# 18.2.249. MPI_Isendrecv_replace

MPI_Isendrecv_replace — Sends and receives a message using a single buffer.

## 18.2.249.1. SYNTAX

### 18.2.249.1.1. C Syntax

    #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)

### 18.2.249.1.2. Fortran Syntax

    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

### 18.2.249.1.3. Fortran 2008 Syntax

    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

## 18.2.249.2. INPUT/OUTPUT PARAMETER

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

## 18.2.249.3. 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).

## 18.2.249.4. OUTPUT PARAMETERS

- `request`: Communication request (handle).

- `ierror`: Fortran only: Error status (integer).

## 18.2.249.5. 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.

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 MPI_Wait, MPI_Waitany, MPI_Test, or MPI_Testany with the request returned by this function.

## 18.2.249.6. ERRORS

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

Before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. If no communication object is associated with the MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler. When MPI_COMM_SELF is not initialized (i.e., before MPI_Init/MPI_Init_thread, after MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler. The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all other MPI functions.

Open MPI includes three predefined error handlers that can be used:

- `MPI_ERRORS_ARE_FATAL` Causes the program to abort all connected MPI processes.

- `MPI_ERRORS_ABORT` An error handler that can be invoked on a communicator, window, file, or session. When called on a communicator, it acts as if MPI_Abort was called on that communicator. If called on a window or file, acts as if MPI_Abort was called on a communicator containing the group of processes in the corresponding window or file. If called on a session, aborts only the local process.

- `MPI_ERRORS_RETURN` Returns an error code to the application.

MPI applications can also implement their own error handlers by calling:

- MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

- MPI_File_create_errhandler then MPI_File_set_errhandler

- MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

- MPI_Win_create_errhandler then MPI_Win_set_errhandler

Note that MPI does not guarantee that an MPI program can continue past an error.

See the MPI man page for a full list of MPI error codes.

See the Error Handling section of the MPI-3.1 standard for more information.

See also

- MPI_Isendrecv

- MPI_Sendrecv

- MPI_Sendrecv_replace