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C portable low-level assemblies for parallelism and threading
C C++ Objective-C
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amp - assemblies for parallelism

amp is a collection of portable low-level C assemblies for parallelism and threading, for example amp_thread, amp_semaphore, or amp_mutex. Use these parallelism atoms to create higher-level parallel solutions by including amp/amp.h. amp tries to be as minimal as possible to be easily portable and usable in different projects so they don't have to write this low-level cross-platform wrappers again and again.

All functions and types use the amp_ prefix, while preprocessor symbols use AMP_.

No platform specific headers and symbols are included by amp/amp.h. However you can access headers containing _raw_ in their file name. These are shallow wrappers around the platforms thread functionality and include platform specific headers.

The following platforms are supported: Mac OS X 10.6, Windows (XP and higher), and platforms supporting POSIX threads (Pthreads). As of yet amp is actively developed and tested on Mac OS X and WindowsXP.

amp is developed using a test-driven methodology. Tests rely on the UnitTest++ library by Noel Llopis and Charles Nicholson. Take a look at the source files in the 'test' subdirectory to get an impression how to use amp.

The code can be downloaded at:
Please file issues with the code or feature requests at:

amp primitives

amp supports the following cross-platform threading and parallelism primitives:

  • amp_thread - launch and join with threads.
  • amp_thread_local_slot - thread specific storage.
  • amp_thread_array - control a whole set of threads.
  • amp_mutex - lock, trylock, or unlock a mutex.
  • amp_condition_variable - signal, broadcast, or wait on a condition variable in combination with a mutex. Works on WindowsXP, too.
  • amp_semaphore - signal or wait on a semaphore.
  • amp_barrier - barrier for a specified number of threads.
  • amp_platform - query the platform for the installed and/or active number of processor cores or hardware-threads.

Usage guidelines

Never pass NULL or invalid pointers to the amp functions if it is not specifically documented to be ok.

Never pass non-created/uninitialized values to amp functions other than to the create and init functions. amp has no way to detect invalid pointers and for performance reasons does not even try to detect them.

Always check return codes that flag errors that can occur, e.g. not enough memory, errors indicating that a threading primitive count has reached its max, or return codes from trylocks which indicate that attaining the lock was not successful. At least assert on return codes that indicate programming errors, e.g. passing out of range count values to create functions. Many programming errors will result in undefined behavior - read the documentation and prevent making these errors, e.g. trying to unlock a mutex owned by another thread.

Never copy raw primitives! It is ok to have multiple pointers to a single raw primitive but care for ownership and lifetime management in that case.

amp should be used to create higher-level parallelism abstractions, e.g. job or task pools, but threads shouldn't be used by the typical programmer working on non-parallelism domain solutions.


amp just started to aggregate in code - and it will change, transform, and grow from version to version.


Many thanks go to the following guys (in order of "appearance", twitter name in brackets) - you are awesome:

  • Anthony Williams (@a_williams) and Dimitriy V'jukov (@dvyukov)(names in order of discussion contacts) for their interest and time to discuss the WindowsXP condition variable implementation, and their invaluable and awesome feedback that opened my eyes and made this code more correct and faster. All remaining errors in the code are mine.

  • Jedd Orion Haberstro (@jhaberstro) for indepth feedback to the documentation of amp_thread_yield which resulted in a clearer explanation of the function.

  • Rick Molloy (@rickmolloy) for insightful discussions and his help to port and test amp on Windows 7.

Author(s) and Contact

You have got feedback, questions, criticism, or just want to say hello? I am looking forward to hear from you!

Bjoern Knafla
Bjoern Knafla Parallelization + AI + Gamedev Consulting
twitter @bjoernknafla

Copyright and License

amp is free software. You may copy, distribute, and modify it under the terms of the license contained in the file COPYRIGHT.txt distributed with this package. This license is equal to the Simplified BSD License.

amp was developed as a foundation to experiment and research job pools for computer and video games and to parallelize the Sandbox.

Joint ownership of the copyright belongs to Bjoern Knafla and


See the BUILDING.txt file in the root directory of the project for build instructions.


  • David R. Butenhof, Programming POSIX Threads, Addison-Wesley, 1997
  • Bil Lewis and Danile J. Berg, Multithreaded Programming with Pthreads, Sun Microsystems Press, 1998
  • Joe Duffy, Concurrent Programming on Windows, Addison-Wesley 2009
  • Maurice Herlihy and Nir Shavit, The Art of Multiprocessor Programming, Morgan Kaufmann, 2008
  • Gadi Taubenfeld, Synchronization Algorithms and Concurrent Programming, Pearson Education, 2006


All trademarks copyrights belong to their respective trademark holders and copyright owners.

Release Notes

Version 0.1.0 (July 06, 2010)

  • Separated raw and non-raw headers. Only raw headers include platform specific headers. Use non-raw headers for minimal compile-time dependencies.
  • Added a platform core count or hardware-threads detection.
  • Added a simple barrier primitive.
  • Added thread arrays to simplify creation, destruction, and control of a whole set of threads.
  • Functions do not return errno or POSIX error codes anymore but only return codes defined in amp_return_code.h.
  • Creation and destruction functions use an amp allocator for memory management.
  • Xcode test and platform check targets build and run different combinations of platform backends for easier testing and error detection than running all tests by hand.
  • Made thread id querying internal because its Pthreads implementation is currently a hack.

Version 0.0.1 (September 10, 2009)

  • Initial release
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