Ubuntu Manpage: MPI_Sendrecv_replace - Sends and receives a message using a single buffer.

Provided by: openmpi-doc_4.1.6-7ubuntu2_all

NAME

       MPI_Sendrecv_replace - Sends and receives a message using a single buffer.

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Sendrecv_replace(void *buf, int count, MPI_Datatype datatype,
            int dest, int sendtag, int source, int recvtag, MPI_Comm comm,
            MPI_Status *status)

Fortran Syntax

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_SENDRECV_REPLACE(BUF, COUNT, DATATYPE, DEST, SENDTAG, SOURCE,
                 RECVTAG, COMM, STATUS, IERROR)
            <type>    BUF(*)
            INTEGER   COUNT, DATATYPE, DEST, SENDTAG
            INTEGER   SOURCE, RECVTAG, COMM
            INTEGER   STATUS(MPI_STATUS_SIZE), IERROR

Fortran 2008 Syntax

       USE mpi_f08
       MPI_Sendrecv_replace(buf, count, datatype, dest, sendtag, source, recvtag,
                 comm, status, ierror)
            TYPE(*), DIMENSION(..) :: buf
            INTEGER, INTENT(IN) :: count, dest, sendtag, source, recvtag
            TYPE(MPI_Datatype), INTENT(IN) :: datatype
            TYPE(MPI_Comm), INTENT(IN) :: comm
            TYPE(MPI_Status) :: status
            INTEGER, OPTIONAL, INTENT(OUT) :: ierror

C++ Syntax

       #include <mpi.h>
       void Comm::Sendrecv_replace(void* buf, int count, const
            Datatype& datatype, int dest, int sendtag, int source,
            int recvtag, Status& status) const

       void Comm::Sendrecv_replace(void* buf, int count, const
            Datatype& datatype, int dest, int sendtag, int source,
            int recvtag) const

INPUT/OUTPUT PARAMETER

       buf       Initial address of send and receive buffer (choice).

INPUT PARAMETERS

       count     Number of elements in send and receive buffer (integer).

       datatype  Type of elements to send and receive (handle).

       dest      Rank of destination (integer).

       sendtag   Send message tag (integer).

       source    Rank of source (integer).

       recvtag   Receive message tag (integer).

       comm      Communicator (handle).

OUTPUT PARAMETERS

       status    Status object (status).

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

The send-receive operations combine in one call the sending of a message to one destination and the
receiving of another message, from another process. The two (source and destination) are possibly the
same. A send-receive operation is useful for executing a shift operation across a chain of processes. If
blocking sends and receives are used for such a shift, then one needs to order the sends and receives
correctly (for example, even processes send, then receive; odd processes receive first, then send) in
order to prevent cyclic dependencies that may lead to deadlock. When a send-receive operation is used,
the communication subsystem takes care of these issues. The send-receive operation can be used in
conjunction with the functions described in Chapter 6 of the MPI Standard, "Process Topologies," in order
to perform shifts on various logical topologies. Also, a send-receive operation is useful for
implementing remote procedure calls.

A message sent by a send-receive operation can be received by a regular receive operation or probed by a
probe operation; a send-receive operation can receive a message sent by a regular send operation.

MPI_Sendrecv_replace executes a blocking send and receive. The same buffer is used both for the send and
for the receive, so that the message sent is replaced by the message received.

The semantics of a send-receive operation is what would be obtained if the caller forked two concurrent
threads, one to execute the send, and one to execute the receive, followed by a join of these two
threads.

ERRORS

       Almost  all  MPI  routines  return  an  error  value; C routines as the value of the function and Fortran
       routines in the last argument. C++ functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the  C++  exception  mechanism  will  be  used  to  throw  an
       MPI::Exception object.

       Before  the  error  value  is  returned,  the current MPI error handler is called. By default, this error
       handler aborts the MPI job, except for I/O function  errors.  The  error  handler  may  be  changed  with
       MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values
       to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.