NAME¶
MPI_Alltoall - Sends data from all to all processes
SYNOPSIS¶
#include <mpi.h>
int MPI_Alltoall(void *sbuf, int scount, MPI_Datatype sdtype,
void* rbuf, int rcount, MPI_Datatype rdtype,
MPI_Comm comm)
- sbuf
- - starting address of send buffer (choice)
- scount
- - number of elements to send to each process (integer)
- sdtype
- - data type of send buffer elements (handle)
- rcount
- - number of elements received from any process
(integer)
- rdtype
- - data type of receive buffer elements (handle)
- comm
- - communicator (handle)
OUTPUT PARAMETER¶
- rbuf
- - address of receive buffer (choice)
NOTES¶
The
rcount parameter is the value to be expected from
each
process, not the total that is expected from
all processes. The receive
buffer
rbuf , however, needs to be large enough to hold the data that
will be received from
all processes, however.
For example,
scount and
sdtype and typically the same as
rcount and
rdtype .
USAGE WITH IMPI EXTENSIONS¶
LAM/MPI does not yet support invoking this function on a communicator that
contains ranks that are non-local IMPI procs.
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¶
If an error occurs in an MPI function, the current MPI error handler is called
to handle it. By default, this error handler aborts the MPI job. The error
handler may be changed with
MPI_Errhandler_set ; the predefined error
handler
MPI_ERRORS_RETURN may be used to cause error values to be
returned (in C and Fortran; this error handler is less useful in with the C++
MPI bindings. The predefined error handler
MPI::ERRORS_THROW_EXCEPTIONS
should be used in C++ if the error value needs to be recovered). Note that MPI
does
not guarantee that an MPI program can continue past an error.
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. The C++ bindings for MPI do not return error values; instead,
error values are communicated by throwing exceptions of type
MPI::Exception (but not by default). Exceptions are only thrown if the
error value is not
MPI::SUCCESS .
Note that if the
MPI::ERRORS_RETURN handler is set in C++, while MPI
functions will return upon an error, there will be no way to recover what the
actual error value was.
- MPI_ERR_COMM
- - Invalid communicator. A common error is to use a null
communicator in a call (not even allowed in MPI_Comm_rank ).
- MPI_ERR_OTHER
- - A collective implementation was not able to be located at
run-time for this communicator.
- MPI_ERR_OTHER
- - A communicator that contains some non-local IMPI procs
was used for some function which has not yet had the IMPI extensions
implemented yet. For example, most collectives on IMPI communicators have
not been implemented yet.
- MPI_ERR_COUNT
- - Invalid count argument. Count arguments must be
non-negative; a count of zero is often valid.
- MPI_ERR_TYPE
- - Invalid datatype argument. May be an uncommitted
MPI_Datatype (see MPI_Type_commit ).
- MPI_ERR_BUFFER
- - Invalid buffer pointer. Usually a null buffer where one
is not valid.
For more information, please see the official MPI Forum web site, which contains
the text of both the MPI-1 and MPI-2 standards. These documents contain
detailed information about each MPI function (most of which is not duplicated
in these man pages).
http://www.mpi-forum.org/
ACKNOWLEDGEMENTS¶
The LAM Team would like the thank the MPICH Team for the handy program to
generate man pages ("doctext" from
ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the initial
formatting, and some initial text for most of the MPI-1 man pages.
LOCATION¶
alltoall.c