activationgroup.java

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/*
 * @(#)ActivationGroup.java	1.43 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.rmi.activation;

import java.lang.reflect.Constructor;

import java.net.URL;
import java.net.MalformedURLException;
import java.rmi.MarshalledObject;
import java.rmi.Naming;
import java.rmi.activation.UnknownGroupException;
import java.rmi.activation.UnknownObjectException;
import java.rmi.Remote;
import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
import java.rmi.server.RMIClassLoader;
import java.security.PrivilegedExceptionAction;
import java.security.PrivilegedActionException;

import sun.security.action.GetIntegerAction;

/**
 * An <code>ActivationGroup</code> is responsible for creating new
 * instances of "activatable" objects in its group, informing its
 * <code>ActivationMonitor</code> when either: its object's become
 * active or inactive, or the group as a whole becomes inactive. <p>
 *
 * An <code>ActivationGroup</code> is <i>initially</i> created in one
 * of several ways: <ul>
 * <li>as a side-effect of creating an <code>ActivationDesc</code>
 *     without an explicit <code>ActivationGroupID</code> for the
 *     first activatable object in the group, or
 * <li>via the <code>ActivationGroup.createGroup</code> method
 * <li>as a side-effect of activating the first object in a group
 *     whose <code>ActivationGroupDesc</code> was only registered.</ul><p>
 *
 * Only the activator can <i>recreate</i> an
 * <code>ActivationGroup</code>.  The activator spawns, as needed, a
 * separate VM (as a child process, for example) for each registered
 * activation group and directs activation requests to the appropriate
 * group. It is implementation specific how VMs are spawned. An
 * activation group is created via the
 * <code>ActivationGroup.createGroup</code> static method. The
 * <code>createGroup</code> method has two requirements on the group
 * to be created: 1) the group must be a concrete subclass of
 * <code>ActivationGroup</code>, and 2) the group must have a
 * constructor that takes two arguments:
 *
 * <ul>
 * <li> the group's <code>ActivationGroupID</code>, and
 * <li> the group's initialization data (in a
 *      <code>java.rmi.MarshalledObject</code>)</ul><p>
 *
 * When created, the default implementation of
 * <code>ActivationGroup</code> will override the system properties
 * with the properties requested when its
 * <code>ActivationGroupDesc</code> was created, and will set a
 * <code>java.rmi.RMISecurityManager</code> as the default system
 * security manager.  If your application requires specific properties
 * to be set when objects are activated in the group, the application
 * should create a special <code>Properties</code> object containing
 * these properties, then create an <code>ActivationGroupDesc</code>
 * with the <code>Properties</code> object, and use
 * <code>ActivationGroup.createGroup</code> before creating any
 * <code>ActivationDesc</code>s (before the default
 * <code>ActivationGroupDesc</code> is created).  If your application
 * requires the use of a security manager other than
 * <code>java.rmi.RMISecurityManager</code>, in the
 * ActivativationGroupDescriptor properties list you can set
 * <code>java.security.manager</code> property to the name of the security
 * manager you would like to install.
 *
 * @author 	Ann Wollrath
 * @version	1.43, 03/01/23
 * @see 	ActivationInstantiator
 * @see		ActivationGroupDesc
 * @see		ActivationGroupID
 * @since	1.2 
 */
public abstract class ActivationGroup
	extends UnicastRemoteObject
	implements ActivationInstantiator
{
    /**
     * @serial the group's identifier 
     */
    private ActivationGroupID groupID;

    /**
     * @serial the group's monitor 
     */
    private ActivationMonitor monitor;

    /** 
     * @serial the group's incarnation number 
     */
    private long incarnation;

    /** the current activation group for this VM */
    private static ActivationGroup currGroup;
    /** the current group's identifier */
    private static ActivationGroupID currGroupID;
    /** the current group's activation system */
    private static ActivationSystem currSystem;
    /** used to control a group being created only once */
    private static boolean canCreate = true;
    /** formal parameters for constructing an activation group */
    private static Class[] groupConstrParams = {
	ActivationGroupID.class, MarshalledObject.class
    };
    
    /** indicate compatibility with the Java 2 SDK v1.2 version of class */
    private static final long serialVersionUID = -7696947875314805420L;
    
    /**
     * Constructs an activation group with the given activation group
     * identifier.  The group is exported as a
     * <code>java.rmi.server.UnicastRemoteObject</code>.
     *
     * @param	groupID the group's identifier
     * @throws	RemoteException if this group could not be exported
     * @since	1.2 
     */
    protected ActivationGroup(ActivationGroupID groupID)
	throws RemoteException 
    {
	// call super constructor to export the object
	super();
	this.groupID = groupID;
    }

    /**
     * The group's <code>inactiveObject</code> method is called
     * indirectly via a call to the <code>Activatable.inactive</code>
     * method. A remote object implementation must call
     * <code>Activatable</code>'s <code>inactive</code> method when
     * that object deactivates (the object deems that it is no longer
     * active). If the object does not call
     * <code>Activatable.inactive</code> when it deactivates, the
     * object will never be garbage collected since the group keeps
     * strong references to the objects it creates. <p>
     *
     * <p>The group's <code>inactiveObject</code> method unexports the
     * remote object from the RMI runtime so that the object can no
     * longer receive incoming RMI calls. An object will only be unexported
     * if the object has no pending or executing calls.
     * The subclass of <code>ActivationGroup</code> must override this
     * method and unexport the object. <p>
     *
     * <p>After removing the object from the RMI runtime, the group
     * must inform its <code>ActivationMonitor</code> (via the monitor's
     * <code>inactiveObject</code> method) that the remote object is
     * not currently active so that the remote object will be
     * re-activated by the activator upon a subsequent activation
     * request.<p>
     *
     * <p>This method simply informs the group's monitor that the object
     * is inactive.  It is up to the concrete subclass of ActivationGroup
     * to fulfill the additional requirement of unexporting the object. <p>
     *
     * @param id the object's activation identifier
     * @return true if the object was successfully deactivated; otherwise
     *         returns false.
     * @exception UnknownObjectException if object is unknown (may already
     * be inactive)
     * @exception RemoteException if call informing monitor fails
     * @exception ActivationException if group is inactive
     * @since 1.2 
     */
    public boolean inactiveObject(ActivationID id)
	throws ActivationException, UnknownObjectException, RemoteException 
    {
	getMonitor().inactiveObject(id);
	return true;
    }

    /**
     * The group's <code>activeObject</code> method is called when an
     * object is exported (either by <code>Activatable</code> object
     * construction or an explicit call to
     * <code>Activatable.exportObject</code>. The group must inform its
     * <code>ActivationMonitor</code> that the object is active (via
     * the monitor's <code>activeObject</code> method) if the group
     * hasn't already done so.
     *
     * @param id the object's identifier
     * @param obj the remote object implementation
     * @exception UnknownObjectException if object is not registered
     * @exception RemoteException if call informing monitor fails
     * @exception ActivationException if group is inactive
     * @since 1.2 
     */
    public abstract void activeObject(ActivationID id, Remote obj)
	throws ActivationException, UnknownObjectException, RemoteException;

    /**
     * Create and set the activation group for the current VM.  The
     * activation group can only be set if it is not currently set.
     * An activation group is set using the <code>createGroup</code>
     * method when the <code>Activator</code> initiates the
     * re-creation of an activation group in order to carry out
     * incoming <code>activate</code> requests. A group must first be
     * registered with the <code>ActivationSystem</code> before it can
     * be created via this method.
     *
     * <p>The group class specified by the
     * <code>ActivationGroupDesc</code> must be a concrete subclass of
     * <code>ActivationGroup</code> and have a public constructor that
     * takes two arguments: the <code>ActivationGroupID</code> for the
     * group and the <code>MarshalledObject</code> containing the
     * group's initialization data (obtained from the
     * <code>ActivationGroupDesc</code>.
     *
     * <p>If the group class name specified in the
     * <code>ActivationGroupDesc</code> is <code>null</code>, then
     * this method will behave as if the group descriptor contained
     * the name of the default activation group implementation class.
     *
     * <p>Note that if your application creates its own custom
     * activation group, a security manager must be set for that
     * group.  Otherwise objects cannot be activated in the group.
     * <code>java.rmi.RMISecurityManager</code> is set by default.
     *
     * <p>If a security manager is already set in the group VM, this
     * method first calls the security manager's
     * <code>checkSetFactory</code> method.  This could result in a
     * <code>SecurityException</code>. If your application needs to
     * set a different security manager, you must ensure that the
     * policy file specified by the group's
     * <code>ActivationGroupDesc</code> grants the group the necessary
     * permissions to set a new security manager.  (Note: This will be
     * necessary if your group downloads and sets a security manager).
     *
     * <p>After the group is created, the
     * <code>ActivationSystem</code> is informed that the group is
     * active by calling the <code>activeGroup</code> method which
     * returns the <code>ActivationMonitor</code> for the group. The
     * application need not call <code>activeGroup</code>
     * independently since it is taken care of by this method.
     *
     * <p>Once a group is created, subsequent calls to the
     * <code>currentGroupID</code> method will return the identifier
     * for this group until the group becomes inactive.
     *
     * @param id the activation group's identifier
     * @param desc the activation group's descriptor
     * @param incarnation the group's incarnation number (zero on group's
     * initial creation)
     * @return the activation group for the VM
     * @exception ActivationException if group already exists or if error
     * occurs during group creation 
     * @exception SecurityException if permission to create group is denied.
     * (Note: The default implementation of the security manager 
     * <code>checkSetFactory</code>
     * method requires the RuntimePermission "setFactory")
     * @see SecurityManager#checkSetFactory
     * @since 1.2
     */
    public static synchronized
	ActivationGroup createGroup(ActivationGroupID id,
				    final ActivationGroupDesc desc,
				    long incarnation)
        throws ActivationException