009 |
sensible content, but you must not modify it (you can modify it while the |
1010 |
watcher is stopped to your hearts content), or I<[read-write]>, which |
1011 |
means you can expect it to have some sensible content while the watcher |
1012 |
is active, but you can also modify it. Modifying it may not do something |
1013 |
sensible or take immediate effect (or do anything at all), but libev will |
1014 |
not crash or malfunction in any way. |
1015 |
|
1016 |
|
1017 |
=head2 C<ev_io> - is this file descriptor readable or writable? |
1018 |
|
1019 |
I/O watchers check whether a file descriptor is readable or writable |
1020 |
in each iteration of the event loop, or, more precisely, when reading |
1021 |
would not block the process and writing would at least be able to write |
1022 |
some data. This behaviour is called level-triggering because you keep |
1023 |
receiving events as long as the condition persists. Remember you can stop |
1024 |
the watcher if you don't want to act on the event and neither want to |
1025 |
receive future events. |
1026 |
|
1027 |
In general you can register as many read and/or write event watchers per |
1028 |
fd as you want (as long as you don't confuse yourself). Setting all file |
1029 |
descriptors to non-blocking mode is also usually a good idea (but not |
1030 |
required if you know what you are doing). |
1031 |
|
1032 |
If you must do this, then force the use of a known-to-be-good backend |
1033 |
(at the time of this writing, this includes only C<EVBACKEND_SELECT> and |
1034 |
C<EVBACKEND_POLL>). |
1035 |
|
1036 |
Another thing you have to watch out for is that it is quite easy to |
1037 |
receive "spurious" readiness notifications, that is your callback might |
1038 |
be called with C<EV_READ> but a subsequent C<read>(2) will actually block |
1039 |
because there is no data. Not only are some backends known to create a |
1040 |
lot of those (for example solaris ports), it is very easy to get into |
1041 |
this situation even with a relatively standard program structure. Thus |
1042 |
it is best to always use non-blocking I/O: An extra C<read>(2) returning |
1043 |
C<EAGAIN> is far preferable to a program hanging until some data arrives. |
1044 |
|
1045 |
If you cannot run the fd in non-blocking mode (for example you should not |
1046 |
play around with an Xlib connection), then you have to seperately re-test |
1047 |
whether a file descriptor is really ready with a known-to-be good interface |
1048 |
such as poll (fortunately in our Xlib example, Xlib already does this on |
1049 |
its own, so its quite safe to use). |
1050 |
|
1051 |
=head3 The special problem of disappearing file descriptors |
1052 |
|
1053 |
Some backends (e.g. kqueue, epoll) need to be told about closing a file |
1054 |
descriptor (either by calling C<close> explicitly or by any other means, |
1055 |
such as C<dup>). The reason is that you register interest in some file |
1056 |
descriptor, but when it goes away, the operating system will silently drop |
1057 |
this interest. If another file descriptor with the same number then is |
1058 |
registered with libev, there is no efficient way to see that this is, in |
1059 |
fact, a different file descriptor. |
1060 |
|
1061 |
To avoid having to explicitly tell libev about such cases, libev follows |
1062 |
the following policy: Each time C<ev_io_set> is being called, libev |
1063 |
will assume that this is potentially a new file descriptor, otherwise |
1064 |
it is assumed that the file descriptor stays the same. That means that |
1065 |
you I<have> to call C<ev_io_set> (or C<ev_io_init>) when you change the |
1066 |
descriptor even if the file descriptor number itself did not change. |
1067 |
|
1068 |
This is how one would do it normally anyway, the important point is that |
1069 |
the libev application should not optimise around libev but should leave |
1070 |
optimisations to libev. |
1071 |
|
1072 |
=head3 The special problem of dup'ed file descriptors |
1073 |
|
1074 |
Some backends (e.g. epoll), cannot register events for file descriptors, |
1075 |
but only events for the underlying file descriptions. That means when you |
1076 |
have C<dup ()>'ed file descriptors or weirder constellations, and register |
1077 |
events for them, only one file descriptor might actually receive events. |
1078 |
|
1079 |
There is no workaround possible except not registering events |
1080 |
for potentially C<dup ()>'ed file descriptors, or to resort to |
1081 |
C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>. |
1082 |
|
1083 |
=head3 The special problem of fork |
1084 |
|
1085 |
Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit |
1086 |
useless behaviour. Libev fully supports fork, but needs to be told about |
1087 |
it in the child. |
1088 |
|
1089 |
To support fork in your programs, you either have to call |
1090 |
C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child, |
1091 |
enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or |
1092 |
C<EVBACKEND_POLL>. |
1093 |
|
1094 |
=head3 The special problem of SIGPIPE |
1095 |
|
1096 |
While not really specific to libev, it is easy to forget about SIGPIPE: |
1097 |
when reading from a pipe whose other end has been closed, your program |
1098 |
gets send a SIGPIPE, which, by default, aborts your program. For most |
1099 |
programs this is sensible behaviour, for daemons, this is usually |
1100 |
undesirable. |
1101 |
|
1102 |
So when you encounter spurious, unexplained daemon exits, make sure you |
1103 |
ignore SIGPIPE (and maybe make sure you log the exit status of your daemon |
1104 |
somewhere, as that would have given you a big clue). |
1105 |
|
1106 |
|
1107 |
=head3 Watcher-Specific Functions |
1108 |
|
1109 |
=over 4 |
1110 |
|
1111 |
=item ev_io_init (ev_io *, callback, int fd, int events) |
1112 |
|
1113 |
=item ev_io_set (ev_io *, int fd, int events) |
1114 |
|
1115 |
Configures an C<ev_io> watcher. The C<fd> is the file descriptor to |
1116 |
rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or |
1117 |
C<EV_READ | EV_WRITE> to receive the given events. |
1118 |
|
1119 |
=item int fd [read-only] |
1120 |
|
1121 |
The file descriptor being watched. |
1122 |
|
1123 |
=item int events [read-only] |
1124 |
|
1125 |
The events being watched. |
1126 |
|
1127 |
=back |
1128 |
|
1129 |
=head3 Examples |
1130 |
|
1131 |
Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well |
1132 |
readable, but only once. Since it is likely line-buffered, you could |
1133 |
attempt to read a whole line in the callback. |
1134 |
|
1135 |
static void |
1136 |
stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
1137 |
{ |
1138 |
ev_io_stop (loop, w); |
1139 |
.. read from stdin here (or from w->fd) and haqndle any I/O errors |
1140 |
} |
1141 |
|
1142 |
... |
1143 |
struct ev_loop *loop = ev_default_init (0); |
1144 |
struct ev_io stdin_readable; |
1145 |
ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); |
1146 |
ev_io_start (loop, &stdin_readable); |
1147 |
ev_loop (loop, 0); |
1148 |
|
1149 |
|
1150 |
=head2 C<ev_timer> - relative and optionally repeating timeouts |
1151 |
|
1152 |
Timer watchers are simple relative timers that generate an event after a |
1153 |
given time, and optionally repeating in regular intervals after that. |
1154 |
|
1155 |
The timers are based on real time, that is, if you register an event that |
1156 |
times out after an hour and you reset your system clock to last years |
1157 |
time, it will still time out after (roughly) and hour. "Roughly" because |
1158 |
detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1159 |
monotonic clock option helps a lot here). |
1160 |
|
1161 |
The relative timeouts are calculated relative to the C<ev_now ()> |
1162 |
time. This is usually the right thing as this timestamp refers to the time |
1163 |
of the event triggering whatever timeout you are modifying/starting. If |
1164 |
you suspect event processing to be delayed and you I<need> to base the timeout |
1165 |
on the current time, use something like this to adjust for this: |
1166 |
|
1167 |
ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); |
1168 |
|
1169 |
The callback is guarenteed to be invoked only when its timeout has passed, |
1170 |
but if multiple timers become ready during the same loop iteration then |
1171 |
order of execution is undefined. |
1172 |
|
1173 |
=head3 Watcher-Specific Functions and Data Members |
1174 |
|
1175 |
=over 4 |
1176 |
|
1177 |
=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) |
1178 |
|
1179 |
=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat) |
1180 |
|
1181 |
Configure the timer to trigger after C<after> seconds. If C<repeat> is |
1182 |
C<0.>, then it will automatically be stopped. If it is positive, then the |
1183 |
timer will automatically be configured to trigger again C<repeat> seconds |
1184 |
later, again, and again, until stopped manually. |
1185 |
|
1186 |
The timer itself will do a best-effort at avoiding drift, that is, if you |
1187 |
configure a timer to trigger every 10 seconds, then it will trigger at |
1188 |
exactly 10 second intervals. If, however, your program cannot keep up with |
1189 |
the timer (because it takes longer than those 10 seconds to do stuff) the |
1190 |
timer will not fire more than once per event loop iteration. |
1191 |
|
1192 |
=item ev_timer_again (loop, ev_timer *) |
1193 |
|
1194 |
This will act as if the timer timed out and restart it again if it is |
1195 |
repeating. The exact semantics are: |
1196 |
|
1197 |
If the timer is pending, its pending status is cleared. |
1198 |
|
1199 |
If the timer is started but nonrepeating, stop it (as if it timed out). |
1200 |
|
1201 |
If the timer is repeating, either start it if necessary (with the |
1202 |
C<repeat> value), or reset the running timer to the C<repeat> value. |
1203 |
|
1204 |
This sounds a bit complicated, but here is a useful and typical |
1205 |
example: Imagine you have a tcp connection and you want a so-called idle |
1206 |
timeout, that is, you want to be called when there have been, say, 60 |
1207 |
seconds of inactivity on the socket. The easiest way to do this is to |
1208 |
configure an C<ev_timer> with a C<repeat> value of C<60> and then call |
1209 |
C<ev_timer_again> each time you successfully read or write some data. If |
1210 |
you go into an idle state where you do not expect data to travel on the |
1211 |
socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will |
1212 |
automatically restart it if need be. |
1213 |
|
1214 |
That means you can ignore the C<after> value and C<ev_timer_start> |
1215 |
altogether and only ever use the C<repeat> value and C<ev_timer_again>: |
1216 |
|
1217 |
ev_timer_init (timer, callback, 0., 5.); |
1218 |
ev_timer_again (loop, timer); |
1219 |
... |
1220 |
timer->again = 17.; |
1221 |
ev_timer_again (loop, timer); |
1222 |
... |
1223 |
timer->again = 10.; |
1224 |
ev_timer_again (loop, timer); |
1225 |
|
1226 |
This is more slightly efficient then stopping/starting the timer each time |
1227 |
you want to modify its timeout value. |
1228 |
|
1229 |
=item ev_tstamp repeat [read-write] |
1230 |
|
1231 |
The current C<repeat> value. Will be used each time the watcher times out |
1232 |
or C<ev_timer_again> is called and determines the next timeout (if any), |
1233 |
which is also when any modifications are taken into account. |
1234 |
|
1235 |
=back |
1236 |
|
1237 |
=head3 Examples |
1238 |
|
1239 |
Example: Create a timer that fires after 60 seconds. |
1240 |
|
1241 |
static void |
1242 |
one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) |
1243 |
{ |
1244 |
.. one minute over, w is actually stopped right here |
1245 |
} |
1246 |
|
1247 |
struct ev_timer mytimer; |
1248 |
ev_timer_init (&mytimer, one_minute_cb, 60., 0.); |
1249 |
ev_timer_start (loop, &mytimer); |
1250 |
|
1251 |
Example: Create a timeout timer that times out after 10 seconds of |
1252 |
inactivity. |
1253 |
|
1254 |
static void |
1255 |
timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) |
1256 |
{ |
1257 |
.. ten seconds without any activity |
1258 |
} |
1259 |
|
1260 |
struct ev_timer mytimer; |
1261 |
ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ |
1262 |
ev_timer_again (&mytimer); /* start timer */ |
1263 |
ev_loop (loop, 0); |
1264 |
|
1265 |
// and in some piece of code that gets executed on any "activity": |
1266 |
// reset the timeout to start ticking again at 10 seconds |
1267 |
ev_timer_again (&mytimer); |
1268 |
|
1269 |
|
1270 |
=head2 C<ev_periodic> - to cron or not to cron? |
1271 |
|
1272 |
Periodic watchers are also timers of a kind, but they are very versatile |
1273 |
(and unfortunately a bit complex). |
1274 |
|
1275 |
Unlike C<ev_timer>'s, they are not based on real time (or relative time) |
1276 |
but on wallclock time (absolute time). You can tell a periodic watcher |
1277 |
to trigger "at" some specific point in time. For example, if you tell a |
1278 |
periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now () |
1279 |
+ 10.>) and then reset your system clock to the last year, then it will |
1280 |
take a year to trigger the event (unlike an C<ev_timer>, which would trigger |
1281 |
roughly 10 seconds later). |
1282 |
|
1283 |
They can also be used to implement vastly more complex timers, such as |
1284 |
triggering an event on each midnight, local time or other, complicated, |
1285 |
rules. |
1286 |
|
1287 |
As with timers, the callback is guarenteed to be invoked only when the |
1288 |
time (C<at>) has been passed, but if multiple periodic timers become ready |
1289 |
during the same loop iteration then order of execution is undefined. |
1290 |
|
1291 |
=head3 Watcher-Specific Functions and Data Members |
1292 |
|
1293 |
=over 4 |
1294 |
|
1295 |
=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb) |
1296 |
|
1297 |
=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb) |
1298 |
|
1299 |
Lots of arguments, lets sort it out... There are basically three modes of |
1300 |
operation, and we will explain them from simplest to complex: |
1301 |
|
1302 |
=over 4 |
1303 |
|
1304 |
=item * absolute timer (at = time, interval = reschedule_cb = 0) |
1305 |
|
1306 |
In this configuration the watcher triggers an event at the wallclock time |
1307 |
C<at> and doesn't repeat. It will not adjust when a time jump occurs, |
1308 |
that is, if it is to be run at January 1st 2011 then it will run when the |
1309 |
system time reaches or surpasses this time. |
1310 |
|
1311 |
=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0) |
1312 |
|
1313 |
In this mode the watcher will always be scheduled to time out at the next |
1314 |
C<at + N * interval> time (for some integer N, which can also be negative) |
1315 |
and then repeat, regardless of any time jumps. |
1316 |
|
1317 |
This can be used to create timers that do not drift with respect to system |
1318 |
time: |
1319 |
|
1320 |
ev_periodic_set (&periodic, 0., 3600., 0); |
1321 |
|
1322 |
This doesn't mean there will always be 3600 seconds in between triggers, |
1323 |
but only that the the callback will be called when the system time shows a |
1324 |
full hour (UTC), or more correctly, when the system time is evenly divisible |
1325 |
by 3600. |
1326 |
|
1327 |
Another way to think about it (for the mathematically inclined) is that |
1328 |
C<ev_periodic> will try to run the callback in this mode at the next possible |
1329 |
time where C<time = at (mod interval)>, regardless of any time jumps. |
1330 |
|
1331 |
For numerical stability it is preferable that the C<at> value is near |
1332 |
C<ev_now ()> (the current time), but there is no range requirement for |
1333 |
this value. |
1334 |
|
1335 |
=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback) |
1336 |
|
1337 |
In this mode the values for C<interval> and C<at> are both being |
1338 |
ignored. Instead, each time the periodic watcher gets scheduled, the |
1339 |
reschedule callback will be called with the watcher as first, and the |
1340 |
current time as second argument. |
1341 |
|
1342 |
NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, |
1343 |
ever, or make any event loop modifications>. If you need to stop it, |
1344 |
return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by |
1345 |
starting an C<ev_prepare> watcher, which is legal). |
1346 |
|
1347 |
Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w, |
1348 |
ev_tstamp now)>, e.g.: |
1349 |
|
1350 |
static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) |
1351 |
{ |
1352 |
return now + 60.; |
1353 |
} |
1354 |
|
1355 |
It must return the next time to trigger, based on the passed time value |
1356 |
(that is, the lowest time value larger than to the second argument). It |
1357 |
will usually be called just before the callback will be triggered, but |
1358 |
might be called at other times, too. |
1359 |
|
1360 |
NOTE: I<< This callback must always return a time that is later than the |
1361 |
passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger. |
1362 |
|
1363 |
This can be used to create very complex timers, such as a timer that |
1364 |
triggers on each midnight, local time. To do this, you would calculate the |
1365 |
next midnight after C<now> and return the timestamp value for this. How |
1366 |
you do this is, again, up to you (but it is not trivial, which is the main |
1367 |
reason I omitted it as an example). |
1368 |
|
1369 |
=back |
1370 |
|
1371 |
=item ev_periodic_again (loop, ev_periodic *) |
1372 |
|
1373 |
Simply stops and restarts the periodic watcher again. This is only useful |
1374 |
when you changed some parameters or the reschedule callback would return |
1375 |
a different time than the last time it was called (e.g. in a crond like |
1376 |
program when the crontabs have changed). |
1377 |
|
1378 |
=item ev_tstamp ev_periodic_at (ev_periodic *) |
1379 |
|
1380 |
When active, returns the absolute time that the watcher is supposed to |
1381 |
trigger next. |
1382 |
|
1383 |
=item ev_tstamp offset [read-write] |
1384 |
|
1385 |
When repeating, this contains the offset value, otherwise this is the |
1386 |
absolute point in time (the C<at> value passed to C<ev_periodic_set>). |
1387 |
|
1388 |
Can be modified any time, but changes only take effect when the periodic |
1389 |
timer fires or C<ev_periodic_again> is being called. |
1390 |
|
1391 |
=item ev_tstamp interval [read-write] |
1392 |
|
1393 |
The current interval value. Can be modified any time, but changes only |
1394 |
take effect when the periodic timer fires or C<ev_periodic_again> is being |
1395 |
called. |
1396 |
|
1397 |
=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write] |
1398 |
|
1399 |
The current reschedule callback, or C<0>, if this functionality is |
1400 |
switched off. Can be changed any time, but changes only take effect when |
1401 |
the periodic timer fires or C<ev_periodic_again> is being called. |
1402 |
|
1403 |
=back |
1404 |
|
1405 |
=head3 Examples |
1406 |
|
1407 |
Example: Call a callback every hour, or, more precisely, whenever the |
1408 |
system clock is divisible by 3600. The callback invocation times have |
1409 |
potentially a lot of jittering, but good long-term stability. |
1410 |
|
1411 |
static void |
1412 |
clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) |
1413 |
{ |
1414 |
... its now a full hour (UTC, or TAI or whatever your clock follows) |
1415 |
} |
1416 |
|
1417 |
struct ev_periodic hourly_tick; |
1418 |
ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); |
1419 |
ev_periodic_start (loop, &hourly_tick); |
1420 |
|
1421 |
Example: The same as above, but use a reschedule callback to do it: |
1422 |
|
1423 |
#include <math.h> |
1424 |
|
1425 |
static ev_tstamp |
1426 |
my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) |
1427 |
{ |
1428 |
return fmod (now, 3600.) + 3600.; |
1429 |
} |
1430 |
|
1431 |
ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); |
1432 |
|
1433 |
Example: Call a callback every hour, starting now: |
1434 |
|
1435 |
struct ev_periodic hourly_tick; |
1436 |
ev_periodic_init (&hourly_tick, clock_cb, |
1437 |
fmod (ev_now (loop), 3600.), 3600., 0); |
1438 |
ev_periodic_start (loop, &hourly_tick); |
1439 |
|
1440 |
|
1441 |
=head2 C<ev_signal> - signal me when a signal gets signalled! |
1442 |
|
1443 |
Signal watchers will trigger an event when the process receives a specific |
1444 |
signal one or more times. Even though signals are very asynchronous, libev |
1445 |
will try it's best to deliver signals synchronously, i.e. as part of the |
1446 |
normal event processing, like any other event. |
1447 |
|
1448 |
You can configure as many watchers as you like per signal. Only when the |
1449 |
first watcher gets started will libev actually register a signal watcher |
1450 |
with the kernel (thus it coexists with your own signal handlers as long |
1451 |
as you don't register any with libev). Similarly, when the last signal |
1452 |
watcher for a signal is stopped libev will reset the signal handler to |
1453 |
SIG_DFL (regardless of what it was set to before). |
1454 |
|
1455 |
If possible and supported, libev will install its handlers with |
1456 |
C<SA_RESTART> behaviour enabled, so syscalls should not be unduly |
1457 |
interrupted. If you have a problem with syscalls getting interrupted by |
1458 |
signals you can block all signals in an C<ev_check> watcher and unblock |
1459 |
them in an C<ev_prepare> watcher. |
1460 |
|
1461 |
=head3 Watcher-Specific Functions and Data Members |
1462 |
|
1463 |
=over 4 |
1464 |
|
1465 |
=item ev_signal_init (ev_signal *, callback, int signum) |
1466 |
|
1467 |
=item ev_signal_set (ev_signal *, int signum) |
1468 |
|
1469 |
Configures the watcher to trigger on the given signal number (usually one |
1470 |
of the C<SIGxxx> constants). |
1471 |
|
1472 |
=item int signum [read-only] |
1473 |
|
1474 |
The signal the watcher watches out for. |
1475 |
|
1476 |
=back |
1477 |
|
1478 |
=head3 Examples |
1479 |
|
1480 |
Example: Try to exit cleanly on SIGINT and SIGTERM. |
1481 |
|
1482 |
static void |
1483 |
sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) |
1484 |
{ |
1485 |
ev_unloop (loop, EVUNLOOP_ALL); |
1486 |
} |
1487 |
|
1488 |
struct ev_signal signal_watcher; |
1489 |
ev_signal_init (&signal_watcher, sigint_cb, SIGINT); |
1490 |
ev_signal_start (loop, &sigint_cb); |
1491 |
|
1492 |
|
1493 |
=head2 C<ev_child> - watch out for process status changes |
1494 |
|
1495 |
Child watchers trigger when your process receives a SIGCHLD in response to |
1496 |
some child status changes (most typically when a child of yours dies). It |
1497 |
is permissible to install a child watcher I<after> the child has been |
1498 |
forked (which implies it might have already exited), as long as the event |
1499 |
loop isn't entered (or is continued from a watcher). |
1500 |
|
1501 |
Only the default event loop is capable of handling signals, and therefore |
1502 |
you can only rgeister child watchers in the default event loop. |
1503 |
|
1504 |
=head3 Process Interaction |
1505 |
|
1506 |
Libev grabs C<SIGCHLD> as soon as the default event loop is |
1507 |
initialised. This is necessary to guarantee proper behaviour even if |
1508 |
the first child watcher is started after the child exits. The occurance |
1509 |
of C<SIGCHLD> is recorded asynchronously, but child reaping is done |
1510 |
synchronously as part of the event loop processing. Libev always reaps all |
1511 |
children, even ones not watched. |
1512 |
|
1513 |
=head3 Overriding the Built-In Processing |
1514 |
|
1515 |
Libev offers no special support for overriding the built-in child |
1516 |
processing, but if your application collides with libev's default child |
1517 |
handler, you can override it easily by installing your own handler for |
1518 |
C<SIGCHLD> after initialising the default loop, and making sure the |
1519 |
default loop never gets destroyed. You are encouraged, however, to use an |
1520 |
event-based approach to child reaping and thus use libev's support for |
1521 |
that, so other libev users can use C<ev_child> watchers freely. |
1522 |
|
1523 |
=head3 Watcher-Specific Functions and Data Members |
1524 |
|
1525 |
=over 4 |
1526 |
|
1527 |
=item ev_child_init (ev_child *, callback, int pid, int trace) |
1528 |
|
1529 |
=item ev_child_set (ev_child *, int pid, int trace) |
1530 |
|
1531 |
Configures the watcher to wait for status changes of process C<pid> (or |
1532 |
I<any> process if C<pid> is specified as C<0>). The callback can look |
1533 |
at the C<rstatus> member of the C<ev_child> watcher structure to see |
1534 |
the status word (use the macros from C<sys/wait.h> and see your systems |
1535 |
C<waitpid> documentation). The C<rpid> member contains the pid of the |
1536 |
process causing the status change. C<trace> must be either C<0> (only |
1537 |
activate the watcher when the process terminates) or C<1> (additionally |
1538 |
activate the watcher when the process is stopped or continued). |
1539 |
|
1540 |
=item int pid [read-only] |
1541 |
|
1542 |
The process id this watcher watches out for, or C<0>, meaning any process id. |
1543 |
|
1544 |
=item int rpid [read-write] |
1545 |
|
1546 |
The process id that detected a status change. |
1547 |
|
1548 |
=item int rstatus [read-write] |
1549 |
|
1550 |
The process exit/trace status caused by C<rpid> (see your systems |
1551 |
C<waitpid> and C<sys/wait.h> documentation for details). |
1552 |
|
1553 |
=back |
1554 |
|
1555 |
=head3 Examples |
1556 |
|
1557 |
Example: C<fork()> a new process and install a child handler to wait for |
1558 |
its completion. |
1559 |
|
1560 |
ev_child cw; |
1561 |
|
1562 |
static void |
1563 |
child_cb (EV_P_ struct ev_child *w, int revents) |
1564 |
{ |
1565 |
ev_child_stop (EV_A_ w); |
1566 |
printf ("process %d exited with status %x\n", w->rpid, w->rstatus); |
1567 |
} |
1568 |
|
1569 |
pid_t pid = fork (); |
1570 |
|
1571 |
if (pid < 0) |
1572 |
// error |
1573 |
else if (pid == 0) |
1574 |
{ |
1575 |
// the forked child executes here |
1576 |
exit (1); |
1577 |
} |
1578 |
else |
1579 |
{ |
1580 |
ev_child_init (&cw, child_cb, pid, 0); |
1581 |
ev_child_start (EV_DEFAULT_ &cw); |
1582 |
} |
1583 |
|
1584 |
|
1585 |
=head2 C<ev_stat> - did the file attributes just change? |
1586 |
|
1587 |
This watches a filesystem path for attribute changes. That is, it calls |
1588 |
C<stat> regularly (or when the OS says it changed) and sees if it changed |
1589 |
compared to the last time, invoking the callback if it did. |
1590 |
|
1591 |
The path does not need to exist: changing from "path exists" to "path does |
1592 |
not exist" is a status change like any other. The condition "path does |
1593 |
not exist" is signified by the C<st_nlink> field being zero (which is |
1594 |
otherwise always forced to be at least one) and all the other fields of |
1595 |
the stat buffer having unspecified contents. |
1596 |
|
1597 |
The path I<should> be absolute and I<must not> end in a slash. If it is |
1598 |
relative and your working directory changes, the behaviour is undefined. |
1599 |
|
1600 |
Since there is no standard to do this, the portable implementation simply |
1601 |
calls C<stat (2)> regularly on the path to see if it changed somehow. You |
1602 |
can specify a recommended polling interval for this case. If you specify |
1603 |
a polling interval of C<0> (highly recommended!) then a I<suitable, |
1604 |
unspecified default> value will be used (which you can expect to be around |
1605 |
five seconds, although this might change dynamically). Libev will also |
1606 |
impose a minimum interval which is currently around C<0.1>, but thats |
1607 |
usually overkill. |
1608 |
|
1609 |
This watcher type is not meant for massive numbers of stat watchers, |
1610 |
as even with OS-supported change notifications, this can be |
1611 |
resource-intensive. |
1612 |
|
1613 |
At the time of this writing, only the Linux inotify interface is |
1614 |
implemented (implementing kqueue support is left as an exercise for the |
1615 |
reader, note, however, that the author sees no way of implementing ev_stat |
1616 |
semantics with kqueue). Inotify will be used to give hints only and should |
1617 |
not change the semantics of C<ev_stat> watchers, which means that libev |
1618 |
sometimes needs to fall back to regular polling again even with inotify, |
1619 |
but changes are usually detected immediately, and if the file exists there |
1620 |
will be no polling. |
1621 |
|
1622 |
=head3 ABI Issues (Largefile Support) |
1623 |
|
1624 |
Libev by default (unless the user overrides this) uses the default |
1625 |
compilation environment, which means that on systems with optionally |
1626 |
disabled large file support, you get the 32 bit version of the stat |
1627 |
structure. When using the library from programs that change the ABI to |
1628 |
use 64 bit file offsets the programs will fail. In that case you have to |
1629 |
compile libev with the same flags to get binary compatibility. This is |
1630 |
obviously the case with any flags that change the ABI, but the problem is |
1631 |
most noticably with ev_stat and largefile support. |
1632 |
|
1633 |
=head3 Inotify |
1634 |
|
1635 |
When C<inotify (7)> support has been compiled into libev (generally only |
1636 |
available on Linux) and present at runtime, it will be used to speed up |
1637 |
change detection where possible. The inotify descriptor will be created lazily |
1638 |
when the first C<ev_stat> watcher is being started. |
1639 |
|
1640 |
Inotify presence does not change the semantics of C<ev_stat> watchers |
1641 |
except that changes might be detected earlier, and in some cases, to avoid |
1642 |
making regular C<stat> calls. Even in the presence of inotify support |
1643 |
there are many cases where libev has to resort to regular C<stat> polling. |
1644 |
|
1645 |
(There is no support for kqueue, as apparently it cannot be used to |
1646 |
implement this functionality, due to the requirement of having a file |
1647 |
descriptor open on the object at all times). |
1648 |
|
1649 |
=head3 The special problem of stat time resolution |
1650 |
|
1651 |
The C<stat ()> syscall only supports full-second resolution portably, and |
1652 |
even on systems where the resolution is higher, many filesystems still |
1653 |
only support whole seconds. |
1654 |
|
1655 |
That means that, if the time is the only thing that changes, you can |
1656 |
easily miss updates: on the first update, C<ev_stat> detects a change and |
1657 |
calls your callback, which does something. When there is another update |
1658 |
within the same second, C<ev_stat> will be unable to detect it as the stat |
1659 |
data does not change. |
1660 |
|
1661 |
The solution to this is to delay acting on a change for slightly more |
1662 |
than a second (or till slightly after the next full second boundary), using |
1663 |
a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02); |
1664 |
ev_timer_again (loop, w)>). |
1665 |
|
1666 |
The C<.02> offset is added to work around small timing inconsistencies |
1667 |
of some operating systems (where the second counter of the current time |
1668 |
might be be delayed. One such system is the Linux kernel, where a call to |
1669 |
C<gettimeofday> might return a timestamp with a full second later than |
1670 |
a subsequent C<time> call - if the equivalent of C<time ()> is used to |
1671 |
update file times then there will be a small window where the kernel uses |
1672 |
the previous second to update file times but libev might already execute |
1673 |
the timer callback). |
1674 |
|
1675 |
=head3 Watcher-Specific Functions and Data Members |
1676 |
|
1677 |
=over 4 |
1678 |
|
1679 |
=item ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval) |
1680 |
|
1681 |
=item ev_stat_set (ev_stat *, const char *path, ev_tstamp interval) |
1682 |
|
1683 |
Configures the watcher to wait for status changes of the given |
1684 |
C<path>. The C<interval> is a hint on how quickly a change is expected to |
1685 |
be detected and should normally be specified as C<0> to let libev choose |
1686 |
a suitable value. The memory pointed to by C<path> must point to the same |
1687 |
path for as long as the watcher is active. |
1688 |
|
1689 |
The callback will receive C<EV_STAT> when a change was detected, relative |
1690 |
to the attributes at the time the watcher was started (or the last change |
1691 |
was detected). |
1692 |
|
1693 |
=item ev_stat_stat (loop, ev_stat *) |
1694 |
|
1695 |
Updates the stat buffer immediately with new values. If you change the |
1696 |
watched path in your callback, you could call this function to avoid |
1697 |
detecting this change (while introducing a race condition if you are not |
1698 |
the only one changing the path). Can also be useful simply to find out the |
1699 |
new values. |
1700 |
|
1701 |
=item ev_statdata attr [read-only] |
1702 |
|
1703 |
The most-recently detected attributes of the file. Although the type is |
1704 |
C<ev_statdata>, this is usually the (or one of the) C<struct stat> types |
1705 |
suitable for your system, but you can only rely on the POSIX-standardised |
1706 |
members to be present. If the C<st_nlink> member is C<0>, then there was |
1707 |
some error while C<stat>ing the file. |
1708 |
|
1709 |
=item ev_statdata prev [read-only] |
1710 |
|
1711 |
The previous attributes of the file. The callback gets invoked whenever |
1712 |
C<prev> != C<attr>, or, more precisely, one or more of these members |
1713 |
differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>, |
1714 |
C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>. |
1715 |
|
1716 |
=item ev_tstamp interval [read-only] |
1717 |
|
1718 |
The specified interval. |
1719 |
|
1720 |
=item const char *path [read-only] |
1721 |
|
1722 |
The filesystem path that is being watched. |
1723 |
|
1724 |
=back |
1725 |
|
1726 |
=head3 Examples |
1727 |
|
1728 |
Example: Watch C</etc/passwd> for attribute changes. |
1729 |
|
1730 |
static void |
1731 |
passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) |
1732 |
{ |
1733 |
/* /etc/passwd changed in some way */ |
1734 |
if (w->attr.st_nlink) |
1735 |
{ |
1736 |
printf ("passwd current size %ld\n", (long)w->attr.st_size); |
1737 |
printf ("passwd current atime %ld\n", (long)w->attr.st_mtime); |
1738 |
printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime); |
1739 |
} |
1740 |
else |
1741 |
/* you shalt not abuse printf for puts */ |
1742 |
puts ("wow, /etc/passwd is not there, expect problems. " |
1743 |
"if this is windows, they already arrived\n"); |
1744 |
} |
1745 |
|
1746 |
... |
1747 |
ev_stat passwd; |
1748 |
|
1749 |
ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.); |
1750 |
ev_stat_start (loop, &passwd); |
1751 |
|
1752 |
Example: Like above, but additionally use a one-second delay so we do not |
1753 |
miss updates (however, frequent updates will delay processing, too, so |
1754 |
one might do the work both on C<ev_stat> callback invocation I<and> on |
1755 |
C<ev_timer> callback invocation). |
1756 |
|
1757 |
static ev_stat passwd; |
1758 |
static ev_timer timer; |
1759 |
|
1760 |
static void |
1761 |
timer_cb (EV_P_ ev_timer *w, int revents) |
1762 |
{ |
1763 |
ev_timer_stop (EV_A_ w); |
1764 |
|
1765 |
/* now it's one second after the most recent passwd change */ |
1766 |
} |
1767 |
|
1768 |
static void |
1769 |
stat_cb (EV_P_ ev_stat *w, int revents) |
1770 |
{ |
1771 |
/* reset the one-second timer */ |
1772 |
ev_timer_again (EV_A_ &timer); |
1773 |
} |
1774 |
|
1775 |
... |
1776 |
ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.); |
1777 |
ev_stat_start (loop, &passwd); |
1778 |
ev_timer_init (&timer, timer_cb, 0., 1.02); |
1779 |
|
1780 |
|
1781 |
=head2 C<ev_idle> - when you've got nothing better to do... |
1782 |
|
1783 |
Idle watchers trigger events when no other events of the same or higher |
1784 |
priority are pending (prepare, check and other idle watchers do not |
1785 |
count). |
1786 |
|
1787 |
That is, as long as your process is busy handling sockets or timeouts |
1788 |
(or even signals, imagine) of the same or higher priority it will not be |
1789 |
triggered. But when your process is idle (or only lower-priority watchers |
1790 |
are pending), the idle watchers are being called once per event loop |
1791 |
iteration - until stopped, that is, or your process receives more events |
1792 |
and becomes busy again with higher priority stuff. |
1793 |
|
1794 |
The most noteworthy effect is that as long as any idle watchers are |
1795 |
active, the process will not block when waiting for new events. |
1796 |
|
1797 |
Apart from keeping your process non-blocking (which is a useful |
1798 |
effect on its own sometimes), idle watchers are a good place to do |
1799 |
"pseudo-background processing", or delay processing stuff to after the |
1800 |
event loop has handled all outstanding events. |
1801 |
|
1802 |
=head3 Watcher-Specific Functions and Data Members |
1803 |
|
1804 |
=over 4 |
1805 |
|
1806 |
=item ev_idle_init (ev_signal *, callback) |
1807 |
|
1808 |
Initialises and configures the idle watcher - it has no parameters of any |
1809 |
kind. There is a C<ev_idle_set> macro, but using it is utterly pointless, |
1810 |
believe me. |
1811 |
|
1812 |
=back |
1813 |
|
1814 |
=head3 Examples |
1815 |
|
1816 |
Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the |
1817 |
callback, free it. Also, use no error checking, as usual. |
1818 |
|
1819 |
static void |
1820 |
idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) |
1821 |
{ |
1822 |
free (w); |
1823 |
// now do something you wanted to do when the program has |
1824 |
// no longer anything immediate to do. |
1825 |
} |
1826 |
|
1827 |
struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); |
1828 |
ev_idle_init (idle_watcher, idle_cb); |
1829 |
ev_idle_start (loop, idle_cb); |
1830 |
|
1831 |
|
1832 |
=head2 C<ev_prepare> and C<ev_check> - customise your event loop! |
1833 |
|
1834 |
Prepare and check watchers are usually (but not always) used in tandem: |
1835 |
prepare watchers get invoked before the process blocks and check watchers |
1836 |
afterwards. |
1837 |
|
1838 |
You I<must not> call C<ev_loop> or similar functions that enter |
1839 |
the current event loop from either C<ev_prepare> or C<ev_check> |
1840 |
watchers. Other loops than the current one are fine, however. The |
1841 |
rationale behind this is that you do not need to check for recursion in |
1842 |
those watchers, i.e. the sequence will always be C<ev_prepare>, blocking, |
1843 |
C<ev_check> so if you have one watcher of each kind they will always be |
1844 |
called in pairs bracketing the blocking call. |
1845 |
|
1846 |
Their main purpose is to integrate other event mechanisms into libev and |
1847 |
their use is somewhat advanced. This could be used, for example, to track |
1848 |
variable changes, implement your own watchers, integrate net-snmp or a |
1849 |
coroutine library and lots more. They are also occasionally useful if |
1850 |
you cache some data and want to flush it before blocking (for example, |
1851 |
in X programs you might want to do an C<XFlush ()> in an C<ev_prepare> |
1852 |
watcher). |
1853 |
|
1854 |
This is done by examining in each prepare call which file descriptors need |
1855 |
to be watched by the other library, registering C<ev_io> watchers for |
1856 |
them and starting an C<ev_timer> watcher for any timeouts (many libraries |
1857 |
provide just this functionality). Then, in the check watcher you check for |
1858 |
any events that occured (by checking the pending status of all watchers |
1859 |
and stopping them) and call back into the library. The I/O and timer |
1860 |
callbacks will never actually be called (but must be valid nevertheless, |
1861 |
because you never know, you know?). |
1862 |
|
1863 |
As another example, the Perl Coro module uses these hooks to integrate |
1864 |
coroutines into libev programs, by yielding to other active coroutines |
1865 |
during each prepare and only letting the process block if no coroutines |
1866 |
are ready to run (it's actually more complicated: it only runs coroutines |
1867 |
with priority higher than or equal to the event loop and one coroutine |
1868 |
of lower priority, but only once, using idle watchers to keep the event |
1869 |
loop from blocking if lower-priority coroutines are active, thus mapping |
1870 |
low-priority coroutines to idle/background tasks). |
1871 |
|
1872 |
It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>) |
1873 |
priority, to ensure that they are being run before any other watchers |
1874 |
after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers, |
1875 |
too) should not activate ("feed") events into libev. While libev fully |
1876 |
supports this, they might get executed before other C<ev_check> watchers |
1877 |
did their job. As C<ev_check> watchers are often used to embed other |
1878 |
(non-libev) event loops those other event loops might be in an unusable |
1879 |
state until their C<ev_check> watcher ran (always remind yourself to |
1880 |
coexist peacefully with others). |
1881 |
|
1882 |
=head3 Watcher-Specific Functions and Data Members |
1883 |
|
1884 |
=over 4 |
1885 |
|
1886 |
=item ev_prepare_init (ev_prepare *, callback) |
1887 |
|
1888 |
=item ev_check_init (ev_check *, callback) |
1889 |
|
1890 |
Initialises and configures the prepare or check watcher - they have no |
1891 |
parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set> |
1892 |
macros, but using them is utterly, utterly and completely pointless. |
1893 |
|
1894 |
=back |
1895 |
|
1896 |
=head3 Examples |
1897 |
|
1898 |
There are a number of principal ways to embed other event loops or modules |
1899 |
into libev. Here are some ideas on how to include libadns into libev |
1900 |
(there is a Perl module named C<EV::ADNS> that does this, which you could |
1901 |
use as a working example. Another Perl module named C<EV::Glib> embeds a |
1902 |
Glib main context into libev, and finally, C<Glib::EV> embeds EV into the |
1903 |
Glib event loop). |
1904 |
|
1905 |
Method 1: Add IO watchers and a timeout watcher in a prepare handler, |
1906 |
and in a check watcher, destroy them and call into libadns. What follows |
1907 |
is pseudo-code only of course. This requires you to either use a low |
1908 |
priority for the check watcher or use C<ev_clear_pending> explicitly, as |
1909 |
the callbacks for the IO/timeout watchers might not have been called yet. |
1910 |
|
1911 |
static ev_io iow [nfd]; |
1912 |
static ev_timer tw; |
1913 |
|
1914 |
static void |
1915 |
io_cb (ev_loop *loop, ev_io *w, int revents) |
1916 |
{ |
1917 |
} |
1918 |
|
1919 |
// create io watchers for each fd and a timer before blocking |
1920 |
static void |
1921 |
adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) |
1922 |
{ |
1923 |
int timeout = 3600000; |
1924 |
struct pollfd fds [nfd]; |
1925 |
// actual code will need to loop here and realloc etc. |
1926 |
adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); |
1927 |
|
1928 |
/* the callback is illegal, but won't be called as we stop during check */ |
1929 |
ev_timer_init (&tw, 0, timeout * 1e-3); |
1930 |
ev_timer_start (loop, &tw); |
1931 |
|
1932 |
// create one ev_io per pollfd |
1933 |
for (int i = 0; i < nfd; ++i) |
1934 |
{ |
1935 |
ev_io_init (iow + i, io_cb, fds [i].fd, |
1936 |
((fds [i].events & POLLIN ? EV_READ : 0) |
1937 |
| (fds [i].events & POLLOUT ? EV_WRITE : 0))); |
1938 |
|
1939 |
fds [i].revents = 0; |
1940 |
ev_io_start (loop, iow + i); |
1941 |
} |
1942 |
} |
1943 |
|
1944 |
// stop all watchers after blocking |
1945 |
static void |
1946 |
adns_check_cb (ev_loop *loop, ev_check *w, int revents) |
1947 |
{ |
1948 |
ev_timer_stop (loop, &tw); |
1949 |
|
1950 |
for (int i = 0; i < nfd; ++i) |
1951 |
{ |
1952 |
// set the relevant poll flags |
1953 |
// could also call adns_processreadable etc. here |
1954 |
struct pollfd *fd = fds + i; |
1955 |
int revents = ev_clear_pending (iow + i); |
1956 |
if (revents & EV_READ ) fd->revents |= fd->events & POLLIN; |
1957 |
if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT; |
1958 |
|
1959 |
// now stop the watcher |
1960 |
ev_io_stop (loop, iow + i); |
1961 |
} |
1962 |
|
1963 |
adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); |
1964 |
} |
1965 |
|
1966 |
Method 2: This would be just like method 1, but you run C<adns_afterpoll> |
1967 |
in the prepare watcher and would dispose of the check watcher. |
1968 |
|
1969 |
Method 3: If the module to be embedded supports explicit event |
1970 |
notification (adns does), you can also make use of the actual watcher |
1971 |
callbacks, and only destroy/create the watchers in the prepare watcher. |
1972 |
|
1973 |
static void |
1974 |
timer_cb (EV_P_ ev_timer *w, int revents) |
1975 |
{ |
1976 |
adns_state ads = (adns_state)w->data; |
1977 |
update_now (EV_A); |
1978 |
|
1979 |
adns_processtimeouts (ads, &tv_now); |
1980 |
} |
1981 |
|
1982 |
static void |
1983 |
io_cb (EV_P_ ev_io *w, int revents) |
1984 |
{ |
1985 |
adns_state ads = (adns_state)w->data; |
1986 |
update_now (EV_A); |
1987 |
|
1988 |
if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now); |
1989 |
if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now); |
1990 |
} |
1991 |
|
1992 |
// do not ever call adns_afterpoll |
1993 |
|
1994 |
Method 4: Do not use a prepare or check watcher because the module you |
1995 |
want to embed is too inflexible to support it. Instead, youc na override |
1996 |
their poll function. The drawback with this solution is that the main |
1997 |
loop is now no longer controllable by EV. The C<Glib::EV> module does |
1998 |
this. |
1999 |
|
2000 |
static gint |
2001 |
event_poll_func (GPollFD *fds, guint nfds, gint timeout) |
2002 |
{ |
2003 |
int got_events = 0; |
2004 |
|
2005 |
for (n = 0; n < nfds; ++n) |
2006 |
// create/start io watcher that sets the relevant bits in fds[n] and increment got_events |
2007 |
|
2008 |
if (timeout >= 0) |
2009 |
// create/start timer |
2010 |
|
2011 |
// poll |
2012 |
ev_loop (EV_A_ 0); |
2013 |
|
2014 |
// stop timer again |
2015 |
if (timeout >= 0) |
2016 |
ev_timer_stop (EV_A_ &to); |
2017 |
|
2018 |
// stop io watchers again - their callbacks should have set |
2019 |
for (n = 0; n < nfds; ++n) |
2020 |
ev_io_stop (EV_A_ iow [n]); |
2021 |
|
2022 |
return got_events; |
2023 |
} |
2024 |
|
2025 |
|
2026 |
=head2 C<ev_embed> - when one backend isn't enough... |
2027 |
|
2028 |
This is a rather advanced watcher type that lets you embed one event loop |
2029 |
into another (currently only C<ev_io> events are supported in the embedded |
2030 |
loop, other types of watchers might be handled in a delayed or incorrect |
2031 |
fashion and must not be used). |
2032 |
|
2033 |
There are primarily two reasons you would want that: work around bugs and |
2034 |
prioritise I/O. |
2035 |
|
2036 |
As an example for a bug workaround, the kqueue backend might only support |
2037 |
sockets on some platform, so it is unusable as generic backend, but you |
2038 |
still want to make use of it because you have many sockets and it scales |
2039 |
so nicely. In this case, you would create a kqueue-based loop and embed it |
2040 |
into your default loop (which might use e.g. poll). Overall operation will |
2041 |
be a bit slower because first libev has to poll and then call kevent, but |
2042 |
at least you can use both at what they are best. |
2043 |
|
2044 |
As for prioritising I/O: rarely you have the case where some fds have |
2045 |
to be watched and handled very quickly (with low latency), and even |
2046 |
priorities and idle watchers might have too much overhead. In this case |
2047 |
you would put all the high priority stuff in one loop and all the rest in |
2048 |
a second one, and embed the second one in the first. |
2049 |
|
2050 |
As long as the watcher is active, the callback will be invoked every time |
2051 |
there might be events pending in the embedded loop. The callback must then |
2052 |
call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke |
2053 |
their callbacks (you could also start an idle watcher to give the embedded |
2054 |
loop strictly lower priority for example). You can also set the callback |
2055 |
to C<0>, in which case the embed watcher will automatically execute the |
2056 |
embedded loop sweep. |
2057 |
|
2058 |
As long as the watcher is started it will automatically handle events. The |
2059 |
callback will be invoked whenever some events have been handled. You can |
2060 |
set the callback to C<0> to avoid having to specify one if you are not |
2061 |
interested in that. |
2062 |
|
2063 |
Also, there have not currently been made special provisions for forking: |
2064 |
when you fork, you not only have to call C<ev_loop_fork> on both loops, |
2065 |
but you will also have to stop and restart any C<ev_embed> watchers |
2066 |
yourself. |
2067 |
|
2068 |
Unfortunately, not all backends are embeddable, only the ones returned by |
2069 |
C<ev_embeddable_backends> are, which, unfortunately, does not include any |
2070 |
portable one. |
2071 |
|
2072 |
So when you want to use this feature you will always have to be prepared |
2073 |
that you cannot get an embeddable loop. The recommended way to get around |
2074 |
this is to have a separate variables for your embeddable loop, try to |
2075 |
create it, and if that fails, use the normal loop for everything. |
2076 |
|
2077 |
=head3 Watcher-Specific Functions and Data Members |
2078 |
|
2079 |
=over 4 |
2080 |
|
2081 |
=item ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop) |
2082 |
|
2083 |
=item ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop) |
2084 |
|
2085 |
Configures the watcher to embed the given loop, which must be |
2086 |
embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be |
2087 |
invoked automatically, otherwise it is the responsibility of the callback |
2088 |
to invoke it (it will continue to be called until the sweep has been done, |
2089 |
if you do not want thta, you need to temporarily stop the embed watcher). |
2090 |
|
2091 |
=item ev_embed_sweep (loop, ev_embed *) |
2092 |
|
2093 |
Make a single, non-blocking sweep over the embedded loop. This works |
2094 |
similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most |
2095 |
apropriate way for embedded loops. |
2096 |
|
2097 |
=item struct ev_loop *other [read-only] |
2098 |
|
2099 |
The embedded event loop. |
2100 |
|
2101 |
=back |
2102 |
|
2103 |
=head3 Examples |
2104 |
|
2105 |
Example: Try to get an embeddable event loop and embed it into the default |
2106 |
event loop. If that is not possible, use the default loop. The default |
2107 |
loop is stored in C<loop_hi>, while the mebeddable loop is stored in |
2108 |
C<loop_lo> (which is C<loop_hi> in the acse no embeddable loop can be |
2109 |
used). |
2110 |
|
2111 |
struct ev_loop *loop_hi = ev_default_init (0); |
2112 |
struct ev_loop *loop_lo = 0; |
2113 |
struct ev_embed embed; |
2114 |
|
2115 |
// see if there is a chance of getting one that works |
2116 |
// (remember that a flags value of 0 means autodetection) |
2117 |
loop_lo = ev_embeddable_backends () & ev_recommended_backends () |
2118 |
? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) |
2119 |
: 0; |
2120 |
|
2121 |
// if we got one, then embed it, otherwise default to loop_hi |
2122 |
if (loop_lo) |
2123 |
{ |
2124 |
ev_embed_init (&embed, 0, loop_lo); |
2125 |
ev_embed_start (loop_hi, &embed); |
2126 |
} |
2127 |
else |
2128 |
loop_lo = loop_hi; |
2129 |
|
2130 |
Example: Check if kqueue is available but not recommended and create |
2131 |
a kqueue backend for use with sockets (which usually work with any |
2132 |
kqueue implementation). Store the kqueue/socket-only event loop in |
2133 |
C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too). |
2134 |
|
2135 |
struct ev_loop *loop = ev_default_init (0); |
2136 |
struct ev_loop *loop_socket = 0; |
2137 |
struct ev_embed embed; |
2138 |
|
2139 |
if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE) |
2140 |
if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE)) |
2141 |
{ |
2142 |
ev_embed_init (&embed, 0, loop_socket); |
2143 |
ev_embed_start (loop, &embed); |
2144 |
} |
2145 |
|
2146 |
if (!loop_socket) |
2147 |
loop_socket = loop; |
2148 |
|
2149 |
// now use loop_socket for all sockets, and loop for everything else |
2150 |
|
2151 |
|
2152 |
=head2 C<ev_fork> - the audacity to resume the event loop after a fork |
2153 |
|
2154 |
Fork watchers are called when a C<fork ()> was detected (usually because |
2155 |
whoever is a good citizen cared to tell libev about it by calling |
2156 |
C<ev_default_fork> or C<ev_loop_fork>). The invocation is done before the |
2157 |
event loop blocks next and before C<ev_check> watchers are being called, |
2158 |
and only in the child after the fork. If whoever good citizen calling |
2159 |
C<ev_default_fork> cheats and calls it in the wrong process, the fork |
2160 |
handlers will be invoked, too, of course. |
2161 |
|
2162 |
=head3 Watcher-Specific Functions and Data Members |
2163 |
|
2164 |
=over 4 |
2165 |
|
2166 |
=item ev_fork_init (ev_signal *, callback) |
2167 |
|
2168 |
Initialises and configures the fork watcher - it has no parameters of any |
2169 |
kind. There is a C<ev_fork_set> macro, but using it is utterly pointless, |
2170 |
believe me. |
2171 |
|
2172 |
=back |
2173 |
|
2174 |
|
2175 |
=head2 C<ev_async> - how to wake up another event loop |
2176 |
|
2177 |
In general, you cannot use an C<ev_loop> from multiple threads or other |
2178 |
asynchronous sources such as signal handlers (as opposed to multiple event |
2179 |
loops - those are of course safe to use in different threads). |
2180 |
|
2181 |
Sometimes, however, you need to wake up another event loop you do not |
2182 |
control, for example because it belongs to another thread. This is what |
2183 |
C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you |
2184 |
can signal it by calling C<ev_async_send>, which is thread- and signal |
2185 |
safe. |
2186 |
|
2187 |
This functionality is very similar to C<ev_signal> watchers, as signals, |
2188 |
too, are asynchronous in nature, and signals, too, will be compressed |
2189 |
(i.e. the number of callback invocations may be less than the number of |
2190 |
C<ev_async_sent> calls). |
2191 |
|
2192 |
Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not |
2193 |
just the default loop. |
2194 |
|
2195 |
=head3 Queueing |
2196 |
|
2197 |
C<ev_async> does not support queueing of data in any way. The reason |
2198 |
is that the author does not know of a simple (or any) algorithm for a |
2199 |
multiple-writer-single-reader queue that works in all cases and doesn't |
2200 |
need elaborate support such as pthreads. |
2201 |
|
2202 |
That means that if you want to queue data, you have to provide your own |
2203 |
queue. But at least I can tell you would implement locking around your |
2204 |
queue: |
2205 |
|
2206 |
=over 4 |
2207 |
|
2208 |
=item queueing from a signal handler context |
2209 |
|
2210 |
To implement race-free queueing, you simply add to the queue in the signal |
2211 |
handler but you block the signal handler in the watcher callback. Here is an example that does that for |
2212 |
some fictitiuous SIGUSR1 handler: |
2213 |
|
2214 |
static ev_async mysig; |
2215 |
|
2216 |
static void |
2217 |
sigusr1_handler (void) |
2218 |
{ |
2219 |
sometype data; |
2220 |
|
2221 |
// no locking etc. |
2222 |
queue_put (data); |
2223 |
ev_async_send (EV_DEFAULT_ &mysig); |
2224 |
} |
2225 |
|
2226 |
static void |
2227 |
mysig_cb (EV_P_ ev_async *w, int revents) |
2228 |
{ |
2229 |
sometype data; |
2230 |
sigset_t block, prev; |
2231 |
|
2232 |
sigemptyset (&block); |
2233 |
sigaddset (&block, SIGUSR1); |
2234 |
sigprocmask (SIG_BLOCK, &block, &prev); |
2235 |
|
2236 |
while (queue_get (&data)) |
2237 |
process (data); |
2238 |
|
2239 |
if (sigismember (&prev, SIGUSR1) |
2240 |
sigprocmask (SIG_UNBLOCK, &block, 0); |
2241 |
} |
2242 |
|
2243 |
(Note: pthreads in theory requires you to use C<pthread_setmask> |
2244 |
instead of C<sigprocmask> when you use threads, but libev doesn't do it |
2245 |
either...). |
2246 |
|
2247 |
=item queueing from a thread context |
2248 |
|
2249 |
The strategy for threads is different, as you cannot (easily) block |
2250 |
threads but you can easily preempt them, so to queue safely you need to |
2251 |
employ a traditional mutex lock, such as in this pthread example: |
2252 |
|
2253 |
static ev_async mysig; |
2254 |
static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER; |
2255 |
|
2256 |
static void |
2257 |
otherthread (void) |
2258 |
{ |
2259 |
// only need to lock the actual queueing operation |
2260 |
pthread_mutex_lock (&mymutex); |
2261 |
queue_put (data); |
2262 |
pthread_mutex_unlock (&mymutex); |
2263 |
|
2264 |
ev_async_send (EV_DEFAULT_ &mysig); |
2265 |
} |
2266 |
|
2267 |
static void |
2268 |
mysig_cb (EV_P_ ev_async *w, int revents) |
2269 |
{ |
2270 |
pthread_mutex_lock (&mymutex); |
2271 |
|
2272 |
while (queue_get (&data)) |
2273 |
process (data); |
2274 |
|
2275 |
pthread_mutex_unlock (&mymutex); |
2276 |
} |
2277 |
|
2278 |
=back |
2279 |
|
2280 |
|
2281 |
=head3 Watcher-Specific Functions and Data Members |
2282 |
|
2283 |
=over 4 |
2284 |
|
2285 |
=item ev_async_init (ev_async *, callback) |
2286 |
|
2287 |
Initialises and configures the async watcher - it has no parameters of any |
2288 |
kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless, |
2289 |
believe me. |
2290 |
|
2291 |
=item ev_async_send (loop, ev_async *) |
2292 |
|
2293 |
Sends/signals/activates the given C<ev_async> watcher, that is, feeds |
2294 |
an C<EV_ASYNC> event on the watcher into the event loop. Unlike |
2295 |
C<ev_feed_event>, this call is safe to do in other threads, signal or |
2296 |
similar contexts (see the dicusssion of C<EV_ATOMIC_T> in the embedding |
2297 |
section below on what exactly this means). |
2298 |
|
2299 |
This call incurs the overhead of a syscall only once per loop iteration, |
2300 |
so while the overhead might be noticable, it doesn't apply to repeated |
2301 |
calls to C<ev_async_send>. |
2302 |
|
2303 |
=item bool = ev_async_pending (ev_async *) |
2304 |
|
2305 |
Returns a non-zero value when C<ev_async_send> has been called on the |
2306 |
watcher but the event has not yet been processed (or even noted) by the |
2307 |
event loop. |
2308 |
|
2309 |
C<ev_async_send> sets a flag in the watcher and wakes up the loop. When |
2310 |
the loop iterates next and checks for the watcher to have become active, |
2311 |
it will reset the flag again. C<ev_async_pending> can be used to very |
2312 |
quickly check wether invoking the loop might be a good idea. |
2313 |
|
2314 |
Not that this does I<not> check wether the watcher itself is pending, only |
2315 |
wether it has been requested to make this watcher pending. |
2316 |
|
2317 |
=back |
2318 |
|
2319 |
|
2320 |
=head1 OTHER FUNCTIONS |
2321 |
|
2322 |
There are some other functions of possible interest. Described. Here. Now. |
2323 |
|
2324 |
=over 4 |
2325 |
|
2326 |
=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback) |
2327 |
|
2328 |
This function combines a simple timer and an I/O watcher, calls your |
2329 |
callback on whichever event happens first and automatically stop both |
2330 |
watchers. This is useful if you want to wait for a single event on an fd |
2331 |
or timeout without having to allocate/configure/start/stop/free one or |
2332 |
more watchers yourself. |
2333 |
|
2334 |
If C<fd> is less than 0, then no I/O watcher will be started and events |
2335 |
is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and |
2336 |
C<events> set will be craeted and started. |
2337 |
|
2338 |
If C<timeout> is less than 0, then no timeout watcher will be |
2339 |
started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and |
2340 |
repeat = 0) will be started. While C<0> is a valid timeout, it is of |
2341 |
dubious value. |
2342 |
|
2343 |
The callback has the type C<void (*cb)(int revents, void *arg)> and gets |
2344 |
passed an C<revents> set like normal event callbacks (a combination of |
2345 |
C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg> |
2346 |
value passed to C<ev_once>: |
2347 |
|
2348 |
static void stdin_ready (int revents, void *arg) |
2349 |
{ |
2350 |
if (revents & EV_TIMEOUT) |
2351 |
/* doh, nothing entered */; |
2352 |
else if (revents & EV_READ) |
2353 |
/* stdin might have data for us, joy! */; |
2354 |
} |
2355 |
|
2356 |
ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); |
2357 |
|
2358 |
=item ev_feed_event (ev_loop *, watcher *, int revents) |
2359 |
|
2360 |
Feeds the given event set into the event loop, as if the specified event |
2361 |
had happened for the specified watcher (which must be a pointer to an |
2362 |
initialised but not necessarily started event watcher). |
2363 |
|
2364 |
=item ev_feed_fd_event (ev_loop *, int fd, int revents) |
2365 |
|
2366 |
Feed an event on the given fd, as if a file descriptor backend detected |
2367 |
the given events it. |
2368 |
|
2369 |
=item ev_feed_signal_event (ev_loop *loop, int signum) |
2370 |
|
2371 |
Feed an event as if the given signal occured (C<loop> must be the default |
2372 |
loop!). |
2373 |
|
2374 |
=back |
2375 |
|
2376 |
|
2377 |
=head1 LIBEVENT EMULATION |
2378 |
|
2379 |
Libev offers a compatibility emulation layer for libevent. It cannot |
2380 |
emulate the internals of libevent, so here are some usage hints: |
2381 |
|
2382 |
=over 4 |
2383 |
|
2384 |
=item * Use it by including <event.h>, as usual. |
2385 |
|
2386 |
=item * The following members are fully supported: ev_base, ev_callback, |
2387 |
ev_arg, ev_fd, ev_res, ev_events. |
2388 |
|
2389 |
=item * Avoid using ev_flags and the EVLIST_*-macros, while it is |
2390 |
maintained by libev, it does not work exactly the same way as in libevent (consider |
2391 |
it a private API). |
2392 |
|
2393 |
=item * Priorities are not currently supported. Initialising priorities |
2394 |
will fail and all watchers will have the same priority, even though there |
2395 |
is an ev_pri field. |
2396 |
|
2397 |
=item * In libevent, the last base created gets the signals, in libev, the |
2398 |
first base created (== the default loop) gets the signals. |
2399 |
|
2400 |
=item * Other members are not supported. |
2401 |
|
2402 |
=item * The libev emulation is I<not> ABI compatible to libevent, you need |
2403 |
to use the libev header file and library. |
2404 |
|
2405 |
=back |
2406 |
|
2407 |
=head1 C++ SUPPORT |
2408 |
|
2409 |
Libev comes with some simplistic wrapper classes for C++ that mainly allow |
2410 |
you to use some convinience methods to start/stop watchers and also change |
2411 |
the callback model to a model using method callbacks on objects. |
2412 |
|
2413 |
To use it, |
2414 |
|
2415 |
#include <ev++.h> |
2416 |
|
2417 |
This automatically includes F<ev.h> and puts all of its definitions (many |
2418 |
of them macros) into the global namespace. All C++ specific things are |
2419 |
put into the C<ev> namespace. It should support all the same embedding |
2420 |
options as F<ev.h>, most notably C<EV_MULTIPLICITY>. |
2421 |
|
2422 |
Care has been taken to keep the overhead low. The only data member the C++ |
2423 |
classes add (compared to plain C-style watchers) is the event loop pointer |
2424 |
that the watcher is associated with (or no additional members at all if |
2425 |
you disable C<EV_MULTIPLICITY> when embedding libev). |
2426 |
|
2427 |
Currently, functions, and static and non-static member functions can be |
2428 |
used as callbacks. Other types should be easy to add as long as they only |
2429 |
need one additional pointer for context. If you need support for other |
2430 |
types of functors please contact the author (preferably after implementing |
2431 |
it). |
2432 |
|
2433 |
Here is a list of things available in the C<ev> namespace: |
2434 |
|
2435 |
=over 4 |
2436 |
|
2437 |
=item C<ev::READ>, C<ev::WRITE> etc. |
2438 |
|
2439 |
These are just enum values with the same values as the C<EV_READ> etc. |
2440 |
macros from F<ev.h>. |
2441 |
|
2442 |
=item C<ev::tstamp>, C<ev::now> |
2443 |
|
2444 |
Aliases to the same types/functions as with the C<ev_> prefix. |
2445 |
|
2446 |
=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc. |
2447 |
|
2448 |
For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of |
2449 |
the same name in the C<ev> namespace, with the exception of C<ev_signal> |
2450 |
which is called C<ev::sig> to avoid clashes with the C<signal> macro |
2451 |
defines by many implementations. |
2452 |
|
2453 |
All of those classes have these methods: |
2454 |
|
2455 |
=over 4 |
2456 |
|
2457 |
=item ev::TYPE::TYPE () |
2458 |
|
2459 |
=item ev::TYPE::TYPE (struct ev_loop *) |
2460 |
|
2461 |
=item ev::TYPE::~TYPE |
2462 |
|
2463 |
The constructor (optionally) takes an event loop to associate the watcher |
2464 |
with. If it is omitted, it will use C<EV_DEFAULT>. |
2465 |
|
2466 |
The constructor calls C<ev_init> for you, which means you have to call the |
2467 |
C<set> method before starting it. |
2468 |
|
2469 |
It will not set a callback, however: You have to call the templated C<set> |
2470 |
method to set a callback before you can start the watcher. |
2471 |
|
2472 |
(The reason why you have to use a method is a limitation in C++ which does |
2473 |
not allow explicit template arguments for constructors). |
2474 |
|
2475 |
The destructor automatically stops the watcher if it is active. |
2476 |
|
2477 |
=item w->set<class, &class::method> (object *) |
2478 |
|
2479 |
This method sets the callback method to call. The method has to have a |
2480 |
signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as |
2481 |
first argument and the C<revents> as second. The object must be given as |
2482 |
parameter and is stored in the C<data> member of the watcher. |
2483 |
|
2484 |
This method synthesizes efficient thunking code to call your method from |
2485 |
the C callback that libev requires. If your compiler can inline your |
2486 |
callback (i.e. it is visible to it at the place of the C<set> call and |
2487 |
your compiler is good :), then the method will be fully inlined into the |
2488 |
thunking function, making it as fast as a direct C callback. |
2489 |
|
2490 |
Example: simple class declaration and watcher initialisation |
2491 |
|
2492 |
struct myclass |
2493 |
{ |
2494 |
void io_cb (ev::io &w, int revents) { } |
2495 |
} |
2496 |
|
2497 |
myclass obj; |
2498 |
ev::io iow; |
2499 |
iow.set <myclass, &myclass::io_cb> (&obj); |
2500 |
|
2501 |
=item w->set<function> (void *data = 0) |
2502 |
|
2503 |
Also sets a callback, but uses a static method or plain function as |
2504 |
callback. The optional C<data> argument will be stored in the watcher's |
2505 |
C<data> member and is free for you to use. |
2506 |
|
2507 |
The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>. |
2508 |
|
2509 |
See the method-C<set> above for more details. |
2510 |
|
2511 |
Example: |
2512 |
|
2513 |
static void io_cb (ev::io &w, int revents) { } |
2514 |
iow.set <io_cb> (); |
2515 |
|
2516 |
=item w->set (struct ev_loop *) |
2517 |
|
2518 |
Associates a different C<struct ev_loop> with this watcher. You can only |
2519 |
do this when the watcher is inactive (and not pending either). |
2520 |
|
2521 |
=item w->set ([args]) |
2522 |
|
2523 |
Basically the same as C<ev_TYPE_set>, with the same args. Must be |
2524 |
called at least once. Unlike the C counterpart, an active watcher gets |
2525 |
automatically stopped and restarted when reconfiguring it with this |
2526 |
method. |
2527 |
|
2528 |
=item w->start () |
2529 |
|
2530 |
Starts the watcher. Note that there is no C<loop> argument, as the |
2531 |
constructor already stores the event loop. |
2532 |
|
2533 |
=item w->stop () |
2534 |
|
2535 |
Stops the watcher if it is active. Again, no C<loop> argument. |
2536 |
|
2537 |
=item w->again () (C<ev::timer>, C<ev::periodic> only) |
2538 |
|
2539 |
For C<ev::timer> and C<ev::periodic>, this invokes the corresponding |
2540 |
C<ev_TYPE_again> function. |
2541 |
|
2542 |
=item w->sweep () (C<ev::embed> only) |
2543 |
|
2544 |
Invokes C<ev_embed_sweep>. |
2545 |
|
2546 |
=item w->update () (C<ev::stat> only) |
2547 |
|
2548 |
Invokes C<ev_stat_stat>. |
2549 |
|
2550 |
=back |
2551 |
|
2552 |
=back |
2553 |
|
2554 |
Example: Define a class with an IO and idle watcher, start one of them in |
2555 |
the constructor. |
2556 |
|
2557 |
class myclass |
2558 |
{ |
2559 |
ev::io io; void io_cb (ev::io &w, int revents); |
2560 |
ev:idle idle void idle_cb (ev::idle &w, int revents); |
2561 |
|
2562 |
myclass (int fd) |
2563 |
{ |
2564 |
io .set <myclass, &myclass::io_cb > (this); |
2565 |
idle.set <myclass, &myclass::idle_cb> (this); |
2566 |
|
2567 |
io.start (fd, ev::READ); |
2568 |
} |
2569 |
}; |
2570 |
|
2571 |
|
2572 |
=head1 OTHER LANGUAGE BINDINGS |
2573 |
|
2574 |
Libev does not offer other language bindings itself, but bindings for a |
2575 |
numbe rof languages exist in the form of third-party packages. If you know |
2576 |
any interesting language binding in addition to the ones listed here, drop |
2577 |
me a note. |
2578 |
|
2579 |
=over 4 |
2580 |
|
2581 |
=item Perl |
2582 |
|
2583 |
The EV module implements the full libev API and is actually used to test |
2584 |
libev. EV is developed together with libev. Apart from the EV core module, |
2585 |
there are additional modules that implement libev-compatible interfaces |
2586 |
to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the |
2587 |
C<libglib> event core (C<Glib::EV> and C<EV::Glib>). |
2588 |
|
2589 |
It can be found and installed via CPAN, its homepage is found at |
2590 |
L<http://software.schmorp.de/pkg/EV>. |
2591 |
|
2592 |
=item Ruby |
2593 |
|
2594 |
Tony Arcieri has written a ruby extension that offers access to a subset |
2595 |
of the libev API and adds filehandle abstractions, asynchronous DNS and |
2596 |
more on top of it. It can be found via gem servers. Its homepage is at |
2597 |
L<http://rev.rubyforge.org/>. |
2598 |
|
2599 |
=item D |
2600 |
|
2601 |
Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
2602 |
be found at L<http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>. |
2603 |
|
2604 |
=back |
2605 |
|
2606 |
|
2607 |
=head1 MACRO MAGIC |
2608 |
|
2609 |
Libev can be compiled with a variety of options, the most fundamantal |
2610 |
of which is C<EV_MULTIPLICITY>. This option determines whether (most) |
2611 |
functions and callbacks have an initial C<struct ev_loop *> argument. |
2612 |
|
2613 |
To make it easier to write programs that cope with either variant, the |
2614 |
following macros are defined: |
2615 |
|
2616 |
=over 4 |
2617 |
|
2618 |
=item C<EV_A>, C<EV_A_> |
2619 |
|
2620 |
This provides the loop I<argument> for functions, if one is required ("ev |
2621 |
loop argument"). The C<EV_A> form is used when this is the sole argument, |
2622 |
C<EV_A_> is used when other arguments are following. Example: |
2623 |
|
2624 |
ev_unref (EV_A); |
2625 |
ev_timer_add (EV_A_ watcher); |
2626 |
ev_loop (EV_A_ 0); |
2627 |
|
2628 |
It assumes the variable C<loop> of type C<struct ev_loop *> is in scope, |
2629 |
which is often provided by the following macro. |
2630 |
|
2631 |
=item C<EV_P>, C<EV_P_> |
2632 |
|
2633 |
This provides the loop I<parameter> for functions, if one is required ("ev |
2634 |
loop parameter"). The C<EV_P> form is used when this is the sole parameter, |
2635 |
C<EV_P_> is used when other parameters are following. Example: |
2636 |
|
2637 |
// this is how ev_unref is being declared |
2638 |
static void ev_unref (EV_P); |
2639 |
|
2640 |
// this is how you can declare your typical callback |
2641 |
static void cb (EV_P_ ev_timer *w, int revents) |
2642 |
|
2643 |
It declares a parameter C<loop> of type C<struct ev_loop *>, quite |
2644 |
suitable for use with C<EV_A>. |
2645 |
|
2646 |
=item C<EV_DEFAULT>, C<EV_DEFAULT_> |
2647 |
|
2648 |
Similar to the other two macros, this gives you the value of the default |
2649 |
loop, if multiple loops are supported ("ev loop default"). |
2650 |
|
2651 |
=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_> |
2652 |
|
2653 |
Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the |
2654 |
default loop has been initialised (C<UC> == unchecked). Their behaviour |
2655 |
is undefined when the default loop has not been initialised by a previous |
2656 |
execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>. |
2657 |
|
2658 |
It is often prudent to use C<EV_DEFAULT> when initialising the first |
2659 |
watcher in a function but use C<EV_DEFAULT_UC> afterwards. |
2660 |
|
2661 |
=back |
2662 |
|
2663 |
Example: Declare and initialise a check watcher, utilising the above |
2664 |
macros so it will work regardless of whether multiple loops are supported |
2665 |
or not. |
2666 |
|
2667 |
static void |
2668 |
check_cb (EV_P_ ev_timer *w, int revents) |
2669 |
{ |
2670 |
ev_check_stop (EV_A_ w); |
2671 |
} |
2672 |
|
2673 |
ev_check check; |
2674 |
ev_check_init (&check, check_cb); |
2675 |
ev_check_start (EV_DEFAULT_ &check); |
2676 |
ev_loop (EV_DEFAULT_ 0); |
2677 |
|
2678 |
=head1 EMBEDDING |
2679 |
|
2680 |
Libev can (and often is) directly embedded into host |
2681 |
applications. Examples of applications that embed it include the Deliantra |
2682 |
Game Server, the EV perl module, the GNU Virtual Private Ethernet (gvpe) |
2683 |
and rxvt-unicode. |
2684 |
|
2685 |
The goal is to enable you to just copy the necessary files into your |
2686 |
source directory without having to change even a single line in them, so |
2687 |
you can easily upgrade by simply copying (or having a checked-out copy of |
2688 |
libev somewhere in your source tree). |
2689 |
|
2690 |
=head2 FILESETS |
2691 |
|
2692 |
Depending on what features you need you need to include one or more sets of files |
2693 |
in your app. |
2694 |
|
2695 |
=head3 CORE EVENT LOOP |
2696 |
|
2697 |
To include only the libev core (all the C<ev_*> functions), with manual |
2698 |
configuration (no autoconf): |
2699 |
|
2700 |
#define EV_STANDALONE 1 |
2701 |
#include "ev.c" |
2702 |
|
2703 |
This will automatically include F<ev.h>, too, and should be done in a |
2704 |
single C source file only to provide the function implementations. To use |
2705 |
it, do the same for F<ev.h> in all files wishing to use this API (best |
2706 |
done by writing a wrapper around F<ev.h> that you can include instead and |
2707 |
where you can put other configuration options): |
2708 |
|
2709 |
#define EV_STANDALONE 1 |
2710 |
#include "ev.h" |
2711 |
|
2712 |
Both header files and implementation files can be compiled with a C++ |
2713 |
compiler (at least, thats a stated goal, and breakage will be treated |
2714 |
as a bug). |
2715 |
|
2716 |
You need the following files in your source tree, or in a directory |
2717 |
in your include path (e.g. in libev/ when using -Ilibev): |
2718 |
|
2719 |
ev.h |
2720 |
ev.c |
2721 |
ev_vars.h |
2722 |
ev_wrap.h |
2723 |
|
2724 |
ev_win32.c required on win32 platforms only |
2725 |
|
2726 |
ev_select.c only when select backend is enabled (which is enabled by default) |
2727 |
ev_poll.c only when poll backend is enabled (disabled by default) |
2728 |
ev_epoll.c only when the epoll backend is enabled (disabled by default) |
2729 |
ev_kqueue.c only when the kqueue backend is enabled (disabled by default) |
2730 |
ev_port.c only when the solaris port backend is enabled (disabled by default) |
2731 |
|
2732 |
F<ev.c> includes the backend files directly when enabled, so you only need |
2733 |
to compile this single file. |
2734 |
|
2735 |
=head3 LIBEVENT COMPATIBILITY API |
2736 |
|
2737 |
To include the libevent compatibility API, also include: |
2738 |
|
2739 |
#include "event.c" |
2740 |
|
2741 |
in the file including F<ev.c>, and: |
2742 |
|
2743 |
#include "event.h" |
2744 |
|
2745 |
in the files that want to use the libevent API. This also includes F<ev.h>. |
2746 |
|
2747 |
You need the following additional files for this: |
2748 |
|
2749 |
event.h |
2750 |
event.c |
2751 |
|
2752 |
=head3 AUTOCONF SUPPORT |
2753 |
|
2754 |
Instead of using C<EV_STANDALONE=1> and providing your config in |
2755 |
whatever way you want, you can also C<m4_include([libev.m4])> in your |
2756 |
F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then |
2757 |
include F<config.h> and configure itself accordingly. |
2758 |
|
2759 |
For this of course you need the m4 file: |
2760 |
|
2761 |
libev.m4 |
2762 |
|
2763 |
=head2 PREPROCESSOR SYMBOLS/MACROS |
2764 |
|
2765 |
Libev can be configured via a variety of preprocessor symbols you have to |
2766 |
define before including any of its files. The default in the absense of |
2767 |
autoconf is noted for every option. |
2768 |
|
2769 |
=over 4 |
2770 |
|
2771 |
=item EV_STANDALONE |
2772 |
|
2773 |
Must always be C<1> if you do not use autoconf configuration, which |
2774 |
keeps libev from including F<config.h>, and it also defines dummy |
2775 |
implementations for some libevent functions (such as logging, which is not |
2776 |
supported). It will also not define any of the structs usually found in |
2777 |
F<event.h> that are not directly supported by the libev core alone. |
2778 |
|
2779 |
=item EV_USE_MONOTONIC |
2780 |
|
2781 |
If defined to be C<1>, libev will try to detect the availability of the |
2782 |
monotonic clock option at both compiletime and runtime. Otherwise no use |
2783 |
of the monotonic clock option will be attempted. If you enable this, you |
2784 |
usually have to link against librt or something similar. Enabling it when |
2785 |
the functionality isn't available is safe, though, although you have |
2786 |
to make sure you link against any libraries where the C<clock_gettime> |
2787 |
function is hiding in (often F<-lrt>). |
2788 |
|
2789 |
=item EV_USE_REALTIME |
2790 |
|
2791 |
If defined to be C<1>, libev will try to detect the availability of the |
2792 |
realtime clock option at compiletime (and assume its availability at |
2793 |
runtime if successful). Otherwise no use of the realtime clock option will |
2794 |
be attempted. This effectively replaces C<gettimeofday> by C<clock_get |
2795 |
(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the |
2796 |
note about libraries in the description of C<EV_USE_MONOTONIC>, though. |
2797 |
|
2798 |
=item EV_USE_NANOSLEEP |
2799 |
|
2800 |
If defined to be C<1>, libev will assume that C<nanosleep ()> is available |
2801 |
and will use it for delays. Otherwise it will use C<select ()>. |
2802 |
|
2803 |
=item EV_USE_EVENTFD |
2804 |
|
2805 |
If defined to be C<1>, then libev will assume that C<eventfd ()> is |
2806 |
available and will probe for kernel support at runtime. This will improve |
2807 |
C<ev_signal> and C<ev_async> performance and reduce resource consumption. |
2808 |
If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc |
2809 |
2.7 or newer, otherwise disabled. |
2810 |
|
2811 |
=item EV_USE_SELECT |
2812 |
|
2813 |
If undefined or defined to be C<1>, libev will compile in support for the |
2814 |
C<select>(2) backend. No attempt at autodetection will be done: if no |
2815 |
other method takes over, select will be it. Otherwise the select backend |
2816 |
will not be compiled in. |
2817 |
|
2818 |
=item EV_SELECT_USE_FD_SET |
2819 |
|
2820 |
If defined to C<1>, then the select backend will use the system C<fd_set> |
2821 |
structure. This is useful if libev doesn't compile due to a missing |
2822 |
C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on |
2823 |
exotic systems. This usually limits the range of file descriptors to some |
2824 |
low limit such as 1024 or might have other limitations (winsocket only |
2825 |
allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might |
2826 |
influence the size of the C<fd_set> used. |
2827 |
|
2828 |
=item EV_SELECT_IS_WINSOCKET |
2829 |
|
2830 |
When defined to C<1>, the select backend will assume that |
2831 |
select/socket/connect etc. don't understand file descriptors but |
2832 |
wants osf handles on win32 (this is the case when the select to |
2833 |
be used is the winsock select). This means that it will call |
2834 |
C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise, |
2835 |
it is assumed that all these functions actually work on fds, even |
2836 |
on win32. Should not be defined on non-win32 platforms. |
2837 |
|
2838 |
=item EV_FD_TO_WIN32_HANDLE |
2839 |
|
2840 |
If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map |
2841 |
file descriptors to socket handles. When not defining this symbol (the |
2842 |
default), then libev will call C<_get_osfhandle>, which is usually |
2843 |
correct. In some cases, programs use their own file descriptor management, |
2844 |
in which case they can provide this function to map fds to socket handles. |
2845 |
|
2846 |
=item EV_USE_POLL |
2847 |
|
2848 |
If defined to be C<1>, libev will compile in support for the C<poll>(2) |
2849 |
backend. Otherwise it will be enabled on non-win32 platforms. It |
2850 |
takes precedence over select. |
2851 |
|
2852 |
=item EV_USE_EPOLL |
2853 |
|
2854 |
If defined to be C<1>, libev will compile in support for the Linux |
2855 |
C<epoll>(7) backend. Its availability will be detected at runtime, |
2856 |
otherwise another method will be used as fallback. This is the preferred |
2857 |
backend for GNU/Linux systems. If undefined, it will be enabled if the |
2858 |
headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. |
2859 |
|
2860 |
=item EV_USE_KQUEUE |
2861 |
|
2862 |
If defined to be C<1>, libev will compile in support for the BSD style |
2863 |
C<kqueue>(2) backend. Its actual availability will be detected at runtime, |
2864 |
otherwise another method will be used as fallback. This is the preferred |
2865 |
backend for BSD and BSD-like systems, although on most BSDs kqueue only |
2866 |
supports some types of fds correctly (the only platform we found that |
2867 |
supports ptys for example was NetBSD), so kqueue might be compiled in, but |
2868 |
not be used unless explicitly requested. The best way to use it is to find |
2869 |
out whether kqueue supports your type of fd properly and use an embedded |
2870 |
kqueue loop. |
2871 |
|
2872 |
=item EV_USE_PORT |
2873 |
|
2874 |
If defined to be C<1>, libev will compile in support for the Solaris |
2875 |
10 port style backend. Its availability will be detected at runtime, |
2876 |
otherwise another method will be used as fallback. This is the preferred |
2877 |
backend for Solaris 10 systems. |
2878 |
|
2879 |
=item EV_USE_DEVPOLL |
2880 |
|
2881 |
reserved for future expansion, works like the USE symbols above. |
2882 |
|
2883 |
=item EV_USE_INOTIFY |
2884 |
|
2885 |
If defined to be C<1>, libev will compile in support for the Linux inotify |
2886 |
interface to speed up C<ev_stat> watchers. Its actual availability will |
2887 |
be detected at runtime. If undefined, it will be enabled if the headers |
2888 |
indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled. |
2889 |
|
2890 |
=item EV_ATOMIC_T |
2891 |
|
2892 |
Libev requires an integer type (suitable for storing C<0> or C<1>) whose |
2893 |
access is atomic with respect to other threads or signal contexts. No such |
2894 |
type is easily found in the C language, so you can provide your own type |
2895 |
that you know is safe for your purposes. It is used both for signal handler "locking" |
2896 |
as well as for signal and thread safety in C<ev_async> watchers. |
2897 |
|
2898 |
In the absense of this define, libev will use C<sig_atomic_t volatile> |
2899 |
(from F<signal.h>), which is usually good enough on most platforms. |
2900 |
|
2901 |
=item EV_H |
2902 |
|
2903 |
The name of the F<ev.h> header file used to include it. The default if |
2904 |
undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be |
2905 |
used to virtually rename the F<ev.h> header file in case of conflicts. |
2906 |
|
2907 |
=item EV_CONFIG_H |
2908 |
|
2909 |
If C<EV_STANDALONE> isn't C<1>, this variable can be used to override |
2910 |
F<ev.c>'s idea of where to find the F<config.h> file, similarly to |
2911 |
C<EV_H>, above. |
2912 |
|
2913 |
=item EV_EVENT_H |
2914 |
|
2915 |
Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea |
2916 |
of how the F<event.h> header can be found, the default is C<"event.h">. |
2917 |
|
2918 |
=item EV_PROTOTYPES |
2919 |
|
2920 |
If defined to be C<0>, then F<ev.h> will not define any function |
2921 |
prototypes, but still define all the structs and other symbols. This is |
2922 |
occasionally useful if you want to provide your own wrapper functions |
2923 |
around libev functions. |
2924 |
|
2925 |
=item EV_MULTIPLICITY |
2926 |
|
2927 |
If undefined or defined to C<1>, then all event-loop-specific functions |
2928 |
will have the C<struct ev_loop *> as first argument, and you can create |
2929 |
additional independent event loops. Otherwise there will be no support |
2930 |
for multiple event loops and there is no first event loop pointer |
2931 |
argument. Instead, all functions act on the single default loop. |
2932 |
|
2933 |
=item EV_MINPRI |
2934 |
|
2935 |
=item EV_MAXPRI |
2936 |
|
2937 |
The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to |
2938 |
C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can |
2939 |
provide for more priorities by overriding those symbols (usually defined |
2940 |
to be C<-2> and C<2>, respectively). |
2941 |
|
2942 |
When doing priority-based operations, libev usually has to linearly search |
2943 |
all the priorities, so having many of them (hundreds) uses a lot of space |
2944 |
and time, so using the defaults of five priorities (-2 .. +2) is usually |
2945 |
fine. |
2946 |
|
2947 |
If your embedding app does not need any priorities, defining these both to |
2948 |
C<0> will save some memory and cpu. |
2949 |
|
2950 |
=item EV_PERIODIC_ENABLE |
2951 |
|
2952 |
If undefined or defined to be C<1>, then periodic timers are supported. If |
2953 |
defined to be C<0>, then they are not. Disabling them saves a few kB of |
2954 |
code. |
2955 |
|
2956 |
=item EV_IDLE_ENABLE |
2957 |
|
2958 |
If undefined or defined to be C<1>, then idle watchers are supported. If |
2959 |
defined to be C<0>, then they are not. Disabling them saves a few kB of |
2960 |
code. |
2961 |
|
2962 |
=item EV_EMBED_ENABLE |
2963 |
|
2964 |
If undefined or defined to be C<1>, then embed watchers are supported. If |
2965 |
defined to be C<0>, then they are not. |
2966 |
|
2967 |
=item EV_STAT_ENABLE |
2968 |
|
2969 |
If undefined or defined to be C<1>, then stat watchers are supported. If |
2970 |
defined to be C<0>, then they are not. |
2971 |
|
2972 |
=item EV_FORK_ENABLE |
2973 |
|
2974 |
If undefined or defined to be C<1>, then fork watchers are supported. If |
2975 |
defined to be C<0>, then they are not. |
2976 |
|
2977 |
=item EV_ASYNC_ENABLE |
2978 |
|
2979 |
If undefined or defined to be C<1>, then async watchers are supported. If |
2980 |
defined to be C<0>, then they are not. |
2981 |
|
2982 |
=item EV_MINIMAL |
2983 |
|
2984 |
If you need to shave off some kilobytes of code at the expense of some |
2985 |
speed, define this symbol to C<1>. Currently this is used to override some |
2986 |
inlining decisions, saves roughly 30% codesize of amd64. It also selects a |
2987 |
much smaller 2-heap for timer management over the default 4-heap. |
2988 |
|
2989 |
=item EV_PID_HASHSIZE |
2990 |
|
2991 |
C<ev_child> watchers use a small hash table to distribute workload by |
2992 |
pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more |
2993 |
than enough. If you need to manage thousands of children you might want to |
2994 |
increase this value (I<must> be a power of two). |
2995 |
|
2996 |
=item EV_INOTIFY_HASHSIZE |
2997 |
|
2998 |
C<ev_stat> watchers use a small hash table to distribute workload by |
2999 |
inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>), |
3000 |
usually more than enough. If you need to manage thousands of C<ev_stat> |
3001 |
watchers you might want to increase this value (I<must> be a power of |
3002 |
two). |
3003 |
|
3004 |
=item EV_USE_4HEAP |
3005 |
|
3006 |
Heaps are not very cache-efficient. To improve the cache-efficiency of the |
3007 |
timer and periodics heap, libev uses a 4-heap when this symbol is defined |
3008 |
to C<1>. The 4-heap uses more complicated (longer) code but has |
3009 |
noticably faster performance with many (thousands) of watchers. |
3010 |
|
3011 |
The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0> |
3012 |
(disabled). |
3013 |
|
3014 |
=item EV_HEAP_CACHE_AT |
3015 |
|
3016 |
Heaps are not very cache-efficient. To improve the cache-efficiency of the |
3017 |
timer and periodics heap, libev can cache the timestamp (I<at>) within |
3018 |
the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>), |
3019 |
which uses 8-12 bytes more per watcher and a few hundred bytes more code, |
3020 |
but avoids random read accesses on heap changes. This improves performance |
3021 |
noticably with with many (hundreds) of watchers. |
3022 |
|
3023 |
The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0> |
3024 |
(disabled). |
3025 |
|
3026 |
=item EV_COMMON |
3027 |
|
3028 |
By default, all watchers have a C<void *data> member. By redefining |
3029 |
this macro to a something else you can include more and other types of |
3030 |
members. You have to define it each time you include one of the files, |
3031 |
though, and it must be identical each time. |
3032 |
|
3033 |
For example, the perl EV module uses something like this: |
3034 |
|
3035 |
#define EV_COMMON \ |
3036 |
SV *self; /* contains this struct */ \ |
3037 |
SV *cb_sv, *fh /* note no trailing ";" */ |
3038 |
|
3039 |
=item EV_CB_DECLARE (type) |
3040 |
|
3041 |
=item EV_CB_INVOKE (watcher, revents) |
3042 |
|
3043 |
=item ev_set_cb (ev, cb) |
3044 |
|
3045 |
Can be used to change the callback member declaration in each watcher, |
3046 |
and the way callbacks are invoked and set. Must expand to a struct member |
3047 |
definition and a statement, respectively. See the F<ev.h> header file for |
3048 |
their default definitions. One possible use for overriding these is to |
3049 |
avoid the C<struct ev_loop *> as first argument in all cases, or to use |
3050 |
method calls instead of plain function calls in C++. |
3051 |
|
3052 |
=head2 EXPORTED API SYMBOLS |
3053 |
|
3054 |
If you need to re-export the API (e.g. via a dll) and you need a list of |
3055 |
exported symbols, you can use the provided F<Symbol.*> files which list |
3056 |
all public symbols, one per line: |
3057 |
|
3058 |
Symbols.ev for libev proper |
3059 |
Symbols.event for the libevent emulation |
3060 |
|
3061 |
This can also be used to rename all public symbols to avoid clashes with |
3062 |
multiple versions of libev linked together (which is obviously bad in |
3063 |
itself, but sometimes it is inconvinient to avoid this). |
3064 |
|
3065 |
A sed command like this will create wrapper C<#define>'s that you need to |
3066 |
include before including F<ev.h>: |
3067 |
|
3068 |
<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h |
3069 |
|
3070 |
This would create a file F<wrap.h> which essentially looks like this: |
3071 |
|
3072 |
#define ev_backend myprefix_ev_backend |
3073 |
#define ev_check_start myprefix_ev_check_start |
3074 |
#define ev_check_stop myprefix_ev_check_stop |
3075 |
... |
3076 |
|
3077 |
=head2 EXAMPLES |
3078 |
|
3079 |
For a real-world example of a program the includes libev |
3080 |
verbatim, you can have a look at the EV perl module |
3081 |
(L<http://software.schmorp.de/pkg/EV.html>). It has the libev files in |
3082 |
the F<libev/> subdirectory and includes them in the F<EV/EVAPI.h> (public |
3083 |
interface) and F<EV.xs> (implementation) files. Only the F<EV.xs> file |
3084 |
will be compiled. It is pretty complex because it provides its own header |
3085 |
file. |
3086 |
|
3087 |
The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file |
3088 |
that everybody includes and which overrides some configure choices: |
3089 |
|
3090 |
#define EV_MINIMAL 1 |
3091 |
#define EV_USE_POLL 0 |
3092 |
#define EV_MULTIPLICITY 0 |
3093 |
#define EV_PERIODIC_ENABLE 0 |
3094 |
#define EV_STAT_ENABLE 0 |
3095 |
#define EV_FORK_ENABLE 0 |
3096 |
#define EV_CONFIG_H <config.h> |
3097 |
#define EV_MINPRI 0 |
3098 |
#define EV_MAXPRI 0 |
3099 |
|
3100 |
#include "ev++.h" |
3101 |
|
3102 |
And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
3103 |
|
3104 |
#include "ev_cpp.h" |
3105 |
#include "ev.c" |
3106 |
|
3107 |
|
3108 |
=head1 THREADS AND COROUTINES |
3109 |
|
3110 |
=head2 THREADS |
3111 |
|
3112 |
Libev itself is completely threadsafe, but it uses no locking. This |
3113 |
means that you can use as many loops as you want in parallel, as long as |
3114 |
only one thread ever calls into one libev function with the same loop |
3115 |
parameter. |
3116 |
|
3117 |
Or put differently: calls with different loop parameters can be done in |
3118 |
parallel from multiple threads, calls with the same loop parameter must be |
3119 |
done serially (but can be done from different threads, as long as only one |
3120 |
thread ever is inside a call at any point in time, e.g. by using a mutex |
3121 |
per loop). |
3122 |
|
3123 |
If you want to know which design is best for your problem, then I cannot |
3124 |
help you but by giving some generic advice: |
3125 |
|
3126 |
=over 4 |
3127 |
|
3128 |
=item * most applications have a main thread: use the default libev loop |
3129 |
in that thread, or create a seperate thread running only the default loop. |
3130 |
|
3131 |
This helps integrating other libraries or software modules that use libev |
3132 |
themselves and don't care/know about threading. |
3133 |
|
3134 |
=item * one loop per thread is usually a good model. |
3135 |
|
3136 |
Doing this is almost never wrong, sometimes a better-performance model |
3137 |
exists, but it is always a good start. |
3138 |
|
3139 |
=item * other models exist, such as the leader/follower pattern, where one |
3140 |
loop is handed through multiple threads in a kind of round-robbin fashion. |
3141 |
|
3142 |
Chosing a model is hard - look around, learn, know that usually you cna do |
3143 |
better than you currently do :-) |
3144 |
|
3145 |
=item * often you need to talk to some other thread which blocks in the |
3146 |
event loop - C<ev_async> watchers can be used to wake them up from other |
3147 |
threads safely (or from signal contexts...). |
3148 |
|
3149 |
=back |
3150 |
|
3151 |
=head2 COROUTINES |
3152 |
|
3153 |
Libev is much more accomodating to coroutines ("cooperative threads"): |
3154 |
libev fully supports nesting calls to it's functions from different |
3155 |
coroutines (e.g. you can call C<ev_loop> on the same loop from two |
3156 |
different coroutines and switch freely between both coroutines running the |
3157 |
loop, as long as you don't confuse yourself). The only exception is that |
3158 |
you must not do this from C<ev_periodic> reschedule callbacks. |
3159 |
|
3160 |
Care has been invested into making sure that libev does not keep local |
3161 |
state inside C<ev_loop>, and other calls do not usually allow coroutine |
3162 |
switches. |
3163 |
|
3164 |
|
3165 |
=head1 COMPLEXITIES |
3166 |
|
3167 |
In this section the complexities of (many of) the algorithms used inside |
3168 |
libev will be explained. For complexity discussions about backends see the |
3169 |
documentation for C<ev_default_init>. |
3170 |
|
3171 |
All of the following are about amortised time: If an array needs to be |
3172 |
extended, libev needs to realloc and move the whole array, but this |
3173 |
happens asymptotically never with higher number of elements, so O(1) might |
3174 |
mean it might do a lengthy realloc operation in rare cases, but on average |
3175 |
it is much faster and asymptotically approaches constant time. |
3176 |
|
3177 |
=over 4 |
3178 |
|
3179 |
=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers) |
3180 |
|
3181 |
This means that, when you have a watcher that triggers in one hour and |
3182 |
there are 100 watchers that would trigger before that then inserting will |
3183 |
have to skip roughly seven (C<ld 100>) of these watchers. |
3184 |
|
3185 |
=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers) |
3186 |
|
3187 |
That means that changing a timer costs less than removing/adding them |
3188 |
as only the relative motion in the event queue has to be paid for. |
3189 |
|
3190 |
=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1) |
3191 |
|
3192 |
These just add the watcher into an array or at the head of a list. |
3193 |
|
3194 |
=item Stopping check/prepare/idle/fork/async watchers: O(1) |
3195 |
|
3196 |
=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE)) |
3197 |
|
3198 |
These watchers are stored in lists then need to be walked to find the |
3199 |
correct watcher to remove. The lists are usually short (you don't usually |
3200 |
have many watchers waiting for the same fd or signal). |
3201 |
|
3202 |
=item Finding the next timer in each loop iteration: O(1) |
3203 |
|
3204 |
By virtue of using a binary or 4-heap, the next timer is always found at a |
3205 |
fixed position in the storage array. |
3206 |
|
3207 |
=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd) |
3208 |
|
3209 |
A change means an I/O watcher gets started or stopped, which requires |
3210 |
libev to recalculate its status (and possibly tell the kernel, depending |
3211 |
on backend and wether C<ev_io_set> was used). |
3212 |
|
3213 |
=item Activating one watcher (putting it into the pending state): O(1) |
3214 |
|
3215 |
=item Priority handling: O(number_of_priorities) |
3216 |
|
3217 |
Priorities are implemented by allocating some space for each |
3218 |
priority. When doing priority-based operations, libev usually has to |
3219 |
linearly search all the priorities, but starting/stopping and activating |
3220 |
watchers becomes O(1) w.r.t. priority handling. |
3221 |
|
3222 |
=item Sending an ev_async: O(1) |
3223 |
|
3224 |
=item Processing ev_async_send: O(number_of_async_watchers) |
3225 |
|
3226 |
=item Processing signals: O(max_signal_number) |
3227 |
|
3228 |
Sending involves a syscall I<iff> there were no other C<ev_async_send> |
3229 |
calls in the current loop iteration. Checking for async and signal events |
3230 |
involves iterating over all running async watchers or all signal numbers. |
3231 |
|
3232 |
=back |
3233 |
|
3234 |
|
3235 |
=head1 Win32 platform limitations and workarounds |
3236 |
|
3237 |
Win32 doesn't support any of the standards (e.g. POSIX) that libev |
3238 |
requires, and its I/O model is fundamentally incompatible with the POSIX |
3239 |
model. Libev still offers limited functionality on this platform in |
3240 |
the form of the C<EVBACKEND_SELECT> backend, and only supports socket |
3241 |
descriptors. This only applies when using Win32 natively, not when using |
3242 |
e.g. cygwin. |
3243 |
|
3244 |
Lifting these limitations would basically require the full |
3245 |
re-implementation of the I/O system. If you are into these kinds of |
3246 |
things, then note that glib does exactly that for you in a very portable |
3247 |
way (note also that glib is the slowest event library known to man). |
3248 |
|
3249 |
There is no supported compilation method available on windows except |
3250 |
embedding it into other applications. |
3251 |
|
3252 |
Due to the many, low, and arbitrary limits on the win32 platform and |
3253 |
the abysmal performance of winsockets, using a large number of sockets |
3254 |
is not recommended (and not reasonable). If your program needs to use |
3255 |
more than a hundred or so sockets, then likely it needs to use a totally |
3256 |
different implementation for windows, as libev offers the POSIX readiness |
3257 |
notification model, which cannot be implemented efficiently on windows |
3258 |
(microsoft monopoly games). |
3259 |
|
3260 |
=over 4 |
3261 |
|
3262 |
=item The winsocket select function |
3263 |
|
3264 |
The winsocket C<select> function doesn't follow POSIX in that it requires |
3265 |
socket I<handles> and not socket I<file descriptors>. This makes select |
3266 |
very inefficient, and also requires a mapping from file descriptors |
3267 |
to socket handles. See the discussion of the C<EV_SELECT_USE_FD_SET>, |
3268 |
C<EV_SELECT_IS_WINSOCKET> and C<EV_FD_TO_WIN32_HANDLE> preprocessor |
3269 |
symbols for more info. |
3270 |
|
3271 |
The configuration for a "naked" win32 using the microsoft runtime |
3272 |
libraries and raw winsocket select is: |
3273 |
|
3274 |
#define EV_USE_SELECT 1 |
3275 |
#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */ |
3276 |
|
3277 |
Note that winsockets handling of fd sets is O(n), so you can easily get a |
3278 |
complexity in the O(n²) range when using win32. |
3279 |
|
3280 |
=item Limited number of file descriptors |
3281 |
|
3282 |
Windows has numerous arbitrary (and low) limits on things. |
3283 |
|
3284 |
Early versions of winsocket's select only supported waiting for a maximum |
3285 |
of C<64> handles (probably owning to the fact that all windows kernels |
3286 |
can only wait for C<64> things at the same time internally; microsoft |
3287 |
recommends spawning a chain of threads and wait for 63 handles and the |
3288 |
previous thread in each. Great). |
3289 |
|
3290 |
Newer versions support more handles, but you need to define C<FD_SETSIZE> |
3291 |
to some high number (e.g. C<2048>) before compiling the winsocket select |
3292 |
call (which might be in libev or elsewhere, for example, perl does its own |
3293 |
select emulation on windows). |
3294 |
|
3295 |
Another limit is the number of file descriptors in the microsoft runtime |
3296 |
libraries, which by default is C<64> (there must be a hidden I<64> fetish |
3297 |
or something like this inside microsoft). You can increase this by calling |
3298 |
C<_setmaxstdio>, which can increase this limit to C<2048> (another |
3299 |
arbitrary limit), but is broken in many versions of the microsoft runtime |
3300 |
libraries. |
3301 |
|
3302 |
This might get you to about C<512> or C<2048> sockets (depending on |
3303 |
windows version and/or the phase of the moon). To get more, you need to |
3304 |
wrap all I/O functions and provide your own fd management, but the cost of |
3305 |
calling select (O(n²)) will likely make this unworkable. |
3306 |
|
3307 |
=back |
3308 |
|
3309 |
|
3310 |
=head1 PORTABILITY REQUIREMENTS |
3311 |
|
3312 |
In addition to a working ISO-C implementation, libev relies on a few |
3313 |
additional extensions: |
3314 |
|
3315 |
=over 4 |
3316 |
|
3317 |
=item C<sig_atomic_t volatile> must be thread-atomic as well |
3318 |
|
3319 |
The type C<sig_atomic_t volatile> (or whatever is defined as |
3320 |
C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different |
3321 |
threads. This is not part of the specification for C<sig_atomic_t>, but is |
3322 |
believed to be sufficiently portable. |
3323 |
|
3324 |
=item C<sigprocmask> must work in a threaded environment |
3325 |
|
3326 |
Libev uses C<sigprocmask> to temporarily block signals. This is not |
3327 |
allowed in a threaded program (C<pthread_sigmask> has to be used). Typical |
3328 |
pthread implementations will either allow C<sigprocmask> in the "main |
3329 |
thread" or will block signals process-wide, both behaviours would |
3330 |
be compatible with libev. Interaction between C<sigprocmask> and |
3331 |
C<pthread_sigmask> could complicate things, however. |
3332 |
|
3333 |
The most portable way to handle signals is to block signals in all threads |
3334 |
except the initial one, and run the default loop in the initial thread as |
3335 |
well. |
3336 |
|
3337 |
=item C<long> must be large enough for common memory allocation sizes |
3338 |
|
3339 |
To improve portability and simplify using libev, libev uses C<long> |
3340 |
internally instead of C<size_t> when allocating its data structures. On |
3341 |
non-POSIX systems (Microsoft...) this might be unexpectedly low, but |
3342 |
is still at least 31 bits everywhere, which is enough for hundreds of |
3343 |
millions of watchers. |
3344 |
|
3345 |
=item C<double> must hold a time value in seconds with enough accuracy |
3346 |
|
3347 |
The type C<double> is used to represent timestamps. It is required to |
3348 |
have at least 51 bits of mantissa (and 9 bits of exponent), which is good |
3349 |
enough for at least into the year 4000. This requirement is fulfilled by |
3350 |
implementations implementing IEEE 754 (basically all existing ones). |
3351 |
|
3352 |
=back |
3353 |
|
3354 |
If you know of other additional requirements drop me a note. |
3355 |
|
3356 |
|
3357 |
=head1 AUTHOR |
3358 |
|
3359 |
Marc Lehmann <libev@schmorp.de>. |
3360 |
|