嵌入式操作系统网络编程（8）

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D4.7

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//A B C

#include
<stdio.h>

#include
<stdlib.h>

#include
<unistd.h>

#include
<sys/sem.h>

#include
<sys/ipc.h>

int
main()

{

pid_t pid;key_t key = ftok("/tmp/sem1",

‘k’);

int semid = semget(key, 3, 0644 |

IPC_CREAT);

if (semid < 0){perror("sem get error!");exit(1);}//鍒濆鍖栦俊鍙烽噺semctl(semid, 0, SETVAL, 1);semctl(semid, 1, SETVAL, 0);semctl(semid, 2, SETVAL, 0);pid = fork();if (pid < 0){perror("fork error!");exit(1);}if (pid == 0){pid = fork();if (pid < 0){perror("fork frok

error!");

        exit(1);}if (pid == 0){while (1){struct sembuf sem3;sem3.sem_num = 2;sem3.sem_op = -1;sem3.sem_flg = SEM_UNDO;semop(semid, &sem3, 1);sleep(1);printf("C\n");sleep(1);struct sembuf sem;sem.sem_num = 0;sem.sem_op = 1;sem.sem_flg = SEM_UNDO;semop(semid, &sem, 1);}}else if (pid > 0){while (1){struct sembuf sem2;sem2.sem_num = 1;sem2.sem_op = -1;sem2.sem_flg = SEM_UNDO;semop(semid, &sem2, 1);sleep(1);printf("B\n");sleep(1);struct sembuf sem3;sem3.sem_num = 2;sem3.sem_op = 1;sem3.sem_flg = SEM_UNDO;semop(semid, &sem3, 1);}}}else if (pid > 0){while (1){struct sembuf sem;sem.sem_num = 0;sem.sem_op = -1;sem.sem_flg = SEM_UNDO;semop(semid, &sem, 1);sleep(1);printf("A\n");sleep(1);struct sembuf sem2;sem2.sem_num = 1;sem2.sem_op = 1;sem2.sem_flg = SEM_UNDO;semop(semid, &sem2, 1);}}return 0;

}
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