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

Comparing libev/ev.pod (file contents):
Revision 1.139 by root, Wed Apr 2 05:51:40 2008 UTC vs.
Revision 1.145 by root, Wed Apr 9 22:07:50 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
…		…
358	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,
359	but it scales phenomenally better. While poll and select usually scale	355	but it scales phenomenally better. While poll and select usually scale
360	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),
361	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
362	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
363	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
364	support for dup.	360	support for dup.
365		361
366	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
367	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
368	(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
…		…
2288		2284
2289	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,
2290	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
2291	calls to C<ev_async_send>.	2287	calls to C<ev_async_send>.
2292		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
2293	=back	2303	=back
2294		2304
2295		2305
2296	=head1 OTHER FUNCTIONS	2306	=head1 OTHER FUNCTIONS
2297		2307
…		…
2619	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	2629	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2620		2630
2621	Similar to the other two macros, this gives you the value of the default	2631	Similar to the other two macros, this gives you the value of the default
2622	loop, if multiple loops are supported ("ev loop default").	2632	loop, if multiple loops are supported ("ev loop default").
2623		2633
		2634	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		2635
		2636	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		2637	default loop has been initialised (C<UC> == unchecked). Their behaviour
		2638	is undefined when the default loop has not been initialised by a previous
		2639	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		2640
		2641	It is often prudent to use C<EV_DEFAULT> when initialising the first
		2642	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
		2643
2624	=back	2644	=back
2625		2645
2626	Example: Declare and initialise a check watcher, utilising the above	2646	Example: Declare and initialise a check watcher, utilising the above
2627	macros so it will work regardless of whether multiple loops are supported	2647	macros so it will work regardless of whether multiple loops are supported
2628	or not.	2648	or not.
…		…
2723		2743
2724	libev.m4	2744	libev.m4
2725		2745
2726	=head2 PREPROCESSOR SYMBOLS/MACROS	2746	=head2 PREPROCESSOR SYMBOLS/MACROS
2727		2747
2728	Libev can be configured via a variety of preprocessor symbols you have to define	2748	Libev can be configured via a variety of preprocessor symbols you have to
2729	before including any of its files. The default is not to build for multiplicity	2749	define before including any of its files. The default in the absense of
2730	and only include the select backend.	2750	autoconf is noted for every option.
2731		2751
2732	=over 4	2752	=over 4
2733		2753
2734	=item EV_STANDALONE	2754	=item EV_STANDALONE
2735		2755
…		…
2761	=item EV_USE_NANOSLEEP	2781	=item EV_USE_NANOSLEEP
2762		2782
2763	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	2783	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2764	and will use it for delays. Otherwise it will use C<select ()>.	2784	and will use it for delays. Otherwise it will use C<select ()>.
2765		2785
		2786	=item EV_USE_EVENTFD
		2787
		2788	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		2789	available and will probe for kernel support at runtime. This will improve
		2790	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		2791	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		2792	2.7 or newer, otherwise disabled.
		2793
2766	=item EV_USE_SELECT	2794	=item EV_USE_SELECT
2767		2795
2768	If undefined or defined to be C<1>, libev will compile in support for the	2796	If undefined or defined to be C<1>, libev will compile in support for the
2769	C<select>(2) backend. No attempt at autodetection will be done: if no	2797	C<select>(2) backend. No attempt at autodetection will be done: if no
2770	other method takes over, select will be it. Otherwise the select backend	2798	other method takes over, select will be it. Otherwise the select backend
…		…
2806		2834
2807	=item EV_USE_EPOLL	2835	=item EV_USE_EPOLL
2808		2836
2809	If defined to be C<1>, libev will compile in support for the Linux	2837	If defined to be C<1>, libev will compile in support for the Linux
2810	C<epoll>(7) backend. Its availability will be detected at runtime,	2838	C<epoll>(7) backend. Its availability will be detected at runtime,
2811	otherwise another method will be used as fallback. This is the	2839	otherwise another method will be used as fallback. This is the preferred
2812	preferred backend for GNU/Linux systems.	2840	backend for GNU/Linux systems. If undefined, it will be enabled if the
		2841	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2813		2842
2814	=item EV_USE_KQUEUE	2843	=item EV_USE_KQUEUE
2815		2844
2816	If defined to be C<1>, libev will compile in support for the BSD style	2845	If defined to be C<1>, libev will compile in support for the BSD style
2817	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	2846	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2836		2865
2837	=item EV_USE_INOTIFY	2866	=item EV_USE_INOTIFY
2838		2867
2839	If defined to be C<1>, libev will compile in support for the Linux inotify	2868	If defined to be C<1>, libev will compile in support for the Linux inotify
2840	interface to speed up C<ev_stat> watchers. Its actual availability will	2869	interface to speed up C<ev_stat> watchers. Its actual availability will
2841	be detected at runtime.	2870	be detected at runtime. If undefined, it will be enabled if the headers
		2871	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2842		2872
2843	=item EV_ATOMIC_T	2873	=item EV_ATOMIC_T
2844		2874
2845	Libev requires an integer type (suitable for storing C<0> or C<1>) whose	2875	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2846	access is atomic with respect to other threads or signal contexts. No such	2876	access is atomic with respect to other threads or signal contexts. No such
…		…
3033		3063
3034	#include "ev_cpp.h"	3064	#include "ev_cpp.h"
3035	#include "ev.c"	3065	#include "ev.c"
3036		3066
3037		3067
		3068	=head1 THREADS AND COROUTINES
		3069
		3070	=head2 THREADS
		3071
		3072	Libev itself is completely threadsafe, but it uses no locking. This
		3073	means that you can use as many loops as you want in parallel, as long as
		3074	only one thread ever calls into one libev function with the same loop
		3075	parameter.
		3076
		3077	Or put differently: calls with different loop parameters can be done in
		3078	parallel from multiple threads, calls with the same loop parameter must be
		3079	done serially (but can be done from different threads, as long as only one
		3080	thread ever is inside a call at any point in time, e.g. by using a mutex
		3081	per loop).
		3082
		3083	If you want to know which design is best for your problem, then I cannot
		3084	help you but by giving some generic advice:
		3085
		3086	=over 4
		3087
		3088	=item * most applications have a main thread: use the default libev loop
		3089	in that thread, or create a seperate thread running only the default loop.
		3090
		3091	This helps integrating other libraries or software modules that use libev
		3092	themselves and don't care/know about threading.
		3093
		3094	=item * one loop per thread is usually a good model.
		3095
		3096	Doing this is almost never wrong, sometimes a better-performance model
		3097	exists, but it is always a good start.
		3098
		3099	=item * other models exist, such as the leader/follower pattern, where one
		3100	loop is handed through multiple threads in a kind of round-robbin fashion.
		3101
		3102	Chosing a model is hard - look around, learn, know that usually you cna do
		3103	better than you currently do :-)
		3104
		3105	=item * often you need to talk to some other thread which blocks in the
		3106	event loop - C<ev_async> watchers can be used to wake them up from other
		3107	threads safely (or from signal contexts...).
		3108
		3109	=back
		3110
		3111	=head2 COROUTINES
		3112
		3113	Libev is much more accomodating to coroutines ("cooperative threads"):
		3114	libev fully supports nesting calls to it's functions from different
		3115	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3116	different coroutines and switch freely between both coroutines running the
		3117	loop, as long as you don't confuse yourself). The only exception is that
		3118	you must not do this from C<ev_periodic> reschedule callbacks.
		3119
		3120	Care has been invested into making sure that libev does not keep local
		3121	state inside C<ev_loop>, and other calls do not usually allow coroutine
		3122	switches.
		3123
		3124
3038	=head1 COMPLEXITIES	3125	=head1 COMPLEXITIES
3039		3126
3040	In this section the complexities of (many of) the algorithms used inside	3127	In this section the complexities of (many of) the algorithms used inside
3041	libev will be explained. For complexity discussions about backends see the	3128	libev will be explained. For complexity discussions about backends see the
3042	documentation for C<ev_default_init>.	3129	documentation for C<ev_default_init>.

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Comparing libev/ev.pod (file contents): Revision 1.139 by root, Wed Apr 2 05:51:40 2008 UTC vs. Revision 1.145 by root, Wed Apr 9 22:07:50 2008 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.139 by root, Wed Apr 2 05:51:40 2008 UTC vs.
Revision 1.145 by root, Wed Apr 9 22:07:50 2008 UTC