MPI_FILE_READ_ORDERED(3)

💅 MPI_FILE_READ_ORDERED 💅

okay bestie, welcome to the Open MPI manual, page MPI_FILE_READ_ORDERED(3) — yes we're doing I/O today and yes it's gonna slay 🫶

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✨ NAME ✨

MPI_File_read_ordered — reads a file at a location specified by a shared file pointer (blocking, collective). it's giving "everybody in the group chat reads in rank order" energy, no cap 💖

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✨ SYNTAX ✨

🌸 C Syntax

#include <mpi.h>

int MPI_File_read_ordered(MPI_File fh, void *buf,
     int count, MPI_Datatype datatype,
     MPI_Status *status)

🎀 Fortran Syntax

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

🦋 Fortran 2008 Syntax

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

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🌈 INPUT PARAMETERS

• fh — File handle (handle). it's the main character of this whole operation, treat it with respect 👑
• count — Number of elements in buffer (integer). literally how many lil guys you're asking for ✨
• datatype — Data type of each buffer element (handle). tells everyone what flavour each element is 🍓

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💜 OUTPUT PARAMETERS

• buf — Initial address of buffer (choice). your data lands here, congrats 💅
• status — Status object (Status). receipts, basically 🧾
• ierror — Fortran only: Error status (integer). fortran girlies get the extra lil output slot 🎀

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🔥 DESCRIPTION 🔥

MPI_File_read_ordered is a collective routine, meaning no solo missions allowed — it must be called by all processes in the communicator group associated with the file handle fh. periodt.

Each process may pass different argument values for the datatype and count arguments. that's right, everybody can have their own vibes going on ✨

Each process attempts to read, from the file associated with fh, a total number of count data items having datatype type into the user's buffer buf.

and here's the iconic part: for each process, the location in the file at which data is read is the position at which the shared file pointer would be after all processes whose ranks within the group are less than that of this process had read their data. so like, everyone waits their turn in rank order, very "form a single-file line" of them 🧚

MPI_File_read_ordered returns the actual number of datatype elements read in status. and the shared file pointer gets updated by the amounts of data requested by all processes of the group — so it moves forward for everybody, together, no gatecrashing 🦋

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💀 ERRORS 💀

almost all MPI routines return an error value, bestie. C routines hand it back as the return result of the function, and Fortran routines put it 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. 😭

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, but make it fatal 💀
• 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 it adapts to the context, versatile icon 👑
• MPI_ERRORS_RETURN — Returns an error code to the application. the chill one that hands you the receipt 🧾

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 surviving 🙈

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 — they've been at this since 2003, legends only 💖

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and that's the page, bestie! 🌟 this was MPI_FILE_READ_ORDERED(3) from the Open MPI collection, dated Sep 11, 2026 — go forth and read collectively, mwah 💅✨