# ImportedServiceReferenceInstance.java

    /*
     * Copyright (c) 2008-2011, Rickard Öberg. All Rights Reserved.
     * Copyright (c) 2008-2013, Niclas Hedhman. All Rights Reserved.
     * Copyright (c) 2012-2014, Paul Merlin. All Rights Reserved.
     *
     * 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
     *
     *   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.qi4j.runtime.service;

    import org.qi4j.api.activation.Activation;
    import org.qi4j.api.activation.ActivationEventListener;
    import org.qi4j.api.activation.ActivationException;
    import org.qi4j.api.activation.PassivationException;
    import org.qi4j.api.service.ServiceImporterException;
    import org.qi4j.api.service.ServiceReference;
    import org.qi4j.api.service.ServiceUnavailableException;
    import org.qi4j.api.structure.Module;
    import org.qi4j.runtime.activation.ActivationDelegate;

    /**
     * Implementation of ServiceReference. This manages the reference to the imported service.
     * <p>
     * Whenever the service is requested it is returned directly to the client. That means that
     * to handle service passivation and unavailability correctly, any proxying must be done in the
     * service importer.
     * </p>
     * @param <T> Service Type
     */
    public final class ImportedServiceReferenceInstance<T>
        implements ServiceReference<T>, Activation
    {
        private volatile ImportedServiceInstance<T> serviceInstance;
        private T instance;
        private final Module module;
        private final ImportedServiceModel serviceModel;
        private final ActivationDelegate activation = new ActivationDelegate( this );
        private boolean active = false;

        public ImportedServiceReferenceInstance( ImportedServiceModel serviceModel, Module module )
        {
            this.module = module;
            this.serviceModel = serviceModel;
        }

        @Override
        public String identity()
        {
            return serviceModel.identity();
        }

        @Override
        public Iterable<Class<?>> types()
        {
            return serviceModel.types();
        }

        @Override
        public <T> T metaInfo( Class<T> infoType )
        {
            return serviceModel.metaInfo( infoType );
        }

        @Override
        public synchronized T get()
        {
            return getInstance();
        }

        public ImportedServiceModel serviceDescriptor()
        {
            return serviceModel;
        }

        @Override
        public void activate()
            throws ActivationException
        {
            if( serviceModel.isImportOnStartup() )
            {
                getInstance();
            }
        }

        @Override
        public void passivate()
            throws PassivationException
        {
            if( serviceInstance != null )
            {
                try
                {
                    activation.passivate( new Runnable()
                    {
                        @Override
                        public void run()
                        {
                            active = false;
                        }
                    } );
                }
                finally
                {
                    serviceInstance = null;
                    active = false;
                }
            }
        }

        @Override
        public boolean isActive()
        {
            return active;
        }

        @Override
        public boolean isAvailable()
        {
            try
            {
                getInstance();
                return serviceInstance.isAvailable();
            }
            catch( ServiceImporterException ex )
            {
                return false;
            }
        }

        public Module module()
        {
            return module;
        }

        private T getInstance()
            throws ServiceImporterException
        {
            // DCL that works with Java 1.5 volatile semantics
            if( serviceInstance == null )
            {
                synchronized( this )
                {
                    if( serviceInstance == null )
                    {
                        serviceInstance = serviceModel.<T>importInstance( module );
                        instance = serviceInstance.instance();

                        try
                        {
                            activation.activate( serviceModel.newActivatorsInstance( module ), serviceInstance, new Runnable()
                            {
                                @Override
                                public void run()
                                {
                                    active = true;
                                }
                            } );
                        }
                        catch( Exception e )
                        {
                            serviceInstance = null;
                            throw new ServiceUnavailableException( "Could not activate service " + serviceModel.identity(), e );
                        }
                    }
                }
            }

            return instance;
        }

        @Override
        public String toString()
        {
            return serviceModel.identity() + ", active=" + isActive() + ", module='" + serviceModel.moduleName() + "'";
        }

        @Override
        public void registerActivationEventListener( ActivationEventListener listener )
        {
            activation.registerActivationEventListener( listener );
        }

        @Override
        public void deregisterActivationEventListener( ActivationEventListener listener )
        {
            activation.deregisterActivationEventListener( listener );
        }

        @Override
        public int hashCode()
        {
            return identity().hashCode();
        }

        @Override
        public boolean equals( Object obj )
        {
            if( obj == null )
            {
                return false;
            }
            if( getClass() != obj.getClass() )
            {
                return false;
            }
            final ServiceReference other = (ServiceReference) obj;
            return identity().equals( other.identity() );
        }
    }