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

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):

       • 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 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.

         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

       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.

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                                  MPI_FILE_OPEN(3)