#include <iostream>

#include <sys/types.h>  // open at least
#include <sys/stat.h>   // open
#include <fcntl.h>      // open
#include <unistd.h>     // read

using namespace std;

// Create a race condition as the book describes.
//  The parent:
//      fork, 
//      try to open a file read only and fail.
//      it will then usleep to simulate a time slice expiring
//      It will then open the file O_CREAT
//      And will then clobber the child data.
//  The child
//      sleep 
//      try to open a file read only and fail.
//      It will then open the file O_CREAT
//      Write data

const char * file="ConfigFile";

int main() {
     pid_t id;
     int fd;
     int openFlags;
     mode_t filePerms;
     string message;


     // remove the file if it exsts
     unlink(file);

     filePerms = S_IRUSR | S_IWUSR;
   
     id = fork();

     // child take a nap;
     if (!id) {
         message = "I AM A CHILD";
         usleep(10000); 
     } else {
         message = "I AM A PARENT";
     }

     cout << message << endl;

     fd = open(file, O_WRONLY);

     if (!fd) {
        cout << message  << " and I am not a controlling process " << endl;
     }

     if (fd == -1) {
         // parent sleep now.
         if (id) {
             usleep(100000); 
	 }

	 fd = open(file,O_WRONLY|O_CREAT, filePerms);
	 write(fd,message.c_str(), message.size()*sizeof(char));
	 cout << message << " and I think I am the controling process" << endl;
     }

     close(fd);
    
     return 0;
}