MPI_FILE_IREAD_ALL(3)

💖 MPI_FILE_IREAD_ALL(3) — Open MPI 💖

okay bestie, sit down, hydrate, because we're about to read a whole file together (well, collectively, but not blocking, iykyk) 🫶 the manual is MPI_FILE_IREAD_ALL(3) from Open MPI and it's giving ✨nonblocking collective I/O✨

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🌸 NAME 🌸

MPI_File_iread_all — reads a file starting at the location specified by the individual file pointer (nonblocking, collective). no cap, that's the whole vibe 💅

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✨ SYNTAX ✨

🎀 C Syntax

#include <mpi.h>

int MPI_File_iread_all(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_ALL(FH, BUF, COUNT, DATATYPE, REQUEST, IERROR)
     <type>  BUF(*)
     INTEGER FH, COUNT, DATATYPE, REQUEST, IERROR

🎀 Fortran 2008 Syntax

USE mpi_f08
MPI_File_iread_all(fh, buf, count, datatype, request, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     TYPE(*), DIMENSION(..) :: 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 literally the glow-up passport to your file 💖

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🌈 INPUT PARAMETERS 🌈

• count — number of elements in the buffer (integer). yes bestie, elements, not bytes, we're fancy 💅
• datatype — data type of each buffer element (handle). 💫

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🎀 OUTPUT PARAMETERS 🎀

• buf — initial address of buffer (choice). this is where the good stuff lands 🍓
• request — request object (handle). hold onto it, you'll need it later bestie 🫶
• ierror — Fortran only: error status (integer). 🌸

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💜 DESCRIPTION 💜

So MPI_File_iread_all is the nonblocking version of MPI_File_read_all. iconic lineage, honestly 👑

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. 👀

Then MPI_File_iread_all stores the number of data-type elements actually read in status. All other fields of status are undefined. so don't go looking at the rest of it, it's giving mystery ✨

🚨 NO CAP WARNING: it is erroneous to call this function if MPI_MODE_SEQUENTIAL mode was specified when the file was opened. that's not a drill bestie, that's an error 💀

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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.

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. it's giving dramatic exit 💀
• 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. nuanced queen 👑
• MPI_ERRORS_RETURN — returns an error code to the application. polite, respectful, we love her 💖

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. 😭

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, ate and left no crumbs 🧚✨ this was the MPI_FILE_IREAD_ALL(3) vibe check, dated Sep 10, 2026, from the Open MPI sweeties at The Open MPI Community — go read something already, nonblocking ofc 💅🫶🌈