MPI_FILE_IREAD_AT_ALL(3)

💅 MPI_FILE_IREAD_AT_ALL(3) — an Open MPI moment 🦋

okay so bestie, welcome to MPI_FILE_IREAD_AT_ALL from the Open MPI manuals, and no cap this one is a bop: it reads a file at an explicitly specified offset, nonblocking and collective. yes, all of that at once. she contains multitudes 💖

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✨ NAME ✨

MPI_File_iread_at_all — Reads a file at an explicitly specified offset (nonblocking, collective).

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🌸 SYNTAX 🌸

C Syntax 🎀

#include <mpi.h>

int MPI_File_iread_at_all(MPI_File fh, MPI_Offset offset,
     void *buf, int count, MPI_Datatype datatype,
     MPI_Request *request)

Fortran Syntax 🧚

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

Fortran 2008 Syntax ⭐

USE mpi_f08
MPI_File_iread_at_all(fh, offset, buf, count, datatype, request, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     INTEGER(KIND=MPI_OFFSET_KIND), INTENT(IN) :: offset
     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 PARAMETERS 🫶

• fh — File handle (handle). the lil passport for your file, iykyk.
• offset — File offset (integer).
• count — Number of elements in the buffer (integer).
• datatype — Data type of each buffer element (handle).

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💜 OUTPUT PARAMETERS 💜

• buf — Initial address of the buffer (choice).
• request — Request object (handle).
• ierror — Fortran only: Error status (integer).

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🔥 DESCRIPTION 🔥

So MPI_File_iread_at_all is literally the nonblocking version of MPI_File_read_at_all. like, same energy, but she doesn't wait around 💀

MPI_File_iread_at_all is a nonblocking routine that attempts to read from the file associated with fh at the offset position, a total number of count data items having datatype type, into the user's buffer buf. iconic behaviour, genuinely.

The offset is in etype units relative to the current view. That is, holes are not counted when locating an offset — so don't go counting the gaps, bestie, that's not the vibe. The data is taken out of those parts of the file specified by the current view. 🌈

MPI_File_iread_at_all stores the number of datatype elements actually read in status. All other fields of status are undefined — so like, don't go reading into them, they're not giving anything useful 🙈

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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. 💀 yeah. all of them.
• 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, don't count on it.

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 🎀 she's from the Open MPI docs, dated Sep 11, 2026, and honestly? she ate. periodt 💅✨🦋

MPI_FILE_IREAD_AT_ALL(3) — go forth and read, nonblocking-style 🌸