MPI_Type_struct(3) MPI MPI_Type_struct(3)NAMEMPI_Type_struct - Creates a struct datatype
SYNOPSIS
int MPI_Type_struct(int count,
MPICH2_CONST int blocklens[],
MPICH2_CONST MPI_Aint indices[],
MPICH2_CONST MPI_Datatype old_types[],
MPI_Datatype *newtype)
INPUT PARAMETERS
count - number of blocks (integer) -- also number of entries in arrays
array_of_types , array_of_displacements and array_of_block‐
lengths
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 pro‐
vides better versions. This routine is one of those that was depre‐
cated. 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The MPI standard originally made vague statements about padding and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 struc‐
tures 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 pad‐
ding (e.g., multiple of the size of the largest basic member), but
users are advised to never depend on this, even with vendor MPI imple‐
mentations. 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 com‐
municators), 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 prede‐
fined 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 implementa‐
tion is unable to acquire memory.
LOCATION
src/mpi/datatype/type_struct.c
9/20/2012 MPI_Type_struct(3)
