1 files changed, 113 insertions, 0 deletions
diff --git a/datarouter-node/src/main/java/com/att/research/datarouter/node/TaskList.java b/datarouter-node/src/main/java/com/att/research/datarouter/node/TaskList.java
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+++ b/datarouter-node/src/main/java/com/att/research/datarouter/node/TaskList.java
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+/*******************************************************************************
+ * ============LICENSE_START==================================================
+ * * org.onap.dmaap
+ * * ===========================================================================
+ * * Copyright © 2017 AT&T Intellectual Property. All rights reserved.
+ * * ===========================================================================
+ * * 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.
+ * * ============LICENSE_END====================================================
+ * *
+ * * ECOMP is a trademark and service mark of AT&T Intellectual Property.
+ * *
+ ******************************************************************************/
+
+
+package com.att.research.datarouter.node;
+
+import java.util.*;
+
+/**
+ *	Manage a list of tasks to be executed when an event occurs.
+ *	This makes the following guarantees:
+ *	<ul>
+ *	<li>Tasks can be safely added and removed in the middle of a run.</li>
+ *	<li>No task will be returned more than once during a run.</li>
+ *	<li>No task will be returned when it is not, at that moment, in the list of tasks.</li>
+ *	<li>At the moment when next() returns null, all tasks on the list have been returned during the run.</li>
+ *	<li>Initially and once next() returns null during a run, next() will continue to return null until startRun() is called.
+ *	</ul>
+ */
+public class TaskList	{
+	private Iterator<Runnable>	runlist;
+	private HashSet<Runnable>	tasks = new HashSet<Runnable>();
+	private HashSet<Runnable>	togo;
+	private HashSet<Runnable>	sofar;
+	private HashSet<Runnable>	added;
+	private HashSet<Runnable>	removed;
+	/**
+	 *	Construct a new TaskList
+	 */
+	public TaskList() {
+	}
+	/**
+	 *	Start executing the sequence of tasks.
+	 */
+	public synchronized void	startRun() {
+		sofar = new HashSet<Runnable>();
+		added = new HashSet<Runnable>();
+		removed = new HashSet<Runnable>();
+		togo = new HashSet<Runnable>(tasks);
+		runlist = togo.iterator();
+	}
+	/**
+	 *	Get the next task to execute
+	 */
+	public synchronized Runnable	next() {
+		while (runlist != null) {
+			if (runlist.hasNext()) {
+				Runnable task = runlist.next();
+				if (removed.contains(task)) {
+					continue;
+				}
+				if (sofar.contains(task)) {
+					continue;
+				}
+				sofar.add(task);
+				return(task);
+			}
+			if (added.size() != 0) {
+				togo = added;
+				added = new HashSet<Runnable>();
+				removed.clear();
+				runlist = togo.iterator();
+				continue;
+			}
+			togo = null;
+			added = null;
+			removed = null;
+			sofar = null;
+			runlist = null;
+		}
+		return(null);
+	}
+	/**
+	 *	Add a task to the list of tasks to run whenever the event occurs.
+	 */
+	public synchronized void addTask(Runnable task) {
+		if (runlist != null) {
+			added.add(task);
+			removed.remove(task);
+		}
+		tasks.add(task);
+	}
+	/**
+	 *	Remove a task from the list of tasks to run whenever the event occurs.
+	 */
+	public synchronized void removeTask(Runnable task) {
+		if (runlist != null) {
+			removed.add(task);
+			added.remove(task);
+		}
+		tasks.remove(task);
+	}
+}