gt:                     nr = cnf.fetchNotifs(startSequenceNumber, 0, 0L);
context: /*
   * Copyright (c) 2002, 2015, 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 com.sun.jmx.remote.internal;
  
  import java.io.IOException;
  import java.io.NotSerializableException;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.concurrent.Executor;
  
  import java.security.AccessControlContext;
  import java.security.AccessController;
  import java.security.PrivilegedAction;
  import javax.security.auth.Subject;
  
  import javax.management.Notification;
  import javax.management.NotificationListener;
  import javax.management.NotificationFilter;
  import javax.management.ObjectName;
  import javax.management.MBeanServerNotification;
  import javax.management.InstanceNotFoundException;
  import javax.management.ListenerNotFoundException;
  
  import javax.management.remote.NotificationResult;
  import javax.management.remote.TargetedNotification;
  
  import com.sun.jmx.remote.util.ClassLogger;
  import com.sun.jmx.remote.util.EnvHelp;
  import java.rmi.UnmarshalException;
  
  
  public abstract class ClientNotifForwarder {
  
      private final AccessControlContext acc;
  
      public ClientNotifForwarder(Map<String, ?> env) {
          this(null, env);
      }
  
      private static int threadId;
  
      /* An Executor that allows at most one executing and one pending
         Runnable.  It uses at most one thread -- as soon as there is
         no pending Runnable the thread can exit.  Another thread is
         created as soon as there is a new pending Runnable.  This
         Executor is adapted for use in a situation where each Runnable
         usually schedules up another Runnable.  On return from the
         first one, the second one is immediately executed.  So this
         just becomes a complicated way to write a while loop, but with
         the advantage that you can replace it with another Executor,
         for instance one that you are using to execute a bunch of other
         unrelated work.
  
         You might expect that a java.util.concurrent.ThreadPoolExecutor
         with corePoolSize=0 and maximumPoolSize=1 would have the same
         behavior, but it does not.  A ThreadPoolExecutor only creates
         a new thread when a new task is submitted and the number of
         existing threads is < corePoolSize.  This can never happen when
         corePoolSize=0, so new threads are never created.  Surprising,
         but there you are.
      */
      private static class LinearExecutor implements Executor {
          public synchronized void execute(Runnable command) {
              if (this.command != null)
                  throw new IllegalArgumentException("More than one command");
              this.command = command;
              if (thread == null) {
                  thread = new Thread(
                      null,
                      ()-> {
                          while (true) {
                              Runnable r;
                              synchronized (LinearExecutor.this) {
                                  if (LinearExecutor.this.command == null) {
                                      thread = null;
                                      return;
                                  } else {
                                      r = LinearExecutor.this.command;
                                      LinearExecutor.this.command = null;
                                  }
                              }
                              r.run();
                          }
                      },
                      "ClientNotifForwarder-" + ++threadId,
                      0,
                      false
                  );
                  thread.setDaemon(true);
                  thread.start();
              }
          }
  
          private Runnable command;
          private Thread thread;
      }
  
      public ClientNotifForwarder(ClassLoader defaultClassLoader, Map<String, ?> env) {
          maxNotifications = EnvHelp.getMaxFetchNotifNumber(env);
          timeout = EnvHelp.getFetchTimeout(env);
  
          /* You can supply an Executor in which the remote call to
             fetchNotifications will be made.  The Executor's execute
             method reschedules another task, so you must not use
             an Executor that executes tasks in the caller's thread.  */
          Executor ex = (Executor)
              env.get("jmx.remote.x.fetch.notifications.executor");
          if (ex == null)
              ex = new LinearExecutor();
          else if (logger.traceOn())
              logger.trace("ClientNotifForwarder", "executor is " + ex);
  
          this.defaultClassLoader = defaultClassLoader;
          this.executor = ex;
          this.acc = AccessController.getContext();
      }
  
      /**
       * Called to fetch notifications from a server.
       */
      abstract protected NotificationResult fetchNotifs(long clientSequenceNumber,
                                                        int maxNotifications,
                                                        long timeout)
              throws IOException, ClassNotFoundException;
  
      abstract protected Integer addListenerForMBeanRemovedNotif()
          throws IOException, InstanceNotFoundException;
  
      abstract protected void removeListenerForMBeanRemovedNotif(Integer id)
          throws IOException, InstanceNotFoundException,
                 ListenerNotFoundException;
  
      /**
       * Used to send out a notification about lost notifs
       */
      abstract protected void lostNotifs(String message, long number);
  
  
      public synchronized void addNotificationListener(Integer listenerID,
                                          ObjectName name,
                                          NotificationListener listener,
                                          NotificationFilter filter,
                                          Object handback,
                                          Subject delegationSubject)
              throws IOException, InstanceNotFoundException {
  
          if (logger.traceOn()) {
              logger.trace("addNotificationListener",
                           "Add the listener "+listener+" at "+name);
          }
  
          infoList.put(listenerID,
                       new ClientListenerInfo(listenerID,
                                              name,
                                              listener,
                                              filter,
                                              handback,
                                              delegationSubject));
  
  
          init(false);
      }
  
      public synchronized Integer[]
          removeNotificationListener(ObjectName name,
                                     NotificationListener listener)
          throws ListenerNotFoundException, IOException {
  
          beforeRemove();
  
          if (logger.traceOn()) {
              logger.trace("removeNotificationListener",
                           "Remove the listener "+listener+" from "+name);
          }
  
          List<Integer> ids = new ArrayList<Integer>();
          List<ClientListenerInfo> values =
                  new ArrayList<ClientListenerInfo>(infoList.values());
          for (int i=values.size()-1; i>=0; i--) {
              ClientListenerInfo li = values.get(i);
  
              if (li.sameAs(name, listener)) {
                  ids.add(li.getListenerID());
  
                  infoList.remove(li.getListenerID());
              }
          }
  
          if (ids.isEmpty())
              throw new ListenerNotFoundException("Listener not found");
  
          return ids.toArray(new Integer[0]);
      }
  
      public synchronized Integer
          removeNotificationListener(ObjectName name,
                                     NotificationListener listener,
                                     NotificationFilter filter,
                                     Object handback)
              throws ListenerNotFoundException, IOException {
  
          if (logger.traceOn()) {
              logger.trace("removeNotificationListener",
                           "Remove the listener "+listener+" from "+name);
          }
  
          beforeRemove();
  
          Integer id = null;
  
          List<ClientListenerInfo> values =
                  new ArrayList<ClientListenerInfo>(infoList.values());
          for (int i=values.size()-1; i>=0; i--) {
              ClientListenerInfo li = values.get(i);
              if (li.sameAs(name, listener, filter, handback)) {
                  id=li.getListenerID();
  
                  infoList.remove(id);
  
                  break;
              }
          }
  
          if (id == null)
              throw new ListenerNotFoundException("Listener not found");
  
          return id;
      }
  
      public synchronized Integer[] removeNotificationListener(ObjectName name) {
          if (logger.traceOn()) {
              logger.trace("removeNotificationListener",
                           "Remove all listeners registered at "+name);
          }
  
          List<Integer> ids = new ArrayList<Integer>();
  
          List<ClientListenerInfo> values =
                  new ArrayList<ClientListenerInfo>(infoList.values());
          for (int i=values.size()-1; i>=0; i--) {
              ClientListenerInfo li = values.get(i);
              if (li.sameAs(name)) {
                  ids.add(li.getListenerID());
  
                  infoList.remove(li.getListenerID());
              }
          }
  
          return ids.toArray(new Integer[0]);
      }
  
      /*
       * Called when a connector is doing reconnection. Like <code>postReconnection</code>,
       * this method is intended to be called only by a client connector:
       * <code>RMIConnector</code> and <code>ClientIntermediary</code>.
       * Call this method will set the flag beingReconnection to <code>true</code>,
       * and the thread used to fetch notifis will be stopped, a new thread can be
       * created only after the method <code>postReconnection</code> is called.
       *
       * It is caller's responsiblity to not re-call this method before calling
       * <code>postReconnection</code>.
       */
      public synchronized ClientListenerInfo[] preReconnection() throws IOException {
          if (state == TERMINATED || beingReconnected) { // should never
              throw new IOException("Illegal state.");
          }
  
          final ClientListenerInfo[] tmp =
              infoList.values().toArray(new ClientListenerInfo[0]);
  
  
          beingReconnected = true;
  
          infoList.clear();
  
          return tmp;
      }
  
      /**
       * Called after reconnection is finished.
       * This method is intended to be called only by a client connector:
       * <code>RMIConnector</code> and <code>ClientIntermediary</code>.
       */
      public synchronized void postReconnection(ClientListenerInfo[] listenerInfos)
          throws IOException {
  
          if (state == TERMINATED) {
              return;
          }
  
          while (state == STOPPING) {
              try {
                  wait();
              } catch (InterruptedException ire) {
                  IOException ioe = new IOException(ire.toString());
                  EnvHelp.initCause(ioe, ire);
                  throw ioe;
              }
          }
  
          final boolean trace = logger.traceOn();
          final int len   = listenerInfos.length;
  
          for (int i=0; i<len; i++) {
              if (trace) {
                  logger.trace("addNotificationListeners",
                               "Add a listener at "+
                               listenerInfos[i].getListenerID());
              }
  
              infoList.put(listenerInfos[i].getListenerID(), listenerInfos[i]);
          }
  
          beingReconnected = false;
          notifyAll();
  
          if (currentFetchThread == Thread.currentThread() ||
                state == STARTING || state == STARTED) { // doing or waiting reconnection
                // only update mbeanRemovedNotifID
              try {
                  mbeanRemovedNotifID = addListenerForMBeanRemovedNotif();
              } catch (Exception e) {
                  final String msg =
                      "Failed to register a listener to the mbean " +
                      "server: the client will not do clean when an MBean " +
                      "is unregistered";
                  if (logger.traceOn()) {
                      logger.trace("init", msg, e);
                  }
              }
          } else {
                while (state == STOPPING) {
                    try {
                        wait();
                    } catch (InterruptedException ire) {
                        IOException ioe = new IOException(ire.toString());
                        EnvHelp.initCause(ioe, ire);
                        throw ioe;
                    }
                }
  
                if (listenerInfos.length > 0) { // old listeners are re-added
                    init(true); // not update clientSequenceNumber
                } else if (infoList.size() > 0) { // only new listeners added during reconnection
                    init(false); // need update clientSequenceNumber
                }
            }
      }
  
      public synchronized void terminate() {
          if (state == TERMINATED) {
              return;
          }
  
          if (logger.traceOn()) {
              logger.trace("terminate", "Terminating...");
          }
  
          if (state == STARTED) {
             infoList.clear();
          }
  
          setState(TERMINATED);
      }
  
  
      // -------------------------------------------------
      // private classes
      // -------------------------------------------------
      //
  
      private class NotifFetcher implements Runnable {
  
          private volatile boolean alreadyLogged = false;
  
          private void logOnce(String msg, SecurityException x) {
              if (alreadyLogged) return;
              // Log only once.
              logger.config("setContextClassLoader",msg);
              if (x != null) logger.fine("setContextClassLoader", x);
              alreadyLogged = true;
          }
  
          // Set new context class loader, returns previous one.
          private final ClassLoader setContextClassLoader(final ClassLoader loader) {
              final AccessControlContext ctxt = ClientNotifForwarder.this.acc;
              // if ctxt is null, log a config message and throw a
              // SecurityException.
              if (ctxt == null) {
                  logOnce("AccessControlContext must not be null.",null);
                  throw new SecurityException("AccessControlContext must not be null");
              }
              return AccessController.doPrivileged(
                  new PrivilegedAction<ClassLoader>() {
                      public ClassLoader run() {
                          try {
                              // get context class loader - may throw
                              // SecurityException - though unlikely.
                              final ClassLoader previous =
                                  Thread.currentThread().getContextClassLoader();
  
                              // if nothing needs to be done, break here...
                              if (loader == previous) return previous;
  
                              // reset context class loader - may throw
                              // SecurityException
                              Thread.currentThread().setContextClassLoader(loader);
                              return previous;
                          } catch (SecurityException x) {
                              logOnce("Permission to set ContextClassLoader missing. " +
                                      "Notifications will not be dispatched. " +
                                      "Please check your Java policy configuration: " +
                                      x, x);
                              throw x;
                          }
                      }
                  }, ctxt);
          }
  
          public void run() {
              final ClassLoader previous;
              if (defaultClassLoader != null) {
                  previous = setContextClassLoader(defaultClassLoader);
              } else {
                  previous = null;
              }
              try {
                  doRun();
              } finally {
                  if (defaultClassLoader != null) {
                      setContextClassLoader(previous);
                  }
              }
          }
  
          private void doRun() {
              synchronized (ClientNotifForwarder.this) {
                  currentFetchThread = Thread.currentThread();
  
                  if (state == STARTING) {
                      setState(STARTED);
                  }
              }
  
  
              NotificationResult nr = null;
              if (!shouldStop() && (nr = fetchNotifs()) != null) {
                  // nr == null means got exception
  
                  final TargetedNotification[] notifs =
                      nr.getTargetedNotifications();
                  final int len = notifs.length;
                  final Map<Integer, ClientListenerInfo> listeners;
                  final Integer myListenerID;
  
                  long missed = 0;
  
                  synchronized(ClientNotifForwarder.this) {
                      // check sequence number.
                      //
                      if (clientSequenceNumber >= 0) {
                          missed = nr.getEarliestSequenceNumber() -
                              clientSequenceNumber;
                      }
  
                      clientSequenceNumber = nr.getNextSequenceNumber();
  
                      listeners = new HashMap<Integer, ClientListenerInfo>();
  
                      for (int i = 0 ; i < len ; i++) {
                          final TargetedNotification tn = notifs[i];
                          final Integer listenerID = tn.getListenerID();
  
                          // check if an mbean unregistration notif
                          if (!listenerID.equals(mbeanRemovedNotifID)) {
                              final ClientListenerInfo li = infoList.get(listenerID);
                              if (li != null) {
                                  listeners.put(listenerID, li);
                              }
                              continue;
                          }
                          final Notification notif = tn.getNotification();
                          final String unreg =
                              MBeanServerNotification.UNREGISTRATION_NOTIFICATION;
                          if (notif instanceof MBeanServerNotification &&
                              notif.getType().equals(unreg)) {
  
                              MBeanServerNotification mbsn =
                                  (MBeanServerNotification) notif;
                              ObjectName name = mbsn.getMBeanName();
  
                              removeNotificationListener(name);
                          }
                      }
                      myListenerID = mbeanRemovedNotifID;
                  }
  
                  if (missed > 0) {
                      final String msg =
                          "May have lost up to " + missed +
                          " notification" + (missed == 1 ? "" : "s");
                      lostNotifs(msg, missed);
                      logger.trace("NotifFetcher.run", msg);
                  }
  
                  // forward
                  for (int i = 0 ; i < len ; i++) {
                      final TargetedNotification tn = notifs[i];
                      dispatchNotification(tn,myListenerID,listeners);
                  }
              }
  
              synchronized (ClientNotifForwarder.this) {
                  currentFetchThread = null;
              }
  
              if (nr == null) {
                  if (logger.traceOn()) {
                      logger.trace("NotifFetcher-run",
                              "Recieved null object as notifs, stops fetching because the "
                                      + "notification server is terminated.");
                  }
              }
              if (nr == null || shouldStop()) {
                  // tell that the thread is REALLY stopped
                  setState(STOPPED);
  
                  try {
                        removeListenerForMBeanRemovedNotif(mbeanRemovedNotifID);
                  } catch (Exception e) {
                      if (logger.traceOn()) {
                          logger.trace("NotifFetcher-run",
                                  "removeListenerForMBeanRemovedNotif", e);
                      }
                  }
              } else {
                  executor.execute(this);
              }
          }
  
          void dispatchNotification(TargetedNotification tn,
                                    Integer myListenerID,
                                    Map<Integer, ClientListenerInfo> listeners) {
              final Notification notif = tn.getNotification();
              final Integer listenerID = tn.getListenerID();
  
              if (listenerID.equals(myListenerID)) return;
              final ClientListenerInfo li = listeners.get(listenerID);
  
              if (li == null) {
                  logger.trace("NotifFetcher.dispatch",
                               "Listener ID not in map");
                  return;
              }
  
              NotificationListener l = li.getListener();
              Object h = li.getHandback();
              try {
                  l.handleNotification(notif, h);
              } catch (RuntimeException e) {
                  final String msg =
                      "Failed to forward a notification " +
                      "to a listener";
                  logger.trace("NotifFetcher-run", msg, e);
              }
  
          }
  
          private NotificationResult fetchNotifs() {
              try {
                  NotificationResult nr = ClientNotifForwarder.this.
                      fetchNotifs(clientSequenceNumber,maxNotifications,
                                  timeout);
  
                  if (logger.traceOn()) {
                      logger.trace("NotifFetcher-run",
                                   "Got notifications from the server: "+nr);
                  }
  
                  return nr;
              } catch (ClassNotFoundException | NotSerializableException | UnmarshalException e) {
                  logger.trace("NotifFetcher.fetchNotifs", e);
                  return fetchOneNotif();
              } catch (IOException ioe) {
                  if (!shouldStop()) {
                      logger.error("NotifFetcher-run",
                                   "Failed to fetch notification, " +
                                   "stopping thread. Error is: " + ioe, ioe);
                      logger.debug("NotifFetcher-run",ioe);
                  }
  
                  // no more fetching
                  return null;
              }
          }
  
          /* Fetch one notification when we suspect that it might be a
             notification that we can't deserialize (because of a
             missing class).  First we ask for 0 notifications with 0
             timeout.  This allows us to skip sequence numbers for
             notifications that don't match our filters.  Then we ask
             for one notification.  If that produces a
             ClassNotFoundException, NotSerializableException or
             UnmarshalException, we increase our sequence number and ask again.
             Eventually we will either get a successful notification, or a
             return with 0 notifications.  In either case we can return a
             NotificationResult.  This algorithm works (albeit less
             well) even if the server implementation doesn't optimize a
             request for 0 notifications to skip sequence numbers for
             notifications that don't match our filters.
  
             If we had at least one
             ClassNotFoundException/NotSerializableException/UnmarshalException,
             then we must emit a JMXConnectionNotification.LOST_NOTIFS.
          */
          private NotificationResult fetchOneNotif() {
              ClientNotifForwarder cnf = ClientNotifForwarder.this;
  
              long startSequenceNumber = clientSequenceNumber;
  
              int notFoundCount = 0;
  
              NotificationResult result = null;
              long firstEarliest = -1;
  
              while (result == null && !shouldStop()) {
                  NotificationResult nr;
  
                  try {
                      // 0 notifs to update startSequenceNumber
  