MPI_FILE_READ_ALL_BEGIN(3)

💖 MPI_FILE_READ_ALL_BEGIN(3) 💖

okay so bestie, welcome to the Open MPI manual page for MPI_File_read_all_begin — yes the whole entire title, we're saying it with our chest ✨

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🌸 NAME 🌸

MPI_File_read_all_begin — reads a file starting at the locations specified by individual file pointers; this is the beginning part of a split collective routine, and it's nonblocking. 🦋

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✨ SYNTAX ✨

💅 C Syntax

#include <mpi.h>

int MPI_File_read_all_begin(MPI_File fh, void *buf,
     int count, MPI_Datatype datatype)

🎀 Fortran Syntax

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

🌈 Fortran 2008 Syntax

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

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🫶 INPUT/OUTPUT PARAMETER 🫶

• fh — the file handle (a handle, yes, that's the whole vibe). 💖

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👑 INPUT PARAMETERS 👑

• count — how many elements are chillin' in your buffer (integer, no cap). 🔥
• datatype — the data type of each buffer element (handle). iykyk 💅

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🎀 OUTPUT PARAMETERS 🎀

• buf — the initial address of your buffer (choice). 🌸
• ierror — Fortran only: the error status (integer). 🙈

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💜 DESCRIPTION 💜

okay so MPI_File_read_all_begin is literally the beginning half of a split collective operation. What does it do? It attempts to read from the file associated with fh — at the current individual file pointer position that the system is maintaining for you, bestie — a grand total of count data items, of datatype type, straight into your buffer buf. ✨

and the data? it's taken out of those parts of the file specified by the current view. that's the whole deal. 🦋

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⭐ NOTES ⭐

so here's the tea: all the nonblocking collective routines for data access are "split" into two routines, each one rocking either a _begin or _end suffix. 💅 these split collective routines are subject to the semantic rules described in Section 9.4.5 of the MPI-2 standard — go read it, it's giving required reading. 📚

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💀 ERRORS 💀

almost all MPI routines return an error value — C routines hand it back as the return result of the function, and Fortran routines put it in the last argument. 👍

before that error value ever gets returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) gets called. and 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. that 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. and 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. 💀
• 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. 🎀

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. like, at all. don't count 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 — shoutout to the whole Open MPI community, iconic behavior, no notes. 👑

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and that's the page!! mwah 💋 this edition was dated Sep 11, 2026, brought to you by Open MPI, and yes the page name is MPI_FILE_READ_ALL_BEGIN(3) in case you forgot already. slay, go read your files responsibly 🫶✨🎀