DeinoMPI

The Great and Terrible implementation of MPI-2

function index

MPI_Recv_init

Create a persistent request for a receive
int MPI_Recv_init(
  void *buf,
  int count,
  MPI_Datatype datatype,
  int source,
  int tag,
  MPI_Comm comm,
  MPI_Request *request
);

Parameters

buf
[in] initial address of receive buffer (choice)
count
[in] number of elements received (integer)
datatype
[in] type of each element (handle)
source
[in] rank of source or MPI_ANY_SOURCE (integer)
tag
[in] message tag or MPI_ANY_TAG (integer)
comm
[in] communicator (handle)
request
[out] communication request (handle)

Remarks

Creates a persistent communication request for a receive operation. The argument buf is marked as OUT because the user gives permission to write on the receive buffer by passing the argument to MPI_RECV_INIT.

A persistent communication request is inactive after it was created --- no active communication is attached to the request.

A communication (send or receive) that uses a persistent request is initiated by the function MPI_START.

Thread and Interrupt Safety

This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as malloc or other non-MPICH runtime routines that are themselves not interrupt-safe.

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) have an additional argument ierr at the end of the argument list. ierr is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the call statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGER in Fortran.

Errors

All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Comm_set_errhandler (for communicators), MPI_File_set_errhandler (for files), and MPI_Win_set_errhandler (for RMA windows). The MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible.

MPI_SUCCESS
No error; MPI routine completed successfully.
MPI_ERR_COUNT
Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
MPI_ERR_TYPE
Invalid datatype argument. May be an uncommitted MPI_Datatype (see MPI_Type_commit).
MPI_ERR_RANK
Invalid source or destination rank. Ranks must be between zero and the size of the communicator minus one; ranks in a receive (MPI_Recv, MPI_Irecv, MPI_Sendrecv, etc.) may also be MPI_ANY_SOURCE.
MPI_ERR_TAG
Invalid tag argument. Tags must be non-negative; tags in a receive (MPI_Recv, MPI_Irecv, MPI_Sendrecv, etc.) may also be MPI_ANY_TAG. The largest tag value is available through the the attribute MPI_TAG_UB.
MPI_ERR_COMM
Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).
MPI_ERR_INTERN
This error is returned when some part of the MPICH implementation is unable to acquire memory.

See Also

MPI_Start, MPI_Startall, MPI_Request_free

Example Code

The following sample code illustrates MPI_Recv_init.

#include "mpi.h"
#include <stdlib.h>
 
int main(int argc, char *argv[])
{
    MPI_Request r;
    MPI_Status s;
    int flag;
   
int buf[10];
    int rbuf[10];
    int tag = 27;
    int dest = 0;
    int rank, size, i;
 
    MPI_Init( &argc, &argv );
    MPI_Comm_size( MPI_COMM_WORLD, &size );
    MPI_Comm_rank( MPI_COMM_WORLD, &rank );
 
    /* Create a persistent send request */
    MPI_Send_init( buf, 10, MPI_INT, dest, tag, MPI_COMM_WORLD, &r );
 
    /* Use that request */
   
if (rank == 0) {
       
int i;
        MPI_Request *rr = (MPI_Request *)malloc(size *
sizeof(MPI_Request));
       
for (i=0; i<size; i++) {
            MPI_Irecv( rbuf, 10, MPI_INT, i, tag, MPI_COMM_WORLD, &rr[i] );
        }
        MPI_Start( &r );
        MPI_Wait( &r, &s );
        MPI_Waitall( size, rr, MPI_STATUSES_IGNORE );
        free(rr);
    }
    else {
        MPI_Start( &r );
        MPI_Wait( &r, &s );
    }
 
    MPI_Request_free( &r );
 
 
    if (rank == 0)
    {
        MPI_Request rr;
        /* Create a persistent receive request */
        MPI_Recv_init( rbuf, 10, MPI_INT, MPI_ANY_SOURCE, tag, MPI_COMM_WORLD, &r );
        MPI_Isend( buf, 10, MPI_INT, 0, tag, MPI_COMM_WORLD, &rr );
        for (i=0; i<size; i++) {
            MPI_Start( &r );
            MPI_Wait( &r, &s );
        }
        MPI_Wait( &rr, &s );
        MPI_Request_free( &r );
    }
   
else {
        MPI_Send( buf, 10, MPI_INT, 0, tag, MPI_COMM_WORLD );
    }
 
    MPI_Finalize();
   
return 0;
}