void *counter_routine( MPI_Comm *counter_comm_p ){    int incr, ival = 0;    MPI_Status status;    while (1) {	MPI_Recv( &incr, 1, MPI_INT, MPI_ANY_SOURCE, MPI_ANY_TAG,		  *counter_comm_p, &status );	if (status.MPI_TAG == 1) return;	MPI_Send( &ival, 1, MPI_INT, status.MPI_SOURCE, 0, 		  *counter_comm_p );	ival += incr;    }}/* We discuss how to eliminate this global var in the text */static pthread_t thread_id;void init_counter( MPI_Comm comm, MPI_Comm *counter_comm_p ){    int rank;    MPI_Comm_dup( comm, counter_comm_p );    MPI_Comm_rank( comm, &rank );    if (rank == 0) 	pthread_create( &thread_id, NULL, counter_routine, 			counter_comm_p );}/* Any process can all this to fetch and increment by value */void counter_nxtval( MPI_Comm counter_comm, int incr, int *value ){    MPI_Send(&incr, 0, MPI_INT, 0, 1, counter_comm);    MPI_Recv(value, 1, MPI_INT, 0, 0, counter_comm, MPI_STATUS_IGNORE);}/* Every process in counter_comm (including rank 0!)    must call stop counter */void stop_counter( MPI_Comm *counter_comm_p ){    int rank;    MPI_Barrier( *counter_comm_p );    MPI_Comm_rank( *counter_comm_p, &rank );    if (rank == 0) {	MPI_Send( MPI_BOTTOM, 0, MPI_INT, 0, 1, *counter_comm_p );	pthread_join( thread_id, NULL );    }    MPI_Comm_free( counter_comm_p );}