NAME

       MPI_File_open - Opens a file (collective).

SYNTAX

C Syntax

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

Fortran Syntax

       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

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  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
       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.