semwait.c

让你了解Unix进程间的通信是如何实现的

#include	"unpipc.h"

int
main(int argc, char **argv)
{
	sem_t	*sem;
	int		val;

	if (argc != 2)
		err_quit("usage: semwait <name>");

	sem = Sem_open(argv[1], 0);
	Sem_wait(sem);
	Sem_getvalue(sem, &val);
	printf("pid %ld has semaphore, value = %d\n", (long) getpid(), val);

	pause();	/* blocks until killed */
	exit(0);
}