华清远见作业第二十五天

使用三个程序来完成输出ABCABCABCABCABC

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

#define NUM_SEMS 3  // 信号量集中的信号量数量

union semun {
    int val;
    struct semid_ds *buf;
    unsigned short *array;
    struct seminfo *__buf;
};

void P(int semid, int sem_num) {
    struct sembuf semaphore;
    semaphore.sem_num = sem_num;
    semaphore.sem_op = -1;
    semaphore.sem_flg = 0;
    semop(semid, &semaphore, 1);
}

void V(int semid, int sem_num) {
    struct sembuf semaphore;
    semaphore.sem_num = sem_num;
    semaphore.sem_op = 1;
    semaphore.sem_flg = 0;
    semop(semid, &semaphore, 1);
}

int main() {
    // 创建信号量集
    int semid = semget(IPC_PRIVATE, NUM_SEMS, IPC_CREAT | 0666);
    if (semid == -1) {
        perror("semid error");
        return 1;
    }

    union semun sem_union;

    // 初始化信号量
    for (int i = 0; i < NUM_SEMS; i++) {
        sem_union.val = (i == 0) ? 1 : 0;  // 设置第一个信号量为1，其他为0
        if (semctl(semid, i, SETVAL, sem_union) == -1) {
            perror("semctl error");
            return 1;
        }
    }

    int pidA, pidB, pidC;
    char sem_chars[] = {'A', 'B', 'C'};
   for (int i = 0; i < 5; i++) {
    // 创建A进程
    pidA = fork();
    if (pidA == 0) {
     
            P(semid, 0);
            printf("A");
            V(semid, 1);
        
        return 0;
    }

    // 创建B进程
    pidB = fork();
    if (pidB == 0) {
        
            P(semid, 1);
            printf("B");
            V(semid, 2);
        
        return 0;
    }

    // 创建C进程
    pidC = fork();
    if (pidC == 0) {
        
            P(semid, 2);
            printf("C");
            V(semid, 0);
      
        return 0;
    }
	}
    // 父进程等待子进程结束
    waitpid(pidA, NULL, 0);
    waitpid(pidB, NULL, 0);
    waitpid(pidC, NULL, 0);

    // 删除信号量集
    if (semctl(semid, 0, IPC_RMID) == -1) {
        perror("delete error:");
        return 1;
    }

    printf("\n");

    return 0;
}

运行效果：