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kc3-lang/libevent/whatsnew-14.txt
Niels Provos
- whatsnew-14.txt
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What's New In Libevent 1.4: 0. About this document This document describes the key differences between Libevent 1.3 and Libevent 1.4, from a user's point of view. It was most recently updated based on features from libevent 1.4.2-rc. 1. Packaging Issues. 1.1. The great library division. The libevent source now builds two libraries: libevent_core and libevent_extra. The libevent_core library includes event loops, timers, buffer code, and various small compatibility functions. The libevent_extra library includes code for HTTP, DNS, RPC, and so on. Thus, if you're writing software that only uses libevent's event loop, you should link against only the libevent_core library, whereas if you're writing software that uses libevent's protocol support as well, you need to link libevent_extra as well. For backward compatibility, libevent also builds a library called "libevent" that includes everything. 1.2. The event-config.h header Libevent configure script now builds two headers from its configure script: config.h (which it uses internally) and event-config.h (which it installs as a header file). All of the macros in event-config.h are modified so that they're safe to include in other projects. This allows libevent's header files (like event.h and evutil.h) information about platform configuration. What does this mean for you? As of 1.4.x, it should never be necessary to include extra files or define extra types before you include event.h (or any other libevent header); event.h can now look at the information in event-config.h and figure out what it needs to include. 1.3. Documentation Libevent now includes better doxygen documentation. It's not perfect or complete, though; if you find a mistake, please let us know. 1.4. Libtool usage We now use libtool's library versioning support correctly. If we don't mess this up, it means that binaries linked against old version of libevent should continue working when we make changes to libevent that don't break backward compatibility. 1.5. Portability Libevent now builds with MSVC again. We've only tested it with MSVC 2005, and the project files might not be right. Please let us know if you run into any issues. Libevent now builds on platforms where /bin/sh is not bash. Libevent's regression test no longer requires Python to be installed. 2. New and Improved APIs: (This list includes functions that are new, functions whose behavior has changed, and functions that were included in previous releases but which never actually worked before.) 2.1. Utility functions are defined in evutil.h Libevent now exposes a small set of functions for cross-platform network programming in evutil.h, on the theory that they've been useful enough to us that other people may likely want to use them too. These are mainly workarounds for Windows issues for now: they include evutil_socketpair (to fake socketpair on platforms that don't have it) and evutil_make_socket_nonblocking (to make a socket nonblocking in a cross-platform way. See the header for more information. 2.2. In the libevent core. The event_base_free() function now works. Previously, it would crash with an assertion failure if there were events pending on a base. Now, it simply deletes all the pending events and frees the base. Be careful -- this might leak fds and memory associated with the old events. To avoid leaks, you should still remove all the events and free their resources before you delete the base. Libevent should now work properly with fork(). Just call event_reinit() on your event base after the fork call, and it should work okay. Please let us know about any bugs you find. There's a new event_base_new() function that acts just like event_init(), but does not replace the default base. If you are using multiple event bases in your code, you should just use event_base_new() instead of event_init(), to avoid accidental bugs. There's new event_loopbreak() function to make a current event loop stop exiting and return. Unlike event_loopexit, it stops subsequent pending events from getting executed. This behavior is useful for scripting languages to implement exceptions from inside callbacks. There's a new event_base_get_method() function, for use in place of event_get_method() in multi-base applications. 2.3. New in HTTP. There's an evhttp_connection_set_local_address() function you can use to set the local address of an HTTP connection. HTTP/1.1 chunking now correctly ends chunks with '\r\n'. 2.4. New in DNS Instead of picking your method for generating DNS transaction IDs at startup, you can use evdns_set_transaction_id() to provide a transaction ID function at runtime. The "class" field in evdns_server_request is now renamed to dns_question_class, so that it won't break compilation under C++. This uses some preprocessor hacks so that C code using the old name won't break. Eventually, the old name will be deprecated entirely; please don't use it. 2.5. New in RPC There are now hooks on RPC input and output; can be used to implement RPC independent processing such as compression or authentication. RPC tags can now be up to 32 bits. This is wire-compatible, but changes some of the types in the APIs. Please let us know if this is problematic for you. 3. Big bugfixes We've done a lot, with help from users on different platforms, to make the different backends behave more similarly with respect to signals and timeouts. The kqueue and solaris backends were the big offenders previously, but they should be better now. Windows should be better too, though it's likely that problems remain there. The libevent headers (though not the source files!) should now build cleanly on C++. (For more bugfixes, see the ChangeLog file. These are only the biggies.) 4. Big performance improvements Libevent now uses a min-heap rather than a red-black tree to track timeouts. This means that finding the next timeout to fire is now O(1) instead of (lg n). The win32 select-based backend now uses a red-black tree to map SOCKET handles to event structures. This changes the performance characteristics of the event loop on win32 from O(n^2) to O(n lg n). Not perfect, but better. 5. Removed code and features The rtsig backend is now removed. It hasn't even compiled for a while, and nobody seemed to miss it very much. All the platforms that have rtsig seem to have a better option instead these days. Please let us know if rtsig was crucial for you.