| /** |
| * Copyright 2011, Big Switch Networks, Inc. |
| * Originally created by David Erickson, Stanford University |
| * |
| * 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.floodlightcontroller.core.util; |
| |
| import java.util.concurrent.ScheduledExecutorService; |
| import java.util.concurrent.TimeUnit; |
| |
| import net.floodlightcontroller.core.annotations.LogMessageDoc; |
| |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| |
| /** |
| * This allows you to represent a task that should be queued for future execution |
| * but where you only want the task to complete once in response to some sequence |
| * of events. For example, if you get a change notification and want to reload state, |
| * you only want to reload the state once, at the end, and don't want to queue |
| * an update for every notification that might come in. |
| * |
| * The semantics are as follows: |
| * * If the task hasn't begun yet, do not queue a new task |
| * * If the task has begun, set a bit to restart it after the current task finishes |
| */ |
| public class SingletonTask { |
| protected final static Logger logger = LoggerFactory.getLogger(SingletonTask.class); |
| |
| protected static class SingletonTaskContext { |
| protected boolean taskShouldRun = false; |
| protected boolean taskRunning = false; |
| |
| protected SingletonTaskWorker waitingTask = null; |
| } |
| |
| protected static class SingletonTaskWorker implements Runnable { |
| SingletonTask parent; |
| boolean canceled = false; |
| long nextschedule = 0; |
| |
| public SingletonTaskWorker(SingletonTask parent) { |
| super(); |
| this.parent = parent; |
| } |
| |
| @Override |
| @LogMessageDoc(level="ERROR", |
| message="Exception while executing task", |
| recommendation=LogMessageDoc.GENERIC_ACTION) |
| public void run() { |
| synchronized (parent.context) { |
| if (canceled || !parent.context.taskShouldRun) |
| return; |
| |
| parent.context.taskRunning = true; |
| parent.context.taskShouldRun = false; |
| } |
| |
| try { |
| parent.task.run(); |
| } catch (Exception e) { |
| logger.error("Exception while executing task", e); |
| } |
| |
| synchronized (parent.context) { |
| parent.context.taskRunning = false; |
| |
| if (parent.context.taskShouldRun) { |
| long now = System.nanoTime(); |
| if ((nextschedule <= 0 || (nextschedule - now) <= 0)) { |
| parent.ses.execute(this); |
| } else { |
| parent.ses.schedule(this, |
| nextschedule-now, |
| TimeUnit.NANOSECONDS); |
| } |
| } |
| } |
| } |
| } |
| |
| protected SingletonTaskContext context = new SingletonTaskContext(); |
| protected Runnable task; |
| protected ScheduledExecutorService ses; |
| |
| |
| /** |
| * Construct a new SingletonTask for the given runnable. The context |
| * is used to manage the state of the task execution and can be shared |
| * by more than one instance of the runnable. |
| * @param context |
| * @param Task |
| */ |
| public SingletonTask(ScheduledExecutorService ses, |
| Runnable task) { |
| super(); |
| this.task = task; |
| this.ses = ses; |
| } |
| |
| /** |
| * Schedule the task to run if there's not already a task scheduled |
| * If there is such a task waiting that has not already started, it |
| * cancel that task and reschedule it to run at the given time. If the |
| * task is already started, it will cause the task to be rescheduled once |
| * it completes to run after delay from the time of reschedule. |
| * |
| * @param delay the delay in scheduling |
| * @param unit the timeunit of the delay |
| */ |
| public void reschedule(long delay, TimeUnit unit) { |
| boolean needQueue = true; |
| SingletonTaskWorker stw = null; |
| |
| synchronized (context) { |
| if (context.taskRunning || context.taskShouldRun) { |
| if (context.taskRunning) { |
| // schedule to restart at the right time |
| if (delay > 0) { |
| long now = System.nanoTime(); |
| long then = |
| now + TimeUnit.NANOSECONDS.convert(delay, unit); |
| context.waitingTask.nextschedule = then; |
| } else { |
| context.waitingTask.nextschedule = 0; |
| } |
| needQueue = false; |
| } else { |
| // cancel and requeue |
| context.waitingTask.canceled = true; |
| context.waitingTask = null; |
| } |
| } |
| |
| context.taskShouldRun = true; |
| |
| if (needQueue) { |
| stw = context.waitingTask = new SingletonTaskWorker(this); |
| } |
| } |
| |
| if (needQueue) { |
| if (delay <= 0) |
| ses.execute(stw); |
| else |
| ses.schedule(stw, delay, unit); |
| } |
| } |
| } |