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Start editing the changelog for 2.1.3-alpha

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149
ChangeLog
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@ -1,4 +1,151 @@
Changes in version 2.1.3-alpha (?? ??? 201?)
Changes in version 2.1.3-alpha (?? ??? 2013)
Libevent 2.1.3-alpha fixes various bugs, adds new unit tests, and cleans
up the code in a couple of places. It has a new callback in evhttp for
reporting errors during a request, a new feature for allowing evdns to
not keep the event_base looping when there are no requests inflight, and
example code for writing an https client.
Libevent 2.1.3-alpha also has an important new (experimental) event
finalization feature to allow safe event teardown in multithreaded
programs. This ought to fix the longstanding bug with deadlocks in
multithreaded use of SSL-based bufferevents that some people have been
experiencing since Libevent 2.0.
Core (event finalization)
o Implement event_finalize() and related functions to avoid certain
deadlocks (8eedeab)
o Use finalization feature so bufferevents can avoid deadlocks (02fbf68)
o Always run pending finalizers when event_base_free() is called (e9ebef8)
o Remove bufferevent_del_generic_timeout_cbs as now unused (4ea4c6a)
o More documentation for finalization feature (a800b91)
o Make the event_finalize* functions return an error code (5d11f4f)
o Mark the finalize stuff as experiemental in case it needs to
change (23e2e29)
Evdns
o evdns: New flag to make evdns not prevent the event loop from
exiting (6b7fa62 Azat Khuzhin)
Bugfixes (Core)
o Make event_remove_timer behave correctly with persistent timers (5623e80)
o Unit test for event_remove_timer with EV_PERSIST. (96150dd)
o Double-check next timeout when adding events (9443868 Nate Rosenblum)
o event_base_update_cache_time should be a no-op if the loop isn't
running (5e6fa2a)
Bugfixes (evhttp, crash fix, from 2.0)
o fix #73 and fix http_connection_fail_test to catch it (b618204 Greg Hazel)
Bugfixes (compilation and portability, from 2.0)
o Fix compilation with WIN32_HAVE_CONDITION_VARIABLES enabled (7e45739)
o Fix missing AC_PROG_SED on older Autoconfs (9ab2b3f Tay Ray Chuan)
o Backport libevent to vanilla Autoconf 2.59 (as used in RHEL5)
(74d4c44 Kevin Bowling)
o Use AC_CONFIG_HEADERS in place of AM_CONFIG_HEADERS for autmake
1.13 compat (817ea36)
o Rename configure.in to configure.ac to appease newer autoconfs (0c79787)
o Avoid using top_srcdir in TESTS: new automakes do not like this (a55514e)
Bugfixes (resource leaks/lock errors on error, from 2.0)
o Avoid leaking fds on evconnlistener with no callback set (69db261)
o Avoid double-close on getsockname error in evutil_ersatz_socketpair
(0a822a6)
o Fix a locking error in bufferevent_socket_get_dns_error. (0a5eb2e)
Documentation Fixes (from 2.0)
o Fix a mistake in evbuffer_remove() arguments in example http server code
(c322c20 Gyepi Sam)
o Fix a typo in a comment in buffer.h. Spotted by Alt_F4 (773b0a5)
Documentation Fixes
o minor documentation typos (809586a Patrick Pelletier)
o Fix cut-and-paste err in whatsnew-2.1 (49905ac)
o Fix comment to refer to sample/include.am correctly (9e8cdf3 Sebastian
Hahn)
o Fix typo : Dispatching instead of Dispaching (0c2bacc Volker Lendecke)
o fix some hinky indentation in evhttp_make_request (80e220e Patrick
Pelletier)
o "buffer" spelling (a452811 Patrick Pelletier)
o Specify return behavior in header for evbuffer_pullup() in corner case
(cf8d1cd Dan Petro)
o Clarify an important point about event_base_foreach_event() (920a5e6)
Compilation Fixes/Tool Support
o avoid valgrind false positive by zeroing epoll_event (1258614 Patrick
Pelletier)
o Fix harmless clang enum warning (b452a43 Sebastian Hahn)
o remove all exes on "make clean", not just regress.exe (974bfa0 Patrick
Pelletier)
o Make --disable-libevent-regress work again (787fd74)
o Do not build strlcpy.c when it will have no code. (4914620)
Portability Fixes
o When EWOULDBLOCK is not EAGAIN, treat it as equivalent to it (bf7a0ff)
o Preliminary changes for Minix3. (0dda56a Nicholas Heath)
o Use AC_CONFIG_HEADERS in place of AM_CONFIG_HEADERS for autmake 1.13
compat (bf278b)
o Avoid using $(top_srcdir) in TESTS. (2863c83)
o build test/test-script.sh on systems with a less-featureful $< (f935e21)
o Implement EVUTIL_ERR_IS_EAGAIN on windows. (42aaf4d)
Evhttp changes:
o Fix ipv6 support for http. When URL contain domain, not IP
address. (71e709c Azat Khuzhin)
o uri decode: fix for warning "use of uninitialised value" (64b6ece Azat
Khuzhin)
o uri decode: changed the test for the existence of the next character
(e1903e3 Azat Khuzhin)
o Move prototype of evhttp_decode_uri_internal() to http-internal.h
(de8101a Azat Khuzhin)
o Test: decoding just part of string with evhttp_decode_uri_internal()
(1367653 Azat Khuzhin)
o Add new error_cb for actual reporting of HTTP request errors. (7b07719
Azat Khuzhin)
o Add test for EVREQ_HTTP_REQUEST_CANCEL into http_cancel_test() (862c217
Azat Khuzhin)
o Drop extra header http_struct.h from regress_http.c (54cc800 Azat Khuzhin)
Testing
o Add regress test ipv6_for_domain. (9ec88bd Azat Khuzhin)
o Add an environment variable (EVENT_DEBUG_MODE) to run unit tests in debug
mode (2fad0f3)
o Add a test with an active_later event at event_base_free time. (1c3147f)
o Make all tests pass under EVENT_DEBUG_MODE=1 (b1b054f)
o Add some verbose notes to bufferevent unit tests (9d893c9)
o New test for active_later->active transition on event_active (a153874)
o New tests for event_base_foreach_event() (0b096ef)
o Unit tests for event_base_gettimeofday_cached() and
event_base_update_cache_time() (30ea291)
o A test for event_get_assignment() (f09629e)
o More unit tests for initializing common timeouts. (d596739)
o Fix a bug in the new main/event_foreach test (702c9aa)
Windows:
o use FormatMessage for winsock errors (0c6ec5d, 2078e9b, 4ccdd53, c9ad3af
Patrick Pelletier)
o a program to print out the error strings for winsock errors (7296512
Patrick Pelletier)
o Fix a warning introduced in 0c6ec5d8 (eeb700c)
o Fix another warning introduced in 0c6ec5d8 (ed26561)
Examples (http)
o Add sample/https-client.c, an example of stacking evhttp as a client on
top of bufferevent_ssl. (be46c99 Catalin Patulea)
o use ${OPENSSL_LIBS} instead of -lssl -lcrypto (bf31fa5 Patrick Pelletier)
o https-client was putting newlines at 256-byte boundaries (42d7441 Patrick
Pelletier)
o better handling of OpenSSL errors (5754d96 Patrick Pelletier)
o use Debian's default root certificate location (aacd674 Patrick Pelletier)
o use iSECPartners code to validate hostname in certificate (64d9f16
Patrick Pelletier)
o avoid sign mismatch warning in openssl_hostname_validation.c (6021cb5
Patrick Pelletier)
o pull in wildcard matching code from cURL (4db9da6 Patrick Pelletier)
o Another tweak to https-client.c (95acdaa)
o Remove http_struct.h usage in sample/https-client.c (8a90a85)
Changes in version 2.1.2-alpha (18 Nov 2012)

132
whatsnew-2.1.txt
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@ -41,7 +41,7 @@
We don't try to do binary compatibility except within stable release
series, so binaries linked against any version of Libevent 2.0 will
probably need to be recompiled against Libevent 2.1.1-alpha if you
probably need to be recompiled against Libevent 2.1.3-alpha if you
want to use it. It is probable that we'll break binary compatibility
again before Libevent 2.1 is stable.
@ -146,7 +146,113 @@
that's a no-op in past versions of Libevent, and we don't want to
break compatibility.)
1.3. New debugging features
1.3. Event finalization
[NOTE: This is an experimental feature in Libevent 2.1.3-alpha. Though
it seems solid so far, its API might change between now and the first
release candidate for Libevent 2.1.]
1.3.1. Why event finalization?
Libevent 2.1 now supports an API for safely "finalizing" events that
might be running in multiple threads, and provides a way to slightly
change the semantics of event_del() to prevent deadlocks in
multithreaded programs.
To motivate this feature, consider the following code, in the context
of a mulithreaded Libevent application:
struct connection *conn = event_get_callback_arg(ev);
event_del(ev);
connection_free(conn);
Suppose that the event's callback might be running in another thread,
and using the value of "conn" concurrently. We wouldn't want to
execute the connection_free() call until "conn" is no longer in use.
How can we make this code safe?
Libevent 2.0 answered that question by saying that the event_del()
call should block if the event's callback is running in another
thread. That way, we can be sure that event_del() has canceled the
callback (if the callback hadn't started running yet), or has waited
for the callback to finish.
But now suppose that the data structure is protected by a lock, and we
have the following code:
void check_disable(struct connection *connection) {
lock(connection);
if (should_stop_reading(connection))
event_del(connection->read_event);
unlock(connection);
}
What happens when we call check_disable() from a callback and from
another thread? Let's say that the other thread gets the lock
first. If it decides to call event_del(), it will wait for the
callback to finish. But meanwhile, the callback will be waiting for
the lock on the connection. Since each threads is waiting for the
other one to release a resource, the program will deadlock.
This bug showed up in multithreaded bufferevent programs in 2.1,
particularly when freeing bufferevents. (For more information, see
the "Deadlock when calling bufferevent_free from an other thread"
thread on libevent-users starting on 6 August 2012 and running through
February of 2013. You might also like to read my earlier writeup at
http://archives.seul.org/libevent/users/Feb-2012/msg00053.html and
the ensuing discussion.)
1.3.2. The EV_FINALIZE flag and avoiding deadlock
To prevent the deadlock condition described above, Libevent
2.1.3-alpha adds a new flag, "EV_FINALIZE". You can pass it to
event_new() and event_assign() along with EV_READ, EV_WRITE, and the
other event flags.
When an event is constructed with the EV_FINALIZE flag, event_del()
will not block on that event, even when the event's callback is
running in another thread. By using EV_FINALIZE, you are therefore
promising not to use the "event_del(ev); free(event_get_callback_arg(ev));"
pattern, but rather to use one of the finalization functions below to
clean up the event.
EV_FINALIZE has no effect on a single-threaded program, or on a
program where events are only used from one thread.
There are also two new variants of event_del() that you can use for
more fine-grained control:
event_del_noblock(ev)
event_del_block(ev)
The event_del_noblock() function will never block, even if the event
callback is running in another thread and doesn't have the EV_FINALIZE
flag. The event_del_block() function will _always_ block if the event
callback is running in another thread, even if the event _does_ have
the EV_FINALIZE flag.
[A future version of Libevent may have a way to make the EV_FINALIZE
flag the default.]
1.3.3. Safely finalizing events
To safely tear down an event that may be running, Libevent 2.1.3-alpha
introduces event_finalize() and event_free_finalize(). You call them
on an event, and provide a finalizer callback to be run on the event
and its callback argument once the event is definitely no longer
running.
With event_free_finalize(), the event is also freed once the finalizer
callback has been invoked.
A finalized event cannot be re-added or activated. The finalizer
callback must not add events, activate events, or attempt to
"resucitate" the event being finalized in any way.
If any finalizer callbacks are pending as the event_base is being
freed, they will be invoked. You can override this behavior with the
new function event_base_free_nofinalize().
1.4. New debugging features
You can now turn on debug logs at runtime using a new function,
event_enable_debug_logging().
@ -158,7 +264,7 @@
There's also been some work done to try to make the debugging logs
more generally useful.
1.4. New evbuffer functions
1.5. New evbuffer functions
In Libevent 2.0, we introduced evbuffer_add_file() to add an entire
file's contents to an evbuffer, and then send them using sendfile() or
@ -198,7 +304,7 @@
evbuffer_readln() now supports an EVBUFFER_EOL_NUL argument to fetch
NUL-terminated strings from buffers.
1.5. New functions and features: bufferevents
1.6. New functions and features: bufferevents
You can now use the bufferevent_getcb() function to find out a
bufferevent's callbacks. Previously, there was no supported way to do
@ -219,7 +325,7 @@
You can find the priority at which a bufferevent runs with
bufferevent_get_priority().
1.6. New functions and features: evdns
1.7. New functions and features: evdns
The previous evdns interface used an "open a test UDP socket" trick in
order to detect IPv6 support. This was a hack, since it would
@ -227,7 +333,14 @@
packets were sent. The current evdns interface-detection code uses
the appropriate OS functions to see which interfaces are configured.
1.7. New functions and features: evconnlistener
The evdns_base_new() function now has multiple possible values for its
second (flags) argument. Using 1 and 0 have their old meanings, though the
1 flag now has a symbolic name of EVDNS_BASE_INITIALIZE_NAMESERVERS.
A second flag is now supported too: the EVDNS_BASE_DISABLE_WHEN_INACTIVE
flag, which tells the evdns_base that it should not prevent Libevent from
exiting while it has no DNS requests in progress.
1.8. New functions and features: evconnlistener
Libevent 2.1 adds the following evconnlistener flags:
@ -245,7 +358,7 @@
the accepted sockets themselves. That's almost never what you want.
Now, it applies both to the listener and the accepted sockets.
1.8. New functions and features: evhttp
1.9. New functions and features: evhttp
**********************************************************************
NOTE: The evhttp module will eventually be deprecated in favor of Mark
@ -274,6 +387,11 @@
The socket errno value is now preserved when invoking an http error
callback.
There's a new kind of request callback for errors; you can set it with
evhttp_request_set_error_cb(). It gets called when there's a request error,
and actually reports the error code and lets you figure out which request
failed.
2. Cross-platform performance improvements
2.1. Better data structures