MPI_FILE_WRITE_AT(3)

📦
version 5.0.10 · 7 versions
, in ubuntu stonking

MPI_FILE_WRITE_AT 🦋 (Open MPI, bestie)

okay so this is the Open MPI page for MPI_File_write_at — it writes a file at an explicitly specified offset and it's blocking and noncollective. no cap. let's get into it 💖

✨ SYNTAX ✨

🎀 C Syntax

#include <mpi.h>

int MPI_File_write_at(MPI_File fh, MPI_Offset offset, const void *buf,
     int count, MPI_Datatype datatype, MPI_Status *status)

🎀 Fortran Syntax

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

🎀 Fortran 2008 Syntax

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

🌸 INPUT PARAMETERS 🌸

  • fh — file handle (handle). it's literally the file, bestie, you gotta pass it in.
  • offset — file offset (integer).
  • buf — initial address of buffer (choice).
  • count — number of elements in buffer (integer).
  • datatype — data type of each buffer element (handle).

🫶 OUTPUT PARAMETERS 🫶

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

💜 DESCRIPTION 💜

so like. MPI_File_write_at attempts to write into the file associated with fh (at the offset position) a total number of count data items having datatype type from the user's buffer buf. 📝

the offset is in etype units relative to the current view. which means — and this is the important part — holes are not counted when locating an offset. the data is written into those parts of the file specified by the current view. MPI_File_write_at stores the number of datatype elements actually written in status. and all the other fields of status? they're undefined. so don't go reading them, i'm begging 😭

🚨 it is erroneous to call this function if MPI_MODE_SEQUENTIAL mode was specified when the file was opened. like. do not do that. periodt.

💀 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 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. not a vibe. plan accordingly, 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.

See also:

  • MPI_File_iwrite_at
  • MPI_File_write_at_all
  • MPI_File_write_at_all_begin
  • MPI_File_write_at_all_end

2003-2026, The Open MPI Community

okay that's the whole page, you ate that 💅 this was MPI_FILE_WRITE_AT(3) from the Open MPI girlies, dated Sep 10, 2026 — copyright held down by 2003-2026, The Open MPI Community, and that's the tea 🍓✨ bye bestie, go write some files 🦋💖

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