-libev is modelled after libevent (http://monkey.org/~provos/libevent/), but aims
-to be faster and more correct, and also more featureful. Examples:
+libev is a high-performance event loop/event model with lots of features.
+(see benchmark at http://libev.schmorp.de/bench.html)
-(comparisons relative to libevent-1.3e and libev-0.00)
+ Homepage: http://software.schmorp.de/pkg/libev
+ E-Mail: libev@lists.schmorp.de
-- multiple watchers can wait for the same event without deregistering others,
- both for file descriptors as well as signals.
- (registering two read events on fd 10 and unregistering one will not
- break the other)
+ It is modelled (very losely) after libevent
+ (http://monkey.org/~provos/libevent/) and the Event perl module, but aims
+ to be faster and more correct, and also more featureful.
-- fork() is supported and can be handled
- (there is no way to recover from a fork when libevent is active)
+ABOUT THIS DISTRIBUTION
-- timers are handled as a priority queue (important operations are O(1))
- (libevent uses a much less efficient but more complex red-black tree)
+ If you downloaded a distribution of libev, you will find it looks
+ very much like libevent. In fact, the distributed libev tarballs are
+ indeed libevent tarballs patched up with the libev event core, taking
+ the evbuffer, evtag, evdns and evhttpd parts from libevent (they use
+ the libevent emulation inside libev). Configure and Makefile stuff is
+ also a more or less direct copy of libevent, and are maintained by the
+ libevent authors.
-- supports absolute (wallclock-based) timers in addition to relative ones,
- i.e. can schedule timers to occur after n seconds, or at a specific time.
+ If you are looking for an easily embeddable version, I recommend using
+ the CVS repository (linked from the homepage, above), which contains
+ only the libev core parts.
-- timers can be repeating (both absolute and relative ones)
+ Examples of programs that embed libev: the EV perl module,
+ rxvt-unicode, gvpe (GNU Virtual Private Ethernet) and deliantra
+ (http://www.deliantra.net).
-- detects time jumps and adjusts timers
- (works for both forward and backward time jumps and also for absolute timers)
+DIFFERENCES AND COMPARISON TO LIBEVENT
-- can correctly remove timers while executing callbacks
- (libevent doesn't handle this reliably and can crash)
+ The comparisons below are relative to libevent-1.3e.
-- race-free signal processing
- (libevent may delay processing signals till after the next event)
+ - multiple watchers can wait for the same event without deregistering others,
+ both for file descriptors as well as signals.
+ (registering two read events on fd 10 and unregistering one will not
+ break the other).
-- less calls to epoll_ctl
- (stopping and starting an io watcher between two loop iterations will now
- result in spuriois epoll_ctl calls)
+ - fork() is supported and can be handled
+ (there is no way to recover from a fork with libevent).
-- usually less calls to gettimeofday and clock_gettime
- (libevent calls it on every timer event change, libev twice per iteration)
+ - timers are handled as a priority queue (important operations are O(1))
+ (libevent uses a much less efficient but more complex red-black tree).
-- watchers use less memory
- (libevent on amd64: 152 bytes, libev: <= 56 bytes)
+ - supports absolute (wallclock-based) timers in addition to relative ones,
+ i.e. can schedule timers to occur after n seconds, or at a specific time.
-- library uses less memory
- (libevent allocates large data structures wether used or not, libev
- scales all its data structures dynamically)
+ - timers can be repeating (both absolute and relative ones).
-- no hardcoded arbitrary limits
- (libevent contains an off-by-one bug and sometimes hardcodes a limit of
- 32000 fds)
+ - absolute timers can have customised rescheduling hooks (suitable for cron-like
+ applications).
-- libev separates timer, signal and io watchers from each other
- (libevent combines them, but with libev you can combine them yourself
- by reusing the same callback and still save memory)
+ - detects time jumps and adjusts timers
+ (works for both forward and backward time jumps and also for absolute timers).
-- simpler design, backends are potentially much simpler
- (in libevent, backends have to deal with watchers, thus the problems)
- (epoll backend in libevent: 366 lines, libev: 90 lines, and more features)
+ - race-free signal processing
+ (libevent may delay processing signals till after the next event).
-- libev handles EBADF gracefully by removing the offending fds.
+ - more efficient epoll backend
+ (stopping and starting an io watcher between two loop iterations will not
+ result in spurious epoll_ctl calls).
-whats missing?
+ - usually less calls to gettimeofday and clock_gettime
+ (libevent calls it on every timer event change, libev twice per iteration).
-- evdns, evhttp, bufferevent are missing, libev is only an even library at
- the moment.
+ - watchers use less memory
+ (libevent watcher on amd64: 152 bytes, libev native: <= 56 bytes, libevent emulation: 144 bytes).
-- no priority support at the moment
+ - library uses less memory
+ (libevent allocates large data structures wether used or not, libev
+ scales all its data structures dynamically).
-- kqueue, poll (libev currently implements epoll and select)
+ - no hardcoded arbitrary limits
+ (libevent contains an off-by-one bug and sometimes hardcodes limits).
-- windows support (whats windows?)
+ - libev separates timer, signal and io watchers from each other
+ (libevent combines them, but with libev you can combine them yourself
+ by reusing the same callback and still save memory).
+
+ - simpler design, backends are potentially much simpler
+ (in libevent, backends have to deal with watchers, thus the problems with
+ wildly different semantics between diferent backends)
+ (epoll backend in libevent: 366 lines no caching, libev: 90 lines full caching).
+
+ - libev handles EBADF gracefully by removing the offending fds.
+
+ - libev communicates errors to the callback, libevent to the
+ event adder or not at all.
+
+ - doesn't rely on nonportable BSD header files.
+
+ - an event.h compatibility header exists, and can be used to run a wide
+ range of libevent programs unchanged (such as evdns.c).
+
+ - win32 compatibility for the core parts.
+ (the backend is fd-based as documented and on other platforms,
+ not handle-based like libevent, and can be used for both winscoket environments
+ and unix-like ones).
+
+ - libev can be embedded easily with or without autoconf support into
+ other programs, with no changes to the source code necessary.
+
+ - the event core library (ev and event layer) compiles and works both as
+ C and C++.
+
+ - a simple C++ wrapper that supports methods as callbacks exists.
+
+ - a full featured and widely used perl module is available.
+
+ whats missing?
+
+ - no event-like priority support at the moment (the ev priorities work
+ differently, but you can use idle watchers to get a similar effect).
+
+AUTHOR
+
+ libev was written and designed by Marc Lehmann and Emanuele Giaquinta.
+
+ The following people sent in patches or made other noteworthy
+ contributions to the design (if I forgot to include you, please shout
+ at me, it was an accident):
+
+ W.C.A. Wijngaards
+ Christopher Layne
+ Chris Brody
projects / software / libev.git / blobdiff