MPI_Sendrecv(3)                    Open MPI                    MPI_Sendrecv(3)



NAME
       MPI_Sendrecv - Sends and receives a message.


SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Sendrecv(void *sendbuf, int sendcount, MPI_Datatype sendtype,
            int dest, int sendtag, void *recvbuf, int recvcount,
            MPI_Datatype recvtype, int source, int recvtag,
            MPI_Comm comm, MPI_Status *status)


Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_SENDRECV(SENDBUF, SENDCOUNT, SENDTYPE, DEST, SENDTAG,
                 RECVBUF, RECVCOUNT, RECVTYPE, SOURCE, RECVTAG, COMM,
                 STATUS, IERROR)
            <type>    SENDBUF(*), RECVBUF(*)
            INTEGER   SENDCOUNT, SENDTYPE, DEST, SENDTAG
            INTEGER   RECVCOUNT, RECVTYPE, SOURCE, RECVTAG, COMM
            INTEGER   STATUS(MPI_STATUS_SIZE), IERROR


C++ Syntax
       #include <mpi.h>
       void Comm::Sendrecv(const void *sendbuf, int sendcount, const
            Datatype& sendtype, int dest, int sendtag, void *recvbuf,
            int recvcount, const Datatype& recvtype, int source,
            int recvtag, Status& status) const

       void Comm::Sendrecv(const void *sendbuf, int sendcount, const
            Datatype& sendtype, int dest, int sendtag, void *recvbuf,
            int recvcount, const Datatype& recvtype, int source,
            int recvtag) const


INPUT PARAMETERS
       sendbuf   Initial address of send buffer (choice).

       sendcount Number of elements to send (integer).

       sendtype  Type of elements in send buffer (handle).

       dest      Rank of destination (integer).

       sendtag   Send tag (integer).

       recvcount Maximum number of elements to receive (integer).

       recvtype  Type of elements in receive buffer (handle).

       source    Rank of source (integer).

       recvtag   Receive tag (integer).

       comm      Communicator (handle).


OUTPUT PARAMETERS
       recvbuf   Initial address of receive buffer (choice).

       status    Status object (status). This refers to the receive operation.

       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-1 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 executes a blocking send and receive operation. Both send
       and receive use the same communicator, but possibly different tags. The
       send buffer and receive buffers must be disjoint, and may have
       different lengths and datatypes.

       If your application does not need to examine the status field, you can
       save resources by using the predefined constant MPI_STATUS_IGNORE as a
       special value for the status argument.


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_replace





1.4.1                            Jan 14, 2010                  MPI_Sendrecv(3)
