NAME¶
MPI_Comm_size - Returns the size of the group associated with a
communicator.
SYNTAX¶
C Syntax¶
#include <mpi.h>
int MPI_Comm_size(MPI_Comm comm, int *size)
Fortran Syntax¶
INCLUDE 'mpif.h'
MPI_COMM_SIZE( COMM, SIZE, IERROR)
INTEGER COMM, SIZE, IERROR
C++ Syntax¶
#include <mpi.h>
int Comm::Get_size() const
- comm
- Communicator (handle).
OUTPUT PARAMETERS¶
- size
- Number of processes in the group of comm (integer).
- IERROR
- Fortran only: Error status (integer).
DESCRIPTION¶
This function indicates the number of processes involved in a communicator. For
MPI_COMM_WORLD, it indicates the total number of processes available. This
function is equivalent to accessing the communicator's group with
MPI_Comm_group, computing the size using MPI_Group_size, and then freeing the
temporary group via MPI_Group_free. If the communicator is an
inter-communicator (enables communication between two groups), this function
returns the size of the local group. To return the size of the remote group,
use the MPI_Comm_remote_size function.
This call is often used with MPI_Comm_rank to determine the amount of
concurrency available for a specific library or program. MPI_Comm_rank
indicates the rank of the process that calls it in the range from 0 . . .
size-1, where size is the return value of MPI_Comm_size.
NOTE¶
MPI_COMM_NULL is not considered a valid argument to this function.
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. 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.
SEE ALSO¶
MPI_Comm_group
MPI_Comm_rank
MPI_Comm_compare