[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

   It is modelled (very losely) after libevent
   (http://monkey.org/~provos/libevent/) and the Event perl module, but aims
   to be faster and more correct, and also more featureful.

ABOUT THIS DISTRIBUTION

   If you downloaded a 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 are looking for an easily embeddable version, I recommend using
   the CVS repository (linked from the homepage, above), which contains
   only the libev core parts.

   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:	1.18
Committed:	Wed Nov 21 05:05:40 2007 UTC (17 years ago) by root
Branch:	MAIN
CVS Tags:	rel-1_71, rel-1_8, rel-1_4, rel-1_72, rel-1_1, rel-1_3, rel-1_2, rel-1_5, rel-1_6, rel-1_81
Changes since 1.17:	+95 -62 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
7			It is modelled (very losely) after libevent
8			(http://monkey.org/~provos/libevent/) and the Event perl module, but aims
9			to be faster and more correct, and also more featureful.
10
11			ABOUT THIS DISTRIBUTION
12
13			If you downloaded a distribution of libev, you will find it looks
14			very much like libevent. In fact, the distributed libev tarballs are
15			indeed libevent tarballs patched up with the libev event core, taking
16			the evbuffer, evtag, evdns and evhttpd parts from libevent (they use
17			the libevent emulation inside libev). Configure and Makefile stuff is
18			also a more or less direct copy of libevent, and are maintained by the
19			libevent authors.
20
21			If you are looking for an easily embeddable version, I recommend using
22			the CVS repository (linked from the homepage, above), which contains
23			only the libev core parts.
24	root	1.16
25	root	1.18	Examples of programs that embed libev: the EV perl module,
26			rxvt-unicode, gvpe (GNU Virtual Private Ethernet) and deliantra
27			(http://www.deliantra.net).
28
29			DIFFERENCES AND COMPARISON TO LIBEVENT
30
31			The comparisons below are relative to libevent-1.3e.
32
33			- multiple watchers can wait for the same event without deregistering others,
34			both for file descriptors as well as signals.
35			(registering two read events on fd 10 and unregistering one will not
36			break the other).
37
38			- fork() is supported and can be handled
39			(there is no way to recover from a fork with libevent).
40	root	1.9
41	root	1.18	- timers are handled as a priority queue (important operations are O(1))
42			(libevent uses a much less efficient but more complex red-black tree).
43	root	1.9
44	root	1.18	- supports absolute (wallclock-based) timers in addition to relative ones,
45			i.e. can schedule timers to occur after n seconds, or at a specific time.
46	root	1.1
47	root	1.18	- timers can be repeating (both absolute and relative ones).
48	root	1.5
49	root	1.18	- absolute timers can have customised rescheduling hooks (suitable for cron-like
50			applications).
51	root	1.2
52	root	1.18	- detects time jumps and adjusts timers
53			(works for both forward and backward time jumps and also for absolute timers).
54	root	1.2
55	root	1.18	- race-free signal processing
56			(libevent may delay processing signals till after the next event).
57	root	1.2
58	root	1.18	- more efficient epoll backend
59			(stopping and starting an io watcher between two loop iterations will not
60			result in spurious epoll_ctl calls).
61	root	1.2
62	root	1.18	- usually less calls to gettimeofday and clock_gettime
63			(libevent calls it on every timer event change, libev twice per iteration).
64	root	1.2
65	root	1.18	- watchers use less memory
66			(libevent watcher on amd64: 152 bytes, libev native: <= 56 bytes, libevent emulation: 144 bytes).
67	root	1.2
68	root	1.18	- library uses less memory
69			(libevent allocates large data structures wether used or not, libev
70			scales all its data structures dynamically).
71	root	1.3
72	root	1.18	- no hardcoded arbitrary limits
73			(libevent contains an off-by-one bug and sometimes hardcodes limits).
74	root	1.2
75	root	1.18	- libev separates timer, signal and io watchers from each other
76			(libevent combines them, but with libev you can combine them yourself
77			by reusing the same callback and still save memory).
78	root	1.2
79	root	1.18	- simpler design, backends are potentially much simpler
80			(in libevent, backends have to deal with watchers, thus the problems with
81			wildly different semantics between diferent backends)
82			(epoll backend in libevent: 366 lines no caching, libev: 90 lines full caching).
83	root	1.2
84	root	1.18	- libev handles EBADF gracefully by removing the offending fds.
85	root	1.2
86	root	1.18	- libev communicates errors to the callback, libevent to the
87			event adder or not at all.
88	root	1.2
89	root	1.18	- doesn't rely on nonportable BSD header files.
90	root	1.2
91	root	1.18	- an event.h compatibility header exists, and can be used to run a wide
92			range of libevent programs unchanged (such as evdns.c).
93	root	1.2
94	root	1.18	- win32 compatibility for the core parts.
95			(the backend is fd-based as documented and on other platforms,
96			not handle-based like libevent, and can be used for both winscoket environments
97			and unix-like ones).
98	root	1.6
99	root	1.18	- libev can be embedded easily with or without autoconf support into
100			other programs, with no changes to the source code necessary.
101	root	1.8
102	root	1.18	- the event core library (ev and event layer) compiles and works both as
103			C and C++.
104	root	1.9
105	root	1.18	- a simple C++ wrapper that supports methods as callbacks exists.
106	root	1.13
107	root	1.18	- a full featured and widely used perl module is available.
108	root	1.13
109	root	1.18	whats missing?
110	root	1.2
111	root	1.18	- no event-like priority support at the moment (the ev priorities work
112			differently, but you can use idle watchers to get a similar effect).
113	root	1.2
114	root	1.16	AUTHOR
115	root	1.1
116	root	1.18	libev was written and designed by Marc Lehmann and Emanuele Giaquinta.
117	root	1.17
118	root	1.18	The following people sent in patches or made other noteworthy
119			contributions to the design (if I forgot to include you, please shout
120			at me, it was an accident):
121
122			W.C.A. Wijngaards
123			Christopher Layne
124			Chris Brody
125	root	1.17