MPI_IBSEND(3)

💌 MPI_IBSEND(3) — the Open MPI girlie's guide 💌

okay so bestie, welcome to MPI_IBSEND(3) from the Open MPI crew — this is the page where we learn how to start a nonblocking buffered send. no cap, it's a whole vibe. 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

like, yes, all three of them, we don't gatekeep language dialects here 💖

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🌈 INPUT PARAMETERS 🌈

• buf — initial address of the send buffer (choice). it's giving "here's where my data lives" energy ✨
• count — number of elements in the send buffer (integer). count 'em, bestie 🔢
• datatype — data type of each send buffer element (handle). very demure, very typed 💅
• dest — rank of the destination (integer). who's receiving this masterpiece 👑
• tag — message tag (integer). the little name tag so your receiver knows what's up 🎀
• comm — communicator (handle). the group chat itself, iykyk 💬

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⭐ OUTPUT PARAMETERS ⭐

• request — communication request (handle). this is your receipt, hold onto it fr fr 🧾
• ierror — Fortran only: error status (integer). literally just Fortran's thing 🙈

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💜 DESCRIPTION 💜

okay so MPI_Ibsend posts a buffered-mode, nonblocking send. nonblocking calls allocate a communication request object and associate it with the request handle — that's the request argument, bestie. you can use that request later to query the status of the communication or to wait for its completion. it's like a little tracker for your message 😭✨

a nonblocking send call indicates that the system may start copying data out of the send buffer. so here's the⚠️ tea: the sender should not modify any part of the send buffer after a nonblocking send operation is called, until the send completes. do not touch. hands off. it's giving "don't move my stuff while I'm packing" 💀

🚨 reminder bestie: no editing the send buffer until the send completes. that's the rule, periodt.

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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. classic 💅

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 the 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. that's a lot, but like, you got this 🫶

Open MPI includes three predefined error handlers that can be used:

• MPI_ERRORS_ARE_FATAL — causes the program to abort all connected MPI processes. dramatic but effective 💀
• 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. situational awareness, love that for us ✨
• MPI_ERRORS_RETURN — returns an error code to the application. the chill one 🌸

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. so like, plan accordingly 😭

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

those two are your besties for checking on and finishing up that request 💖

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🎀 COPYRIGHT 🎀

2003-2026, The Open MPI Community

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and that's the whole page, bestie! 💜 this iconic lil number is dated Sep 11, 2026 — shoutout to the Open MPI Community for keeping MPI_IBSEND(3) on the menu since 2003 and into 2026. slay, honestly 👑✨🦋