MPI_IRSEND(3)

💖 MPI_IRSEND 💖 — like, the manual page, but make it make sense

okay bestie, welcome to MPI_IRSEND(3) from the Open MPI collection 🎀 this is the page for MPI_Irsend, and yes it's giving "nonblocking ready-mode send" energy. stay with me, it's actually so good.

---

✨ SYNTAX ✨

🌸 C Syntax

#include <mpi.h>

int MPI_Irsend(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_IRSEND(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_Irsend(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 🫶

the stuff you hand over, no take-backsies:

• buf — the initial address of the send buffer (choice). like, where your data lives 💖
• count — number of elements in the send buffer (integer).
• datatype — datatype of each send buffer element (handle).
• dest — rank of the destination (integer). who's getting this 🎯
• tag — message tag (integer).
• comm — communicator (handle).

💅 OUTPUT PARAMETERS 💅

the stuff it hands back to you:

• request — communication request (handle). hold onto this, bestie, it's your receipt 🧾
• ierror — Fortran only: error status (integer).

---

🌈 DESCRIPTION 🌈

MPI_Irsend starts a ready-mode nonblocking send. nonblocking calls allocate a communication request object and associate it with the request handle — that's the request argument, the one we just talked about 💖. you can use that request later to query the status of the communication, or to wait for its completion. it's literally your little tracker for the vibe of this send ✨

a nonblocking send call indicates that the system may start copying data out of the send buffer. so here's the rule that matters, no cap:

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 it. hands off. main character restraint.

---

😭 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 that error value comes back, 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 counts as attached to MPI_COMM_SELF and will call the associated MPI error handler. and 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. the initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or with the mpi_initial_errhandler CLI argument to mpiexec, or 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 includes three predefined error handlers you can use:

• 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. so like, don't count on it 🫠

see the MPI man page for a full list of MPI error codes, and see the Error Handling section of the MPI-3.1 standard for more information.

also see:

• MPI_Rsend 👑

---

🎀 Copyright 🎀

2003-2026, The Open MPI Community

---

okay that's the whole page, you ate it 💅✨ this was the MPI_IRSEND(3) manual page from Open MPI, dated Sep 10, 2026, and the copyright is held by The Open MPI Community (2003-2026). go forth and send in ready mode, bestie 🦋 no cap. periodt. 💖