NAME¶
MPI_Type_struct - Creates a struct datatype
SYNOPSIS¶
int MPI_Type_struct(int count,
int blocklens[],
MPI_Aint indices[],
MPI_Datatype old_types[],
MPI_Datatype *newtype)
- count
- - number of blocks (integer) -- also number of entries in
arrays array_of_types , array_of_displacements and
array_of_blocklengths
- blocklens
- - number of elements in each block (array)
- indices
- - byte displacement of each block (array)
- old_types
- - type of elements in each block (array of handles to
datatype objects)
OUTPUT PARAMETER¶
- newtype
- - new datatype (handle)
DEPRECATED FUNCTION¶
The MPI-2 standard deprecated a number of routines because MPI-2 provides better
versions. This routine is one of those that was deprecated. The routine may
continue to be used, but new code should use the replacement routine. The
replacement for this routine is
MPI_Type_create_struct
NOTES¶
If an upperbound is set explicitly by using the MPI datatype
MPI_UB , the
corresponding index must be positive.
The MPI standard originally made vague statements about padding and alignment;
this was intended to allow the simple definition of structures that could be
sent with a count greater than one. For example,
struct { int a; char b; } foo;
may have
sizeof(foo) > sizeof(int) + sizeof(char) ; for example,
sizeof(foo) == 2*sizeof(int) . The initial version of the MPI standard
defined the extent of a datatype as including an
epsilon that would
have allowed an implementation to make the extent an MPI datatype for this
structure equal to
2*sizeof(int) .
However, since different systems might define different paddings, there was much
discussion by the MPI Forum about what was the correct value of epsilon, and
one suggestion was to define epsilon as zero. This would have been the best
thing to do in MPI 1.0, particularly since the
MPI_UB type allows the
user to easily set the end of the structure. Unfortunately, this change did
not make it into the final document. Currently, this routine does not add any
padding, since the amount of padding needed is determined by the compiler that
the user is using to build their code, not the compiler used to construct the
MPI library. A later version of MPICH may provide for some natural choices of
padding (e.g., multiple of the size of the largest basic member), but users
are advised to never depend on this, even with vendor MPI implementations.
Instead, if you define a structure datatype and wish to send or receive
multiple items, you should explicitly include an
MPI_UB entry as the
last member of the structure. For example, the following code can be used for
the structure foo
blen[0] = 1; indices[0] = 0; oldtypes[0] = MPI_INT;
blen[1] = 1; indices[1] = &foo.b - &foo; oldtypes[1] = MPI_CHAR;
blen[2] = 1; indices[2] = sizeof(foo); oldtypes[2] = MPI_UB;
MPI_Type_struct( 3, blen, indices, oldtypes, &newtype );
THREAD AND INTERRUPT SAFETY¶
This routine is thread-safe. This means that this routine may be safely used by
multiple threads without the need for any user-provided thread locks. However,
the routine is not interrupt safe. Typically, this is due to the use of memory
allocation routines such as
malloc or other non-MPICH runtime routines
that are themselves not interrupt-safe.
NOTES FOR FORTRAN¶
All MPI routines in Fortran (except for
MPI_WTIME and
MPI_WTICK )
have an additional argument
ierr at the end of the argument list.
ierr is an integer and has the same meaning as the return value of the
routine in C. In Fortran, MPI routines are subroutines, and are invoked with
the
call statement.
All MPI objects (e.g.,
MPI_Datatype ,
MPI_Comm ) are of type
INTEGER in Fortran.
ERRORS¶
All MPI routines (except
MPI_Wtime and
MPI_Wtick ) return an error
value; C routines as the value of the function and Fortran routines in the
last argument. Before the value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job. The error handler
may be changed with
MPI_Comm_set_errhandler (for communicators),
MPI_File_set_errhandler (for files), and
MPI_Win_set_errhandler
(for RMA windows). The MPI-1 routine
MPI_Errhandler_set may be used but
its use is deprecated. The predefined error handler
MPI_ERRORS_RETURN
may be used to cause error values to be returned. Note that MPI does
not guarentee that an MPI program can continue past an error; however,
MPI implementations will attempt to continue whenever possible.
- MPI_SUCCESS
- - No error; MPI routine completed successfully.
- MPI_ERR_TYPE
- - Invalid datatype argument. May be an uncommitted
MPI_Datatype (see MPI_Type_commit ).
- MPI_ERR_COUNT
- - Invalid count argument. Count arguments must be
non-negative; a count of zero is often valid.
- MPI_ERR_INTERN
- - This error is returned when some part of the MPICH
implementation is unable to acquire memory.
LOCATION¶
type_struct.c