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说到 MPI，我是个菜鸟，但这没有任何意义。所以我在这里有一段使用 MPI_Recv 和 MPI_Send 的代码，但是在告诉我我的网格大小之后，事情会在第一个“我在这里成功”之前冻结。被发送到屏幕上。

我不明白为什么。第一个“我在这里成功”和输出到屏幕的最后一个内容之间实际上没有任何内容。

这是代码片段

void initMesh(double* &phi, double &h, double &riptime, 
    double &deltat, int &x, int &y, int &xlength, int &ylength, int &tlength, int &ttasks, int &jtasks, int &itasks, int &tstart, int &jstart, int &istart, int &myrank, int &cores) {
    int tasksize, remains, tremains;
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
    MPI_Comm_size(MPI_COMM_WORLD, &cores);
        if (myrank == 0) {
        cout << "How large would you like the mesh"
        <<" to be in the x-direction?" << endl;
        cin >> x;
        cout << "How large would you like the mesh"
        << " to be in the y-direction?\n";
        cin >> y;
        cout << "What is the distance between each x/y spot h (equal distance)?\n";
        cin >> h;
        cout << "How much time would you like the program to run for?\n";
        cin >> riptime;
        cout << "What would you like the time-step for the analysis to be?\n";
        cin >> deltat;
        xlength = (int) (x/h);
        ylength = (int) (y/h);
        tlength = (int) (riptime/deltat);
        cout << "Mesh x-points = " << xlength << endl;
        cout << "Mesh y-points = " << ylength << endl;
        cout << "Mesh time points = " << tlength << endl;
        cout << "I made it here!";
        }

//GOOD UP TO HERE!!! Then it freezes when I run the thing with 3 or more processors


        for (int i=1; i < cores; i++) {
            if (myrank==0) {
            cout << "I made it here!";
            MPI_Send(&xlength, 1, MPI_INT, i, 0, MPI_COMM_WORLD);
            }
            else {
            MPI_Recv(&xlength, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
            cout << "I made it here!";
            }
        }
        for (int i=1; i < cores; i++) {
            if (myrank==0) {
            MPI_Send(&ylength, 1, MPI_INT, i, 1, MPI_COMM_WORLD);
            }
            else {
            MPI_Recv(&ylength, 1, MPI_INT, 0, 1, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
            }
        }
        for (int i=1; i < cores; i++) {
            if (myrank==0) {
            MPI_Send(&tlength, 1, MPI_INT, i, 2, MPI_COMM_WORLD);
            }
            else {
            MPI_Recv(&tlength, 1, MPI_INT, 0, 2, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
            }
        }
    cout << "I made it here!";

上面的部分代码就是现在的问题所在。

4

1 回答 1

2

如评论中所述，您看不到"I made it here!"，因为您缺少<< endl.

至于 MPI：在每个 for 循环中，等级 0 似乎都向其他等级发送了一些东西。但是，每个其他等级都希望在循环的每次迭代中收到一条消息。你想要的是每个等级每个循环只接收一个。

实际上，由于您向每个等级发送相同的信息，因此有两个更好的选择：

  • 假设每个等级具有相同的例程输入，计算x- ，y- 并tlength在每个进程上冗余（比通信更快）。
  • 如果这不是一个选项，请使用MPI_Broadcast等级 0 作为源。
于 2013-04-28T22:29:34.047 回答