semaphore.java

本程序是国外经典的操作系统调度试验

import java.util.Vector ;

public class Semaphore {

   private int value ;
   private Vector queue ;

   public Semaphore(int i) {
      value = i ;
      queue = new Vector() ;
   }

// This should be called V() in usual semaphore parlance, but
// it was called signal() last year, and the decision to use the
// proper names for the operations was taken after the lab manual
// was printed. So we will stick with signal()!
   public synchronized void signal() {
	// you need to write this
   }

// This should be called P() in usual semaphore parlance ... 
// but the above explanation applies.
   public void wait(SemProc t) {
	// you need to write this too. Note it is not synchronized
	// because it may end by removing the current process, t, 
	// from the ready queue and that would leave the semaphore locked!
	// However it IS important to exclude the possibility that two 
	// processes could confuse each other - even though this is only a 
	// theorectical possibility. You will not observe it "going wrong" 
	// in the lab configuration - but you will lose a mark of you don't
	// get it right!
   }
}