ServiceGroup.groovy

/*
   Copyright 2012-now  Jex Jexler (Alain Stalder)

   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

       https://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 ch.grengine.jexler.service

import groovy.transform.CompileStatic
import org.slf4j.Logger
import org.slf4j.LoggerFactory

import static ch.grengine.jexler.service.ServiceState.BUSY_EVENT
import static ch.grengine.jexler.service.ServiceState.BUSY_STARTING
import static ch.grengine.jexler.service.ServiceState.BUSY_STOPPING
import static ch.grengine.jexler.service.ServiceState.IDLE
import static ch.grengine.jexler.service.ServiceState.OFF

/**
 * Service which is a group of services.
 * Starting starts all, stopping stops all.
 *
 * @author Jex Jexler (Alain Stalder)
 */
@CompileStatic
class ServiceGroup implements Service {

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

    private final String id

    /** List of services in this group. */
    private final List<Service> services

    /**
     * Constructor.
     * @param id the service group id
     */
    ServiceGroup(final String id) {
        this.id = id
        this.services = new LinkedList<>()
    }
    
    /**
     * Start all services in the group.
     * Runtime exceptions are not caught, hence if the
     * first service throws while starting up, no attempt
     * is made to start the others.
     */
    @Override
    void start() {
        synchronized(services) {
            for (final Service service : services) {
                service.start()
            }
        }
    }

    /**
     * Stop all services in a group.
     * Runtime exceptions are only logged, hence it is always
     * attempted to stop all services.
     */
    @Override
    void stop() {
        RuntimeException ex = null
        synchronized(services) {
            for (final Service service : services) {
                try {
                    service.stop()
                } catch (RuntimeException e) {
                    if (ex == null) {
                        ex = e
                    }
                    LOG.trace("Could not stop service '$id'", e)
                }
            }
        }
        if (ex != null) {
            throw ex
        }
    }

    /**
     * Get service state of the group.
     * @return If there is no service in the group, OFF is returned,
     *   if all services are in the same state, that state is returned,
     *   else BUSY_STARTING, BUSY_STOPPING, BUSY_EVENT, IDLE, OFF is returned,
     *   in that order of priority, if it is the state of at least one service.
     */
    @Override
    ServiceState getState() {
        final Set<ServiceState> set = new HashSet<>()
        synchronized(services) {
            for (final Service service : services) {
                set.add(service.state)
            }
        }
        if (set.contains(BUSY_STARTING)) {
            return BUSY_STARTING
        } else if (set.contains(BUSY_STOPPING)) {
            return BUSY_STOPPING
        } else if (set.contains(BUSY_EVENT)) {
            return BUSY_EVENT
        } else if (set.contains(IDLE)) {
            return IDLE
        } else {
            return OFF
        }
    }

    @Override
    void zap() {
        synchronized(services) {
            for (final Service service : services) {
                service.zap()
            }
        }
    }

    @Override
    String getId() {
        return id
    }

    /**
     * Add given service to the group of services.
     */
    void add(final Service service) {
        synchronized(services) {
            services.add(service)
        }
    }

    /**
     * Get the list of services.
     * Use also to modify the group of services.
     * @return list of services, never null
     */
    List<Service> getServices() {
        synchronized(services) {
            return services
        }
    }

    
}