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Revision 1.17 by root, Mon Nov 12 05:40:55 2007 UTC vs.
Revision 1.19 by root, Fri Dec 14 21:07:13 2007 UTC

1Homepage: http://software.schmorp.de/pkg/libev 1libev is a high-performance event loop/event model with lots of features.
2E-Mail: libev@schmorp.de 2(see benchmark at http://libev.schmorp.de/bench.html)
3 3
4libev is a high-performance event loop/event model with lots of features. 4 Homepage: http://software.schmorp.de/pkg/libev
5 E-Mail: libev@lists.schmorp.de
6 Library Documentation: http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod
5 7
6It is modelled (very losely) after libevent 8 It is modelled (very losely) after libevent and the Event perl module,
7(http://monkey.org/~provos/libevent/) and the Event perl module, but aims
8to be faster and more correct, and also more featureful. 9 but aims to be faster and more correct, and also more featureful. And
10 also smaller. Yay.
9 11
10DIFFERENCES AND COMPARISON TO LIBEVENT: 12ABOUT THIS DISTRIBUTION
11 13
12(comparisons relative to libevent-1.3e and libev-0.00, see also the benchmark 14 If you downloaded the libevent+libev distribution of libev, you will
13at http://libev.schmorp.de/bench.html). 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.
14 21
15- multiple watchers can wait for the same event without deregistering others, 22 If you downloaded the libev distribution (without libevent), then
16 both for file descriptors as well as signals. 23 you only get the core parts of the library, meaning http and dns
17 (registering two read events on fd 10 and unregistering one will not 24 client/server code and similar things are missing. Only the core event
18 break the other). 25 loop is included.
19 26
20- fork() is supported and can be handled 27 If you are looking for an easily embeddable version, I recommend using
21 (there is no way to recover from a fork when libevent is active). 28 the libev standalone distribution or the CVS repository.
22 29
23- timers are handled as a priority queue (important operations are O(1)) 30 Examples of programs that embed libev: the EV perl module,
24 (libevent uses a much less efficient but more complex red-black tree). 31 rxvt-unicode, gvpe (GNU Virtual Private Ethernet) and deliantra
32 (http://www.deliantra.net).
25 33
26- supports absolute (wallclock-based) timers in addition to relative ones, 34DIFFERENCES AND COMPARISON TO LIBEVENT
27 i.e. can schedule timers to occur after n seconds, or at a specific time.
28 35
29- timers can be repeating (both absolute and relative ones). 36 The comparisons below are relative to libevent-1.3e.
30 37
31- detects time jumps and adjusts timers 38 - multiple watchers can wait for the same event without deregistering others,
32 (works for both forward and backward time jumps and also for absolute timers). 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).
33 42
34- race-free signal processing 43 - fork() is supported and can be handled
35 (libevent may delay processing signals till after the next event). 44 (there is no way to recover from a fork with libevent).
36 45
37- less calls to epoll_ctl 46 - timers are handled as a priority queue (important operations are O(1))
38 (stopping and starting an io watcher between two loop iterations will now 47 (libevent uses a much less efficient but more complex red-black tree).
39 result in spuriois epoll_ctl calls).
40 48
41- usually less calls to gettimeofday and clock_gettime 49 - supports absolute (wallclock-based) timers in addition to relative ones,
42 (libevent calls it on every timer event change, libev twice per iteration). 50 i.e. can schedule timers to occur after n seconds, or at a specific time.
43 51
44- watchers use less memory 52 - timers can be repeating (both absolute and relative ones).
45 (libevent on amd64: 152 bytes, libev: <= 56 bytes).
46 53
47- library uses less memory 54 - absolute timers can have customised rescheduling hooks (suitable for cron-like
48 (libevent allocates large data structures wether used or not, libev 55 applications).
49 scales all its data structures dynamically).
50 56
51- no hardcoded arbitrary limits 57 - detects time jumps and adjusts timers
52 (libevent contains an off-by-one bug and sometimes hardcodes a limit of 58 (works for both forward and backward time jumps and also for absolute timers).
53 32000 fds).
54 59
55- libev separates timer, signal and io watchers from each other 60 - race-free signal processing
56 (libevent combines them, but with libev you can combine them yourself 61 (libevent may delay processing signals till after the next event).
57 by reusing the same callback and still save memory).
58 62
59- simpler design, backends are potentially much simpler 63 - more efficient epoll backend
60 (in libevent, backends have to deal with watchers, thus the problems) 64 (stopping and starting an io watcher between two loop iterations will not
61 (epoll backend in libevent: 366 lines, libev: 90 lines, and more features). 65 result in spurious epoll_ctl calls).
62 66
63- libev handles EBADF gracefully by removing the offending fds. 67 - usually less calls to gettimeofday and clock_gettime
68 (libevent calls it on every timer event change, libev twice per iteration).
64 69
65- doesn't rely on nonportable BSD header files. 70 - watchers use less memory
71 (libevent watcher on amd64: 152 bytes, libev native: <= 56 bytes, libevent emulation: 144 bytes).
66 72
67- a event.h compatibility header exists, and can be used to run a wide 73 - library uses less memory
68 range of libevent programs unchanged (such as evdns.c). 74 (libevent allocates large data structures wether used or not, libev
75 scales all its data structures dynamically).
69 76
70- win32 compatibility for the core parts. 77 - no hardcoded arbitrary limits
78 (libevent contains an off-by-one bug and sometimes hardcodes limits).
71 79
72- the event core library (ev and event layer) compiles and works both as 80 - libev separates timer, signal and io watchers from each other
73 C and C++. 81 (libevent combines them, but with libev you can combine them yourself
82 by reusing the same callback and still save memory).
74 83
75whats missing? 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).
76 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
77- no event-like priority support at the moment (the ev priorities 116 - no event-like priority support at the moment (the ev priorities work
78 are not yet finished and work differently, but you can use idle watchers 117 differently, but you can use idle watchers to get a similar effect).
79 to get a similar effect).
80 118
81AUTHOR 119AUTHOR
82 120
83libev was written and designed by Marc Lehmann and Emanuele Giaquinta. 121 libev was written and designed by Marc Lehmann and Emanuele Giaquinta.
84 122
85The following people sent in patches or made other noteworthy 123 The following people sent in patches or made other noteworthy
86contributions (if I forgot to include you, please shout at me, it was an 124 contributions to the design (if I forgot to include you, please shout
87accident): 125 at me, it was an accident):
88 126
89W.C.A. Wijngaards 127 W.C.A. Wijngaards
90Christopher Layne 128 Christopher Layne
91Chris Brody 129 Chris Brody
92 130

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