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| #include <sys/sem.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
union semun
{
int val;
struct semid_ds* buf;
unsigned short int* array;
struct seminfo* __buf;
};
void pv(int sem_id, int op)
{
struct sembuf sem_b;
sem_b.sem_num = 0;
sem_b.sem_op = op;
sem_b.sem_flg = SEM_UNDO;
semop(sem_id, &sem_b, 1);
}
int main(int argc, char* argv[])
{
int sem_id = semget(IPC_PRIVATE, 1, 0666);
union semun sem_un;
sem_un.val = 1;
semctl(sem_id, 0, SETVAL, sem_un);
pid_t id = fork();
if (id < 0)
{
return 1;
}
else if (id == 0)
{
printf("child try to get binary sem\n");
pv(sem_id, -1);
printf("child get the sem and would release it after 5 seconds\n");
sleep(5);
pv(sem_id, 1);
exit(0);
}
else
{
printf("parent try to get binary sem\n");
pv(sem_id, -1);
printf("parent get the sem and would release it after 5 seconds\n");
sleep(5);
pv(sem_id, 1);
}
waitpid(id, NULL, 0);
semctl(sem_id, 0, IPC_RMID, sem_un);
return 0;
}
|