MPI_FILE_IREAD(3)

💅 MPI_FILE_IREAD(3) — Open MPI, bestie ✨

okay so this is the Open MPI page for MPI_File_iread, and yes we're gonna get through it together 🫶

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🌸 NAME 🌸

MPI_File_iread — reads a file starting at the location specified by the individual file pointer (nonblocking, noncollective). like, it does NOT wait around for you, it's got main character energy 💅

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✨ SYNTAX ✨

🎀 C Syntax

#include <mpi.h>

int MPI_File_iread(MPI_File fh, void  *buf, int  count,
     MPI_Datatype  datatype, MPI_Request  *request)

🎀 Fortran Syntax

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

🎀 Fortran 2008 Syntax

USE mpi_f08
MPI_File_iread(fh, buf, count, datatype, request, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     TYPE(*), DIMENSION(..), ASYNCHRONOUS :: buf
     INTEGER, INTENT(IN) :: count
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     TYPE(MPI_Request), INTENT(OUT) :: request
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🦋 INPUT/OUTPUT PARAMETER 🦋

• fh — file handle (handle). it's the file, bestie, the whole vibe check for which file we're talking to.

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🌈 INPUT PARAMETERS 🌈

• count — number of elements in the buffer (integer). how many lil guys are we reading 👀
• datatype — data type of each buffer element (handle). what kind of guys are they.

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⭐ OUTPUT PARAMETERS ⭐

• buf — initial address of buffer (choice). your lil landing spot for the data 💖
• request — request object (handle). this is your ticket to check on it later, don't lose it.
• ierror — Fortran only: error status (integer).

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🔥 DESCRIPTION 🔥

MPI_File_iread is the nonblocking version of MPI_File_read. literally the same energy, just doesn't make you wait around 😌

So it attempts to read from the file associated with fh at the current individual file pointer position maintained by the system, in which a total number of count data items having datatype type are read into the user's buffer buf. The data is taken out of those parts of the file specified by the current view. MPI_File_iread stores the number of data-type elements actually read in status. All other fields of status are undefined. 🫠

🚨 it is erroneous to call this function if MPI_MODE_SEQUENTIAL mode was specified when the file was opened. like, don't. fr fr.

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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. iykyk.

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. bestie, that is a LOT of responsibility on one error handler 😭

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 much? 💀
• 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. so many contexts, so much power 👑
• MPI_ERRORS_RETURN — returns an error code to the application. the chill one, the reasonable one, the one you probably want 🫶

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 bank on it, bestie.

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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🧚 COPYRIGHT 🧚

2003-2026, The Open MPI Community

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and that's the whole page, bestie, you ate that 💖✨ this was MPI_FILE_IREAD(3) from Open MPI, dated Sep 11, 2026 — go forth and read nonblockingly, periodt 🎀🦋