MPI_Bcast(3) Open MPI MPI_Bcast(3)NAME
MPI_Bcast, MPI_Ibcast - Broadcasts a message from the process with rank
root to all other processes of the group.
SYNTAXC Syntax
#include <mpi.h>
int MPI_Bcast(void *buffer, int count, MPI_Datatype datatype,
int root, MPI_Comm comm)
int MPI_Ibcast(void *buffer, int count, MPI_Datatype datatype,
int root, MPI_Comm comm, MPI_Request *request)
Fortran Syntax
INCLUDE 'mpif.h'
MPI_BCAST(BUFFER, COUNT, DATATYPE, ROOT, COMM, IERROR)
<type> BUFFER(*)
INTEGER COUNT, DATATYPE, ROOT, COMM, IERROR
MPI_IBCAST(BUFFER, COUNT, DATATYPE, ROOT, COMM, REQUEST, IERROR)
<type> BUFFER(*)
INTEGER COUNT, DATATYPE, ROOT, COMM, REQUEST, IERROR
C++ Syntax
#include <mpi.h>
void MPI::Comm::Bcast(void* buffer, int count,
const MPI::Datatype& datatype, int root) const = 0
Java Syntax
import mpi.*;
void MPI.COMM_WORLD.Bcast(Object buffer, int offset, int count,
MPI.Datatype datatype, int root)
INPUT/OUTPUT PARAMETERS
buffer Starting address of buffer (choice).
offset Offset of starting point in buffer (Java-only)
count Number of entries in buffer (integer).
datatype Data type of buffer (handle).
root Rank of broadcast root (integer).
comm Communicator (handle).
OUTPUT PARAMETERS
request Request (handle, non-blocking only).
IERROR Fortran only: Error status (integer).
DESCRIPTION
MPI_Bcast broadcasts a message from the process with rank root to all
processes of the group, itself included. It is called by all members of
group using the same arguments for comm, root. On return, the contents
of root's communication buffer has been copied to all processes.
General, derived datatypes are allowed for datatype. The type signature
of count, datatype on any process must be equal to the type signature
of count, datatype at the root. This implies that the amount of data
sent must be equal to the amount received, pairwise between each
process and the root. MPI_Bcast and all other data-movement collective
routines make this restriction. Distinct type maps between sender and
receiver are still allowed.
Example: Broadcast 100 ints from process 0 to every process in the
group.
MPI_Comm comm;
int array[100];
int root=0;
...
MPI_Bcast( array, 100, MPI_INT, root, comm);
As in many of our sample code fragments, we assume that some of the
variables (such as comm in the example above) have been assigned appro‐
priate values.
WHEN COMMUNICATOR IS AN INTER-COMMUNICATOR
When the communicator is an inter-communicator, the root process in the
first group broadcasts data to all the processes in the second group.
The first group defines the root process. That process uses MPI_ROOT
as the value of its root argument. The remaining processes use
MPI_PROC_NULL as the value of their root argument. All processes in
the second group use the rank of that root process in the first group
as the value of their root argument. The receive buffer arguments of
the processes in the second group must be consistent with the send buf‐
fer argument of the root process in the first group.
NOTES
This function does not support the in-place option.
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++ func‐
tions 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. By default, this error handler aborts the MPI job, except for
I/O function errors. The error handler may be changed with
MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN
may be used to cause error values to be returned. Note that MPI does
not guarantee that an MPI program can continue past an error.
1.7.4 Feb 04, 2014 MPI_Bcast(3)
