/* * Copyright (c) 1996, 2005, Oracle and/or its affiliates. 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.  Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package sun.rmi.transport; import java.rmi.server.UID;import java.security.AccessController;import java.util.ArrayList;import java.util.Collections;import java.util.HashMap;import java.util.List;import java.util.Map;import java.util.concurrent.Future;import java.util.concurrent.ScheduledExecutorService;import java.util.concurrent.TimeUnit;import sun.rmi.runtime.RuntimeUtil;import sun.security.action.GetLongAction; /** * Holds strong references to a set of remote objects, or live remote * references to remote objects, after they have been marshalled (as * remote references) as parts of the arguments or the result of a * remote invocation.  The purpose is to prevent remote objects or * live remote references that might otherwise be determined to be * unreachable in this VM from being locally garbage collected before * the receiver has had an opportunity to register the unmarshalled * remote references for DGC. * * The references are held strongly until an acknowledgment has been * received that the receiver has had an opportunity to process the * remote references or until a timeout has expired.  For remote * references sent as parts of the arguments of a remote invocation, * the acknowledgment is the beginning of the response indicating * completion of the remote invocation.  For remote references sent as * parts of the result of a remote invocation, a UID is included as * part of the result, and the acknowledgment is a transport-level * "DGCAck" message containing that UID. * * @author      Ann Wollrath * @author      Peter Jones **/public class DGCAckHandler {     /** timeout for holding references without receiving an acknowledgment */    private static final long dgcAckTimeout =           // default 5 minutes        AccessController.doPrivileged(            new GetLongAction("sun.rmi.dgc.ackTimeout", 300000));     /** thread pool for scheduling delayed tasks */    private static final ScheduledExecutorService scheduler =        AccessController.doPrivileged(            new RuntimeUtil.GetInstanceAction()).getScheduler();     /** table mapping ack ID to handler */    private static final Map<UID,DGCAckHandler> idTable =        Collections.synchronizedMap(new HashMap<UID,DGCAckHandler>());     private final UID id;    private List<Object> objList = new ArrayList<Object>(); // null if released    private Future<?> task = null;     /**     * Creates a new DGCAckHandler, associated with the specified UID     * if the argument is not null.     *     * References added to this DGCAckHandler will be held strongly     * until its "release" method is invoked or (after the     * "startTimer" method has been invoked) the timeout has expired.     * If the argument is not null, then invoking the static     * "received" method with the specified UID is equivalent to     * invoking this instance's "release" method.     **/    DGCAckHandler(UID id) {        this.id = id;        if (id != null) {            assert !idTable.containsKey(id);            idTable.put(id, this);        }    }     /**     * Adds the specified reference to this DGCAckHandler.     **/    synchronized void add(Object obj) {        if (objList != null) {            objList.add(obj);        }    }     /**     * Starts the timer for this DGCAckHandler.  After the timeout has     * expired, the references are released even if the acknowledgment     * has not been received.     **/    synchronized void startTimer() {        if (objList != null && task == null) {            task = scheduler.schedule(new Runnable() {                public void run() {                    release();                }            }, dgcAckTimeout, TimeUnit.MILLISECONDS);        }    }     /**     * Releases the references held by this DGCAckHandler.     **/    synchronized void release() {        if (task != null) {            task.cancel(false);            task = null;        }        objList = null;    }     /**     * Causes the DGCAckHandler associated with the specified UID to     * release its references.     **/    public static void received(UID id) {        DGCAckHandler h = idTable.remove(id);        if (h != null) {            h.release();        }    }}