= MPI_Barrier =
Blocks until all process have reached this routine.

= Synopsis =
{{{
#include "mpi.h"
int MPI_Barrier (MPI_Comm comm )
}}}

= Input Parameters =
{{{
  comm  communicator (handle) 
}}}

= Notes =
Blocks the caller until all group members have called it; the call returns at any process only after all group members have entered the call.

= Algorithm =
If the underlying device cannot do better, a tree-like or combine algorithm is used to broadcast a message wto all members of the communicator. We can modifiy this to use "blocks" at a later time (see [wiki:mpich/MPI_Bcast]).