Bug 379317 - This change coalesces runnables into one.

This improves perceived performance as repaints are not interleaved with
updates.

Change-Id: If9674e45adf1aa5b4d8530e22dfcd494d228f329
Reviewed-on: https://git.eclipse.org/r/5956
Reviewed-by: Pawel Piech <pawel.piech@windriver.com>
IP-Clean: Pawel Piech <pawel.piech@windriver.com>
Tested-by: Pawel Piech <pawel.piech@windriver.com>

dsf/org.eclipse.cdt.dsf.ui/src/org/eclipse/cdt/dsf/ui/concurrent/SimpleDisplayExecutor.java

@@ -4,15 +4,18 @@
  * 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:
  *     Wind River Systems - initial API and implementation
+ *     NVIDIA - coalesce runnable in the single event loop iteration
  *******************************************************************************/
 package org.eclipse.cdt.dsf.ui.concurrent;
 
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.LinkedList;
 import java.util.Map;
+import java.util.Queue;
 import java.util.concurrent.Executor;
 import java.util.concurrent.RejectedExecutionException;
 
@@ -22,13 +25,13 @@ import org.eclipse.swt.SWTException;
 import org.eclipse.swt.widgets.Display;
 
 /**
- * A simple executor which uses the display thread to run the submitted 
+ * A simple executor which uses the display thread to run the submitted
  * runnables. It only implements the {@link Executor}, and NOT the more
- * sophisticated {@link DsfExecutor} (which extends 
- * {@link java.util.concurrent.ScheduledExecutorService}). However, this 
+ * sophisticated {@link DsfExecutor} (which extends
+ * {@link java.util.concurrent.ScheduledExecutorService}). However, this
  * implementation is much more efficient than DisplayDsfExecutor as it does
  * not use a separate thread or maintain its own queue.
- * 
+ *
  * @since 1.0
  */
 public class SimpleDisplayExecutor implements Executor{
@@ -36,13 +39,13 @@ public class SimpleDisplayExecutor implements Executor{
      * Internal mapping of display objects to executors.
      */
     private static Map<Display, SimpleDisplayExecutor> fExecutors = Collections.synchronizedMap( new HashMap<Display, SimpleDisplayExecutor>() );
-    
+
     /**
      * Factory method for display executors.
      * @param display Display to create an executor for.
      * @return The new (or re-used) executor.
      */
-    public static SimpleDisplayExecutor getSimpleDisplayExecutor(Display display) {
+    public static SimpleDisplayExecutor getSimpleDisplayExecutor(final Display display) {
         synchronized (fExecutors) {
             SimpleDisplayExecutor executor = fExecutors.get(display);
             if (executor == null) {
@@ -52,26 +55,65 @@ public class SimpleDisplayExecutor implements Executor{
             return executor;
         }
     }
-    
+
     /**
-     * The display class used by this executor to execute the submitted runnables. 
+     * The display class used by this executor to execute the submitted runnables.
      */
     private final Display fDisplay;
-    
-    private SimpleDisplayExecutor(Display display) {
+    /**
+     * Runnables waiting for the UI loop iteration
+     */
+    private Queue<Runnable> runnables;
+
+    private SimpleDisplayExecutor(final Display display) {
         fDisplay = display;
     }
 
     @Override
-	public void execute(Runnable command) {
-        try {
-            fDisplay.asyncExec(command);
-        } catch (SWTException e) {
-            if (e.code == SWT.ERROR_DEVICE_DISPOSED) {
-                throw new RejectedExecutionException("Display " + fDisplay + " is disposed", e); //$NON-NLS-1$ //$NON-NLS-2$
-            } else {
-                throw e;
+    public void execute(final Runnable command) {
+        final boolean needsPosting = enqueue(command);
+        if (needsPosting) {
+            try {
+                fDisplay.asyncExec(new Runnable() {
+                    @Override
+                    public void run() {
+                        runInSwtThread();
+                    }
+                });
+            } catch (final SWTException e) {
+                if (e.code == SWT.ERROR_DEVICE_DISPOSED) {
+                    throw new RejectedExecutionException("Display " + fDisplay + " is disposed", e); //$NON-NLS-1$ //$NON-NLS-2$
+                } else {
+                    throw e;
+                }
             }
         }
     }
+
+    private synchronized boolean enqueue(final Runnable runnable) {
+        boolean needsPosting = false;
+        if (runnables == null) {
+            runnables = new LinkedList<Runnable>();
+            needsPosting = true;
+        }
+        runnables.offer(runnable);
+        return needsPosting;
+    }
+
+    private synchronized Runnable getNextRunnable() {
+        final Runnable runnable = runnables.poll();
+        if (runnable == null) {
+            runnables = null;
+            return null;
+        } else {
+            return runnable;
+        }
+    }
+
+    protected void runInSwtThread() {
+        Runnable runnable;
+        while ((runnable = getNextRunnable()) != null) {
+            runnable.run();
+        }
+    }
 }