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//
// ========================================================================
// Copyright (c) 1995-2016 Mort Bay Consulting Pty. Ltd.
// ------------------------------------------------------------------------
// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
//
// The Eclipse Public License is available at
// http://www.eclipse.org/legal/epl-v10.html
//
// The Apache License v2.0 is available at
// http://www.opensource.org/licenses/apache2.0.php
//
// You may elect to redistribute this code under either of these licenses.
// ========================================================================
//
package org.eclipse.jetty.util.thread;
import java.lang.reflect.Constructor;
import java.util.concurrent.Executor;
import org.eclipse.jetty.util.Loader;
import org.eclipse.jetty.util.log.Log;
import org.eclipse.jetty.util.log.Logger;
import org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume;
/**
* <p>An {@link ExecutionStrategy} executes {@link Runnable} tasks produced by a {@link Producer}.
* The strategy to execute the task may vary depending on the implementation; the task may be
* run in the calling thread, or in a new thread, etc.</p>
* <p>The strategy delegates the production of tasks to a {@link Producer}, and continues to
* execute tasks until the producer continues to produce them.</p>
*/
public interface ExecutionStrategy
{
/**
* <p>Initiates (or resumes) the task production and execution.</p>
* <p>This method guarantees that the task is never run by the
* thread that called this method.</p>
*
* @see #execute()
*/
public void dispatch();
/**
* <p>Initiates (or resumes) the task production and execution.</p>
* <p>The produced task may be run by the same thread that called
* this method.</p>
*
* @see #dispatch()
*/
public void execute();
/**
* <p>A producer of {@link Runnable} tasks to run.</p>
* <p>The {@link ExecutionStrategy} will repeatedly invoke {@link #produce()} until
* the producer returns null, indicating that it has nothing more to produce.</p>
* <p>When no more tasks can be produced, implementations should arrange for the
* {@link ExecutionStrategy} to be invoked again in case an external event resumes
* the tasks production.</p>
*/
public interface Producer
{
/**
* <p>Produces a task to be executed.</p>
*
* @return a task to executed or null if there are no more tasks to execute
*/
Runnable produce();
}
public static class Factory
{
private static final Logger LOG = Log.getLogger(Factory.class);
public static ExecutionStrategy instanceFor(Producer producer, Executor executor)
{
// TODO remove this mechanism before release
String strategy = System.getProperty(producer.getClass().getName()+".ExecutionStrategy");
if (strategy!=null)
{
try
{
Class<? extends ExecutionStrategy> c = Loader.loadClass(strategy);
Constructor<? extends ExecutionStrategy> m = c.getConstructor(Producer.class,Executor.class);
LOG.info("Use {} for {}",c.getSimpleName(),producer.getClass().getName());
return m.newInstance(producer,executor);
}
catch(Exception e)
{
LOG.warn(e);
}
}
return new ExecuteProduceConsume(producer,executor);
}
}
}
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