.. _mpi_isendrecv_replace:


MPI_Isendrecv_replace
=====================

.. include_body

:ref:`MPI_Isendrecv_replace` - Sends and receives a message using a single
buffer.


SYNTAX
------


C Syntax
^^^^^^^^

.. code-block:: c

   #include <mpi.h>

   int MPI_Isendrecv_replace(void *buf, int count, MPI_Datatype datatype,
       int dest, int sendtag, int source, int recvtag, MPI_Comm comm,
       MPI_Request *request)


Fortran Syntax
^^^^^^^^^^^^^^

.. code-block:: fortran

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


Fortran 2008 Syntax
^^^^^^^^^^^^^^^^^^^

.. code-block:: fortran

   USE mpi_f08
   MPI_Isendrecv_replace(buf, count, datatype, dest, sendtag, source, recvtag,
           comm, request, 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_Request) :: request
       INTEGER, OPTIONAL, INTENT(OUT) :: ierror


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
-----------------
* ``request``: Communication request (handle).
* ``IERROR``: Fortran only: Error status (integer).

DESCRIPTION
-----------

The non-blocking 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. The send-receive operation can be used in
conjunction with the functions described in the "Process Topologies"
chapter of the MPI Standard 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.

:ref:`MPI_Isendrecv_replace` executes a non-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.

A non-blocking send-receive request can be determined to be completed by
calling the :ref:`MPI_Wait`, :ref:`MPI_Waitany`, :ref:`MPI_Test`, or :ref:`MPI_Testany` with the
request returned by this function.


ERRORS
------

Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument.

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
:ref:`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.


.. seealso::
   :ref:`MPI_Isendrecv` :ref:`MPI_Sendrecv` :ref:`MPI_Sendrecv_replace`
