Subroutines for parallel I/O

Current implementations do not contain support for parallel I/O operations, since at this time there is little consensus about how to support parallel I/O in a portable way. It is not difficult, however, for applications to perform a simple type of parallel I/O using the following approach. Data can be written as follows:

1. Each grid process opens a uniquely-named file. (The filename should be generated using the subroutine fname, described below.)
2. Each grid process writes its local section to its file using standard Fortran I/O in whatever format the user chooses.
3. If necessary, after the program completes, a separate utility program combines the separate files (each containing data from a single local section) into a single file containing data from the whole array.

Reading data is analogous; if necessary, a separate utility program splits a single file into separate files for the individual grid processes.

In addition, one of our implementations contains a set of routines for ``portable parallel I/O'', which take the above approach but use machine-independent formats for disk data. Two formats are provided, compressed and uncompressed. Additional utility programs are required to translate this machine-independent format to a standard Fortran I/O format.

These subroutines and utility programs are briefly described below. For more information, communicate with the author of this document (berna@cs.caltech.edu) or Rajit Manohar (rajit@cs.caltech.edu).

Subroutines

• Subroutines to open parallel I/O files:

          subroutine mesh_openwrite(filename, ifd)
          subroutine mesh_openread(filename, ifd)
          subroutine mesh_copenwrite(filename, ifd)
          subroutine mesh_copenread(filename, ifd)

• Subroutines to write to parallel I/O files:

          subroutine mesh_cwrite(ifd, array)
          subroutine mesh_write(ifd, array)

• Subroutines to read from parallel I/O files:

          subroutine mesh_cread(ifd, array)
          subroutine mesh_read(ifd, array)

• Subroutines to close parallel I/O files:

          subroutine mesh_cclose(ifd)
          subroutine mesh_close(ifd)

Utility programs

• Program split splits a single file (compressed or uncompressed format) into files for use by the parallel I/O read subroutines.
• Program merge merges files generated by the parallel I/O write routines (compressed or uncompressed format) into a single file.
• Programs to convert from standard formats to the machine-independent compressed or uncompressed format are in work.