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A library for orchestrating beans and asynchronous events using regular POJOs rather than XML
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.servicemix.beanflow;

import org.apache.servicemix.beanflow.support.CallablesFactory;
import org.apache.servicemix.beanflow.support.FindCallableMethods;

import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.concurrent.Callable;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executor;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * An activity which invokes a collection of {@link Callable} methods.
 * 
 * @version $Revision: $
 */
public class ParallelActivity extends ProxyActivity {
    private JoinSupport joinActivity;
    private List> activities;
    private AtomicBoolean started = new AtomicBoolean();
    private Object lock = new Object();
    private CountDownLatch countDownLatch;

    /**
     * A helper method to create a new {@link ParallelActivity} which invokes a
     * number of methods on a POJO in parallel and then joins on them all
     * completing
     */
    public static ParallelActivity newParallelMethodActivity(Executor executor, Object bean) {
        return newParallelMethodActivity(new JoinAll(), executor, bean);
    }

    /**
     * A helper method to create a new {@link ParallelActivity} which invokes a
     * number of methods on a POJO in parallel and then performs a custom join
     */
    @SuppressWarnings("unchecked")
    public static ParallelActivity newParallelMethodActivity(JoinSupport join, Executor executor, Object bean) {
        return new ParallelActivity(join, executor, new FindCallableMethods(bean));
    }

    public ParallelActivity(JoinSupport activity, Executor executor, CallablesFactory callablesFactory) {
        this(activity, executor, callablesFactory.createCallables());
    }

    public ParallelActivity(JoinSupport activity, Executor executor, List> callables) {
        super(activity);
        this.joinActivity = activity;
        this.activities = new ArrayList>();
        for (Callable callable : callables) {
            activities.add(new CallableActivity(executor, callable));
        }
    }

    public ParallelActivity(JoinSupport activity, List> activities) {
        super(activity);
        this.joinActivity = activity;
        this.activities = activities;
    }

    public List> getFutures() {
        List> answer = new ArrayList>();
        synchronized (lock) {
            for (CallableActivity activity : activities) {
                answer.add(activity.getFuture());
            }
        }
        return answer;
    }

    @Override
    public void start() {
        super.start();
        init();
    }

    @Override
    public void startWithTimeout(Timer timer, long timeout) {
        init();
        super.startWithTimeout(timer, timeout);
    }

    public void sync() {
        try {
            CountDownLatch latch = getCountDownLatch();
            latch.countDown();
            latch.await();
        }
        catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
        finally {
            resetCountDownLatch();
        }
    }

    public boolean sync(long millis) {
        try {
            CountDownLatch latch = getCountDownLatch();
            latch.countDown();
            return latch.await(millis, TimeUnit.MILLISECONDS);
        }
        catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            return false;
        }
        finally {
            resetCountDownLatch();
        }
    }


    // Implementation methods
    // -------------------------------------------------------------------------
    protected void resetCountDownLatch() {
        synchronized (lock) {
            if (countDownLatch != null && countDownLatch.getCount() == 0) {
                countDownLatch = null;
            }
        }
        
    }

    protected CountDownLatch getCountDownLatch() {
        synchronized (lock) {
            int count = activities.size();
            if (countDownLatch == null) {
                countDownLatch = new CountDownLatch(count);
            }
            return countDownLatch;
        }
    }

    private void init() {
        if (started.compareAndSet(false, true)) {
            doStart();
        }
    }

    protected void doStart() {
        for (CallableActivity activity : activities) {
            joinActivity.fork(activity);
        }
    }

}