MPP FUNCTION DESCRIPTIONS

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MPP FUNCTION DESCRIPTIONS

Additional functions for use on SGI/Cray MPP machines (_CRAYMPP). These are used to set and inquire which PE is the base for MPP for a particular netCDF. These are only relevant when using the SGI/Cray ``global'' Flexible File I/O layer and desire to have only a subset of PEs to open the specific netCDF file. For technical reasons, these functions are available on all platforms. On a platform other than SGI/Cray MPP, it is as if only processor avail- able were processor 0.

To use this feature, you need to specify a communicator group and call glio_group_mpi() or glio_group_shmem() prior to the netCDF nc_open() and nc_create() calls.

int nc__create_mp(const char path[], int cmode, size_t ini- tialsize, int pe, size_t* chunksize, int* ncid)

Like nc__create() but allows the base PE to be set.

The argument pe sets the base PE at creation time. In the MPP environment, nc__create() and nc_create() set the base PE to processor zero by default.

int nc__open_mp(const char path[], int mode, int pe, size_t* chunksize, int* ncid)

Like nc__open() but allows the base PE to be set. The argument pe sets the base PE at creation time. In the MPP environment, nc__open() and nc_open() set the base PE to processor zero by default.

int nc_inq_base_pe(int ncid, int* pe)

Inquires of the netCDF dataset which PE is being used as the base for MPP use. This is safe to use at any time.

int nc_set_base_pe(int ncid, int pe)

Resets the base PE for the netCDF dataset. Only per- form this operation when the affected communicator group synchronizes before and after the call. This operation is very risky and should only be contemplated under only the most extreme cases.

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