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Revision 1.6 by root, Wed Oct 31 18:28:00 2007 UTC vs.
Revision 1.18 by root, Wed Nov 21 05:05:40 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(comparisons relative to libevent-1.3e and libev-0.00) 4 Homepage: http://software.schmorp.de/pkg/libev
5 E-Mail: libev@lists.schmorp.de
5 6
6- multiple watchers can wait for the same event without deregistering others, 7 It is modelled (very losely) after libevent
7 both for file descriptors as well as signals. 8 (http://monkey.org/~provos/libevent/) and the Event perl module, but aims
8 (registering two read events on fd 10 and unregistering one will not 9 to be faster and more correct, and also more featureful.
9 break the other)
10 10
11- fork() is supported and can be handled 11ABOUT THIS DISTRIBUTION
12 (there is no way to recover from a fork when libevent is active)
13 12
14- timers are handled as a priority queue 13 If you downloaded a distribution of libev, you will find it looks
15 (libevent uses a less efficient red-black tree) 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.
16 20
17- supports absolute (wallclock-based) timers in addition to relative ones, 21 If you are looking for an easily embeddable version, I recommend using
18 i.e. can schedule timers to occur after n seconds, or at a specific time. 22 the CVS repository (linked from the homepage, above), which contains
23 only the libev core parts.
19 24
20- timers can be repeating (both absolute and relative ones) 25 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).
21 28
22- detects time jumps and adjusts timers 29DIFFERENCES AND COMPARISON TO LIBEVENT
23 (works for both forward and backward time jumps and also for absolute timers)
24 30
25- can correctly remove timers while executing callbacks 31 The comparisons below are relative to libevent-1.3e.
26 (libevent doesn't handle this reliably and can crash)
27 32
28- race-free signal processing 33 - multiple watchers can wait for the same event without deregistering others,
29 (libevent may delay processing signals till after the next event) 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).
30 37
31- less calls to epoll_ctl 38 - fork() is supported and can be handled
32 (stopping and starting an io watcher between two loop iterations will now 39 (there is no way to recover from a fork with libevent).
33 result in spuriois epoll_ctl calls)
34 40
35- usually less calls to gettimeofday and clock_gettime 41 - timers are handled as a priority queue (important operations are O(1))
36 (libevent calls it on every timer event change, libev twice per iteration) 42 (libevent uses a much less efficient but more complex red-black tree).
37 43
38- watchers use less memory 44 - supports absolute (wallclock-based) timers in addition to relative ones,
39 (libevent on amd64: 152 bytes, libev: <= 56 bytes) 45 i.e. can schedule timers to occur after n seconds, or at a specific time.
40 46
41- library uses less memory 47 - timers can be repeating (both absolute and relative ones).
42 (libevent allocates large data structures wether used or not, libev
43 scales all its data structures dynamically)
44 48
45- no hardcoded arbitrary limits 49 - absolute timers can have customised rescheduling hooks (suitable for cron-like
46 (libevent contains an off-by-one bug and sometimes hardcodes a limit of 50 applications).
47 32000 fds)
48 51
49- libev separates timer, signal and io watchers from each other 52 - detects time jumps and adjusts timers
50 (libevent combines them, but with libev you can combine them yourself 53 (works for both forward and backward time jumps and also for absolute timers).
51 by reusing the same callback and still save memory)
52 54
53- simpler design, backends are potentially much simpler 55 - race-free signal processing
54 (in libevent, backends have to deal with watchers, thus the problems) 56 (libevent may delay processing signals till after the next event).
55 (epoll backend in libevent: 366 lines, libev: 90 lines, and more features)
56 57
57- libev handles EBADF gracefully by removing the offending fds. 58 - more efficient epoll backend
59 (stopping and starting an io watcher between two loop iterations will not
60 result in spurious epoll_ctl calls).
58 61
59whats missing? 62 - usually less calls to gettimeofday and clock_gettime
63 (libevent calls it on every timer event change, libev twice per iteration).
60 64
61- evdns, evhttp, bufferevent are missing, libev is only an even library at 65 - watchers use less memory
62 the moment. 66 (libevent watcher on amd64: 152 bytes, libev native: <= 56 bytes, libevent emulation: 144 bytes).
63 67
64- no priority support at the moment 68 - library uses less memory
69 (libevent allocates large data structures wether used or not, libev
70 scales all its data structures dynamically).
65 71
66- kqueue, poll (libev currently implements epoll and select) 72 - no hardcoded arbitrary limits
73 (libevent contains an off-by-one bug and sometimes hardcodes limits).
67 74
68- windows support (whats windows?) 75 - 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).
69 78
79 - 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
84 - libev handles EBADF gracefully by removing the offending fds.
85
86 - libev communicates errors to the callback, libevent to the
87 event adder or not at all.
88
89 - doesn't rely on nonportable BSD header files.
90
91 - 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
94 - 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
99 - libev can be embedded easily with or without autoconf support into
100 other programs, with no changes to the source code necessary.
101
102 - the event core library (ev and event layer) compiles and works both as
103 C and C++.
104
105 - a simple C++ wrapper that supports methods as callbacks exists.
106
107 - a full featured and widely used perl module is available.
108
109 whats missing?
110
111 - 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
114AUTHOR
115
116 libev was written and designed by Marc Lehmann and Emanuele Giaquinta.
117
118 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

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