// An implementation of a general semaphore adapted from
// that given in Doug Lea's book on concurrent programming in Java.
// A   while(condition) {..wait()..}   loop is used to suspend the process
// invoking a P().

class semaphore2 {

  private int value ;

  public semaphore2(int i) {
    value = i ;
  }

  synchronized void P() {
    while ( value <= 0 )
       try { wait() ; } catch (InterruptedException e) { } 
    value-- ;
  }

  synchronized void V() {
    value++ ;
    notify() ;
  }
}