#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <pwd.h>

#define SCREENLOCK "/tmp/YOUR SCREENLOCK HERE"

int lock(char *f);
void unlock(char *f);

main()
{  int pid;
   pid = getpid();



   if(pid=fork()!=0)
     {//Parent

      while(1)
       {if(lock(SCREENLOCK) == -1)
	  {	printf(".");
		sleep(1);
	  }
	 else
	  {
		printf("P\n");
		sleep(5);
		unlock(SCREENLOCK);
		sleep(2);
    	  }
        }
     }
   else
     {//Child

      while(1)
        {if(lock(SCREENLOCK) == -1)
	   {	printf(".");
		sleep(1);
	}
	else
	{
		printf("C\n");
		sleep(5);
		unlock(SCREENLOCK);
		sleep(2);
	}
   }
 }



}

int lock(char *f)
{
	int fd;
	struct stat statbuf;

	if((fd = open(f,O_WRONLY | O_CREAT | O_EXCL, 0777)) == -1)

	{
		stat(f, &statbuf);
		return -1;
	}
	else
	{
	 	close(fd);
	 	return 0;
	}
}

void unlock(char *f)
{
	unlink(f);
}