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libev is a high-performanc3 event loop/event model with lots of features. |
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It is modelled (very losely) after libevent |
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(http://monkey.org/~provos/libevent/) and the Event perl module, but aims |
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to be faster and more correct, and also more featureful. |
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DIFFERENCES AND COMPARISON TO LIBEVENT: |
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(comparisons relative to libevent-1.3e and libev-0.00) |
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- multiple watchers can wait for the same event without deregistering others, |
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both for file descriptors as well as signals. |
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(registering two read events on fd 10 and unregistering one will not |
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break the other). |
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- fork() is supported and can be handled |
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(there is no way to recover from a fork when libevent is active). |
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- timers are handled as a priority queue (important operations are O(1)) |
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(libevent uses a much less efficient but more complex red-black tree). |
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- supports absolute (wallclock-based) timers in addition to relative ones, |
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i.e. can schedule timers to occur after n seconds, or at a specific time. |
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- timers can be repeating (both absolute and relative ones). |
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- detects time jumps and adjusts timers |
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(works for both forward and backward time jumps and also for absolute timers). |
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- can correctly remove timers while executing callbacks |
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(libevent doesn't handle this reliably and can crash). |
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- race-free signal processing |
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(libevent may delay processing signals till after the next event). |
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- less calls to epoll_ctl |
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(stopping and starting an io watcher between two loop iterations will now |
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result in spuriois epoll_ctl calls). |
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- usually less calls to gettimeofday and clock_gettime |
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(libevent calls it on every timer event change, libev twice per iteration). |
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- watchers use less memory |
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(libevent on amd64: 152 bytes, libev: <= 56 bytes). |
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- library uses less memory |
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(libevent allocates large data structures wether used or not, libev |
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scales all its data structures dynamically). |
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- no hardcoded arbitrary limits |
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(libevent contains an off-by-one bug and sometimes hardcodes a limit of |
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32000 fds). |
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- libev separates timer, signal and io watchers from each other |
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(libevent combines them, but with libev you can combine them yourself |
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by reusing the same callback and still save memory). |
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- simpler design, backends are potentially much simpler |
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(in libevent, backends have to deal with watchers, thus the problems) |
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(epoll backend in libevent: 366 lines, libev: 90 lines, and more features). |
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- libev handles EBADF gracefully by removing the offending fds. |
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- doesn't rely on nonportable BSD header files. |
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- a event.h compatibility header exists, and can be used to run a wide |
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range of libevent programs unchanged (such as evdns.c). |
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whats missing? |
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- evbuffer, evhttp, bufferevent are missing. |
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- no priority support at the moment (but likely to be delivered later). |
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- kqueue, poll (libev currently implements epoll and select). |
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- windows support (whats windows?). |
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