/*

 * Copyright 1997-2005 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

package java.rmi.activation;

import java.rmi.MarshalledObject;

import java.rmi.Remote;

import java.rmi.RemoteException;

import java.rmi.activation.UnknownObjectException;

/**

 * The <code>Activator</code> facilitates remote object activation. A

 * "faulting" remote reference calls the activator's

 * <code>activate</code> method to obtain a "live" reference to a

 * "activatable" remote object. Upon receiving a request for activation,

 * the activator looks up the activation descriptor for the activation

 * identifier, <code>id</code>, determines the group in which the

 * object should be activated initiates object re-creation via the

 * group's <code>ActivationInstantiator</code> (via a call to the

 * <code>newInstance</code> method). The activator initiates the

 * execution of activation groups as necessary. For example, if an

 * activation group for a specific group identifier is not already

 * executing, the activator initiates the execution of a VM for the

 * group. <p>

 *

 * The <code>Activator</code> works closely with

 * <code>ActivationSystem</code>, which provides a means for registering

 * groups and objects within those groups, and <code>ActivationMonitor</code>,

 * which recives information about active and inactive objects and inactive

 * groups. <p>

 *

 * The activator is responsible for monitoring and detecting when

 * activation groups fail so that it can remove stale remote references

 * to groups and active object's within those groups.<p>

 *

 * @author      Ann Wollrath

 * @see         ActivationInstantiator

 * @see         ActivationGroupDesc

 * @see         ActivationGroupID

 * @since       1.2

 */

public interface Activator extends Remote {

    /**

     * Activate the object associated with the activation identifier,

     * <code>id</code>. If the activator knows the object to be active

     * already, and <code>force</code> is false , the stub with a

     * "live" reference is returned immediately to the caller;

     * otherwise, if the activator does not know that corresponding

     * the remote object is active, the activator uses the activation

     * descriptor information (previously registered) to determine the

     * group (VM) in which the object should be activated. If an

     * <code>ActivationInstantiator</code> corresponding to the

     * object's group descriptor already exists, the activator invokes

     * the activation group's <code>newInstance</code> method passing

     * it the object's id and descriptor. <p>

     *

     * If the activation group for the object's group descriptor does

     * not yet exist, the activator starts an

     * <code>ActivationInstantiator</code> executing (by spawning a

     * child process, for example). When the activator receives the

     * activation group's call back (via the

     * <code>ActivationSystem</code>'s <code>activeGroup</code>

     * method) specifying the activation group's reference, the

     * activator can then invoke that activation instantiator's

     * <code>newInstance</code> method to forward each pending

     * activation request to the activation group and return the

     * result (a marshalled remote object reference, a stub) to the

     * caller.<p>

     *

     * Note that the activator receives a "marshalled" object instead of a

     * Remote object so that the activator does not need to load the

     * code for that object, or participate in distributed garbage

     * collection for that object. If the activator kept a strong

     * reference to the remote object, the activator would then

     * prevent the object from being garbage collected under the

     * normal distributed garbage collection mechanism. <p>

     *

     * @param id the activation identifier for the object being activated

     * @param force if true, the activator contacts the group to obtain

     * the remote object's reference; if false, returning the cached value

     * is allowed.

     * @return the remote object (a stub) in a marshalled form

     * @exception ActivationException if object activation fails

     * @exception UnknownObjectException if object is unknown (not registered)

     * @exception RemoteException if remote call fails

     * @since 1.2

     */

    public MarshalledObject<? extends Remote> activate(ActivationID id,

                                                       boolean force)

        throws ActivationException, UnknownObjectException, RemoteException;

}