Activator.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * accompanied this code).
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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;

}