[Libevent-users] Fun facts about Libevent 2.0.4-alpha

[Nick Mathewson <nickm@xxxxxxxxxxxxx>]

Hi, all!

As a followup to Niels's announcement, I'd like to go into a little
more detail about what's up with the 2.0.4-alpha release.

STATISTICS AND TRIVIA:
* Libevent 2.0.4-alpha is about 4000 lines longer than Libevent
2.0.3-alpha.  about 1700 of these are in tests and samples; the rest
is in actual code.

* Our unit test coverage has dipped a bit; in 2.0.3-alpha we were
around 80.5%; now we're around 79.3% coverage.  (Both numbers are from
my Linux box.)

* About 58% of Libevent's public functions, structures, and defines
are now documented in my reference manual at
http://www.wangafu.net/~nickm/libevent-book/ .

WHAT'S NEW:

For a full list of changes, see the ChangeLog on the website and
distributed with Libevent 2.0.4-alpha.  I'm only mentioning the stuff
I find interesting here.

* There are a ton of bugfixes, including a few memory corruption
issues and race conditions.  Everybody who's been writing
multithreaded code should upgrade.
* Bufferevents now support rate-limiting.  You can rate-limit
bufferevents individually, or in groups.  Right now, this feature is
underdocumented, since I suspect we'll want to tweak the APIs a bit
before 2.0.x goes stable.
* Our evdns_getaddrinfo()  and evutil_getaddrinfo() functions now
support looking at the /etc/hosts file, or local equivalent.
* The http subsystem can now use evdns to do non-blocking hostname
lookups for outgoing connections.
* Libevent backends can now use a "changelist" feature to minimize
calls to functions like epoll() and argument lengths to functions like
kqueue().  Right now the epoll and kqueue backends use this feature;
somebody could port evport and devpoll to do so as well.
* There's a new event_get_struct_event_size() function so you can use
event_assign() and friends without losing binary compatibility.
* There are new event_get_callback(), event_get_callback_arg()
functions to expose the remaining assigned members of an event, and an
event_get_assignment() function to get every member of an event at
once.
* There's now support for running Libevent in a "debug mode" that can
use a bit more memory and time, but detect some common programming
errors.  See the documentation for event_enable_debug_mode() for more
information.
* Libevent now uses a secure PRNG for the entropy that evdns needs to
be secure.  This is arc4random() on platforms that provide it, and our
own copy of arc4random() on platforms that don't.  You no longer need
to replace the evdns transaction ID or random_bytes functions for
security.

WHAT'S GONE OR CHANGED:

* If you have been manually providing locking functions with
evthread_set_lock_create_callback and evthread_set_locking_callback,
those functions are now deprecated.  You should use the more
future-proof evthread_set_lock_callbacks() function instead.  (Or you
could just use evthread_use_windows_threads() or
evthread_use_pthreads(), and not worry about low-level locking details
at all.)
* The EVENT_FD and EVENT_SIGNAL macros are now deprecated.
* Our vcproj files were completely incorrect; they built the wrong
files with the wrong options.  Nobody on the development team uses the
MSVC IDE, so   instead we're shipping makefiles for use with nmake.
These we can actually inspect by hand, and use reproducibly.
* We try to keep backward source compatibility with pre-2.0 versions
of Libevent.  Once Libevent 2.0.x is stable, we'll keep backward
compatibility with that too.  While 2.0.x is in alpha, though, we
occasionally change or remove APIs introduced in earlier 2.0.x alphas
so that we don't have to keep supporting bad ideas indefinitely.
   * The evhttp_connection_base_new() function now takes an optional
evdns_base argument.
   * The flags argument of evdns_base_set_option() has been removed.
   * The EVUTIL_CHECK_FMT macro has been removed.


hth,
-- 
Nick
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