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This is another example of writing data into disconnected locations in a file. Each process writes data from the contiguous buffer into regularly scattered locations in the file.

Each process defines a hyperslab in the file as described below and writes data to it. The C and Fortran 90 examples below result in the same data layout in the file.

 

Figure a   C ExampleFigure b   FORTRAN 90 Example

The C and Fortran 90 examples use four processes to write the pattern shown above. Each process defines a hyperslab by:

  • Specifying a stride of 2 for each dimension, which indicates that you wish to write to every other position along a dimension.

     

  • Specifying a different offset for each process:
    C:
       Process 0        Process 1       Process 2       Process 3
       ---------        ---------       ---------       ---------
       offset[0] = 0    offset[0] = 1   offset[0] = 0   offset[0] = 1
       offset[1] = 0    offset[1] = 0   offset[1] = 1   offset[1] = 1
    
    FORTRAN 90:
    
       offset(1) = 0    offset(1) = 0   offset(1) = 1   offset(1) = 1
       offset(2) = 0    offset(2) = 1   offset(2) = 0   offset(2) = 1
    
    
  • Specifying the size of the slab to write. The count is the number of positions along a dimension to write to. If writing a 4 x 2 slab, then the count would be:
    C:                        FORTRAN 90:
       count[0] = 4             count(1) =  2
       count[1] = 2             count(2) =  4 
    

For example, the offset, count, and stride parameters for Process 2 would look like:

 

Figure a   C ExampleFigure b   FORTRAN 90 Example

Below are example programs for writing hyperslabs by pattern in Parallel HDF5:

     C    F90

The following is the output from h5dump for the HDF5 file created in this example:

HDF5 "SDS_pat.h5" {
GROUP "/" {
   DATASET "IntArray" {
      DATATYPE  H5T_STD_I32BE  
      DATASPACE  SIMPLE { ( 8, 4 ) / ( 8, 4 ) } 
      DATA {
         1, 3, 1, 3,
         2, 4, 2, 4,
         1, 3, 1, 3,
         2, 4, 2, 4,
         1, 3, 1, 3,
         2, 4, 2, 4,
         1, 3, 1, 3,
         2, 4, 2, 4
      } 
   } 
} 
} 

The h5dump utility is written in C so the output is in C order.

--- Last Modified: August 16, 2017 | 03:46 PM