ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/libev/ev.pod
(Generate patch)

Comparing libev/ev.pod (file contents):
Revision 1.442 by root, Mon Jul 30 22:23:50 2018 UTC vs.
Revision 1.446 by root, Mon Mar 18 19:28:15 2019 UTC

… …
265 265
266You could override this function in high-availability programs to, say, 266You could override this function in high-availability programs to, say,
267free some memory if it cannot allocate memory, to use a special allocator, 267free some memory if it cannot allocate memory, to use a special allocator,
268or even to sleep a while and retry until some memory is available. 268or even to sleep a while and retry until some memory is available.
269 269
270Example: The following is the C<realloc> function that libev itself uses
271which should work with C<realloc> and C<free> functions of all kinds and
272is probably a good basis for your own implementation.
273
274 static void *
275 ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
276 {
277 if (size)
278 return realloc (ptr, size);
279
280 free (ptr);
281 return 0;
282 }
283
270Example: Replace the libev allocator with one that waits a bit and then 284Example: Replace the libev allocator with one that waits a bit and then
271retries (example requires a standards-compliant C<realloc>). 285retries.
272 286
273 static void * 287 static void *
274 persistent_realloc (void *ptr, size_t size) 288 persistent_realloc (void *ptr, size_t size)
275 { 289 {
290 if (!size)
291 {
292 free (ptr);
293 return 0;
294 }
295
276 for (;;) 296 for (;;)
277 { 297 {
278 void *newptr = realloc (ptr, size); 298 void *newptr = realloc (ptr, size);
279 299
280 if (newptr) 300 if (newptr)
… …
2114 2134
2115=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat) 2135=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
2116 2136
2117=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat) 2137=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
2118 2138
2119Configure the timer to trigger after C<after> seconds. If C<repeat> 2139Configure the timer to trigger after C<after> seconds (fractional and
2120is C<0.>, then it will automatically be stopped once the timeout is 2140negative values are supported). If C<repeat> is C<0.>, then it will
2121reached. If it is positive, then the timer will automatically be 2141automatically be stopped once the timeout is reached. If it is positive,
2122configured to trigger again C<repeat> seconds later, again, and again, 2142then the timer will automatically be configured to trigger again C<repeat>
2123until stopped manually. 2143seconds later, again, and again, until stopped manually.
2124 2144
2125The timer itself will do a best-effort at avoiding drift, that is, if 2145The timer itself will do a best-effort at avoiding drift, that is, if
2126you configure a timer to trigger every 10 seconds, then it will normally 2146you configure a timer to trigger every 10 seconds, then it will normally
2127trigger at exactly 10 second intervals. If, however, your program cannot 2147trigger at exactly 10 second intervals. If, however, your program cannot
2128keep up with the timer (because it takes longer than those 10 seconds to 2148keep up with the timer (because it takes longer than those 10 seconds to
… …
2225C<ev_timer>, which would still trigger roughly 10 seconds after starting 2245C<ev_timer>, which would still trigger roughly 10 seconds after starting
2226it, as it uses a relative timeout). 2246it, as it uses a relative timeout).
2227 2247
2228C<ev_periodic> watchers can also be used to implement vastly more complex 2248C<ev_periodic> watchers can also be used to implement vastly more complex
2229timers, such as triggering an event on each "midnight, local time", or 2249timers, such as triggering an event on each "midnight, local time", or
2230other complicated rules. This cannot be done with C<ev_timer> watchers, as 2250other complicated rules. This cannot easily be done with C<ev_timer>
2231those cannot react to time jumps. 2251watchers, as those cannot react to time jumps.
2232 2252
2233As with timers, the callback is guaranteed to be invoked only when the 2253As with timers, the callback is guaranteed to be invoked only when the
2234point in time where it is supposed to trigger has passed. If multiple 2254point in time where it is supposed to trigger has passed. If multiple
2235timers become ready during the same loop iteration then the ones with 2255timers become ready during the same loop iteration then the ones with
2236earlier time-out values are invoked before ones with later time-out values 2256earlier time-out values are invoked before ones with later time-out values
… …
2322 2342
2323NOTE: I<< This callback must always return a time that is higher than or 2343NOTE: I<< This callback must always return a time that is higher than or
2324equal to the passed C<now> value >>. 2344equal to the passed C<now> value >>.
2325 2345
2326This can be used to create very complex timers, such as a timer that 2346This can be used to create very complex timers, such as a timer that
2327triggers on "next midnight, local time". To do this, you would calculate the 2347triggers on "next midnight, local time". To do this, you would calculate
2328next midnight after C<now> and return the timestamp value for this. How 2348the next midnight after C<now> and return the timestamp value for
2329you do this is, again, up to you (but it is not trivial, which is the main 2349this. Here is a (completely untested, no error checking) example on how to
2330reason I omitted it as an example). 2350do this:
2351
2352 #include <time.h>
2353
2354 static ev_tstamp
2355 my_rescheduler (ev_periodic *w, ev_tstamp now)
2356 {
2357 time_t tnow = (time_t)now;
2358 struct tm tm;
2359 localtime_r (&tnow, &tm);
2360
2361 tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
2362 ++tm.tm_mday; // midnight next day
2363
2364 return mktime (&tm);
2365 }
2366
2367Note: this code might run into trouble on days that have more then two
2368midnights (beginning and end).
2331 2369
2332=back 2370=back
2333 2371
2334=item ev_periodic_again (loop, ev_periodic *) 2372=item ev_periodic_again (loop, ev_periodic *)
2335 2373
… …
3960The normal C API should work fine when used from C++: both ev.h and the 3998The normal C API should work fine when used from C++: both ev.h and the
3961libev sources can be compiled as C++. Therefore, code that uses the C API 3999libev sources can be compiled as C++. Therefore, code that uses the C API
3962will work fine. 4000will work fine.
3963 4001
3964Proper exception specifications might have to be added to callbacks passed 4002Proper exception specifications might have to be added to callbacks passed
3965to libev: exceptions may be thrown only from watcher callbacks, all 4003to libev: exceptions may be thrown only from watcher callbacks, all other
3966other callbacks (allocator, syserr, loop acquire/release and periodic 4004callbacks (allocator, syserr, loop acquire/release and periodic reschedule
3967reschedule callbacks) must not throw exceptions, and might need a C<throw 4005callbacks) must not throw exceptions, and might need a C<noexcept>
3968()> specification. If you have code that needs to be compiled as both C 4006specification. If you have code that needs to be compiled as both C and
3969and C++ you can use the C<EV_THROW> macro for this: 4007C++ you can use the C<EV_NOEXCEPT> macro for this:
3970 4008
3971 static void 4009 static void
3972 fatal_error (const char *msg) EV_THROW 4010 fatal_error (const char *msg) EV_NOEXCEPT
3973 { 4011 {
3974 perror (msg); 4012 perror (msg);
3975 abort (); 4013 abort ();
3976 } 4014 }
3977 4015

Diff Legend

– Removed lines
+ Added lines
< Changed lines
> Changed lines