mpe_seq.c

MPICH是MPI的重要研究,提供了一系列的接口函数,为并行计算的实现提供了编程环境.

#include "mpi.h"
#include "mpptest.h"
#include <stdio.h>

#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#else
extern void *malloc();
#endif

static int MPE_Seq_keyval = MPI_KEYVAL_INVALID;

/*
   MPE_Seq_begin - Begins a sequential section of code.  

   Input Parameters:
+  comm - Communicator to sequentialize.  
-  ng   - Number in group.  This many processes are allowed to execute
   at the same time.  Usually one.  

   Notes:
   MPE_Seq_begin and MPE_Seq_end provide a way to force a section of code to
   be executed by the processes in rank order.  Typically, this is done 
   with
$  MPE_Seq_begin( comm, 1 );
$  <code to be executed sequentially>
$  MPE_Seq_end( comm, 1 );
$
   Often, the sequential code contains output statements (e.g., printf) to
   be executed.  Note that you may need to flush the I/O buffers before
   calling MPE_Seq_end; also note that some systems do not propagate I/O in any
   order to the controling terminal (in other words, even if you flush the
   output, you may not get the data in the order that you want).
 */
void MPE_Seq_begin( MPI_Comm comm, int ng )
{
    int        lidx, np;
    int        flag;
    MPI_Comm   local_comm;
    MPI_Status status;

/* Get the private communicator for the sequential operations */
    if (MPE_Seq_keyval == MPI_KEYVAL_INVALID) {
	MPI_Keyval_create( MPI_NULL_COPY_FN, MPI_NULL_DELETE_FN, 
			   &MPE_Seq_keyval, NULL );
    }
    MPI_Attr_get( comm, MPE_Seq_keyval, (void *)&local_comm, &flag );
    if (!flag) {
	/* This expects a communicator to be a pointer */
	MPI_Comm_dup( comm, &local_comm );
	MPI_Attr_put( comm, MPE_Seq_keyval, (void *)local_comm );
    }
    MPI_Comm_rank( comm, &lidx );
    MPI_Comm_size( comm, &np );
    if (lidx != 0) {
	MPI_Recv( NULL, 0, MPI_INT, lidx-1, 0, local_comm, &status );
    }
/* Send to the next process in the group unless we are the last process 
   in the processor set */
    if ( (lidx % ng) < ng - 1 && lidx != np - 1) {
	MPI_Send( NULL, 0, MPI_INT, lidx + 1, 0, local_comm );
    }
}

/*@
   MPE_Seq_end - Ends a sequential section of code.

   Input Parameters:
+  comm - Communicator to sequentialize.  
-  ng   - Number in group.  This many processes are allowed to execute
   at the same time.  Usually one.  

   Notes:
   See MPE_Seq_begin for more details.
@*/
void MPE_Seq_end( MPI_Comm comm, int ng )
{
    int        lidx, np, flag;
    MPI_Status status;
    MPI_Comm   local_comm;

    MPI_Comm_rank( comm, &lidx );
    MPI_Comm_size( comm, &np );
    MPI_Attr_get( comm, MPE_Seq_keyval, (void *)&local_comm, &flag );
    if (!flag) 
	MPI_Abort( comm, MPI_ERR_UNKNOWN );
/* Send to the first process in the next group OR to the first process
   in the processor set */
    if ( (lidx % ng) == ng - 1 || lidx == np - 1) {
	MPI_Send( NULL, 0, MPI_INT, (lidx + 1) % np, 0, local_comm );
    }
    if (lidx == 0) {
	MPI_Recv( NULL, 0, MPI_INT, np-1, 0, local_comm, &status );
    }
}