| 1 | libev is modelled after libevent (http://monkey.org/~provos/libevent/), but aims |
1 | libev is a high-performance event loop/event model with lots of features. |
| 2 | to be faster and more correct, and also more featureful. Examples: |
2 | (see benchmark at http://libev.schmorp.de/bench.html) |
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3 | |
| 4 | (comparisons relative to libevent-1.3e and libev-0.00) |
4 | Homepage: http://software.schmorp.de/pkg/libev |
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5 | E-Mail: libev@lists.schmorp.de |
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6 | Library Documentation: http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod |
| 5 | |
7 | |
| 6 | - multiple watchers can wait for the same event without deregistering others, |
8 | It is modelled (very losely) after libevent and the Event perl module, |
| 7 | both for file descriptors as well as signals. |
9 | but aims to be faster and more correct, and also more featureful. And |
| 8 | (registering two read events on fd 10 and unregistering one will not |
10 | also smaller. Yay. |
| 9 | break the other) |
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| 10 | |
11 | |
| 11 | - fork() is supported and can be handled |
12 | ABOUT THIS DISTRIBUTION |
| 12 | (there is no way to recover from a fork when libevent is active) |
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| 13 | |
13 | |
| 14 | - timers are handled as a priority queue (important operations are O(1)) |
14 | If you downloaded the libevent+libev distribution of libev, you will |
| 15 | (libevent uses a much less efficient but more complex red-black tree) |
15 | find it looks very much like libevent. In fact, the distributed libev |
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16 | tarballs are indeed libevent tarballs patched up with the libev |
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17 | event core, taking the evbuffer, evtag, evdns and evhttpd parts from |
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18 | libevent (they use the libevent emulation inside libev). Configure and |
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19 | Makefile stuff is also a more or less direct copy of libevent, and are |
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20 | maintained by the libevent authors. |
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21 | |
| 17 | - supports absolute (wallclock-based) timers in addition to relative ones, |
22 | If you downloaded the libev distribution (without libevent), then |
| 18 | i.e. can schedule timers to occur after n seconds, or at a specific time. |
23 | you only get the core parts of the library, meaning http and dns |
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24 | client/server code and similar things are missing. Only the core event |
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25 | loop is included. |
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26 | |
| 20 | - timers can be repeating (both absolute and relative ones) |
27 | If you are looking for an easily embeddable version, I recommend using |
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28 | the libev standalone distribution or the CVS repository. |
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29 | |
| 22 | - detects time jumps and adjusts timers |
30 | Examples of programs that embed libev: the EV perl module, |
| 23 | (works for both forward and backward time jumps and also for absolute timers) |
31 | rxvt-unicode, gvpe (GNU Virtual Private Ethernet) and deliantra |
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32 | (http://www.deliantra.net). |
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33 | |
| 25 | - can correctly remove timers while executing callbacks |
34 | DIFFERENCES AND COMPARISON TO LIBEVENT |
| 26 | (libevent doesn't handle this reliably and can crash) |
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| 27 | |
35 | |
| 28 | - race-free signal processing |
36 | The comparisons below are relative to libevent-1.3e. |
| 29 | (libevent may delay processing signals till after the next event) |
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| 30 | |
37 | |
| 31 | - less calls to epoll_ctl |
38 | - multiple watchers can wait for the same event without deregistering others, |
| 32 | (stopping and starting an io watcher between two loop iterations will now |
39 | both for file descriptors as well as signals. |
| 33 | result in spuriois epoll_ctl calls) |
40 | (registering two read events on fd 10 and unregistering one will not |
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41 | break the other). |
| 34 | |
42 | |
| 35 | - usually less calls to gettimeofday and clock_gettime |
43 | - fork() is supported and can be handled |
| 36 | (libevent calls it on every timer event change, libev twice per iteration) |
44 | (there is no way to recover from a fork with libevent). |
| 37 | |
45 | |
| 38 | - watchers use less memory |
46 | - timers are handled as a priority queue (important operations are O(1)) |
| 39 | (libevent on amd64: 152 bytes, libev: <= 56 bytes) |
47 | (libevent uses a much less efficient but more complex red-black tree). |
| 40 | |
48 | |
| 41 | - library uses less memory |
49 | - supports absolute (wallclock-based) timers in addition to relative ones, |
| 42 | (libevent allocates large data structures wether used or not, libev |
50 | i.e. can schedule timers to occur after n seconds, or at a specific time. |
| 43 | scales all its data structures dynamically) |
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| 44 | |
51 | |
| 45 | - no hardcoded arbitrary limits |
52 | - timers can be repeating (both absolute and relative ones). |
| 46 | (libevent contains an off-by-one bug and sometimes hardcodes a limit of |
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| 47 | 32000 fds) |
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| 48 | |
53 | |
| 49 | - libev separates timer, signal and io watchers from each other |
54 | - absolute timers can have customised rescheduling hooks (suitable for cron-like |
| 50 | (libevent combines them, but with libev you can combine them yourself |
55 | applications). |
| 51 | by reusing the same callback and still save memory) |
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| 52 | |
56 | |
| 53 | - simpler design, backends are potentially much simpler |
57 | - detects time jumps and adjusts timers |
| 54 | (in libevent, backends have to deal with watchers, thus the problems) |
58 | (works for both forward and backward time jumps and also for absolute timers). |
| 55 | (epoll backend in libevent: 366 lines, libev: 90 lines, and more features) |
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| 56 | |
59 | |
| 57 | - libev handles EBADF gracefully by removing the offending fds. |
60 | - race-free signal processing |
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61 | (libevent may delay processing signals till after the next event). |
| 58 | |
62 | |
| 59 | whats missing? |
63 | - more efficient epoll backend |
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64 | (stopping and starting an io watcher between two loop iterations will not |
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65 | result in spurious epoll_ctl calls). |
| 60 | |
66 | |
| 61 | - evdns, evhttp, bufferevent are missing, libev is only an even library at |
67 | - usually less calls to gettimeofday and clock_gettime |
| 62 | the moment. |
68 | (libevent calls it on every timer event change, libev twice per iteration). |
| 63 | |
69 | |
| 64 | - no priority support at the moment |
70 | - watchers use less memory |
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71 | (libevent watcher on amd64: 152 bytes, libev native: <= 56 bytes, libevent emulation: 144 bytes). |
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72 | |
| 66 | - kqueue, poll (libev currently implements epoll and select) |
73 | - library uses less memory |
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74 | (libevent allocates large data structures wether used or not, libev |
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75 | scales all its data structures dynamically). |
| 67 | |
76 | |
| 68 | - windows support (whats windows?) |
77 | - no hardcoded arbitrary limits |
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78 | (libevent contains an off-by-one bug and sometimes hardcodes limits). |
| 69 | |
79 | |
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80 | - libev separates timer, signal and io watchers from each other |
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81 | (libevent combines them, but with libev you can combine them yourself |
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82 | by reusing the same callback and still save memory). |
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83 | |
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84 | - simpler design, backends are potentially much simpler |
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85 | (in libevent, backends have to deal with watchers, thus the problems with |
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86 | wildly different semantics between diferent backends) |
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87 | (epoll backend in libevent: 366 lines no caching, libev: 90 lines full caching). |
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88 | |
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89 | - libev handles EBADF gracefully by removing the offending fds. |
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90 | |
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91 | - libev communicates errors to the callback, libevent to the |
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92 | event adder or not at all. |
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93 | |
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94 | - doesn't rely on nonportable BSD header files. |
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95 | |
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96 | - an event.h compatibility header exists, and can be used to run a wide |
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97 | range of libevent programs unchanged (such as evdns.c). |
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98 | |
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99 | - win32 compatibility for the core parts. |
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100 | (the backend is fd-based as documented and on other platforms, |
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101 | not handle-based like libevent, and can be used for both winscoket environments |
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102 | and unix-like ones). |
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103 | |
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104 | - libev can be embedded easily with or without autoconf support into |
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105 | other programs, with no changes to the source code necessary. |
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106 | |
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107 | - the event core library (ev and event layer) compiles and works both as |
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108 | C and C++. |
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109 | |
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110 | - a simple C++ wrapper that supports methods as callbacks exists. |
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111 | |
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112 | - a full featured and widely used perl module is available. |
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113 | |
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114 | whats missing? |
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115 | |
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116 | - no event-like priority support at the moment (the ev priorities work |
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117 | differently, but you can use idle watchers to get a similar effect). |
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118 | |
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119 | AUTHOR |
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120 | |
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121 | libev was written and designed by Marc Lehmann and Emanuele Giaquinta. |
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122 | |
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123 | The following people sent in patches or made other noteworthy |
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124 | contributions to the design (if I forgot to include you, please shout |
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125 | at me, it was an accident): |
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126 | |
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127 | W.C.A. Wijngaards |
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128 | Christopher Layne |
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129 | Chris Brody |
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130 | |
