Compile and Execute Programs Containing Coarrays

There are various commands, tools, and products available in the programming environment to use for compiling and executing programs containing coarrays.

ftn and aprun Options Affecting Coarrays

The compiler recognizes coarray syntax by default. The -h nocaf disables coarray syntax recognition.

Upon execution of an a.out file that has been compiled and linked with the -h caf option, an image is created and executed on every processing element assigned to the job. Images 1 through NUM_IMAGES are assigned to processing elements 0 through N$PES-1, consecutively. The functions THIS_IMAGE() and NUM_IMAGES() may be used to retrieve the image number of the current image, or the total number of images at run time, respectively.

Set the number of processing elements assigned to a job at compile time by specifying the -X option on the ftn command. The number of processing elements can also be set at run time by executing the a.out file by using the aprun command with the -n option specified. If mixed -X values are used when compiling and linking different object files, or the number of PEs specified at run time differs from that specified when compiling and linking, a run time error will be received.

Bounds checking is performed by specifying the -Rb option on the ftn command line. This feature is not implemented for codimensions of coarrays.

For more information about the ftn and aprun commands, see the ftn(1) and aprun(1) man pages.

Interoperate with Other Message Passing and Data Passing Models

Coarrays can interoperate with all other message and data passing models. This allows for the introduction of coarrays into existing application codes incrementally. However, while it may work in some cases, mixing language-based PGAS with SHMEM is not officially supported.

These models are implemented through procedure calls, so the language interaction between coarrays and these models is well defined.

MPI and SHMEM generally use processing element numbers, which start at zero, but the coarray model generally deals with image numbers, which start at one.

Coarrays are symmetric for the purposes of SHMEM programming. Pointers in coarrays of derived type, however, may not necessarily point to symmetric data.

For more information about the other message passing and data passing models, see the following man pages:

intro_mpi(3)
intro_shmem(3)

Optimize Programs with Coarrays

Programs containing coarrays benefit from all the usual steps taken to improve run time performance of code that runs on a single image.