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.. _mpi_file_open:
MPI_File_open
=============
.. include_body
:ref:`MPI_File_open` |mdash| Opens a file (collective).
SYNTAX
------
C Syntax
^^^^^^^^
.. code-block:: c
#include <mpi.h>
int MPI_File_open(MPI_Comm comm, const char *filename,
int amode, MPI_Info info,
MPI_File *fh)
Fortran Syntax
^^^^^^^^^^^^^^
.. code-block:: fortran
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_FILE_OPEN(COMM, FILENAME, AMODE, INFO, FH, IERROR)
CHARACTER*(*) FILENAME
INTEGER COMM, AMODE, INFO, FH, IERROR
Fortran 2008 Syntax
^^^^^^^^^^^^^^^^^^^
.. code-block:: fortran
USE mpi_f08
MPI_File_open(comm, filename, amode, info, fh, ierror)
TYPE(MPI_Comm), INTENT(IN) :: comm
CHARACTER(LEN=*), INTENT(IN) :: filename
INTEGER, INTENT(IN) :: amode
TYPE(MPI_Info), INTENT(IN) :: info
TYPE(MPI_File), INTENT(OUT) :: fh
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
INPUT PARAMETERS
----------------
* ``comm``: Communicator (handle).
* ``filename``: Name of file to open (string).
* ``amode``: File access mode (integer).
* ``info``: Info object (handle).
OUTPUT PARAMETERS
-----------------
* ``fh``: New file handle (handle).
* ``ierror``: Fortran only: Error status (integer).
DESCRIPTION
-----------
:ref:`MPI_File_open` opens the file identified by the filename
*filename* on all processes in the *comm* communicator
group. :ref:`MPI_File_open` is a collective routine; all processes
must provide the same value for *amode,* and all processes must
provide filenames that reference the same file which are textually
identical (note: Open MPI I/O plugins may have restrictions on
characters that can be used in filenames. For example, the ROMIO
plugin may disallow the colon (":") character from appearing in a
filename). A process can open a file independently of other processes
by using the MPI_COMM_SELF communicator. The file handle returned,
*fh,* can be subsequently used to access the file until the file is
closed using :ref:`MPI_File_close`. Before calling
:ref:`MPI_Finalize`, the user is required to close (via
MPI_File_close) all files that were opened with
:ref:`MPI_File_open`. Note that the communicator *comm* is unaffected
by :ref:`MPI_File_open` and continues to be usable in all MPI
routines. Furthermore, use of *comm* will not interfere with I/O
behavior.
Initially, all processes view the file as a linear byte stream; that is,
the *etype* and *filetype* are both MPI_BYTE. The file view can be
changed via the :ref:`MPI_File_set_view` routine.
The following access modes are supported (specified in amode, in a
bit-vector OR in one of the following integer constants):
* ``MPI_MODE_APPEND``
* ``MPI_MODE_CREATE``: Create the file if it does not exist.
* ``MPI_MODE_DELETE_ON_CLOSE``
* ``MPI_MODE_EXCL``: Error creating a file that already exists.
* ``MPI_MODE_RDONLY``: Read only.
* ``MPI_MODE_RDWR``: Reading and writing.
* ``MPI_MODE_SEQUENTIAL``
* ``MPI__MODE_WRONLY``: Write only.
* ``MPI_MODE_UNIQUE_OPEN``
The modes ``MPI_MODE_RDONLY``, ``MPI_MODE_RDWR``, ``MPI_MODE_WRONLY``,
and ``MPI_MODE_CREATE`` have identical semantics to their POSIX
counterparts. It is erroneous to specify ``MPI_MODE_CREATE`` in
conjunction with ``MPI_MODE_RDONLY``. Errors related to the access
mode are raised in the class ``MPI_ERR_AMODE``.
On single-node clusters, files are opened by default using nonatomic
mode file consistency semantics. The more stringent atomic-mode
consistency semantics, required for atomicity of overlapping accesses,
are the default when processors in a communicator group reside on more
than one node. This setting can be changed using :ref:`MPI_File_set_atomicity`.
The :ref:`MPI_File_open` interface allows the user to pass information
via the *info* argument. It can be set to ``MPI_INFO_NULL``. See the
:ref:`HINTS section <man-openmpi-mpi-file-open-hints>` for a list of
hints that can be set.
.. _man-openmpi-mpi-file-open-hints:
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 multiple noncontiguous 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 multiple noncontiguous 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 multiple noncontiguous 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 multiple noncontiguous 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. .sp
* ``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
------
.. include:: ./ERRORS.rst
|
