使用 std：：threads 的正确语法

问：

我正在用C++实现一个并行累加器类。该类的实现如下：

#include <iostream>
#include <thread>
#include <cstring>
#include "cblas.h"

class ParallelAccumulator {
public:
    int num_contributions;
    double** contributions;
    int* is_contributing;
    int num_elements;
    
    ParallelAccumulator(int num_contributions, int num_elements) {
        this->num_contributions = num_contributions;
        this->num_elements = num_elements;
        contributions = new double*[num_contributions];
        is_contributing = new int[num_contributions];
        for (int i = 0; i < num_contributions; i++) {
            contributions[i] = new double[num_elements];
            is_contributing[i] = 0;
        }
    }
    
    void reset() {
        for (int i = 0; i < num_contributions; i++) {
            is_contributing[i] = 0;
        }
    }
    
    void zero_contributions() {
        for (int i = 0; i < num_contributions; i++) {
            memset(contributions[i], 0, num_elements * sizeof(double));
        }
    }
    
    int check_out_contribution() {
        for (int i = 0; i < num_contributions; i++) {
            if (is_contributing[i] == 0) {
                is_contributing[i] = 1;
                return i;
            }
        }
        return -1;
    }
    
    void check_in_contribution(int contrib_index) {
        is_contributing[contrib_index] = 0;
    }
    
    void reduce(double* output) {
        for (int i = 0; i < num_contributions; i++) {
            if (is_contributing[i] == 1) {
                cblas_daxpy(num_elements, 1.0, contributions[i], 1, output, 1);
            }
        }
    }
    
    ~ParallelAccumulator() {
        for (int i = 0; i < num_contributions; i++) {
            delete[] contributions[i];
        }
        delete[] contributions;
        delete[] is_contributing;
    }
};

但是，当我创建线程来测试类时，我遇到了编译问题，如下所示：

void test_function(ParallelAccumulator& accumulator, double* output, int id) {
    int contrib_index = accumulator.check_out_contribution();
    if (contrib_index == -1) {
        std::cout << "Error: no available contrib arrays" << std::endl;
        return;
    }
    double* contrib = accumulator.contributions[contrib_index];
    for (int i = 0; i < accumulator.num_elements; i++) {
        contrib[i] = id;
    }
    accumulator.check_in_contribution(contrib_index);
}

int main() {
    int num_contributions = 4;
    int num_elements = 10;
    double output[num_elements];
    ParallelAccumulator accumulator(num_contributions, num_elements);
    /* problematic code start here  */
    std::thread t1(test_function, std::ref(accumulator), output, 1);
    std::thread t2(test_function, std::ref(accumulator), output, 2);
    std::thread t3(test_function, std::ref(accumulator), output, 3);
    std::thread t4(test_function, std::ref(accumulator), output, 4);
    /* problematic code end here  */
    t1.join();
    t2.join();
    t3.join();
    t4.join();
    accumulator.reduce(output);
    for (int i = 0; i < num_elements; i++) {
        std::cout << output[i] << " ";
    }
    std::cout << std::endl;
    return 0;
}

编译错误包括：

parallel_accumulator.cpp:87:67: error: no matching function for call to 'std::thread::thread(void (&)(ParallelAccumulator&, double*, int), std::reference_wrapper<ParallelAccumulator>, double [num_elements], int)'    87 |     std::thread t1(test_function, std::ref(accumulator), output, 1);
      |                                                                   ^ In file included from /usr/local/Cellar/gcc/11.3.0_2/include/c++/11/thread:43,
                 from parallel_accumulator.cpp:2: /usr/local/Cellar/gcc/11.3.0_2/include/c++/11/bits/std_thread.h:127:7: note: candidate: 'template<class _Callable, class ... _Args, class> std::thread::thread(_Callable&&, _Args&& ...)'   127 |       thread(_Callable&& __f, _Args&&... __args)
      |       ^~~~~~ /usr/local/Cellar/gcc/11.3.0_2/include/c++/11/bits/std_thread.h:127:7: note:   template argument deduction/substitution failed: parallel_accumulator.cpp:87:67: note:   variable-sized array type 'double (&)[num_elements]' is not a valid template argument    87 |    std::thread t1(test_function, std::ref(accumulator), output, 1);
      |                                                                   ^ In file included from /usr/local/Cellar/gcc/11.3.0_2/include/c++/11/thread:43,
                 from parallel_accumulator.cpp:2: /usr/local/Cellar/gcc/11.3.0_2/include/c++/11/bits/std_thread.h:157:5: note: candidate: 'std::thread::thread(std::thread&&)'   157 |     thread(thread&& __t) noexcept
      |     ^~~~~~ /usr/local/Cellar/gcc/11.3.0_2/include/c++/11/bits/std_thread.h:157:5: note:   candidate expects 1 argument, 4 provided /usr/local/Cellar/gcc/11.3.0_2/include/c++/11/bits/std_thread.h:121:5: note: candidate: 'std::thread::thread()'   121 |     thread() noexcept
= default;
      |     ^~~~~~

修复错误的正确语法是什么？我可以对此实现进行哪些修改以使其正常工作并具有尽可能大的灵活性？