Java tutorial
/************************************************************************************** * Copyright (C) 2008 EsperTech, Inc. All rights reserved. * * http://esper.codehaus.org * * http://www.espertech.com * * ---------------------------------------------------------------------------------- * * The software in this package is published under the terms of the GPL license * * a copy of which has been included with this distribution in the license.txt file. * **************************************************************************************/ package com.espertech.esper.core; import com.espertech.esper.dispatch.Dispatchable; import com.espertech.esper.timer.TimeSourceService; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; /** * UpdateDispatchFutureSpin can be added to a dispatch queue that is thread-local. It represents * is a stand-in for a future dispatching of a statement result to statement listeners. * <p> * UpdateDispatchFutureSpin is aware of future and past dispatches: * (newest) DF3 <--> DF2 <--> DF1 (oldest), and uses a spin lock to block if required */ public class UpdateDispatchFutureSpin implements Dispatchable { private static final Log log = LogFactory.getLog(UpdateDispatchFutureSpin.class); private UpdateDispatchViewBlockingSpin view; private UpdateDispatchFutureSpin earlier; private volatile boolean isCompleted; private long msecTimeout; private TimeSourceService timeSourceService; /** * Ctor. * @param view is the blocking dispatch view through which to execute a dispatch * @param earlier is the older future * @param msecTimeout is the timeout period to wait for listeners to complete a prior dispatch * @param timeSourceService time source provider */ public UpdateDispatchFutureSpin(UpdateDispatchViewBlockingSpin view, UpdateDispatchFutureSpin earlier, long msecTimeout, TimeSourceService timeSourceService) { this.view = view; this.earlier = earlier; this.msecTimeout = msecTimeout; this.timeSourceService = timeSourceService; } /** * Ctor - use for the first future to indicate completion. * @param timeSourceService time source provider */ public UpdateDispatchFutureSpin(TimeSourceService timeSourceService) { isCompleted = true; this.timeSourceService = timeSourceService; } /** * Returns true if the dispatch completed for this future. * @return true for completed, false if not */ public boolean isCompleted() { return isCompleted; } public void execute() { if (!earlier.isCompleted) { long spinStartTime = timeSourceService.getTimeMillis(); while (!earlier.isCompleted) { Thread.yield(); long spinDelta = timeSourceService.getTimeMillis() - spinStartTime; if (spinDelta > msecTimeout) { log.info("Spin wait timeout exceeded in listener dispatch"); break; } } } view.execute(); isCompleted = true; earlier = null; } }