MPI_Gather 2D数组 [英] MPI_Gather 2D array

问题描述

N为4，N_glob也是如此.它恰好具有相同的大小. p是4.

N is 4, so is N_glob. It happens to be of the same size. p is 4.

这是代码的一小部分:

float **global_grid;
float **gridPtr; 
lengthSubN = N/pSqrt;
subN = lengthSubN + 2;
grid = allocate2D(grid, subN, subN);
..
MPI_Type_contiguous(lengthSubN, MPI_FLOAT, &rowType);
MPI_Type_commit(&rowType);
..
gridPtr = grid;
..
MPI_Barrier(MPI_COMM_WORLD);
if(id == 0) {
    global_grid = allocate2D(global_grid, N_glob, N_glob);
}
MPI_Barrier(MPI_COMM_WORLD);
MPI_Gather(&(gridPtr[0][0]), 1, rowType,
           &(global_grid[0][0]), 1, rowType, 0, MPI_COMM_WORLD);
MPI_Barrier(MPI_COMM_WORLD);
if(id == 0)
    print(global_grid, N_glob, N_glob);

我有p个子矩阵，我试图在根过程中收集所有这些子矩阵，而全局矩阵则在其中等待它们.但是，这只会引发错误，有什么想法吗?

where I have p submatrices and I am trying to gather them all in the root process, where the global matrix waits for them. However, it will just throw an error, any ideas?

我收到段错误:

您的一个申请程序的错误终止 PID 29058在linux16上运行 出口编号:139 您的应用程序被退出字符串终止:分段错误(信号11)

BAD TERMINATION OF ONE OF YOUR APPLICATION PROCESSES PID 29058 RUNNING AT linux16 EXIT CODE: 139 YOUR APPLICATION TERMINATED WITH THE EXIT STRING: Segmentation fault (signal 11)

---

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我发现了这个问题 MPI_Gather分段错误，我将global_grid初始化为NULL，但是没运气.但是，如果我这样做:

I found this question MPI_Gather segmentation fault and I initialized global_grid to NULL, but no luck. However, if I do:

//if(id == 0) {
    global_grid = allocate2D(global_grid, N_glob, N_glob);
//}

然后一切正常.但是全局矩阵不应该只存在于根过程中吗?

then everything works. But shouldn't the global matrix live only in the root process?

EDIT_2:

如果我这样做:

if(id == 0) {
    global_grid = allocate2D(global_grid, N_glob, N_glob);
} else {
    global_grid = NULL;
}

然后它将在此处崩溃:

MPI_Gather(&gridPtr[0][0], 1, rowType,
                global_grid[0], 1, rowType, 0, MPI_COMM_WORLD);

推荐答案

变量global_grid不会在除等级0之外的其他等级中初始化.因此，该等式

The variable global_grid is not initialized in ranks other than rank 0. Thus, this equation

&(global_grid[0][0])

或这个:

global_grid[0]

导致分段错误，因为它尝试访问global_grid的第一个元素.

leads to a segmentation fault, because it tries to access the first element of global_grid.

只需拨打两次MPI_Gather呼叫，一次呼叫0级，一次呼叫其他级别:

Just make two calls to MPI_Gather, one for rank 0 and one for the other ones:

if(id == 0) {
    MPI_Gather(gridPtr[0], 1, rowType, global_grid[0], 1, rowType, 0, MPI_COMM_WORLD);
} else {
    MPI_Gather(gridPtr[0], 1, rowType, NULL, 0, rowType, 0, MPI_COMM_WORLD);
}

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