Update ANNOUNCE.
David Chisnall
7 years ago
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GNUstep Objective-C Runtime 2.0
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===============================
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This the second major release of the GNUstep Objective-C runtime (a.k.a.
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libobjc2). This runtime was designed to support the features of modern
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dialects of Objective-C for use with GNUstep and other Objective-C programs.
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This release introduces a new Objective-C ABI, which is designed to be forward
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compatible with future changes and removes a large number of hacks that were
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required for compatibility with the prior ABI that included features introduced
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in the 1980s. Highlights include:
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- The linker now removes duplicate selectors within a library.
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- The linker will remove duplicate protocol definitions within a library.
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- Protocols and classes are now always accessed via an indirection layer, so
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they can be extended by future versions of the ABI without breaking
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compatibility.
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- Categories can include property metadata and both categories.
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- Constant strings are now emitted with a richer structure, which provides
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faster hashing and better unicode support.
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- Instance variable metadata includes size and alignment, allowing better object
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layout and more accurate introspection. Instance variable metadata now
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includes more accurate information about ARC ownership semantics.
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- Method metadata now includes extended type information, allowing bridged
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languages to understand the class that methods expect and not just the fact
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that they take an object. This was previously an obstacle to supporting
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JavaScriptCore's Objective-C bridge with GNUstep.
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In addition to the new ABI, there are several improvements on Windows:
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- The runtime now uses SEH-based exception handling on Windows. This
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interoperates with C++ exceptions in libraries compiled with MSVC or
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MSVC-compatible compilers.
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- All of the assembly code paths now fully support i386 and x64 Windows.
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- Object allocations on 32-bit Windows now use `_aligned_malloc` to guarantee
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sufficient alignment for AVX vectors in instance variables.
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- The runtime now uses fibre-local storage and critical sections on Windows,
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improving performance in multithreaded workloads on Windows.
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- Public runtime functions are now marked dllexport, so the runtime can be built
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as objc.dll on Windows.
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**WARNING**: The new ABI is currently incompatible with incremental linking on
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Windows, so projects built with Microsoft's linker must disable incremental
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linking.
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Note: Microsoft's WinObjC project contains a friendly fork of this library that
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includes a work around for the incremental linking issue. If you wish to use
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incremental linking on Windows, please use that version. A subsequent version
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of clang and link.exe should include a fix that will make it possible to use
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this version with incremental linking.
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The runtime will now use the new ABI's data structures internally and will
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automatically upgrade on-disk structures from old ABIs when used with the old
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ABI. As a result, memory usage will be higher when using the old ABI and users
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who are unable to recompile their code may prefer to stick with the 1.9.x
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release series. Mixing libraries compiled with the old and new ABIs is not
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supported and will abort at run time.
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The new ABI provides better run-time introspection metadata and smaller
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binaries. When used with the new ABI, this version of the runtime will consume
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less memory than the previous release.
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You may obtain the code for this release from git and use the 2.0 branch:
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https://github.com/gnustep/libobjc2.git
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Alternatively, a tarball is available from:
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https://github.com/gnustep/libobjc2/archive/v2.0.zip
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https://github.com/gnustep/libobjc2/archive/v2.0.tar.gz
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The runtime library is responsible for implementing the core features of the
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object model, as well as exposing introspection features to the user. The
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GNUstep runtime implements a superset of Apple's Objective-C Runtime APIs.
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If you come across any problems, please file them in the issue tracker:
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https://github.com/gnustep/libobjc2/issues
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