[182574] prevent duplicate deferred queries to avoid empty list scenario.

rse/plugins/org.eclipse.rse.ui/UI/org/eclipse/rse/ui/operations/SystemDeferredTreeContentManager.java

@@ -13,20 +13,27 @@
  ********************************************************************************/
 package org.eclipse.rse.ui.operations;
 
+import java.util.ArrayList;
+import java.util.List;
+
+import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.jface.viewers.AbstractTreeViewer;
 import org.eclipse.jface.viewers.ITreeContentProvider;
 import org.eclipse.rse.ui.view.IContextObject;
 import org.eclipse.ui.progress.DeferredTreeContentManager;
 import org.eclipse.ui.progress.IDeferredWorkbenchAdapter;
+import org.eclipse.ui.progress.PendingUpdateAdapter;
 
 public class SystemDeferredTreeContentManager extends
 		DeferredTreeContentManager {
 
+	private List _pendingQueries;
+	
 	public SystemDeferredTreeContentManager(ITreeContentProvider provider,
 			AbstractTreeViewer viewer) 
 	{
 		super(provider, viewer);
-		// TODO Auto-generated constructor stub
+		_pendingQueries = new ArrayList();
 	}
 
     /**
@@ -47,4 +54,36 @@ public class SystemDeferredTreeContentManager extends
         return super.getAdapter(element);
     }
 
+    /**
+     * Returns the child elements of the given element, or in the case of a
+     * deferred element, returns a placeholder. If a deferred element is used, a
+     * job is created to fetch the children in the background.
+     * 
+     * @param parent
+     *            The parent object.
+     * @return Object[] or <code>null</code> if parent is not an instance of
+     *         IDeferredWorkbenchAdapter.
+     */
+    public Object[] getChildren(final Object parent) {
+        IDeferredWorkbenchAdapter element = getAdapter(parent);
+        if (element == null) {
+			return null;
+		}
+        PendingUpdateAdapter placeholder = createPendingUpdateAdapter();
+       
+        if (!_pendingQueries.contains(parent))
+        {
+        	startFetchingDeferredChildren(parent, element, placeholder);
+        	_pendingQueries.add(parent);
+        	return new Object[] { placeholder };
+        }
+        return null;
+    }
+    
+    protected void addChildren(final Object parent, final Object[] children,
+            IProgressMonitor monitor) 
+    {
+    	super.addChildren(parent, children, monitor);
+    	_pendingQueries.remove(parent);
+    }
 }