---
name: "MPI_Bsend"
section: "3"
platform: "linux"
package: "openmpi"
version: "5.0.11-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/MPI_Bsend"
---

# MPI\_Bsend(3)

*MPI\_Bsend* — Basic send with user-specified buffering.

## SYNTAX

### C Syntax

```
#include <mpi.h>
int MPI_Bsend(const void *buf, int count, MPI_Datatype datatype,
   int dest, int tag, MPI_Comm comm)
```

### Fortran Syntax

```
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_BSEND(BUF, COUNT,DATATYPE, DEST, TAG, COMM, IERROR)
    <type>  BUF(*)
    INTEGER COUNT, DATATYPE, DEST, TAG, COMM, IERROR
```

### Fortran 2008 Syntax

```
USE mpi_f08
MPI_Bsend(buf, count, datatype, dest, tag, comm, ierror)
    TYPE(*), DIMENSION(..), INTENT(IN) :: buf
    INTEGER, INTENT(IN) :: count, dest, tag
    TYPE(MPI_Datatype), INTENT(IN) :: datatype
    TYPE(MPI_Comm), INTENT(IN) :: comm
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror
```

## INPUT PARAMETERS

- •

  **buf** : Initial address of send buffer (choice).

- •

  **count** : Number of entries in send buffer (nonnegative integer).

- •

  **datatype** : Datatype of each send buffer element (handle).

- •

  **dest** : Rank of destination (integer).

- •

  **tag** : Message tag (integer).

- •

  **comm** : Communicator (handle).

## OUTPUT PARAMETERS

- •

  **ierror** : Fortran only: Error status (integer).

## DESCRIPTION

*MPI\_Bsend* performs a buffered-mode, blocking send.

## NOTES

This send is provided as a convenience function; it allows the user to send messages without worrying about where they are buffered (because the user must have provided buffer space with *MPI\_Buffer\_attach*).

In deciding how much buffer space to allocate, remember that the buffer space is not available for reuse by subsequent *MPI\_Bsend*s unless you are certain that the message has been received (not just that it should have been received). For example, this code does not allocate enough buffer space:

```
MPI_Buffer_attach( b, n*sizeof(double) + MPI_BSEND_OVERHEAD );
for (i=0; i<m; i++) {
    MPI_Bsend( buf, n, MPI_DOUBLE, ... );
}
```

because only enough buffer space is provided for a single send, and the loop may start a second **MPI\_Bsend** before the first is done making use of the buffer.

In C, you can force the messages to be delivered by **MPI\_Buffer\_detach( &b, &n );** **MPI\_Buffer\_attach( b, n );** (The **MPI\_Buffer\_detach** will not complete until all buffered messages are delivered.)

## 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.

## COPYRIGHT

2003-2026, The Open MPI Community