org.apache.slider.server.services.workflow.WorkflowCompositeService.java Source code

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Here is the source code for org.apache.slider.server.services.workflow.WorkflowCompositeService.java

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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.slider.server.services.workflow;

import com.google.common.base.Preconditions;
import org.apache.hadoop.service.CompositeService;
import org.apache.hadoop.service.Service;
import org.apache.hadoop.service.ServiceStateChangeListener;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.List;

/**
 * An extended composite service which stops itself if any child service
 * fails, or when all its children have successfully stopped without failure.
 *
 * Lifecycle
 * <ol>
 *   <li>If any child exits with a failure: this service stops, propagating
 *   the exception.</li>
 *   <li>When all child services has stopped, this service stops itself</li>
 * </ol>
 *
 */
public class WorkflowCompositeService extends CompositeService
        implements ServiceParent, ServiceStateChangeListener {

    private static final Logger LOG = LoggerFactory.getLogger(WorkflowCompositeService.class);

    /**
     * Construct an instance
     * @param name name of this service instance
     */
    public WorkflowCompositeService(String name) {
        super(name);
    }

    /**
     * Construct an instance with the default name.
     */
    public WorkflowCompositeService() {
        this("WorkflowCompositeService");
    }

    /**
     * Varargs constructor
     * @param name name of this service instance
     * @param children children
     */
    public WorkflowCompositeService(String name, Service... children) {
        this(name);
        for (Service child : children) {
            addService(child);
        }
    }

    /**
     * Construct with a list of children
     * @param name name of this service instance
     * @param children children to add
     */
    public WorkflowCompositeService(String name, List<Service> children) {
        this(name);
        for (Service child : children) {
            addService(child);
        }
    }

    /**
     * Add a service, and register it
     * @param service the {@link Service} to be added.
     * Important: do not add a service to a parent during your own serviceInit/start,
     * in Hadoop 2.2; you will trigger a ConcurrentModificationException.
     */
    @Override
    public synchronized void addService(Service service) {
        Preconditions.checkArgument(service != null, "null service argument");
        service.registerServiceListener(this);
        super.addService(service);
    }

    /**
     * When this service is started, any service stopping with a failure
     * exception is converted immediately into a failure of this service, 
     * storing the failure and stopping ourselves.
     * @param child the service that has changed.
     */
    @Override
    public void stateChanged(Service child) {
        //if that child stopped while we are running:
        if (isInState(STATE.STARTED) && child.isInState(STATE.STOPPED)) {
            // a child service has stopped
            //did the child fail? if so: propagate
            Throwable failureCause = child.getFailureCause();
            if (failureCause != null) {
                LOG.info("Child service " + child + " failed", failureCause);
                //failure. Convert to an exception
                Exception e = (failureCause instanceof Exception) ? (Exception) failureCause
                        : new Exception(failureCause);
                //flip ourselves into the failed state
                noteFailure(e);
                stop();
            } else {
                LOG.info("Child service completed {}", child);
                if (areAllChildrenStopped()) {
                    LOG.info("All children are halted: stopping");
                    stop();
                }
            }
        }
    }

    /**
     * Probe to query if all children are stopped -simply
     * by taking a snapshot of the child service list and enumerating
     * their state. 
     * The state of the children may change during this operation -that will
     * not get picked up.
     * @return true if all the children are stopped.
     */
    private boolean areAllChildrenStopped() {
        List<Service> children = getServices();
        boolean stopped = true;
        for (Service child : children) {
            if (!child.isInState(STATE.STOPPED)) {
                stopped = false;
                break;
            }
        }
        return stopped;
    }
}