| 1 | libev is a high-performanc3 event loop/event model with lots of features. |
1 | libev is a high-performance event loop/event model with lots of features. |
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2 | (see benchmark at http://libev.schmorp.de/bench.html) |
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3 | |
| 3 | It is modelled (very losely) after libevent |
4 | Homepage: http://software.schmorp.de/pkg/libev |
| 4 | (http://monkey.org/~provos/libevent/) and the Event perl module, but aims |
5 | E-Mail: libev@lists.schmorp.de |
| 5 | to be faster and more correct, and also more featureful. |
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| 6 | |
6 | |
| 7 | DIFFERENCES AND COMPARISON TO LIBEVENT: |
7 | It is modelled (very losely) after libevent |
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8 | (http://monkey.org/~provos/libevent/) and the Event perl module, but aims |
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9 | to be faster and more correct, and also more featureful. |
| 8 | |
10 | |
| 9 | (comparisons relative to libevent-1.3e and libev-0.00, see also the benchmark |
11 | ABOUT THIS DISTRIBUTION |
| 10 | at http://libev.schmorp.de/bench.html). |
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| 11 | |
12 | |
| 12 | - multiple watchers can wait for the same event without deregistering others, |
13 | If you downloaded a distribution of libev, you will find it looks |
| 13 | both for file descriptors as well as signals. |
14 | very much like libevent. In fact, the distributed libev tarballs are |
| 14 | (registering two read events on fd 10 and unregistering one will not |
15 | indeed libevent tarballs patched up with the libev event core, taking |
| 15 | break the other). |
16 | the evbuffer, evtag, evdns and evhttpd parts from libevent (they use |
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17 | the libevent emulation inside libev). Configure and Makefile stuff is |
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18 | also a more or less direct copy of libevent, and are maintained by the |
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19 | libevent authors. |
| 16 | |
20 | |
| 17 | - fork() is supported and can be handled |
21 | If you are looking for an easily embeddable version, I recommend using |
| 18 | (there is no way to recover from a fork when libevent is active). |
22 | the CVS repository (linked from the homepage, above), which contains |
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23 | only the libev core parts. |
| 19 | |
24 | |
| 20 | - timers are handled as a priority queue (important operations are O(1)) |
25 | Examples of programs that embed libev: the EV perl module, |
| 21 | (libevent uses a much less efficient but more complex red-black tree). |
26 | rxvt-unicode, gvpe (GNU Virtual Private Ethernet) and deliantra |
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27 | (http://www.deliantra.net). |
| 22 | |
28 | |
| 23 | - supports absolute (wallclock-based) timers in addition to relative ones, |
29 | DIFFERENCES AND COMPARISON TO LIBEVENT |
| 24 | i.e. can schedule timers to occur after n seconds, or at a specific time. |
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| 25 | |
30 | |
| 26 | - timers can be repeating (both absolute and relative ones). |
31 | The comparisons below are relative to libevent-1.3e. |
| 27 | |
32 | |
| 28 | - detects time jumps and adjusts timers |
33 | - multiple watchers can wait for the same event without deregistering others, |
| 29 | (works for both forward and backward time jumps and also for absolute timers). |
34 | both for file descriptors as well as signals. |
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35 | (registering two read events on fd 10 and unregistering one will not |
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36 | break the other). |
| 30 | |
37 | |
| 31 | - can correctly remove timers while executing callbacks |
38 | - fork() is supported and can be handled |
| 32 | (libevent doesn't handle this reliably and can crash). |
39 | (there is no way to recover from a fork with libevent). |
| 33 | |
40 | |
| 34 | - race-free signal processing |
41 | - timers are handled as a priority queue (important operations are O(1)) |
| 35 | (libevent may delay processing signals till after the next event). |
42 | (libevent uses a much less efficient but more complex red-black tree). |
| 36 | |
43 | |
| 37 | - less calls to epoll_ctl |
44 | - supports absolute (wallclock-based) timers in addition to relative ones, |
| 38 | (stopping and starting an io watcher between two loop iterations will now |
45 | i.e. can schedule timers to occur after n seconds, or at a specific time. |
| 39 | result in spuriois epoll_ctl calls). |
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| 40 | |
46 | |
| 41 | - usually less calls to gettimeofday and clock_gettime |
47 | - timers can be repeating (both absolute and relative ones). |
| 42 | (libevent calls it on every timer event change, libev twice per iteration). |
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| 43 | |
48 | |
| 44 | - watchers use less memory |
49 | - absolute timers can have customised rescheduling hooks (suitable for cron-like |
| 45 | (libevent on amd64: 152 bytes, libev: <= 56 bytes). |
50 | applications). |
| 46 | |
51 | |
| 47 | - library uses less memory |
52 | - detects time jumps and adjusts timers |
| 48 | (libevent allocates large data structures wether used or not, libev |
53 | (works for both forward and backward time jumps and also for absolute timers). |
| 49 | scales all its data structures dynamically). |
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| 50 | |
54 | |
| 51 | - no hardcoded arbitrary limits |
55 | - race-free signal processing |
| 52 | (libevent contains an off-by-one bug and sometimes hardcodes a limit of |
56 | (libevent may delay processing signals till after the next event). |
| 53 | 32000 fds). |
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| 54 | |
57 | |
| 55 | - libev separates timer, signal and io watchers from each other |
58 | - more efficient epoll backend |
| 56 | (libevent combines them, but with libev you can combine them yourself |
59 | (stopping and starting an io watcher between two loop iterations will not |
| 57 | by reusing the same callback and still save memory). |
60 | result in spurious epoll_ctl calls). |
| 58 | |
61 | |
| 59 | - simpler design, backends are potentially much simpler |
62 | - usually less calls to gettimeofday and clock_gettime |
| 60 | (in libevent, backends have to deal with watchers, thus the problems) |
63 | (libevent calls it on every timer event change, libev twice per iteration). |
| 61 | (epoll backend in libevent: 366 lines, libev: 90 lines, and more features). |
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| 62 | |
64 | |
| 63 | - libev handles EBADF gracefully by removing the offending fds. |
65 | - watchers use less memory |
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66 | (libevent watcher on amd64: 152 bytes, libev native: <= 56 bytes, libevent emulation: 144 bytes). |
| 64 | |
67 | |
| 65 | - doesn't rely on nonportable BSD header files. |
68 | - library uses less memory |
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69 | (libevent allocates large data structures wether used or not, libev |
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70 | scales all its data structures dynamically). |
| 66 | |
71 | |
| 67 | - a event.h compatibility header exists, and can be used to run a wide |
72 | - no hardcoded arbitrary limits |
| 68 | range of libevent programs unchanged (such as evdns.c). |
73 | (libevent contains an off-by-one bug and sometimes hardcodes limits). |
| 69 | |
74 | |
| 70 | whats missing? |
75 | - libev separates timer, signal and io watchers from each other |
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76 | (libevent combines them, but with libev you can combine them yourself |
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77 | by reusing the same callback and still save memory). |
| 71 | |
78 | |
| 72 | - evbuffer, evhttp, bufferevent are missing. |
79 | - simpler design, backends are potentially much simpler |
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80 | (in libevent, backends have to deal with watchers, thus the problems with |
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81 | wildly different semantics between diferent backends) |
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82 | (epoll backend in libevent: 366 lines no caching, libev: 90 lines full caching). |
| 73 | |
83 | |
| 74 | - no priority support at the moment (but likely to be delivered later). |
84 | - libev handles EBADF gracefully by removing the offending fds. |
| 75 | |
85 | |
| 76 | - kqueue, poll (libev currently implements epoll and select). |
86 | - libev communicates errors to the callback, libevent to the |
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87 | event adder or not at all. |
| 77 | |
88 | |
| 78 | - windows support (whats windows?). |
89 | - doesn't rely on nonportable BSD header files. |
| 79 | |
90 | |
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91 | - an event.h compatibility header exists, and can be used to run a wide |
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92 | range of libevent programs unchanged (such as evdns.c). |
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93 | |
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94 | - win32 compatibility for the core parts. |
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95 | (the backend is fd-based as documented and on other platforms, |
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96 | not handle-based like libevent, and can be used for both winscoket environments |
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97 | and unix-like ones). |
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98 | |
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99 | - libev can be embedded easily with or without autoconf support into |
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100 | other programs, with no changes to the source code necessary. |
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101 | |
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102 | - the event core library (ev and event layer) compiles and works both as |
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103 | C and C++. |
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104 | |
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105 | - a simple C++ wrapper that supports methods as callbacks exists. |
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106 | |
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107 | - a full featured and widely used perl module is available. |
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108 | |
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109 | whats missing? |
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110 | |
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111 | - no event-like priority support at the moment (the ev priorities work |
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112 | differently, but you can use idle watchers to get a similar effect). |
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113 | |
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114 | AUTHOR |
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115 | |
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116 | libev was written and designed by Marc Lehmann and Emanuele Giaquinta. |
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117 | |
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118 | The following people sent in patches or made other noteworthy |
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119 | contributions to the design (if I forgot to include you, please shout |
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120 | at me, it was an accident): |
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121 | |
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122 | W.C.A. Wijngaards |
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123 | Christopher Layne |
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124 | Chris Brody |
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125 | |
