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