MPI\_ISEND(3) Open MPI MPI\_ISEND(3)

MPI\_Isend — Starts a standard-mode, nonblocking send.

# [SYNTAX](#SYNTAX)

## [C Syntax](#C_Syntax)

```
#include <mpi.h>
int MPI_Isend(const void *buf, int count, MPI_Datatype datatype, int dest,


     int tag, MPI_Comm comm, MPI_Request *request)
```

## [Fortran Syntax](#Fortran_Syntax)

```
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_ISEND(BUF, COUNT, DATATYPE, DEST, TAG, COMM, REQUEST, IERROR)


     <type>  BUF(*)


     INTEGER COUNT, DATATYPE, DEST, TAG, COMM, REQUEST, IERROR
```

## [Fortran 2008 Syntax](#Fortran_2008_Syntax)

```
USE mpi_f08
MPI_Isend(buf, count, datatype, dest, tag, comm, request, ierror)


     TYPE(*), DIMENSION(..), INTENT(IN), ASYNCHRONOUS :: buf


     INTEGER, INTENT(IN) :: count, dest, tag


     TYPE(MPI_Datatype), INTENT(IN) :: datatype


     TYPE(MPI_Comm), INTENT(IN) :: comm


     TYPE(MPI_Request), INTENT(OUT) :: request


     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
```

# [INPUT PARAMETERS](#INPUT_PARAMETERS)

- **buf**: Initial address of send buffer (choice).
- **count**: Number of elements in send buffer (integer).
- **datatype**: Datatype of each send buffer element (handle).
- **dest**: Rank of destination (integer).
- **tag**: Message tag (integer).
- **comm**: Communicator (handle).

# [OUTPUT PARAMETERS](#OUTPUT_PARAMETERS)

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

# [DESCRIPTION](#DESCRIPTION)

MPI\_Isend starts a standard-mode, nonblocking send. Nonblocking calls allocate a communication request object and associate it with the request handle (the argument request). The request can be used later to query the status of the communication or wait for its completion.

A nonblocking send call indicates that the system may start copying data out of the send buffer. The sender should not modify any part of the send buffer after a nonblocking send operation is called, until the send completes.

A send request can be determined being completed by calling the MPI\_Wait &lt;#mpi-wait&gt;, MPI\_Waitany &lt;#mpi-waitany&gt;, MPI\_Test &lt;#mpi-test&gt;, or MPI\_Testany &lt;#mpi-testany&gt; with request returned by this function.

# [ERRORS](#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 &lt;#mpi-init&gt;/MPI\_Init\_thread &lt;#mpi-init-thread&gt;, after MPI\_Finalize &lt;#mpi-finalize&gt;, 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 &lt;#mpi-comm-set-errhandler&gt; 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 &lt;#mpi-comm-spawn&gt;/MPI\_Comm\_spawn\_multiple &lt;#mpi-comm-spawn-multiple&gt;. 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 &lt;#mpi-abort&gt; was called on that communicator. If called on a window or file, acts as if MPI\_Abort &lt;#mpi-abort&gt; 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 &lt;#mpi-comm-create-errhandler&gt; then MPI\_Comm\_set\_errhandler &lt;#mpi-comm-set-errhandler&gt;
- MPI\_File\_create\_errhandler &lt;#mpi-file-create-errhandler&gt; then MPI\_File\_set\_errhandler &lt;#mpi-file-set-errhandler&gt;
- MPI\_Session\_create\_errhandler &lt;#mpi-session-create-errhandler&gt; then MPI\_Session\_set\_errhandler &lt;#mpi-session-set-errhandler&gt; or at MPI\_Session\_init &lt;#mpi-session-init&gt;
- MPI\_Win\_create\_errhandler &lt;#mpi-win-create-errhandler&gt; then MPI\_Win\_set\_errhandler &lt;#mpi-win-set-errhandler&gt;

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

See the MPI man page &lt;#open-mpi&gt; for a full list of MPI error codes &lt;#open-mpi-errors&gt;.

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

**See also:**

- MPI\_Send &lt;#mpi-send&gt;
- MPI\_Wait &lt;#mpi-wait&gt;
- MPI\_Waitany &lt;#mpi-waitany&gt;
- MPI\_Test &lt;#mpi-test&gt;
- MPI\_Testany &lt;#mpi-testany&gt;

# [Copyright](#Copyright)

2003-2026, The Open MPI Community

October 9, 2026

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Document: MPI_Isend(3) from openmpi-cuda-13.2 5.0.11-r1 (Chainguard OS)
Source: https://github.com/open-mpi/ompi