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/*
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* Copyright 1996-2008 Sun Microsystems, Inc. All Rights Reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Sun designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Sun in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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* CA 95054 USA or visit www.sun.com if you need additional information or
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* have any questions.
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*/
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package sun.rmi.transport;
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import java.rmi.Remote;
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import java.rmi.NoSuchObjectException;
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import java.rmi.dgc.VMID;
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import java.rmi.server.ObjID;
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import java.rmi.server.Unreferenced;
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import java.security.AccessControlContext;
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import java.security.AccessController;
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import java.util.*;
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import sun.rmi.runtime.Log;
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import sun.rmi.runtime.NewThreadAction;
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import sun.rmi.server.Dispatcher;
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/**
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* A target contains information pertaining to a remote object that
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* resides in this address space. Targets are located via the
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* ObjectTable.
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*/
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public final class Target {
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/** object id for target */
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private final ObjID id;
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/** flag indicating whether target is subject to collection */
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private final boolean permanent;
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/** weak reference to remote object implementation */
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private final WeakRef weakImpl;
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/** dispatcher for remote object */
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private volatile Dispatcher disp;
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/** stub for remote object */
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private final Remote stub;
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/** set of clients that hold references to this target */
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private final Vector refSet = new Vector();
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/** table that maps client endpoints to sequence numbers */
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private final Hashtable sequenceTable = new Hashtable(5);
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/** access control context in which target was created */
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private final AccessControlContext acc;
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/** context class loader in which target was created */
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private final ClassLoader ccl;
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/** number of pending/executing calls */
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private int callCount = 0;
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/** true if this target has been removed from the object table */
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private boolean removed = false;
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/**
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* the transport through which this target was exported and
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* through which remote calls will be allowed
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*/
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private volatile Transport exportedTransport = null;
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/** number to identify next callback thread created here */
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private static int nextThreadNum = 0;
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/**
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* Construct a Target for a remote object "impl" with
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* a specific object id.
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*
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* If "permanent" is true, then the impl is pinned permanently
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* (the impl will not be collected via distributed and/or local
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* GC). If "on" is false, than the impl is subject to
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* collection. Permanent objects do not keep a server from
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* exiting.
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*/
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public Target(Remote impl, Dispatcher disp, Remote stub, ObjID id,
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boolean permanent)
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{
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this.weakImpl = new WeakRef(impl, ObjectTable.reapQueue);
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this.disp = disp;
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this.stub = stub;
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this.id = id;
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this.acc = AccessController.getContext();
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/*
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* Fix for 4149366: so that downloaded parameter types unmarshalled
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* for this impl will be compatible with types known only to the
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* impl class's class loader (when it's not identical to the
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* exporting thread's context class loader), mark the impl's class
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* loader as the loader to use as the context class loader in the
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* server's dispatch thread while a call to this impl is being
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* processed (unless this exporting thread's context class loader is
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* a child of the impl's class loader, such as when a registry is
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* exported by an application, in which case this thread's context
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* class loader is preferred).
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*/
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ClassLoader threadContextLoader =
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Thread.currentThread().getContextClassLoader();
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ClassLoader serverLoader = impl.getClass().getClassLoader();
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if (checkLoaderAncestry(threadContextLoader, serverLoader)) {
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this.ccl = threadContextLoader;
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} else {
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this.ccl = serverLoader;
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}
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this.permanent = permanent;
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if (permanent) {
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pinImpl();
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}
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}
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/**
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* Return true if the first class loader is a child of (or identical
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* to) the second class loader. Either loader may be "null", which is
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* considered to be the parent of any non-null class loader.
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*
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* (utility method added for the 1.2beta4 fix for 4149366)
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*/
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private static boolean checkLoaderAncestry(ClassLoader child,
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ClassLoader ancestor)
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{
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if (ancestor == null) {
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return true;
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} else if (child == null) {
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return false;
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} else {
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for (ClassLoader parent = child;
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parent != null;
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parent = parent.getParent())
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{
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if (parent == ancestor) {
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return true;
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}
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}
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return false;
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}
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}
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/** Get the stub (proxy) object for this target
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*/
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public Remote getStub() {
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return stub;
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}
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/**
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* Returns the object endpoint for the target.
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*/
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ObjectEndpoint getObjectEndpoint() {
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return new ObjectEndpoint(id, exportedTransport);
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}
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/**
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* Get the weak reference for the Impl of this target.
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*/
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WeakRef getWeakImpl() {
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return weakImpl;
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}
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/**
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* Returns the dispatcher for this remote object target.
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*/
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Dispatcher getDispatcher() {
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return disp;
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}
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AccessControlContext getAccessControlContext() {
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return acc;
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}
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ClassLoader getContextClassLoader() {
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return ccl;
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}
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/**
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* Get the impl for this target.
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* Note: this may return null if the impl has been garbage collected.
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* (currently, there is no need to make this method public)
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*/
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Remote getImpl() {
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return (Remote)weakImpl.get();
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}
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/**
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* Returns true if the target is permanent.
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*/
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boolean isPermanent() {
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return permanent;
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}
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/**
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* Pin impl in target. Pin the WeakRef object so it holds a strong
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* reference to the object to it will not be garbage collected locally.
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* This way there is a single object responsible for the weak ref
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* mechanism.
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*/
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synchronized void pinImpl() {
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weakImpl.pin();
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}
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/**
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* Unpin impl in target. Weaken the reference to impl so that it
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* can be garbage collected locally. But only if there the refSet
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* is empty. All of the weak/strong handling is in WeakRef
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*/
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synchronized void unpinImpl() {
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/* only unpin if:
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* a) impl is not permanent, and
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* b) impl is not already unpinned, and
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* c) there are no external references (outside this
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* address space) for the impl
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*/
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if (!permanent && refSet.isEmpty()) {
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weakImpl.unpin();
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}
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}
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/**
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* Enable the transport through which remote calls to this target
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* are allowed to be set if it has not already been set.
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*/
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void setExportedTransport(Transport exportedTransport) {
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if (this.exportedTransport == null) {
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this.exportedTransport = exportedTransport;
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}
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}
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/**
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* Add an endpoint to the remembered set. Also adds a notifier
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* to call back if the address space associated with the endpoint
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* dies.
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*/
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synchronized void referenced(long sequenceNum, VMID vmid) {
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// check sequence number for vmid
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SequenceEntry entry = (SequenceEntry) sequenceTable.get(vmid);
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if (entry == null) {
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sequenceTable.put(vmid, new SequenceEntry(sequenceNum));
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} else if (entry.sequenceNum < sequenceNum) {
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entry.update(sequenceNum);
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} else {
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// late dirty call; ignore.
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return;
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}
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if (!refSet.contains(vmid)) {
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/*
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* A Target must be pinned while its refSet is not empty. It may
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* have become unpinned if external LiveRefs only existed in
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* serialized form for some period of time, or if a client failed
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* to renew its lease due to a transient network failure. So,
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* make sure that it is pinned here; this fixes bugid 4069644.
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*/
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pinImpl();
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if (getImpl() == null) // too late if impl was collected
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return;
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if (DGCImpl.dgcLog.isLoggable(Log.VERBOSE)) {
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DGCImpl.dgcLog.log(Log.VERBOSE, "add to dirty set: " + vmid);
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}
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refSet.addElement(vmid);
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DGCImpl.getDGCImpl().registerTarget(vmid, this);
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}
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}
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/**
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* Remove endpoint from remembered set. If set becomes empty,
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* remove server from Transport's object table.
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*/
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synchronized void unreferenced(long sequenceNum, VMID vmid, boolean strong)
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{
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// check sequence number for vmid
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SequenceEntry entry = (SequenceEntry) sequenceTable.get(vmid);
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if (entry == null || entry.sequenceNum > sequenceNum) {
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// late clean call; ignore
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return;
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} else if (strong) {
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// strong clean call; retain sequenceNum
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entry.retain(sequenceNum);
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} else if (entry.keep == false) {
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// get rid of sequence number
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sequenceTable.remove(vmid);
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}
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if (DGCImpl.dgcLog.isLoggable(Log.VERBOSE)) {
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DGCImpl.dgcLog.log(Log.VERBOSE, "remove from dirty set: " + vmid);
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}
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refSetRemove(vmid);
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}
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/**
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* Remove endpoint from the reference set.
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*/
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synchronized private void refSetRemove(VMID vmid) {
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// remove notification request
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DGCImpl.getDGCImpl().unregisterTarget(vmid, this);
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if (refSet.removeElement(vmid) && refSet.isEmpty()) {
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// reference set is empty, so server can be garbage collected.
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// remove object from table.
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if (DGCImpl.dgcLog.isLoggable(Log.VERBOSE)) {
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DGCImpl.dgcLog.log(Log.VERBOSE,
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"reference set is empty: target = " + this);
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}
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/*
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* If the remote object implements the Unreferenced interface,
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* invoke its unreferenced callback in a separate thread.
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*/
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Remote obj = getImpl();
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if (obj instanceof Unreferenced) {
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final Unreferenced unrefObj = (Unreferenced) obj;
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final Thread t =
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2
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java.security.AccessController.doPrivileged(
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new NewThreadAction(new Runnable() {
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public void run() {
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unrefObj.unreferenced();
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}
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}, "Unreferenced-" + nextThreadNum++, false, true));
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// REMIND: access to nextThreadNum not synchronized; you care?
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/*
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* We must manually set the context class loader appropriately
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* for threads that may invoke user code (see bugid 4171278).
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*/
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java.security.AccessController.doPrivileged(
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new java.security.PrivilegedAction<Void>() {
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public Void run() {
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2
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t.setContextClassLoader(ccl);
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return null;
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}
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});
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t.start();
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}
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unpinImpl();
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}
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}
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/**
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* Mark this target as not accepting new calls if any of the
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* following conditions exist: a) the force parameter is true,
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* b) the target's call count is zero, or c) the object is already
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* not accepting calls. Returns true if target is marked as not
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* accepting new calls; returns false otherwise.
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*/
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synchronized boolean unexport(boolean force) {
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if ((force == true) || (callCount == 0) || (disp == null)) {
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disp = null;
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/*
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* Fix for 4331349: unpin object so that it may be gc'd.
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* Also, unregister all vmids referencing this target
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* so target can be gc'd.
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*/
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unpinImpl();
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DGCImpl dgc = DGCImpl.getDGCImpl();
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Enumeration enum_ = refSet.elements();
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while (enum_.hasMoreElements()) {
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VMID vmid = (VMID) enum_.nextElement();
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dgc.unregisterTarget(vmid, this);
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}
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return true;
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} else {
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return false;
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}
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}
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/**
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* Mark this target as having been removed from the object table.
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*/
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synchronized void markRemoved() {
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if (!(!removed)) { throw new AssertionError(); }
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removed = true;
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if (!permanent && callCount == 0) {
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ObjectTable.decrementKeepAliveCount();
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}
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if (exportedTransport != null) {
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exportedTransport.targetUnexported();
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}
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}
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396 |
/**
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* Increment call count.
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*/
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399 |
synchronized void incrementCallCount() throws NoSuchObjectException {
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401 |
if (disp != null) {
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callCount ++;
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} else {
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throw new NoSuchObjectException("object not accepting new calls");
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}
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}
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407 |
|
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408 |
/**
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* Decrement call count.
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*/
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411 |
synchronized void decrementCallCount() {
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412 |
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413 |
if (--callCount < 0) {
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throw new Error("internal error: call count less than zero");
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}
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416 |
|
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417 |
/*
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|
418 |
* The "keep-alive count" is the number of non-permanent remote
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419 |
* objects that are either in the object table or still have calls
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420 |
* in progress. Therefore, this state change may affect the
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421 |
* keep-alive count: if this target is for a non-permanent remote
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422 |
* object that has been removed from the object table and now has a
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* call count of zero, it needs to be decremented.
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424 |
*/
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425 |
if (!permanent && removed && callCount == 0) {
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ObjectTable.decrementKeepAliveCount();
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427 |
}
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428 |
}
|
|
429 |
|
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430 |
/**
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431 |
* Returns true if remembered set is empty; otherwise returns
|
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432 |
* false
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433 |
*/
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434 |
boolean isEmpty() {
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435 |
return refSet.isEmpty();
|
|
436 |
}
|
|
437 |
|
|
438 |
/**
|
|
439 |
* This method is called if the address space associated with the
|
|
440 |
* vmid dies. In that case, the vmid should be removed
|
|
441 |
* from the reference set.
|
|
442 |
*/
|
|
443 |
synchronized public void vmidDead(VMID vmid) {
|
|
444 |
if (DGCImpl.dgcLog.isLoggable(Log.BRIEF)) {
|
|
445 |
DGCImpl.dgcLog.log(Log.BRIEF, "removing endpoint " +
|
|
446 |
vmid + " from reference set");
|
|
447 |
}
|
|
448 |
|
|
449 |
sequenceTable.remove(vmid);
|
|
450 |
refSetRemove(vmid);
|
|
451 |
}
|
|
452 |
}
|
|
453 |
|
|
454 |
class SequenceEntry {
|
|
455 |
long sequenceNum;
|
|
456 |
boolean keep;
|
|
457 |
|
|
458 |
SequenceEntry(long sequenceNum) {
|
|
459 |
this.sequenceNum = sequenceNum;
|
|
460 |
keep = false;
|
|
461 |
}
|
|
462 |
|
|
463 |
void retain(long sequenceNum) {
|
|
464 |
this.sequenceNum = sequenceNum;
|
|
465 |
keep = true;
|
|
466 |
}
|
|
467 |
|
|
468 |
void update(long sequenceNum) {
|
|
469 |
this.sequenceNum = sequenceNum;
|
|
470 |
}
|
|
471 |
}
|