Insight has to keep track of rend. engines in use itself

With ome#5513 the java gateway removes stale connectors (e.g. after
server restart). So Insight can't use the gateway any longer to
provide the information which images are currently viewed, the
stale references are removed after server restart / reconnect.

components/insight/SRC/org/openmicroscopy/shoola/env/data/OMEROGateway.java

@@ -1,6 +1,6 @@
 /*
  *------------------------------------------------------------------------------
- *  Copyright (C) 2006-2017 University of Dundee. All rights reserved.
+ *  Copyright (C) 2006-2018 University of Dundee. All rights reserved.
  *
  *
  *  This program is free software; you can redistribute it and/or modify
@@ -387,6 +387,9 @@ class OMEROGateway
 
 	private Gateway gw;
 
+    // Keep track of the rendering engines currently in use
+    private Map<SecurityContext, Set<Long>> renderingEngines = new HashMap<SecurityContext, Set<Long>>();
+
 	/**
 	 * Creates the query to load the file set corresponding to a given image.
 	 *
@@ -514,7 +517,17 @@ private ScriptCallback runScript(SecurityContext ctx, long scriptID,
 	void closeService(SecurityContext ctx,
             StatefulServiceInterfacePrx svc)
     {
-        if (ctx == null || svc == null) return;
+        if (ctx == null || svc == null)
+            return;
+        if (svc instanceof RenderingEnginePrx && renderingEngines.containsKey(ctx)) { 
+            try {
+                renderingEngines.get(ctx).remove(
+                        ((RenderingEnginePrx) svc).getPixels().getId()
+                                .getValue());
+            } catch (ServerError e) {
+                // do nothing
+            }
+        }
         gw.closeService(ctx, svc);
     }
 
@@ -1602,7 +1615,7 @@ String lookupLdapAuthExperimenter(SecurityContext ctx, long userID)
 	 */
 	Map<SecurityContext, Set<Long>> getRenderingEngines()
 	{
-		return gw.getRenderingEngines();
+		return renderingEngines;
 	}
 
 	boolean joinSession() {
@@ -2397,6 +2410,12 @@ private RenderingEnginePrx generateRenderingEngine(
 			service.lookupPixels(pixelsID);
 			needDefault(pixelsID, service);
 			service.load();
+            Set<Long> pixIds = renderingEngines.get(ctx);
+            if (pixIds == null) {
+                pixIds = new HashSet<Long>();
+                renderingEngines.put(ctx, pixIds);
+            }
+            pixIds.add(pixelsID);
 			return service;
 		} catch (Throwable t) {
 		    log(t.getMessage());