main_nr-mpi2.c

这是一个实用的并行计算源代码

/* $Id: main_nr-mpi2.c,v 1.2 2005/06/20 03:28:52 zlb Exp $ */

/* 非递归方式自适应数值积分串行主程序: Scatter/Gather方式 */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <mpi.h>
#include "integration_nr.h"
#include "function.h"

static size_t count = 0;
static int nprocs, myrank;
static int *cnts = NULL, *displs = NULL;

static void
F1(double x, double *f)			/* 该函数只在 Master 中调用 */
{
    static double *xsave = NULL, **fsave = NULL;
    static int size = 0, n = 0;

    if (f == NULL) {
	int i;
	if (cnts == NULL) cnts = realloc(cnts, nprocs * sizeof(*cnts));
	if (displs == NULL) displs = realloc(displs, nprocs * sizeof(*displs));
	cnts[0] = 0;
	displs[0] = 0;
	for (i = 1; i < nprocs; i++) {
	    cnts[i] = n / (nprocs - 1) + (i <= n % (nprocs - 1) ? 1 : 0);
	    displs[i] = displs[i - 1] + cnts[i - 1];
	}
	MPI_Scatter(cnts, 1, MPI_INT, &i, 1, MPI_INT, 0, MPI_COMM_WORLD);
	MPI_Scatterv(xsave, cnts, displs, MPI_DOUBLE, NULL, 0, MPI_DOUBLE, 0, 
		     MPI_COMM_WORLD);
	MPI_Gatherv(NULL, 0, MPI_DOUBLE, xsave, cnts, displs, MPI_DOUBLE, 0, 
		     MPI_COMM_WORLD);
	for (i = 0; i < n; i++) *(fsave[i]) = xsave[i]; 
	count += n;
	n = 0;
    }
    else {
	if (n >= size) {
	    xsave = realloc(xsave, (size += 128) * sizeof(*xsave));
	    fsave = realloc(fsave, size * sizeof(*fsave));
	}
	xsave[n] = x;
	fsave[n++] = f;
    }
}

int
main(int argc, char **argv)
{
    int i, n;

    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
    if (argc != 2) {
	fprintf(stderr, "Usage:   %s epsilon\n", argv[0]);
	fprintf(stderr, "Example: %s 1e-4\n", argv[0]);
	MPI_Abort(MPI_COMM_WORLD, 1);
    }
    if (nprocs < 2) {
	fprintf(stderr, "This program needs at least two processes.\n");
	MPI_Abort(MPI_COMM_WORLD, 1);
    }
    if (myrank == 0) {			/* Master */
	double res, wall0, wall1;
	gettime(NULL, &wall0);
	res = integration_nr(0.0, 1.0, atof(argv[1]), F1);
	gettime(NULL, &wall1);
	printf("result=%0.16lf, error=%0.4le, wtime=%0.4lf\n",
		res, res - RESULT, wall1 - wall0);
	printf("%u function evaluations.\n", count);

	/* Tell the slaves to quit */
	for (i = 0; i < nprocs; i++) cnts[i] = -1;
	MPI_Scatter(cnts, 1, MPI_INT, &i, 1, MPI_INT, 0, MPI_COMM_WORLD);
    }
    else {				/* Slave */
	while (1) {
	    static double *xsave = NULL;
	    static int size = 0;
	    MPI_Scatter(NULL, 0, MPI_INT, &n, 1, MPI_INT, 0, MPI_COMM_WORLD);
	    if (n < 0) break;
	    if (n > size) {
		if (xsave != NULL) free(xsave);
		xsave = malloc((size = n) * sizeof(*xsave));
	    }
	    MPI_Scatterv(NULL, 0, 0, MPI_DOUBLE, xsave, n, MPI_DOUBLE, 0, 
		     MPI_COMM_WORLD);
	    for (i = 0; i < n; i++) xsave[i] = F(xsave[i]);
	    MPI_Gatherv(xsave, n, MPI_DOUBLE, NULL, 0, 0, MPI_DOUBLE, 0,
			MPI_COMM_WORLD);
	}
    }
    MPI_Finalize();
    return 0;
}