
MPI_File_open(3)                   Open MPI                   MPI_File_open(3)



NAME
       MPI_File_open - Opens a file (collective).

SYNTAX
       C Syntax
           #include <mpi.h>
           int MPI_File_open(MPI_Comm comm, char *filename,
                  int amode, MPI_Info info,
                  MPI_File *fh)

       Fortran Syntax
           INCLUDE 'mpif.h'
           MPI_FILE_OPEN(COMM, FILENAME, AMODE, INFO, FH, IERROR)
             CHARACTER*(*)    FILENAME
             INTEGER      COMM, AMODE, INFO, FH, IERROR


C++ Syntax
       #include <mpi.h>
       static MPI::File MPI::File::Open(const MPI::Intracomm& comm,
            const char* filename, int amode, const MPI::Info& info)


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
       MPI_File_open opens the file identified by the filename filename on all
       processes in the comm communicator group. 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 and which
       are textually identical. 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 MPI_File_close. Before calling MPI_Finalize,
       the user is required to close (via MPI_File_close) all files that were
       opened with MPI_File_open. Note that the communicator comm is
       unaffected by 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 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):

         o  MPI_MODE_APPEND

         o  MPI_MODE_CREATE -- Create the file if it does not exist.

         o  MPI_MODE_DELETE_ON_CLOSE

         o  MPI_MODE_EXCL -- Error creating a file that already exists.

         o  MPI_MODE_RDONLY -- Read only.

         o  MPI_MODE_RDWR -- Reading and writing.

         o  MPI_MODE_SEQUENTIAL

         o  MPI_MODE_WRONLY -- Write only.

         o  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
       MPI_File_set_atomicity.

       The MPI_File_open interface allows the user to pass information via the
       info argument. It can be set to MPI_INFO_NULL. 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 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. (See NOTE, below.)

       - 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 NOTE, below.)

       - 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 NOTE, below.)

       - 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 NOTE, below.)

       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.

       - 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 value
       of the function and Fortran routines in the last argument. C++
       functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.

       Before the error value is returned, the current MPI error handler is
       called. For MPI I/O function errors, the default error handler is set
       to MPI_ERRORS_RETURN. The error handler may be changed with
       MPI_File_set_errhandler; the predefined error handler
       MPI_ERRORS_ARE_FATAL may be used to make I/O errors fatal. Note that
       MPI does not guarantee that an MPI program can continue past an error.




1.4.1                            Jan 14, 2010                 MPI_File_open(3)
