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

Comparing libev/ev.pod (file contents):
Revision 1.141 by root, Wed Apr 2 19:19:33 2008 UTC vs.
Revision 1.154 by root, Sun May 11 11:47:27 2008 UTC

…		…
64		64
65	=head1 DESCRIPTION	65	=head1 DESCRIPTION
66		66
67	The newest version of this document is also available as an html-formatted	67	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	68	web page you might find easier to navigate when reading it for the first
69	time: L<http://cvs.schmorp.de/libev/ev.html>.	69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
70		70
71	Libev is an event loop: you register interest in certain events (such as a	71	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	72	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	73	these event sources and provide your program with events.
74		74
…		…
196	See the description of C<ev_embed> watchers for more info.	196	See the description of C<ev_embed> watchers for more info.
197		197
198	=item ev_set_allocator (void (cb)(void *ptr, long size))	198	=item ev_set_allocator (void (cb)(void *ptr, long size))
199		199
200	Sets the allocation function to use (the prototype is similar - the	200	Sets the allocation function to use (the prototype is similar - the
201	semantics is identical - to the realloc C function). It is used to	201	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
202	allocate and free memory (no surprises here). If it returns zero when	202	used to allocate and free memory (no surprises here). If it returns zero
203	memory needs to be allocated, the library might abort or take some	203	when memory needs to be allocated (C<size != 0>), the library might abort
204	potentially destructive action. The default is your system realloc	204	or take some potentially destructive action.
205	function.	205
		206	Since some systems (at least OpenBSD and Darwin) fail to implement
		207	correct C<realloc> semantics, libev will use a wrapper around the system
		208	C<realloc> and C<free> functions by default.
206		209
207	You could override this function in high-availability programs to, say,	210	You could override this function in high-availability programs to, say,
208	free some memory if it cannot allocate memory, to use a special allocator,	211	free some memory if it cannot allocate memory, to use a special allocator,
209	or even to sleep a while and retry until some memory is available.	212	or even to sleep a while and retry until some memory is available.
210		213
211	Example: Replace the libev allocator with one that waits a bit and then	214	Example: Replace the libev allocator with one that waits a bit and then
212	retries).	215	retries (example requires a standards-compliant C<realloc>).
213		216
214	static void *	217	static void *
215	persistent_realloc (void *ptr, size_t size)	218	persistent_realloc (void *ptr, size_t size)
216	{	219	{
217	for (;;)	220	for (;;)
…		…
255	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	258	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
256		259
257	An event loop is described by a C<struct ev_loop *>. The library knows two	260	An event loop is described by a C<struct ev_loop *>. The library knows two
258	types of such loops, the I<default> loop, which supports signals and child	261	types of such loops, the I<default> loop, which supports signals and child
259	events, and dynamically created loops which do not.	262	events, and dynamically created loops which do not.
260
261	If you use threads, a common model is to run the default event loop
262	in your main thread (or in a separate thread) and for each thread you
263	create, you also create another event loop. Libev itself does no locking
264	whatsoever, so if you mix calls to the same event loop in different
265	threads, make sure you lock (this is usually a bad idea, though, even if
266	done correctly, because it's hideous and inefficient).
267		263
268	=over 4	264	=over 4
269		265
270	=item struct ev_loop *ev_default_loop (unsigned int flags)	266	=item struct ev_loop *ev_default_loop (unsigned int flags)
271		267
…		…
1377	Simply stops and restarts the periodic watcher again. This is only useful	1373	Simply stops and restarts the periodic watcher again. This is only useful
1378	when you changed some parameters or the reschedule callback would return	1374	when you changed some parameters or the reschedule callback would return
1379	a different time than the last time it was called (e.g. in a crond like	1375	a different time than the last time it was called (e.g. in a crond like
1380	program when the crontabs have changed).	1376	program when the crontabs have changed).
1381		1377
		1378	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1379
		1380	When active, returns the absolute time that the watcher is supposed to
		1381	trigger next.
		1382
1382	=item ev_tstamp offset [read-write]	1383	=item ev_tstamp offset [read-write]
1383		1384
1384	When repeating, this contains the offset value, otherwise this is the	1385	When repeating, this contains the offset value, otherwise this is the
1385	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1386	absolute point in time (the C<at> value passed to C<ev_periodic_set>).
1386		1387
…		…
1396	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]	1397	=item ev_tstamp (reschedule_cb)(struct ev_periodic w, ev_tstamp now) [read-write]
1397		1398
1398	The current reschedule callback, or C<0>, if this functionality is	1399	The current reschedule callback, or C<0>, if this functionality is
1399	switched off. Can be changed any time, but changes only take effect when	1400	switched off. Can be changed any time, but changes only take effect when
1400	the periodic timer fires or C<ev_periodic_again> is being called.	1401	the periodic timer fires or C<ev_periodic_again> is being called.
1401
1402	=item ev_tstamp at [read-only]
1403
1404	When active, contains the absolute time that the watcher is supposed to
1405	trigger next.
1406		1402
1407	=back	1403	=back
1408		1404
1409	=head3 Examples	1405	=head3 Examples
1410		1406
…		…
1614	as even with OS-supported change notifications, this can be	1610	as even with OS-supported change notifications, this can be
1615	resource-intensive.	1611	resource-intensive.
1616		1612
1617	At the time of this writing, only the Linux inotify interface is	1613	At the time of this writing, only the Linux inotify interface is
1618	implemented (implementing kqueue support is left as an exercise for the	1614	implemented (implementing kqueue support is left as an exercise for the
		1615	reader, note, however, that the author sees no way of implementing ev_stat
1619	reader). Inotify will be used to give hints only and should not change the	1616	semantics with kqueue). Inotify will be used to give hints only and should
1620	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1617	not change the semantics of C<ev_stat> watchers, which means that libev
1621	to fall back to regular polling again even with inotify, but changes are	1618	sometimes needs to fall back to regular polling again even with inotify,
1622	usually detected immediately, and if the file exists there will be no	1619	but changes are usually detected immediately, and if the file exists there
1623	polling.	1620	will be no polling.
1624		1621
1625	=head3 ABI Issues (Largefile Support)	1622	=head3 ABI Issues (Largefile Support)
1626		1623
1627	Libev by default (unless the user overrides this) uses the default	1624	Libev by default (unless the user overrides this) uses the default
1628	compilation environment, which means that on systems with optionally	1625	compilation environment, which means that on systems with optionally
…		…
1638	When C<inotify (7)> support has been compiled into libev (generally only	1635	When C<inotify (7)> support has been compiled into libev (generally only
1639	available on Linux) and present at runtime, it will be used to speed up	1636	available on Linux) and present at runtime, it will be used to speed up
1640	change detection where possible. The inotify descriptor will be created lazily	1637	change detection where possible. The inotify descriptor will be created lazily
1641	when the first C<ev_stat> watcher is being started.	1638	when the first C<ev_stat> watcher is being started.
1642		1639
1643	Inotify presense does not change the semantics of C<ev_stat> watchers	1640	Inotify presence does not change the semantics of C<ev_stat> watchers
1644	except that changes might be detected earlier, and in some cases, to avoid	1641	except that changes might be detected earlier, and in some cases, to avoid
1645	making regular C<stat> calls. Even in the presense of inotify support	1642	making regular C<stat> calls. Even in the presence of inotify support
1646	there are many cases where libev has to resort to regular C<stat> polling.	1643	there are many cases where libev has to resort to regular C<stat> polling.
1647		1644
1648	(There is no support for kqueue, as apparently it cannot be used to	1645	(There is no support for kqueue, as apparently it cannot be used to
1649	implement this functionality, due to the requirement of having a file	1646	implement this functionality, due to the requirement of having a file
1650	descriptor open on the object at all times).	1647	descriptor open on the object at all times).
…		…
1653		1650
1654	The C<stat ()> syscall only supports full-second resolution portably, and	1651	The C<stat ()> syscall only supports full-second resolution portably, and
1655	even on systems where the resolution is higher, many filesystems still	1652	even on systems where the resolution is higher, many filesystems still
1656	only support whole seconds.	1653	only support whole seconds.
1657		1654
1658	That means that, if the time is the only thing that changes, you might	1655	That means that, if the time is the only thing that changes, you can
1659	miss updates: on the first update, C<ev_stat> detects a change and calls	1656	easily miss updates: on the first update, C<ev_stat> detects a change and
1660	your callback, which does something. When there is another update within	1657	calls your callback, which does something. When there is another update
1661	the same second, C<ev_stat> will be unable to detect it.	1658	within the same second, C<ev_stat> will be unable to detect it as the stat
		1659	data does not change.
1662		1660
1663	The solution to this is to delay acting on a change for a second (or till	1661	The solution to this is to delay acting on a change for slightly more
1664	the next second boundary), using a roughly one-second delay C<ev_timer>	1662	than second (or till slightly after the next full second boundary), using
1665	(C<ev_timer_set (w, 0., 1.01); ev_timer_again (loop, w)>). The C<.01>	1663	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1666	is added to work around small timing inconsistencies of some operating	1664	ev_timer_again (loop, w)>).
1667	systems.	1665
		1666	The C<.02> offset is added to work around small timing inconsistencies
		1667	of some operating systems (where the second counter of the current time
		1668	might be be delayed. One such system is the Linux kernel, where a call to
		1669	C<gettimeofday> might return a timestamp with a full second later than
		1670	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		1671	update file times then there will be a small window where the kernel uses
		1672	the previous second to update file times but libev might already execute
		1673	the timer callback).
1668		1674
1669	=head3 Watcher-Specific Functions and Data Members	1675	=head3 Watcher-Specific Functions and Data Members
1670		1676
1671	=over 4	1677	=over 4
1672		1678
…		…
1678	C<path>. The C<interval> is a hint on how quickly a change is expected to	1684	C<path>. The C<interval> is a hint on how quickly a change is expected to
1679	be detected and should normally be specified as C<0> to let libev choose	1685	be detected and should normally be specified as C<0> to let libev choose
1680	a suitable value. The memory pointed to by C<path> must point to the same	1686	a suitable value. The memory pointed to by C<path> must point to the same
1681	path for as long as the watcher is active.	1687	path for as long as the watcher is active.
1682		1688
1683	The callback will be receive C<EV_STAT> when a change was detected,	1689	The callback will receive C<EV_STAT> when a change was detected, relative
1684	relative to the attributes at the time the watcher was started (or the	1690	to the attributes at the time the watcher was started (or the last change
1685	last change was detected).	1691	was detected).
1686		1692
1687	=item ev_stat_stat (loop, ev_stat *)	1693	=item ev_stat_stat (loop, ev_stat *)
1688		1694
1689	Updates the stat buffer immediately with new values. If you change the	1695	Updates the stat buffer immediately with new values. If you change the
1690	watched path in your callback, you could call this fucntion to avoid	1696	watched path in your callback, you could call this function to avoid
1691	detecting this change (while introducing a race condition). Can also be	1697	detecting this change (while introducing a race condition if you are not
1692	useful simply to find out the new values.	1698	the only one changing the path). Can also be useful simply to find out the
		1699	new values.
1693		1700
1694	=item ev_statdata attr [read-only]	1701	=item ev_statdata attr [read-only]
1695		1702
1696	The most-recently detected attributes of the file. Although the type is of	1703	The most-recently detected attributes of the file. Although the type is
1697	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	1704	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1698	suitable for your system. If the C<st_nlink> member is C<0>, then there	1705	suitable for your system, but you can only rely on the POSIX-standardised
		1706	members to be present. If the C<st_nlink> member is C<0>, then there was
1699	was some error while C<stat>ing the file.	1707	some error while C<stat>ing the file.
1700		1708
1701	=item ev_statdata prev [read-only]	1709	=item ev_statdata prev [read-only]
1702		1710
1703	The previous attributes of the file. The callback gets invoked whenever	1711	The previous attributes of the file. The callback gets invoked whenever
1704	C<prev> != C<attr>.	1712	C<prev> != C<attr>, or, more precisely, one or more of these members
		1713	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		1714	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1705		1715
1706	=item ev_tstamp interval [read-only]	1716	=item ev_tstamp interval [read-only]
1707		1717
1708	The specified interval.	1718	The specified interval.
1709		1719
…		…
1763	}	1773	}
1764		1774
1765	...	1775	...
1766	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	1776	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1767	ev_stat_start (loop, &passwd);	1777	ev_stat_start (loop, &passwd);
1768	ev_timer_init (&timer, timer_cb, 0., 1.01);	1778	ev_timer_init (&timer, timer_cb, 0., 1.02);
1769		1779
1770		1780
1771	=head2 C<ev_idle> - when you've got nothing better to do...	1781	=head2 C<ev_idle> - when you've got nothing better to do...
1772		1782
1773	Idle watchers trigger events when no other events of the same or higher	1783	Idle watchers trigger events when no other events of the same or higher
…		…
1861		1871
1862	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	1872	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1863	priority, to ensure that they are being run before any other watchers	1873	priority, to ensure that they are being run before any other watchers
1864	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	1874	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
1865	too) should not activate ("feed") events into libev. While libev fully	1875	too) should not activate ("feed") events into libev. While libev fully
1866	supports this, they will be called before other C<ev_check> watchers	1876	supports this, they might get executed before other C<ev_check> watchers
1867	did their job. As C<ev_check> watchers are often used to embed other	1877	did their job. As C<ev_check> watchers are often used to embed other
1868	(non-libev) event loops those other event loops might be in an unusable	1878	(non-libev) event loops those other event loops might be in an unusable
1869	state until their C<ev_check> watcher ran (always remind yourself to	1879	state until their C<ev_check> watcher ran (always remind yourself to
1870	coexist peacefully with others).	1880	coexist peacefully with others).
1871		1881
…		…
1886	=head3 Examples	1896	=head3 Examples
1887		1897
1888	There are a number of principal ways to embed other event loops or modules	1898	There are a number of principal ways to embed other event loops or modules
1889	into libev. Here are some ideas on how to include libadns into libev	1899	into libev. Here are some ideas on how to include libadns into libev
1890	(there is a Perl module named C<EV::ADNS> that does this, which you could	1900	(there is a Perl module named C<EV::ADNS> that does this, which you could
1891	use for an actually working example. Another Perl module named C<EV::Glib>	1901	use as a working example. Another Perl module named C<EV::Glib> embeds a
1892	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	1902	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1893	into the Glib event loop).	1903	Glib event loop).
1894		1904
1895	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	1905	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1896	and in a check watcher, destroy them and call into libadns. What follows	1906	and in a check watcher, destroy them and call into libadns. What follows
1897	is pseudo-code only of course. This requires you to either use a low	1907	is pseudo-code only of course. This requires you to either use a low
1898	priority for the check watcher or use C<ev_clear_pending> explicitly, as	1908	priority for the check watcher or use C<ev_clear_pending> explicitly, as
…		…
2382		2392
2383	=item * Priorities are not currently supported. Initialising priorities	2393	=item * Priorities are not currently supported. Initialising priorities
2384	will fail and all watchers will have the same priority, even though there	2394	will fail and all watchers will have the same priority, even though there
2385	is an ev_pri field.	2395	is an ev_pri field.
2386		2396
		2397	=item * In libevent, the last base created gets the signals, in libev, the
		2398	first base created (== the default loop) gets the signals.
		2399
2387	=item * Other members are not supported.	2400	=item * Other members are not supported.
2388		2401
2389	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2402	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2390	to use the libev header file and library.	2403	to use the libev header file and library.
2391		2404
…		…
2633	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	2646	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2634		2647
2635	Similar to the other two macros, this gives you the value of the default	2648	Similar to the other two macros, this gives you the value of the default
2636	loop, if multiple loops are supported ("ev loop default").	2649	loop, if multiple loops are supported ("ev loop default").
2637		2650
		2651	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2652
		2653	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2654	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2655	is undefined when the default loop has not been initialised by a previous
		2656	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2657
		2658	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2659	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2660
2638	=back	2661	=back
2639		2662
2640	Example: Declare and initialise a check watcher, utilising the above	2663	Example: Declare and initialise a check watcher, utilising the above
2641	macros so it will work regardless of whether multiple loops are supported	2664	macros so it will work regardless of whether multiple loops are supported
2642	or not.	2665	or not.
…		…
2737		2760
2738	libev.m4	2761	libev.m4
2739		2762
2740	=head2 PREPROCESSOR SYMBOLS/MACROS	2763	=head2 PREPROCESSOR SYMBOLS/MACROS
2741		2764
2742	Libev can be configured via a variety of preprocessor symbols you have to define	2765	Libev can be configured via a variety of preprocessor symbols you have to
2743	before including any of its files. The default is not to build for multiplicity	2766	define before including any of its files. The default in the absense of
2744	and only include the select backend.	2767	autoconf is noted for every option.
2745		2768
2746	=over 4	2769	=over 4
2747		2770
2748	=item EV_STANDALONE	2771	=item EV_STANDALONE
2749		2772
…		…
2775	=item EV_USE_NANOSLEEP	2798	=item EV_USE_NANOSLEEP
2776		2799
2777	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	2800	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2778	and will use it for delays. Otherwise it will use C<select ()>.	2801	and will use it for delays. Otherwise it will use C<select ()>.
2779		2802
		2803	=item EV_USE_EVENTFD
		2804
		2805	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2806	available and will probe for kernel support at runtime. This will improve
		2807	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2808	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2809	2.7 or newer, otherwise disabled.
		2810
2780	=item EV_USE_SELECT	2811	=item EV_USE_SELECT
2781		2812
2782	If undefined or defined to be C<1>, libev will compile in support for the	2813	If undefined or defined to be C<1>, libev will compile in support for the
2783	C<select>(2) backend. No attempt at autodetection will be done: if no	2814	C<select>(2) backend. No attempt at autodetection will be done: if no
2784	other method takes over, select will be it. Otherwise the select backend	2815	other method takes over, select will be it. Otherwise the select backend
…		…
2820		2851
2821	=item EV_USE_EPOLL	2852	=item EV_USE_EPOLL
2822		2853
2823	If defined to be C<1>, libev will compile in support for the Linux	2854	If defined to be C<1>, libev will compile in support for the Linux
2824	C<epoll>(7) backend. Its availability will be detected at runtime,	2855	C<epoll>(7) backend. Its availability will be detected at runtime,
2825	otherwise another method will be used as fallback. This is the	2856	otherwise another method will be used as fallback. This is the preferred
2826	preferred backend for GNU/Linux systems.	2857	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2858	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2827		2859
2828	=item EV_USE_KQUEUE	2860	=item EV_USE_KQUEUE
2829		2861
2830	If defined to be C<1>, libev will compile in support for the BSD style	2862	If defined to be C<1>, libev will compile in support for the BSD style
2831	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	2863	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2850		2882
2851	=item EV_USE_INOTIFY	2883	=item EV_USE_INOTIFY
2852		2884
2853	If defined to be C<1>, libev will compile in support for the Linux inotify	2885	If defined to be C<1>, libev will compile in support for the Linux inotify
2854	interface to speed up C<ev_stat> watchers. Its actual availability will	2886	interface to speed up C<ev_stat> watchers. Its actual availability will
2855	be detected at runtime.	2887	be detected at runtime. If undefined, it will be enabled if the headers
		2888	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2856		2889
2857	=item EV_ATOMIC_T	2890	=item EV_ATOMIC_T
2858		2891
2859	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	2892	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2860	access is atomic with respect to other threads or signal contexts. No such	2893	access is atomic with respect to other threads or signal contexts. No such
…		…
2947	defined to be C<0>, then they are not.	2980	defined to be C<0>, then they are not.
2948		2981
2949	=item EV_MINIMAL	2982	=item EV_MINIMAL
2950		2983
2951	If you need to shave off some kilobytes of code at the expense of some	2984	If you need to shave off some kilobytes of code at the expense of some
2952	speed, define this symbol to C<1>. Currently only used for gcc to override	2985	speed, define this symbol to C<1>. Currently this is used to override some
2953	some inlining decisions, saves roughly 30% codesize of amd64.	2986	inlining decisions, saves roughly 30% codesize of amd64. It also selects a
		2987	much smaller 2-heap for timer management over the default 4-heap.
2954		2988
2955	=item EV_PID_HASHSIZE	2989	=item EV_PID_HASHSIZE
2956		2990
2957	C<ev_child> watchers use a small hash table to distribute workload by	2991	C<ev_child> watchers use a small hash table to distribute workload by
2958	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	2992	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
2964	C<ev_stat> watchers use a small hash table to distribute workload by	2998	C<ev_stat> watchers use a small hash table to distribute workload by
2965	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	2999	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2966	usually more than enough. If you need to manage thousands of C<ev_stat>	3000	usually more than enough. If you need to manage thousands of C<ev_stat>
2967	watchers you might want to increase this value (I<must> be a power of	3001	watchers you might want to increase this value (I<must> be a power of
2968	two).	3002	two).
		3003
		3004	=item EV_USE_4HEAP
		3005
		3006	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3007	timer and periodics heap, libev uses a 4-heap when this symbol is defined
		3008	to C<1>. The 4-heap uses more complicated (longer) code but has a
		3009	noticable after performance with many (thousands) of watchers.
		3010
		3011	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3012	(disabled).
		3013
		3014	=item EV_HEAP_CACHE_AT
		3015
		3016	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3017	timer and periodics heap, libev can cache the timestamp (I<at>) within
		3018	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3019	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3020	but avoids random read accesses on heap changes. This noticably improves
		3021	performance noticably with with many (hundreds) of watchers.
		3022
		3023	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3024	(disabled).
2969		3025
2970	=item EV_COMMON	3026	=item EV_COMMON
2971		3027
2972	By default, all watchers have a C<void *data> member. By redefining	3028	By default, all watchers have a C<void *data> member. By redefining
2973	this macro to a something else you can include more and other types of	3029	this macro to a something else you can include more and other types of
…		…
3047		3103
3048	#include "ev_cpp.h"	3104	#include "ev_cpp.h"
3049	#include "ev.c"	3105	#include "ev.c"
3050		3106
3051		3107
		3108	=head1 THREADS AND COROUTINES
		3109
		3110	=head2 THREADS
		3111
		3112	Libev itself is completely threadsafe, but it uses no locking. This
		3113	means that you can use as many loops as you want in parallel, as long as
		3114	only one thread ever calls into one libev function with the same loop
		3115	parameter.
		3116
		3117	Or put differently: calls with different loop parameters can be done in
		3118	parallel from multiple threads, calls with the same loop parameter must be
		3119	done serially (but can be done from different threads, as long as only one
		3120	thread ever is inside a call at any point in time, e.g. by using a mutex
		3121	per loop).
		3122
		3123	If you want to know which design is best for your problem, then I cannot
		3124	help you but by giving some generic advice:
		3125
		3126	=over 4
		3127
		3128	=item * most applications have a main thread: use the default libev loop
		3129	in that thread, or create a seperate thread running only the default loop.
		3130
		3131	This helps integrating other libraries or software modules that use libev
		3132	themselves and don't care/know about threading.
		3133
		3134	=item * one loop per thread is usually a good model.
		3135
		3136	Doing this is almost never wrong, sometimes a better-performance model
		3137	exists, but it is always a good start.
		3138
		3139	=item * other models exist, such as the leader/follower pattern, where one
		3140	loop is handed through multiple threads in a kind of round-robbin fashion.
		3141
		3142	Chosing a model is hard - look around, learn, know that usually you cna do
		3143	better than you currently do :-)
		3144
		3145	=item * often you need to talk to some other thread which blocks in the
		3146	event loop - C<ev_async> watchers can be used to wake them up from other
		3147	threads safely (or from signal contexts...).
		3148
		3149	=back
		3150
		3151	=head2 COROUTINES
		3152
		3153	Libev is much more accomodating to coroutines ("cooperative threads"):
		3154	libev fully supports nesting calls to it's functions from different
		3155	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3156	different coroutines and switch freely between both coroutines running the
		3157	loop, as long as you don't confuse yourself). The only exception is that
		3158	you must not do this from C<ev_periodic> reschedule callbacks.
		3159
		3160	Care has been invested into making sure that libev does not keep local
		3161	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3162	switches.
		3163
		3164
3052	=head1 COMPLEXITIES	3165	=head1 COMPLEXITIES
3053		3166
3054	In this section the complexities of (many of) the algorithms used inside	3167	In this section the complexities of (many of) the algorithms used inside
3055	libev will be explained. For complexity discussions about backends see the	3168	libev will be explained. For complexity discussions about backends see the
3056	documentation for C<ev_default_init>.	3169	documentation for C<ev_default_init>.
…		…
3086	correct watcher to remove. The lists are usually short (you don't usually	3199	correct watcher to remove. The lists are usually short (you don't usually
3087	have many watchers waiting for the same fd or signal).	3200	have many watchers waiting for the same fd or signal).
3088		3201
3089	=item Finding the next timer in each loop iteration: O(1)	3202	=item Finding the next timer in each loop iteration: O(1)
3090		3203
3091	By virtue of using a binary heap, the next timer is always found at the	3204	By virtue of using a binary or 4-heap, the next timer is always found at a
3092	beginning of the storage array.	3205	fixed position in the storage array.
3093		3206
3094	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3207	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3095		3208
3096	A change means an I/O watcher gets started or stopped, which requires	3209	A change means an I/O watcher gets started or stopped, which requires
3097	libev to recalculate its status (and possibly tell the kernel, depending	3210	libev to recalculate its status (and possibly tell the kernel, depending
…		…
3126	model. Libev still offers limited functionality on this platform in	3239	model. Libev still offers limited functionality on this platform in
3127	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3240	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3128	descriptors. This only applies when using Win32 natively, not when using	3241	descriptors. This only applies when using Win32 natively, not when using
3129	e.g. cygwin.	3242	e.g. cygwin.
3130		3243
		3244	Lifting these limitations would basically require the full
		3245	re-implementation of the I/O system. If you are into these kinds of
		3246	things, then note that glib does exactly that for you in a very portable
		3247	way (note also that glib is the slowest event library known to man).
		3248
3131	There is no supported compilation method available on windows except	3249	There is no supported compilation method available on windows except
3132	embedding it into other applications.	3250	embedding it into other applications.
3133		3251
3134	Due to the many, low, and arbitrary limits on the win32 platform and the	3252	Due to the many, low, and arbitrary limits on the win32 platform and
3135	abysmal performance of winsockets, using a large number of sockets is not	3253	the abysmal performance of winsockets, using a large number of sockets
3136	recommended (and not reasonable). If your program needs to use more than	3254	is not recommended (and not reasonable). If your program needs to use
3137	a hundred or so sockets, then likely it needs to use a totally different	3255	more than a hundred or so sockets, then likely it needs to use a totally
3138	implementation for windows, as libev offers the POSIX model, which cannot	3256	different implementation for windows, as libev offers the POSIX readyness
3139	be implemented efficiently on windows (microsoft monopoly games).	3257	notification model, which cannot be implemented efficiently on windows
		3258	(microsoft monopoly games).
3140		3259
3141	=over 4	3260	=over 4
3142		3261
3143	=item The winsocket select function	3262	=item The winsocket select function
3144		3263
…		…
3158	Note that winsockets handling of fd sets is O(n), so you can easily get a	3277	Note that winsockets handling of fd sets is O(n), so you can easily get a
3159	complexity in the O(n²) range when using win32.	3278	complexity in the O(n²) range when using win32.
3160		3279
3161	=item Limited number of file descriptors	3280	=item Limited number of file descriptors
3162		3281
3163	Windows has numerous arbitrary (and low) limits on things. Early versions	3282	Windows has numerous arbitrary (and low) limits on things.
3164	of winsocket's select only supported waiting for a max. of C<64> handles	3283
		3284	Early versions of winsocket's select only supported waiting for a maximum
3165	(probably owning to the fact that all windows kernels can only wait for	3285	of C<64> handles (probably owning to the fact that all windows kernels
3166	C<64> things at the same time internally; microsoft recommends spawning a	3286	can only wait for C<64> things at the same time internally; microsoft
3167	chain of threads and wait for 63 handles and the previous thread in each).	3287	recommends spawning a chain of threads and wait for 63 handles and the
		3288	previous thread in each. Great).
3168		3289
3169	Newer versions support more handles, but you need to define C<FD_SETSIZE>	3290	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3170	to some high number (e.g. C<2048>) before compiling the winsocket select	3291	to some high number (e.g. C<2048>) before compiling the winsocket select
3171	call (which might be in libev or elsewhere, for example, perl does its own	3292	call (which might be in libev or elsewhere, for example, perl does its own
3172	select emulation on windows).	3293	select emulation on windows).
…		…
3184	calling select (O(n²)) will likely make this unworkable.	3305	calling select (O(n²)) will likely make this unworkable.
3185		3306
3186	=back	3307	=back
3187		3308
3188		3309
		3310	=head1 PORTABILITY REQUIREMENTS
		3311
		3312	In addition to a working ISO-C implementation, libev relies on a few
		3313	additional extensions:
		3314
		3315	=over 4
		3316
		3317	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3318
		3319	The type C<sig_atomic_t volatile> (or whatever is defined as
		3320	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3321	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3322	believed to be sufficiently portable.
		3323
		3324	=item C<sigprocmask> must work in a threaded environment
		3325
		3326	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3327	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3328	pthread implementations will either allow C<sigprocmask> in the "main
		3329	thread" or will block signals process-wide, both behaviours would
		3330	be compatible with libev. Interaction between C<sigprocmask> and
		3331	C<pthread_sigmask> could complicate things, however.
		3332
		3333	The most portable way to handle signals is to block signals in all threads
		3334	except the initial one, and run the default loop in the initial thread as
		3335	well.
		3336
		3337	=item C<long> must be large enough for common memory allocation sizes
		3338
		3339	To improve portability and simplify using libev, libev uses C<long>
		3340	internally instead of C<size_t> when allocating its data structures. On
		3341	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3342	is still at least 31 bits everywhere, which is enough for hundreds of
		3343	millions of watchers.
		3344
		3345	=item C<double> must hold a time value in seconds with enough accuracy
		3346
		3347	The type C<double> is used to represent timestamps. It is required to
		3348	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3349	enough for at least into the year 4000. This requirement is fulfilled by
		3350	implementations implementing IEEE 754 (basically all existing ones).
		3351
		3352	=back
		3353
		3354	If you know of other additional requirements drop me a note.
		3355
		3356
3189	=head1 AUTHOR	3357	=head1 AUTHOR
3190		3358
3191	Marc Lehmann <libev@schmorp.de>.	3359	Marc Lehmann <libev@schmorp.de>.
3192		3360

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Revision 1.141 by root, Wed Apr 2 19:19:33 2008 UTC vs.
Revision 1.154 by root, Sun May 11 11:47:27 2008 UTC