[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.354 by root, Tue Jan 11 01:40:25 2011 UTC vs.
Revision 1.395 by root, Tue Jan 24 16:38:55 2012 UTC

…		…
58	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
59		59
60	// now wait for events to arrive	60	// now wait for events to arrive
61	ev_run (loop, 0);	61	ev_run (loop, 0);
62		62
63	// unloop was called, so exit	63	// break was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 ABOUT THIS DOCUMENT	67	=head1 ABOUT THIS DOCUMENT
68		68
…		…
174	=item ev_tstamp ev_time ()	174	=item ev_tstamp ev_time ()
175		175
176	Returns the current time as libev would use it. Please note that the	176	Returns the current time as libev would use it. Please note that the
177	C<ev_now> function is usually faster and also often returns the timestamp	177	C<ev_now> function is usually faster and also often returns the timestamp
178	you actually want to know. Also interesting is the combination of	178	you actually want to know. Also interesting is the combination of
179	C<ev_update_now> and C<ev_now>.	179	C<ev_now_update> and C<ev_now>.
180		180
181	=item ev_sleep (ev_tstamp interval)	181	=item ev_sleep (ev_tstamp interval)
182		182
183	Sleep for the given interval: The current thread will be blocked until	183	Sleep for the given interval: The current thread will be blocked
184	either it is interrupted or the given time interval has passed. Basically	184	until either it is interrupted or the given time interval has
		185	passed (approximately - it might return a bit earlier even if not
		186	interrupted). Returns immediately if C<< interval <= 0 >>.
		187
185	this is a sub-second-resolution C<sleep ()>.	188	Basically this is a sub-second-resolution C<sleep ()>.
		189
		190	The range of the C<interval> is limited - libev only guarantees to work
		191	with sleep times of up to one day (C<< interval <= 86400 >>).
186		192
187	=item int ev_version_major ()	193	=item int ev_version_major ()
188		194
189	=item int ev_version_minor ()	195	=item int ev_version_minor ()
190		196
…		…
435	example) that can't properly initialise their signal masks.	441	example) that can't properly initialise their signal masks.
436		442
437	=item C<EVFLAG_NOSIGMASK>	443	=item C<EVFLAG_NOSIGMASK>
438		444
439	When this flag is specified, then libev will avoid to modify the signal	445	When this flag is specified, then libev will avoid to modify the signal
440	mask. Specifically, this means you ahve to make sure signals are unblocked	446	mask. Specifically, this means you have to make sure signals are unblocked
441	when you want to receive them.	447	when you want to receive them.
442		448
443	This behaviour is useful when you want to do your own signal handling, or	449	This behaviour is useful when you want to do your own signal handling, or
444	want to handle signals only in specific threads and want to avoid libev	450	want to handle signals only in specific threads and want to avoid libev
445	unblocking the signals.	451	unblocking the signals.
		452
		453	It's also required by POSIX in a threaded program, as libev calls
		454	C<sigprocmask>, whose behaviour is officially unspecified.
446		455
447	This flag's behaviour will become the default in future versions of libev.	456	This flag's behaviour will become the default in future versions of libev.
448		457
449	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	458	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
450		459
…		…
480	=item C<EVBACKEND_EPOLL> (value 4, Linux)	489	=item C<EVBACKEND_EPOLL> (value 4, Linux)
481		490
482	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9	491	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
483	kernels).	492	kernels).
484		493
485	For few fds, this backend is a bit little slower than poll and select,	494	For few fds, this backend is a bit little slower than poll and select, but
486	but it scales phenomenally better. While poll and select usually scale	495	it scales phenomenally better. While poll and select usually scale like
487	like O(total_fds) where n is the total number of fds (or the highest fd),	496	O(total_fds) where total_fds is the total number of fds (or the highest
488	epoll scales either O(1) or O(active_fds).	497	fd), epoll scales either O(1) or O(active_fds).
489		498
490	The epoll mechanism deserves honorable mention as the most misdesigned	499	The epoll mechanism deserves honorable mention as the most misdesigned
491	of the more advanced event mechanisms: mere annoyances include silently	500	of the more advanced event mechanisms: mere annoyances include silently
492	dropping file descriptors, requiring a system call per change per file	501	dropping file descriptors, requiring a system call per change per file
493	descriptor (and unnecessary guessing of parameters), problems with dup,	502	descriptor (and unnecessary guessing of parameters), problems with dup,
…		…
496	0.1ms) and so on. The biggest issue is fork races, however - if a program	505	0.1ms) and so on. The biggest issue is fork races, however - if a program
497	forks then I<both> parent and child process have to recreate the epoll	506	forks then I<both> parent and child process have to recreate the epoll
498	set, which can take considerable time (one syscall per file descriptor)	507	set, which can take considerable time (one syscall per file descriptor)
499	and is of course hard to detect.	508	and is of course hard to detect.
500		509
501	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but	510	Epoll is also notoriously buggy - embedding epoll fds I<should> work,
502	of course I<doesn't>, and epoll just loves to report events for totally	511	but of course I<doesn't>, and epoll just loves to report events for
503	I<different> file descriptors (even already closed ones, so one cannot	512	totally I<different> file descriptors (even already closed ones, so
504	even remove them from the set) than registered in the set (especially	513	one cannot even remove them from the set) than registered in the set
505	on SMP systems). Libev tries to counter these spurious notifications by	514	(especially on SMP systems). Libev tries to counter these spurious
506	employing an additional generation counter and comparing that against the	515	notifications by employing an additional generation counter and comparing
507	events to filter out spurious ones, recreating the set when required. Last	516	that against the events to filter out spurious ones, recreating the set
		517	when required. Epoll also erroneously rounds down timeouts, but gives you
		518	no way to know when and by how much, so sometimes you have to busy-wait
		519	because epoll returns immediately despite a nonzero timeout. And last
508	not least, it also refuses to work with some file descriptors which work	520	not least, it also refuses to work with some file descriptors which work
509	perfectly fine with C<select> (files, many character devices...).	521	perfectly fine with C<select> (files, many character devices...).
510		522
511	Epoll is truly the train wreck analog among event poll mechanisms,	523	Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
512	a frankenpoll, cobbled together in a hurry, no thought to design or	524	cobbled together in a hurry, no thought to design or interaction with
513	interaction with others.	525	others. Oh, the pain, will it ever stop...
514		526
515	While stopping, setting and starting an I/O watcher in the same iteration	527	While stopping, setting and starting an I/O watcher in the same iteration
516	will result in some caching, there is still a system call per such	528	will result in some caching, there is still a system call per such
517	incident (because the same I<file descriptor> could point to a different	529	incident (because the same I<file descriptor> could point to a different
518	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	530	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
596	among the OS-specific backends (I vastly prefer correctness over speed	608	among the OS-specific backends (I vastly prefer correctness over speed
597	hacks).	609	hacks).
598		610
599	On the negative side, the interface is I<bizarre> - so bizarre that	611	On the negative side, the interface is I<bizarre> - so bizarre that
600	even sun itself gets it wrong in their code examples: The event polling	612	even sun itself gets it wrong in their code examples: The event polling
601	function sometimes returning events to the caller even though an error	613	function sometimes returns events to the caller even though an error
602	occurred, but with no indication whether it has done so or not (yes, it's	614	occurred, but with no indication whether it has done so or not (yes, it's
603	even documented that way) - deadly for edge-triggered interfaces where	615	even documented that way) - deadly for edge-triggered interfaces where you
604	you absolutely have to know whether an event occurred or not because you	616	absolutely have to know whether an event occurred or not because you have
605	have to re-arm the watcher.	617	to re-arm the watcher.
606		618
607	Fortunately libev seems to be able to work around these idiocies.	619	Fortunately libev seems to be able to work around these idiocies.
608		620
609	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	621	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
610	C<EVBACKEND_POLL>.	622	C<EVBACKEND_POLL>.
…		…
822	This is useful if you are waiting for some external event in conjunction	834	This is useful if you are waiting for some external event in conjunction
823	with something not expressible using other libev watchers (i.e. "roll your	835	with something not expressible using other libev watchers (i.e. "roll your
824	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is	836	own C<ev_run>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
825	usually a better approach for this kind of thing.	837	usually a better approach for this kind of thing.
826		838
827	Here are the gory details of what C<ev_run> does:	839	Here are the gory details of what C<ev_run> does (this is for your
		840	understanding, not a guarantee that things will work exactly like this in
		841	future versions):
828		842
829	- Increment loop depth.	843	- Increment loop depth.
830	- Reset the ev_break status.	844	- Reset the ev_break status.
831	- Before the first iteration, call any pending watchers.	845	- Before the first iteration, call any pending watchers.
832	LOOP:	846	LOOP:
…		…
865	anymore.	879	anymore.
866		880
867	... queue jobs here, make sure they register event watchers as long	881	... queue jobs here, make sure they register event watchers as long
868	... as they still have work to do (even an idle watcher will do..)	882	... as they still have work to do (even an idle watcher will do..)
869	ev_run (my_loop, 0);	883	ev_run (my_loop, 0);
870	... jobs done or somebody called unloop. yeah!	884	... jobs done or somebody called break. yeah!
871		885
872	=item ev_break (loop, how)	886	=item ev_break (loop, how)
873		887
874	Can be used to make a call to C<ev_run> return early (but only after it	888	Can be used to make a call to C<ev_run> return early (but only after it
875	has processed all outstanding events). The C<how> argument must be either	889	has processed all outstanding events). The C<how> argument must be either
…		…
938	overhead for the actual polling but can deliver many events at once.	952	overhead for the actual polling but can deliver many events at once.
939		953
940	By setting a higher I<io collect interval> you allow libev to spend more	954	By setting a higher I<io collect interval> you allow libev to spend more
941	time collecting I/O events, so you can handle more events per iteration,	955	time collecting I/O events, so you can handle more events per iteration,
942	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	956	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
943	C<ev_timer>) will be not affected. Setting this to a non-null value will	957	C<ev_timer>) will not be affected. Setting this to a non-null value will
944	introduce an additional C<ev_sleep ()> call into most loop iterations. The	958	introduce an additional C<ev_sleep ()> call into most loop iterations. The
945	sleep time ensures that libev will not poll for I/O events more often then	959	sleep time ensures that libev will not poll for I/O events more often then
946	once per this interval, on average.	960	once per this interval, on average (as long as the host time resolution is
		961	good enough).
947		962
948	Likewise, by setting a higher I<timeout collect interval> you allow libev	963	Likewise, by setting a higher I<timeout collect interval> you allow libev
949	to spend more time collecting timeouts, at the expense of increased	964	to spend more time collecting timeouts, at the expense of increased
950	latency/jitter/inexactness (the watcher callback will be called	965	latency/jitter/inexactness (the watcher callback will be called
951	later). C<ev_io> watchers will not be affected. Setting this to a non-null	966	later). C<ev_io> watchers will not be affected. Setting this to a non-null
…		…
1005	can be done relatively simply by putting mutex_lock/unlock calls around	1020	can be done relatively simply by putting mutex_lock/unlock calls around
1006	each call to a libev function.	1021	each call to a libev function.
1007		1022
1008	However, C<ev_run> can run an indefinite time, so it is not feasible	1023	However, C<ev_run> can run an indefinite time, so it is not feasible
1009	to wait for it to return. One way around this is to wake up the event	1024	to wait for it to return. One way around this is to wake up the event
1010	loop via C<ev_break> and C<av_async_send>, another way is to set these	1025	loop via C<ev_break> and C<ev_async_send>, another way is to set these
1011	I<release> and I<acquire> callbacks on the loop.	1026	I<release> and I<acquire> callbacks on the loop.
1012		1027
1013	When set, then C<release> will be called just before the thread is	1028	When set, then C<release> will be called just before the thread is
1014	suspended waiting for new events, and C<acquire> is called just	1029	suspended waiting for new events, and C<acquire> is called just
1015	afterwards.	1030	afterwards.
…		…
1357	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1372	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1358	functions that do not need a watcher.	1373	functions that do not need a watcher.
1359		1374
1360	=back	1375	=back
1361		1376
1362	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1377	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1363		1378	OWN COMPOSITE WATCHERS> idioms.
1364	Each watcher has, by default, a member C<void *data> that you can change
1365	and read at any time: libev will completely ignore it. This can be used
1366	to associate arbitrary data with your watcher. If you need more data and
1367	don't want to allocate memory and store a pointer to it in that data
1368	member, you can also "subclass" the watcher type and provide your own
1369	data:
1370
1371	struct my_io
1372	{
1373	ev_io io;
1374	int otherfd;
1375	void *somedata;
1376	struct whatever *mostinteresting;
1377	};
1378
1379	...
1380	struct my_io w;
1381	ev_io_init (&w.io, my_cb, fd, EV_READ);
1382
1383	And since your callback will be called with a pointer to the watcher, you
1384	can cast it back to your own type:
1385
1386	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1387	{
1388	struct my_io w = (struct my_io )w_;
1389	...
1390	}
1391
1392	More interesting and less C-conformant ways of casting your callback type
1393	instead have been omitted.
1394
1395	Another common scenario is to use some data structure with multiple
1396	embedded watchers:
1397
1398	struct my_biggy
1399	{
1400	int some_data;
1401	ev_timer t1;
1402	ev_timer t2;
1403	}
1404
1405	In this case getting the pointer to C<my_biggy> is a bit more
1406	complicated: Either you store the address of your C<my_biggy> struct
1407	in the C<data> member of the watcher (for woozies), or you need to use
1408	some pointer arithmetic using C<offsetof> inside your watchers (for real
1409	programmers):
1410
1411	#include <stddef.h>
1412
1413	static void
1414	t1_cb (EV_P_ ev_timer *w, int revents)
1415	{
1416	struct my_biggy big = (struct my_biggy *)
1417	(((char *)w) - offsetof (struct my_biggy, t1));
1418	}
1419
1420	static void
1421	t2_cb (EV_P_ ev_timer *w, int revents)
1422	{
1423	struct my_biggy big = (struct my_biggy *)
1424	(((char *)w) - offsetof (struct my_biggy, t2));
1425	}
1426		1379
1427	=head2 WATCHER STATES	1380	=head2 WATCHER STATES
1428		1381
1429	There are various watcher states mentioned throughout this manual -	1382	There are various watcher states mentioned throughout this manual -
1430	active, pending and so on. In this section these states and the rules to	1383	active, pending and so on. In this section these states and the rules to
…		…
1433		1386
1434	=over 4	1387	=over 4
1435		1388
1436	=item initialiased	1389	=item initialiased
1437		1390
1438	Before a watcher can be registered with the event looop it has to be	1391	Before a watcher can be registered with the event loop it has to be
1439	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to	1392	initialised. This can be done with a call to C<ev_TYPE_init>, or calls to
1440	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.	1393	C<ev_init> followed by the watcher-specific C<ev_TYPE_set> function.
1441		1394
1442	In this state it is simply some block of memory that is suitable for use	1395	In this state it is simply some block of memory that is suitable for
1443	in an event loop. It can be moved around, freed, reused etc. at will.	1396	use in an event loop. It can be moved around, freed, reused etc. at
		1397	will - as long as you either keep the memory contents intact, or call
		1398	C<ev_TYPE_init> again.
1444		1399
1445	=item started/running/active	1400	=item started/running/active
1446		1401
1447	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes	1402	Once a watcher has been started with a call to C<ev_TYPE_start> it becomes
1448	property of the event loop, and is actively waiting for events. While in	1403	property of the event loop, and is actively waiting for events. While in
…		…
1476	latter will clear any pending state the watcher might be in, regardless	1431	latter will clear any pending state the watcher might be in, regardless
1477	of whether it was active or not, so stopping a watcher explicitly before	1432	of whether it was active or not, so stopping a watcher explicitly before
1478	freeing it is often a good idea.	1433	freeing it is often a good idea.
1479		1434
1480	While stopped (and not pending) the watcher is essentially in the	1435	While stopped (and not pending) the watcher is essentially in the
1481	initialised state, that is it can be reused, moved, modified in any way	1436	initialised state, that is, it can be reused, moved, modified in any way
1482	you wish.	1437	you wish (but when you trash the memory block, you need to C<ev_TYPE_init>
		1438	it again).
1483		1439
1484	=back	1440	=back
1485		1441
1486	=head2 WATCHER PRIORITY MODELS	1442	=head2 WATCHER PRIORITY MODELS
1487		1443
…		…
1680	always get a readiness notification instantly, and your read (or possibly	1636	always get a readiness notification instantly, and your read (or possibly
1681	write) will still block on the disk I/O.	1637	write) will still block on the disk I/O.
1682		1638
1683	Another way to view it is that in the case of sockets, pipes, character	1639	Another way to view it is that in the case of sockets, pipes, character
1684	devices and so on, there is another party (the sender) that delivers data	1640	devices and so on, there is another party (the sender) that delivers data
1685	on it's own, but in the case of files, there is no such thing: the disk	1641	on its own, but in the case of files, there is no such thing: the disk
1686	will not send data on it's own, simply because it doesn't know what you	1642	will not send data on its own, simply because it doesn't know what you
1687	wish to read - you would first have to request some data.	1643	wish to read - you would first have to request some data.
1688		1644
1689	Since files are typically not-so-well supported by advanced notification	1645	Since files are typically not-so-well supported by advanced notification
1690	mechanism, libev tries hard to emulate POSIX behaviour with respect	1646	mechanism, libev tries hard to emulate POSIX behaviour with respect
1691	to files, even though you should not use it. The reason for this is	1647	to files, even though you should not use it. The reason for this is
…		…
1815	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1771	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1816	monotonic clock option helps a lot here).	1772	monotonic clock option helps a lot here).
1817		1773
1818	The callback is guaranteed to be invoked only I<after> its timeout has	1774	The callback is guaranteed to be invoked only I<after> its timeout has
1819	passed (not I<at>, so on systems with very low-resolution clocks this	1775	passed (not I<at>, so on systems with very low-resolution clocks this
1820	might introduce a small delay). If multiple timers become ready during the	1776	might introduce a small delay, see "the special problem of being too
		1777	early", below). If multiple timers become ready during the same loop
1821	same loop iteration then the ones with earlier time-out values are invoked	1778	iteration then the ones with earlier time-out values are invoked before
1822	before ones of the same priority with later time-out values (but this is	1779	ones of the same priority with later time-out values (but this is no
1823	no longer true when a callback calls C<ev_run> recursively).	1780	longer true when a callback calls C<ev_run> recursively).
1824		1781
1825	=head3 Be smart about timeouts	1782	=head3 Be smart about timeouts
1826		1783
1827	Many real-world problems involve some kind of timeout, usually for error	1784	Many real-world problems involve some kind of timeout, usually for error
1828	recovery. A typical example is an HTTP request - if the other side hangs,	1785	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1903		1860
1904	In this case, it would be more efficient to leave the C<ev_timer> alone,	1861	In this case, it would be more efficient to leave the C<ev_timer> alone,
1905	but remember the time of last activity, and check for a real timeout only	1862	but remember the time of last activity, and check for a real timeout only
1906	within the callback:	1863	within the callback:
1907		1864
		1865	ev_tstamp timeout = 60.;
1908	ev_tstamp last_activity; // time of last activity	1866	ev_tstamp last_activity; // time of last activity
		1867	ev_timer timer;
1909		1868
1910	static void	1869	static void
1911	callback (EV_P_ ev_timer *w, int revents)	1870	callback (EV_P_ ev_timer *w, int revents)
1912	{	1871	{
1913	ev_tstamp now = ev_now (EV_A);	1872	// calculate when the timeout would happen
1914	ev_tstamp timeout = last_activity + 60.;	1873	ev_tstamp after = last_activity - ev_now (EV_A) + timeout;
1915		1874
1916	// if last_activity + 60. is older than now, we did time out	1875	// if negative, it means we the timeout already occured
1917	if (timeout < now)	1876	if (after < 0.)
1918	{	1877	{
1919	// timeout occurred, take action	1878	// timeout occurred, take action
1920	}	1879	}
1921	else	1880	else
1922	{	1881	{
1923	// callback was invoked, but there was some activity, re-arm	1882	// callback was invoked, but there was some recent
1924	// the watcher to fire in last_activity + 60, which is	1883	// activity. simply restart the timer to time out
1925	// guaranteed to be in the future, so "again" is positive:	1884	// after "after" seconds, which is the earliest time
1926	w->repeat = timeout - now;	1885	// the timeout can occur.
		1886	ev_timer_set (w, after, 0.);
1927	ev_timer_again (EV_A_ w);	1887	ev_timer_start (EV_A_ w);
1928	}	1888	}
1929	}	1889	}
1930		1890
1931	To summarise the callback: first calculate the real timeout (defined	1891	To summarise the callback: first calculate in how many seconds the
1932	as "60 seconds after the last activity"), then check if that time has	1892	timeout will occur (by calculating the absolute time when it would occur,
1933	been reached, which means something I<did>, in fact, time out. Otherwise	1893	C<last_activity + timeout>, and subtracting the current time, C<ev_now
1934	the callback was invoked too early (C<timeout> is in the future), so	1894	(EV_A)> from that).
1935	re-schedule the timer to fire at that future time, to see if maybe we have
1936	a timeout then.
1937		1895
1938	Note how C<ev_timer_again> is used, taking advantage of the	1896	If this value is negative, then we are already past the timeout, i.e. we
1939	C<ev_timer_again> optimisation when the timer is already running.	1897	timed out, and need to do whatever is needed in this case.
		1898
		1899	Otherwise, we now the earliest time at which the timeout would trigger,
		1900	and simply start the timer with this timeout value.
		1901
		1902	In other words, each time the callback is invoked it will check whether
		1903	the timeout cocured. If not, it will simply reschedule itself to check
		1904	again at the earliest time it could time out. Rinse. Repeat.
1940		1905
1941	This scheme causes more callback invocations (about one every 60 seconds	1906	This scheme causes more callback invocations (about one every 60 seconds
1942	minus half the average time between activity), but virtually no calls to	1907	minus half the average time between activity), but virtually no calls to
1943	libev to change the timeout.	1908	libev to change the timeout.
1944		1909
1945	To start the timer, simply initialise the watcher and set C<last_activity>	1910	To start the machinery, simply initialise the watcher and set
1946	to the current time (meaning we just have some activity :), then call the	1911	C<last_activity> to the current time (meaning there was some activity just
1947	callback, which will "do the right thing" and start the timer:	1912	now), then call the callback, which will "do the right thing" and start
		1913	the timer:
1948		1914
		1915	last_activity = ev_now (EV_A);
1949	ev_init (timer, callback);	1916	ev_init (&timer, callback);
1950	last_activity = ev_now (loop);	1917	callback (EV_A_ &timer, 0);
1951	callback (loop, timer, EV_TIMER);
1952		1918
1953	And when there is some activity, simply store the current time in	1919	When there is some activity, simply store the current time in
1954	C<last_activity>, no libev calls at all:	1920	C<last_activity>, no libev calls at all:
1955		1921
		1922	if (activity detected)
1956	last_activity = ev_now (loop);	1923	last_activity = ev_now (EV_A);
		1924
		1925	When your timeout value changes, then the timeout can be changed by simply
		1926	providing a new value, stopping the timer and calling the callback, which
		1927	will agaion do the right thing (for example, time out immediately :).
		1928
		1929	timeout = new_value;
		1930	ev_timer_stop (EV_A_ &timer);
		1931	callback (EV_A_ &timer, 0);
1957		1932
1958	This technique is slightly more complex, but in most cases where the	1933	This technique is slightly more complex, but in most cases where the
1959	time-out is unlikely to be triggered, much more efficient.	1934	time-out is unlikely to be triggered, much more efficient.
1960
1961	Changing the timeout is trivial as well (if it isn't hard-coded in the
1962	callback :) - just change the timeout and invoke the callback, which will
1963	fix things for you.
1964		1935
1965	=item 4. Wee, just use a double-linked list for your timeouts.	1936	=item 4. Wee, just use a double-linked list for your timeouts.
1966		1937
1967	If there is not one request, but many thousands (millions...), all	1938	If there is not one request, but many thousands (millions...), all
1968	employing some kind of timeout with the same timeout value, then one can	1939	employing some kind of timeout with the same timeout value, then one can
…		…
1995	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1966	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1996	rather complicated, but extremely efficient, something that really pays	1967	rather complicated, but extremely efficient, something that really pays
1997	off after the first million or so of active timers, i.e. it's usually	1968	off after the first million or so of active timers, i.e. it's usually
1998	overkill :)	1969	overkill :)
1999		1970
		1971	=head3 The special problem of being too early
		1972
		1973	If you ask a timer to call your callback after three seconds, then
		1974	you expect it to be invoked after three seconds - but of course, this
		1975	cannot be guaranteed to infinite precision. Less obviously, it cannot be
		1976	guaranteed to any precision by libev - imagine somebody suspending the
		1977	process with a STOP signal for a few hours for example.
		1978
		1979	So, libev tries to invoke your callback as soon as possible I<after> the
		1980	delay has occurred, but cannot guarantee this.
		1981
		1982	A less obvious failure mode is calling your callback too early: many event
		1983	loops compare timestamps with a "elapsed delay >= requested delay", but
		1984	this can cause your callback to be invoked much earlier than you would
		1985	expect.
		1986
		1987	To see why, imagine a system with a clock that only offers full second
		1988	resolution (think windows if you can't come up with a broken enough OS
		1989	yourself). If you schedule a one-second timer at the time 500.9, then the
		1990	event loop will schedule your timeout to elapse at a system time of 500
		1991	(500.9 truncated to the resolution) + 1, or 501.
		1992
		1993	If an event library looks at the timeout 0.1s later, it will see "501 >=
		1994	501" and invoke the callback 0.1s after it was started, even though a
		1995	one-second delay was requested - this is being "too early", despite best
		1996	intentions.
		1997
		1998	This is the reason why libev will never invoke the callback if the elapsed
		1999	delay equals the requested delay, but only when the elapsed delay is
		2000	larger than the requested delay. In the example above, libev would only invoke
		2001	the callback at system time 502, or 1.1s after the timer was started.
		2002
		2003	So, while libev cannot guarantee that your callback will be invoked
		2004	exactly when requested, it I<can> and I<does> guarantee that the requested
		2005	delay has actually elapsed, or in other words, it always errs on the "too
		2006	late" side of things.
		2007
2000	=head3 The special problem of time updates	2008	=head3 The special problem of time updates
2001		2009
2002	Establishing the current time is a costly operation (it usually takes at	2010	Establishing the current time is a costly operation (it usually takes
2003	least two system calls): EV therefore updates its idea of the current	2011	at least one system call): EV therefore updates its idea of the current
2004	time only before and after C<ev_run> collects new events, which causes a	2012	time only before and after C<ev_run> collects new events, which causes a
2005	growing difference between C<ev_now ()> and C<ev_time ()> when handling	2013	growing difference between C<ev_now ()> and C<ev_time ()> when handling
2006	lots of events in one iteration.	2014	lots of events in one iteration.
2007		2015
2008	The relative timeouts are calculated relative to the C<ev_now ()>	2016	The relative timeouts are calculated relative to the C<ev_now ()>
…		…
2014	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	2022	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
2015		2023
2016	If the event loop is suspended for a long time, you can also force an	2024	If the event loop is suspended for a long time, you can also force an
2017	update of the time returned by C<ev_now ()> by calling C<ev_now_update	2025	update of the time returned by C<ev_now ()> by calling C<ev_now_update
2018	()>.	2026	()>.
		2027
		2028	=head3 The special problem of unsynchronised clocks
		2029
		2030	Modern systems have a variety of clocks - libev itself uses the normal
		2031	"wall clock" clock and, if available, the monotonic clock (to avoid time
		2032	jumps).
		2033
		2034	Neither of these clocks is synchronised with each other or any other clock
		2035	on the system, so C<ev_time ()> might return a considerably different time
		2036	than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example,
		2037	a call to C<gettimeofday> might return a second count that is one higher
		2038	than a directly following call to C<time>.
		2039
		2040	The moral of this is to only compare libev-related timestamps with
		2041	C<ev_time ()> and C<ev_now ()>, at least if you want better precision than
		2042	a second or so.
		2043
		2044	One more problem arises due to this lack of synchronisation: if libev uses
		2045	the system monotonic clock and you compare timestamps from C<ev_time>
		2046	or C<ev_now> from when you started your timer and when your callback is
		2047	invoked, you will find that sometimes the callback is a bit "early".
		2048
		2049	This is because C<ev_timer>s work in real time, not wall clock time, so
		2050	libev makes sure your callback is not invoked before the delay happened,
		2051	I<measured according to the real time>, not the system clock.
		2052
		2053	If your timeouts are based on a physical timescale (e.g. "time out this
		2054	connection after 100 seconds") then this shouldn't bother you as it is
		2055	exactly the right behaviour.
		2056
		2057	If you want to compare wall clock/system timestamps to your timers, then
		2058	you need to use C<ev_periodic>s, as these are based on the wall clock
		2059	time, where your comparisons will always generate correct results.
2019		2060
2020	=head3 The special problems of suspended animation	2061	=head3 The special problems of suspended animation
2021		2062
2022	When you leave the server world it is quite customary to hit machines that	2063	When you leave the server world it is quite customary to hit machines that
2023	can suspend/hibernate - what happens to the clocks during such a suspend?	2064	can suspend/hibernate - what happens to the clocks during such a suspend?
…		…
2067	keep up with the timer (because it takes longer than those 10 seconds to	2108	keep up with the timer (because it takes longer than those 10 seconds to
2068	do stuff) the timer will not fire more than once per event loop iteration.	2109	do stuff) the timer will not fire more than once per event loop iteration.
2069		2110
2070	=item ev_timer_again (loop, ev_timer *)	2111	=item ev_timer_again (loop, ev_timer *)
2071		2112
2072	This will act as if the timer timed out and restart it again if it is	2113	This will act as if the timer timed out, and restarts it again if it is
2073	repeating. The exact semantics are:	2114	repeating. It basically works like calling C<ev_timer_stop>, updating the
		2115	timeout to the C<repeat> value and calling C<ev_timer_start>.
2074		2116
		2117	The exact semantics are as in the following rules, all of which will be
		2118	applied to the watcher:
		2119
		2120	=over 4
		2121
2075	If the timer is pending, its pending status is cleared.	2122	=item If the timer is pending, the pending status is always cleared.
2076		2123
2077	If the timer is started but non-repeating, stop it (as if it timed out).	2124	=item If the timer is started but non-repeating, stop it (as if it timed
		2125	out, without invoking it).
2078		2126
2079	If the timer is repeating, either start it if necessary (with the	2127	=item If the timer is repeating, make the C<repeat> value the new timeout
2080	C<repeat> value), or reset the running timer to the C<repeat> value.	2128	and start the timer, if necessary.
		2129
		2130	=back
2081		2131
2082	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a	2132	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
2083	usage example.	2133	usage example.
2084		2134
2085	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)	2135	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
…		…
2207		2257
2208	Another way to think about it (for the mathematically inclined) is that	2258	Another way to think about it (for the mathematically inclined) is that
2209	C<ev_periodic> will try to run the callback in this mode at the next possible	2259	C<ev_periodic> will try to run the callback in this mode at the next possible
2210	time where C<time = offset (mod interval)>, regardless of any time jumps.	2260	time where C<time = offset (mod interval)>, regardless of any time jumps.
2211		2261
2212	For numerical stability it is preferable that the C<offset> value is near	2262	The C<interval> I<MUST> be positive, and for numerical stability, the
2213	C<ev_now ()> (the current time), but there is no range requirement for	2263	interval value should be higher than C<1/8192> (which is around 100
2214	this value, and in fact is often specified as zero.	2264	microseconds) and C<offset> should be higher than C<0> and should have
		2265	at most a similar magnitude as the current time (say, within a factor of
		2266	ten). Typical values for offset are, in fact, C<0> or something between
		2267	C<0> and C<interval>, which is also the recommended range.
2215		2268
2216	Note also that there is an upper limit to how often a timer can fire (CPU	2269	Note also that there is an upper limit to how often a timer can fire (CPU
2217	speed for example), so if C<interval> is very small then timing stability	2270	speed for example), so if C<interval> is very small then timing stability
2218	will of course deteriorate. Libev itself tries to be exact to be about one	2271	will of course deteriorate. Libev itself tries to be exact to be about one
2219	millisecond (if the OS supports it and the machine is fast enough).	2272	millisecond (if the OS supports it and the machine is fast enough).
…		…
2362	=head3 The special problem of inheritance over fork/execve/pthread_create	2415	=head3 The special problem of inheritance over fork/execve/pthread_create
2363		2416
2364	Both the signal mask (C<sigprocmask>) and the signal disposition	2417	Both the signal mask (C<sigprocmask>) and the signal disposition
2365	(C<sigaction>) are unspecified after starting a signal watcher (and after	2418	(C<sigaction>) are unspecified after starting a signal watcher (and after
2366	stopping it again), that is, libev might or might not block the signal,	2419	stopping it again), that is, libev might or might not block the signal,
2367	and might or might not set or restore the installed signal handler.	2420	and might or might not set or restore the installed signal handler (but
		2421	see C<EVFLAG_NOSIGMASK>).
2368		2422
2369	While this does not matter for the signal disposition (libev never	2423	While this does not matter for the signal disposition (libev never
2370	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2424	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2371	C<execve>), this matters for the signal mask: many programs do not expect	2425	C<execve>), this matters for the signal mask: many programs do not expect
2372	certain signals to be blocked.	2426	certain signals to be blocked.
…		…
3243	atexit (program_exits);	3297	atexit (program_exits);
3244		3298
3245		3299
3246	=head2 C<ev_async> - how to wake up an event loop	3300	=head2 C<ev_async> - how to wake up an event loop
3247		3301
3248	In general, you cannot use an C<ev_run> from multiple threads or other	3302	In general, you cannot use an C<ev_loop> from multiple threads or other
3249	asynchronous sources such as signal handlers (as opposed to multiple event	3303	asynchronous sources such as signal handlers (as opposed to multiple event
3250	loops - those are of course safe to use in different threads).	3304	loops - those are of course safe to use in different threads).
3251		3305
3252	Sometimes, however, you need to wake up an event loop you do not control,	3306	Sometimes, however, you need to wake up an event loop you do not control,
3253	for example because it belongs to another thread. This is what C<ev_async>	3307	for example because it belongs to another thread. This is what C<ev_async>
…		…
3260	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind	3314	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
3261	of "global async watchers" by using a watcher on an otherwise unused	3315	of "global async watchers" by using a watcher on an otherwise unused
3262	signal, and C<ev_feed_signal> to signal this watcher from another thread,	3316	signal, and C<ev_feed_signal> to signal this watcher from another thread,
3263	even without knowing which loop owns the signal.	3317	even without knowing which loop owns the signal.
3264		3318
3265	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3266	just the default loop.
3267
3268	=head3 Queueing	3319	=head3 Queueing
3269		3320
3270	C<ev_async> does not support queueing of data in any way. The reason	3321	C<ev_async> does not support queueing of data in any way. The reason
3271	is that the author does not know of a simple (or any) algorithm for a	3322	is that the author does not know of a simple (or any) algorithm for a
3272	multiple-writer-single-reader queue that works in all cases and doesn't	3323	multiple-writer-single-reader queue that works in all cases and doesn't
…		…
3363	trust me.	3414	trust me.
3364		3415
3365	=item ev_async_send (loop, ev_async *)	3416	=item ev_async_send (loop, ev_async *)
3366		3417
3367	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3418	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
3368	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3419	an C<EV_ASYNC> event on the watcher into the event loop, and instantly
		3420	returns.
		3421
3369	C<ev_feed_event>, this call is safe to do from other threads, signal or	3422	Unlike C<ev_feed_event>, this call is safe to do from other threads,
3370	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3423	signal or similar contexts (see the discussion of C<EV_ATOMIC_T> in the
3371	section below on what exactly this means).	3424	embedding section below on what exactly this means).
3372		3425
3373	Note that, as with other watchers in libev, multiple events might get	3426	Note that, as with other watchers in libev, multiple events might get
3374	compressed into a single callback invocation (another way to look at this	3427	compressed into a single callback invocation (another way to look at
3375	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,	3428	this is that C<ev_async> watchers are level-triggered: they are set on
3376	reset when the event loop detects that).	3429	C<ev_async_send>, reset when the event loop detects that).
3377		3430
3378	This call incurs the overhead of a system call only once per event loop	3431	This call incurs the overhead of at most one extra system call per event
3379	iteration, so while the overhead might be noticeable, it doesn't apply to	3432	loop iteration, if the event loop is blocked, and no syscall at all if
3380	repeated calls to C<ev_async_send> for the same event loop.	3433	the event loop (or your program) is processing events. That means that
		3434	repeated calls are basically free (there is no need to avoid calls for
		3435	performance reasons) and that the overhead becomes smaller (typically
		3436	zero) under load.
3381		3437
3382	=item bool = ev_async_pending (ev_async *)	3438	=item bool = ev_async_pending (ev_async *)
3383		3439
3384	Returns a non-zero value when C<ev_async_send> has been called on the	3440	Returns a non-zero value when C<ev_async_send> has been called on the
3385	watcher but the event has not yet been processed (or even noted) by the	3441	watcher but the event has not yet been processed (or even noted) by the
…		…
3440	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3496	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3441		3497
3442	=item ev_feed_fd_event (loop, int fd, int revents)	3498	=item ev_feed_fd_event (loop, int fd, int revents)
3443		3499
3444	Feed an event on the given fd, as if a file descriptor backend detected	3500	Feed an event on the given fd, as if a file descriptor backend detected
3445	the given events it.	3501	the given events.
3446		3502
3447	=item ev_feed_signal_event (loop, int signum)	3503	=item ev_feed_signal_event (loop, int signum)
3448		3504
3449	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,	3505	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3450	which is async-safe.	3506	which is async-safe.
…		…
3456		3512
3457	This section explains some common idioms that are not immediately	3513	This section explains some common idioms that are not immediately
3458	obvious. Note that examples are sprinkled over the whole manual, and this	3514	obvious. Note that examples are sprinkled over the whole manual, and this
3459	section only contains stuff that wouldn't fit anywhere else.	3515	section only contains stuff that wouldn't fit anywhere else.
3460		3516
3461	=over 4	3517	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
3462		3518
3463	=item Model/nested event loop invocations and exit conditions.	3519	Each watcher has, by default, a C<void *data> member that you can read
		3520	or modify at any time: libev will completely ignore it. This can be used
		3521	to associate arbitrary data with your watcher. If you need more data and
		3522	don't want to allocate memory separately and store a pointer to it in that
		3523	data member, you can also "subclass" the watcher type and provide your own
		3524	data:
		3525
		3526	struct my_io
		3527	{
		3528	ev_io io;
		3529	int otherfd;
		3530	void *somedata;
		3531	struct whatever *mostinteresting;
		3532	};
		3533
		3534	...
		3535	struct my_io w;
		3536	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3537
		3538	And since your callback will be called with a pointer to the watcher, you
		3539	can cast it back to your own type:
		3540
		3541	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3542	{
		3543	struct my_io w = (struct my_io )w_;
		3544	...
		3545	}
		3546
		3547	More interesting and less C-conformant ways of casting your callback
		3548	function type instead have been omitted.
		3549
		3550	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3551
		3552	Another common scenario is to use some data structure with multiple
		3553	embedded watchers, in effect creating your own watcher that combines
		3554	multiple libev event sources into one "super-watcher":
		3555
		3556	struct my_biggy
		3557	{
		3558	int some_data;
		3559	ev_timer t1;
		3560	ev_timer t2;
		3561	}
		3562
		3563	In this case getting the pointer to C<my_biggy> is a bit more
		3564	complicated: Either you store the address of your C<my_biggy> struct in
		3565	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3566	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3567	real programmers):
		3568
		3569	#include <stddef.h>
		3570
		3571	static void
		3572	t1_cb (EV_P_ ev_timer *w, int revents)
		3573	{
		3574	struct my_biggy big = (struct my_biggy *)
		3575	(((char *)w) - offsetof (struct my_biggy, t1));
		3576	}
		3577
		3578	static void
		3579	t2_cb (EV_P_ ev_timer *w, int revents)
		3580	{
		3581	struct my_biggy big = (struct my_biggy *)
		3582	(((char *)w) - offsetof (struct my_biggy, t2));
		3583	}
		3584
		3585	=head2 AVOIDING FINISHING BEFORE RETURNING
		3586
		3587	Often you have structures like this in event-based programs:
		3588
		3589	callback ()
		3590	{
		3591	free (request);
		3592	}
		3593
		3594	request = start_new_request (..., callback);
		3595
		3596	The intent is to start some "lengthy" operation. The C<request> could be
		3597	used to cancel the operation, or do other things with it.
		3598
		3599	It's not uncommon to have code paths in C<start_new_request> that
		3600	immediately invoke the callback, for example, to report errors. Or you add
		3601	some caching layer that finds that it can skip the lengthy aspects of the
		3602	operation and simply invoke the callback with the result.
		3603
		3604	The problem here is that this will happen I<before> C<start_new_request>
		3605	has returned, so C<request> is not set.
		3606
		3607	Even if you pass the request by some safer means to the callback, you
		3608	might want to do something to the request after starting it, such as
		3609	canceling it, which probably isn't working so well when the callback has
		3610	already been invoked.
		3611
		3612	A common way around all these issues is to make sure that
		3613	C<start_new_request> I<always> returns before the callback is invoked. If
		3614	C<start_new_request> immediately knows the result, it can artificially
		3615	delay invoking the callback by e.g. using a C<prepare> or C<idle> watcher
		3616	for example, or more sneakily, by reusing an existing (stopped) watcher
		3617	and pushing it into the pending queue:
		3618
		3619	ev_set_cb (watcher, callback);
		3620	ev_feed_event (EV_A_ watcher, 0);
		3621
		3622	This way, C<start_new_request> can safely return before the callback is
		3623	invoked, while not delaying callback invocation too much.
		3624
		3625	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
3464		3626
3465	Often (especially in GUI toolkits) there are places where you have	3627	Often (especially in GUI toolkits) there are places where you have
3466	I<modal> interaction, which is most easily implemented by recursively	3628	I<modal> interaction, which is most easily implemented by recursively
3467	invoking C<ev_run>.	3629	invoking C<ev_run>.
3468		3630
…		…
3480	int exit_main_loop = 0;	3642	int exit_main_loop = 0;
3481		3643
3482	while (!exit_main_loop)	3644	while (!exit_main_loop)
3483	ev_run (EV_DEFAULT_ EVRUN_ONCE);	3645	ev_run (EV_DEFAULT_ EVRUN_ONCE);
3484		3646
3485	// in a model watcher	3647	// in a modal watcher
3486	int exit_nested_loop = 0;	3648	int exit_nested_loop = 0;
3487		3649
3488	while (!exit_nested_loop)	3650	while (!exit_nested_loop)
3489	ev_run (EV_A_ EVRUN_ONCE);	3651	ev_run (EV_A_ EVRUN_ONCE);
3490		3652
…		…
3497	exit_main_loop = 1;	3659	exit_main_loop = 1;
3498		3660
3499	// exit both	3661	// exit both
3500	exit_main_loop = exit_nested_loop = 1;	3662	exit_main_loop = exit_nested_loop = 1;
3501		3663
3502	=item Thread locking example	3664	=head2 THREAD LOCKING EXAMPLE
3503		3665
3504	Here is a fictitious example of how to run an event loop in a different	3666	Here is a fictitious example of how to run an event loop in a different
3505	thread than where callbacks are being invoked and watchers are	3667	thread from where callbacks are being invoked and watchers are
3506	created/added/removed.	3668	created/added/removed.
3507		3669
3508	For a real-world example, see the C<EV::Loop::Async> perl module,	3670	For a real-world example, see the C<EV::Loop::Async> perl module,
3509	which uses exactly this technique (which is suited for many high-level	3671	which uses exactly this technique (which is suited for many high-level
3510	languages).	3672	languages).
…		…
3536	// now associate this with the loop	3698	// now associate this with the loop
3537	ev_set_userdata (EV_A_ u);	3699	ev_set_userdata (EV_A_ u);
3538	ev_set_invoke_pending_cb (EV_A_ l_invoke);	3700	ev_set_invoke_pending_cb (EV_A_ l_invoke);
3539	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);	3701	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3540		3702
3541	// then create the thread running ev_loop	3703	// then create the thread running ev_run
3542	pthread_create (&u->tid, 0, l_run, EV_A);	3704	pthread_create (&u->tid, 0, l_run, EV_A);
3543	}	3705	}
3544		3706
3545	The callback for the C<ev_async> watcher does nothing: the watcher is used	3707	The callback for the C<ev_async> watcher does nothing: the watcher is used
3546	solely to wake up the event loop so it takes notice of any new watchers	3708	solely to wake up the event loop so it takes notice of any new watchers
…		…
3635	Note that sending the C<ev_async> watcher is required because otherwise	3797	Note that sending the C<ev_async> watcher is required because otherwise
3636	an event loop currently blocking in the kernel will have no knowledge	3798	an event loop currently blocking in the kernel will have no knowledge
3637	about the newly added timer. By waking up the loop it will pick up any new	3799	about the newly added timer. By waking up the loop it will pick up any new
3638	watchers in the next event loop iteration.	3800	watchers in the next event loop iteration.
3639		3801
3640	=back	3802	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3803
		3804	While the overhead of a callback that e.g. schedules a thread is small, it
		3805	is still an overhead. If you embed libev, and your main usage is with some
		3806	kind of threads or coroutines, you might want to customise libev so that
		3807	doesn't need callbacks anymore.
		3808
		3809	Imagine you have coroutines that you can switch to using a function
		3810	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3811	and that due to some magic, the currently active coroutine is stored in a
		3812	global called C<current_coro>. Then you can build your own "wait for libev
		3813	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3814	the differing C<;> conventions):
		3815
		3816	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3817	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3818
		3819	That means instead of having a C callback function, you store the
		3820	coroutine to switch to in each watcher, and instead of having libev call
		3821	your callback, you instead have it switch to that coroutine.
		3822
		3823	A coroutine might now wait for an event with a function called
		3824	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3825	matter when, or whether the watcher is active or not when this function is
		3826	called):
		3827
		3828	void
		3829	wait_for_event (ev_watcher *w)
		3830	{
		3831	ev_cb_set (w) = current_coro;
		3832	switch_to (libev_coro);
		3833	}
		3834
		3835	That basically suspends the coroutine inside C<wait_for_event> and
		3836	continues the libev coroutine, which, when appropriate, switches back to
		3837	this or any other coroutine.
		3838
		3839	You can do similar tricks if you have, say, threads with an event queue -
		3840	instead of storing a coroutine, you store the queue object and instead of
		3841	switching to a coroutine, you push the watcher onto the queue and notify
		3842	any waiters.
		3843
		3844	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3845	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3846
		3847	// my_ev.h
		3848	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3849	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3850	#include "../libev/ev.h"
		3851
		3852	// my_ev.c
		3853	#define EV_H "my_ev.h"
		3854	#include "../libev/ev.c"
		3855
		3856	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3857	F<my_ev.c> into your project. When properly specifying include paths, you
		3858	can even use F<ev.h> as header file name directly.
3641		3859
3642		3860
3643	=head1 LIBEVENT EMULATION	3861	=head1 LIBEVENT EMULATION
3644		3862
3645	Libev offers a compatibility emulation layer for libevent. It cannot	3863	Libev offers a compatibility emulation layer for libevent. It cannot
…		…
3717	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.	3935	=item C<ev::io>, C<ev::timer>, C<ev::periodic>, C<ev::idle>, C<ev::sig> etc.
3718		3936
3719	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of	3937	For each C<ev_TYPE> watcher in F<ev.h> there is a corresponding class of
3720	the same name in the C<ev> namespace, with the exception of C<ev_signal>	3938	the same name in the C<ev> namespace, with the exception of C<ev_signal>
3721	which is called C<ev::sig> to avoid clashes with the C<signal> macro	3939	which is called C<ev::sig> to avoid clashes with the C<signal> macro
3722	defines by many implementations.	3940	defined by many implementations.
3723		3941
3724	All of those classes have these methods:	3942	All of those classes have these methods:
3725		3943
3726	=over 4	3944	=over 4
3727		3945
…		…
3860	watchers in the constructor.	4078	watchers in the constructor.
3861		4079
3862	class myclass	4080	class myclass
3863	{	4081	{
3864	ev::io io ; void io_cb (ev::io &w, int revents);	4082	ev::io io ; void io_cb (ev::io &w, int revents);
3865	ev::io2 io2 ; void io2_cb (ev::io &w, int revents);	4083	ev::io io2 ; void io2_cb (ev::io &w, int revents);
3866	ev::idle idle; void idle_cb (ev::idle &w, int revents);	4084	ev::idle idle; void idle_cb (ev::idle &w, int revents);
3867		4085
3868	myclass (int fd)	4086	myclass (int fd)
3869	{	4087	{
3870	io .set <myclass, &myclass::io_cb > (this);	4088	io .set <myclass, &myclass::io_cb > (this);
…		…
3921	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.	4139	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
3922		4140
3923	=item D	4141	=item D
3924		4142
3925	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	4143	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
3926	be found at L<http://proj.llucax.com.ar/wiki/evd>.	4144	be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>.
3927		4145
3928	=item Ocaml	4146	=item Ocaml
3929		4147
3930	Erkki Seppala has written Ocaml bindings for libev, to be found at	4148	Erkki Seppala has written Ocaml bindings for libev, to be found at
3931	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.	4149	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
…		…
3979	suitable for use with C<EV_A>.	4197	suitable for use with C<EV_A>.
3980		4198
3981	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	4199	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
3982		4200
3983	Similar to the other two macros, this gives you the value of the default	4201	Similar to the other two macros, this gives you the value of the default
3984	loop, if multiple loops are supported ("ev loop default").	4202	loop, if multiple loops are supported ("ev loop default"). The default loop
		4203	will be initialised if it isn't already initialised.
		4204
		4205	For non-multiplicity builds, these macros do nothing, so you always have
		4206	to initialise the loop somewhere.
3985		4207
3986	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>	4208	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
3987		4209
3988	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the	4210	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
3989	default loop has been initialised (C<UC> == unchecked). Their behaviour	4211	default loop has been initialised (C<UC> == unchecked). Their behaviour
…		…
4134	supported). It will also not define any of the structs usually found in	4356	supported). It will also not define any of the structs usually found in
4135	F<event.h> that are not directly supported by the libev core alone.	4357	F<event.h> that are not directly supported by the libev core alone.
4136		4358
4137	In standalone mode, libev will still try to automatically deduce the	4359	In standalone mode, libev will still try to automatically deduce the
4138	configuration, but has to be more conservative.	4360	configuration, but has to be more conservative.
		4361
		4362	=item EV_USE_FLOOR
		4363
		4364	If defined to be C<1>, libev will use the C<floor ()> function for its
		4365	periodic reschedule calculations, otherwise libev will fall back on a
		4366	portable (slower) implementation. If you enable this, you usually have to
		4367	link against libm or something equivalent. Enabling this when the C<floor>
		4368	function is not available will fail, so the safe default is to not enable
		4369	this.
4139		4370
4140	=item EV_USE_MONOTONIC	4371	=item EV_USE_MONOTONIC
4141		4372
4142	If defined to be C<1>, libev will try to detect the availability of the	4373	If defined to be C<1>, libev will try to detect the availability of the
4143	monotonic clock option at both compile time and runtime. Otherwise no	4374	monotonic clock option at both compile time and runtime. Otherwise no
…		…
4276	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.	4507	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4277		4508
4278	=item EV_ATOMIC_T	4509	=item EV_ATOMIC_T
4279		4510
4280	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	4511	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
4281	access is atomic with respect to other threads or signal contexts. No such	4512	access is atomic and serialised with respect to other threads or signal
4282	type is easily found in the C language, so you can provide your own type	4513	contexts. No such type is easily found in the C language, so you can
4283	that you know is safe for your purposes. It is used both for signal handler "locking"	4514	provide your own type that you know is safe for your purposes. It is used
4284	as well as for signal and thread safety in C<ev_async> watchers.	4515	both for signal handler "locking" as well as for signal and thread safety
		4516	in C<ev_async> watchers.
4285		4517
4286	In the absence of this define, libev will use C<sig_atomic_t volatile>	4518	In the absence of this define, libev will use C<sig_atomic_t volatile>
4287	(from F<signal.h>), which is usually good enough on most platforms.	4519	(from F<signal.h>), which is usually good enough on most platforms,
		4520	although strictly speaking using a type that also implies a memory fence
		4521	is required.
4288		4522
4289	=item EV_H (h)	4523	=item EV_H (h)
4290		4524
4291	The name of the F<ev.h> header file used to include it. The default if	4525	The name of the F<ev.h> header file used to include it. The default if
4292	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	4526	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
…		…
4316	will have the C<struct ev_loop *> as first argument, and you can create	4550	will have the C<struct ev_loop *> as first argument, and you can create
4317	additional independent event loops. Otherwise there will be no support	4551	additional independent event loops. Otherwise there will be no support
4318	for multiple event loops and there is no first event loop pointer	4552	for multiple event loops and there is no first event loop pointer
4319	argument. Instead, all functions act on the single default loop.	4553	argument. Instead, all functions act on the single default loop.
4320		4554
		4555	Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a
		4556	default loop when multiplicity is switched off - you always have to
		4557	initialise the loop manually in this case.
		4558
4321	=item EV_MINPRI	4559	=item EV_MINPRI
4322		4560
4323	=item EV_MAXPRI	4561	=item EV_MAXPRI
4324		4562
4325	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to	4563	The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
…		…
4422		4660
4423	With an intelligent-enough linker (gcc+binutils are intelligent enough	4661	With an intelligent-enough linker (gcc+binutils are intelligent enough
4424	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by	4662	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
4425	your program might be left out as well - a binary starting a timer and an	4663	your program might be left out as well - a binary starting a timer and an
4426	I/O watcher then might come out at only 5Kb.	4664	I/O watcher then might come out at only 5Kb.
		4665
		4666	=item EV_API_STATIC
		4667
		4668	If this symbol is defined (by default it is not), then all identifiers
		4669	will have static linkage. This means that libev will not export any
		4670	identifiers, and you cannot link against libev anymore. This can be useful
		4671	when you embed libev, only want to use libev functions in a single file,
		4672	and do not want its identifiers to be visible.
		4673
		4674	To use this, define C<EV_API_STATIC> and include F<ev.c> in the file that
		4675	wants to use libev.
		4676
		4677	This option only works when libev is compiled with a C compiler, as C++
		4678	doesn't support the required declaration syntax.
4427		4679
4428	=item EV_AVOID_STDIO	4680	=item EV_AVOID_STDIO
4429		4681
4430	If this is set to C<1> at compiletime, then libev will avoid using stdio	4682	If this is set to C<1> at compiletime, then libev will avoid using stdio
4431	functions (printf, scanf, perror etc.). This will increase the code size	4683	functions (printf, scanf, perror etc.). This will increase the code size
…		…
4575	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4827	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4576		4828
4577	#include "ev_cpp.h"	4829	#include "ev_cpp.h"
4578	#include "ev.c"	4830	#include "ev.c"
4579		4831
4580	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4832	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4581		4833
4582	=head2 THREADS AND COROUTINES	4834	=head2 THREADS AND COROUTINES
4583		4835
4584	=head3 THREADS	4836	=head3 THREADS
4585		4837
…		…
4636	default loop and triggering an C<ev_async> watcher from the default loop	4888	default loop and triggering an C<ev_async> watcher from the default loop
4637	watcher callback into the event loop interested in the signal.	4889	watcher callback into the event loop interested in the signal.
4638		4890
4639	=back	4891	=back
4640		4892
4641	See also L<Thread locking example>.	4893	See also L<THREAD LOCKING EXAMPLE>.
4642		4894
4643	=head3 COROUTINES	4895	=head3 COROUTINES
4644		4896
4645	Libev is very accommodating to coroutines ("cooperative threads"):	4897	Libev is very accommodating to coroutines ("cooperative threads"):
4646	libev fully supports nesting calls to its functions from different	4898	libev fully supports nesting calls to its functions from different
…		…
4811	requires, and its I/O model is fundamentally incompatible with the POSIX	5063	requires, and its I/O model is fundamentally incompatible with the POSIX
4812	model. Libev still offers limited functionality on this platform in	5064	model. Libev still offers limited functionality on this platform in
4813	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	5065	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
4814	descriptors. This only applies when using Win32 natively, not when using	5066	descriptors. This only applies when using Win32 natively, not when using
4815	e.g. cygwin. Actually, it only applies to the microsofts own compilers,	5067	e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4816	as every compielr comes with a slightly differently broken/incompatible	5068	as every compiler comes with a slightly differently broken/incompatible
4817	environment.	5069	environment.
4818		5070
4819	Lifting these limitations would basically require the full	5071	Lifting these limitations would basically require the full
4820	re-implementation of the I/O system. If you are into this kind of thing,	5072	re-implementation of the I/O system. If you are into this kind of thing,
4821	then note that glib does exactly that for you in a very portable way (note	5073	then note that glib does exactly that for you in a very portable way (note
…		…
4954		5206
4955	The type C<double> is used to represent timestamps. It is required to	5207	The type C<double> is used to represent timestamps. It is required to
4956	have at least 51 bits of mantissa (and 9 bits of exponent), which is	5208	have at least 51 bits of mantissa (and 9 bits of exponent), which is
4957	good enough for at least into the year 4000 with millisecond accuracy	5209	good enough for at least into the year 4000 with millisecond accuracy
4958	(the design goal for libev). This requirement is overfulfilled by	5210	(the design goal for libev). This requirement is overfulfilled by
4959	implementations using IEEE 754, which is basically all existing ones. With	5211	implementations using IEEE 754, which is basically all existing ones.
		5212
4960	IEEE 754 doubles, you get microsecond accuracy until at least 2200.	5213	With IEEE 754 doubles, you get microsecond accuracy until at least the
		5214	year 2255 (and millisecond accuracy till the year 287396 - by then, libev
		5215	is either obsolete or somebody patched it to use C<long double> or
		5216	something like that, just kidding).
4961		5217
4962	=back	5218	=back
4963		5219
4964	If you know of other additional requirements drop me a note.	5220	If you know of other additional requirements drop me a note.
4965		5221
…		…
5027	=item Processing ev_async_send: O(number_of_async_watchers)	5283	=item Processing ev_async_send: O(number_of_async_watchers)
5028		5284
5029	=item Processing signals: O(max_signal_number)	5285	=item Processing signals: O(max_signal_number)
5030		5286
5031	Sending involves a system call I<iff> there were no other C<ev_async_send>	5287	Sending involves a system call I<iff> there were no other C<ev_async_send>
5032	calls in the current loop iteration. Checking for async and signal events	5288	calls in the current loop iteration and the loop is currently
		5289	blocked. Checking for async and signal events involves iterating over all
5033	involves iterating over all running async watchers or all signal numbers.	5290	running async watchers or all signal numbers.
5034		5291
5035	=back	5292	=back
5036		5293
5037		5294
5038	=head1 PORTING FROM LIBEV 3.X TO 4.X	5295	=head1 PORTING FROM LIBEV 3.X TO 4.X
…		…
5155	The physical time that is observed. It is apparently strictly monotonic :)	5412	The physical time that is observed. It is apparently strictly monotonic :)
5156		5413
5157	=item wall-clock time	5414	=item wall-clock time
5158		5415
5159	The time and date as shown on clocks. Unlike real time, it can actually	5416	The time and date as shown on clocks. Unlike real time, it can actually
5160	be wrong and jump forwards and backwards, e.g. when the you adjust your	5417	be wrong and jump forwards and backwards, e.g. when you adjust your
5161	clock.	5418	clock.
5162		5419
5163	=item watcher	5420	=item watcher
5164		5421
5165	A data structure that describes interest in certain events. Watchers need	5422	A data structure that describes interest in certain events. Watchers need
…		…
5168	=back	5425	=back
5169		5426
5170	=head1 AUTHOR	5427	=head1 AUTHOR
5171		5428
5172	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael	5429	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5173	Magnusson and Emanuele Giaquinta.	5430	Magnusson and Emanuele Giaquinta, and minor corrections by many others.
5174		5431

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Comparing libev/ev.pod (file contents): Revision 1.354 by root, Tue Jan 11 01:40:25 2011 UTC vs. Revision 1.395 by root, Tue Jan 24 16:38:55 2012 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.354 by root, Tue Jan 11 01:40:25 2011 UTC vs.
Revision 1.395 by root, Tue Jan 24 16:38:55 2012 UTC