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

Comparing libev/ev.pod (file contents):
Revision 1.136 by root, Thu Mar 13 13:06:16 2008 UTC vs.
Revision 1.146 by root, Fri Apr 11 00:31:19 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 (;;)
…		…
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		263
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
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
272	This will initialise the default event loop if it hasn't been initialised	268	This will initialise the default event loop if it hasn't been initialised
…		…
274	false. If it already was initialised it simply returns it (and ignores the	270	false. If it already was initialised it simply returns it (and ignores the
275	flags. If that is troubling you, check C<ev_backend ()> afterwards).	271	flags. If that is troubling you, check C<ev_backend ()> afterwards).
276		272
277	If you don't know what event loop to use, use the one returned from this	273	If you don't know what event loop to use, use the one returned from this
278	function.	274	function.
		275
		276	Note that this function is I<not> thread-safe, so if you want to use it
		277	from multiple threads, you have to lock (note also that this is unlikely,
		278	as loops cannot bes hared easily between threads anyway).
279		279
280	The default loop is the only loop that can handle C<ev_signal> and	280	The default loop is the only loop that can handle C<ev_signal> and
281	C<ev_child> watchers, and to do this, it always registers a handler	281	C<ev_child> watchers, and to do this, it always registers a handler
282	for C<SIGCHLD>. If this is a problem for your app you can either	282	for C<SIGCHLD>. If this is a problem for your app you can either
283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	283	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
354	For few fds, this backend is a bit little slower than poll and select,	354	For few fds, this backend is a bit little slower than poll and select,
355	but it scales phenomenally better. While poll and select usually scale	355	but it scales phenomenally better. While poll and select usually scale
356	like O(total_fds) where n is the total number of fds (or the highest fd),	356	like O(total_fds) where n is the total number of fds (or the highest fd),
357	epoll scales either O(1) or O(active_fds). The epoll design has a number	357	epoll scales either O(1) or O(active_fds). The epoll design has a number
358	of shortcomings, such as silently dropping events in some hard-to-detect	358	of shortcomings, such as silently dropping events in some hard-to-detect
359	cases and rewiring a syscall per fd change, no fork support and bad	359	cases and requiring a syscall per fd change, no fork support and bad
360	support for dup.	360	support for dup.
361		361
362	While stopping, setting and starting an I/O watcher in the same iteration	362	While stopping, setting and starting an I/O watcher in the same iteration
363	will result in some caching, there is still a syscall per such incident	363	will result in some caching, there is still a syscall per such incident
364	(because the fd could point to a different file description now), so its	364	(because the fd could point to a different file description now), so its
…		…
465		465
466	Similar to C<ev_default_loop>, but always creates a new event loop that is	466	Similar to C<ev_default_loop>, but always creates a new event loop that is
467	always distinct from the default loop. Unlike the default loop, it cannot	467	always distinct from the default loop. Unlike the default loop, it cannot
468	handle signal and child watchers, and attempts to do so will be greeted by	468	handle signal and child watchers, and attempts to do so will be greeted by
469	undefined behaviour (or a failed assertion if assertions are enabled).	469	undefined behaviour (or a failed assertion if assertions are enabled).
		470
		471	Note that this function I<is> thread-safe, and the recommended way to use
		472	libev with threads is indeed to create one loop per thread, and using the
		473	default loop in the "main" or "initial" thread.
470		474
471	Example: Try to create a event loop that uses epoll and nothing else.	475	Example: Try to create a event loop that uses epoll and nothing else.
472		476
473	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL \| EVFLAG_NOENV);	477	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL \| EVFLAG_NOENV);
474	if (!epoller)	478	if (!epoller)
…		…
1085	To support fork in your programs, you either have to call	1089	To support fork in your programs, you either have to call
1086	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1090	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
1087	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1091	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1088	C<EVBACKEND_POLL>.	1092	C<EVBACKEND_POLL>.
1089		1093
		1094	=head3 The special problem of SIGPIPE
		1095
		1096	While not really specific to libev, it is easy to forget about SIGPIPE:
		1097	when reading from a pipe whose other end has been closed, your program
		1098	gets send a SIGPIPE, which, by default, aborts your program. For most
		1099	programs this is sensible behaviour, for daemons, this is usually
		1100	undesirable.
		1101
		1102	So when you encounter spurious, unexplained daemon exits, make sure you
		1103	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1104	somewhere, as that would have given you a big clue).
		1105
1090		1106
1091	=head3 Watcher-Specific Functions	1107	=head3 Watcher-Specific Functions
1092		1108
1093	=over 4	1109	=over 4
1094		1110
…		…
1599	reader). Inotify will be used to give hints only and should not change the	1615	reader). Inotify will be used to give hints only and should not change the
1600	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1616	semantics of C<ev_stat> watchers, which means that libev sometimes needs
1601	to fall back to regular polling again even with inotify, but changes are	1617	to fall back to regular polling again even with inotify, but changes are
1602	usually detected immediately, and if the file exists there will be no	1618	usually detected immediately, and if the file exists there will be no
1603	polling.	1619	polling.
		1620
		1621	=head3 ABI Issues (Largefile Support)
		1622
		1623	Libev by default (unless the user overrides this) uses the default
		1624	compilation environment, which means that on systems with optionally
		1625	disabled large file support, you get the 32 bit version of the stat
		1626	structure. When using the library from programs that change the ABI to
		1627	use 64 bit file offsets the programs will fail. In that case you have to
		1628	compile libev with the same flags to get binary compatibility. This is
		1629	obviously the case with any flags that change the ABI, but the problem is
		1630	most noticably with ev_stat and largefile support.
1604		1631
1605	=head3 Inotify	1632	=head3 Inotify
1606		1633
1607	When C<inotify (7)> support has been compiled into libev (generally only	1634	When C<inotify (7)> support has been compiled into libev (generally only
1608	available on Linux) and present at runtime, it will be used to speed up	1635	available on Linux) and present at runtime, it will be used to speed up
…		…
2257		2284
2258	This call incurs the overhead of a syscall only once per loop iteration,	2285	This call incurs the overhead of a syscall only once per loop iteration,
2259	so while the overhead might be noticable, it doesn't apply to repeated	2286	so while the overhead might be noticable, it doesn't apply to repeated
2260	calls to C<ev_async_send>.	2287	calls to C<ev_async_send>.
2261		2288
		2289	=item bool = ev_async_pending (ev_async *)
		2290
		2291	Returns a non-zero value when C<ev_async_send> has been called on the
		2292	watcher but the event has not yet been processed (or even noted) by the
		2293	event loop.
		2294
		2295	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2296	the loop iterates next and checks for the watcher to have become active,
		2297	it will reset the flag again. C<ev_async_pending> can be used to very
		2298	quickly check wether invoking the loop might be a good idea.
		2299
		2300	Not that this does I<not> check wether the watcher itself is pending, only
		2301	wether it has been requested to make this watcher pending.
		2302
2262	=back	2303	=back
2263		2304
2264		2305
2265	=head1 OTHER FUNCTIONS	2306	=head1 OTHER FUNCTIONS
2266		2307
…		…
2337		2378
2338	=item * Priorities are not currently supported. Initialising priorities	2379	=item * Priorities are not currently supported. Initialising priorities
2339	will fail and all watchers will have the same priority, even though there	2380	will fail and all watchers will have the same priority, even though there
2340	is an ev_pri field.	2381	is an ev_pri field.
2341		2382
		2383	=item * In libevent, the last base created gets the signals, in libev, the
		2384	first base created (== the default loop) gets the signals.
		2385
2342	=item * Other members are not supported.	2386	=item * Other members are not supported.
2343		2387
2344	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2388	=item * The libev emulation is I<not> ABI compatible to libevent, you need
2345	to use the libev header file and library.	2389	to use the libev header file and library.
2346		2390
…		…
2588	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	2632	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2589		2633
2590	Similar to the other two macros, this gives you the value of the default	2634	Similar to the other two macros, this gives you the value of the default
2591	loop, if multiple loops are supported ("ev loop default").	2635	loop, if multiple loops are supported ("ev loop default").
2592		2636
		2637	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2638
		2639	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2640	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2641	is undefined when the default loop has not been initialised by a previous
		2642	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2643
		2644	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2645	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2646
2593	=back	2647	=back
2594		2648
2595	Example: Declare and initialise a check watcher, utilising the above	2649	Example: Declare and initialise a check watcher, utilising the above
2596	macros so it will work regardless of whether multiple loops are supported	2650	macros so it will work regardless of whether multiple loops are supported
2597	or not.	2651	or not.
…		…
2692		2746
2693	libev.m4	2747	libev.m4
2694		2748
2695	=head2 PREPROCESSOR SYMBOLS/MACROS	2749	=head2 PREPROCESSOR SYMBOLS/MACROS
2696		2750
2697	Libev can be configured via a variety of preprocessor symbols you have to define	2751	Libev can be configured via a variety of preprocessor symbols you have to
2698	before including any of its files. The default is not to build for multiplicity	2752	define before including any of its files. The default in the absense of
2699	and only include the select backend.	2753	autoconf is noted for every option.
2700		2754
2701	=over 4	2755	=over 4
2702		2756
2703	=item EV_STANDALONE	2757	=item EV_STANDALONE
2704		2758
…		…
2730	=item EV_USE_NANOSLEEP	2784	=item EV_USE_NANOSLEEP
2731		2785
2732	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	2786	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2733	and will use it for delays. Otherwise it will use C<select ()>.	2787	and will use it for delays. Otherwise it will use C<select ()>.
2734		2788
		2789	=item EV_USE_EVENTFD
		2790
		2791	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2792	available and will probe for kernel support at runtime. This will improve
		2793	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2794	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2795	2.7 or newer, otherwise disabled.
		2796
2735	=item EV_USE_SELECT	2797	=item EV_USE_SELECT
2736		2798
2737	If undefined or defined to be C<1>, libev will compile in support for the	2799	If undefined or defined to be C<1>, libev will compile in support for the
2738	C<select>(2) backend. No attempt at autodetection will be done: if no	2800	C<select>(2) backend. No attempt at autodetection will be done: if no
2739	other method takes over, select will be it. Otherwise the select backend	2801	other method takes over, select will be it. Otherwise the select backend
…		…
2775		2837
2776	=item EV_USE_EPOLL	2838	=item EV_USE_EPOLL
2777		2839
2778	If defined to be C<1>, libev will compile in support for the Linux	2840	If defined to be C<1>, libev will compile in support for the Linux
2779	C<epoll>(7) backend. Its availability will be detected at runtime,	2841	C<epoll>(7) backend. Its availability will be detected at runtime,
2780	otherwise another method will be used as fallback. This is the	2842	otherwise another method will be used as fallback. This is the preferred
2781	preferred backend for GNU/Linux systems.	2843	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2844	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2782		2845
2783	=item EV_USE_KQUEUE	2846	=item EV_USE_KQUEUE
2784		2847
2785	If defined to be C<1>, libev will compile in support for the BSD style	2848	If defined to be C<1>, libev will compile in support for the BSD style
2786	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	2849	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2805		2868
2806	=item EV_USE_INOTIFY	2869	=item EV_USE_INOTIFY
2807		2870
2808	If defined to be C<1>, libev will compile in support for the Linux inotify	2871	If defined to be C<1>, libev will compile in support for the Linux inotify
2809	interface to speed up C<ev_stat> watchers. Its actual availability will	2872	interface to speed up C<ev_stat> watchers. Its actual availability will
2810	be detected at runtime.	2873	be detected at runtime. If undefined, it will be enabled if the headers
		2874	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2811		2875
2812	=item EV_ATOMIC_T	2876	=item EV_ATOMIC_T
2813		2877
2814	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	2878	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2815	access is atomic with respect to other threads or signal contexts. No such	2879	access is atomic with respect to other threads or signal contexts. No such
…		…
3002		3066
3003	#include "ev_cpp.h"	3067	#include "ev_cpp.h"
3004	#include "ev.c"	3068	#include "ev.c"
3005		3069
3006		3070
		3071	=head1 THREADS AND COROUTINES
		3072
		3073	=head2 THREADS
		3074
		3075	Libev itself is completely threadsafe, but it uses no locking. This
		3076	means that you can use as many loops as you want in parallel, as long as
		3077	only one thread ever calls into one libev function with the same loop
		3078	parameter.
		3079
		3080	Or put differently: calls with different loop parameters can be done in
		3081	parallel from multiple threads, calls with the same loop parameter must be
		3082	done serially (but can be done from different threads, as long as only one
		3083	thread ever is inside a call at any point in time, e.g. by using a mutex
		3084	per loop).
		3085
		3086	If you want to know which design is best for your problem, then I cannot
		3087	help you but by giving some generic advice:
		3088
		3089	=over 4
		3090
		3091	=item * most applications have a main thread: use the default libev loop
		3092	in that thread, or create a seperate thread running only the default loop.
		3093
		3094	This helps integrating other libraries or software modules that use libev
		3095	themselves and don't care/know about threading.
		3096
		3097	=item * one loop per thread is usually a good model.
		3098
		3099	Doing this is almost never wrong, sometimes a better-performance model
		3100	exists, but it is always a good start.
		3101
		3102	=item * other models exist, such as the leader/follower pattern, where one
		3103	loop is handed through multiple threads in a kind of round-robbin fashion.
		3104
		3105	Chosing a model is hard - look around, learn, know that usually you cna do
		3106	better than you currently do :-)
		3107
		3108	=item * often you need to talk to some other thread which blocks in the
		3109	event loop - C<ev_async> watchers can be used to wake them up from other
		3110	threads safely (or from signal contexts...).
		3111
		3112	=back
		3113
		3114	=head2 COROUTINES
		3115
		3116	Libev is much more accomodating to coroutines ("cooperative threads"):
		3117	libev fully supports nesting calls to it's functions from different
		3118	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3119	different coroutines and switch freely between both coroutines running the
		3120	loop, as long as you don't confuse yourself). The only exception is that
		3121	you must not do this from C<ev_periodic> reschedule callbacks.
		3122
		3123	Care has been invested into making sure that libev does not keep local
		3124	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3125	switches.
		3126
		3127
3007	=head1 COMPLEXITIES	3128	=head1 COMPLEXITIES
3008		3129
3009	In this section the complexities of (many of) the algorithms used inside	3130	In this section the complexities of (many of) the algorithms used inside
3010	libev will be explained. For complexity discussions about backends see the	3131	libev will be explained. For complexity discussions about backends see the
3011	documentation for C<ev_default_init>.	3132	documentation for C<ev_default_init>.

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Comparing libev/ev.pod (file contents): Revision 1.136 by root, Thu Mar 13 13:06:16 2008 UTC vs. Revision 1.146 by root, Fri Apr 11 00:31:19 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.136 by root, Thu Mar 13 13:06:16 2008 UTC vs.
Revision 1.146 by root, Fri Apr 11 00:31:19 2008 UTC