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OpenCoarrays supports the GNU Compiler Collection (GCC) Fortran compiler (gfortran) by providing a parallel application binary interface (ABI) that abstracts away the underlying communication library. OpenCoarrays thus enables gfortran to support Fortran's parallel programming features, often called "Coarray Fortran," without making direct reference to the back-end communication library: the Message Passing Interface (MPI). This ensures that Fortran programs and Fortran compilers may take advantage of other communication libraries without costly refactoring. Work is underway on the Caffeine project to support alternative communication libraries and alternative compilers by defining a compiler-independent parallel ABI atop the GASNet-EX exascale networking middleware.

OpenCoarrays provides a compiler wrapper (caf), a parallel runtime library (libcaf_mpi), and a program launcher (cafrun). The wrapper and launcher provide a uniform abstraction for compiling and executing Coarray Fortran without direct reference to the underlying MPI layer.


Please see our Releases page.


The OpenCoarrays ABI was adopted by gfortran in release the GCC 5.1.0 release and gfortran continues to work with OpenCoarrays as of this writing.


Building OpenCoarrays requires

  • An MPI implementation,
  • CMake, and
  • The GCC C and Fortran compilers: gcc and gfortran.

If you use a package manager or the OpenCoarrays installer, any missing prerequisites will be built for you.


Please see the file.

Or try OpenCoarrays online as a Jupyter notebook kernel using Binder with no downloads, configuration or installation required. The default index.ipynb notebook is read only, but you can execute it, copy it to make changes, or create an entirely new CAF kernel notebook.

Packaged Version

If you would like to be able to install OpenCoarrays through your favorite package manager, please ask them to add it, or contribute it yourself. If you see your favorite package manager has an outdated version, please ask them to update it, or contribute an update yourself.

Packaging status

Getting Started

To start using OpenCoarrays, please see the file.


Please see the file.


A list of open issues can be viewed on the issues page.


Please submit bug reports and feature requests via our Issues page.


We gratefully acknowledge support from the following institutions:

  • The U.S. Nuclear Regulatory Commission (NRC) for funding the work that led to support for
    • the Windows operating system,
    • the random_init subroutine, and
    • co_broadcast of derived-type objects with allocatable components.
  • The National Aeronautics and Space Administration NASA for funding the work that led to support for the co_broadcast of derived-type objects.
  • Arm for approving compiler engineer contributions of code.
  • National Center for Atmospheric Research for access to the Yellowstone/Caldera supercomputers and for logistics support during the initial development of OpenCoarrays.
  • CINECA for access to Eurora/PLX for the project HyPS- BLAS under the ISCRA grant program for 2014.
  • Google for support of a related Google Summer of Code 2014 project.
  • The National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, for access to the Hopper and Edison supercomputers under the OpenCoarrays project start allocation.
  • Archaeologic Inc. for financial support for the domain registration, web hosting, advanced development, and conference travel.


If you find this software useful, please consider donating your time or your money to aid in development efforts.

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