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

Comparing libev/ev.pod (file contents):
Revision 1.202 by root, Fri Oct 24 08:30:01 2008 UTC vs.
Revision 1.216 by root, Thu Nov 13 15:55:38 2008 UTC

…		…
298	If you don't know what event loop to use, use the one returned from this	298	If you don't know what event loop to use, use the one returned from this
299	function.	299	function.
300		300
301	Note that this function is I<not> thread-safe, so if you want to use it	301	Note that this function is I<not> thread-safe, so if you want to use it
302	from multiple threads, you have to lock (note also that this is unlikely,	302	from multiple threads, you have to lock (note also that this is unlikely,
303	as loops cannot bes hared easily between threads anyway).	303	as loops cannot be shared easily between threads anyway).
304		304
305	The default loop is the only loop that can handle C<ev_signal> and	305	The default loop is the only loop that can handle C<ev_signal> and
306	C<ev_child> watchers, and to do this, it always registers a handler	306	C<ev_child> watchers, and to do this, it always registers a handler
307	for C<SIGCHLD>. If this is a problem for your application you can either	307	for C<SIGCHLD>. If this is a problem for your application you can either
308	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	308	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
384	=item C<EVBACKEND_EPOLL> (value 4, Linux)	384	=item C<EVBACKEND_EPOLL> (value 4, Linux)
385		385
386	For few fds, this backend is a bit little slower than poll and select,	386	For few fds, this backend is a bit little slower than poll and select,
387	but it scales phenomenally better. While poll and select usually scale	387	but it scales phenomenally better. While poll and select usually scale
388	like O(total_fds) where n is the total number of fds (or the highest fd),	388	like O(total_fds) where n is the total number of fds (or the highest fd),
389	epoll scales either O(1) or O(active_fds). The epoll design has a number	389	epoll scales either O(1) or O(active_fds).
390	of shortcomings, such as silently dropping events in some hard-to-detect	390
391	cases and requiring a system call per fd change, no fork support and bad	391	The epoll mechanism deserves honorable mention as the most misdesigned
392	support for dup.	392	of the more advanced event mechanisms: mere annoyances include silently
		393	dropping file descriptors, requiring a system call per change per file
		394	descriptor (and unnecessary guessing of parameters), problems with dup and
		395	so on. The biggest issue is fork races, however - if a program forks then
		396	I<both> parent and child process have to recreate the epoll set, which can
		397	take considerable time (one syscall per file descriptor) and is of course
		398	hard to detect.
		399
		400	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		401	of course I<doesn't>, and epoll just loves to report events for totally
		402	I<different> file descriptors (even already closed ones, so one cannot
		403	even remove them from the set) than registered in the set (especially
		404	on SMP systems). Libev tries to counter these spurious notifications by
		405	employing an additional generation counter and comparing that against the
		406	events to filter out spurious ones, recreating the set when required.
393		407
394	While stopping, setting and starting an I/O watcher in the same iteration	408	While stopping, setting and starting an I/O watcher in the same iteration
395	will result in some caching, there is still a system call per such incident	409	will result in some caching, there is still a system call per such
396	(because the fd could point to a different file description now), so its	410	incident (because the same I<file descriptor> could point to a different
397	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	411	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
398	very well if you register events for both fds.	412	file descriptors might not work very well if you register events for both
399		413	file descriptors.
400	Please note that epoll sometimes generates spurious notifications, so you
401	need to use non-blocking I/O or other means to avoid blocking when no data
402	(or space) is available.
403		414
404	Best performance from this backend is achieved by not unregistering all	415	Best performance from this backend is achieved by not unregistering all
405	watchers for a file descriptor until it has been closed, if possible,	416	watchers for a file descriptor until it has been closed, if possible,
406	i.e. keep at least one watcher active per fd at all times. Stopping and	417	i.e. keep at least one watcher active per fd at all times. Stopping and
407	starting a watcher (without re-setting it) also usually doesn't cause	418	starting a watcher (without re-setting it) also usually doesn't cause
408	extra overhead.	419	extra overhead. A fork can both result in spurious notifications as well
		420	as in libev having to destroy and recreate the epoll object, which can
		421	take considerable time and thus should be avoided.
		422
		423	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		424	faster than epoll for maybe up to a hundred file descriptors, depending on
		425	the usage. So sad.
409		426
410	While nominally embeddable in other event loops, this feature is broken in	427	While nominally embeddable in other event loops, this feature is broken in
411	all kernel versions tested so far.	428	all kernel versions tested so far.
412		429
413	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	430	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
414	C<EVBACKEND_POLL>.	431	C<EVBACKEND_POLL>.
415		432
416	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	433	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
417		434
418	Kqueue deserves special mention, as at the time of this writing, it was	435	Kqueue deserves special mention, as at the time of this writing, it
419	broken on all BSDs except NetBSD (usually it doesn't work reliably with	436	was broken on all BSDs except NetBSD (usually it doesn't work reliably
420	anything but sockets and pipes, except on Darwin, where of course it's	437	with anything but sockets and pipes, except on Darwin, where of course
421	completely useless). For this reason it's not being "auto-detected" unless	438	it's completely useless). Unlike epoll, however, whose brokenness
422	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	439	is by design, these kqueue bugs can (and eventually will) be fixed
423	libev was compiled on a known-to-be-good (-enough) system like NetBSD.	440	without API changes to existing programs. For this reason it's not being
		441	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		442	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		443	system like NetBSD.
424		444
425	You still can embed kqueue into a normal poll or select backend and use it	445	You still can embed kqueue into a normal poll or select backend and use it
426	only for sockets (after having made sure that sockets work with kqueue on	446	only for sockets (after having made sure that sockets work with kqueue on
427	the target platform). See C<ev_embed> watchers for more info.	447	the target platform). See C<ev_embed> watchers for more info.
428		448
429	It scales in the same way as the epoll backend, but the interface to the	449	It scales in the same way as the epoll backend, but the interface to the
430	kernel is more efficient (which says nothing about its actual speed, of	450	kernel is more efficient (which says nothing about its actual speed, of
431	course). While stopping, setting and starting an I/O watcher does never	451	course). While stopping, setting and starting an I/O watcher does never
432	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	452	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
433	two event changes per incident. Support for C<fork ()> is very bad and it	453	two event changes per incident. Support for C<fork ()> is very bad (but
434	drops fds silently in similarly hard-to-detect cases.	454	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		455	cases
435		456
436	This backend usually performs well under most conditions.	457	This backend usually performs well under most conditions.
437		458
438	While nominally embeddable in other event loops, this doesn't work	459	While nominally embeddable in other event loops, this doesn't work
439	everywhere, so you might need to test for this. And since it is broken	460	everywhere, so you might need to test for this. And since it is broken
…		…
468	might perform better.	489	might perform better.
469		490
470	On the positive side, with the exception of the spurious readiness	491	On the positive side, with the exception of the spurious readiness
471	notifications, this backend actually performed fully to specification	492	notifications, this backend actually performed fully to specification
472	in all tests and is fully embeddable, which is a rare feat among the	493	in all tests and is fully embeddable, which is a rare feat among the
473	OS-specific backends.	494	OS-specific backends (I vastly prefer correctness over speed hacks).
474		495
475	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	496	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
476	C<EVBACKEND_POLL>.	497	C<EVBACKEND_POLL>.
477		498
478	=item C<EVBACKEND_ALL>	499	=item C<EVBACKEND_ALL>
…		…
531	responsibility to either stop all watchers cleanly yourself I<before>	552	responsibility to either stop all watchers cleanly yourself I<before>
532	calling this function, or cope with the fact afterwards (which is usually	553	calling this function, or cope with the fact afterwards (which is usually
533	the easiest thing, you can just ignore the watchers and/or C<free ()> them	554	the easiest thing, you can just ignore the watchers and/or C<free ()> them
534	for example).	555	for example).
535		556
536	Note that certain global state, such as signal state, will not be freed by	557	Note that certain global state, such as signal state (and installed signal
537	this function, and related watchers (such as signal and child watchers)	558	handlers), will not be freed by this function, and related watchers (such
538	would need to be stopped manually.	559	as signal and child watchers) would need to be stopped manually.
539		560
540	In general it is not advisable to call this function except in the	561	In general it is not advisable to call this function except in the
541	rare occasion where you really need to free e.g. the signal handling	562	rare occasion where you really need to free e.g. the signal handling
542	pipe fds. If you need dynamically allocated loops it is better to use	563	pipe fds. If you need dynamically allocated loops it is better to use
543	C<ev_loop_new> and C<ev_loop_destroy>).	564	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
635	the loop.	656	the loop.
636		657
637	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	658	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
638	necessary) and will handle those and any already outstanding ones. It	659	necessary) and will handle those and any already outstanding ones. It
639	will block your process until at least one new event arrives (which could	660	will block your process until at least one new event arrives (which could
640	be an event internal to libev itself, so there is no guarentee that a	661	be an event internal to libev itself, so there is no guarantee that a
641	user-registered callback will be called), and will return after one	662	user-registered callback will be called), and will return after one
642	iteration of the loop.	663	iteration of the loop.
643		664
644	This is useful if you are waiting for some external event in conjunction	665	This is useful if you are waiting for some external event in conjunction
645	with something not expressible using other libev watchers (i.e. "roll your	666	with something not expressible using other libev watchers (i.e. "roll your
…		…
1398	else	1419	else
1399	{	1420	{
1400	// callback was invoked, but there was some activity, re-arm	1421	// callback was invoked, but there was some activity, re-arm
1401	// the watcher to fire in last_activity + 60, which is	1422	// the watcher to fire in last_activity + 60, which is
1402	// guaranteed to be in the future, so "again" is positive:	1423	// guaranteed to be in the future, so "again" is positive:
1403	w->again = timeout - now;	1424	w->repeat = timeout - now;
1404	ev_timer_again (EV_A_ w);	1425	ev_timer_again (EV_A_ w);
1405	}	1426	}
1406	}	1427	}
1407		1428
1408	To summarise the callback: first calculate the real timeout (defined	1429	To summarise the callback: first calculate the real timeout (defined
…		…
1910		1931
1911		1932
1912	=head2 C<ev_stat> - did the file attributes just change?	1933	=head2 C<ev_stat> - did the file attributes just change?
1913		1934
1914	This watches a file system path for attribute changes. That is, it calls	1935	This watches a file system path for attribute changes. That is, it calls
1915	C<stat> regularly (or when the OS says it changed) and sees if it changed	1936	C<stat> on that path in regular intervals (or when the OS says it changed)
1916	compared to the last time, invoking the callback if it did.	1937	and sees if it changed compared to the last time, invoking the callback if
		1938	it did.
1917		1939
1918	The path does not need to exist: changing from "path exists" to "path does	1940	The path does not need to exist: changing from "path exists" to "path does
1919	not exist" is a status change like any other. The condition "path does	1941	not exist" is a status change like any other. The condition "path does not
1920	not exist" is signified by the C<st_nlink> field being zero (which is	1942	exist" (or more correctly "path cannot be stat'ed") is signified by the
1921	otherwise always forced to be at least one) and all the other fields of	1943	C<st_nlink> field being zero (which is otherwise always forced to be at
1922	the stat buffer having unspecified contents.	1944	least one) and all the other fields of the stat buffer having unspecified
		1945	contents.
1923		1946
1924	The path I<should> be absolute and I<must not> end in a slash. If it is	1947	The path I<must not> end in a slash or contain special components such as
		1948	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1925	relative and your working directory changes, the behaviour is undefined.	1949	your working directory changes, then the behaviour is undefined.
1926		1950
1927	Since there is no standard kernel interface to do this, the portable	1951	Since there is no portable change notification interface available, the
1928	implementation simply calls C<stat (2)> regularly on the path to see if	1952	portable implementation simply calls C<stat(2)> regularly on the path
1929	it changed somehow. You can specify a recommended polling interval for	1953	to see if it changed somehow. You can specify a recommended polling
1930	this case. If you specify a polling interval of C<0> (highly recommended!)	1954	interval for this case. If you specify a polling interval of C<0> (highly
1931	then a I<suitable, unspecified default> value will be used (which	1955	recommended!) then a I<suitable, unspecified default> value will be used
1932	you can expect to be around five seconds, although this might change	1956	(which you can expect to be around five seconds, although this might
1933	dynamically). Libev will also impose a minimum interval which is currently	1957	change dynamically). Libev will also impose a minimum interval which is
1934	around C<0.1>, but thats usually overkill.	1958	currently around C<0.1>, but that's usually overkill.
1935		1959
1936	This watcher type is not meant for massive numbers of stat watchers,	1960	This watcher type is not meant for massive numbers of stat watchers,
1937	as even with OS-supported change notifications, this can be	1961	as even with OS-supported change notifications, this can be
1938	resource-intensive.	1962	resource-intensive.
1939		1963
1940	At the time of this writing, the only OS-specific interface implemented	1964	At the time of this writing, the only OS-specific interface implemented
1941	is the Linux inotify interface (implementing kqueue support is left as	1965	is the Linux inotify interface (implementing kqueue support is left as an
1942	an exercise for the reader. Note, however, that the author sees no way	1966	exercise for the reader. Note, however, that the author sees no way of
1943	of implementing C<ev_stat> semantics with kqueue).	1967	implementing C<ev_stat> semantics with kqueue, except as a hint).
1944		1968
1945	=head3 ABI Issues (Largefile Support)	1969	=head3 ABI Issues (Largefile Support)
1946		1970
1947	Libev by default (unless the user overrides this) uses the default	1971	Libev by default (unless the user overrides this) uses the default
1948	compilation environment, which means that on systems with large file	1972	compilation environment, which means that on systems with large file
1949	support disabled by default, you get the 32 bit version of the stat	1973	support disabled by default, you get the 32 bit version of the stat
1950	structure. When using the library from programs that change the ABI to	1974	structure. When using the library from programs that change the ABI to
1951	use 64 bit file offsets the programs will fail. In that case you have to	1975	use 64 bit file offsets the programs will fail. In that case you have to
1952	compile libev with the same flags to get binary compatibility. This is	1976	compile libev with the same flags to get binary compatibility. This is
1953	obviously the case with any flags that change the ABI, but the problem is	1977	obviously the case with any flags that change the ABI, but the problem is
1954	most noticeably disabled with ev_stat and large file support.	1978	most noticeably displayed with ev_stat and large file support.
1955		1979
1956	The solution for this is to lobby your distribution maker to make large	1980	The solution for this is to lobby your distribution maker to make large
1957	file interfaces available by default (as e.g. FreeBSD does) and not	1981	file interfaces available by default (as e.g. FreeBSD does) and not
1958	optional. Libev cannot simply switch on large file support because it has	1982	optional. Libev cannot simply switch on large file support because it has
1959	to exchange stat structures with application programs compiled using the	1983	to exchange stat structures with application programs compiled using the
1960	default compilation environment.	1984	default compilation environment.
1961		1985
1962	=head3 Inotify and Kqueue	1986	=head3 Inotify and Kqueue
1963		1987
1964	When C<inotify (7)> support has been compiled into libev (generally	1988	When C<inotify (7)> support has been compiled into libev and present at
1965	only available with Linux 2.6.25 or above due to bugs in earlier	1989	runtime, it will be used to speed up change detection where possible. The
1966	implementations) and present at runtime, it will be used to speed up	1990	inotify descriptor will be created lazily when the first C<ev_stat>
1967	change detection where possible. The inotify descriptor will be created	1991	watcher is being started.
1968	lazily when the first C<ev_stat> watcher is being started.
1969		1992
1970	Inotify presence does not change the semantics of C<ev_stat> watchers	1993	Inotify presence does not change the semantics of C<ev_stat> watchers
1971	except that changes might be detected earlier, and in some cases, to avoid	1994	except that changes might be detected earlier, and in some cases, to avoid
1972	making regular C<stat> calls. Even in the presence of inotify support	1995	making regular C<stat> calls. Even in the presence of inotify support
1973	there are many cases where libev has to resort to regular C<stat> polling,	1996	there are many cases where libev has to resort to regular C<stat> polling,
1974	but as long as the path exists, libev usually gets away without polling.	1997	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		1998	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		1999	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2000	xfs are fully working) libev usually gets away without polling.
1975		2001
1976	There is no support for kqueue, as apparently it cannot be used to	2002	There is no support for kqueue, as apparently it cannot be used to
1977	implement this functionality, due to the requirement of having a file	2003	implement this functionality, due to the requirement of having a file
1978	descriptor open on the object at all times, and detecting renames, unlinks	2004	descriptor open on the object at all times, and detecting renames, unlinks
1979	etc. is difficult.	2005	etc. is difficult.
1980		2006
		2007	=head3 C<stat ()> is a synchronous operation
		2008
		2009	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2010	the process. The exception are C<ev_stat> watchers - those call C<stat
		2011	()>, which is a synchronous operation.
		2012
		2013	For local paths, this usually doesn't matter: unless the system is very
		2014	busy or the intervals between stat's are large, a stat call will be fast,
		2015	as the path data is suually in memory already (except when starting the
		2016	watcher).
		2017
		2018	For networked file systems, calling C<stat ()> can block an indefinite
		2019	time due to network issues, and even under good conditions, a stat call
		2020	often takes multiple milliseconds.
		2021
		2022	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2023	paths, although this is fully supported by libev.
		2024
1981	=head3 The special problem of stat time resolution	2025	=head3 The special problem of stat time resolution
1982		2026
1983	The C<stat ()> system call only supports full-second resolution portably, and	2027	The C<stat ()> system call only supports full-second resolution portably,
1984	even on systems where the resolution is higher, most file systems still	2028	and even on systems where the resolution is higher, most file systems
1985	only support whole seconds.	2029	still only support whole seconds.
1986		2030
1987	That means that, if the time is the only thing that changes, you can	2031	That means that, if the time is the only thing that changes, you can
1988	easily miss updates: on the first update, C<ev_stat> detects a change and	2032	easily miss updates: on the first update, C<ev_stat> detects a change and
1989	calls your callback, which does something. When there is another update	2033	calls your callback, which does something. When there is another update
1990	within the same second, C<ev_stat> will be unable to detect unless the	2034	within the same second, C<ev_stat> will be unable to detect unless the
…		…
2629	=over 4	2673	=over 4
2630		2674
2631	=item ev_async_init (ev_async *, callback)	2675	=item ev_async_init (ev_async *, callback)
2632		2676
2633	Initialises and configures the async watcher - it has no parameters of any	2677	Initialises and configures the async watcher - it has no parameters of any
2634	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	2678	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2635	trust me.	2679	trust me.
2636		2680
2637	=item ev_async_send (loop, ev_async *)	2681	=item ev_async_send (loop, ev_async *)
2638		2682
2639	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	2683	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
…		…
3072		3116
3073	#define EV_STANDALONE 1	3117	#define EV_STANDALONE 1
3074	#include "ev.h"	3118	#include "ev.h"
3075		3119
3076	Both header files and implementation files can be compiled with a C++	3120	Both header files and implementation files can be compiled with a C++
3077	compiler (at least, thats a stated goal, and breakage will be treated	3121	compiler (at least, that's a stated goal, and breakage will be treated
3078	as a bug).	3122	as a bug).
3079		3123
3080	You need the following files in your source tree, or in a directory	3124	You need the following files in your source tree, or in a directory
3081	in your include path (e.g. in libev/ when using -Ilibev):	3125	in your include path (e.g. in libev/ when using -Ilibev):
3082		3126
…		…
3554	loop, as long as you don't confuse yourself). The only exception is that	3598	loop, as long as you don't confuse yourself). The only exception is that
3555	you must not do this from C<ev_periodic> reschedule callbacks.	3599	you must not do this from C<ev_periodic> reschedule callbacks.
3556		3600
3557	Care has been taken to ensure that libev does not keep local state inside	3601	Care has been taken to ensure that libev does not keep local state inside
3558	C<ev_loop>, and other calls do not usually allow for coroutine switches as	3602	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3559	they do not clal any callbacks.	3603	they do not call any callbacks.
3560		3604
3561	=head2 COMPILER WARNINGS	3605	=head2 COMPILER WARNINGS
3562		3606
3563	Depending on your compiler and compiler settings, you might get no or a	3607	Depending on your compiler and compiler settings, you might get no or a
3564	lot of warnings when compiling libev code. Some people are apparently	3608	lot of warnings when compiling libev code. Some people are apparently
…		…
3598	==2274== definitely lost: 0 bytes in 0 blocks.	3642	==2274== definitely lost: 0 bytes in 0 blocks.
3599	==2274== possibly lost: 0 bytes in 0 blocks.	3643	==2274== possibly lost: 0 bytes in 0 blocks.
3600	==2274== still reachable: 256 bytes in 1 blocks.	3644	==2274== still reachable: 256 bytes in 1 blocks.
3601		3645
3602	Then there is no memory leak, just as memory accounted to global variables	3646	Then there is no memory leak, just as memory accounted to global variables
3603	is not a memleak - the memory is still being refernced, and didn't leak.	3647	is not a memleak - the memory is still being referenced, and didn't leak.
3604		3648
3605	Similarly, under some circumstances, valgrind might report kernel bugs	3649	Similarly, under some circumstances, valgrind might report kernel bugs
3606	as if it were a bug in libev (e.g. in realloc or in the poll backend,	3650	as if it were a bug in libev (e.g. in realloc or in the poll backend,
3607	although an acceptable workaround has been found here), or it might be	3651	although an acceptable workaround has been found here), or it might be
3608	confused.	3652	confused.
…		…
3846	=back	3890	=back
3847		3891
3848		3892
3849	=head1 AUTHOR	3893	=head1 AUTHOR
3850		3894
3851	Marc Lehmann <libev@schmorp.de>.	3895	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3852		3896

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Comparing libev/ev.pod (file contents): Revision 1.202 by root, Fri Oct 24 08:30:01 2008 UTC vs. Revision 1.216 by root, Thu Nov 13 15:55:38 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.202 by root, Fri Oct 24 08:30:01 2008 UTC vs.
Revision 1.216 by root, Thu Nov 13 15:55:38 2008 UTC