File: WaitableRef.java

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/*
  File: WaitableRef.java

  Originally written by Doug Lea and released into the public domain.
  This may be used for any purposes whatsoever without acknowledgment.
  Thanks for the assistance and support of Sun Microsystems Labs,
  and everyone contributing, testing, and using this code.

  History:
  Date       Who                What
  19Jun1998  dl               Create public version
*/

package EDU.oswego.cs.dl.util.concurrent;

/**
 * A class useful for offloading synch for Object reference instance variables.
 *
 * <p>[<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>]
 **/

public class WaitableRef extends SynchronizedRef {

  /** 
   * Create a WaitableRef initially holding the given reference 
   * and using its own internal lock.
   **/
  public WaitableRef(Object initialValue) { 
    super(initialValue);
  }

  /** 
   * Make a new WaitableRef with the given initial value,
   * and using the supplied lock.
   **/
  public WaitableRef(Object initialValue, Object lock) { 
    super(initialValue, lock); 
  }

  public Object set(Object newValue) { 
    synchronized (lock_) {
      lock_.notifyAll();
      return super.set(newValue);
    }
  }

  public boolean commit(Object assumedValue, Object newValue) {
    synchronized (lock_) {
      boolean success = super.commit(assumedValue, newValue);
      if (success) lock_.notifyAll();
      return success;
    }
  }

  /**
   * Wait until value is null, then run action if nonnull.
   * The action is run with the synchronization lock held.
   **/

  public void whenNull(Runnable action) throws InterruptedException {
    synchronized (lock_) {
      while (value_ != null) lock_.wait();
      if (action != null) action.run();
    }
  }

  /**
   * wait until value is nonnull, then run action if nonnull.
   * The action is run with the synchronization lock held.
   **/
  public void whenNotNull(Runnable action) throws InterruptedException {
    synchronized (lock_) {
      while (value_ == null) lock_.wait();
      if (action != null) action.run();
    }
  }

  /**
   * Wait until value equals c, then run action if nonnull.
   * The action is run with the synchronization lock held.
   **/

  public void whenEqual(Object c, Runnable action) throws InterruptedException {
    synchronized (lock_) {
      while (!(value_ == c)) lock_.wait();
      if (action != null) action.run();
    }
  }

  /**
   * wait until value not equal to c, then run action if nonnull.
   * The action is run with the synchronization lock held.
   **/
  public void whenNotEqual(Object c, Runnable action) throws InterruptedException {
    synchronized (lock_) {
      while (!(value_ != c)) lock_.wait();
      if (action != null) action.run();
    }
  }

}