MPI_ISSEND(3)

📦
version 5.0.10 · 7 versions
, in ubuntu stonking

🦋 NAME 🦋

MPI_Issend — starts a nonblocking synchronous send. That's it, that's the whole vibe: start the send, don't wait around for it, go live your life. 💅

And hi bestie, welcome to the Open MPI manual, page MPI_ISSEND(3). This is the little corner of the docs where you learn how to fire off a message and immediately move on with your day. Iconic behavior honestly. ✨

🌸 SYNTAX 🌸

Pick your language, they all do the same slay. 💖

C Syntax

#include <mpi.h>

int MPI_Issend(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_ISSEND(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_Issend(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

🎀 INPUT PARAMETERS 🎀

Everything you gotta hand over. No gatekeeping here. 🫶

  • buf — Initial address of send buffer (choice).
  • count — Number of elements in send buffer (integer).
  • datatype — Datatype of each send buffer element (handle).
  • dest — Rank of destination (integer).
  • tag — Message tag (integer).
  • comm — Communicator (handle).

✨ OUTPUT PARAMETERS ✨

What you get back, because giving is a two-way street. 💖

  • request — Communication request (handle).
  • ierror — Fortran only: Error status (integer).

💫 DESCRIPTION 💫

Starts a synchronous mode, nonblocking send. Yes, both. It's giving multitasking main character energy. 🔥

Nonblocking calls allocate a communication request object and associate it with the request handle (the argument request). The request can be used later to query the status of the communication or wait for its completion. Basically you get a little receipt 🧾 and you can check on it whenever.

A nonblocking send call indicates that the system may start copying data out of the send buffer. The sender should not modify any part of the send buffer after a nonblocking send operation is called, until the send completes.

⚠️ Bestie. Listen. Once you call this, that buffer is not yours until the send completes. Do not touch it. Do not "just tweak one field." The buffer is booked and busy. 🙈

💀 ERRORS 💀

Okay so, error handling. Buckle up, this part is long but it's all tea you actually need. 😭

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.

💀 fr fr, do not assume your program lives through an error. It might just be over. Periodt.

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_Ssend

2003-2026, The Open MPI Community

And that's the whole page, bestie, you made it to the end and I'm so proud of you. 🥹💜 This edition of the Open MPI MPI_ISSEND(3) manual page was dated Sep 10, 2026 — go forth and send synchronously-but-nonblockingly, and remember: don't touch the buffer. 🌈✨

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