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

Comparing libev/ev.pod (file contents):
Revision 1.283 by root, Wed Mar 10 09:18:25 2010 UTC vs.
Revision 1.286 by root, Tue Mar 16 00:26:41 2010 UTC

…		…
1538		1538
1539	So when you encounter spurious, unexplained daemon exits, make sure you	1539	So when you encounter spurious, unexplained daemon exits, make sure you
1540	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1540	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1541	somewhere, as that would have given you a big clue).	1541	somewhere, as that would have given you a big clue).
1542		1542
		1543	=head3 The special problem of accept()ing when you can't
		1544
		1545	Many implementations of the POSIX C<accept> function (for example,
		1546	found in port-2004 Linux) have the peculiar behaviour of not removing a
		1547	connection from the pending queue in all error cases.
		1548
		1549	For example, larger servers often run out of file descriptors (because
		1550	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1551	rejecting the connection, leading to libev signalling readiness on
		1552	the next iteration again (the connection still exists after all), and
		1553	typically causing the program to loop at 100% CPU usage.
		1554
		1555	Unfortunately, the set of errors that cause this issue differs between
		1556	operating systems, there is usually little the app can do to remedy the
		1557	situation, and no known thread-safe method of removing the connection to
		1558	cope with overload is known (to me).
		1559
		1560	One of the easiest ways to handle this situation is to just ignore it
		1561	- when the program encounters an overload, it will just loop until the
		1562	situation is over. While this is a form of busy waiting, no OS offers an
		1563	event-based way to handle this situation, so it's the best one can do.
		1564
		1565	A better way to handle the situation is to log any errors other than
		1566	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1567	messages, and continue as usual, which at least gives the user an idea of
		1568	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1569	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1570	usage.
		1571
		1572	If your program is single-threaded, then you could also keep a dummy file
		1573	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1574	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1575	close that fd, and create a new dummy fd. This will gracefully refuse
		1576	clients under typical overload conditions.
		1577
		1578	The last way to handle it is to simply log the error and C<exit>, as
		1579	is often done with C<malloc> failures, but this results in an easy
		1580	opportunity for a DoS attack.
1543		1581
1544	=head3 Watcher-Specific Functions	1582	=head3 Watcher-Specific Functions
1545		1583
1546	=over 4	1584	=over 4
1547		1585
…		…
3846		3884
3847	If undefined or defined to be C<1> (and the platform supports it), then	3885	If undefined or defined to be C<1> (and the platform supports it), then
3848	the respective watcher type is supported. If defined to be C<0>, then it	3886	the respective watcher type is supported. If defined to be C<0>, then it
3849	is not. Disabling watcher types mainly saves codesize.	3887	is not. Disabling watcher types mainly saves codesize.
3850		3888
3851	=item EV_MINIMAL	3889	=item EV_FEATURES
3852		3890
3853	If you need to shave off some kilobytes of code at the expense of some	3891	If you need to shave off some kilobytes of code at the expense of some
3854	speed (but with the full API), define this symbol to C<1>. Currently this	3892	speed (but with the full API), you can define this symbol to request
3855	is used to override some inlining decisions, saves roughly 30% code size	3893	certain subsets of functionality. The default is to enable all features
3856	on amd64. It also selects a much smaller 2-heap for timer management over	3894	that can be enabled on the platform.
3857	the default 4-heap.
3858		3895
3859	You can save even more by disabling watcher types you do not need	3896	Note that using autoconf will usually override most of the features, so
3860	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>	3897	using this symbol makes sense mostly when embedding libev.
3861	(C<-DNDEBUG>) will usually reduce code size a lot. Disabling inotify,
3862	eventfd and signalfd will further help, and disabling backends one doesn't
3863	need (e.g. poll, epoll, kqueue, ports) will help further.
3864		3898
3865	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to	3899	A typical way to use this symbol is to define it to C<0> (or to a bitset
3866	provide a bare-bones event library. See C<ev.h> for details on what parts	3900	with some broad features you want) and then selectively re-enable
3867	of the API are still available, and do not complain if this subset changes	3901	additional parts you want, for example if you want everything minimal,
3868	over time.	3902	but multiple event loop support, async and child watchers and the poll
		3903	backend, use this:
3869		3904
3870	This example set of settings reduces the compiled size of libev from	3905	#define EV_FEATURES 0
3871	23.9Kb to 7.7Kb on my GNU/Linux amd64 system (and leaves little
3872	in - there is also an effect on the amount of memory used). With
3873	an intelligent-enough linker (gcc+binutils do this when you use
3874	C<-Wl,--gc-sections -ffunction-sections>) further unused functions might
3875	be left out as well automatically - a binary starting a timer and an I/O
3876	watcher then might come out at only 5Kb.
3877
3878	// tuning and API changes
3879	#define EV_MINIMAL 2
3880	#define EV_MULTIPLICITY 0	3906	#define EV_MULTIPLICITY 1
3881	#define EV_MINPRI 0
3882	#define EV_MAXPRI 0
3883
3884	// OS-specific backends
3885	#define EV_USE_INOTIFY 0
3886	#define EV_USE_EVENTFD 0
3887	#define EV_USE_SIGNALFD 0
3888	#define EV_USE_REALTIME 0
3889	#define EV_USE_MONOTONIC 0
3890	#define EV_USE_CLOCK_SYSCALL 0
3891
3892	// disable all backends except select
3893	#define EV_USE_POLL 0	3907	#define EV_USE_POLL 1
3894	#define EV_USE_PORT 0
3895	#define EV_USE_KQUEUE 0
3896	#define EV_USE_EPOLL 0
3897
3898	// disable all watcher types that cna be disabled
3899	#define EV_STAT_ENABLE 0
3900	#define EV_PERIODIC_ENABLE 0
3901	#define EV_IDLE_ENABLE 0
3902	#define EV_CHECK_ENABLE 0
3903	#define EV_PREPARE_ENABLE 0
3904	#define EV_FORK_ENABLE 0
3905	#define EV_SIGNAL_ENABLE 0
3906	#define EV_CHILD_ENABLE 0	3908	#define EV_CHILD_ENABLE 1
3907	#define EV_ASYNC_ENABLE 0	3909	#define EV_ASYNC_ENABLE 1
3908	#define EV_EMBED_ENABLE 0	3910
		3911	The actual value is a bitset, it can be a combination of the following
		3912	values:
		3913
		3914	=over 4
		3915
		3916	=item C<1> - faster/larger code
		3917
		3918	Use larger code to speed up some operations.
		3919
		3920	Currently this is used to override some inlining decisions (enlarging the roughly
		3921	30% code size on amd64.
		3922
		3923	When optimising for size, use of compiler flags such as C<-Os> with
		3924	gcc recommended, as well as C<-DNDEBUG>, as libev contains a number of
		3925	assertions.
		3926
		3927	=item C<2> - faster/larger data structures
		3928
		3929	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		3930	hash table sizes and so on. This will usually further increase codesize
		3931	and can additionally have an effect on the size of data structures at
		3932	runtime.
		3933
		3934	=item C<4> - full API configuration
		3935
		3936	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		3937	enables multiplicity (C<EV_MULTIPLICITY>=1).
		3938
		3939	It also enables a lot of the "lesser used" core API functions. See C<ev.h>
		3940	for details on which parts of the API are still available without this
		3941	feature, and do not complain if this subset changes over time.
		3942
		3943	=item C<8> - enable all optional watcher types
		3944
		3945	Enables all optional watcher types. If you want to selectively enable
		3946	only some watcher types other than I/O and timers (e.g. prepare,
		3947	embed, async, child...) you can enable them manually by defining
		3948	C<EV_watchertype_ENABLE> to C<1> instead.
		3949
		3950	=item C<16> - enable all backends
		3951
		3952	This enables all backends - without this feature, you need to enable at
		3953	least one backend manually (C<EV_USE_SELECT> is a good choice).
		3954
		3955	=item C<32> - enable OS-specific "helper" APIs
		3956
		3957	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		3958	default.
		3959
		3960	=back
		3961
		3962	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		3963	reduces the compiled size of libev from 24.7Kb to 6.5Kb on my GNU/Linux
		3964	amd64 system, while still giving you I/O watchers, timers and monotonic
		3965	clock support.
		3966
		3967	With an intelligent-enough linker (gcc+binutils are intelligent enough
		3968	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		3969	your program might be left out as well - a binary starting a timer and an
		3970	I/O watcher then might come out at only 5Kb.
3909		3971
3910	=item EV_AVOID_STDIO	3972	=item EV_AVOID_STDIO
3911		3973
3912	If this is set to C<1> at compiletime, then libev will avoid using stdio	3974	If this is set to C<1> at compiletime, then libev will avoid using stdio
3913	functions (printf, scanf, perror etc.). This will increase the codesize	3975	functions (printf, scanf, perror etc.). This will increase the codesize
…		…
3928	statically allocates some 12-24 bytes per signal number.	3990	statically allocates some 12-24 bytes per signal number.
3929		3991
3930	=item EV_PID_HASHSIZE	3992	=item EV_PID_HASHSIZE
3931		3993
3932	C<ev_child> watchers use a small hash table to distribute workload by	3994	C<ev_child> watchers use a small hash table to distribute workload by
3933	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3995	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3934	than enough. If you need to manage thousands of children you might want to	3996	usually more than enough. If you need to manage thousands of children you
3935	increase this value (I<must> be a power of two).	3997	might want to increase this value (I<must> be a power of two).
3936		3998
3937	=item EV_INOTIFY_HASHSIZE	3999	=item EV_INOTIFY_HASHSIZE
3938		4000
3939	C<ev_stat> watchers use a small hash table to distribute workload by	4001	C<ev_stat> watchers use a small hash table to distribute workload by
3940	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	4002	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3941	usually more than enough. If you need to manage thousands of C<ev_stat>	4003	disabled), usually more than enough. If you need to manage thousands of
3942	watchers you might want to increase this value (I<must> be a power of	4004	C<ev_stat> watchers you might want to increase this value (I<must> be a
3943	two).	4005	power of two).
3944		4006
3945	=item EV_USE_4HEAP	4007	=item EV_USE_4HEAP
3946		4008
3947	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4009	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3948	timer and periodics heaps, libev uses a 4-heap when this symbol is defined	4010	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3949	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably	4011	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3950	faster performance with many (thousands) of watchers.	4012	faster performance with many (thousands) of watchers.
3951		4013
3952	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4014	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3953	(disabled).	4015	will be C<0>.
3954		4016
3955	=item EV_HEAP_CACHE_AT	4017	=item EV_HEAP_CACHE_AT
3956		4018
3957	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4019	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3958	timer and periodics heaps, libev can cache the timestamp (I<at>) within	4020	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3959	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	4021	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3960	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	4022	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3961	but avoids random read accesses on heap changes. This improves performance	4023	but avoids random read accesses on heap changes. This improves performance
3962	noticeably with many (hundreds) of watchers.	4024	noticeably with many (hundreds) of watchers.
3963		4025
3964	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4026	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3965	(disabled).	4027	will be C<0>.
3966		4028
3967	=item EV_VERIFY	4029	=item EV_VERIFY
3968		4030
3969	Controls how much internal verification (see C<ev_loop_verify ()>) will	4031	Controls how much internal verification (see C<ev_loop_verify ()>) will
3970	be done: If set to C<0>, no internal verification code will be compiled	4032	be done: If set to C<0>, no internal verification code will be compiled
…		…
3972	called. If set to C<2>, then the internal verification code will be	4034	called. If set to C<2>, then the internal verification code will be
3973	called once per loop, which can slow down libev. If set to C<3>, then the	4035	called once per loop, which can slow down libev. If set to C<3>, then the
3974	verification code will be called very frequently, which will slow down	4036	verification code will be called very frequently, which will slow down
3975	libev considerably.	4037	libev considerably.
3976		4038
3977	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	4039	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3978	C<0>.	4040	will be C<0>.
3979		4041
3980	=item EV_COMMON	4042	=item EV_COMMON
3981		4043
3982	By default, all watchers have a C<void *data> member. By redefining	4044	By default, all watchers have a C<void *data> member. By redefining
3983	this macro to a something else you can include more and other types of	4045	this macro to a something else you can include more and other types of
…		…
4041	file.	4103	file.
4042		4104
4043	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4105	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
4044	that everybody includes and which overrides some configure choices:	4106	that everybody includes and which overrides some configure choices:
4045		4107
4046	#define EV_MINIMAL 1	4108	#define EV_FEATURES 0
4047	#define EV_USE_POLL 0	4109	#define EV_USE_SELECT 1
4048	#define EV_MULTIPLICITY 0
4049	#define EV_PERIODIC_ENABLE 0
4050	#define EV_STAT_ENABLE 0
4051	#define EV_FORK_ENABLE 0
4052	#define EV_CONFIG_H <config.h>	4110	#define EV_CONFIG_H <config.h>
4053	#define EV_MINPRI 0
4054	#define EV_MAXPRI 0
4055		4111
4056	#include "ev++.h"	4112	#include "ev++.h"
4057		4113
4058	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4114	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
4059		4115

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Comparing libev/ev.pod (file contents): Revision 1.283 by root, Wed Mar 10 09:18:25 2010 UTC vs. Revision 1.286 by root, Tue Mar 16 00:26:41 2010 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.283 by root, Wed Mar 10 09:18:25 2010 UTC vs.
Revision 1.286 by root, Tue Mar 16 00:26:41 2010 UTC