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Revision 1.2 by root, Tue Oct 30 23:10:33 2007 UTC vs.
Revision 1.19 by root, Fri Dec 14 21:07:13 2007 UTC

1libev is modelled after libevent (http://monkey.org/~provos/libevent/), but aims 1libev is a high-performance event loop/event model with lots of features.
2to be faster and more correct, and also more featureful. Examples: 2(see benchmark at http://libev.schmorp.de/bench.html)
3 3
4- multiple watchers can wait for the same event without deregistering others. 4 Homepage: http://software.schmorp.de/pkg/libev
5 (registering two read events on fd 10 and unregistering one will not 5 E-Mail: libev@lists.schmorp.de
6 break the other) 6 Library Documentation: http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod
7 7
8- fork() is supported and can be handled 8 It is modelled (very losely) after libevent and the Event perl module,
9 (there is no way to recover from a fork when libevent is active) 9 but aims to be faster and more correct, and also more featureful. And
10 also smaller. Yay.
10 11
11- timers are handled as a priority queue 12ABOUT THIS DISTRIBUTION
12 (libevent uses a less efficient red-black tree)
13 13
14- supports absolute (wallclock-based) timers in addition to relative ones, 14 If you downloaded the libevent+libev distribution of libev, you will
15 i.e. can schedule timers to occur after n seconds, or at a specific time. 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.
16 21
17- timers can be repeating (both absolute and relative ones) 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.
18 26
19- detects time jumps and adjusts timers 27 If you are looking for an easily embeddable version, I recommend using
20 (works for both forward and backward time jumps and also for absolute timers) 28 the libev standalone distribution or the CVS repository.
21 29
22- can correctly remove timers while executing callbacks 30 Examples of programs that embed libev: the EV perl module,
23 (libevent doesn't handle this reliably and can crash) 31 rxvt-unicode, gvpe (GNU Virtual Private Ethernet) and deliantra
32 (http://www.deliantra.net).
24 33
25- less calls to epoll_ctl 34DIFFERENCES AND COMPARISON TO LIBEVENT
26 (stopping and starting an io watcher between two loop iterations will now
27 result in spuriois epoll_ctl calls)
28 35
29- usually less calls to gettimeofday and clock_gettime 36 The comparisons below are relative to libevent-1.3e.
30 (libevent calls it on every timer event change, libev twice per iteration)
31 37
32- watchers use less memory 38 - multiple watchers can wait for the same event without deregistering others,
33 (libevent on amd64: 152 bytes, libev: <= 56 bytes) 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).
34 42
35- library uses less memory 43 - fork() is supported and can be handled
36 (libevent allocates large data structures wether used or not, libev 44 (there is no way to recover from a fork with libevent).
37 scales all its data structures dynamically)
38 45
39- no hardcoded arbitrary limits 46 - timers are handled as a priority queue (important operations are O(1))
40 (libevent contains an off-by-one bug and sometimes hardcodes a limit of 47 (libevent uses a much less efficient but more complex red-black tree).
41 32000 fds)
42 48
43- libev separates timer, signal and io watchers from each other 49 - supports absolute (wallclock-based) timers in addition to relative ones,
44 (libevent combines them, but with libev you can combine them yourself 50 i.e. can schedule timers to occur after n seconds, or at a specific time.
45 by reusing the same callback and still save memory)
46 51
47- simpler design, backends are potentially much simpler 52 - timers can be repeating (both absolute and relative ones).
48 (in libevent, backends have to deal with watchers, thus the problems)
49 (epoll backend in libevent: 366 lines, libev: 89 lines, and more features)
50 53
51whats missing? 54 - absolute timers can have customised rescheduling hooks (suitable for cron-like
55 applications).
52 56
53- evdns, evhttp, bufferevent are missing, libev is only an even library at 57 - detects time jumps and adjusts timers
54 the moment. 58 (works for both forward and backward time jumps and also for absolute timers).
55 59
56- no priority support at the moment. 60 - race-free signal processing
61 (libevent may delay processing signals till after the next event).
57 62
58- kqueue, poll (libev currently implements epoll and select). 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).
59 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
121 libev was written and designed by Marc Lehmann and Emanuele Giaquinta.
122
123 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

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