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Homepage: http://software.schmorp.de/pkg/libev
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E-Mail: libev@schmorp.de
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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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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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ABOUT THIS DISTRIBUTION
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If you downloaded a distribution of libev, you will find it looks
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very much like libevent. In fact, the distributed libev tarballs are
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indeed libevent tarballs patched up with the libev event core, taking
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the evbuffer, evtag, evdns and evhttpd parts from libevent (they use
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the libevent emulation inside libev). Configure and Makefile stuff is
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also a more or less direct copy of libevent, and are maintained by the
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libevent authors.
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If you are looking for an easily embeddable version, I recommend using
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the CVS repository (linked from the homepage, above), which contains
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only the libev core parts.
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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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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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- 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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DIFFERENCES AND COMPARISON TO LIBEVENT:
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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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(comparisons relative to libevent-1.3e and libev-0.00, see also the benchmark
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at http://libev.schmorp.de/bench.html).
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- timers can be repeating (both absolute and relative ones).
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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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- absolute timers can have customised rescheduling hooks (suitable for cron-like
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applications).
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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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- 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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- 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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- race-free signal processing
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(libevent may delay processing signals till after the next event).
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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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- 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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- timers can be repeating (both absolute and relative ones).
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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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- 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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- 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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- race-free signal processing
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(libevent may delay processing signals till after the next event).
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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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- 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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- no hardcoded arbitrary limits
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(libevent contains an off-by-one bug and sometimes hardcodes limits).
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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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- 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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- watchers use less memory
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(libevent on amd64: 152 bytes, libev: <= 56 bytes).
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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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- 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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- libev handles EBADF gracefully by removing the offending fds.
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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 communicates errors to the callback, libevent to the
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event adder or not at all.
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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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- doesn't rely on nonportable BSD header files.
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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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- 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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- libev handles EBADF gracefully by removing the offending fds.
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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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- doesn't rely on nonportable BSD header files.
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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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- 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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- the event core library (ev and event layer) compiles and works both as
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C and C++.
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- win32 compatibility for the core parts.
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- a simple C++ wrapper that supports methods as callbacks exists.
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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 full featured and widely used perl module is available.
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whats missing?
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whats missing?
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- no event-like priority support at the moment (the ev priorities
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are not yet finished and work differently, but you can use idle watchers
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to get a similar effect).
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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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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 (if I forgot to include you, please shout at me, it was an
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accident):
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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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W.C.A. Wijngaards
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Christopher Layne
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Chris Brody
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