MPI_IBSEND(3)

💅 MPI_Ibsend 💅

okay bestie, gather round, because this one is literally the Open MPI manual page for MPI_Ibsend, and it's giving buffered nonblocking send energy. Sit down, hydrate, and let's get into it. 🫶

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✨ SYNTAX ✨

🌸 C Syntax

#include <mpi.h>

int MPI_Ibsend(const void *buf, int count, MPI_Datatype datatype,
     int dest, int tag, MPI_Comm comm, MPI_Request *request)

🌸 Fortran Syntax

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

🌸 Fortran 2008 Syntax

USE mpi_f08
MPI_Ibsend(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

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📥 INPUT PARAMETERS 📥

• buf — the initial address of your send buffer (choice).
• count — how many elements are in that send buffer (integer).
• datatype — the data type of each element in the send buffer (handle).
• dest — rank of the destination, aka who you're sending to (integer).
• tag — the message tag (integer).
• comm — the communicator (handle).

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📤 OUTPUT PARAMETERS 📤

• request — the communication request (handle).
• ierror — Fortran only: error status (integer).

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🌈 DESCRIPTION 🌈

So MPI_Ibsend posts a buffered-mode, nonblocking send. Nonblocking calls allocate a communication request object and then associate it with the request handle — that's your request argument, bestie, she's the one holding the receipts. 💅 You can use that request later to query the status of the communication or to wait for it to complete.

A nonblocking send call means the system may start copying data out of the send buffer. So here's the thing that will absolutely ruin your whole day if you ignore it: the sender should not modify any part of the send buffer after a nonblocking send operation is called, until the send completes. No cap. Do not touch the buffer. She is busy. 🚫

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😭 ERRORS 😭

Almost all MPI routines return an error value — C routines hand it back as the return result of the function, and Fortran routines put it in the last argument.

Before that error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) gets called. If there's no communication object associated with the MPI call, then the call is considered attached to MPI_COMM_SELF and it 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 you're using the Sessions Model exclusively — the error raises the initial error handler. That initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or by the mpi_initial_errhandler CLI argument to mpiexec, or by the info key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. And 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 ships three predefined error handlers, bestie, and they are:

• 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, it 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, it 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. 🫠

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_Test
• MPI_Wait

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👑 Copyright 👑

2003-2026, The Open MPI Community

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and that's the whole page, babe — written by the Open MPI girlies, dated Sep 10, 2026, living in section 3 of the manual as MPI_IBSEND(3) under the Open MPI banner. go forth and send, but do not touch that buffer. mwah. 💖🦋✨