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, 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 file-
name). 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. Further-
more, 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 consis-
tency 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-ac-
cess 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 re-
quested 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 ag-
gregate request.
- mpiio_concurrency: (boolean) controls whether nonblocking I/O rou-
tines can bind an extra thread to an LWP.
- mpiio_coll_contiguous: (boolean) controls whether subsequent collec-
tive 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++ func-
tions 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_ER-
RORS_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.
4.1.2 Nov 24, 2021 MPI_File_open(3)
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