Noncontiguous Operations

Noncontiguous operations are much like their contiguous counterparts, except that the buf, len pair is replaced by buf, count, datatype. The datatype is an struct MPIR_DATATYPE *, and the count (number of elements) replaces the len (number of bytes). The other arguments are unchanged. The routine names replace Contig with Datatype; thus, the general version of MPID_IrsendContig is MPID_IrsendDatatype.

In a heterogeneous system, all communication takes place through the noncontiguous routines (because these are the only ones with the struct MPIR_DATATYPE * needed for converting data formats). A typical use of these routines in the MPI implementation is something like

int MPI_Send( ... ) 
{ 
... 
#if !defined(MPID_HAS_HETEROGENEOUS) 
if (datatype->is_contig) { 
    MPID_SendContig( ... &error_code ); 
    } else 
#endif 
    { 
    MPID_SendDatatype( ... &error_code ); 
    } 
return error_code; 
}