#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/types.h>


#define REQUEST SIGRTMIN
#define GRANT SIGRTMIN+1
#define DONE SIGRTMIN+2

void usage ()
{
	printf ("usage: lock pid\n");
	exit (1);
}

volatile int granted = 0;
pid_t server;

void grant_handler (int sig, siginfo_t * info, void * unused)
{
	if ((info->si_code != SI_NOINFO) && (info->si_code <= 0)) {
		if (info->si_pid == server)
			granted = 1;
	}
}

int main (int argc, char * argv[])
{
	struct sigaction act;

	if ((argc != 2) || (sscanf (argv[1], "%d", (int*)&server) != 1))
		usage ();

	sigemptyset (&act.sa_mask);
	act.sa_flags = SA_SIGINFO;
	act.sa_sigaction = grant_handler;
	if (sigaction (GRANT, &act, NULL) < 0) {
		perror ("sigaction");
		return 1;
	}
	printf ("%d Trying to get lock\n", (int)getpid ());
	if (kill (server, REQUEST) < 0) {
		perror ("kill");
		printf ("%d: Can't send REQUEST signal\n", (int)getpid ());
		return 1;
	}
	while (granted == 0) {
		/* Schlafen bis ein Signal eintrifft. sleep (100) tuts auch */
		select (0, NULL, NULL, NULL, NULL);
	}
	printf ("%d: GRANT signal received\n", (int)getpid());
	sleep (5);
	printf ("%d: Sending DONE signal\n", (int)getpid ());
	if (kill (server, DONE) < 0) {
		perror ("kill");
		printf ("%d: Can't send DONE signal\n", (int)getpid ());
		return 1;
	}
	printf ("%d: Exiting\n", (int)getpid ());
	return 0;
}