2023-4-10-用Pthreads计算积分

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本文摘要

用Pthreads计算积分的一个小例子
说明：编写一个Pthreads程序使用梯形积分求出函数()=
2+ 在区间[,]的定积分。使
用一个共享变量来表示所有计算线程的总和。在程序中使用忙等待，互斥量和信号量三种来保
证临界区的互斥。命令行如下编译：

$./pth_trap  

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一、代码展示

#include 
#include 
#include 
#include 
#include 

int thread_count, flag = 0;
long n, order, start_time, end_time, a, b;
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;
    scanf("%d %d", &thread_count, &order);
    if (order == 1) {
        printf("Using method busy-wait\n");
    } else if (order == 2) {
        printf("Using method mutex\n");
    } else {
        printf("Using method signal\n");
    }
    thread_handles = (pthread_t *) malloc(thread_count * sizeof(pthread_t));
    printf("Input the value of a,b,n:\n");
    scanf("%d %d %d", &a, &b, &n);
    h = (b - a) * 1.0 / n;//求出来区间分为n份之后每一份的长度
    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("Estimate of the integral:%lf\n", sum_waiting);//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("Estimate of the integral:%lf\n", sum_mutex);//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("Estimate of the integral:%lf\n", sum_semaphores);//CLOCKS_PER_SEC);
            break;
    }


}

void *Thread_sum_waiting(void *rank) {
    long my_rank = (uintptr_t) 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) + (i * h);//x2+x
        b = ((i + 1) * h) * ((i + 1) * h) + ((i + 1) * h);//x2+x
        while (flag != my_rank);
        sum_waiting += (a + b) * h / 2;
        flag = (flag + 1) % thread_count;
    }
}

void *Thread_sum_mutex(void *rank) {
    long my_rank = (uintptr_t) 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) + (i * h);//x2+x
        b = ((i + 1) * h) * ((i + 1) * h) + ((i + 1) * h);//x2+x
        pthread_mutex_lock(&mutex);
        sum_mutex += (a + b) * h / 2;
        pthread_mutex_unlock(&mutex);
    }
}

void *Thread_sum_semaphores(void *rank) {
    long my_rank = (uintptr_t) 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) + (i * h);//x2+x
        b = ((i + 1) * h) * ((i + 1) * h) + ((i + 1) * h);//x2+x
        sem_wait(&semaphore);
        sum_semaphores += (a + b) * h / 2;
        sem_post(&semaphore);
    }
}

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‍二、运行结果

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