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168 lines
6.5 KiB
Plaintext
168 lines
6.5 KiB
Plaintext
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What's New In Libevent 1.4:
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0. About this document
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This document describes the key differences between Libevent 1.3 and
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Libevent 1.4, from a user's point of view. It was most recently
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updated based on features from libevent 1.4.2-rc.
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1. Packaging Issues.
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1.1. The great library division.
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The libevent source now builds two libraries: libevent_core and
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libevent_extra. The libevent_core library includes event loops,
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timers, buffer code, and various small compatibility functions. The
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libevent_extra library includes code for HTTP, DNS, RPC, and so on.
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Thus, if you're writing software that only uses libevent's event
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loop, you should link against only the libevent_core library,
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whereas if you're writing software that uses libevent's protocol
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support as well, you need to link libevent_extra as well.
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For backward compatibility, libevent also builds a library called
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"libevent" that includes everything.
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1.2. The event-config.h header
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Libevent configure script now builds two headers from its configure
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script: config.h (which it uses internally) and event-config.h
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(which it installs as a header file). All of the macros in
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event-config.h are modified so that they're safe to include in other
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projects. This allows libevent's header files (like event.h and
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evutil.h) information about platform configuration.
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What does this mean for you? As of 1.4.x, it should never be
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necessary to include extra files or define extra types before you
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include event.h (or any other libevent header); event.h can now look
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at the information in event-config.h and figure out what it needs to
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include.
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1.3. Documentation
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Libevent now includes better doxygen documentation. It's not
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perfect or complete, though; if you find a mistake, please let us
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know.
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1.4. Libtool usage
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We now use libtool's library versioning support correctly. If we
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don't mess this up, it means that binaries linked against old
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version of libevent should continue working when we make changes to
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libevent that don't break backward compatibility.
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1.5. Portability
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Libevent now builds with MSVC again. We've only tested it with MSVC
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2005, and the project files might not be right. Please let us know
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if you run into any issues.
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Libevent now builds on platforms where /bin/sh is not bash.
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Libevent's regression test no longer requires Python to be
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installed.
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2. New and Improved APIs:
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(This list includes functions that are new, functions whose behavior
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has changed, and functions that were included in previous releases
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but which never actually worked before.)
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2.1. Utility functions are defined in evutil.h
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Libevent now exposes a small set of functions for cross-platform
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network programming in evutil.h, on the theory that they've been
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useful enough to us that other people may likely want to use them
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too. These are mainly workarounds for Windows issues for now: they
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include evutil_socketpair (to fake socketpair on platforms that
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don't have it) and evutil_make_socket_nonblocking (to make a socket
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nonblocking in a cross-platform way. See the header for more
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information.
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2.2. In the libevent core.
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The event_base_free() function now works. Previously, it would
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crash with an assertion failure if there were events pending on a
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base. Now, it simply deletes all the pending events and frees the
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base. Be careful -- this might leak fds and memory associated with
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the old events. To avoid leaks, you should still remove all the
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events and free their resources before you delete the base.
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Libevent should now work properly with fork(). Just call
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event_reinit() on your event base after the fork call, and it should
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work okay. Please let us know about any bugs you find.
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There's a new event_base_new() function that acts just like
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event_init(), but does not replace the default base. If you are
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using multiple event bases in your code, you should just use
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event_base_new() instead of event_init(), to avoid accidental bugs.
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There's new event_loopbreak() function to make a current event loop
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stop exiting and return. Unlike event_loopexit, it stops subsequent
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pending events from getting executed. This behavior is useful for
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scripting languages to implement exceptions from inside callbacks.
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There's a new event_base_get_method() function, for use in place of
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event_get_method() in multi-base applications.
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2.3. New in HTTP.
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There's an evhttp_connection_set_local_address() function you can
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use to set the local address of an HTTP connection.
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HTTP/1.1 chunking now correctly ends chunks with '\r\n'.
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2.4. New in DNS
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Instead of picking your method for generating DNS transaction IDs at
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startup, you can use evdns_set_transaction_id() to provide a
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transaction ID function at runtime.
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The "class" field in evdns_server_request is now renamed to
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dns_question_class, so that it won't break compilation under C++.
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This uses some preprocessor hacks so that C code using the old name
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won't break. Eventually, the old name will be deprecated entirely;
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please don't use it.
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2.5. New in RPC
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There are now hooks on RPC input and output; can be used to
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implement RPC independent processing such as compression or
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authentication.
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RPC tags can now be up to 32 bits. This is wire-compatible, but
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changes some of the types in the APIs. Please let us know if this
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is problematic for you.
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3. Big bugfixes
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We've done a lot, with help from users on different platforms, to
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make the different backends behave more similarly with respect to
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signals and timeouts. The kqueue and solaris backends were the big
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offenders previously, but they should be better now. Windows should
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be better too, though it's likely that problems remain there.
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The libevent headers (though not the source files!) should now build
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cleanly on C++.
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(For more bugfixes, see the ChangeLog file. These are only the
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biggies.)
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4. Big performance improvements
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Libevent now uses a min-heap rather than a red-black tree to track
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timeouts. This means that finding the next timeout to fire is now
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O(1) instead of (lg n).
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The win32 select-based backend now uses a red-black tree to map
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SOCKET handles to event structures. This changes the performance
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characteristics of the event loop on win32 from O(n^2) to O(n lg n).
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Not perfect, but better.
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5. Removed code and features
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The rtsig backend is now removed. It hasn't even compiled for a
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while, and nobody seemed to miss it very much. All the platforms
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that have rtsig seem to have a better option instead these days.
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Please let us know if rtsig was crucial for you.
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