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

Comparing libev/ev.pod (file contents):
Revision 1.138 by root, Mon Mar 31 01:14:12 2008 UTC vs.
Revision 1.148 by root, Thu Apr 24 01:42:11 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)
…		…
1630	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
1631	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
1632	change detection where possible. The inotify descriptor will be created lazily	1636	change detection where possible. The inotify descriptor will be created lazily
1633	when the first C<ev_stat> watcher is being started.	1637	when the first C<ev_stat> watcher is being started.
1634		1638
1635	Inotify presense does not change the semantics of C<ev_stat> watchers	1639	Inotify presence does not change the semantics of C<ev_stat> watchers
1636	except that changes might be detected earlier, and in some cases, to avoid	1640	except that changes might be detected earlier, and in some cases, to avoid
1637	making regular C<stat> calls. Even in the presense of inotify support	1641	making regular C<stat> calls. Even in the presence of inotify support
1638	there are many cases where libev has to resort to regular C<stat> polling.	1642	there are many cases where libev has to resort to regular C<stat> polling.
1639		1643
1640	(There is no support for kqueue, as apparently it cannot be used to	1644	(There is no support for kqueue, as apparently it cannot be used to
1641	implement this functionality, due to the requirement of having a file	1645	implement this functionality, due to the requirement of having a file
1642	descriptor open on the object at all times).	1646	descriptor open on the object at all times).
…		…
2280		2284
2281	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,
2282	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
2283	calls to C<ev_async_send>.	2287	calls to C<ev_async_send>.
2284		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
2285	=back	2303	=back
2286		2304
2287		2305
2288	=head1 OTHER FUNCTIONS	2306	=head1 OTHER FUNCTIONS
2289		2307
…		…
2360		2378
2361	=item * Priorities are not currently supported. Initialising priorities	2379	=item * Priorities are not currently supported. Initialising priorities
2362	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
2363	is an ev_pri field.	2381	is an ev_pri field.
2364		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
2365	=item * Other members are not supported.	2386	=item * Other members are not supported.
2366		2387
2367	=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
2368	to use the libev header file and library.	2389	to use the libev header file and library.
2369		2390
…		…
2611	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	2632	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2612		2633
2613	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
2614	loop, if multiple loops are supported ("ev loop default").	2635	loop, if multiple loops are supported ("ev loop default").
2615		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
2616	=back	2647	=back
2617		2648
2618	Example: Declare and initialise a check watcher, utilising the above	2649	Example: Declare and initialise a check watcher, utilising the above
2619	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
2620	or not.	2651	or not.
…		…
2715		2746
2716	libev.m4	2747	libev.m4
2717		2748
2718	=head2 PREPROCESSOR SYMBOLS/MACROS	2749	=head2 PREPROCESSOR SYMBOLS/MACROS
2719		2750
2720	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
2721	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
2722	and only include the select backend.	2753	autoconf is noted for every option.
2723		2754
2724	=over 4	2755	=over 4
2725		2756
2726	=item EV_STANDALONE	2757	=item EV_STANDALONE
2727		2758
…		…
2753	=item EV_USE_NANOSLEEP	2784	=item EV_USE_NANOSLEEP
2754		2785
2755	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
2756	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 ()>.
2757		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
2758	=item EV_USE_SELECT	2797	=item EV_USE_SELECT
2759		2798
2760	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
2761	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
2762	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
…		…
2798		2837
2799	=item EV_USE_EPOLL	2838	=item EV_USE_EPOLL
2800		2839
2801	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
2802	C<epoll>(7) backend. Its availability will be detected at runtime,	2841	C<epoll>(7) backend. Its availability will be detected at runtime,
2803	otherwise another method will be used as fallback. This is the	2842	otherwise another method will be used as fallback. This is the preferred
2804	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.
2805		2845
2806	=item EV_USE_KQUEUE	2846	=item EV_USE_KQUEUE
2807		2847
2808	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
2809	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,
…		…
2828		2868
2829	=item EV_USE_INOTIFY	2869	=item EV_USE_INOTIFY
2830		2870
2831	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
2832	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
2833	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.
2834		2875
2835	=item EV_ATOMIC_T	2876	=item EV_ATOMIC_T
2836		2877
2837	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
2838	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
…		…
3025		3066
3026	#include "ev_cpp.h"	3067	#include "ev_cpp.h"
3027	#include "ev.c"	3068	#include "ev.c"
3028		3069
3029		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
3030	=head1 COMPLEXITIES	3128	=head1 COMPLEXITIES
3031		3129
3032	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
3033	libev will be explained. For complexity discussions about backends see the	3131	libev will be explained. For complexity discussions about backends see the
3034	documentation for C<ev_default_init>.	3132	documentation for C<ev_default_init>.
…		…
3162	calling select (O(n²)) will likely make this unworkable.	3260	calling select (O(n²)) will likely make this unworkable.
3163		3261
3164	=back	3262	=back
3165		3263
3166		3264
		3265	=head1 PORTABILITY REQUIREMENTS
		3266
		3267	In addition to a working ISO-C implementation, libev relies on a few
		3268	additional extensions:
		3269
		3270	=over 4
		3271
		3272	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3273
		3274	The type C<sig_atomic_t volatile> (or whatever is defined as
		3275	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different
		3276	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3277	believed to be sufficiently portable.
		3278
		3279	=item C<sigprocmask> must work in a threaded environment
		3280
		3281	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3282	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3283	pthread implementations will either allow C<sigprocmask> in the "main
		3284	thread" or will block signals process-wide, both behaviours would
		3285	be compatible with libev. Interaction between C<sigprocmask> and
		3286	C<pthread_sigmask> could complicate things, however.
		3287
		3288	The most portable way to handle signals is to block signals in all threads
		3289	except the initial one, and run the default loop in the initial thread as
		3290	well.
		3291
		3292	=back
		3293
		3294	If you know of other additional requirements drop me a note.
		3295
		3296
3167	=head1 AUTHOR	3297	=head1 AUTHOR
3168		3298
3169	Marc Lehmann <libev@schmorp.de>.	3299	Marc Lehmann <libev@schmorp.de>.
3170		3300

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Comparing libev/ev.pod (file contents): Revision 1.138 by root, Mon Mar 31 01:14:12 2008 UTC vs. Revision 1.148 by root, Thu Apr 24 01:42:11 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.138 by root, Mon Mar 31 01:14:12 2008 UTC vs.
Revision 1.148 by root, Thu Apr 24 01:42:11 2008 UTC