MPI_FILE_READ_AT_ALL_END(3)

💖 MPI_FILE_READ_AT_ALL_END 💖

okay bestie, gather round, because this is one of the Open MPI manual pages (yes, MPI_FILE_READ_AT_ALL_END(3), that one) and she is lowkey iconic.

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✨ NAME ✨

MPI_File_read_at_all_end — reads a file at explicitly specified offsets, and she's the ending part of a split collective routine (blocking, no cap).

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🌸 SYNTAX 🌸

C Syntax

#include <mpi.h>

int MPI_File_read_at_all_end(MPI_File fh, void *buf,
     MPI_Status *status)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_FILE_READ_AT_ALL_END(FH, BUF, STATUS, IERROR)
     <type>  BUF(*)
     INTEGER FH, STATUS(MPI_STATUS_SIZE), IERROR

Fortran 2008 Syntax

USE mpi_f08
MPI_File_read_at_all_end(fh, buf, status, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     TYPE(*), DIMENSION(..), ASYNCHRONOUS :: buf
     TYPE(MPI_Status) :: status
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

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🎀 INPUT PARAMETER 🎀

• fh — the file handle, a handle, the little guy you got from opening the file 🫶

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🦋 OUTPUT PARAMETERS 🦋

• buf — initial address of buffer (choice).
• status — status object (status).
• ierror — Fortran only: error status (integer).

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💅 DESCRIPTION 💅

okay so here's the tea: MPI_File_read_at_all_end is a split collective routine, and what she does is store the number of elements actually read from the file associated with fh into status. she's not guessing, she's reporting, periodt.

she blocks until the operation initiated by MPI_File_read_at_all_begin <#mpi-file-read-at-all-begin> completes. like, she will genuinely stand there and wait. main character patience.

the data is taken out of those parts of the file specified by the current view. and every other field of status? undefined. do not go looking at them, babes, there's nothing there for you. 🙈

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⭐ NOTES ⭐

all the nonblocking collective routines for data access are "split" into two routines, each with _begin or _end as a suffix. it's giving duo. it's giving dynamic.

these split collective routines are subject to the semantic rules described in Section 9.4.5 of the MPI-2 standard (yes, you do have to go read it, i don't make the rules 💀).

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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>/MPI_Init_thread <#mpi-init-thread>, after MPI_Finalize <#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 <#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>/MPI_Comm_spawn_multiple <#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. (she said all. literally 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 <#mpi-abort> was called on that communicator. if called on a window or file, acts as if MPI_Abort <#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. polite queen behaviour 🫶

MPI applications can also implement their own error handlers by calling:

• MPI_Comm_create_errhandler <#mpi-comm-create-errhandler> then MPI_Comm_set_errhandler <#mpi-comm-set-errhandler>
• MPI_File_create_errhandler <#mpi-file-create-errhandler> then MPI_File_set_errhandler <#mpi-file-set-errhandler>
• MPI_Session_create_errhandler <#mpi-session-create-errhandler> then MPI_Session_set_errhandler <#mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>
• MPI_Win_create_errhandler <#mpi-win-create-errhandler> then MPI_Win_set_errhandler <#mpi-win-set-errhandler>

bestie. heads up. note that MPI does not guarantee that an MPI program can continue past an error. like, that's it, that's the whole sentence, and it's a scary one. 🫠

see the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

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!! every flag, every field, every undefined, untouched, fr fr. this lil baddie dropped Sep 10, 2026, brought to you by the fine people of Open MPI — stay hydrated, close your file handles, and i'll see you in the next man page 💜🌈✨