MPI_BSEND(3)

📦
version 5.0.10 · 7 versions
, in ubuntu stonking

💖 MPI_Bsend — bestie edition 💖

okay so this is the Open MPI manual page for MPI_Bsend(3), and yes we are doing a buffered send today. grab a snack. 🍓

✨ SYNTAX ✨

bestie, pick your language, they all do the same iconic thing:

🌸 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 📥

the stuff you gotta hand over, no cap:

  • 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 📤

just the one, and honestly she's lowkey optional depending on your language:

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

💅 DESCRIPTION 💅

MPI_Bsend performs a buffered-mode, blocking send. that's it, that's the tea. 🫖

🎀 NOTES 🎀

okay so this send is basically a convenience function — she lets you send messages without worrying about where they get buffered, because you (yes you, main character) must have provided that buffer space with MPI_Buffer_attach <#mpi-buffer-attach>. 👑

when you're deciding how much buffer space to allocate, remember this: the buffer space is NOT available for reuse by subsequent MPI_Bsends unless you are certain that the message has been received — not just that it should have been received. like, certain certain. fr fr. 💀

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. it's giving chaos. 🙈

in C, you can force the messages to be delivered by MPI_Buffer_detach( &b, &n ); MPI_Buffer_attach( b, n ); — and yes, the MPI_Buffer_detach will not complete until all buffered messages are delivered. she waits. patiently. ✨

😭 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>/MPI_Init_thread <#mpi-init-thread>, after MPI_Finalize <#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 <#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>/MPI_Comm_spawn_multiple <#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 <#mpi-abort> was called on that communicator. If called on a window or file, acts as if MPI_Abort <#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 <#mpi-comm-create-errhandler> then MPI_Comm_set_errhandler <#mpi-comm-set-errhandler>
  • MPI_File_create_errhandler <#mpi-file-create-errhandler> then MPI_File_set_errhandler <#mpi-file-set-errhandler>
  • MPI_Session_create_errhandler <#mpi-session-create-errhandler> then MPI_Session_set_errhandler <#mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>
  • MPI_Win_create_errhandler <#mpi-win-create-errhandler> then MPI_Win_set_errhandler <#mpi-win-set-errhandler>
note that MPI does not guarantee that an MPI program can continue past an error. like, that's not a vibe, that's the rules. 😭

see the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>. 🌈

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

2003-2026, The Open MPI Community

aaaand that's the whole page, bestie!! 🦋 this was the Open MPI MPI_BSEND(3) manpage, dated Sep 10, 2026, copyright 2003-2026, The Open MPI Community. go forth and buffer responsibly, ily, mwah 💜✨🎀

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