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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);
}
}
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