[509141] Provide CDORegistrationHandler callbacks

https://bugs.eclipse.org/bugs/show_bug.cgi?id=509141

10 files changed, 440 insertions, 35 deletions

diff --git a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/CDOAdapter.java b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/CDOAdapter.java
index 1f12acb231..987bc9a8b3 100644
--- a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/CDOAdapter.java
+++ b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/CDOAdapter.java
@@ -18,12 +18,12 @@ import org.eclipse.emf.cdo.view.CDOView.Options;
 import org.eclipse.emf.common.notify.Adapter;
 
 /**
- * A marker interface for {@link Adapter adpters} to indicate that change subscriptions should be registered with the
+ * A marker interface for {@link Adapter adapters} to indicate that change subscriptions should be registered with the
  * repository if they are attached to {@link CDOObject objects}.
  * <p>
  * This special marker interface is intended to be used with {@link CDOAdapterPolicy#CDO}. Note that you can also define
  * your own {@link CDOAdapterPolicy adapter policy} and {@link Options#addChangeSubscriptionPolicy(CDOAdapterPolicy)
- * register} it with the {@link CDOView view} to make your own adapters trigger change subscription.
+ * register} it with the {@link CDOView view} to make your own adapters trigger change subscriptions.
  *
  * @author Simon McDuff
  * @since 2.0
diff --git a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/CDOLocalAdapter.java b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/CDOLocalAdapter.java
new file mode 100644
index 0000000000..ac7e4240b4
--- /dev/null
+++ b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/CDOLocalAdapter.java
@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2016 Eike Stepper (Berlin, Germany) and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *    Eike Stepper - initial API and implementation
+ */
+package org.eclipse.emf.cdo;
+
+import org.eclipse.emf.common.notify.Adapter;
+
+/**
+ * A marker interface for {@link Adapter adapters} to indicate that change subscriptions should <b>not</b> be registered with the
+ * repository if they are attached to {@link CDOObject objects}.
+ *
+ * @author Eike Stepper
+ * @since 4.6
+ */
+public interface CDOLocalAdapter extends Adapter
+{
+}
diff --git a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/transaction/CDOPostEventTransactionHandler.java b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/transaction/CDOPostEventTransactionHandler.java
index b33a634806..616de0231c 100644
--- a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/transaction/CDOPostEventTransactionHandler.java
+++ b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/transaction/CDOPostEventTransactionHandler.java
@@ -144,23 +144,32 @@ public abstract class CDOPostEventTransactionHandler implements CDOTransactionHa
           {
             postEvent((CDOTransaction)object.cdoView(), object, msg);
 
-            boolean eDeliver = object.eDeliver();
+            boolean deliver = object.eDeliver();
 
             try
             {
-              object.eSetDeliver(false);
+              if (deliver)
+              {
+                object.eSetDeliver(false);
+              }
+
               adapters.remove(this);
             }
             finally
             {
-              object.eSetDeliver(eDeliver);
+              if (deliver)
+              {
+                object.eSetDeliver(true);
+              }
             }
           }
         }
       }
     }
 
-    private boolean isModifyingEvent(int eventType)
+    protected abstract void postEvent(CDOTransaction transaction, CDOObject object, Notification msg);
+
+    private static boolean isModifyingEvent(int eventType)
     {
       switch (eventType)
       {
@@ -177,7 +186,5 @@ public abstract class CDOPostEventTransactionHandler implements CDOTransactionHa
         return false;
       }
     }
-
-    protected abstract void postEvent(CDOTransaction transaction, CDOObject object, Notification msg);
   }
 }
diff --git a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/transaction/CDOPushTransaction.java b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/transaction/CDOPushTransaction.java
index 70f82c7eef..c68dc5e2ee 100644
--- a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/transaction/CDOPushTransaction.java
+++ b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/transaction/CDOPushTransaction.java
@@ -33,6 +33,7 @@ import org.eclipse.emf.cdo.session.CDOSession;
 import org.eclipse.emf.cdo.util.CommitException;
 import org.eclipse.emf.cdo.view.CDOObjectHandler;
 import org.eclipse.emf.cdo.view.CDOQuery;
+import org.eclipse.emf.cdo.view.CDORegistrationHandler;
 import org.eclipse.emf.cdo.view.CDOUnitManager;
 import org.eclipse.emf.cdo.view.CDOView;
 import org.eclipse.emf.cdo.view.CDOViewProvider;
@@ -330,6 +331,14 @@ public class CDOPushTransaction extends Notifier implements CDOTransaction
   }
 
   /**
+   * @since 4.6
+   */
+  public void addRegistrationHandler(CDORegistrationHandler handler)
+  {
+    delegate.addRegistrationHandler(handler);
+  }
+
+  /**
    * @since 4.0
    */
   public void addTransactionHandler(CDOTransactionHandlerBase handler)
@@ -491,6 +500,14 @@ public class CDOPushTransaction extends Notifier implements CDOTransaction
     return delegate.getObjectHandlers();
   }
 
+  /**
+   * @since 4.6
+   */
+  public CDORegistrationHandler[] getRegistrationHandlers()
+  {
+    return delegate.getRegistrationHandlers();
+  }
+
   public CDOResource getOrCreateResource(String path)
   {
     return delegate.getOrCreateResource(path);
@@ -818,6 +835,14 @@ public class CDOPushTransaction extends Notifier implements CDOTransaction
   }
 
   /**
+   * @since 4.6
+   */
+  public void removeRegistrationHandler(CDORegistrationHandler handler)
+  {
+    delegate.removeRegistrationHandler(handler);
+  }
+
+  /**
    * @since 4.0
    */
   public void removeTransactionHandler(CDOTransactionHandlerBase handler)
diff --git a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/view/CDORegistrationHandler.java b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/view/CDORegistrationHandler.java
new file mode 100644
index 0000000000..743f585ae9
--- /dev/null
+++ b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/view/CDORegistrationHandler.java
@@ -0,0 +1,156 @@
+/*
+ * Copyright (c) 2016 Eike Stepper (Berlin, Germany) and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *    Eike Stepper - initial API and implementation
+ */
+package org.eclipse.emf.cdo.view;
+
+import org.eclipse.emf.cdo.CDOObject;
+import org.eclipse.emf.cdo.common.id.CDOID;
+
+import org.eclipse.net4j.util.event.IListener;
+import org.eclipse.net4j.util.lifecycle.ILifecycle;
+import org.eclipse.net4j.util.lifecycle.LifecycleEventAdapter;
+import org.eclipse.net4j.util.lifecycle.LifecycleUtil;
+
+import org.eclipse.emf.spi.cdo.InternalCDOObject;
+import org.eclipse.emf.spi.cdo.InternalCDOView;
+
+/**
+ * Call-back handler used by {@link CDOView views} to tell implementors of this interface about registrations and deregistrations
+ * of {@link CDOObject objects} with {@link CDOView views}.
+ *
+ * @author Eike Stepper
+ * @since 4.6
+ * @see CDOView#addRegistrationHandler(CDORegistrationHandler)
+ * @see CDOView#removeRegistrationHandler(CDORegistrationHandler)
+ * @see CDOView#isObjectRegistered(org.eclipse.emf.cdo.common.id.CDOID)
+ */
+public interface CDORegistrationHandler
+{
+  public void objectRegistered(CDOView view, CDOObject object);
+
+  public void objectDeregistered(CDOView view, CDOObject object);
+
+  public void objectCollected(CDOView view, CDOID id);
+
+  /**
+   * @author Eike Stepper
+   */
+  public static class Default implements CDORegistrationHandler
+  {
+    private final IListener deactivateListener = new LifecycleEventAdapter()
+    {
+      @Override
+      protected void onDeactivated(ILifecycle lifecycle)
+      {
+        dispose();
+      }
+    };
+
+    private CDOView view;
+
+    public Default(final CDOView view)
+    {
+      view.syncExec(new Runnable()
+      {
+        public void run()
+        {
+          doInitialize(view);
+        }
+      });
+
+      this.view = view;
+    }
+
+    public final CDOView getView()
+    {
+      return view;
+    }
+
+    public final boolean isDisposed()
+    {
+      return view == null;
+    }
+
+    public synchronized void dispose()
+    {
+      if (view != null)
+      {
+        final CDOView finalView = view;
+        view = null;
+
+        finalView.syncExec(new Runnable()
+        {
+          public void run()
+          {
+            doDispose(finalView);
+          }
+        });
+      }
+    }
+
+    /**
+     * Called by the view for each registered object.
+     * <p>
+     * Also called during initialization for already loaded objects;
+     * {@link #isDisposed()} returns <code>true</code> in these cases.
+     */
+    public void objectRegistered(CDOView view, CDOObject object)
+    {
+      // Subclasses may override.
+    }
+
+    /**
+     * Called by the view for each deregistered object.
+     * <p>
+     * Also called during dispose for already loaded objects;
+     * {@link #isDisposed()} returns <code>true</code> in these cases.
+     */
+    public void objectDeregistered(CDOView view, CDOObject object)
+    {
+      // Subclasses may override.
+    }
+
+    /**
+     * Called by the view for each garbage-collected object.
+     */
+    public void objectCollected(CDOView view, CDOID id)
+    {
+      // Subclasses may override.
+    }
+
+    protected void doInitialize(CDOView view)
+    {
+      if (LifecycleUtil.isActive(view))
+      {
+        for (InternalCDOObject object : ((InternalCDOView)view).getObjects().values())
+        {
+          objectRegistered(view, object);
+        }
+      }
+
+      view.addRegistrationHandler(this);
+      view.addListener(deactivateListener);
+    }
+
+    protected void doDispose(CDOView view)
+    {
+      view.removeListener(deactivateListener);
+      view.removeRegistrationHandler(this);
+
+      if (LifecycleUtil.isActive(view))
+      {
+        for (InternalCDOObject object : ((InternalCDOView)view).getObjects().values())
+        {
+          objectDeregistered(view, object);
+        }
+      }
+    }
+  }
+}
diff --git a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/view/CDOView.java b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/view/CDOView.java
index 98c1a0d89d..d13a555836 100644
--- a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/view/CDOView.java
+++ b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/cdo/view/CDOView.java
@@ -565,6 +565,21 @@ public interface CDOView extends CDOCommonView, CDOUpdatable, CDOCommitHistory.P
   public CDOObjectHandler[] getObjectHandlers();
 
   /**
+   * @since 4.6
+   */
+  public void addRegistrationHandler(CDORegistrationHandler handler);
+
+  /**
+   * @since 4.6
+   */
+  public void removeRegistrationHandler(CDORegistrationHandler handler);
+
+  /**
+   * @since 4.6
+   */
+  public CDORegistrationHandler[] getRegistrationHandlers();
+
+  /**
    * Same as <code>createQuery(language, queryString, null)</code>.
    *
    * @see #createQuery(String, String, Object)
diff --git a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/internal/cdo/view/AbstractCDOView.java b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/internal/cdo/view/AbstractCDOView.java
index c502eaae3d..5562d069da 100644
--- a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/internal/cdo/view/AbstractCDOView.java
+++ b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/internal/cdo/view/AbstractCDOView.java
@@ -66,6 +66,7 @@ import org.eclipse.emf.cdo.util.ReadOnlyException;
 import org.eclipse.emf.cdo.view.CDOAdapterPolicy;
 import org.eclipse.emf.cdo.view.CDOObjectHandler;
 import org.eclipse.emf.cdo.view.CDOQuery;
+import org.eclipse.emf.cdo.view.CDORegistrationHandler;
 import org.eclipse.emf.cdo.view.CDOView;
 import org.eclipse.emf.cdo.view.CDOViewAdaptersNotifiedEvent;
 import org.eclipse.emf.cdo.view.CDOViewEvent;
@@ -81,6 +82,7 @@ import org.eclipse.emf.internal.cdo.transaction.CDOTransactionImpl;
 import org.eclipse.net4j.util.AdapterUtil;
 import org.eclipse.net4j.util.CheckUtil;
 import org.eclipse.net4j.util.ImplementationError;
+import org.eclipse.net4j.util.ReflectUtil;
 import org.eclipse.net4j.util.ReflectUtil.ExcludeFromDump;
 import org.eclipse.net4j.util.StringUtil;
 import org.eclipse.net4j.util.WrappedException;
@@ -127,6 +129,7 @@ import org.eclipse.emf.spi.cdo.InternalCDOViewSet;
 import org.eclipse.core.runtime.IProgressMonitor;
 
 import java.io.IOException;
+import java.lang.reflect.Method;
 import java.text.MessageFormat;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -186,6 +189,15 @@ public abstract class AbstractCDOView extends CDOCommitHistoryProviderImpl<CDOOb
     }
   };
 
+  private final ConcurrentArray<CDORegistrationHandler> registrationHandlers = new ConcurrentArray<CDORegistrationHandler>()
+  {
+    @Override
+    protected CDORegistrationHandler[] newArray(int length)
+    {
+      return new CDORegistrationHandler[length];
+    }
+  };
+
   private final IRegistry<String, Object> properties = new HashMapRegistry<String, Object>()
   {
     @Override
@@ -294,6 +306,18 @@ public abstract class AbstractCDOView extends CDOCommitHistoryProviderImpl<CDOOb
     }
   }
 
+  public int purgeUnusedObjects()
+  {
+    if (objects instanceof ReferenceValueMap2)
+    {
+      ReferenceValueMap2<CDOID, InternalCDOObject> map = (ReferenceValueMap2<CDOID, InternalCDOObject>)objects;
+      Method method = ReflectUtil.getMethod(ReferenceValueMap2.class, "internalPurgeQueue");
+      return (Integer)ReflectUtil.invokeMethod(method, map);
+    }
+
+    return 0;
+  }
+
   public Map<CDOID, InternalCDOObject> getObjects()
   {
     synchronized (getViewMonitor())
@@ -347,7 +371,15 @@ public abstract class AbstractCDOView extends CDOCommitHistoryProviderImpl<CDOOb
       }
 
       Map<CDOID, KeyedReference<CDOID, InternalCDOObject>> map = CDOIDUtil.createMap();
-      newObjects = new ReferenceValueMap2.Strong<CDOID, InternalCDOObject>(map);
+      newObjects = new ReferenceValueMap2.Strong<CDOID, InternalCDOObject>(map)
+      {
+        @Override
+        protected void purged(CDOID id)
+        {
+          objectCollected(id);
+        }
+      };
+
       break;
     }
 
@@ -359,7 +391,15 @@ public abstract class AbstractCDOView extends CDOCommitHistoryProviderImpl<CDOOb
       }
 
       Map<CDOID, KeyedReference<CDOID, InternalCDOObject>> map = CDOIDUtil.createMap();
-      newObjects = new ReferenceValueMap2.Soft<CDOID, InternalCDOObject>(map);
+      newObjects = new ReferenceValueMap2.Soft<CDOID, InternalCDOObject>(map)
+      {
+        @Override
+        protected void purged(CDOID id)
+        {
+          objectCollected(id);
+        }
+      };
+
       break;
     }
 
@@ -371,7 +411,15 @@ public abstract class AbstractCDOView extends CDOCommitHistoryProviderImpl<CDOOb
       }
 
       Map<CDOID, KeyedReference<CDOID, InternalCDOObject>> map = CDOIDUtil.createMap();
-      newObjects = new ReferenceValueMap2.Weak<CDOID, InternalCDOObject>(map);
+      newObjects = new ReferenceValueMap2.Weak<CDOID, InternalCDOObject>(map)
+      {
+        @Override
+        protected void purged(CDOID id)
+        {
+          objectCollected(id);
+        }
+      };
+
       break;
     }
 
@@ -1948,11 +1996,6 @@ public abstract class AbstractCDOView extends CDOCommitHistoryProviderImpl<CDOOb
     }
   }
 
-  protected void objectDeregistered(InternalCDOObject object)
-  {
-    // Subclasses may override.
-  }
-
   /**
    * @return Never <code>null</code>
    */
@@ -2432,11 +2475,6 @@ public abstract class AbstractCDOView extends CDOCommitHistoryProviderImpl<CDOOb
     }
   }
 
-  protected void objectRegistered(InternalCDOObject object)
-  {
-    // Subclasses may override.
-  }
-
   public void deregisterObject(InternalCDOObject object)
   {
     synchronized (getViewMonitor())
@@ -2459,6 +2497,81 @@ public abstract class AbstractCDOView extends CDOCommitHistoryProviderImpl<CDOOb
     }
   }
 
+  protected void objectRegistered(InternalCDOObject object)
+  {
+    CDORegistrationHandler[] handlers = getRegistrationHandlers();
+    if (handlers.length != 0)
+    {
+      synchronized (getViewMonitor())
+      {
+        lockView();
+
+        try
+        {
+          for (int i = 0; i < handlers.length; i++)
+          {
+            CDORegistrationHandler handler = handlers[i];
+            handler.objectRegistered(this, object);
+          }
+        }
+        finally
+        {
+          unlockView();
+        }
+      }
+    }
+  }
+
+  protected void objectDeregistered(InternalCDOObject object)
+  {
+    CDORegistrationHandler[] handlers = getRegistrationHandlers();
+    if (handlers.length != 0)
+    {
+      synchronized (getViewMonitor())
+      {
+        lockView();
+
+        try
+        {
+          for (int i = 0; i < handlers.length; i++)
+          {
+            CDORegistrationHandler handler = handlers[i];
+            handler.objectDeregistered(this, object);
+          }
+        }
+        finally
+        {
+          unlockView();
+        }
+      }
+    }
+  }
+
+  protected void objectCollected(CDOID id)
+  {
+    CDORegistrationHandler[] handlers = getRegistrationHandlers();
+    if (handlers.length != 0)
+    {
+      synchronized (getViewMonitor())
+      {
+        lockView();
+
+        try
+        {
+          for (int i = 0; i < handlers.length; i++)
+          {
+            CDORegistrationHandler handler = handlers[i];
+            handler.objectCollected(this, id);
+          }
+        }
+        finally
+        {
+          unlockView();
+        }
+      }
+    }
+  }
+
   public void remapObject(CDOID oldID)
   {
     synchronized (getViewMonitor())
@@ -2508,26 +2621,44 @@ public abstract class AbstractCDOView extends CDOCommitHistoryProviderImpl<CDOOb
 
   public void handleObjectStateChanged(InternalCDOObject object, CDOState oldState, CDOState newState)
   {
-    synchronized (getViewMonitor())
+    CDOObjectHandler[] handlers = getObjectHandlers();
+    if (handlers.length != 0)
     {
-      lockView();
-
-      try
+      synchronized (getViewMonitor())
       {
-        CDOObjectHandler[] handlers = getObjectHandlers();
-        for (int i = 0; i < handlers.length; i++)
+        lockView();
+
+        try
         {
-          CDOObjectHandler handler = handlers[i];
-          handler.objectStateChanged(this, object, oldState, newState);
+          for (int i = 0; i < handlers.length; i++)
+          {
+            CDOObjectHandler handler = handlers[i];
+            handler.objectStateChanged(this, object, oldState, newState);
+          }
+        }
+        finally
+        {
+          unlockView();
         }
-      }
-      finally
-      {
-        unlockView();
       }
     }
   }
 
+  public void addRegistrationHandler(CDORegistrationHandler handler)
+  {
+    registrationHandlers.add(handler);
+  }
+
+  public void removeRegistrationHandler(CDORegistrationHandler handler)
+  {
+    registrationHandlers.remove(handler);
+  }
+
+  public CDORegistrationHandler[] getRegistrationHandlers()
+  {
+    return registrationHandlers.get();
+  }
+
   /*
    * Synchronized through InvalidationRunner.run()
    */
diff --git a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/internal/cdo/view/CDOViewImpl.java b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/internal/cdo/view/CDOViewImpl.java
index 601aa997a0..b68084b1d8 100644
--- a/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/internal/cdo/view/CDOViewImpl.java
+++ b/plugins/org.eclipse.emf.cdo/src/org/eclipse/emf/internal/cdo/view/CDOViewImpl.java
@@ -12,6 +12,7 @@
  */
 package org.eclipse.emf.internal.cdo.view;
 
+import org.eclipse.emf.cdo.CDOLocalAdapter;
 import org.eclipse.emf.cdo.CDONotification;
 import org.eclipse.emf.cdo.CDOObject;
 import org.eclipse.emf.cdo.common.CDOCommonView;
@@ -970,6 +971,7 @@ public class CDOViewImpl extends AbstractCDOView implements IExecutorServiceProv
   @Override
   protected void objectRegistered(InternalCDOObject object)
   {
+    super.objectRegistered(object);
     unitManager.addObject(object);
   }
 
@@ -977,6 +979,7 @@ public class CDOViewImpl extends AbstractCDOView implements IExecutorServiceProv
   protected void objectDeregistered(InternalCDOObject object)
   {
     removeLockState(object);
+    super.objectDeregistered(object);
   }
 
   public CDOLockState[] getLockStates(Collection<CDOID> ids)
@@ -1379,7 +1382,7 @@ public class CDOViewImpl extends AbstractCDOView implements IExecutorServiceProv
             }
           }
 
-          getChangeSubscriptionManager().handleDetachedObjects(detachedObjects);
+          changeSubscriptionManager.handleDetachedObjects(detachedObjects);
         }
       }
       finally
@@ -2529,6 +2532,11 @@ public class CDOViewImpl extends AbstractCDOView implements IExecutorServiceProv
 
     private boolean shouldSubscribe(EObject eObject, Adapter adapter)
     {
+      if (adapter instanceof CDOLocalAdapter)
+      {
+        return false;
+      }
+
       if (unitManager.getOpenUnitUnsynced(eObject) != null)
       {
         return false;
diff --git a/plugins/org.eclipse.net4j.tests/src/org/eclipse/net4j/util/tests/AbstractOMTest.java b/plugins/org.eclipse.net4j.tests/src/org/eclipse/net4j/util/tests/AbstractOMTest.java
index 33a1b5eafc..b056bee2e9 100644
--- a/plugins/org.eclipse.net4j.tests/src/org/eclipse/net4j/util/tests/AbstractOMTest.java
+++ b/plugins/org.eclipse.net4j.tests/src/org/eclipse/net4j/util/tests/AbstractOMTest.java
@@ -768,6 +768,30 @@ public abstract class AbstractOMTest extends TestCase
     skipTest(true);
   }
 
+  public static void triggerGC()
+  {
+    List<byte[]> bigdata = new ArrayList<byte[]>();
+
+    try
+    {
+      while (true)
+      {
+        try
+        {
+          bigdata.add(new byte[1024 * 1024]);
+        }
+        catch (Throwable ex)
+        {
+          break;
+        }
+      }
+    }
+    catch (Throwable ex)
+    {
+      //$FALL-THROUGH$
+    }
+  }
+
   public static void disableLog4j()
   {
     BasicConfigurator.configure(new Appender()
diff --git a/plugins/org.eclipse.net4j.util/src/org/eclipse/net4j/util/ref/ReferenceValueMap2.java b/plugins/org.eclipse.net4j.util/src/org/eclipse/net4j/util/ref/ReferenceValueMap2.java
index 2f95a4c97c..6d934c6f50 100644
--- a/plugins/org.eclipse.net4j.util/src/org/eclipse/net4j/util/ref/ReferenceValueMap2.java
+++ b/plugins/org.eclipse.net4j.util/src/org/eclipse/net4j/util/ref/ReferenceValueMap2.java
@@ -169,19 +169,34 @@ public abstract class ReferenceValueMap2<K, V> extends AbstractMap<K, V>
     return new ReferenceQueue<V>();
   }
 
+  /**
+   * @since 3.7
+   */
   @SuppressWarnings("unchecked")
-  protected void purgeQueue()
+  protected int internalPurgeQueue()
   {
     if (queue != null)
     {
+      int purged = 0;
       KeyedReference<K, V> ref;
+
       while ((ref = (KeyedReference<K, V>)queue.poll()) != null)
       {
         K key = ref.getKey();
         map.remove(key);
         purged(key);
+        ++purged;
       }
+
+      return purged;
     }
+
+    return 0;
+  }
+
+  protected void purgeQueue()
+  {
+    internalPurgeQueue();
   }
 
   protected void purged(K key)