--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/EDU/oswego/cs/dl/util/concurrent/WaitableRef.java	Sat Mar 21 11:00:06 2009 +0000
@@ -0,0 +1,102 @@
+/*
+  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();
+    }
+  }
+
+}
+