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libev is a high-performance event loop/event model with lots of features. |
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(see benchmark at http://libev.schmorp.de/bench.html) |
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Homepage: http://software.schmorp.de/pkg/libev |
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E-Mail: libev@lists.schmorp.de |
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Library Documentation: http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod |
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It is modelled (very losely) after libevent and the Event perl module, |
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but aims to be faster and more correct, and also more featureful. And |
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also smaller. Yay. |
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ABOUT THIS DISTRIBUTION |
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If you downloaded the libevent+libev distribution of libev, you will |
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find it looks very much like libevent. In fact, the distributed libev |
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tarballs are indeed libevent tarballs patched up with the libev |
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event core, taking the evbuffer, evtag, evdns and evhttpd parts from |
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libevent (they use the libevent emulation inside libev). Configure and |
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Makefile stuff is also a more or less direct copy of libevent, and are |
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maintained by the libevent authors. |
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If you downloaded the libev distribution (without libevent), then |
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you only get the core parts of the library, meaning http and dns |
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client/server code and similar things are missing. Only the core event |
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loop is included. |
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If you are looking for an easily embeddable version, I recommend using |
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the libev standalone distribution or the CVS repository. |
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Examples of programs that embed libev: the EV perl module, |
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rxvt-unicode, gvpe (GNU Virtual Private Ethernet) and deliantra |
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(http://www.deliantra.net). |
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DIFFERENCES AND COMPARISON TO LIBEVENT |
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The comparisons below are relative to libevent-1.3e. |
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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 with libevent). |
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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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- absolute timers can have customised rescheduling hooks (suitable for cron-like |
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applications). |
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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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- race-free signal processing |
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(libevent may delay processing signals till after the next event). |
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- more efficient epoll backend |
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(stopping and starting an io watcher between two loop iterations will not |
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result in spurious 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 watcher on amd64: 152 bytes, libev native: <= 56 bytes, libevent emulation: 144 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 limits). |
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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 with |
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wildly different semantics between diferent backends) |
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(epoll backend in libevent: 366 lines no caching, libev: 90 lines full caching). |
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- libev handles EBADF gracefully by removing the offending fds. |
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- libev communicates errors to the callback, libevent to the |
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event adder or not at all. |
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- doesn't rely on nonportable BSD header files. |
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- an 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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- win32 compatibility for the core parts. |
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(the backend is fd-based as documented and on other platforms, |
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not handle-based like libevent, and can be used for both winscoket environments |
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and unix-like ones). |
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- libev can be embedded easily with or without autoconf support into |
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other programs, with no changes to the source code necessary. |
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- the event core library (ev and event layer) compiles and works both as |
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C and C++. |
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- a simple C++ wrapper that supports methods as callbacks exists. |
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- a full featured and widely used perl module is available. |
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whats missing? |
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- no event-like priority support at the moment (the ev priorities work |
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differently, but you can use idle watchers to get a similar effect). |
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AUTHOR |
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libev was written and designed by Marc Lehmann and Emanuele Giaquinta. |
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The following people sent in patches or made other noteworthy |
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contributions to the design (if I forgot to include you, please shout |
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at me, it was an accident): |
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W.C.A. Wijngaards |
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Christopher Layne |
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Chris Brody |
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