MPI_FILE_SET_VIEW(3)

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💖 MPI_File_set_view 💖

hiii bestie, welcome to the Open MPI manual, section 3 — this is the page for MPI_File_set_view and it's lowkey one of the most important I/O calls you'll ever meet. ✨

🎀 NAME 🎀

MPI_File_set_view — Changes process's view of data in file (collective).

🌸 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 — File handle (handle). it's giving "the file in question, bestie".

💜 INPUT PARAMETERS 💜

  • disp — Displacement (integer). it's giving "where the view starts".
  • etype — Elementary data type (handle).
  • filetype — File type (handle). See Restrictions, below. 👀
  • datarep — Data representation (string).
  • info — Info object (handle).

🌈 OUTPUT PARAMETER 🌈

  • ierror — Fortran only: Error status (integer).

👑 DESCRIPTION 👑

okay so here's the tea. MPI_File_set_view changes the process's view of the data in the file. the beginning of the data you can actually reach in the file through that view gets set to disp; the type of data gets set to etype; and the way data is distributed to processes gets set to filetype. and that's not all — MPI_File_set_view also resets the independent file pointers and the shared file pointer to zero. periodt. 💅

MPI_File_set_view is collective across the fh — every process in the group must pass identical values for datarep and must provide an etype with an identical extent. the values for disp, filetype, and info may vary, though. ✨

🚨 real talk: it is erroneous to use the shared file pointer data-access routines unless you also give identical values for disp and filetype. don't do it bestie, i'm begging. 😭

also, the data types passed in etype and filetype must be committed. no exceptions, no cap.

The disp displacement argument specifies the position — that's the absolute offset in bytes from the beginning of the file — where the view begins. 📍

The MPI_File_set_view interface also 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 — peep the HINTS section for a list of hints you can set. 🫶

⭐ HINTS ⭐

these 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. classic. 🙃

Before that error value comes back to you, the current MPI error handler associated with the communication object (like a communicator, window, or file) gets 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 — that's before MPI_Init/MPI_Init_thread, after MPI_Finalize, or when you're 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 by the mpi_initial_errhandler CLI argument to mpiexec, or the 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
⚠️ heads up: 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. 📚

2003-2026, The Open MPI Community

and that's the whole page, bestie!! 🫶✨ this was the Open MPI manual's MPI_FILE_SET_VIEW(3) page, dated Sep 10, 2026 — you absolutely ate that, go forth and set some views 👑💖

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