线程为什么会堵塞[Java编程]

//: Blocking.java
// Demonstrates the various ways a thread
// can be blocked.
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.io.*;

//////////// The basic framework ///////////
class Blockable extends Thread {
  private Peeker peeker;
  protected TextField state = new TextField(40);
  protected int i;
  public Blockable(Container c) {
    c.add(state);
    peeker = new Peeker(this, c);
  }
  public synchronized int read() { return i; }
  protected synchronized void update() {
    state.setText(getClass().getName()
      + " state: i = " + i);
  }
  public void stopPeeker() { 
    // peeker.stop(); Deprecated in Java 1.2
    peeker.terminate(); // The preferred approach
  }
}

class Peeker extends Thread {
  private Blockable b;
  private int session;
  private TextField status = new TextField(40);
  private boolean stop = false;
  public Peeker(Blockable b, Container c) {
    c.add(status);
    this.b = b;
    start();
  }
  public void terminate() { stop = true; }
  public void run() {
    while (!stop) {
      status.setText(b.getClass().getName()
        + " Peeker " + (++session)
        + "; value = " + b.read());
       try {
        sleep(100);
      } catch (InterruptedException e){}
    }
  }
} ///:Continued

///:Continuing
///////////// Blocking via sleep() ///////////
class Sleeper1 extends Blockable {
  public Sleeper1(Container c) { super(c); }
  public synchronized void run() {
    while(true) {
      i++;
      update();
       try {
        sleep(1000);
      } catch (InterruptedException e){}
    }
  }
}
  
class Sleeper2 extends Blockable {
  public Sleeper2(Container c) { super(c); }
  public void run() {
    while(true) {
      change();
       try {
        sleep(1000);
      } catch (InterruptedException e){}
    }
  }
  public synchronized void change() {
      i++;
      update();
  }
} ///:Continued

///:Continuing
/////////// Blocking via suspend() ///////////
class SuspendResume extends Blockable {
  public SuspendResume(Container c) {
    super(c);    
    new Resumer(this); 
  }
}

class SuspendResume1 extends SuspendResume {
  public SuspendResume1(Container c) { super(c);}
  public synchronized void run() {
    while(true) {
      i++;
      update();
      suspend(); // Deprecated in Java 1.2
    }
  }
}

class SuspendResume2 extends SuspendResume {
  public SuspendResume2(Container c) { super(c);}
  public void run() {
    while(true) {
      change();
      suspend(); // Deprecated in Java 1.2
    }
  }
  public synchronized void change() {
      i++;
      update();
  }
}

class Resumer extends Thread {
  private SuspendResume sr;
  public Resumer(SuspendResume sr) {
    this.sr = sr;
    start();
  }
  public void run() {
    while(true) {
       try {
        sleep(1000);
      } catch (InterruptedException e){}
      sr.resume(); // Deprecated in Java 1.2
    }
  }
} ///:Continued

synchronized(wn2) {
  wn2.notify();
}

///:Continuing
/////////// Blocking via wait() ///////////
class WaitNotify1 extends Blockable {
  public WaitNotify1(Container c) { super(c); }
  public synchronized void run() {
    while(true) {
      i++;
      update();
       try {
        wait(1000);
      } catch (InterruptedException e){}
    }
  }
}

class WaitNotify2 extends Blockable {
  public WaitNotify2(Container c) {
    super(c);
    new Notifier(this); 
  }
  public synchronized void run() {
    while(true) {
      i++;
      update();
       try {
        wait();
      } catch (InterruptedException e){}
    }
  }
}

class Notifier extends Thread {
  private WaitNotify2 wn2;
  public Notifier(WaitNotify2 wn2) {
    this.wn2 = wn2;
    start();
  }
  public void run() {
    while(true) {
       try {
        sleep(2000);
      } catch (InterruptedException e){}
      synchronized(wn2) {
        wn2.notify();
      }
    }
  }
} ///:Continued

///:Continuing
class Sender extends Blockable { // send
  private Writer out;
  public Sender(Container c, Writer out) { 
    super(c);
    this.out = out; 
  }
  public void run() {
    while(true) {
      for(char c = 'A'; c <= 'z'; c++) {
         try {
          i++;
          out.write(c);
          state.setText("Sender sent: " 
            + (char)c);
          sleep((int)(3000 * Math.random()));
        } catch (InterruptedException e){}
          catch (IOException e) {}
      }
    }
  }
}

class Receiver extends Blockable {
  private Reader in;
  public Receiver(Container c, Reader in) { 
    super(c);
    this.in = in; 
  }
  public void run() {
    try {
      while(true) {
        i++; // Show peeker it's alive
        // Blocks until characters are there:
        state.setText("Receiver read: "
          + (char)in.read());
      }
    } catch(IOException e) { e.printStackTrace();}
  }
} ///:Continued

///:Continuing
/////////// Testing Everything ///////////
public class Blocking extends Applet {
  private Button 
    start = new Button("Start"),
    stopPeekers = new Button("Stop Peekers");
  private boolean started = false;
  private Blockable[] b;
  private PipedWriter out;
  private PipedReader in;
  public void init() {
     out = new PipedWriter();
    try {
      in = new PipedReader(out);
    } catch(IOException e) {}
    b = new Blockable[] {
      new Sleeper1(this),
      new Sleeper2(this),
      new SuspendResume1(this),
      new SuspendResume2(this),
      new WaitNotify1(this),
      new WaitNotify2(this),
      new Sender(this, out),
      new Receiver(this, in)
    };
    start.addActionListener(new StartL());
    add(start);
    stopPeekers.addActionListener(
      new StopPeekersL());
    add(stopPeekers);
  }
  class StartL implements ActionListener {
    public void actionPerformed(ActionEvent e) {
      if(!started) {
        started = true;
        for(int i = 0; i < b.length; i++)
          b[i].start();
      }
    }
  }
  class StopPeekersL implements ActionListener {
    public void actionPerformed(ActionEvent e) {
      // Demonstration of the preferred 
      // alternative to Thread.stop():
      for(int i = 0; i < b.length; i++)
        b[i].stopPeeker();
    }
  }
  public static void main(String[] args) {
    Blocking applet = new Blocking();
    Frame aFrame = new Frame("Blocking");
    aFrame.addWindowListener(
      new WindowAdapter() {
        public void windowClosing(WindowEvent e) {
          System.exit(0);
        }
      });
    aFrame.add(applet, BorderLayout.CENTER);
    aFrame.setSize(350,550);
    applet.init();
    applet.start();
    aFrame.setVisible(true);
  }
} ///:~