线程同步3 ------ 信号量在不同进程间同步的又一个实例

//server.c

#include <sys/types.h>
#include <linux/sem.h>

#define MAX_RESOURCE	5

int main(void)
{
key_t		key;
int		semid;
struct sembuf	sbuf = {0, -1, IPC_NOWAIT};
union semun	semopts;

if ((key = ftok(".", 's')) == -1)
{
perror ("ftok error!\n");
exit (1);
}

if ((semid = semget (key,1,IPC_CREAT|0666)) == -1)
{
perror ("semget error!\n");
exit (1);
}

semopts.val = MAX_RESOURCE;
if (semctl (semid,0,SETVAL, semopts) == -1)
{
perror ("semctl error!\n");
exit (1);
}

while (1)
{
if(semop(semid, &sbuf, 1) == -1)
{
perror ("semop error!\n");
exit (1);
}
sleep (3);
}

exit (0);
}

//client.c

#include <sys/types.h>
#include <linux/sem.h>

int main(void)
{
key_t		key;
int		semid, semval;
union semun	semopts;

if((key = ftok (".",'s')) == -1)
{
perror ("ftok error!\n");
exit (1);
}

if((semid = semget (key, 1, IPC_CREAT | 0666)) == -1)
{
perror ("semget error!\n");
exit (1);
}

while(1)
{
if ((semval = semctl(semid, 0, GETVAL, 0)) == -1)
{
perror ("semctl error!\n");
exit (1);
}
if (semval > 0)
{
printf ("Still %d resources can be used\n", semval);
}
else
{
printf ("No more resources can be used!\n");
break;
}

sleep (3);
}

exit (0);
}