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A fast, portable Objective-C runtime written 100% in C11

A portable Objective-C runtime written in C11. No Assembler required. It follows the Apple "Objective-C 1 Runtime" and adds many features from "Objective-C 2.0", but the runtime function calls are completely different. It is designed to be suitable for massive multi-threading.

Release Version
Mulle kybernetiK tag Build Status

What's so different ?

  • Runtime objects (like classes and selectors) are not referenced by name, but by a unique ID. No special linker action required.

  • Parameters outside of self and _cmd are passed via _param, a single pointer to a struct. This simplifies a lot of code, especially forwarding code. Return values are also returned with the same struct. Optimizations are done for simple methods with only none or one parameter and none or one return value.

  • It uses inlineable method calls for superior performance. The user can specify "fast" classes and "fast" methods for extra speed in performance critical cases.

  • retain/release semantics are built in. These are non-overridable, which makes them a lot faster.

  • isa is not part of the instance, but instead prefixed to the instance.

  • Protocol as a type and an object does not exist anymore. Instead there is PROTOCOL which is basically the same as SEL and has compiler support.

  • No global lock, except when loading code. The runtime in normal operation only locks during +initialize on a per class basis.

  • Protections against the fragile base class problem

  • Multiple runtimes can coexist in differently named "universes".

Required Libraries and Tools

Libraries and Tools

Name Release Version
mulle-aba Mulle kybernetiK tag Build Status
mulle-allocator Mulle kybernetiK tag Build Status
mulle-c11 Mulle kybernetiK tag Build Status
mulle-concurrent Mulle kybernetiK tag Build Status
mulle-thread Mulle kybernetiK tag Build Status
mulle-vararg Mulle kybernetiK tag Build Status

How to use it

If you haven't used an Objective-C runtime before, it is useful to get to know the much better documented "Mac OS X Objective-C 1.0" runtime first. Intro to the Objective-C Runtime could be a good starting point.

C Caveat

It you use .c files that include <mulle-objc-runtime/mulle-objc-runtime.h> make sure that you compile with __MULLE_OBJC_TPS__, __MULLE_OBJC_NO_TPS__ __MULLE_OBJC_FCS__ __MULLE_OBJC_NO_FCS__ as defined when compiling the runtime. Since C-only compilations do not emit runtime information, mismatches can not be checked by the runtime. Easy fix: rename .c to .m and use mulle-clang

Data structures

API Description
_mulle_objc_class Deal with Classes
_mulle_objc_ivar et al. Instance variables
_mulle_objc_loadinfo Install Classes, Categories, Methods, Strings into the runtime
_mulle_objc_method et al. Deal with Methods
_mulle_objc_object et al. Deal with Instances
_mulle_objc_property et al. Handle Properties
_mulle_objc_runtime Work with the runtime

Other functions

API Description
Global Functions Global functions and conveniences
Exceptions Raising exceptions
Vararg extensions Dealing with variable arguments


These articles give you some background about the mulle-objc runtime:

  1. mulle-objc: a new Objective-C runtime
  2. mulle-objc: a meta calling convention
  3. mulle-objc: removing superflous ifs
  4. mulle-objc: inlined messaging
  5. mulle-objc: some research about selectors
  6. mulle-objc: hashes for classes, selectors and protocols
  7. mulle_objc: object layout, retain counting, finalize
  8. mulle_objc: inheriting methods from protocols
  9. mulle_objc: present and absent language features
  10. mulle_objc: the trouble with @property
  11. mulle_objc: ivar layout with @property
  12. mulle_objc: technically speaking
  13. mulle-clang, technically speaking
  14. mulle-objc-runtime, technically speaking
  15. MulleFoundation, technically speaking

If something is unclear, feel free to contact the author.

Platforms and Compilers

All platforms and compilers supported by mulle-c11 and mulle-thread.


Use mulle-sde to add mulle-objc-runtime to your project:

mulle-sde dependency add --c --github mulle-objc mulle-objc-runtime

Executables will need to link with mulle-objc-runtime-startup as well.


See mulle-objc-developer for the preferred way to installation mulle-objc-runtime.


Use mulle-sde to build and install mulle-objc-runtime and all dependencies:

mulle-sde install --prefix /usr/local \

Manual Installation

Install the requirements:

Requirements Description
mulle-atinit Cross-platform atinit support
mulle-atexit Cross-platform atexitsupport
mulle-concurrent Concurrent hashmap and array
mulle-dlfcn Cross-platform dlfcn support
mulle-stacktrace Cross-platform stacktrace support
mulle-vararg Cross-platform atexit support

Install into /usr/local:

mkdir build 2> /dev/null
   cd build ;
   cmake -DCMAKE_INSTALL_PREFIX=/usr/local \
         -DCMAKE_PREFIX_PATH=/usr/local \
         -DCMAKE_BUILD_TYPE=Release .. ;
   make install


Nat! for Mulle kybernetiK and Codeon GmbH