MPI_Sendrecv_replace(3)            Open MPI            MPI_Sendrecv_replace(3)



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
       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


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.


SEE ALSO
       MPI_Sendrecv






1.4.1                            Jan 14, 2010          MPI_Sendrecv_replace(3)
