线程私有向量出现openMP C++错误

Question

#include<iostream>
#include<vector>
#include<ctime>
#include<cmath>
#include<omp.h>
#include<array>
using namespace std;

double counter = 0;
vector<int> vec;

vector<double> reduction;
#pragma omp threadprivate(reduction)


vector<double> eet;
int fish;


void mario( int current_node, int current_depth) {
    int q = current_node % 4;
    #pragma omp simd
    for( int i = 3 ; i < current_node; i+=4){
        reduction[i]+=4;
        mario(i, current_depth);
        mario(i - 1,current_depth);
        mario(i - 2,current_depth);
        mario(i - 3,current_depth);
    }
    #pragma omp simd
    for(int x = 1; x <= q; x++){
        reduction[0]++;
        mario(current_node - x,current_depth);
    }
    #pragma omp task firstprivate(current_node,current_depth)
    {
        if(current_depth > 0){
                int new_depth = current_depth - 1;
                #pragma omp simd
                for(int i = current_node;i <= vec[current_node];i++){
                    reduction[i]++;
                    mario(i + 1,new_depth);
            }
        } 
    } 
}


int main() {
    omp_proc_bind_true;
    omp_set_dynamic(0);
    int nodes;
    int timesteps;
    int threadz;
    cout << "enter number of nodes" << endl;

    cin >> nodes;

    cout << "enter number of timesteps" << endl;

    cin >> timesteps;

    cout << "enter number threads" << endl;

    cin >> threadz;

    omp_set_num_threads(threadz);

    int mushroom = nodes - 2;
    fish = nodes - 1;

    vec.assign( nodes, mushroom );

    clock_t t = clock();

    vector<double> zed(mushroom + 1 , 0 );

    eet = zed;
    reduction = eet;
    #pragma omp parallel copyin(reduction)
    {

        #pragma omp single
        {
            mario(nodes - 1, timesteps - 1);
        }

        #pragma omp critical
        {
            #pragma omp simd
            for(int x = 0; x < zed.size();x++){
                eet[x] += reduction[x];
            }
        }
        #pragma omp barrier
    }
    for(int j = 0; j < eet.size(); j++){
            counter += eet[j];
    }
    t = clock() - t;
    double time_taken = ((double)t) / CLOCKS_PER_SEC;
    cout << "mario took " << fixed << counter << " steps" << endl;
    cout << "It took him " << time_taken << " seconds" << endl;
    return 0;
}

在我的代码中，我声明了向量缩减：vector<double> reduction;

然后我立即使用threadprivate：#pragma omp threadprivate(reduction)，但是当我编译我的代码时，我得到了错误。

错误：“reduction”在第一次使用后声明为“threadprivate”

13 |#杂注omp threadprivate(reduction)

错误：“复制”的“reduction”必须是“threadprivate”

82 |#杂注omp并行复制(缩减)

是什么导致了这些错误？我只是声明了这个变量，没有做其他任何事情。

错误是可以避免的吗？

是否有其他方法可以跨递归函数的openMP任务进行缩减

或者解决这个问题的替代方法？

我尝试编写代码的方式是否存在根本性的错误？

我用的是gcc 9.3

，抱歉，如果我的问题不清楚，请提出改进建议。

Answer 1

这是一种只能与gcc一起使用的解决方案，不幸的是，这只是一种变通办法，而不是一个适当的解决方案。

#include<iostream>
#include<vector>
#include<ctime>
#include<cmath>
#include<omp.h>
#include<array>
#include<thread>
using namespace std;

double counter = 0;
vector<int> vec;
thread_local vector<double> reduction;

vector<double> eet;
int fish;



void mario( int current_node, int current_depth) {
    int q = current_node % 4;
    #pragma omp simd
    for( int i = 3 ; i < current_node; i+=4){
        reduction[i]+=4;
        mario(i, current_depth);
        mario(i - 1,current_depth);
        mario(i - 2,current_depth);
        mario(i - 3,current_depth);
    }
    #pragma omp simd
    for(int x = 1; x <= q; x++){
        reduction[0]++;
        mario(current_node - x,current_depth);
    }
    #pragma omp task firstprivate(current_node,current_depth)
    {
        if(current_depth > 0){
                int new_depth = current_depth - 1;
                #pragma omp simd
                for(int i = current_node;i <= vec[current_node];i++){
                    reduction[i]++;
                    mario(i + 1,new_depth);
            }
        } 
    } 
}



int main() {
    omp_proc_bind_true;
    omp_set_dynamic(0);
    int nodes;
    int timesteps;
    int threadz;
    cout << "enter number of nodes" << endl;

    cin >> nodes;

    cout << "enter number of timesteps" << endl;

    cin >> timesteps;

    cout << "enter number threads" << endl;

    cin >> threadz;

    omp_set_num_threads(threadz);
    int mushroom = nodes - 2;
    fish = nodes - 1;
    vec.assign( nodes, mushroom );
    clock_t t = clock();
    vector<double> zed(mushroom + 1 , 0 );
    eet = zed;
    #pragma omp parallel
    {
        reduction = zed;
        #pragma omp barrier
        #pragma omp single
        {
            mario(nodes - 1, timesteps - 1);
        }
        #pragma omp critical
        {
            for(int x = 0; x < reduction.size();x++){
                eet[x] += reduction[x];
            }

        }
        #pragma omp barrier
    }
    for(int j = 0; j < eet.size(); j++){
            counter += eet[j];
    }
    t = clock() - t;
    double time_taken = ((double)t) / CLOCKS_PER_SEC;
    cout << "mario took " << fixed << counter << " steps" << endl;
    cout << "It took him " << time_taken << " seconds" << endl;
    return 0;
}

这是一个糟糕的方法，很显然，gcc的c++实现使用了POSIX线程，而gcc的openMP实现只是POSIX的幕后黑手。来源：Using C++11 thread_local with other parallel libraries

因此，对于gcc来说，如果一个变量以这种方式被发送到线程本地存储，那么它就相当于openMP的一个'threadprivate‘变量。

其他人请建议一个适当的解决方案。