Interruptible Synchronized Block : Lock Synchronize « Threads « Java

1. Java
2. Threads
3. Lock Synchronize

Interruptible Synchronized Block

     
public class InterruptibleSyncBlock extends Object {
  private Object longLock;

  private BooleanLock busyLock;

  public InterruptibleSyncBlock() {
    longLock = new Object();
    busyLock = new BooleanLock(false);
  }

  public void doStuff() throws InterruptedException {
    print("about to try to get exclusive access " + "to busyLock");
    busyLock.waitToSetTrue(0);

    try {
      print("about to try to get exclusive access " + "to longLock");
      synchronized (longLock) {
        print("got exclusive access to longLock");
        try {
          Thread.sleep(10000);
        } catch (InterruptedException x) {
          // ignore
        }
        print("about to relinquish exclusive access " + "to longLock");
      }
    } finally {
      print("about to free up busyLock");
      busyLock.setValue(false);
    }
  }

  private static void print(String msg) {
    String name = Thread.currentThread().getName();
    System.err.println(name + ": " + msg);
  }

  private static Thread launch(final InterruptibleSyncBlock sb, String name) {

    Runnable r = new Runnable() {
      public void run() {
        print("in run()");
        try {
          sb.doStuff();
        } catch (InterruptedException x) {
          print("InterruptedException thrown " + "from doStuff()");
        }
      }
    };

    Thread t = new Thread(r, name);
    t.start();

    return t;
  }

  public static void main(String[] args) {
    try {
      InterruptibleSyncBlock sb = new InterruptibleSyncBlock();

      Thread t1 = launch(sb, "T1");
      Thread.sleep(500);

      Thread t2 = launch(sb, "T2");
      Thread t3 = launch(sb, "T3");

      Thread.sleep(1000);

      print("about to interrupt T2");
      t2.interrupt();
      print("just interrupted T2");

    } catch (InterruptedException x) {
      x.printStackTrace();
    }
  }
}

class BooleanLock extends Object {
  private boolean value;

  public BooleanLock(boolean initialValue) {
    value = initialValue;
  }

  public BooleanLock() {
    this(false);
  }

  public synchronized void setValue(boolean newValue) {
    if ( newValue != value ) {
      value = newValue;
      notifyAll();
    }
  }

  public synchronized boolean waitToSetTrue(long msTimeout) 
      throws InterruptedException {

    boolean success = waitUntilFalse(msTimeout);
    if ( success ) {
      setValue(true);
    }

    return success;
  }

  public synchronized boolean waitToSetFalse(long msTimeout) 
      throws InterruptedException {

    boolean success = waitUntilTrue(msTimeout);
    if ( success ) {
      setValue(false);
    }

    return success;
  }

  public synchronized boolean isTrue() {
    return value;
  }

  public synchronized boolean isFalse() {
    return !value;
  }

  public synchronized boolean waitUntilTrue(long msTimeout) 
      throws InterruptedException {

    return waitUntilStateIs(true, msTimeout);
  }

  public synchronized boolean waitUntilFalse(long msTimeout) 
      throws InterruptedException {

    return waitUntilStateIs(false, msTimeout);
  }

  public synchronized boolean waitUntilStateIs(
        boolean state, 
        long msTimeout
      ) throws InterruptedException {

    if ( msTimeout == 0L ) {
      while ( value != state ) {
        wait();  // wait indefinitely until notified
      }

      // condition has finally been met
      return true;
    } 

    // only wait for the specified amount of time
    long endTime = System.currentTimeMillis() + msTimeout;
    long msRemaining = msTimeout;

    while ( ( value != state ) && ( msRemaining > 0L ) ) {
      wait(msRemaining);
      msRemaining = endTime - System.currentTimeMillis();
    }

    // May have timed out, or may have met value, 
    // calculate return value.
    return ( value == state );
  }
}


           
         
    
    
    
    
  

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