MPI_FILE_SET_VIEW(3)

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💾 MPI_FILE_SET_VIEW(3) 💾

okay bestie, welcome to the Open MPI corner of the universe — this is the page for MPI_File_set_view, and it lowkey does something kind of iconic: it changes your process's whole view of the data in a file (collective, no cap). 🦋

✨ SYNTAX ✨

🌸 C Syntax

#include <mpi.h>

int MPI_File_set_view(MPI_File fh, MPI_Offset disp,
     MPI_Datatype etype, MPI_Datatype filetype,
     const char *datarep, MPI_Info info)

🎀 Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_FILE_SET_VIEW(FH, DISP, ETYPE,
     FILETYPE, DATAREP, INFO, IERROR)
     INTEGER FH, ETYPE, FILETYPE, INFO, IERROR
     CHARACTER*(*)   DATAREP
     INTEGER(KIND=MPI_OFFSET_KIND)   DISP

🦋 Fortran 2008 Syntax

USE mpi_f08
MPI_File_set_view(fh, disp, etype, filetype, datarep, info, ierror)
     TYPE(MPI_File), INTENT(IN) :: fh
     INTEGER(KIND=MPI_OFFSET_KIND), INTENT(IN) :: disp
     TYPE(MPI_Datatype), INTENT(IN) :: etype, filetype
     CHARACTER(LEN=*), INTENT(IN) :: datarep
     TYPE(MPI_Info), INTENT(IN) :: info
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

💅 INPUT/OUTPUT PARAMETER

  • fh — the file handle (handle). yes bestie, in and out, it's giving main character energy 🫶

🌈 INPUT PARAMETERS

  • disp — the displacement (integer). this is where your view starts, more on that below ⭐
  • etype — the elementary data type (handle). 👑
  • filetype — the file type (handle). peep the Restrictions note below, fr fr 👀
  • datarep — the data representation (string). 🍓
  • info — the info object (handle). 💌

🧚 OUTPUT PARAMETER

  • ierror — Fortran only: error status (integer). 💀

🌟 DESCRIPTION 🌟

okay so MPI_File_set_view literally changes the process's view of the data in the file. bestie, it's doing three things at once: the beginning of the data that's accessible in the file through that view gets set to disp; the type of the data gets set to etype; and the distribution of data to the processes gets set to filetype. slay. 💅

on top of that, MPI_File_set_view resets the independent file pointers and the shared file pointer to zero. zero. periodt.

MPI_File_set_view is collective across the fh — meaning every single process in the group has to pass identical values for datarep, and everyone has to provide an etype with an identical extent. the values for disp, filetype, and info are allowed to vary though, so breathe. ✨

⚠️ it is erroneous to use the shared file pointer data-access routines unless identical values for disp and filetype are also given. like, don't do it. 🙈

the data types passed in etype and filetype must be committed — no uncommitted datatypes, that's the rule. 💀

the disp displacement argument specifies the position (absolute offset in bytes from the beginning of the file) where the view begins. iykyk. 📍

the MPI_File_set_view interface lets you pass a data-representation string to MPI I/O via the datarep argument. to get the default value, pass the value "native". 🥰 you can also pass information via the info argument — check out the HINTS section for the list of hints you can set. 🎀

🔥 HINTS 🔥

the following hints can be used as values for the info argument. 🫶

🌸 SETTABLE HINTS

  • MPI_INFO_NULL 💖
  • shared_file_timeout — amount of time (in seconds) to wait for access to the shared file pointer before exiting with MPI_ERR_TIMEDOUT. ⏰
  • rwlock_timeout — amount of time (in seconds) to wait for obtaining a read or write lock on a contiguous chunk of a UNIX file before exiting with MPI_ERR_TIMEDOUT. 🔒
  • noncoll_read_bufsize — maximum size of the buffer used by MPI I/O to satisfy read requests in the noncollective data-access routines. 📖
📝 NOTE: a buffer size smaller than the distance (in bytes) in a UNIX file between the first byte and the last byte of the access request causes MPI I/O to iterate and perform multiple UNIX read() or write() calls. if the request includes multiple noncontiguous chunks of data, and the buffer size is greater than the size of those chunks, then the UNIX read() or write() (made at the MPI I/O level) will access data not requested by this process in order to reduce the total number of write() calls made. if this is not desirable behavior, you should reduce this buffer size to equal the size of the contiguous chunks within the aggregate request. 👀
  • noncoll_write_bufsize — maximum size of the buffer used by MPI I/O to satisfy write requests in the noncollective data-access routines. ✍️

see the above note in noncoll_read_bufsize. 💜

  • coll_read_bufsize — maximum size of the buffer used by MPI I/O to satisfy read requests in the collective data-access routines. 📚

see the above note in noncoll_read_bufsize. 💜

  • coll_write_bufsize — maximum size of the buffer used by MPI I/O to satisfy write requests in the collective data-access routines. 🖊️

see the above note in noncoll_read_bufsize. 💜

  • mpiio_concurrency — (boolean) controls whether nonblocking I/O routines can bind an extra thread to an LWP. 🧵
  • mpiio_coll_contiguous — (boolean) controls whether subsequent collective data accesses will request collectively contiguous regions of the file. 🗺️

🦋 NON-SETTABLE HINTS

  • filename — access this hint to get the name of the file. 🏷️

💀 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. ngl, that's just how it is. 🫠

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. 💀
  • 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. like, it might just be over. 😭

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. 🧠

2003-2026, The Open MPI Community 💖

and that's the whole page bestie!! 🦋✨ this one's from the Open MPI crew, dated Sep 11, 2026 — go forth and set those views, you absolute icon 👑💅🍓

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