Reduce number of LabelProviderChangedEvents

When a resource changes there are several events fired that lead
towards re-decoration of this resource (and parent resources). These
events are often redundant, e.g. when checking out a different
branch, JGit fires a RefsChangedEvent and an IndexChangedEvent.
Furthermore Eclipse detects that a resource changed and thus fires a
ResourceChangeEvent. But in the end only one re-decoration should be
triggered, thus a mechanism is introduced that delays firing an event
for 100ms and ignores further events within this time frame.

Change-Id: I4dfb4156e289d573f5f115613f3c55604e9c6746
Signed-off-by: Philipp Thun <philipp.thun@sap.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

1 files changed, 74 insertions, 21 deletions

diff --git a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/decorators/GitLightweightDecorator.java b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/decorators/GitLightweightDecorator.java
index f1d68208cf..af63b8f1dd 100644
--- a/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/decorators/GitLightweightDecorator.java
+++ b/org.eclipse.egit.ui/src/org/eclipse/egit/ui/internal/decorators/GitLightweightDecorator.java
@@ -32,8 +32,11 @@ import org.eclipse.core.resources.ResourcesPlugin;
 import org.eclipse.core.resources.mapping.ResourceMapping;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IAdaptable;
+import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.core.runtime.IStatus;
 import org.eclipse.core.runtime.QualifiedName;
+import org.eclipse.core.runtime.Status;
+import org.eclipse.core.runtime.jobs.Job;
 import org.eclipse.egit.core.internal.util.ExceptionCollector;
 import org.eclipse.egit.core.project.GitProjectData;
 import org.eclipse.egit.core.project.RepositoryChangeListener;
@@ -333,8 +336,8 @@ public class GitLightweightDecorator extends LabelProvider implements
 			}
 		}
 
-		// Re-trigger decoration process (in UI thread)
-		fireLabelEvent(new LabelProviderChangedEvent(this));
+		// Immediately fire label provider changed event
+		fireLabelEvent();
 	}
 
 	/**
@@ -659,12 +662,12 @@ public class GitLightweightDecorator extends LabelProvider implements
 		if (prop.equals(TeamUI.GLOBAL_IGNORES_CHANGED)
 				|| prop.equals(TeamUI.GLOBAL_FILE_TYPES_CHANGED)
 				|| prop.equals(Activator.DECORATORS_CHANGED)) {
-			postLabelEvent(new LabelProviderChangedEvent(this));
+			postLabelEvent(null);
 		} else if (prop.equals(UIPreferences.THEME_UncommittedChangeBackgroundColor)
 				|| prop.equals(UIPreferences.THEME_UncommittedChangeFont)
 				|| prop.equals(UIPreferences.THEME_UncommittedChangeForegroundColor)) {
 			ensureFontAndColorsCreated(fonts, colors);
-			postLabelEvent(new LabelProviderChangedEvent(this)); // TODO do I really need this?
+			postLabelEvent(null); // TODO do I really need this?
 		}
 	}
 
@@ -757,16 +760,15 @@ public class GitLightweightDecorator extends LabelProvider implements
 			}
 		}
 
-		postLabelEvent(new LabelProviderChangedEvent(this, resourcesToUpdate
-				.toArray()));
+		postLabelEvent(resourcesToUpdate.toArray());
 	}
 
 	public void onIndexChanged(IndexChangedEvent e) {
-		postLabelEvent(new LabelProviderChangedEvent(this));
+		postLabelEvent(null);
 	}
 
 	public void onRefsChanged(RefsChangedEvent e) {
-		postLabelEvent(new LabelProviderChangedEvent(this));
+		postLabelEvent(null);
 	}
 
 	/**
@@ -778,7 +780,7 @@ public class GitLightweightDecorator extends LabelProvider implements
 	public void repositoryChanged(RepositoryMapping mapping) {
 		// Until we find a way to refresh visible labels within a project
 		// we have to use this blanket refresh that includes all projects.
-		postLabelEvent(new LabelProviderChangedEvent(this));
+		postLabelEvent(null);
 	}
 
 	// -------- Helper methods --------
@@ -807,13 +809,13 @@ public class GitLightweightDecorator extends LabelProvider implements
 	}
 
 	/**
-	 * Post the label event to the UI thread
+	 * Post a label event to the LabelEventJob
 	 *
-	 * @param event
-	 *            The event to post
+	 * @param elements
+	 *            The elements to update
 	 */
-	private void postLabelEvent(final LabelProviderChangedEvent event) {
-		if (event.getElement() == null) {
+	private void postLabelEvent(final Object[] elements) {
+		if (elements == null) {
 			// Update all elements
 			final IWorkspaceRoot root = ResourcesPlugin.getWorkspace()
 					.getRoot();
@@ -824,11 +826,8 @@ public class GitLightweightDecorator extends LabelProvider implements
 			} catch (CoreException e) {
 				handleException(root, e);
 			}
-
-			fireLabelEvent(event);
 		} else {
 			// Update specific elements
-			Object[] elements = event.getElements();
 			for (Object element : elements) {
 				final IResource resource = getResource(element);
 				if (resource != null)
@@ -839,13 +838,15 @@ public class GitLightweightDecorator extends LabelProvider implements
 						// Ignore
 					}
 			}
-
-			// Fire a generic event
-			fireLabelEvent(new LabelProviderChangedEvent(this));
 		}
+
+		LabelEventJob.getInstance().postLabelEvent(this);
 	}
 
-	private void fireLabelEvent(final LabelProviderChangedEvent event) {
+	void fireLabelEvent() {
+		final LabelProviderChangedEvent event = new LabelProviderChangedEvent(
+				this);
+		// Re-trigger decoration process (in UI thread)
 		Display.getDefault().asyncExec(new Runnable() {
 			public void run() {
 				fireLabelProviderChanged(event);
@@ -867,3 +868,55 @@ public class GitLightweightDecorator extends LabelProvider implements
 			exceptions.handleException(e);
 	}
 }
+
+/**
+ * Job reducing label events to prevent unnecessary (i.e. redundant) event
+ * processing
+ */
+class LabelEventJob extends Job {
+
+	/**
+	 * Constant defining the waiting time (in milliseconds) until an event is
+	 * fired
+	 */
+	private static final long DELAY = 100L;
+
+	private static LabelEventJob instance = new LabelEventJob("LabelEventJob"); //$NON-NLS-1$
+
+	/**
+	 * Get the LabelEventJob singleton
+	 *
+	 * @return the LabelEventJob singleton
+	 */
+	static LabelEventJob getInstance() {
+		return instance;
+	}
+
+	private LabelEventJob(final String name) {
+		super(name);
+	}
+
+	private GitLightweightDecorator glwDecorator = null;
+
+	/**
+	 * Post a label event
+	 *
+	 * @param decorator
+	 *            The GitLightweightDecorator that is used to fire a
+	 *            LabelProviderChangedEvent
+	 */
+	void postLabelEvent(final GitLightweightDecorator decorator) {
+		if (this.glwDecorator == null)
+			this.glwDecorator = decorator;
+		if (getState() == SLEEPING || getState() == WAITING)
+			cancel();
+		schedule(DELAY);
+	}
+
+	@Override
+	protected IStatus run(IProgressMonitor monitor) {
+		if (glwDecorator != null)
+			glwDecorator.fireLabelEvent();
+		return Status.OK_STATUS;
+	}
+}