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

Comparing libev/ev.pod (file contents):
Revision 1.144 by root, Mon Apr 7 12:33:29 2008 UTC vs.
Revision 1.150 by root, Tue May 6 23:34:16 2008 UTC

…		…
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 (;;)
…		…
1370	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
1371	when you changed some parameters or the reschedule callback would return	1374	when you changed some parameters or the reschedule callback would return
1372	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
1373	program when the crontabs have changed).	1376	program when the crontabs have changed).
1374		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
1375	=item ev_tstamp offset [read-write]	1383	=item ev_tstamp offset [read-write]
1376		1384
1377	When repeating, this contains the offset value, otherwise this is the	1385	When repeating, this contains the offset value, otherwise this is the
1378	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>).
1379		1387
…		…
1389	=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]
1390		1398
1391	The current reschedule callback, or C<0>, if this functionality is	1399	The current reschedule callback, or C<0>, if this functionality is
1392	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
1393	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.
1394
1395	=item ev_tstamp at [read-only]
1396
1397	When active, contains the absolute time that the watcher is supposed to
1398	trigger next.
1399		1402
1400	=back	1403	=back
1401		1404
1402	=head3 Examples	1405	=head3 Examples
1403		1406
…		…
1607	as even with OS-supported change notifications, this can be	1610	as even with OS-supported change notifications, this can be
1608	resource-intensive.	1611	resource-intensive.
1609		1612
1610	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
1611	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
1612	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
1613	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
1614	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,
1615	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
1616	polling.	1620	will be no polling.
1617		1621
1618	=head3 ABI Issues (Largefile Support)	1622	=head3 ABI Issues (Largefile Support)
1619		1623
1620	Libev by default (unless the user overrides this) uses the default	1624	Libev by default (unless the user overrides this) uses the default
1621	compilation environment, which means that on systems with optionally	1625	compilation environment, which means that on systems with optionally
…		…
1631	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
1632	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
1633	change detection where possible. The inotify descriptor will be created lazily	1637	change detection where possible. The inotify descriptor will be created lazily
1634	when the first C<ev_stat> watcher is being started.	1638	when the first C<ev_stat> watcher is being started.
1635		1639
1636	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
1637	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
1638	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
1639	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.
1640		1644
1641	(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
1642	implement this functionality, due to the requirement of having a file	1646	implement this functionality, due to the requirement of having a file
1643	descriptor open on the object at all times).	1647	descriptor open on the object at all times).
…		…
1646		1650
1647	The C<stat ()> syscall only supports full-second resolution portably, and	1651	The C<stat ()> syscall only supports full-second resolution portably, and
1648	even on systems where the resolution is higher, many filesystems still	1652	even on systems where the resolution is higher, many filesystems still
1649	only support whole seconds.	1653	only support whole seconds.
1650		1654
1651	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
1652	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
1653	your callback, which does something. When there is another update within	1657	calls your callback, which does something. When there is another update
1654	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.
1655		1660
1656	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
1657	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
1658	(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);
1659	is added to work around small timing inconsistencies of some operating	1664	ev_timer_again (loop, w)>).
1660	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).
1661		1674
1662	=head3 Watcher-Specific Functions and Data Members	1675	=head3 Watcher-Specific Functions and Data Members
1663		1676
1664	=over 4	1677	=over 4
1665		1678
…		…
1671	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
1672	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
1673	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
1674	path for as long as the watcher is active.	1687	path for as long as the watcher is active.
1675		1688
1676	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
1677	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
1678	last change was detected).	1691	was detected).
1679		1692
1680	=item ev_stat_stat (loop, ev_stat *)	1693	=item ev_stat_stat (loop, ev_stat *)
1681		1694
1682	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
1683	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
1684	detecting this change (while introducing a race condition). Can also be	1697	detecting this change (while introducing a race condition if you are not
1685	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.
1686		1700
1687	=item ev_statdata attr [read-only]	1701	=item ev_statdata attr [read-only]
1688		1702
1689	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
1690	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
1691	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
1692	was some error while C<stat>ing the file.	1707	some error while C<stat>ing the file.
1693		1708
1694	=item ev_statdata prev [read-only]	1709	=item ev_statdata prev [read-only]
1695		1710
1696	The previous attributes of the file. The callback gets invoked whenever	1711	The previous attributes of the file. The callback gets invoked whenever
1697	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>.
1698		1715
1699	=item ev_tstamp interval [read-only]	1716	=item ev_tstamp interval [read-only]
1700		1717
1701	The specified interval.	1718	The specified interval.
1702		1719
…		…
1756	}	1773	}
1757		1774
1758	...	1775	...
1759	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);	1776	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1760	ev_stat_start (loop, &passwd);	1777	ev_stat_start (loop, &passwd);
1761	ev_timer_init (&timer, timer_cb, 0., 1.01);	1778	ev_timer_init (&timer, timer_cb, 0., 1.02);
1762		1779
1763		1780
1764	=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...
1765		1782
1766	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
…		…
1854		1871
1855	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>)
1856	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
1857	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,
1858	too) should not activate ("feed") events into libev. While libev fully	1875	too) should not activate ("feed") events into libev. While libev fully
1859	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
1860	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
1861	(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
1862	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
1863	coexist peacefully with others).	1880	coexist peacefully with others).
1864		1881
…		…
1879	=head3 Examples	1896	=head3 Examples
1880		1897
1881	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
1882	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
1883	(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
1884	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
1885	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
1886	into the Glib event loop).	1903	Glib event loop).
1887		1904
1888	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,
1889	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
1890	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
1891	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
…		…
2375		2392
2376	=item * Priorities are not currently supported. Initialising priorities	2393	=item * Priorities are not currently supported. Initialising priorities
2377	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
2378	is an ev_pri field.	2395	is an ev_pri field.
2379		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
2380	=item * Other members are not supported.	2400	=item * Other members are not supported.
2381		2401
2382	=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
2383	to use the libev header file and library.	2403	to use the libev header file and library.
2384		2404
…		…
3196	model. Libev still offers limited functionality on this platform in	3216	model. Libev still offers limited functionality on this platform in
3197	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3217	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
3198	descriptors. This only applies when using Win32 natively, not when using	3218	descriptors. This only applies when using Win32 natively, not when using
3199	e.g. cygwin.	3219	e.g. cygwin.
3200		3220
		3221	Lifting these limitations would basically require the full
		3222	re-implementation of the I/O system. If you are into these kinds of
		3223	things, then note that glib does exactly that for you in a very portable
		3224	way (note also that glib is the slowest event library known to man).
		3225
3201	There is no supported compilation method available on windows except	3226	There is no supported compilation method available on windows except
3202	embedding it into other applications.	3227	embedding it into other applications.
3203		3228
3204	Due to the many, low, and arbitrary limits on the win32 platform and the	3229	Due to the many, low, and arbitrary limits on the win32 platform and
3205	abysmal performance of winsockets, using a large number of sockets is not	3230	the abysmal performance of winsockets, using a large number of sockets
3206	recommended (and not reasonable). If your program needs to use more than	3231	is not recommended (and not reasonable). If your program needs to use
3207	a hundred or so sockets, then likely it needs to use a totally different	3232	more than a hundred or so sockets, then likely it needs to use a totally
3208	implementation for windows, as libev offers the POSIX model, which cannot	3233	different implementation for windows, as libev offers the POSIX readyness
3209	be implemented efficiently on windows (microsoft monopoly games).	3234	notification model, which cannot be implemented efficiently on windows
		3235	(microsoft monopoly games).
3210		3236
3211	=over 4	3237	=over 4
3212		3238
3213	=item The winsocket select function	3239	=item The winsocket select function
3214		3240
…		…
3228	Note that winsockets handling of fd sets is O(n), so you can easily get a	3254	Note that winsockets handling of fd sets is O(n), so you can easily get a
3229	complexity in the O(n²) range when using win32.	3255	complexity in the O(n²) range when using win32.
3230		3256
3231	=item Limited number of file descriptors	3257	=item Limited number of file descriptors
3232		3258
3233	Windows has numerous arbitrary (and low) limits on things. Early versions	3259	Windows has numerous arbitrary (and low) limits on things.
3234	of winsocket's select only supported waiting for a max. of C<64> handles	3260
		3261	Early versions of winsocket's select only supported waiting for a maximum
3235	(probably owning to the fact that all windows kernels can only wait for	3262	of C<64> handles (probably owning to the fact that all windows kernels
3236	C<64> things at the same time internally; microsoft recommends spawning a	3263	can only wait for C<64> things at the same time internally; microsoft
3237	chain of threads and wait for 63 handles and the previous thread in each).	3264	recommends spawning a chain of threads and wait for 63 handles and the
		3265	previous thread in each. Great).
3238		3266
3239	Newer versions support more handles, but you need to define C<FD_SETSIZE>	3267	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3240	to some high number (e.g. C<2048>) before compiling the winsocket select	3268	to some high number (e.g. C<2048>) before compiling the winsocket select
3241	call (which might be in libev or elsewhere, for example, perl does its own	3269	call (which might be in libev or elsewhere, for example, perl does its own
3242	select emulation on windows).	3270	select emulation on windows).
…		…
3254	calling select (O(n²)) will likely make this unworkable.	3282	calling select (O(n²)) will likely make this unworkable.
3255		3283
3256	=back	3284	=back
3257		3285
3258		3286
		3287	=head1 PORTABILITY REQUIREMENTS
		3288
		3289	In addition to a working ISO-C implementation, libev relies on a few
		3290	additional extensions:
		3291
		3292	=over 4
		3293
		3294	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3295
		3296	The type C<sig_atomic_t volatile> (or whatever is defined as
		3297	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3298	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3299	believed to be sufficiently portable.
		3300
		3301	=item C<sigprocmask> must work in a threaded environment
		3302
		3303	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3304	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3305	pthread implementations will either allow C<sigprocmask> in the "main
		3306	thread" or will block signals process-wide, both behaviours would
		3307	be compatible with libev. Interaction between C<sigprocmask> and
		3308	C<pthread_sigmask> could complicate things, however.
		3309
		3310	The most portable way to handle signals is to block signals in all threads
		3311	except the initial one, and run the default loop in the initial thread as
		3312	well.
		3313
		3314	=item C<long> must be large enough for common memory allocation sizes
		3315
		3316	To improve portability and simplify using libev, libev uses C<long>
		3317	internally instead of C<size_t> when allocating its data structures. On
		3318	non-POSIX systems (Microsoft...) this might be unexpectedly low, but
		3319	is still at least 31 bits everywhere, which is enough for hundreds of
		3320	millions of watchers.
		3321
		3322	=item C<double> must hold a time value in seconds with enough accuracy
		3323
		3324	The type C<double> is used to represent timestamps. It is required to have
		3325	at least 51 bits of mantissa, which is good enough for at least into the
		3326	year 4000. This requirement is fulfilled by implementations implementing
		3327	IEEE 754 (basically all existing ones).
		3328
		3329	=back
		3330
		3331	If you know of other additional requirements drop me a note.
		3332
		3333
3259	=head1 AUTHOR	3334	=head1 AUTHOR
3260		3335
3261	Marc Lehmann <libev@schmorp.de>.	3336	Marc Lehmann <libev@schmorp.de>.
3262		3337

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Comparing libev/ev.pod (file contents): Revision 1.144 by root, Mon Apr 7 12:33:29 2008 UTC vs. Revision 1.150 by root, Tue May 6 23:34:16 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.144 by root, Mon Apr 7 12:33:29 2008 UTC vs.
Revision 1.150 by root, Tue May 6 23:34:16 2008 UTC