[ViewVC] Annotation of: cvs/libev/README

libev is a high-performance event loop/event model with lots of features.

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.

DIFFERENCES AND COMPARISON TO LIBEVENT:

(comparisons relative to libevent-1.3e and libev-0.00, see also the benchmark
at http://libev.schmorp.de/bench.html).

- 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).

- fork() is supported and can be handled
  (there is no way to recover from a fork when libevent is active).

- timers are handled as a priority queue (important operations are O(1))
  (libevent uses a much less efficient but more complex red-black tree).

- 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.

- timers can be repeating (both absolute and relative ones).

- detects time jumps and adjusts timers
  (works for both forward and backward time jumps and also for absolute timers).

- race-free signal processing
  (libevent may delay processing signals till after the next event).

- less calls to epoll_ctl
  (stopping and starting an io watcher between two loop iterations will now
  result in spuriois epoll_ctl calls).

- usually less calls to gettimeofday and clock_gettime
  (libevent calls it on every timer event change, libev twice per iteration).

- watchers use less memory
  (libevent on amd64: 152 bytes, libev: <= 56 bytes).

- library uses less memory
  (libevent allocates large data structures wether used or not, libev
  scales all its data structures dynamically).

- no hardcoded arbitrary limits
  (libevent contains an off-by-one bug and sometimes hardcodes a limit of
  32000 fds).

- 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)
  (epoll backend in libevent: 366 lines, libev: 90 lines, and more features).

- libev handles EBADF gracefully by removing the offending fds.

- doesn't rely on nonportable BSD header files.

- a 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 event core library (ev and event layer) compiles and works both as
  C and C++.

whats missing?

- no event-like priority support at the moment (the ev priorities
  are not yet finished and work differently, but you cna use idle watchers
  to get a similar effect).


Revision:	1.14
Committed:	Thu Nov 8 16:58:00 2007 UTC (16 years, 6 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_7, rel-0_6
Changes since 1.13:	+3 -6 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.11	libev is a high-performance event loop/event model with lots of features.
2	root	1.9
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	root	1.1
9	root	1.10	(comparisons relative to libevent-1.3e and libev-0.00, see also the benchmark
10			at http://libev.schmorp.de/bench.html).
11	root	1.5
12	root	1.4	- multiple watchers can wait for the same event without deregistering others,
13			both for file descriptors as well as signals.
14	root	1.2	(registering two read events on fd 10 and unregistering one will not
15	root	1.9	break the other).
16	root	1.2
17			- fork() is supported and can be handled
18	root	1.9	(there is no way to recover from a fork when libevent is active).
19	root	1.2
20	root	1.7	- timers are handled as a priority queue (important operations are O(1))
21	root	1.9	(libevent uses a much less efficient but more complex red-black tree).
22	root	1.2
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	root	1.9	- timers can be repeating (both absolute and relative ones).
27	root	1.2
28			- detects time jumps and adjusts timers
29	root	1.9	(works for both forward and backward time jumps and also for absolute timers).
30	root	1.2
31	root	1.3	- race-free signal processing
32	root	1.9	(libevent may delay processing signals till after the next event).
33	root	1.3
34	root	1.2	- less calls to epoll_ctl
35			(stopping and starting an io watcher between two loop iterations will now
36	root	1.9	result in spuriois epoll_ctl calls).
37	root	1.2
38			- usually less calls to gettimeofday and clock_gettime
39	root	1.9	(libevent calls it on every timer event change, libev twice per iteration).
40	root	1.2
41			- watchers use less memory
42	root	1.9	(libevent on amd64: 152 bytes, libev: <= 56 bytes).
43	root	1.2
44			- library uses less memory
45			(libevent allocates large data structures wether used or not, libev
46	root	1.9	scales all its data structures dynamically).
47	root	1.2
48			- no hardcoded arbitrary limits
49			(libevent contains an off-by-one bug and sometimes hardcodes a limit of
50	root	1.9	32000 fds).
51	root	1.2
52			- libev separates timer, signal and io watchers from each other
53			(libevent combines them, but with libev you can combine them yourself
54	root	1.9	by reusing the same callback and still save memory).
55	root	1.2
56			- simpler design, backends are potentially much simpler
57			(in libevent, backends have to deal with watchers, thus the problems)
58	root	1.9	(epoll backend in libevent: 366 lines, libev: 90 lines, and more features).
59	root	1.2
60	root	1.6	- libev handles EBADF gracefully by removing the offending fds.
61
62	root	1.8	- doesn't rely on nonportable BSD header files.
63
64	root	1.9	- 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	root	1.13	- win32 compatibility for the core parts.
68
69			- the event core library (ev and event layer) compiles and works both as
70			C and C++.
71
72	root	1.2	whats missing?
73
74	root	1.14	- no event-like priority support at the moment (the ev priorities
75			are not yet finished and work differently, but you cna use idle watchers
76			to get a similar effect).
77	root	1.2
78	root	1.1