oracular (3) MPI_File_open.openmpi.3.gz

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

Fortran 2008 Syntax

       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

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.