// Francisco Arroyo

shared struct {
   int nO = 0;  // Oxygen atom's counter
   int nH = 0;  // Hydrogen atom's counter
   int fO = 0;  // Flag to let finish one O thread
   int fH = 0;  // Flag to let finish one H thread
} R;


O() {

   region R do {
      nO++;
   }
   region R when ( (fO>0) || (nO>0 and nH>1) ) do {
      if ( fO ) {
         fO--;
      } else {  // Enough atoms to make water
         printf("Making water ... \n");
         nO--;
         nH -= 2;
         fH = 2;
      }
   }
// Thread finish, atom used to make water
}

H() {

   region R do {
      nH++;
   }
   region R when ( (fH>0) || (nO>0 and nH>1) ) do {
      if ( fH ) {
         fH--;
      } else {  // Enough atoms to make water
         printf("Making water ... \n");
         nO--;
         nH -= 2;
         fH = 1;
         fO = 1;
      }
   }
// Thread finish, atom used to make water
}