| 1 |
libev is a high-performance event loop/event model with lots of features. |
| 2 |
|
| 3 |
It is modelled (very losely) after libevent |
| 4 |
(http://monkey.org/~provos/libevent/) and the Event perl module, but aims |
| 5 |
to be faster and more correct, and also more featureful. |
| 6 |
|
| 7 |
DIFFERENCES AND COMPARISON TO LIBEVENT: |
| 8 |
|
| 9 |
(comparisons relative to libevent-1.3e and libev-0.00, see also the benchmark |
| 10 |
at http://libev.schmorp.de/bench.html). |
| 11 |
|
| 12 |
- multiple watchers can wait for the same event without deregistering others, |
| 13 |
both for file descriptors as well as signals. |
| 14 |
(registering two read events on fd 10 and unregistering one will not |
| 15 |
break the other). |
| 16 |
|
| 17 |
- fork() is supported and can be handled |
| 18 |
(there is no way to recover from a fork when libevent is active). |
| 19 |
|
| 20 |
- timers are handled as a priority queue (important operations are O(1)) |
| 21 |
(libevent uses a much less efficient but more complex red-black tree). |
| 22 |
|
| 23 |
- supports absolute (wallclock-based) timers in addition to relative ones, |
| 24 |
i.e. can schedule timers to occur after n seconds, or at a specific time. |
| 25 |
|
| 26 |
- timers can be repeating (both absolute and relative ones). |
| 27 |
|
| 28 |
- detects time jumps and adjusts timers |
| 29 |
(works for both forward and backward time jumps and also for absolute timers). |
| 30 |
|
| 31 |
- race-free signal processing |
| 32 |
(libevent may delay processing signals till after the next event). |
| 33 |
|
| 34 |
- less calls to epoll_ctl |
| 35 |
(stopping and starting an io watcher between two loop iterations will now |
| 36 |
result in spuriois epoll_ctl calls). |
| 37 |
|
| 38 |
- usually less calls to gettimeofday and clock_gettime |
| 39 |
(libevent calls it on every timer event change, libev twice per iteration). |
| 40 |
|
| 41 |
- watchers use less memory |
| 42 |
(libevent on amd64: 152 bytes, libev: <= 56 bytes). |
| 43 |
|
| 44 |
- library uses less memory |
| 45 |
(libevent allocates large data structures wether used or not, libev |
| 46 |
scales all its data structures dynamically). |
| 47 |
|
| 48 |
- no hardcoded arbitrary limits |
| 49 |
(libevent contains an off-by-one bug and sometimes hardcodes a limit of |
| 50 |
32000 fds). |
| 51 |
|
| 52 |
- libev separates timer, signal and io watchers from each other |
| 53 |
(libevent combines them, but with libev you can combine them yourself |
| 54 |
by reusing the same callback and still save memory). |
| 55 |
|
| 56 |
- simpler design, backends are potentially much simpler |
| 57 |
(in libevent, backends have to deal with watchers, thus the problems) |
| 58 |
(epoll backend in libevent: 366 lines, libev: 90 lines, and more features). |
| 59 |
|
| 60 |
- libev handles EBADF gracefully by removing the offending fds. |
| 61 |
|
| 62 |
- doesn't rely on nonportable BSD header files. |
| 63 |
|
| 64 |
- a event.h compatibility header exists, and can be used to run a wide |
| 65 |
range of libevent programs unchanged (such as evdns.c). |
| 66 |
|
| 67 |
whats missing? |
| 68 |
|
| 69 |
- evbuffer, evhttp, bufferevent are missing. |
| 70 |
|
| 71 |
- no priority support at the moment (but likely to be delivered later). |
| 72 |
|
| 73 |
- kqueue, poll (libev currently implements epoll and select). |
| 74 |
|
| 75 |
- windows support (whats windows?). |
| 76 |
|
