+/*******************************************************************************\r
+ * ============LICENSE_START==================================================\r
+ * * org.onap.dmaap\r
+ * * ===========================================================================\r
+ * * Copyright © 2017 AT&T Intellectual Property. All rights reserved.\r
+ * * ===========================================================================\r
+ * * Licensed under the Apache License, Version 2.0 (the "License");\r
+ * * you may not use this file except in compliance with the License.\r
+ * * You may obtain a copy of the License at\r
+ * * \r
+ * * http://www.apache.org/licenses/LICENSE-2.0\r
+ * * \r
+ * * Unless required by applicable law or agreed to in writing, software\r
+ * * distributed under the License is distributed on an "AS IS" BASIS,\r
+ * * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\r
+ * * See the License for the specific language governing permissions and\r
+ * * limitations under the License.\r
+ * * ============LICENSE_END====================================================\r
+ * *\r
+ * * ECOMP is a trademark and service mark of AT&T Intellectual Property.\r
+ * *\r
+ ******************************************************************************/\r
+\r
+\r
+package org.onap.dmaap.datarouter.node;\r
+\r
+import java.util.*;\r
+\r
+/**\r
+ * Manage a list of tasks to be executed when an event occurs.\r
+ * This makes the following guarantees:\r
+ * <ul>\r
+ * <li>Tasks can be safely added and removed in the middle of a run.</li>\r
+ * <li>No task will be returned more than once during a run.</li>\r
+ * <li>No task will be returned when it is not, at that moment, in the list of tasks.</li>\r
+ * <li>At the moment when next() returns null, all tasks on the list have been returned during the run.</li>\r
+ * <li>Initially and once next() returns null during a run, next() will continue to return null until startRun() is called.\r
+ * </ul>\r
+ */\r
+public class TaskList {\r
+ private Iterator<Runnable> runlist;\r
+ private HashSet<Runnable> tasks = new HashSet<Runnable>();\r
+ private HashSet<Runnable> togo;\r
+ private HashSet<Runnable> sofar;\r
+ private HashSet<Runnable> added;\r
+ private HashSet<Runnable> removed;\r
+ /**\r
+ * Construct a new TaskList\r
+ */\r
+ public TaskList() {\r
+ }\r
+ /**\r
+ * Start executing the sequence of tasks.\r
+ */\r
+ public synchronized void startRun() {\r
+ sofar = new HashSet<Runnable>();\r
+ added = new HashSet<Runnable>();\r
+ removed = new HashSet<Runnable>();\r
+ togo = new HashSet<Runnable>(tasks);\r
+ runlist = togo.iterator();\r
+ }\r
+ /**\r
+ * Get the next task to execute\r
+ */\r
+ public synchronized Runnable next() {\r
+ while (runlist != null) {\r
+ if (runlist.hasNext()) {\r
+ Runnable task = runlist.next();\r
+ if (removed.contains(task)) {\r
+ continue;\r
+ }\r
+ if (sofar.contains(task)) {\r
+ continue;\r
+ }\r
+ sofar.add(task);\r
+ return(task);\r
+ }\r
+ if (added.size() != 0) {\r
+ togo = added;\r
+ added = new HashSet<Runnable>();\r
+ removed.clear();\r
+ runlist = togo.iterator();\r
+ continue;\r
+ }\r
+ togo = null;\r
+ added = null;\r
+ removed = null;\r
+ sofar = null;\r
+ runlist = null;\r
+ }\r
+ return(null);\r
+ }\r
+ /**\r
+ * Add a task to the list of tasks to run whenever the event occurs.\r
+ */\r
+ public synchronized void addTask(Runnable task) {\r
+ if (runlist != null) {\r
+ added.add(task);\r
+ removed.remove(task);\r
+ }\r
+ tasks.add(task);\r
+ }\r
+ /**\r
+ * Remove a task from the list of tasks to run whenever the event occurs.\r
+ */\r
+ public synchronized void removeTask(Runnable task) {\r
+ if (runlist != null) {\r
+ removed.add(task);\r
+ added.remove(task);\r
+ }\r
+ tasks.remove(task);\r
+ }\r
+}\r