6.20 Change between Collective and Independent Parallel Access: NF90_VAR_PAR_ACCESS
The function NF90_VAR_PAR_ACCESS changes whether read/write operations
on a parallel file system are performed collectively (the default) or
independently on the variable. This function can only be called if the
file was created with NF90_CREATE_PAR (see NF90_CREATE_PAR) or opened
with NF90_OPEN_PAR (see NF90_OPEN_PAR).
This function is only available if the netCDF library was built with a
HDF5 library for which –enable-parallel was used, and which was
linked (like HDF5) to MPI libraries.
Calling this function affects only the open file - information about
whether a variable is to be accessed collectively or independently is
not written to the data file. Every time you open a file on a parallel
file system, all variables default to collective operations. The change
a variable to independent lasts only as long as that file is open.
The variable can be changed from collective to independent, and back,
as often as desired.
Usage
function nf90_var_par_access(ncid, varid, access)
integer, intent(in) :: ncid
integer, intent(in) :: varid
integer, intent(in) :: access
integer :: nf90_var_par_access
end function nf90_var_par_access
ncid- NetCDF ID, from a previous call to NF90_OPEN_PAR (see NF90_OPEN_PAR) or
NF90_CREATE_PAR (see NF90_CREATE_PAR).
varid- Variable ID.
access- NF90_INDEPENDENT to set this variable to independent
operations. NF90_COLLECTIVE to set it to collective operations.
Return Values
NF90_NOERR- No error.
NF90_ENOTVAR- No variable found.
NF90_ENOTNC4- Not a netCDF-4 file.
NF90_NOPAR- File not opened for parallel access.
Example
This example comes from test program nf_test/f90tst_parallel.f90. For
this test to be run, netCDF must have been built with a
parallel-enabled HDF5, and –enable-parallel-tests must have been used
when configuring netcdf.
call handle_err(nf90_var_par_access(ncid, varid, nf90_collective))
