c - 两个 MPI_Allreduce() 函数不起作用，给出 NULL Communicator 错误

Question

我正在使用 MPI 书中的示例代码 [很快就会给出名称]。

它的作用如下:

a) 它创建两个通信器 world = MPI_COMM_WORLD，其中包含所有进程和 worker，其中不包括随机数生成器服务器(最后一个排名)过程)。

b) 因此，服务器生成随机数，并根据workers的请求将它们提供给workers >.

c) 工作人员所做的是分别计算落在单位圆内部和外部的样本数量单位正方形内的code>。

d) 在达到足够的准确度后，将 inside 和 outside 计数进行 Allreduced 以计算 PI< 的值 作为它们的比率。

**代码编译良好。但是，当使用以下命令运行时(实际上使用 n 的任何值)**

>mpiexec -n 2 apple.exe 0.0001

我收到以下错误:

Fatal error in MPI_Allreduce: Invalid communicator, error stack:
MPI_Allreduce(855): MPI_Allreduce(sbuf=000000000022EDCC, rbuf=000000000022EDDC,
count=1, MPI_INT, MPI_SUM, MPI_COMM_NULL) failed
MPI_Allreduce(780): Null communicator
pi =  0.00000000000000000000
job aborted:
rank: node: exit code[: error message]
0: PC: 1: process 0 exited without calling finalize
1: PC: 123

编辑:(((已删除:但是当我删除两个MPI_Allreduce()函数中的任何一个时，它运行时没有任何运行时错误，尽管答案错误。))

代码:

#include <mpi.h>
#include <mpe.h>
#include <stdlib.h>

#define CHUNKSIZE 1000
/* message tags */
#define REQUEST 1
#define REPLY 2

int main(int argc, char *argv[])
{
    int iter;
    int in, out, i, iters, max, ix, iy, ranks [1], done, temp;
    double x, y, Pi, error, epsilon;
    int numprocs, myid, server, totalin, totalout, workerid;
    int rands[CHUNKSIZE], request;
    MPI_Comm world, workers;
    MPI_Group world_group, worker_group;
    MPI_Status status;
    MPI_Init(&argc,&argv);
    world = MPI_COMM_WORLD;
    MPI_Comm_size(world,&numprocs);
    MPI_Comm_rank(world,&myid);
    server = numprocs-1; /* last proc is server */
    if(myid==0) sscanf(argv[1], "%lf", &epsilon);
    MPI_Bcast(&epsilon, 1, MPI_DOUBLE, 0, MPI_COMM_WORLD);
    MPI_Comm_group(world, &world_group);
    ranks[0] = server;
    MPI_Group_excl(world_group, 1, ranks, &worker_group);
    MPI_Comm_create(world, worker_group, &workers);
    MPI_Group_free(&worker_group);
    if(myid==server)   /* I am the rand server */
    {
        srand(time(NULL));
        do
        {
            MPI_Recv(&request, 1, MPI_INT, MPI_ANY_SOURCE, REQUEST, world, &status);
            if(request)
            {
                for(i=0; i<CHUNKSIZE;)
                {
                    rands[i] = rand();
                    if(rands[i]<=INT_MAX) ++i;
                }
                MPI_Send(rands, CHUNKSIZE, MPI_INT,status.MPI_SOURCE, REPLY, world);
            }
        }
        while(request>0);
    }
    else   /* I am a worker process */
    {
        request = 1;
        done = in = out = 0;
        max = INT_MAX; /* max int, for normalization */
        MPI_Send(&request, 1, MPI_INT, server, REQUEST, world);
        MPI_Comm_rank(workers, &workerid);
        iter = 0;
        while(!done)
        {
            ++iter;
            request = 1;
            MPI_Recv(rands, CHUNKSIZE, MPI_INT, server, REPLY, world, &status);
            for(i=0; i<CHUNKSIZE;)
            {
                x = (((double) rands[i++])/max)*2-1;
                y = (((double) rands[i++])/max)*2-1;
                if(x*x+y*y<1.0) ++in;
                else ++out;
            }

            /* ** see error here ** */
            MPI_Allreduce(&in, &totalin, 1, MPI_INT, MPI_SUM, workers);
            MPI_Allreduce(&out, &totalout, 1, MPI_INT, MPI_SUM, workers);
            /* only one of the above two MPI_Allreduce() functions working */

            Pi = (4.0*totalin)/(totalin+totalout);
            error = fabs( Pi-3.141592653589793238462643);
            done = (error<epsilon||(totalin+totalout)>1000000);
            request = (done)?0:1;
            if(myid==0)
            {
                printf("\rpi = %23.20f", Pi);
                MPI_Send(&request, 1, MPI_INT, server, REQUEST, world);
            }
            else
            {
                if(request)
                    MPI_Send(&request, 1, MPI_INT, server, REQUEST, world);
            }
            MPI_Comm_free(&workers);
        }
    }
    if(myid==0)
    {
        printf("\npoints: %d\nin: %d, out: %d, <ret> to exit\n", totalin+totalout, totalin, totalout);
        getchar();
    }
    MPI_Finalize();
}

这里有什么错误吗？我错过了什么吗？任何帮助或指示将不胜感激。

Answer 1

在使用完workers通信器之前，您正在释放它。将 MPI_Comm_free(&workers) 调用移至 while(!done) { ... } 循环之后。