ANN: GNUstep Objective-C Runtime 1.4

[David Chisnall]

GNUstep Objective-C Runtime 1.4
===============================

This is the fifth official release of the GNUstep Objective-C runtime (a.k.a.
libobjc2).  This runtime was designed to support the features of Objective-C 2
for use with GNUstep and other Objective-C programs.  Highlights of this
release include:

- Support for the associated reference APIs introduced with OS X 10.6.  This
  allows storing arbitrary objects associated with another object.

- Concurrent, thread-safe, +initialize.  The runtime will now send +initialize
  messages to different classes concurrently in multiple threads, but still
  ensures that no class receives another message until it has returned from
  +initialize.  This mirrors OS X behaviour.  Care must be taken that
  +initialize methods do not deadlock - if two classes are simultaneously
  initialised from two different threads, and there +initialize methods call
  methods in the other class, then deadlock will result.
  
- Exceptions can now safely propagate out of +initialize methods.

- Better hiding of local symbols.  Now the internal runtime functions are not
  visible from outside of the runtime.  This may break code that attempts to
  use private APIs, but means that it is now impossible to accidentally use
  private APIs.

- Dispatch table updates have been improved.  Category loading now longer
  triggers dtable creation and partial dtable updates are faster.  

- Improvements to the low memory profile.  Uses 5-10% less (total) memory
  running Gorm, and now passes the entire GNUstep and EtoileFoundation test
  suites.  Build with [g]make low_memory=yes to enable this mode.  Note that
  the low memory profile trades some CPU time for memory usage, so don't use it
  for CPU-bound tasks.

- The class lookup cache optimisation (LLVM) now caches lookups irrespective of
  the ABI.  It will insert direct references to the class structures if
  possible (i.e. if the symbol is visible).  If not, then it will cache the
  result of objc_class_lookup().  The cache is shared across the module (the
  library, if run as a link-time optimisation), so the lookup only needs to be
  run once.  This eliminates the need for explicit class lookup caching in the
  source code (when using LLVM-based compilers, such as Clang, LanguageKit, or
  DragonEgg).

- Added some missing runtime API functions, such as those for setting and
  getting instance variables.  These are required by some language bridges,
  although using them safely is not actually possible with the non-fragile ABI
  (also true on OS X), since instance variables are no longer uniquely
  identified by name. 
  
- Added support for accessing property type encodings.  These are extended type
  encodings, allowing code introspecting the properties to learn if they are
  read-only, their assignment policy, the methods used to implement them, and
  so on.

You may obtain the code for this release from subversion at the following
subversion branch:

svn://svn.gna.org/svn/gnustep/libs/libobjc2/1.4

Alternatively, a tarball is available from:

http://download.gna.org/gnustep/libobjc2-1.4.tar.bz2

The runtime library is responsible for implementing the core features of the
object model, as well as exposing introspection features to the user.  The
GNUstep runtime implements Apple's Objective-C Runtime APIs, and a small number
of GCC APIs for legacy compatibility.

This library is based on the Étoilé Objective-C Runtime, an earlier research
prototype, and includes support for non-fragile instance variables,
type-dependent dispatch, and object planes.  It is fully compatible with the
FSF's GCC Objective-C ABI and also implements a new ABI that is supported by
Clang and Étoilé's LanguageKit and is required for some of the newer features.

Although the runtime has been tested by several people, and is being used
extensively by the Étoilé project, it is entirely new (MIT licensed) code and
may still contain bugs.  If you come across any problems, please report them to
the GNUstep Developer mailing list <gnustep-dev@gnu.org>.