added Waiting in build queue

pom.xml

@@ -42,7 +42,7 @@
 		<dependency>
 			<groupId>net.bull.javamelody</groupId>
 			<artifactId>javamelody-core</artifactId>
-			<version>1.79.0</version>
+			<version>1.80.0-SNAPSHOT</version>
 		</dependency>
 		<!-- slf4j-api for Jenkins issue https://issues.jenkins-ci.org/browse/JENKINS-11293
 		NoClassDefFoundError: org.slf4j.ILoggerFactory on IBM J9 JVM,

src/main/java/net/bull/javamelody/NodesCollector.java

@@ -165,6 +165,8 @@ public void collectWithoutErrorsNow() {
 			// note: this BUILD_QUEUE_LENGTH needs at least javamelody-core 1.35.0-SNAPSHOT
 			// including values for buildQueueLength in translations*.properties
 			JdbcWrapper.BUILD_QUEUE_LENGTH.set(queueLength);
+			final long waitingDurationsSum = WaitingDurationQueueListener.getWaitingDurationsSum();
+			JdbcWrapper.BUILD_QUEUE_WAITING_DURATIONS_SUM.set(waitingDurationsSum);
 
 			final List<JavaInformations> javaInformations = new ArrayList<>(
 					getLastJavaInformationsList().values());

src/main/java/net/bull/javamelody/WaitingDurationQueueListener.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2008-2019 by Emeric Vernat
+ *
+ *     This file is part of the Monitoring plugin.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package net.bull.javamelody;
+
+import java.util.Date;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+import hudson.Extension;
+import hudson.model.Queue.LeftItem;
+import hudson.model.Queue.WaitingItem;
+import hudson.model.queue.QueueListener;
+
+/**
+ * Listener d'entrée et de sortie de la file d'attente pour calculer un indicateur d'attente.
+ * @author Emeric Vernat
+ */
+@Extension
+public class WaitingDurationQueueListener extends QueueListener {
+	private static final ConcurrentMap<Long, Date> START_TIMES_BY_ID = new ConcurrentHashMap<>();
+
+	/** {@inheritDoc} */
+	@Override
+	public void onEnterWaiting(WaitingItem wi) {
+		START_TIMES_BY_ID.put(wi.getId(), new Date());
+	}
+
+	/** {@inheritDoc} */
+	@Override
+	public void onLeft(LeftItem li) {
+		START_TIMES_BY_ID.remove(li.getId());
+	}
+
+	static long getWaitingDurationsSum() {
+		final long now = System.currentTimeMillis();
+		long sum = 0;
+		for (final Date date : START_TIMES_BY_ID.values()) {
+			// now can be a bit before date
+			sum += now - date.getTime();
+		}
+		return Math.max(sum, 0);
+	}
+}