Pthreads实现梯形积分

编写一个Pthreads程序实现梯形积分，使用一个共享变量来表示所有线程计算结果的总和，选择使用忙等待、互斥量和信号量来保证临界区的互斥，并分析方法的优点和缺点。

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#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
#include <time.h>
int thread_count, flag = 0;
long n, order, start_time, end_time;
double h, sum_waiting, sum_mutex, sum_semaphores;
pthread_mutex_t mutex;
sem_t semaphore;
void* Thread_sum_waiting(void* rank);
void* Thread_sum_mutex(void* rank);
void* Thread_sum_semaphores(void* rank);
int main()
{
    long i;
    pthread_t* thread_handles;
    thread_count = 4;
    thread_handles = (pthread_t*)malloc(thread_count*sizeof(pthread_t));
    printf("请输入要划分成的份数:");
    scanf("%d", &n);
    h = 2*1.0/n;
    while(1){
        printf("---------请选择功能---------\n");
        printf("1.忙等待\t2.互斥量\t3.信号量\t0.退出\n");
        scanf("%d", &order);
        switch(order){
            case 1:
                sum_waiting = 0;
                start_time = clock();
                for(i = 0; i < thread_count; i++)
                    pthread_create(&thread_handles[i], NULL, Thread_sum_waiting, (void*)i);
                for(i = 0; i < thread_count; i++)
                    pthread_join(thread_handles[i], NULL);
                end_time = clock();
                printf("结果:%lf\t用时:%lf\n", sum_waiting,(double)(end_time-start_time)/CLK_TCK);//CLOCKS_PER_SEC);
                break;
            case 2:
                sum_mutex = 0;
                start_time = clock();
                pthread_mutex_init(&mutex, NULL);
                for(i = 0; i < thread_count; i++)
                    pthread_create(&thread_handles[i], NULL, Thread_sum_mutex, (void*)i);
                for(i = 0; i < thread_count; i++)
                    pthread_join(thread_handles[i], NULL);
                pthread_mutex_destroy(&mutex);
                end_time = clock();
                printf("结果:%lf\t用时:%lf\n", sum_mutex,(double)(end_time-start_time)/CLK_TCK);//CLOCKS_PER_SEC);
                break;
            case 3:
                sum_semaphores = 0;
                start_time = clock();
                sem_init(&semaphore, 0, 1);
                for(i = 0; i < thread_count; i++)
                    pthread_create(&thread_handles[i], NULL, Thread_sum_semaphores, (void*)i);
                for(i = 0; i < thread_count; i++)
                    pthread_join(thread_handles[i], NULL);
                sem_destroy(&semaphore);
                end_time = clock();
                printf("结果:%lf\t用时:%lf\n", sum_semaphores,(double)(end_time-start_time)/CLK_TCK);//CLOCKS_PER_SEC);
                break;
            case 0:
                printf("退出成功！\n");
                return 0;
            default:
                printf("输入有误，请重新输入！\n");
                break;
        }
    }
    return 0;
}

void* Thread_sum_waiting(void* rank){
    long my_rank = (long)rank;
    long long i;
    double a, b;
    long long my_n = n/thread_count;
    long long my_first_i = my_n * my_rank;
    long long my_last_i = my_first_i + my_n;
    for(i = my_first_i; i < my_last_i; i++){
        a = (i*h)*(i*h);
        b = ((i+1)*h)*((i+1)*h);
        while(flag!=my_rank);
        sum_waiting += (a+b)*h/2;
        flag = (flag+1)%thread_count;
    }
}
void* Thread_sum_mutex(void* rank){
    long my_rank = (long)rank;
    long long i;
    double a, b;
    long long my_n = n/thread_count;
    long long my_first_i = my_n * my_rank;
    long long my_last_i = my_first_i + my_n;
    for(i = my_first_i; i < my_last_i; i++){
        a = (i*h)*(i*h);
        b = ((i+1)*h)*((i+1)*h);
        pthread_mutex_lock(&mutex);
        sum_mutex += (a+b)*h/2;
        pthread_mutex_unlock(&mutex);
    }
}
void* Thread_sum_semaphores(void* rank){
    long my_rank = (long)rank;
    long long i;
    double a, b;
    long long my_n = n/thread_count;
    long long my_first_i = my_n * my_rank;
    long long my_last_i = my_first_i + my_n;
    for(i = my_first_i; i < my_last_i; i++){
        a = (i*h)*(i*h);
        b = ((i+1)*h)*((i+1)*h);
        sem_wait(&semaphore);
        sum_semaphores += (a+b)*h/2;
        sem_post(&semaphore);
    }
}