int MPI_Ssend(
  void *buf,
  int count,
  MPI_Datatype datatype,
  int dest,
  int tag,
  MPI_Comm comm
);

Parameters

buf

[in] initial address of send buffer (choice)

count

[in] number of elements in send buffer (nonnegative integer)

datatype

[in] datatype of each send buffer element (handle)

dest

[in] rank of destination (integer)

tag

[in] message tag (integer)

comm

[in] communicator (handle)

Remarks

Send in synchronous mode.

A send that uses the synchronous mode can be started whether or not a matching receive was posted. However, the send will complete successfully only if a matching receive is posted, and the receive operation has started to receive the message sent by the synchronous send. Thus, the completion of a synchronous send not only indicates that the send buffer can be reused, but also indicates that the receiver has reached a certain point in its execution, namely that it has started executing the matching receive. If both sends and receives are blocking operations then the use of the synchronous mode provides synchronous communication semantics: a communication does not complete at either end before both processes rendezvous at the communication. A send executed in this mode is non-local.

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 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_COMM

Invalid communicator. A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank).

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_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_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.

Example Code

The following sample code illustrates MPI_Ssend.

#include "mpi.h"
#include <stdio.h>
 
int main(int argc, char *argv[])
{
    int rank, size, i;
    int buffer[10];
    MPI_Status status;
 
    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    if (size < 2)
    {
        printf("Please run with two processes.\n");fflush(stdout);
        MPI_Finalize();
        return 0;
    }
    if (rank == 0)
    {
        for (i=0; i<10; i++)
            buffer[i] = i;
        MPI_Ssend(buffer, 10, MPI_INT, 1, 123, MPI_COMM_WORLD);
    }
    if (rank == 1)
    {
        for (i=0; i<10; i++)
            buffer[i] = -1;
        MPI_Recv(buffer, 10, MPI_INT, 0, 123, MPI_COMM_WORLD, &status);
        for (i=0; i<10; i++)
        {
            if (buffer[i] != i)
                printf("Error: buffer[%d] = %d but is expected to be %d\n", i, buffer[i], i);
        }
        fflush(stdout);
    }
    MPI_Finalize();
    return 0;
}