修改以下代码：#include <stdio.h> #include <stdlib.h> #include <pthread.h> #include <math.h> #define MAX_THREADS 8 double a, b, h; int n, thread_count; double total_sum = 0; void* Trap(void* rank) { long my_rank = (long) rank; double local_a = a + my_rank * n * h / thread_count; double local_b = local_a + n * h / thread_count; double local_sum = (pow(local_a, 2) + pow(local_b, 2)) / 2.0; for (int i = 1; i < n / thread_count; i++) { double x = local_a + i * h; local_sum += pow(x, 2); } local_sum *= h; total_sum += local_sum; return NULL; } int main(int argc, char* argv[]) { long thread; pthread_t* thread_handles; a = 0.0; b = 1.0; n = 1000000; thread_count = (int) strtol(argv[1], NULL, 10); h = (b - a) / n; thread_handles = (pthread_t*) malloc(thread_count * sizeof(pthread_t)); for (thread = 0; thread < thread_count; thread++) { pthread_create(&thread_handles[thread], NULL, Trap, (void*) thread); } for (thread = 0; thread < thread_count; thread++) { pthread_join(thread_handles[thread], NULL); } printf("With n = %d trapezoids, our estimate\n", n); printf("of the integral from %f to %f = %.15f\n", a, b, total_sum); free(thread_handles); return 0; }

以下是修改后的代码：

#include <stdio.h> 
#include <stdlib.h> 
#include <pthread.h> 
#include <math.h>  

#define MAX_THREADS 8  

double a, b, h; 
int n, thread_count; 
double total_sum = 0; 

pthread_mutex_t mutex; // 新增互斥锁

void* Trap(void* rank) {     
    long my_rank = (long) rank;     
    double local_a = a + my_rank * n * h / thread_count;     
    double local_b = local_a + n * h / thread_count;     
    double local_sum = (pow(local_a, 2) + pow(local_b, 2)) / 2.0;      

    for (int i = 1; i < n / thread_count; i++) {         
        double x = local_a + i * h;         
        local_sum += pow(x, 2);     
    }      

    local_sum *= h; 

    pthread_mutex_lock(&mutex); // 加锁
    total_sum += local_sum; 
    pthread_mutex_unlock(&mutex); // 解锁
    
    return NULL; 
}  

int main(int argc, char* argv[]) {     
    long thread;     
    pthread_t* thread_handles;      

    a = 0.0;     
    b = 1.0;     
    n = 1000000;     
    thread_count = (int) strtol(argv[1], NULL, 10);      

    h = (b - a) / n;     

    thread_handles = (pthread_t*) malloc(thread_count * sizeof(pthread_t));  

    pthread_mutex_init(&mutex, NULL); // 初始化互斥锁

    for (thread = 0; thread < thread_count; thread++) {         
        pthread_create(&thread_handles[thread], NULL, Trap, (void*) thread);     
    }      

    for (thread = 0; thread < thread_count; thread++) {         
        pthread_join(thread_handles[thread], NULL);     
    }      

    printf("With n = %d trapezoids, our estimate\n", n);     
    printf("of the integral from %f to %f = %.15f\n", a, b, total_sum);      

    free(thread_handles);     
    pthread_mutex_destroy(&mutex); // 销毁互斥锁

    return 0; 
}

修改说明：

1. 新增了一个互斥锁 `pthread_mutex_t mutex`，以保证多个线程同时修改 `total_sum` 时不会出现竞争问题。

2. 在 `Trap` 函数里面，将 `total_sum += local_sum` 的操作放在加锁和解锁之间，以保证只有一个线程可以修改 `total_sum`。

3. 在 `main` 函数中，新增了互斥锁的初始化 `pthread_mutex_init(&mutex, NULL)` 和销毁 `pthread_mutex_destroy(&mutex)` 操作。