trusty (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, char *filename,
int amode, MPI_Info info,
MPI_File *fh)
Fortran Syntax
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 and which are textually
identical. 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.