MPI_BUFFER_ATTACH(3)

🎀 MPI_Buffer_attach 🎀

okay bestie, this is the Open MPI manual page for MPI_Buffer_attach — the (3) one, yes. No cap, the whole vibe is: you hand MPI a user buffer so it can do buffered sends. 💅

🌸 NAME 🌸

MPI_Buffer_attach — attaches a user-defined buffer for sending. that's it, that's the function, and it's lowkey iconic. ✨

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✨ SYNTAX ✨

💻 C Syntax 💻

#include <mpi.h>

int MPI_Buffer_attach(void *buf, int size)

🧚 Fortran Syntax 🧚

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_BUFFER_ATTACH(BUF, SIZE, IERROR)
    <type>  BUF(*)
    INTEGER SIZE, IERROR

🦋 Fortran 2008 Syntax 🦋

USE mpi_f08

MPI_Buffer_attach(buffer, size, ierror)
    TYPE(*), DIMENSION(..), ASYNCHRONOUS :: buffer
    INTEGER, INTENT(IN) :: size
    INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🌸 INPUT PARAMETERS 🌸

• buf — Initial buffer address (choice). 🫶
• size — Buffer size, in bytes (integer). 📏

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🎀 OUTPUT PARAMETER 🎀

• ierror — Fortran only: Error status (integer). 💖

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✨ DESCRIPTION ✨

So basically, you're providing to MPI a buffer that lives in the user's memory, and MPI uses it for buffering outgoing messages. The buffer is used only by messages sent in buffered mode. And listen: only one buffer can be attached to a process at a time. one buffer, one process, no sharing, periodt. 💅

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📝 NOTES 📝

The size you give should be the sum of the sizes of all outstanding Bsends that you intend to have, plus MPI_BSEND_OVERHEAD bytes for each Bsend that you do. For the purposes of calculating size, you should use MPI_Pack_size. In other words, in the code

MPI_Buffer_attach( buf, size )
MPI_Bsend( ..., count=20, datatype=type1, ... );
MPI_Bsend( ..., count=40, datatype=type2, ... );

the value of size in the MPI_Buffer_attach call should be greater than the value computed by

MPI_Pack_size( 20, type1, comm, &s1 );
MPI_Pack_size( 40, type2, comm, &s2 );
size = s1 + s2 + 2 * MPI_BSEND_OVERHEAD;

MPI_BSEND_OVERHEAD gives the maximum amount of buffer space that may be used by the Bsend routines. This value is in mpi.h for C and mpif.h for Fortran. 📎

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😭 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. bestie, that's just how MPI does. 🫠

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. fr fr, do not test this unless you're ready. ⚠️

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.

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👀 SEE ALSO 👀

• MPI_Buffer_detach

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👑 COPYRIGHT 👑

2003-2026, The Open MPI Community. 💖

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xoxo, your Open MPI bestie 🫶 — this page comes from Open MPI and is dated Sep 11, 2026. slay and read the docs. 💅