MPI_IRSEND(3)

💌 MPI_IRSEND(3) — like, the whole glow-up

okay bestie, welcome to MPI_IRSEND(3), straight out of the Open MPI manual. this is the page for MPI_Irsend and she is iconic in a very specific "i already know you're ready for this message" kind of way. sit down, hydrate, let's get into it 🫶

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✨ NAME ✨

MPI_Irsend — starts a ready-mode nonblocking send. yes. all three of those words matter. nonblocking send but make it ready mode. iykyk 💅

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🌸 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

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🎀 INPUT PARAMETERS 🎀

• buf — initial address of the send buffer (choice). this is the moment, this is the data ✨
• count — number of elements in the send buffer (integer). count her blessings, count her elements.
• datatype — datatype of each send buffer element (handle). what kind of girl is each element.
• dest — rank of destination (integer). who's getting this text 👀
• tag — message tag (integer). the little label so the receiver knows what's up.
• comm — communicator (handle). the group chat, basically.

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💖 OUTPUT PARAMETERS 💖

• request — communication request (handle). your receipt for the whole operation, keep it safe 🧾
• ierror — Fortran only: error status (integer). C girlies, you get the return value instead.

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👑 DESCRIPTION 👑

so 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, bestie). you can use that request later to query the status of the communication or to wait for its completion — literally your little tracker for the vibe check ⭐

a nonblocking send call indicates that the system may start copying data out of the send buffer. and like… here's the important part, 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. hands off. she's busy.

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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. (that's ierror, we love a consistent queen.)

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. and 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.

Open MPI includes three predefined error handlers that can be used, and they are lowkey the whole personality of this section:

• 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.
• 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. fr fr. 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. 📚

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🌈 SEE ALSO 🌈

• MPI_Rsend — her blocking cousin, go say hi 🫶

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🎀 COPYRIGHT 🎀

2003-2026, The Open MPI Community — thank you for the lore, legends 👑

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<div align="left">💅 that's the page, bestie. sign-off szn: this beauty is dated Sep 11, 2026, from MPI_IRSEND(3) with love. now go send that message — but only if they're ready ✨🦋</div>