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Revision 1.19 by root, Fri Dec 14 21:07:13 2007 UTC vs.
Revision 1.20 by root, Thu Apr 24 08:02:15 2008 UTC

1libev is a high-performance event loop/event model with lots of features. 1libev is a high-performance event loop/event model with lots of features.
2(see benchmark at http://libev.schmorp.de/bench.html) 2(see benchmark at http://libev.schmorp.de/bench.html)
3 3
4
5ABOUT
6
4 Homepage: http://software.schmorp.de/pkg/libev 7 Homepage: http://software.schmorp.de/pkg/libev
5 E-Mail: libev@lists.schmorp.de 8 Mailinglist: libev@lists.schmorp.de
9 http://lists.schmorp.de/cgi-bin/mailman/listinfo/libev
6 Library Documentation: http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod 10 Library Documentation: http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod
7 11
8 It is modelled (very losely) after libevent and the Event perl module, 12 Libev is modelled (very losely) after libevent and the Event perl
9 but aims to be faster and more correct, and also more featureful. And 13 module, but is faster, scales better and is more correct, and also more
10 also smaller. Yay. 14 featureful. And also smaller. Yay.
11 15
12ABOUT THIS DISTRIBUTION 16 Some of the specialties of libev not commonly found elsewhere are:
13 17
14 If you downloaded the libevent+libev distribution of libev, you will 18 - extensive and detailed, readable documentation (not doxygen garbage).
15 find it looks very much like libevent. In fact, the distributed libev 19 - fully supports fork, can detect fork in various ways and automatically
16 tarballs are indeed libevent tarballs patched up with the libev 20 re-arms kernel mechanisms that do not support fork.
17 event core, taking the evbuffer, evtag, evdns and evhttpd parts from 21 - highly optimised select, poll, epoll, kqueue and event ports backends.
18 libevent (they use the libevent emulation inside libev). Configure and 22 - filesystem object (path) watching (with optional linux inotify support).
19 Makefile stuff is also a more or less direct copy of libevent, and are 23 - wallclock-based times (using absolute time, cron-like).
20 maintained by the libevent authors. 24 - relative timers/timeouts (handle time jumps).
21 25 - fast intra-thread communication between multiple
22 If you downloaded the libev distribution (without libevent), then 26 event loops (with optional fast linux eventfd backend).
23 you only get the core parts of the library, meaning http and dns 27 - extremely easy to embed.
24 client/server code and similar things are missing. Only the core event 28 - very small codebase, no bloated library.
25 loop is included. 29 - fully extensible by being able to plug into the event loop,
26 30 integrate other event loops, integrate other event loop users.
27 If you are looking for an easily embeddable version, I recommend using 31 - very little memory use (small watchers, small event loop data).
28 the libev standalone distribution or the CVS repository. 32 - optional C++ interface allowing method and function callbacks
33 at no extra memory or runtime overhead.
34 - optional Perl interface with similar characteristics (capable
35 of running Glib/Gtk2 on libev, interfaces with Net::SNMP and
36 libadns).
37 - support for other languages (multiple C++ interfaces, D, Ruby,
38 Python) available from third-parties.
29 39
30 Examples of programs that embed libev: the EV perl module, 40 Examples of programs that embed libev: the EV perl module,
31 rxvt-unicode, gvpe (GNU Virtual Private Ethernet) and deliantra 41 rxvt-unicode, gvpe (GNU Virtual Private Ethernet), the Deliantra MMORPG
32 (http://www.deliantra.net). 42 server (http://www.deliantra.net/), Rubinius (a next-generation Ruby
43 VM), the Ebb web server, the Rev event toolkit.
33 44
34DIFFERENCES AND COMPARISON TO LIBEVENT
35 45
36 The comparisons below are relative to libevent-1.3e. 46CONTRIBUTORS
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
46 - 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
49 - 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
52 - timers can be repeating (both absolute and relative ones).
53
54 - absolute timers can have customised rescheduling hooks (suitable for cron-like
55 applications).
56
57 - detects time jumps and adjusts timers
58 (works for both forward and backward time jumps and also for absolute timers).
59
60 - race-free signal processing
61 (libevent may delay processing signals till after the next event).
62
63 - 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
67 - usually less calls to gettimeofday and clock_gettime
68 (libevent calls it on every timer event change, libev twice per iteration).
69
70 - watchers use less memory
71 (libevent watcher on amd64: 152 bytes, libev native: <= 56 bytes, libevent emulation: 144 bytes).
72
73 - library uses less memory
74 (libevent allocates large data structures wether used or not, libev
75 scales all its data structures dynamically).
76
77 - no hardcoded arbitrary limits
78 (libevent contains an off-by-one bug and sometimes hardcodes limits).
79
80 - 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
84 - 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
89 - libev handles EBADF gracefully by removing the offending fds.
90
91 - libev communicates errors to the callback, libevent to the
92 event adder or not at all.
93
94 - doesn't rely on nonportable BSD header files.
95
96 - 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
99 - 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
104 - libev can be embedded easily with or without autoconf support into
105 other programs, with no changes to the source code necessary.
106
107 - the event core library (ev and event layer) compiles and works both as
108 C and C++.
109
110 - a simple C++ wrapper that supports methods as callbacks exists.
111
112 - a full featured and widely used perl module is available.
113
114 whats missing?
115
116 - 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
119AUTHOR
120 47
121 libev was written and designed by Marc Lehmann and Emanuele Giaquinta. 48 libev was written and designed by Marc Lehmann and Emanuele Giaquinta.
122 49
123 The following people sent in patches or made other noteworthy 50 The following people sent in patches or made other noteworthy
124 contributions to the design (if I forgot to include you, please shout 51 contributions to the design (for minor patches, see the Changes
125 at me, it was an accident): 52 file. If I forgot to include you, please shout at me, it was an
53 accident):
126 54
127 W.C.A. Wijngaards 55 W.C.A. Wijngaards
128 Christopher Layne 56 Christopher Layne
129 Chris Brody 57 Chris Brody
130 58

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