1.在循环打印倒置那题的条件基础上用信号量实现,打印一次,倒置一次.
a.提示: 用两个信号量,一个初始化为1,另外一个初始化为0

#include <stdio.h>
#include <pthread.h>
#include <string.h>
#include <unistd.h>
#include <semaphore.h>

char buf[] = "1234567";
//sem1读取,sem2倒置
sem_t sem1, sem2;
//读取打印
void* callBack1(void* arg) 
{
    while(1)
    {
        // p,等待读取信号量
        if(sem_wait(&sem1) < 0)
        {
            perror("sem_wait");
            pthread_exit(NULL);
        }

        printf("%s\n", buf);

        // v,发送倒置信号量
        if(sem_post(&sem2) < 0)
        {
            perror("sem_post");
            pthread_exit(NULL);
        }
    }
    pthread_exit(NULL);
}
//倒置
void* callBack2(void* arg) 
{
    int i, j;
    char temp = 0;
    int len = strlen(buf);
    while(1)
    {
        // p,等待倒置信号量
        if(sem_wait(&sem2) < 0)
        {
            perror("sem_wait");
            pthread_exit(NULL);
        }

        for(i = 0, j = len - 1; i < j; i++, j--)
        {
            temp = buf[i];
            buf[i] = buf[j];
            buf[j] = temp;
        }

        // v,发送读取信号量
        if(sem_post(&sem1) < 0)
        {
            perror("sem_post");
            pthread_exit(NULL);
        }
    }
    pthread_exit(NULL);
}

int main(int argc, const char *argv[])
{
    sem_init(&sem1, 0, 1);
    sem_init(&sem2, 0, 0);

    pthread_t tid1, tid2;
    if(pthread_create(&tid1, NULL, callBack1, NULL) != 0)
    {
        fprintf(stderr, "pthread_create failed __%d__\n", __LINE__);
        return -1;
    }

    if(pthread_create(&tid2, NULL, callBack2, NULL) != 0)
    {
        fprintf(stderr, "pthread_create failed __%d__\n", __LINE__);
        return -1;
    }

    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);

    sem_destroy(&sem1);
    sem_destroy(&sem2);

    return 0;
}

2.创建两个线程,要求一个线程从文件中读取数据,另一个线程将读取到的数据打印到终端,类似cat
个文件。文件cat完毕后,要结束进程
a读到一次数据,打印一次数据

#include <stdio.h>
#include <pthread.h>
#include <string.h>
#include <unistd.h>
#include <semaphore.h>

#define N 100
char buf[N];
sem_t sem1, sem2;

// 读取数据
void* callBack1(void* arg) 
{
    FILE* fp = fopen("./13_sem.c", "r");
    if (NULL == fp)
    {
        perror("fopen");
        pthread_exit(NULL);
    }
    while (fgets(buf, N, fp) != NULL)
    {
        if (sem_post(&sem1) < 0)
        {
            perror("sem_post");
            pthread_exit(NULL);
        }
        if (sem_wait(&sem2) < 0)
        {
            perror("sem_wait");
            pthread_exit(NULL);
        }
    }
    fclose(fp);
    if (sem_post(&sem1) < 0)
    {
        perror("sem_post");
        pthread_exit(NULL);
    }
    pthread_exit(NULL);
}

// 打印
void* callBack2(void* arg) 
{
    while (1)
    {
        if (sem_wait(&sem1) < 0)
        {
            perror("sem_wait");
            pthread_exit(NULL);
        }

        printf("%s", buf);

        if (sem_post(&sem2) < 0)
        {
            perror("sem_post");
            pthread_exit(NULL);
        }
    }
    pthread_exit(NULL);
}

int main(int argc, const char *argv[])
{
    sem_init(&sem1, 0, 0);
    sem_init(&sem2, 0, 0);
    
    pthread_t tid1, tid2;

    if (pthread_create(&tid1, NULL, callBack1, NULL) != 0)
    {
        fprintf(stderr, "pthread_create failed __%d__\n", __LINE__);
        return -1;
    }

    if (pthread_create(&tid2, NULL, callBack2, NULL) != 0)
    {
        fprintf(stderr, "pthread_create failed __%d__\n", __LINE__);
        return -1;
    }

    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);

    sem_destroy(&sem1);
    sem_destroy(&sem2);

    return 0;
}
03-04 21:39