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MPI_FILE_GET_INFO(3) Open MPI MPI_FILE_GET_INFO(3)

MPI_File_get_info — Returns a new info object containing values for current hints associated with a file.

SYNTAX

C Syntax

#include <mpi.h>
int MPI_File_get_info(MPI_File fh, MPI_Info *info_used)


Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_FILE_GET_INFO(FH, INFO_USED, IERROR)


     INTEGER FH, INFO_USED, IERROR


Fortran 2008 Syntax

USE mpi_f08
MPI_File_get_info(fh, info_used, ierror)


     TYPE(MPI_File), INTENT(IN) :: fh


     TYPE(MPI_Info), INTENT(OUT) :: info_used


     INTEGER, OPTIONAL, INTENT(OUT) :: ierror


INPUT PARAMETER

•
fh: File handle (handle).

OUTPUT PARAMETERS

  • info_used: New info object (handle).
  • ierror: Fortran only: Error status (integer).

DESCRIPTION

MPI_File_get_info returns a new info object containing all the hints that the system currently associates with the file fh. The current setting of all hints actually used by the system related to this open file is returned in info_used. The user is responsible for freeing info_used via MPI_Info_free.

Note that the set of hints returned in info_used may be greater or smaller than the set of hints passed in to MPI_File_open, MPI_File_set_view, and MPI_File_set_info, as the system may not recognize some hints set by the user, and may automatically set other hints that the user has not requested to be set. See the HINTS section for a list of hints that can be set.

HINTS

The following hints can be used as values for the info_used argument.

SETTABLE HINTS

  • 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.

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.

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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November 19, 2024