Updatethrottle singleton

app/display/representation/src/main/java/org/csstudio/display/builder/representation/RepresentationUpdateThrottle.java

@@ -38,8 +38,8 @@
 @SuppressWarnings("nls")
 public class RepresentationUpdateThrottle
 {
-    /** Instance counter to aid in debugging the throttle start/shutdown */
-    private static final AtomicInteger instance = new AtomicInteger();
+    /** Reference counter to aid in debugging the throttle start/shutdown */
+    private static final AtomicInteger reference_count = new AtomicInteger();
 
     /** Period in seconds for logging update performance */
     private static final int performance_log_period_secs = Preferences.performance_log_period_secs;
@@ -53,6 +53,9 @@ public class RepresentationUpdateThrottle
     /** Pause between updates to prevent flooding the UI thread */
     private static final long update_delay = Preferences.update_delay;
 
+    /** Singleton instance of this class */
+    private static RepresentationUpdateThrottle instance;
+
     /** Executor for UI thread */
     private final Executor gui_executor;
 
@@ -73,12 +76,28 @@ public class RepresentationUpdateThrottle
      */
     private final Set<WidgetRepresentation<?, ?, ?>> updateable = new LinkedHashSet<>();
 
-    /** @param gui_executor Executor for UI thread */
-    public RepresentationUpdateThrottle(final Executor gui_executor)
+    /** Get instance of this class to perform updates on the UI thread. This class
+     * is a singleton to ensure that only one thread is scheduling jobs on the UI
+     * thread.
+     *
+     *  @param guiExecutor Executor for UI thread
+     */
+    public static synchronized RepresentationUpdateThrottle getInstance(final Executor guiExecutor) {
+        if(instance == null) {
+            instance = new RepresentationUpdateThrottle(guiExecutor);
+        }
+        reference_count.incrementAndGet();
+        logger.log(Level.FINE, () -> "RepresentationUpdateThrottle getInstance() reference count: "
+                + reference_count.get());
+        return instance;
+    }
+
+    /** @param guiExecutor Executor for UI thread */
+    private RepresentationUpdateThrottle(final Executor guiExecutor)
     {
-        final String name = "RepresentationUpdateThrottle" + instance.incrementAndGet();
+        final String name = "RepresentationUpdateThrottle";
         logger.log(Level.FINE, "Create " + name);
-        this.gui_executor = gui_executor;
+        this.gui_executor = guiExecutor;
         throttle_thread = new Thread(this::doRun);
         throttle_thread.setName(name);
         throttle_thread.setDaemon(true);
@@ -218,20 +237,8 @@ private void updateInUI(final WidgetRepresentation<?, ?, ?>[] representations,
     /** Shutdown the throttle thread and wait for it to exit */
     public void shutdown()
     {
-        run = false;
-        synchronized (updateable)
-        {
-            updateable.notifyAll();
-        }
-        try
-        {
-            throttle_thread.join(2000);
-        }
-        catch (final InterruptedException ex)
-        {
-            // Ignore, closing down anyway
-        }
-        if (throttle_thread.isAlive())
-            logger.log(Level.WARNING, "Representation update throttle fails to terminate within 2 seconds");
+        reference_count.decrementAndGet();
+        logger.log(Level.FINE, () -> "RepresentationUpdateThrottle shutdown() reference count: "
+                + reference_count.get());
     }
 }

app/display/representation/src/main/java/org/csstudio/display/builder/representation/ToolkitRepresentation.java

@@ -74,7 +74,7 @@ abstract public class ToolkitRepresentation<TWP extends Object, TW> implements E
 
     private final boolean edit_mode;
 
-    private final RepresentationUpdateThrottle throttle = new RepresentationUpdateThrottle(this);
+    private final RepresentationUpdateThrottle throttle = RepresentationUpdateThrottle.getInstance(this);
 
     /**
      * Listener list

app/display/representation/src/test/java/org/csstudio/display/builder/representation/UpdateThrottleTest.java

@@ -26,9 +26,9 @@
  *  @author Kay Kasemir
  */
 @SuppressWarnings("nls")
-public class UpdateThrottleTest
+class UpdateThrottleTest
 {
-    private final RepresentationUpdateThrottle throttle = new RepresentationUpdateThrottle(Executors.newSingleThreadExecutor());
+    private final RepresentationUpdateThrottle throttle = RepresentationUpdateThrottle.getInstance(Executors.newSingleThreadExecutor());
 
     private class TestWidgetRepresentation extends WidgetRepresentation<Object, Object, Widget>
     {
@@ -79,7 +79,7 @@ public void updateOrder()
     }
 
     @Test
-    public void demonstrateUpdateThrottle() throws Throwable
+    void demonstrateUpdateThrottle() throws Throwable
     {
         final AtomicInteger updates_a = new AtomicInteger();
         final AtomicInteger updates_b = new AtomicInteger();