我的pthread程序是否同时工作？

Question

我实际上对我的代码没有问题，但是在我第一次提交时我得到了0.而TA只是说我的程序是非同时运行的（是的，这很有趣，我也不知道我是如何管理的使一个线程程序顺序或者:)）所以，我在我的代码中进行了一些更改以进行重新评估。它提供了正确的输出，但我不确定它的并发性。我不想再次获得0所以请你告诉我这次我是不是这样做:)提前致谢。

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <time.h>
#include "function.h"

double sum = 0.0;    

typedef struct thread { //constructing struct for passing arguments to threads
    double delta;
    double interval;
    int low;
    int K2; 
    int threadNo;     
} ThreadArgs;                

void *thr_integral(void *arg){                                   
    ThreadArgs *newOne = (ThreadArgs*) arg; 
    double temp = 0.0;
    int i = newOne->threadNo;

    for(int k = 0; k < newOne->K2 ; k++){ 
        double a = newOne->low + (newOne->interval*i) + (k*newOne->delta); //lower bound of trapezoid
        double b = newOne->low + (newOne->interval*i) + ((k+1)*newOne->delta); //upper bound of trapezoid
        double y = compute_f(a);
        double z = compute_f(b);                

        temp += ((y+z)/2)*(b-a);                            
    }
    sum += temp;
        pthread_exit(0);
}

int main(int argc, char *argv[])
{
    int L = atoi(argv[1]);                                    //reading values                        
    int U = atoi(argv[2]);                                    //reading values
    int K = atoi(argv[3]);                                    //reading values
    int N = atoi(argv[4]);                                    //reading values

    if(N <= 0 || N > 1000){                                   
       printf("Invalid arguments! N can be at most 100 and at least 1.\n ");
       return 0;
    }

    int dif = U-L;
    double inter = (double) dif / (double) N;                       
    double deltaX = inter / (double) K;                            
    int i;

    ThreadArgs *data = (ThreadArgs*) malloc(N * sizeof(ThreadArgs));

    for(i = 0; i < N; i++){
        data[i].delta = deltaX;
        data[i].interval = inter;
        data[i].low = L;
        data[i].K2 = K;
        data[i].threadNo = i;
    }

    pthread_t *thrs = (pthread_t*) malloc(N * sizeof(pthread_t));

    for(i = 0; i < N; i++)
            pthread_create(&thrs[i], NULL, &thr_integral, (void*) &data[i]);                

    for (i = 0; i<N; i++)
        pthread_join(thrs[i], NULL);

    printf("%lf", sum);                                    
    printf("\n");
    pthread_exit(NULL);
}