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

Comparing libev/ev.pod (file contents):
Revision 1.199 by root, Thu Oct 23 07:18:21 2008 UTC vs.
Revision 1.214 by root, Wed Nov 5 03:52:15 2008 UTC

…		…
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
14	// every watcher type has its own typedef'd struct	14	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	15	// with the name ev_TYPE
16	ev_io stdin_watcher;	16	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	17	ev_timer timeout_watcher;
18		18
19	// all watcher callbacks have a similar signature	19	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	20	// this callback is called when data is readable on stdin
…		…
276		276
277	=back	277	=back
278		278
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		280
281	An event loop is described by a C<ev_loop *>. The library knows two	281	An event loop is described by a C<struct ev_loop *> (the C<struct>
282	types of such loops, the I<default> loop, which supports signals and child	282	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	283	I<function>).
		284
		285	The library knows two types of such loops, the I<default> loop, which
		286	supports signals and child events, and dynamically created loops which do
		287	not.
284		288
285	=over 4	289	=over 4
286		290
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	291	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		292
…		…
294	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
295	function.	299	function.
296		300
297	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
298	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,
299	as loops cannot bes hared easily between threads anyway).	303	as loops cannot be shared easily between threads anyway).
300		304
301	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
302	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
303	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
304	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
…		…
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	384	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		385
382	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,
383	but it scales phenomenally better. While poll and select usually scale	387	but it scales phenomenally better. While poll and select usually scale
384	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),
385	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).
386	of shortcomings, such as silently dropping events in some hard-to-detect	390
387	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
388	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.
389		407
390	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
391	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
392	(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
393	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
394	very well if you register events for both fds.	412	file descriptors might not work very well if you register events for both
395		413	file descriptors.
396	Please note that epoll sometimes generates spurious notifications, so you
397	need to use non-blocking I/O or other means to avoid blocking when no data
398	(or space) is available.
399		414
400	Best performance from this backend is achieved by not unregistering all	415	Best performance from this backend is achieved by not unregistering all
401	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,
402	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
403	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
404	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 practise, C<EVBACKEND_SELECT> can be as fast or
		424	faster then epoll for maybe up to a hundred file descriptors, depending on
		425	the usage. So sad.
405		426
406	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
407	all kernel versions tested so far.	428	all kernel versions tested so far.
408		429
409	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
410	C<EVBACKEND_POLL>.	431	C<EVBACKEND_POLL>.
411		432
412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	433	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
413		434
414	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
415	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
416	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
417	completely useless). For this reason it's not being "auto-detected" unless	438	it's completely useless). Unlike epoll, however, whose brokenness
418	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
419	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.
420		444
421	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
422	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
423	the target platform). See C<ev_embed> watchers for more info.	447	the target platform). See C<ev_embed> watchers for more info.
424		448
425	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
426	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
427	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
428	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
429	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
430	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
431		456
432	This backend usually performs well under most conditions.	457	This backend usually performs well under most conditions.
433		458
434	While nominally embeddable in other event loops, this doesn't work	459	While nominally embeddable in other event loops, this doesn't work
435	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
…		…
464	might perform better.	489	might perform better.
465		490
466	On the positive side, with the exception of the spurious readiness	491	On the positive side, with the exception of the spurious readiness
467	notifications, this backend actually performed fully to specification	492	notifications, this backend actually performed fully to specification
468	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
469	OS-specific backends.	494	OS-specific backends (I vastly prefer correctness over speed hacks).
470		495
471	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
472	C<EVBACKEND_POLL>.	497	C<EVBACKEND_POLL>.
473		498
474	=item C<EVBACKEND_ALL>	499	=item C<EVBACKEND_ALL>
…		…
527	responsibility to either stop all watchers cleanly yourself I<before>	552	responsibility to either stop all watchers cleanly yourself I<before>
528	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
529	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
530	for example).	555	for example).
531		556
532	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
533	this function, and related watchers (such as signal and child watchers)	558	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	559	as signal and child watchers) would need to be stopped manually.
535		560
536	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
537	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
538	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
539	C<ev_loop_new> and C<ev_loop_destroy>).	564	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
631	the loop.	656	the loop.
632		657
633	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
634	necessary) and will handle those and any already outstanding ones. It	659	necessary) and will handle those and any already outstanding ones. It
635	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
636	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
637	user-registered callback will be called), and will return after one	662	user-registered callback will be called), and will return after one
638	iteration of the loop.	663	iteration of the loop.
639		664
640	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
641	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
…		…
768	they fire on, say, one-second boundaries only.	793	they fire on, say, one-second boundaries only.
769		794
770	=item ev_loop_verify (loop)	795	=item ev_loop_verify (loop)
771		796
772	This function only does something when C<EV_VERIFY> support has been	797	This function only does something when C<EV_VERIFY> support has been
773	compiled in. which is the default for non-minimal builds. It tries to go	798	compiled in, which is the default for non-minimal builds. It tries to go
774	through all internal structures and checks them for validity. If anything	799	through all internal structures and checks them for validity. If anything
775	is found to be inconsistent, it will print an error message to standard	800	is found to be inconsistent, it will print an error message to standard
776	error and call C<abort ()>.	801	error and call C<abort ()>.
777		802
778	This can be used to catch bugs inside libev itself: under normal	803	This can be used to catch bugs inside libev itself: under normal
…		…
781		806
782	=back	807	=back
783		808
784		809
785	=head1 ANATOMY OF A WATCHER	810	=head1 ANATOMY OF A WATCHER
		811
		812	In the following description, uppercase C<TYPE> in names stands for the
		813	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		814	watchers and C<ev_io_start> for I/O watchers.
786		815
787	A watcher is a structure that you create and register to record your	816	A watcher is a structure that you create and register to record your
788	interest in some event. For instance, if you want to wait for STDIN to	817	interest in some event. For instance, if you want to wait for STDIN to
789	become readable, you would create an C<ev_io> watcher for that:	818	become readable, you would create an C<ev_io> watcher for that:
790		819
…		…
793	ev_io_stop (w);	822	ev_io_stop (w);
794	ev_unloop (loop, EVUNLOOP_ALL);	823	ev_unloop (loop, EVUNLOOP_ALL);
795	}	824	}
796		825
797	struct ev_loop *loop = ev_default_loop (0);	826	struct ev_loop *loop = ev_default_loop (0);
		827
798	ev_io stdin_watcher;	828	ev_io stdin_watcher;
		829
799	ev_init (&stdin_watcher, my_cb);	830	ev_init (&stdin_watcher, my_cb);
800	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	831	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
801	ev_io_start (loop, &stdin_watcher);	832	ev_io_start (loop, &stdin_watcher);
		833
802	ev_loop (loop, 0);	834	ev_loop (loop, 0);
803		835
804	As you can see, you are responsible for allocating the memory for your	836	As you can see, you are responsible for allocating the memory for your
805	watcher structures (and it is usually a bad idea to do this on the stack,	837	watcher structures (and it is I<usually> a bad idea to do this on the
806	although this can sometimes be quite valid).	838	stack).
		839
		840	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		841	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
807		842
808	Each watcher structure must be initialised by a call to C<ev_init	843	Each watcher structure must be initialised by a call to C<ev_init
809	(watcher *, callback)>, which expects a callback to be provided. This	844	(watcher *, callback)>, which expects a callback to be provided. This
810	callback gets invoked each time the event occurs (or, in the case of I/O	845	callback gets invoked each time the event occurs (or, in the case of I/O
811	watchers, each time the event loop detects that the file descriptor given	846	watchers, each time the event loop detects that the file descriptor given
812	is readable and/or writable).	847	is readable and/or writable).
813		848
814	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	849	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
815	with arguments specific to this watcher type. There is also a macro	850	macro to configure it, with arguments specific to the watcher type. There
816	to combine initialisation and setting in one call: C<< ev_<type>_init	851	is also a macro to combine initialisation and setting in one call: C<<
817	(watcher *, callback, ...) >>.	852	ev_TYPE_init (watcher *, callback, ...) >>.
818		853
819	To make the watcher actually watch out for events, you have to start it	854	To make the watcher actually watch out for events, you have to start it
820	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	855	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
821	*) >>), and you can stop watching for events at any time by calling the	856	*) >>), and you can stop watching for events at any time by calling the
822	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	857	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
823		858
824	As long as your watcher is active (has been started but not stopped) you	859	As long as your watcher is active (has been started but not stopped) you
825	must not touch the values stored in it. Most specifically you must never	860	must not touch the values stored in it. Most specifically you must never
826	reinitialise it or call its C<set> macro.	861	reinitialise it or call its C<ev_TYPE_set> macro.
827		862
828	Each and every callback receives the event loop pointer as first, the	863	Each and every callback receives the event loop pointer as first, the
829	registered watcher structure as second, and a bitset of received events as	864	registered watcher structure as second, and a bitset of received events as
830	third argument.	865	third argument.
831		866
…		…
912		947
913	=back	948	=back
914		949
915	=head2 GENERIC WATCHER FUNCTIONS	950	=head2 GENERIC WATCHER FUNCTIONS
916		951
917	In the following description, C<TYPE> stands for the watcher type,
918	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
919
920	=over 4	952	=over 4
921		953
922	=item C<ev_init> (ev_TYPE *watcher, callback)	954	=item C<ev_init> (ev_TYPE *watcher, callback)
923		955
924	This macro initialises the generic portion of a watcher. The contents	956	This macro initialises the generic portion of a watcher. The contents
…		…
1032	The default priority used by watchers when no priority has been set is	1064	The default priority used by watchers when no priority has been set is
1033	always C<0>, which is supposed to not be too high and not be too low :).	1065	always C<0>, which is supposed to not be too high and not be too low :).
1034		1066
1035	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1067	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1036	fine, as long as you do not mind that the priority value you query might	1068	fine, as long as you do not mind that the priority value you query might
1037	or might not have been adjusted to be within valid range.	1069	or might not have been clamped to the valid range.
1038		1070
1039	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1071	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1040		1072
1041	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1073	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1042	C<loop> nor C<revents> need to be valid as long as the watcher callback	1074	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1426		1458
1427	Changing the timeout is trivial as well (if it isn't hard-coded in the	1459	Changing the timeout is trivial as well (if it isn't hard-coded in the
1428	callback :) - just change the timeout and invoke the callback, which will	1460	callback :) - just change the timeout and invoke the callback, which will
1429	fix things for you.	1461	fix things for you.
1430		1462
1431	=item 4. Whee, use a double-linked list for your timeouts.	1463	=item 4. Wee, just use a double-linked list for your timeouts.
1432		1464
1433	If there is not one request, but many thousands, all employing some kind	1465	If there is not one request, but many thousands (millions...), all
1434	of timeout with the same timeout value, then one can do even better:	1466	employing some kind of timeout with the same timeout value, then one can
		1467	do even better:
1435		1468
1436	When starting the timeout, calculate the timeout value and put the timeout	1469	When starting the timeout, calculate the timeout value and put the timeout
1437	at the I<end> of the list.	1470	at the I<end> of the list.
1438		1471
1439	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of	1472	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
…		…
1448	complication, and having to use a constant timeout. The constant timeout	1481	complication, and having to use a constant timeout. The constant timeout
1449	ensures that the list stays sorted.	1482	ensures that the list stays sorted.
1450		1483
1451	=back	1484	=back
1452		1485
1453	So what method is the best?	1486	So which method the best?
1454		1487
1455	The method #2 is a simple no-brain-required solution that is adequate in	1488	Method #2 is a simple no-brain-required solution that is adequate in most
1456	most situations. Method #3 requires a bit more thinking, but handles many	1489	situations. Method #3 requires a bit more thinking, but handles many cases
1457	cases better, and isn't very complicated either. In most case, choosing	1490	better, and isn't very complicated either. In most case, choosing either
1458	either one is fine.	1491	one is fine, with #3 being better in typical situations.
1459		1492
1460	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is	1493	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1461	rather complicated, but extremely efficient, something that really pays	1494	rather complicated, but extremely efficient, something that really pays
1462	off after the first or so million of active timers, i.e. it's usually	1495	off after the first million or so of active timers, i.e. it's usually
1463	overkill :)	1496	overkill :)
1464		1497
1465	=head3 The special problem of time updates	1498	=head3 The special problem of time updates
1466		1499
1467	Establishing the current time is a costly operation (it usually takes at	1500	Establishing the current time is a costly operation (it usually takes at
…		…
1898		1931
1899		1932
1900	=head2 C<ev_stat> - did the file attributes just change?	1933	=head2 C<ev_stat> - did the file attributes just change?
1901		1934
1902	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
1903	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)
1904	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.
1905		1939
1906	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
1907	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
1908	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
1909	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
1910	the stat buffer having unspecified contents.	1944	least one) and all the other fields of the stat buffer having unspecified
		1945	contents.
1911		1946
1912	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
1913	relative and your working directory changes, the behaviour is undefined.	1949	your working directory changes, then the behaviour is undefined.
1914		1950
1915	Since there is no standard kernel interface to do this, the portable	1951	Since there is no portable change notification interface available, the
1916	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
1917	it changed somehow. You can specify a recommended polling interval for	1953	to see if it changed somehow. You can specify a recommended polling
1918	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
1919	then a I<suitable, unspecified default> value will be used (which	1955	recommended!) then a I<suitable, unspecified default> value will be used
1920	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
1921	dynamically). Libev will also impose a minimum interval which is currently	1957	change dynamically). Libev will also impose a minimum interval which is
1922	around C<0.1>, but thats usually overkill.	1958	currently around C<0.1>, but that's usually overkill.
1923		1959
1924	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,
1925	as even with OS-supported change notifications, this can be	1961	as even with OS-supported change notifications, this can be
1926	resource-intensive.	1962	resource-intensive.
1927		1963
1928	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
1929	is the Linux inotify interface (implementing kqueue support is left as	1965	is the Linux inotify interface (implementing kqueue support is left as an
1930	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
1931	of implementing C<ev_stat> semantics with kqueue).	1967	implementing C<ev_stat> semantics with kqueue, except as a hint).
1932		1968
1933	=head3 ABI Issues (Largefile Support)	1969	=head3 ABI Issues (Largefile Support)
1934		1970
1935	Libev by default (unless the user overrides this) uses the default	1971	Libev by default (unless the user overrides this) uses the default
1936	compilation environment, which means that on systems with large file	1972	compilation environment, which means that on systems with large file
1937	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
1938	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
1939	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
1940	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
1941	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
1942	most noticeably disabled with ev_stat and large file support.	1978	most noticeably displayed with ev_stat and large file support.
1943		1979
1944	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
1945	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
1946	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
1947	to exchange stat structures with application programs compiled using the	1983	to exchange stat structures with application programs compiled using the
1948	default compilation environment.	1984	default compilation environment.
1949		1985
1950	=head3 Inotify and Kqueue	1986	=head3 Inotify and Kqueue
1951		1987
1952	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
1953	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
1954	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>
1955	change detection where possible. The inotify descriptor will be created	1991	watcher is being started.
1956	lazily when the first C<ev_stat> watcher is being started.
1957		1992
1958	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
1959	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
1960	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
1961	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,
1962	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.
1963		2001
1964	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
1965	implement this functionality, due to the requirement of having a file	2003	implement this functionality, due to the requirement of having a file
1966	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
1967	etc. is difficult.	2005	etc. is difficult.
1968		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
1969	=head3 The special problem of stat time resolution	2025	=head3 The special problem of stat time resolution
1970		2026
1971	The C<stat ()> system call only supports full-second resolution portably, and	2027	The C<stat ()> system call only supports full-second resolution portably,
1972	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
1973	only support whole seconds.	2029	still only support whole seconds.
1974		2030
1975	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
1976	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
1977	calls your callback, which does something. When there is another update	2033	calls your callback, which does something. When there is another update
1978	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
…		…
2617	=over 4	2673	=over 4
2618		2674
2619	=item ev_async_init (ev_async *, callback)	2675	=item ev_async_init (ev_async *, callback)
2620		2676
2621	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
2622	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,
2623	trust me.	2679	trust me.
2624		2680
2625	=item ev_async_send (loop, ev_async *)	2681	=item ev_async_send (loop, ev_async *)
2626		2682
2627	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
…		…
2946	=item D	3002	=item D
2947		3003
2948	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3004	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2949	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3005	be found at L<http://proj.llucax.com.ar/wiki/evd>.
2950		3006
		3007	=item Ocaml
		3008
		3009	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3010	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3011
2951	=back	3012	=back
2952		3013
2953		3014
2954	=head1 MACRO MAGIC	3015	=head1 MACRO MAGIC
2955		3016
…		…
3055		3116
3056	#define EV_STANDALONE 1	3117	#define EV_STANDALONE 1
3057	#include "ev.h"	3118	#include "ev.h"
3058		3119
3059	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++
3060	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
3061	as a bug).	3122	as a bug).
3062		3123
3063	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
3064	in your include path (e.g. in libev/ when using -Ilibev):	3125	in your include path (e.g. in libev/ when using -Ilibev):
3065		3126
…		…
3537	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
3538	you must not do this from C<ev_periodic> reschedule callbacks.	3599	you must not do this from C<ev_periodic> reschedule callbacks.
3539		3600
3540	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
3541	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
3542	they do not clal any callbacks.	3603	they do not call any callbacks.
3543		3604
3544	=head2 COMPILER WARNINGS	3605	=head2 COMPILER WARNINGS
3545		3606
3546	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
3547	lot of warnings when compiling libev code. Some people are apparently	3608	lot of warnings when compiling libev code. Some people are apparently
…		…
3581	==2274== definitely lost: 0 bytes in 0 blocks.	3642	==2274== definitely lost: 0 bytes in 0 blocks.
3582	==2274== possibly lost: 0 bytes in 0 blocks.	3643	==2274== possibly lost: 0 bytes in 0 blocks.
3583	==2274== still reachable: 256 bytes in 1 blocks.	3644	==2274== still reachable: 256 bytes in 1 blocks.
3584		3645
3585	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
3586	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.
3587		3648
3588	Similarly, under some circumstances, valgrind might report kernel bugs	3649	Similarly, under some circumstances, valgrind might report kernel bugs
3589	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,
3590	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
3591	confused.	3652	confused.
…		…
3829	=back	3890	=back
3830		3891
3831		3892
3832	=head1 AUTHOR	3893	=head1 AUTHOR
3833		3894
3834	Marc Lehmann <libev@schmorp.de>.	3895	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3835		3896

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing libev/ev.pod (file contents): Revision 1.199 by root, Thu Oct 23 07:18:21 2008 UTC vs. Revision 1.214 by root, Wed Nov 5 03:52:15 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.199 by root, Thu Oct 23 07:18:21 2008 UTC vs.
Revision 1.214 by root, Wed Nov 5 03:52:15 2008 UTC