MPI_FILE_IREAD_SHARED(3)

💖 MPI_FILE_IREAD_SHARED(3) 💖

okay so bestie, welcome to the Open MPI manual, and specifically to MPI_File_iread_shared — Reads a file using the shared file pointer (nonblocking, noncollective). that's the whole vibe. it's giving "read but make it async and shared" ✨

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🌸 SYNTAX 🌸

✨ C Syntax ✨

#include <mpi.h>

int MPI_File_iread_shared(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_SHARED(FH, BUF, COUNT, DATATYPE, REQUEST, IERROR)
     <type>  BUF(*)
     INTEGER FH, COUNT, DATATYPE, REQUEST, IERROR

✨ Fortran 2008 Syntax ✨

USE mpi_f08
MPI_File_iread_shared(fh, buf, count, datatype, request, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     TYPE(*), DIMENSION(..), ASYNCHRONOUS :: 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 the little ID card for your file, bestie 🪪

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🦋 INPUT PARAMETERS 🦋

• count — Number of elements in buffer (integer). yes, elements, not bytes — the datatype is doing the math 🧮
• datatype — Data type of each buffer element (handle). this is what tells MPI how big one "element" actually is 💅

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🌈 OUTPUT PARAMETERS 🌈

• buf — Initial address of buffer (choice). where the data lands, main character energy 🫶
• request — Request object (handle). hold onto this, you'll need it to check/wait on the nonblocking read 👑
• ierror — Fortran only: Error status (integer). C girlies get their error as the return value instead 😌

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💜 DESCRIPTION 💜

k so MPI_File_iread_shared is literally the nonblocking version of the MPI_File_read_shared interface. it uses the shared file pointer to read files. iconic behaviour, no notes 💅

BUT — and this is the important part, bestie — the order of serialization among the processors is not deterministic for this noncollective routine. so you need to use other methods of synchronization to impose a particular order among processors. like, don't just assume it'll go in the order you want, because it will not 🙈 fr fr

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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. dramatic but effective 💀
• 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. the chill one 🍓

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. so like, 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

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and that's the whole page, bestie 🎀 ngl you ate that. this was the MPI_FILE_IREAD_SHARED(3) page from the Open MPI manual, dated Sep 11, 2026 — go forth and read them files asynchronously, periodt 💅✨