[ViewVC] Annotation of: cvs/libev/README

libev is a high-performance event loop/event model with lots of features.
(see benchmark at http://libev.schmorp.de/bench.html)

   Homepage: http://software.schmorp.de/pkg/libev
   E-Mail: libev@lists.schmorp.de
   Library Documentation: http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod

   It is modelled (very losely) after libevent and the Event perl module,
   but aims to be faster and more correct, and also more featureful. And
   also smaller. Yay.

ABOUT THIS DISTRIBUTION

   If you downloaded the libevent+libev distribution of libev, you will
   find it looks very much like libevent. In fact, the distributed libev
   tarballs are indeed libevent tarballs patched up with the libev
   event core, taking the evbuffer, evtag, evdns and evhttpd parts from
   libevent (they use the libevent emulation inside libev). Configure and
   Makefile stuff is also a more or less direct copy of libevent, and are
   maintained by the libevent authors.

   If you downloaded the libev distribution (without libevent), then
   you only get the core parts of the library, meaning http and dns
   client/server code and similar things are missing. Only the core event
   loop is included.

   If you are looking for an easily embeddable version, I recommend using
   the libev standalone distribution or the CVS repository.

   Examples of programs that embed libev: the EV perl module,
   rxvt-unicode, gvpe (GNU Virtual Private Ethernet) and deliantra
   (http://www.deliantra.net).

DIFFERENCES AND COMPARISON TO LIBEVENT

   The comparisons below are relative to libevent-1.3e.

   - multiple watchers can wait for the same event without deregistering others,
     both for file descriptors as well as signals.
     (registering two read events on fd 10 and unregistering one will not
     break the other).

   - fork() is supported and can be handled
     (there is no way to recover from a fork with libevent).

   - timers are handled as a priority queue (important operations are O(1))
     (libevent uses a much less efficient but more complex red-black tree).

   - supports absolute (wallclock-based) timers in addition to relative ones,
     i.e. can schedule timers to occur after n seconds, or at a specific time.

   - timers can be repeating (both absolute and relative ones).

   - absolute timers can have customised rescheduling hooks (suitable for cron-like
     applications).

   - detects time jumps and adjusts timers
     (works for both forward and backward time jumps and also for absolute timers).

   - race-free signal processing
     (libevent may delay processing signals till after the next event).

   - more efficient epoll backend
     (stopping and starting an io watcher between two loop iterations will not
     result in spurious epoll_ctl calls).

   - usually less calls to gettimeofday and clock_gettime
     (libevent calls it on every timer event change, libev twice per iteration).

   - watchers use less memory
     (libevent watcher on amd64: 152 bytes, libev native: <= 56 bytes, libevent emulation: 144 bytes).

   - library uses less memory
     (libevent allocates large data structures wether used or not, libev
     scales all its data structures dynamically).

   - no hardcoded arbitrary limits
     (libevent contains an off-by-one bug and sometimes hardcodes limits).

   - libev separates timer, signal and io watchers from each other
     (libevent combines them, but with libev you can combine them yourself
     by reusing the same callback and still save memory).

   - simpler design, backends are potentially much simpler
     (in libevent, backends have to deal with watchers, thus the problems with
     wildly different semantics between diferent backends)
     (epoll backend in libevent: 366 lines no caching, libev: 90 lines full caching).

   - libev handles EBADF gracefully by removing the offending fds.

   - libev communicates errors to the callback, libevent to the
     event adder or not at all.

   - doesn't rely on nonportable BSD header files.

   - an event.h compatibility header exists, and can be used to run a wide
     range of libevent programs unchanged (such as evdns.c).

   - win32 compatibility for the core parts.
     (the backend is fd-based as documented and on other platforms,
     not handle-based like libevent, and can be used for both winscoket environments
     and unix-like ones).

   - libev can be embedded easily with or without autoconf support into
     other programs, with no changes to the source code necessary.

   - the event core library (ev and event layer) compiles and works both as
     C and C++.

   - a simple C++ wrapper that supports methods as callbacks exists.

   - a full featured and widely used perl module is available.

   whats missing?

   - no event-like priority support at the moment (the ev priorities work
     differently, but you can use idle watchers to get a similar effect).

AUTHOR

   libev was written and designed by Marc Lehmann and Emanuele Giaquinta.

   The following people sent in patches or made other noteworthy
   contributions to the design (if I forgot to include you, please shout
   at me, it was an accident):

   W.C.A. Wijngaards
   Christopher Layne
   Chris Brody

Revision:	1.19
Committed:	Fri Dec 14 21:07:13 2007 UTC (16 years, 5 months ago) by root
Branch:	MAIN
CVS Tags:	rel-2_01, rel-2_0, rel-3_31, rel-3_3, rel-3_2, rel-3_1, rel-3_0, rel-1_86, rel-1_85
Changes since 1.18:	+17 -12 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.18	libev is a high-performance event loop/event model with lots of features.
2			(see benchmark at http://libev.schmorp.de/bench.html)
3
4			Homepage: http://software.schmorp.de/pkg/libev
5			E-Mail: libev@lists.schmorp.de
6	root	1.19	Library Documentation: http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod
7	root	1.18
8	root	1.19	It is modelled (very losely) after libevent and the Event perl module,
9			but aims to be faster and more correct, and also more featureful. And
10			also smaller. Yay.
11	root	1.18
12			ABOUT THIS DISTRIBUTION
13
14	root	1.19	If you downloaded the libevent+libev distribution of libev, you will
15			find it looks very much like libevent. In fact, the distributed libev
16			tarballs are indeed libevent tarballs patched up with the libev
17			event core, taking the evbuffer, evtag, evdns and evhttpd parts from
18			libevent (they use the libevent emulation inside libev). Configure and
19			Makefile stuff is also a more or less direct copy of libevent, and are
20			maintained by the libevent authors.
21
22			If you downloaded the libev distribution (without libevent), then
23			you only get the core parts of the library, meaning http and dns
24			client/server code and similar things are missing. Only the core event
25			loop is included.
26	root	1.18
27			If you are looking for an easily embeddable version, I recommend using
28	root	1.19	the libev standalone distribution or the CVS repository.
29	root	1.16
30	root	1.18	Examples of programs that embed libev: the EV perl module,
31			rxvt-unicode, gvpe (GNU Virtual Private Ethernet) and deliantra
32			(http://www.deliantra.net).
33
34			DIFFERENCES AND COMPARISON TO LIBEVENT
35
36			The comparisons below are relative to libevent-1.3e.
37
38			- multiple watchers can wait for the same event without deregistering others,
39			both for file descriptors as well as signals.
40			(registering two read events on fd 10 and unregistering one will not
41			break the other).
42
43			- fork() is supported and can be handled
44			(there is no way to recover from a fork with libevent).
45	root	1.9
46	root	1.18	- timers are handled as a priority queue (important operations are O(1))
47			(libevent uses a much less efficient but more complex red-black tree).
48	root	1.9
49	root	1.18	- supports absolute (wallclock-based) timers in addition to relative ones,
50			i.e. can schedule timers to occur after n seconds, or at a specific time.
51	root	1.1
52	root	1.18	- timers can be repeating (both absolute and relative ones).
53	root	1.5
54	root	1.18	- absolute timers can have customised rescheduling hooks (suitable for cron-like
55			applications).
56	root	1.2
57	root	1.18	- detects time jumps and adjusts timers
58			(works for both forward and backward time jumps and also for absolute timers).
59	root	1.2
60	root	1.18	- race-free signal processing
61			(libevent may delay processing signals till after the next event).
62	root	1.2
63	root	1.18	- more efficient epoll backend
64			(stopping and starting an io watcher between two loop iterations will not
65			result in spurious epoll_ctl calls).
66	root	1.2
67	root	1.18	- usually less calls to gettimeofday and clock_gettime
68			(libevent calls it on every timer event change, libev twice per iteration).
69	root	1.2
70	root	1.18	- watchers use less memory
71			(libevent watcher on amd64: 152 bytes, libev native: <= 56 bytes, libevent emulation: 144 bytes).
72	root	1.2
73	root	1.18	- library uses less memory
74			(libevent allocates large data structures wether used or not, libev
75			scales all its data structures dynamically).
76	root	1.3
77	root	1.18	- no hardcoded arbitrary limits
78			(libevent contains an off-by-one bug and sometimes hardcodes limits).
79	root	1.2
80	root	1.18	- libev separates timer, signal and io watchers from each other
81			(libevent combines them, but with libev you can combine them yourself
82			by reusing the same callback and still save memory).
83	root	1.2
84	root	1.18	- simpler design, backends are potentially much simpler
85			(in libevent, backends have to deal with watchers, thus the problems with
86			wildly different semantics between diferent backends)
87			(epoll backend in libevent: 366 lines no caching, libev: 90 lines full caching).
88	root	1.2
89	root	1.18	- libev handles EBADF gracefully by removing the offending fds.
90	root	1.2
91	root	1.18	- libev communicates errors to the callback, libevent to the
92			event adder or not at all.
93	root	1.2
94	root	1.18	- doesn't rely on nonportable BSD header files.
95	root	1.2
96	root	1.18	- an event.h compatibility header exists, and can be used to run a wide
97			range of libevent programs unchanged (such as evdns.c).
98	root	1.2
99	root	1.18	- win32 compatibility for the core parts.
100			(the backend is fd-based as documented and on other platforms,
101			not handle-based like libevent, and can be used for both winscoket environments
102			and unix-like ones).
103	root	1.6
104	root	1.18	- libev can be embedded easily with or without autoconf support into
105			other programs, with no changes to the source code necessary.
106	root	1.8
107	root	1.18	- the event core library (ev and event layer) compiles and works both as
108			C and C++.
109	root	1.9
110	root	1.18	- a simple C++ wrapper that supports methods as callbacks exists.
111	root	1.13
112	root	1.18	- a full featured and widely used perl module is available.
113	root	1.13
114	root	1.18	whats missing?
115	root	1.2
116	root	1.18	- no event-like priority support at the moment (the ev priorities work
117			differently, but you can use idle watchers to get a similar effect).
118	root	1.2
119	root	1.16	AUTHOR
120	root	1.1
121	root	1.18	libev was written and designed by Marc Lehmann and Emanuele Giaquinta.
122	root	1.17
123	root	1.18	The following people sent in patches or made other noteworthy
124			contributions to the design (if I forgot to include you, please shout
125			at me, it was an accident):
126
127			W.C.A. Wijngaards
128			Christopher Layne
129			Chris Brody
130	root	1.17