[jboss-dev-forums] [Design the new POJO MicroContainer] - Re: Composite Map key and weak reference

[bstansberry@jboss.com]

I believe Jason's #2 is what I was thinking about in our chat discussion.  A rough impl:


  | package hacks;
  | 
  | import java.lang.annotation.Annotation;
  | import java.lang.ref.Reference;
  | import java.lang.ref.ReferenceQueue;
  | import java.lang.ref.WeakReference;
  | 
  | public class Key
  | {
  |    private static final ReferenceQueue refQueue = new ReferenceQueue();
  |    
  |    private final KeyRef keyRef;
  |    private final WeakReference<Annotation>[] annotations;
  |    
  |    public Key(Class clazz, Annotation[] annotations)
  |    {
  |       this.keyRef = new KeyRef(this, clazz, refQueue);
  |       this.annotations = new WeakReference[annotations.length];
  |       for (int j = 0; j < annotations.length; j++)
  |       {
  |          this.annotations[j]= new WeakReference<Annotation>(annotations[j]);
  |       }
  |    }
  |    
  |    @Override
  |    public boolean equals(Object obj)
  |    {
  |       if (obj instanceof Key)
  |       {
  |          Key other = (Key) obj;
  |          Class clazz = keyRef.get();
  |          Class otherClass = other.keyRef.get();
  |          if (clazz == null || otherClass == null)
  |          {
  |             cleanKeyRefs();
  |             return false;
  |          }
  |          else 
  |          {
  |             if (shouldCleanKeyRefs())
  |                cleanKeyRefs();
  |             return clazz.equals(otherClass); // need to add in annotations
  |          }
  |       }
  |       
  |       return false;
  |    }
  |    
  |    /** Allows optimization; i.e. change to only poll the queue every X invocations */ 
  |    private boolean shouldCleanKeyRefs()
  |    {
  |       return true;
  |    }
  |    
  |    /**
  |     * Poll the reference queue and clear the strong ref to Key from all
  |     * reference objects.  This allows the Key to get removed from
  |     * WeakHashMap.
  |     */
  |    private void cleanKeyRefs()
  |    {
  |       Reference ref = null;
  |       while ((ref = refQueue.poll()) != null)
  |       {
  |          ((KeyRef) ref).key = null;
  |       }      
  |    }
  | 
  |    private static class KeyRef extends WeakReference<Class>
  |    {
  |       private Key key;
  |       
  |       KeyRef(Key key, Class clazz, ReferenceQueue queue)
  |       {
  |          super(clazz, queue);
  |          this.key = key;
  |       }
  |    }
  | }

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