Make the debounce adaptive for validation job

org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/MovingAverage.java

@@ -0,0 +1,50 @@
+/*******************************************************************************
+ * Copyright (c) 2021 Microsoft Corporation and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Microsoft Corporation - initial API and implementation
+ *******************************************************************************/
+
+package org.eclipse.jdt.ls.core.internal;
+
+/**
+ * A class used to calculate the cumulative moving average.
+ * @see <a href="https://en.wikipedia.org/wiki/Moving_average#Cumulative_moving_average">Definition from Wikipedia</a>.
+ */
+public class MovingAverage {
+	/**
+	 * The average value
+	 */
+	public long value;
+
+	private long n = 1;
+
+	public MovingAverage() {
+		this(0);
+	}
+
+	/**
+	 * Initialize the moving average with a initial value
+	 * @param initValue The initial value of the moving average
+	 */
+	public MovingAverage(long initValue) {
+		this.value = initValue;
+	}
+
+	/**
+	 * Update the moving average value
+	 * @param value A new value used to update the moving average
+	 * @return The <code>MovingAverage</code> instance
+	 */
+	public MovingAverage update(long value) {
+		this.value = this.value + (value - this.value) / this.n;
+		this.n += 1;
+		return this;
+	}
+}

org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/handlers/BaseDocumentLifeCycleHandler.java

@@ -54,6 +54,7 @@
 import org.eclipse.jdt.ls.core.internal.JDTUtils;
 import org.eclipse.jdt.ls.core.internal.JavaLanguageServerPlugin;
 import org.eclipse.jdt.ls.core.internal.JobHelpers;
+import org.eclipse.jdt.ls.core.internal.MovingAverage;
 import org.eclipse.jdt.ls.core.internal.corrections.DiagnosticsHelper;
 import org.eclipse.jdt.ls.core.internal.managers.ProjectsManager;
 import org.eclipse.jface.text.BadLocationException;
@@ -78,19 +79,28 @@ public abstract class BaseDocumentLifeCycleHandler {
 	public static final String DOCUMENT_LIFE_CYCLE_JOBS = "DocumentLifeCycleJobs";
 	public static final String PUBLISH_DIAGNOSTICS_JOBS = "DocumentLifeCyclePublishDiagnosticsJobs";
 
+	/**
+	 * The max & init value of adaptive debounce time for document lifecycle job.
+	 */
+	private static final long DOCUMENT_LIFECYCLE_MAX_DEBOUNCE = 400; /*ms*/
+
 	private CoreASTProvider sharedASTProvider;
 	private WorkspaceJob validationTimer;
 	private WorkspaceJob publishDiagnosticsJob;
 	private Set<ICompilationUnit> toReconcile = new HashSet<>();
 	private Map<String, Integer> documentVersions = new HashMap<>();
+	private MovingAverage movingAverage = new MovingAverage(DOCUMENT_LIFECYCLE_MAX_DEBOUNCE);
 
 	public BaseDocumentLifeCycleHandler(boolean delayValidation) {
 		this.sharedASTProvider = CoreASTProvider.getInstance();
 		if (delayValidation) {
 			this.validationTimer = new WorkspaceJob("Validate documents") {
 				@Override
 				public IStatus runInWorkspace(IProgressMonitor monitor) throws CoreException {
-					return performValidation(monitor);
+					long start = System.currentTimeMillis();
+					IStatus status = performValidation(monitor);
+					movingAverage.update(System.currentTimeMillis() - start);
+					return status;
 				}
 
 				/* (non-Javadoc)
@@ -125,7 +135,7 @@ public boolean belongsTo(Object family) {
 	public abstract ICompilationUnit resolveCompilationUnit(String uri);
 
 	protected void triggerValidation(ICompilationUnit cu) throws JavaModelException {
-		triggerValidation(cu, 400);
+		triggerValidation(cu, getDocumentLifecycleDelay());
 	}
 
 	protected void triggerValidation(ICompilationUnit cu, long delay) throws JavaModelException {
@@ -150,6 +160,10 @@ protected void triggerValidation(ICompilationUnit cu, long delay) throws JavaMod
 		}
 	}
 
+	private long getDocumentLifecycleDelay() {
+		return Math.min(DOCUMENT_LIFECYCLE_MAX_DEBOUNCE, Math.round(1.5 * movingAverage.value));
+	}
+
 	private ISchedulingRule getRule(Set<ICompilationUnit> units) {
 		ISchedulingRule result = null;
 		IResourceRuleFactory ruleFactory = ResourcesPlugin.getWorkspace().getRuleFactory();

org.eclipse.jdt.ls.tests/src/org/eclipse/jdt/ls/core/internal/MovingAverageTest.java

@@ -0,0 +1,37 @@
+/*******************************************************************************
+ * Copyright (c) 2021 Microsoft Corporation and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Microsoft Corporation - initial API and implementation
+ *******************************************************************************/
+
+package org.eclipse.jdt.ls.core.internal;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class MovingAverageTest {
+
+	@Test
+	public void testUpdate() {
+		MovingAverage average = new MovingAverage(400);
+
+		// initialize to 400 at first
+		assertEquals(400, average.value);
+
+		average.update(200);
+		// the first input value takes over the initial value
+		assertEquals(200, average.value);
+
+		average.update(100);
+		// (200 + 100) / 2
+		assertEquals(150, average.value);
+	}
+}