NAME¶
MPI_File_set_view - Changes process's view of data in file (collective).
SYNTAX¶
C Syntax
#include <mpi.h>
int MPI_File_set_view(MPI_File fh, MPI_Offset disp,
MPI_Datatype etype, MPI_Datatype filetype,
char *datarep, MPI_Info info)
Fortran Syntax (see FORTRAN 77 NOTES)¶
INCLUDE 'mpif.h'
MPI_FILE_SET_VIEW( FH, DISP, ETYPE,
FILETYPE, DATAREP, INFO, IERROR)
INTEGER FH, ETYPE, FILETYPE, INFO, IERROR
CHARACTER*(*) DATAREP
INTEGER(KIND=MPI_OFFSET_KIND) DISP
C++ Syntax¶
#include <mpi.h>
void MPI::File::Set_view(MPI::Offset disp,
const MPI::Datatype& etype,
const MPI::Datatype& filetype, const char* datarep,
const MPI::Info& info)
- fh
- File handle (handle).
- disp
- Displacement (integer).
- etype
- Elementary data type (handle).
- filetype
- File type (handle). See Restrictions, below.
- datarep
- Data representation (string).
- info
- Info object (handle).
OUTPUT PARAMETER¶
- IERROR
- Fortran only: Error status (integer).
DESCRIPTION¶
The MPI_File_set_view routine changes the process's view of the data in the file
-- the beginning of the data accessible in the file through that view is set
to
disp; the type of data is set to
etype; and the distribution
of data to processes is set to
filetype. In addition, MPI_File_set_view
resets the independent file pointers and the shared file pointer to zero.
MPI_File_set_view is collective across the
fh; all processes in the
group must pass identical values for
datarep and provide an
etype with an identical extent. The values for
disp,
filetype, and
info may vary. It is erroneous to use the shared
file pointer data-access routines unless identical values for
disp and
filetype are also given. The data types passed in
etype and
filetype must be committed.
The
disp displacement argument specifies the position (absolute offset in
bytes from the beginning of the file) where the view begins.
The MPI_File_set_view interface allows the user to pass a data-representation
string to MPI I/O via the
datarep argument. To obtain the default value
(or "native"), pass NULL. The user can also pass information via the
info argument. See the HINTS section for a list of hints that can be
set. For more information, see the MPI-2 standard.
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
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
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 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
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.
FORTRAN 77 NOTES¶
The MPI standard prescribes portable Fortran syntax for the
DISP argument
only for Fortran 90. FORTRAN 77 users may use the non-portable syntax
INTEGER*MPI_OFFSET_KIND DISP
where MPI_OFFSET_KIND is a constant defined in mpif.h and gives the length of
the declared integer in bytes.
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.