plucky (3) MPI_File_open.openmpi.3.gz
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)