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

Comparing libev/ev.pod (file contents):
Revision 1.343 by root, Wed Nov 10 13:39:10 2010 UTC vs.
Revision 1.360 by root, Mon Jan 17 12:11:12 2011 UTC

…		…
299	}	299	}
300		300
301	...	301	...
302	ev_set_syserr_cb (fatal_error);	302	ev_set_syserr_cb (fatal_error);
303		303
		304	=item ev_feed_signal (int signum)
		305
		306	This function can be used to "simulate" a signal receive. It is completely
		307	safe to call this function at any time, from any context, including signal
		308	handlers or random threads.
		309
		310	Its main use is to customise signal handling in your process, especially
		311	in the presence of threads. For example, you could block signals
		312	by default in all threads (and specifying C<EVFLAG_NOSIGMASK> when
		313	creating any loops), and in one thread, use C<sigwait> or any other
		314	mechanism to wait for signals, then "deliver" them to libev by calling
		315	C<ev_feed_signal>.
		316
304	=back	317	=back
305		318
306	=head1 FUNCTIONS CONTROLLING EVENT LOOPS	319	=head1 FUNCTIONS CONTROLLING EVENT LOOPS
307		320
308	An event loop is described by a C<struct ev_loop *> (the C<struct> is	321	An event loop is described by a C<struct ev_loop *> (the C<struct> is
…		…
418	threads that are not interested in handling them.	431	threads that are not interested in handling them.
419		432
420	Signalfd will not be used by default as this changes your signal mask, and	433	Signalfd will not be used by default as this changes your signal mask, and
421	there are a lot of shoddy libraries and programs (glib's threadpool for	434	there are a lot of shoddy libraries and programs (glib's threadpool for
422	example) that can't properly initialise their signal masks.	435	example) that can't properly initialise their signal masks.
		436
		437	=item C<EVFLAG_NOSIGMASK>
		438
		439	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
		441	when you want to receive them.
		442
		443	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
		445	unblocking the signals.
		446
		447	It's also required by POSIX in a threaded program, as libev calls
		448	C<sigprocmask>, whose behaviour is officially unspecified.
		449
		450	This flag's behaviour will become the default in future versions of libev.
423		451
424	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	452	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
425		453
426	This is your standard select(2) backend. Not I<completely> standard, as	454	This is your standard select(2) backend. Not I<completely> standard, as
427	libev tries to roll its own fd_set with no limits on the number of fds,	455	libev tries to roll its own fd_set with no limits on the number of fds,
…		…
481	employing an additional generation counter and comparing that against the	509	employing an additional generation counter and comparing that against the
482	events to filter out spurious ones, recreating the set when required. Last	510	events to filter out spurious ones, recreating the set when required. Last
483	not least, it also refuses to work with some file descriptors which work	511	not least, it also refuses to work with some file descriptors which work
484	perfectly fine with C<select> (files, many character devices...).	512	perfectly fine with C<select> (files, many character devices...).
485		513
486	Epoll is truly the train wreck analog among event poll mechanisms.	514	Epoll is truly the train wreck analog among event poll mechanisms,
		515	a frankenpoll, cobbled together in a hurry, no thought to design or
		516	interaction with others.
487		517
488	While stopping, setting and starting an I/O watcher in the same iteration	518	While stopping, setting and starting an I/O watcher in the same iteration
489	will result in some caching, there is still a system call per such	519	will result in some caching, there is still a system call per such
490	incident (because the same I<file descriptor> could point to a different	520	incident (because the same I<file descriptor> could point to a different
491	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed	521	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
…		…
557	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	587	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
558		588
559	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	589	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
560	it's really slow, but it still scales very well (O(active_fds)).	590	it's really slow, but it still scales very well (O(active_fds)).
561		591
562	Please note that Solaris event ports can deliver a lot of spurious
563	notifications, so you need to use non-blocking I/O or other means to avoid
564	blocking when no data (or space) is available.
565
566	While this backend scales well, it requires one system call per active	592	While this backend scales well, it requires one system call per active
567	file descriptor per loop iteration. For small and medium numbers of file	593	file descriptor per loop iteration. For small and medium numbers of file
568	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	594	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
569	might perform better.	595	might perform better.
570		596
571	On the positive side, with the exception of the spurious readiness	597	On the positive side, this backend actually performed fully to
572	notifications, this backend actually performed fully to specification
573	in all tests and is fully embeddable, which is a rare feat among the	598	specification in all tests and is fully embeddable, which is a rare feat
574	OS-specific backends (I vastly prefer correctness over speed hacks).	599	among the OS-specific backends (I vastly prefer correctness over speed
		600	hacks).
		601
		602	On the negative side, the interface is I<bizarre> - so bizarre that
		603	even sun itself gets it wrong in their code examples: The event polling
		604	function sometimes returning events to the caller even though an error
		605	occurred, but with no indication whether it has done so or not (yes, it's
		606	even documented that way) - deadly for edge-triggered interfaces where
		607	you absolutely have to know whether an event occurred or not because you
		608	have to re-arm the watcher.
		609
		610	Fortunately libev seems to be able to work around these idiocies.
575		611
576	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	612	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
577	C<EVBACKEND_POLL>.	613	C<EVBACKEND_POLL>.
578		614
579	=item C<EVBACKEND_ALL>	615	=item C<EVBACKEND_ALL>
580		616
581	Try all backends (even potentially broken ones that wouldn't be tried	617	Try all backends (even potentially broken ones that wouldn't be tried
582	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	618	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
583	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	619	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
584		620
585	It is definitely not recommended to use this flag.	621	It is definitely not recommended to use this flag, use whatever
		622	C<ev_recommended_backends ()> returns, or simply do not specify a backend
		623	at all.
		624
		625	=item C<EVBACKEND_MASK>
		626
		627	Not a backend at all, but a mask to select all backend bits from a
		628	C<flags> value, in case you want to mask out any backends from a flags
		629	value (e.g. when modifying the C<LIBEV_FLAGS> environment variable).
586		630
587	=back	631	=back
588		632
589	If one or more of the backend flags are or'ed into the flags value,	633	If one or more of the backend flags are or'ed into the flags value,
590	then only these backends will be tried (in the reverse order as listed	634	then only these backends will be tried (in the reverse order as listed
…		…
867	running when nothing else is active.	911	running when nothing else is active.
868		912
869	ev_signal exitsig;	913	ev_signal exitsig;
870	ev_signal_init (&exitsig, sig_cb, SIGINT);	914	ev_signal_init (&exitsig, sig_cb, SIGINT);
871	ev_signal_start (loop, &exitsig);	915	ev_signal_start (loop, &exitsig);
872	evf_unref (loop);	916	ev_unref (loop);
873		917
874	Example: For some weird reason, unregister the above signal handler again.	918	Example: For some weird reason, unregister the above signal handler again.
875		919
876	ev_ref (loop);	920	ev_ref (loop);
877	ev_signal_stop (loop, &exitsig);	921	ev_signal_stop (loop, &exitsig);
…		…
989	See also the locking example in the C<THREADS> section later in this	1033	See also the locking example in the C<THREADS> section later in this
990	document.	1034	document.
991		1035
992	=item ev_set_userdata (loop, void *data)	1036	=item ev_set_userdata (loop, void *data)
993		1037
994	=item ev_userdata (loop)	1038	=item void *ev_userdata (loop)
995		1039
996	Set and retrieve a single C<void *> associated with a loop. When	1040	Set and retrieve a single C<void *> associated with a loop. When
997	C<ev_set_userdata> has never been called, then C<ev_userdata> returns	1041	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
998	C<0>.	1042	C<0>.
999		1043
…		…
1316	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related	1360	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
1317	functions that do not need a watcher.	1361	functions that do not need a watcher.
1318		1362
1319	=back	1363	=back
1320		1364
1321	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1365	See also the L<ASSOCIATING CUSTOM DATA WITH A WATCHER> and L<BUILDING YOUR
1322		1366	OWN COMPOSITE WATCHERS> idioms.
1323	Each watcher has, by default, a member C<void *data> that you can change
1324	and read at any time: libev will completely ignore it. This can be used
1325	to associate arbitrary data with your watcher. If you need more data and
1326	don't want to allocate memory and store a pointer to it in that data
1327	member, you can also "subclass" the watcher type and provide your own
1328	data:
1329
1330	struct my_io
1331	{
1332	ev_io io;
1333	int otherfd;
1334	void *somedata;
1335	struct whatever *mostinteresting;
1336	};
1337
1338	...
1339	struct my_io w;
1340	ev_io_init (&w.io, my_cb, fd, EV_READ);
1341
1342	And since your callback will be called with a pointer to the watcher, you
1343	can cast it back to your own type:
1344
1345	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
1346	{
1347	struct my_io w = (struct my_io )w_;
1348	...
1349	}
1350
1351	More interesting and less C-conformant ways of casting your callback type
1352	instead have been omitted.
1353
1354	Another common scenario is to use some data structure with multiple
1355	embedded watchers:
1356
1357	struct my_biggy
1358	{
1359	int some_data;
1360	ev_timer t1;
1361	ev_timer t2;
1362	}
1363
1364	In this case getting the pointer to C<my_biggy> is a bit more
1365	complicated: Either you store the address of your C<my_biggy> struct
1366	in the C<data> member of the watcher (for woozies), or you need to use
1367	some pointer arithmetic using C<offsetof> inside your watchers (for real
1368	programmers):
1369
1370	#include <stddef.h>
1371
1372	static void
1373	t1_cb (EV_P_ ev_timer *w, int revents)
1374	{
1375	struct my_biggy big = (struct my_biggy *)
1376	(((char *)w) - offsetof (struct my_biggy, t1));
1377	}
1378
1379	static void
1380	t2_cb (EV_P_ ev_timer *w, int revents)
1381	{
1382	struct my_biggy big = (struct my_biggy *)
1383	(((char *)w) - offsetof (struct my_biggy, t2));
1384	}
1385		1367
1386	=head2 WATCHER STATES	1368	=head2 WATCHER STATES
1387		1369
1388	There are various watcher states mentioned throughout this manual -	1370	There are various watcher states mentioned throughout this manual -
1389	active, pending and so on. In this section these states and the rules to	1371	active, pending and so on. In this section these states and the rules to
…		…
1575	In general you can register as many read and/or write event watchers per	1557	In general you can register as many read and/or write event watchers per
1576	fd as you want (as long as you don't confuse yourself). Setting all file	1558	fd as you want (as long as you don't confuse yourself). Setting all file
1577	descriptors to non-blocking mode is also usually a good idea (but not	1559	descriptors to non-blocking mode is also usually a good idea (but not
1578	required if you know what you are doing).	1560	required if you know what you are doing).
1579		1561
1580	If you cannot use non-blocking mode, then force the use of a
1581	known-to-be-good backend (at the time of this writing, this includes only
1582	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
1583	descriptors for which non-blocking operation makes no sense (such as
1584	files) - libev doesn't guarantee any specific behaviour in that case.
1585
1586	Another thing you have to watch out for is that it is quite easy to	1562	Another thing you have to watch out for is that it is quite easy to
1587	receive "spurious" readiness notifications, that is your callback might	1563	receive "spurious" readiness notifications, that is, your callback might
1588	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1564	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1589	because there is no data. Not only are some backends known to create a	1565	because there is no data. It is very easy to get into this situation even
1590	lot of those (for example Solaris ports), it is very easy to get into	1566	with a relatively standard program structure. Thus it is best to always
1591	this situation even with a relatively standard program structure. Thus	1567	use non-blocking I/O: An extra C<read>(2) returning C<EAGAIN> is far
1592	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1593	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1568	preferable to a program hanging until some data arrives.
1594		1569
1595	If you cannot run the fd in non-blocking mode (for example you should	1570	If you cannot run the fd in non-blocking mode (for example you should
1596	not play around with an Xlib connection), then you have to separately	1571	not play around with an Xlib connection), then you have to separately
1597	re-test whether a file descriptor is really ready with a known-to-be good	1572	re-test whether a file descriptor is really ready with a known-to-be good
1598	interface such as poll (fortunately in our Xlib example, Xlib already	1573	interface such as poll (fortunately in the case of Xlib, it already does
1599	does this on its own, so its quite safe to use). Some people additionally	1574	this on its own, so its quite safe to use). Some people additionally
1600	use C<SIGALRM> and an interval timer, just to be sure you won't block	1575	use C<SIGALRM> and an interval timer, just to be sure you won't block
1601	indefinitely.	1576	indefinitely.
1602		1577
1603	But really, best use non-blocking mode.	1578	But really, best use non-blocking mode.
1604		1579
…		…
1632		1607
1633	There is no workaround possible except not registering events	1608	There is no workaround possible except not registering events
1634	for potentially C<dup ()>'ed file descriptors, or to resort to	1609	for potentially C<dup ()>'ed file descriptors, or to resort to
1635	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1610	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1636		1611
		1612	=head3 The special problem of files
		1613
		1614	Many people try to use C<select> (or libev) on file descriptors
		1615	representing files, and expect it to become ready when their program
		1616	doesn't block on disk accesses (which can take a long time on their own).
		1617
		1618	However, this cannot ever work in the "expected" way - you get a readiness
		1619	notification as soon as the kernel knows whether and how much data is
		1620	there, and in the case of open files, that's always the case, so you
		1621	always get a readiness notification instantly, and your read (or possibly
		1622	write) will still block on the disk I/O.
		1623
		1624	Another way to view it is that in the case of sockets, pipes, character
		1625	devices and so on, there is another party (the sender) that delivers data
		1626	on its own, but in the case of files, there is no such thing: the disk
		1627	will not send data on its own, simply because it doesn't know what you
		1628	wish to read - you would first have to request some data.
		1629
		1630	Since files are typically not-so-well supported by advanced notification
		1631	mechanism, libev tries hard to emulate POSIX behaviour with respect
		1632	to files, even though you should not use it. The reason for this is
		1633	convenience: sometimes you want to watch STDIN or STDOUT, which is
		1634	usually a tty, often a pipe, but also sometimes files or special devices
		1635	(for example, C<epoll> on Linux works with F</dev/random> but not with
		1636	F</dev/urandom>), and even though the file might better be served with
		1637	asynchronous I/O instead of with non-blocking I/O, it is still useful when
		1638	it "just works" instead of freezing.
		1639
		1640	So avoid file descriptors pointing to files when you know it (e.g. use
		1641	libeio), but use them when it is convenient, e.g. for STDIN/STDOUT, or
		1642	when you rarely read from a file instead of from a socket, and want to
		1643	reuse the same code path.
		1644
1637	=head3 The special problem of fork	1645	=head3 The special problem of fork
1638		1646
1639	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1647	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
1640	useless behaviour. Libev fully supports fork, but needs to be told about	1648	useless behaviour. Libev fully supports fork, but needs to be told about
1641	it in the child.	1649	it in the child if you want to continue to use it in the child.
1642		1650
1643	To support fork in your programs, you either have to call	1651	To support fork in your child processes, you have to call C<ev_loop_fork
1644	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1652	()> after a fork in the child, enable C<EVFLAG_FORKCHECK>, or resort to
1645	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1653	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
1646	C<EVBACKEND_POLL>.
1647		1654
1648	=head3 The special problem of SIGPIPE	1655	=head3 The special problem of SIGPIPE
1649		1656
1650	While not really specific to libev, it is easy to forget about C<SIGPIPE>:	1657	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1651	when writing to a pipe whose other end has been closed, your program gets	1658	when writing to a pipe whose other end has been closed, your program gets
…		…
2296	=head3 The special problem of inheritance over fork/execve/pthread_create	2303	=head3 The special problem of inheritance over fork/execve/pthread_create
2297		2304
2298	Both the signal mask (C<sigprocmask>) and the signal disposition	2305	Both the signal mask (C<sigprocmask>) and the signal disposition
2299	(C<sigaction>) are unspecified after starting a signal watcher (and after	2306	(C<sigaction>) are unspecified after starting a signal watcher (and after
2300	stopping it again), that is, libev might or might not block the signal,	2307	stopping it again), that is, libev might or might not block the signal,
2301	and might or might not set or restore the installed signal handler.	2308	and might or might not set or restore the installed signal handler (but
		2309	see C<EVFLAG_NOSIGMASK>).
2302		2310
2303	While this does not matter for the signal disposition (libev never	2311	While this does not matter for the signal disposition (libev never
2304	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on	2312	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
2305	C<execve>), this matters for the signal mask: many programs do not expect	2313	C<execve>), this matters for the signal mask: many programs do not expect
2306	certain signals to be blocked.	2314	certain signals to be blocked.
…		…
2319	I<has> to modify the signal mask, at least temporarily.	2327	I<has> to modify the signal mask, at least temporarily.
2320		2328
2321	So I can't stress this enough: I<If you do not reset your signal mask when	2329	So I can't stress this enough: I<If you do not reset your signal mask when
2322	you expect it to be empty, you have a race condition in your code>. This	2330	you expect it to be empty, you have a race condition in your code>. This
2323	is not a libev-specific thing, this is true for most event libraries.	2331	is not a libev-specific thing, this is true for most event libraries.
		2332
		2333	=head3 The special problem of threads signal handling
		2334
		2335	POSIX threads has problematic signal handling semantics, specifically,
		2336	a lot of functionality (sigfd, sigwait etc.) only really works if all
		2337	threads in a process block signals, which is hard to achieve.
		2338
		2339	When you want to use sigwait (or mix libev signal handling with your own
		2340	for the same signals), you can tackle this problem by globally blocking
		2341	all signals before creating any threads (or creating them with a fully set
		2342	sigprocmask) and also specifying the C<EVFLAG_NOSIGMASK> when creating
		2343	loops. Then designate one thread as "signal receiver thread" which handles
		2344	these signals. You can pass on any signals that libev might be interested
		2345	in by calling C<ev_feed_signal>.
2324		2346
2325	=head3 Watcher-Specific Functions and Data Members	2347	=head3 Watcher-Specific Functions and Data Members
2326		2348
2327	=over 4	2349	=over 4
2328		2350
…		…
3175	it by calling C<ev_async_send>, which is thread- and signal safe.	3197	it by calling C<ev_async_send>, which is thread- and signal safe.
3176		3198
3177	This functionality is very similar to C<ev_signal> watchers, as signals,	3199	This functionality is very similar to C<ev_signal> watchers, as signals,
3178	too, are asynchronous in nature, and signals, too, will be compressed	3200	too, are asynchronous in nature, and signals, too, will be compressed
3179	(i.e. the number of callback invocations may be less than the number of	3201	(i.e. the number of callback invocations may be less than the number of
3180	C<ev_async_sent> calls).	3202	C<ev_async_sent> calls). In fact, you could use signal watchers as a kind
		3203	of "global async watchers" by using a watcher on an otherwise unused
		3204	signal, and C<ev_feed_signal> to signal this watcher from another thread,
		3205	even without knowing which loop owns the signal.
3181		3206
3182	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not	3207	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
3183	just the default loop.	3208	just the default loop.
3184		3209
3185	=head3 Queueing	3210	=head3 Queueing
…		…
3361	Feed an event on the given fd, as if a file descriptor backend detected	3386	Feed an event on the given fd, as if a file descriptor backend detected
3362	the given events it.	3387	the given events it.
3363		3388
3364	=item ev_feed_signal_event (loop, int signum)	3389	=item ev_feed_signal_event (loop, int signum)
3365		3390
3366	Feed an event as if the given signal occurred (C<loop> must be the default	3391	Feed an event as if the given signal occurred. See also C<ev_feed_signal>,
3367	loop!).	3392	which is async-safe.
3368		3393
3369	=back	3394	=back
		3395
		3396
		3397	=head1 COMMON OR USEFUL IDIOMS (OR BOTH)
		3398
		3399	This section explains some common idioms that are not immediately
		3400	obvious. Note that examples are sprinkled over the whole manual, and this
		3401	section only contains stuff that wouldn't fit anywhere else.
		3402
		3403	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
		3404
		3405	Each watcher has, by default, a C<void *data> member that you can read
		3406	or modify at any time: libev will completely ignore it. This can be used
		3407	to associate arbitrary data with your watcher. If you need more data and
		3408	don't want to allocate memory separately and store a pointer to it in that
		3409	data member, you can also "subclass" the watcher type and provide your own
		3410	data:
		3411
		3412	struct my_io
		3413	{
		3414	ev_io io;
		3415	int otherfd;
		3416	void *somedata;
		3417	struct whatever *mostinteresting;
		3418	};
		3419
		3420	...
		3421	struct my_io w;
		3422	ev_io_init (&w.io, my_cb, fd, EV_READ);
		3423
		3424	And since your callback will be called with a pointer to the watcher, you
		3425	can cast it back to your own type:
		3426
		3427	static void my_cb (struct ev_loop loop, ev_io w_, int revents)
		3428	{
		3429	struct my_io w = (struct my_io )w_;
		3430	...
		3431	}
		3432
		3433	More interesting and less C-conformant ways of casting your callback
		3434	function type instead have been omitted.
		3435
		3436	=head2 BUILDING YOUR OWN COMPOSITE WATCHERS
		3437
		3438	Another common scenario is to use some data structure with multiple
		3439	embedded watchers, in effect creating your own watcher that combines
		3440	multiple libev event sources into one "super-watcher":
		3441
		3442	struct my_biggy
		3443	{
		3444	int some_data;
		3445	ev_timer t1;
		3446	ev_timer t2;
		3447	}
		3448
		3449	In this case getting the pointer to C<my_biggy> is a bit more
		3450	complicated: Either you store the address of your C<my_biggy> struct in
		3451	the C<data> member of the watcher (for woozies or C++ coders), or you need
		3452	to use some pointer arithmetic using C<offsetof> inside your watchers (for
		3453	real programmers):
		3454
		3455	#include <stddef.h>
		3456
		3457	static void
		3458	t1_cb (EV_P_ ev_timer *w, int revents)
		3459	{
		3460	struct my_biggy big = (struct my_biggy *)
		3461	(((char *)w) - offsetof (struct my_biggy, t1));
		3462	}
		3463
		3464	static void
		3465	t2_cb (EV_P_ ev_timer *w, int revents)
		3466	{
		3467	struct my_biggy big = (struct my_biggy *)
		3468	(((char *)w) - offsetof (struct my_biggy, t2));
		3469	}
		3470
		3471	=head2 MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS
		3472
		3473	Often (especially in GUI toolkits) there are places where you have
		3474	I<modal> interaction, which is most easily implemented by recursively
		3475	invoking C<ev_run>.
		3476
		3477	This brings the problem of exiting - a callback might want to finish the
		3478	main C<ev_run> call, but not the nested one (e.g. user clicked "Quit", but
		3479	a modal "Are you sure?" dialog is still waiting), or just the nested one
		3480	and not the main one (e.g. user clocked "Ok" in a modal dialog), or some
		3481	other combination: In these cases, C<ev_break> will not work alone.
		3482
		3483	The solution is to maintain "break this loop" variable for each C<ev_run>
		3484	invocation, and use a loop around C<ev_run> until the condition is
		3485	triggered, using C<EVRUN_ONCE>:
		3486
		3487	// main loop
		3488	int exit_main_loop = 0;
		3489
		3490	while (!exit_main_loop)
		3491	ev_run (EV_DEFAULT_ EVRUN_ONCE);
		3492
		3493	// in a model watcher
		3494	int exit_nested_loop = 0;
		3495
		3496	while (!exit_nested_loop)
		3497	ev_run (EV_A_ EVRUN_ONCE);
		3498
		3499	To exit from any of these loops, just set the corresponding exit variable:
		3500
		3501	// exit modal loop
		3502	exit_nested_loop = 1;
		3503
		3504	// exit main program, after modal loop is finished
		3505	exit_main_loop = 1;
		3506
		3507	// exit both
		3508	exit_main_loop = exit_nested_loop = 1;
		3509
		3510	=head2 THREAD LOCKING EXAMPLE
		3511
		3512	Here is a fictitious example of how to run an event loop in a different
		3513	thread from where callbacks are being invoked and watchers are
		3514	created/added/removed.
		3515
		3516	For a real-world example, see the C<EV::Loop::Async> perl module,
		3517	which uses exactly this technique (which is suited for many high-level
		3518	languages).
		3519
		3520	The example uses a pthread mutex to protect the loop data, a condition
		3521	variable to wait for callback invocations, an async watcher to notify the
		3522	event loop thread and an unspecified mechanism to wake up the main thread.
		3523
		3524	First, you need to associate some data with the event loop:
		3525
		3526	typedef struct {
		3527	mutex_t lock; /* global loop lock */
		3528	ev_async async_w;
		3529	thread_t tid;
		3530	cond_t invoke_cv;
		3531	} userdata;
		3532
		3533	void prepare_loop (EV_P)
		3534	{
		3535	// for simplicity, we use a static userdata struct.
		3536	static userdata u;
		3537
		3538	ev_async_init (&u->async_w, async_cb);
		3539	ev_async_start (EV_A_ &u->async_w);
		3540
		3541	pthread_mutex_init (&u->lock, 0);
		3542	pthread_cond_init (&u->invoke_cv, 0);
		3543
		3544	// now associate this with the loop
		3545	ev_set_userdata (EV_A_ u);
		3546	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		3547	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		3548
		3549	// then create the thread running ev_loop
		3550	pthread_create (&u->tid, 0, l_run, EV_A);
		3551	}
		3552
		3553	The callback for the C<ev_async> watcher does nothing: the watcher is used
		3554	solely to wake up the event loop so it takes notice of any new watchers
		3555	that might have been added:
		3556
		3557	static void
		3558	async_cb (EV_P_ ev_async *w, int revents)
		3559	{
		3560	// just used for the side effects
		3561	}
		3562
		3563	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		3564	protecting the loop data, respectively.
		3565
		3566	static void
		3567	l_release (EV_P)
		3568	{
		3569	userdata *u = ev_userdata (EV_A);
		3570	pthread_mutex_unlock (&u->lock);
		3571	}
		3572
		3573	static void
		3574	l_acquire (EV_P)
		3575	{
		3576	userdata *u = ev_userdata (EV_A);
		3577	pthread_mutex_lock (&u->lock);
		3578	}
		3579
		3580	The event loop thread first acquires the mutex, and then jumps straight
		3581	into C<ev_run>:
		3582
		3583	void *
		3584	l_run (void *thr_arg)
		3585	{
		3586	struct ev_loop loop = (struct ev_loop )thr_arg;
		3587
		3588	l_acquire (EV_A);
		3589	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		3590	ev_run (EV_A_ 0);
		3591	l_release (EV_A);
		3592
		3593	return 0;
		3594	}
		3595
		3596	Instead of invoking all pending watchers, the C<l_invoke> callback will
		3597	signal the main thread via some unspecified mechanism (signals? pipe
		3598	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		3599	have been called (in a while loop because a) spurious wakeups are possible
		3600	and b) skipping inter-thread-communication when there are no pending
		3601	watchers is very beneficial):
		3602
		3603	static void
		3604	l_invoke (EV_P)
		3605	{
		3606	userdata *u = ev_userdata (EV_A);
		3607
		3608	while (ev_pending_count (EV_A))
		3609	{
		3610	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		3611	pthread_cond_wait (&u->invoke_cv, &u->lock);
		3612	}
		3613	}
		3614
		3615	Now, whenever the main thread gets told to invoke pending watchers, it
		3616	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		3617	thread to continue:
		3618
		3619	static void
		3620	real_invoke_pending (EV_P)
		3621	{
		3622	userdata *u = ev_userdata (EV_A);
		3623
		3624	pthread_mutex_lock (&u->lock);
		3625	ev_invoke_pending (EV_A);
		3626	pthread_cond_signal (&u->invoke_cv);
		3627	pthread_mutex_unlock (&u->lock);
		3628	}
		3629
		3630	Whenever you want to start/stop a watcher or do other modifications to an
		3631	event loop, you will now have to lock:
		3632
		3633	ev_timer timeout_watcher;
		3634	userdata *u = ev_userdata (EV_A);
		3635
		3636	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		3637
		3638	pthread_mutex_lock (&u->lock);
		3639	ev_timer_start (EV_A_ &timeout_watcher);
		3640	ev_async_send (EV_A_ &u->async_w);
		3641	pthread_mutex_unlock (&u->lock);
		3642
		3643	Note that sending the C<ev_async> watcher is required because otherwise
		3644	an event loop currently blocking in the kernel will have no knowledge
		3645	about the newly added timer. By waking up the loop it will pick up any new
		3646	watchers in the next event loop iteration.
		3647
		3648	=head2 THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS
		3649
		3650	While the overhead of a callback that e.g. schedules a thread is small, it
		3651	is still an overhead. If you embed libev, and your main usage is with some
		3652	kind of threads or coroutines, you might want to customise libev so that
		3653	doesn't need callbacks anymore.
		3654
		3655	Imagine you have coroutines that you can switch to using a function
		3656	C<switch_to (coro)>, that libev runs in a coroutine called C<libev_coro>
		3657	and that due to some magic, the currently active coroutine is stored in a
		3658	global called C<current_coro>. Then you can build your own "wait for libev
		3659	event" primitive by changing C<EV_CB_DECLARE> and C<EV_CB_INVOKE> (note
		3660	the differing C<;> conventions):
		3661
		3662	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3663	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb)
		3664
		3665	That means instead of having a C callback function, you store the
		3666	coroutine to switch to in each watcher, and instead of having libev call
		3667	your callback, you instead have it switch to that coroutine.
		3668
		3669	A coroutine might now wait for an event with a function called
		3670	C<wait_for_event>. (the watcher needs to be started, as always, but it doesn't
		3671	matter when, or whether the watcher is active or not when this function is
		3672	called):
		3673
		3674	void
		3675	wait_for_event (ev_watcher *w)
		3676	{
		3677	ev_cb_set (w) = current_coro;
		3678	switch_to (libev_coro);
		3679	}
		3680
		3681	That basically suspends the coroutine inside C<wait_for_event> and
		3682	continues the libev coroutine, which, when appropriate, switches back to
		3683	this or any other coroutine. I am sure if you sue this your own :)
		3684
		3685	You can do similar tricks if you have, say, threads with an event queue -
		3686	instead of storing a coroutine, you store the queue object and instead of
		3687	switching to a coroutine, you push the watcher onto the queue and notify
		3688	any waiters.
		3689
		3690	To embed libev, see L<EMBEDDING>, but in short, it's easiest to create two
		3691	files, F<my_ev.h> and F<my_ev.c> that include the respective libev files:
		3692
		3693	// my_ev.h
		3694	#define EV_CB_DECLARE(type) struct my_coro *cb;
		3695	#define EV_CB_INVOKE(watcher) switch_to ((watcher)->cb);
		3696	#include "../libev/ev.h"
		3697
		3698	// my_ev.c
		3699	#define EV_H "my_ev.h"
		3700	#include "../libev/ev.c"
		3701
		3702	And then use F<my_ev.h> when you would normally use F<ev.h>, and compile
		3703	F<my_ev.c> into your project. When properly specifying include paths, you
		3704	can even use F<ev.h> as header file name directly.
3370		3705
3371		3706
3372	=head1 LIBEVENT EMULATION	3707	=head1 LIBEVENT EMULATION
3373		3708
3374	Libev offers a compatibility emulation layer for libevent. It cannot	3709	Libev offers a compatibility emulation layer for libevent. It cannot
3375	emulate the internals of libevent, so here are some usage hints:	3710	emulate the internals of libevent, so here are some usage hints:
3376		3711
3377	=over 4	3712	=over 4
		3713
		3714	=item * Only the libevent-1.4.1-beta API is being emulated.
		3715
		3716	This was the newest libevent version available when libev was implemented,
		3717	and is still mostly unchanged in 2010.
3378		3718
3379	=item * Use it by including <event.h>, as usual.	3719	=item * Use it by including <event.h>, as usual.
3380		3720
3381	=item * The following members are fully supported: ev_base, ev_callback,	3721	=item * The following members are fully supported: ev_base, ev_callback,
3382	ev_arg, ev_fd, ev_res, ev_events.	3722	ev_arg, ev_fd, ev_res, ev_events.
…		…
3417	Care has been taken to keep the overhead low. The only data member the C++	3757	Care has been taken to keep the overhead low. The only data member the C++
3418	classes add (compared to plain C-style watchers) is the event loop pointer	3758	classes add (compared to plain C-style watchers) is the event loop pointer
3419	that the watcher is associated with (or no additional members at all if	3759	that the watcher is associated with (or no additional members at all if
3420	you disable C<EV_MULTIPLICITY> when embedding libev).	3760	you disable C<EV_MULTIPLICITY> when embedding libev).
3421		3761
3422	Currently, functions, and static and non-static member functions can be	3762	Currently, functions, static and non-static member functions and classes
3423	used as callbacks. Other types should be easy to add as long as they only	3763	with C<operator ()> can be used as callbacks. Other types should be easy
3424	need one additional pointer for context. If you need support for other	3764	to add as long as they only need one additional pointer for context. If
3425	types of functors please contact the author (preferably after implementing	3765	you need support for other types of functors please contact the author
3426	it).	3766	(preferably after implementing it).
3427		3767
3428	Here is a list of things available in the C<ev> namespace:	3768	Here is a list of things available in the C<ev> namespace:
3429		3769
3430	=over 4	3770	=over 4
3431		3771
…		…
4299	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4639	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4300		4640
4301	#include "ev_cpp.h"	4641	#include "ev_cpp.h"
4302	#include "ev.c"	4642	#include "ev.c"
4303		4643
4304	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES	4644	=head1 INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT
4305		4645
4306	=head2 THREADS AND COROUTINES	4646	=head2 THREADS AND COROUTINES
4307		4647
4308	=head3 THREADS	4648	=head3 THREADS
4309		4649
…		…
4360	default loop and triggering an C<ev_async> watcher from the default loop	4700	default loop and triggering an C<ev_async> watcher from the default loop
4361	watcher callback into the event loop interested in the signal.	4701	watcher callback into the event loop interested in the signal.
4362		4702
4363	=back	4703	=back
4364		4704
4365	=head4 THREAD LOCKING EXAMPLE	4705	See also L<THREAD LOCKING EXAMPLE>.
4366
4367	Here is a fictitious example of how to run an event loop in a different
4368	thread than where callbacks are being invoked and watchers are
4369	created/added/removed.
4370
4371	For a real-world example, see the C<EV::Loop::Async> perl module,
4372	which uses exactly this technique (which is suited for many high-level
4373	languages).
4374
4375	The example uses a pthread mutex to protect the loop data, a condition
4376	variable to wait for callback invocations, an async watcher to notify the
4377	event loop thread and an unspecified mechanism to wake up the main thread.
4378
4379	First, you need to associate some data with the event loop:
4380
4381	typedef struct {
4382	mutex_t lock; /* global loop lock */
4383	ev_async async_w;
4384	thread_t tid;
4385	cond_t invoke_cv;
4386	} userdata;
4387
4388	void prepare_loop (EV_P)
4389	{
4390	// for simplicity, we use a static userdata struct.
4391	static userdata u;
4392
4393	ev_async_init (&u->async_w, async_cb);
4394	ev_async_start (EV_A_ &u->async_w);
4395
4396	pthread_mutex_init (&u->lock, 0);
4397	pthread_cond_init (&u->invoke_cv, 0);
4398
4399	// now associate this with the loop
4400	ev_set_userdata (EV_A_ u);
4401	ev_set_invoke_pending_cb (EV_A_ l_invoke);
4402	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4403
4404	// then create the thread running ev_loop
4405	pthread_create (&u->tid, 0, l_run, EV_A);
4406	}
4407
4408	The callback for the C<ev_async> watcher does nothing: the watcher is used
4409	solely to wake up the event loop so it takes notice of any new watchers
4410	that might have been added:
4411
4412	static void
4413	async_cb (EV_P_ ev_async *w, int revents)
4414	{
4415	// just used for the side effects
4416	}
4417
4418	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
4419	protecting the loop data, respectively.
4420
4421	static void
4422	l_release (EV_P)
4423	{
4424	userdata *u = ev_userdata (EV_A);
4425	pthread_mutex_unlock (&u->lock);
4426	}
4427
4428	static void
4429	l_acquire (EV_P)
4430	{
4431	userdata *u = ev_userdata (EV_A);
4432	pthread_mutex_lock (&u->lock);
4433	}
4434
4435	The event loop thread first acquires the mutex, and then jumps straight
4436	into C<ev_run>:
4437
4438	void *
4439	l_run (void *thr_arg)
4440	{
4441	struct ev_loop loop = (struct ev_loop )thr_arg;
4442
4443	l_acquire (EV_A);
4444	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4445	ev_run (EV_A_ 0);
4446	l_release (EV_A);
4447
4448	return 0;
4449	}
4450
4451	Instead of invoking all pending watchers, the C<l_invoke> callback will
4452	signal the main thread via some unspecified mechanism (signals? pipe
4453	writes? C<Async::Interrupt>?) and then waits until all pending watchers
4454	have been called (in a while loop because a) spurious wakeups are possible
4455	and b) skipping inter-thread-communication when there are no pending
4456	watchers is very beneficial):
4457
4458	static void
4459	l_invoke (EV_P)
4460	{
4461	userdata *u = ev_userdata (EV_A);
4462
4463	while (ev_pending_count (EV_A))
4464	{
4465	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4466	pthread_cond_wait (&u->invoke_cv, &u->lock);
4467	}
4468	}
4469
4470	Now, whenever the main thread gets told to invoke pending watchers, it
4471	will grab the lock, call C<ev_invoke_pending> and then signal the loop
4472	thread to continue:
4473
4474	static void
4475	real_invoke_pending (EV_P)
4476	{
4477	userdata *u = ev_userdata (EV_A);
4478
4479	pthread_mutex_lock (&u->lock);
4480	ev_invoke_pending (EV_A);
4481	pthread_cond_signal (&u->invoke_cv);
4482	pthread_mutex_unlock (&u->lock);
4483	}
4484
4485	Whenever you want to start/stop a watcher or do other modifications to an
4486	event loop, you will now have to lock:
4487
4488	ev_timer timeout_watcher;
4489	userdata *u = ev_userdata (EV_A);
4490
4491	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4492
4493	pthread_mutex_lock (&u->lock);
4494	ev_timer_start (EV_A_ &timeout_watcher);
4495	ev_async_send (EV_A_ &u->async_w);
4496	pthread_mutex_unlock (&u->lock);
4497
4498	Note that sending the C<ev_async> watcher is required because otherwise
4499	an event loop currently blocking in the kernel will have no knowledge
4500	about the newly added timer. By waking up the loop it will pick up any new
4501	watchers in the next event loop iteration.
4502		4706
4503	=head3 COROUTINES	4707	=head3 COROUTINES
4504		4708
4505	Libev is very accommodating to coroutines ("cooperative threads"):	4709	Libev is very accommodating to coroutines ("cooperative threads"):
4506	libev fully supports nesting calls to its functions from different	4710	libev fully supports nesting calls to its functions from different

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Comparing libev/ev.pod (file contents): Revision 1.343 by root, Wed Nov 10 13:39:10 2010 UTC vs. Revision 1.360 by root, Mon Jan 17 12:11:12 2011 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.343 by root, Wed Nov 10 13:39:10 2010 UTC vs.
Revision 1.360 by root, Mon Jan 17 12:11:12 2011 UTC