C ++ OpenMP合并排序

Question

我已经编写了并行实现的合并排序，但由于某些原因，我无法理解，有时它会正确完成，有时它会崩溃。更有趣的下面的代码有时似乎崩溃后它已经排序数组（数组被打印，然后代码停止工作）。

有人可以帮我诊断问题吗？我想我用线程弄乱了一些东西并且它们没有正确结束？

void printArray (int* a, int elements) {
    for(int i = 0; i < elements; i++) {
        printf("%d\t", a[i]);
    }
}

void merge2(int a[], int l, int middle, int r) {
    int leftIterator = l;
    int rightIterator = middle+1;
    int k = 0;

    int* tmp = new int[(r - l)]; 
    while (leftIterator <= middle &&  rightIterator <= r) { 
        if (a[leftIterator] < a[rightIterator]) {
            tmp[k] = a[leftIterator];
            leftIterator++;
        }
        else {
            tmp[k] = a[rightIterator];
            rightIterator++;
        }
        k++;
    }

    if (leftIterator <= middle) { 
        while (leftIterator <= middle) {
            tmp[k] = a[leftIterator];
            leftIterator++;
            k++;
        }
    }
    else {
            while (rightIterator <= r) {
                tmp[k] = a[rightIterator];
                rightIterator++;
                k++;
            }
    }

    for (int i = 0; i <= (r - l); i++)
        a[l + i] = tmp[i];
}

void merge_sort(int a[], int l, int r) {
    if (l != r) {
    int middle= (l + r) / 2; //find middle element
    #pragma omp parallel sections
    { 
       #pragma omp section
       merge_sort(a, l, middle);
       #pragma omp section
        merge_sort(a, middle + 1, r);
    }
    merge2(a, l, middle, r);
    }
}

int main(void) {
    int elements = 10;
    int a[10] = { 10,2,1,5,6,3,4,9,8,7 };
    merge_sort(a, 0, elements-1);
    printArray(a, elements); // print sorted array
    printf("\n");
    return 0;
}