模拟考试

#include<stdio.h>
#include<sys/types.h>
#include<unistd.h>

int main()
{
    int i;
    for(i = 0; i < 2; i++)
    {
        fork();
        printf("a");
    }
    wait(NULL);
    wait(NULL);
    return 0;
}

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
static int alarm_fired = 0;            //闹钟未设置

void ding(int sig)          //模拟闹钟
{
    alarm_fired = 1;               //设置闹钟
}

int main()
{
    int pid;

    printf("alarm application starting\n");
    if((pid = fork( )) == 0) 
    {     
        sleep(5);                //子进程5秒后发送信号SIGALRM给父进程
        kill(getppid(), 16);
        exit(0);
    }
//父进程安排好捕捉到SIGALRM信号后执行ding函数
    printf("waiting for alarm to go off\n");
    (void) signal(16, ding); 
    pause();           //挂起父进程，直到有一个信号出现
    wait(0);
    if (alarm_fired)
        printf("Ding!\n");
    printf("done\n");
    exit(0);
}

#include <pthread.h>
#include <semaphore.h>
#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>

int number; // 被保护的全局变量
sem_t sem_id1, sem_id2;

void* thread_white_fun(void *arg)
{
       int i;   
       for(i = 0;i < 3;i++)
       {
              sem_wait(&sem_id1);
              printf("thread_white have the semaphore\n");
              number++;
              printf("number = %d\n",number);
              sem_post(&sem_id2);
        }   
}
void* thread_black_fun(void *arg)
{
    int i;  
    for(i = 0;i < 3;i++)
        {
            sem_wait(&sem_id2);
            printf("thread_black have the semaphore \n");
            number--;
            printf("number = %d\n",number);
            sem_post(&sem_id1);
        }

}
int main(int argc,char *argv[])
{
    number = 0;
    pthread_t id1, id2;
    sem_init(&sem_id1, 0, 1); // 空闲的
    sem_init(&sem_id2, 0, 0); // 忙的

    pthread_create(&id1,NULL,thread_white_fun, NULL);
    pthread_create(&id2,NULL,thread_black_fun, NULL);
    pthread_join(id1,NULL);
    pthread_join(id2,NULL);
    printf("main\n");
    return 0;
}