os.java

操作系统实验的程序

import java.io.*;
import java.util.*;
public class os
{
  public static void main(String args[])
  {
       Database d= new Database();
       d.napping();
       Writer  w1= new Writer(d);
       w1.start();
       Reader  r1= new Reader(d);
       r1.start();
       
       
  }
}
class Database{

   private static final int NAP_TIME=5;
   private  int readercount;
   private  boolean dbreading;
   private  boolean dbwriting;
   private  File   afile;
   
   public Database()
      {
         readercount=0;
         dbreading= false;
         dbwriting= false;
         afile= new File("test.txt");
        }
    public static void napping()
       {
        int sleepTime= (int)(NAP_TIME*Math.random());
        try{
             Thread.sleep(sleepTime*1000);
            }
         catch(InterruptedException e){ }
         }
     public synchronized int startread()
        {
          while(dbwriting==true)
           {
             try{
                 wait();
                 }
             catch(InterruptedException e){ }
            }
           ++readercount;
           if(readercount==1)
                dbreading= true;
           try{
            FileInputStream fin= new FileInputStream(afile);
            byte buf[]= new byte[10];
            fin.read(buf);
            System.out.println("Thread Reader reading now(printout)");
            System.out.println(new String(buf,0,10));
             fin.close();
               }
            catch(FileNotFoundException e)
              { 
                     e.printStackTrace();
                }
             catch(IOException exp)
               {
                    exp.printStackTrace();
                 }   
             return readercount;
           }
        public synchronized int endread()
          {
              --readercount;
              if(readercount==0)
                 dbreading= false;
              System.out.println("End reading\n");
              notifyAll();
              return readercount;
            }
         public synchronized void startwrite()
          {
             while(dbreading== true||dbwriting== true)
              {
                   try{
                       wait();
                       }
                   catch(InterruptedException e){ }
               }
              dbwriting= true;
              try{
               String[] source= {"honghejinji ","tianlei ","recursion "};
               Random tian=new Random();
               int mm=tian.nextInt(3);
               byte buf[]= source[mm].getBytes();
               FileOutputStream fout= new FileOutputStream(afile);
               System.out.println("Thread Writer writing now");
                 fout.write(buf);
                fout.close();
                  }
               catch(FileNotFoundException e)
              { 
                     e.printStackTrace();
                }
             catch(IOException exp)
               {
                    exp.printStackTrace();
                 }   
             }
           public synchronized void endwrite()
             {
                 dbwriting= false;
                 System.out.println("End writing\n");
                 notifyAll();
                 
              }
}

class Reader extends Thread
{    
     private boolean done=false;
     private Database d;
     Reader(Database d)
     {
       this.d= d;
      }   
      synchronized boolean ok()
      {
         return(!done);
       }   
       public void run() 
       {
          while(ok())
          {
            d.startread();
            d.endread();
            try{
            Thread.sleep(3000);
                }
             catch(InterruptedException e)
              {
                     e.printStackTrace();
                }
           }
         }
}

class Writer extends Thread
{
     private boolean done=false;
     private Database d;
     Writer(Database d)
     {
       this.d= d;
      }   
      synchronized boolean ok()
      {
         return(!done);
       }   
       public void run() 
       {
          while(ok()) 
          {
             d.startwrite();
             d.endwrite();
             try{
              Thread.sleep(5000);
                 }
              catch(InterruptedException e)
              {
                     e.printStackTrace();
                }
            }
         }

}