jdk/src/share/classes/com/sun/jmx/remote/internal/ArrayNotificationBuffer.java

/*
 * Copyright 2003-2006 Sun Microsystems, Inc.  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.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

package com.sun.jmx.remote.internal;

import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.HashMap;
import java.util.Map;

import javax.management.InstanceNotFoundException;
import javax.management.MBeanServer;
import javax.management.MBeanServerDelegate;
import javax.management.MBeanServerNotification;
import javax.management.Notification;
import javax.management.NotificationBroadcaster;
import javax.management.NotificationFilter;
import javax.management.NotificationFilterSupport;
import javax.management.NotificationListener;
import javax.management.ObjectName;
import javax.management.QueryEval;
import javax.management.QueryExp;

import javax.management.remote.NotificationResult;
import javax.management.remote.TargetedNotification;

import com.sun.jmx.remote.util.EnvHelp;
import com.sun.jmx.remote.util.ClassLogger;

/** A circular buffer of notifications received from an MBean server. */
/*
  There is one instance of ArrayNotificationBuffer for every
  MBeanServer object that has an attached ConnectorServer.  Then, for
  every ConnectorServer attached to a given MBeanServer, there is an
  instance of the inner class ShareBuffer.  So for example with two
  ConnectorServers it looks like this:

  ConnectorServer1 -> ShareBuffer1 -\
                                     }-> ArrayNotificationBuffer
  ConnectorServer2 -> ShareBuffer2 -/              |
                                                   |
                                                   v
                                              MBeanServer

  The ArrayNotificationBuffer has a circular buffer of
  NamedNotification objects.  Each ConnectorServer defines a
  notification buffer size, and this size is recorded by the
  corresponding ShareBuffer.  The buffer size of the
  ArrayNotificationBuffer is the maximum of all of its ShareBuffers.
  When a ShareBuffer is added or removed, the ArrayNotificationBuffer
  size is adjusted accordingly.

  An ArrayNotificationBuffer also has a BufferListener (which is a
  NotificationListener) registered on every NotificationBroadcaster
  MBean in the MBeanServer to which it is attached.  The cost of this
  potentially large set of listeners is the principal motivation for
  sharing the ArrayNotificationBuffer between ConnectorServers, and
  also the reason that we are careful to discard the
  ArrayNotificationBuffer (and its BufferListeners) when there are no
  longer any ConnectorServers using it.

  The synchronization of this class is inherently complex.  In an attempt
  to limit the complexity, we use just two locks:

  - globalLock controls access to the mapping between an MBeanServer
    and its ArrayNotificationBuffer and to the set of ShareBuffers for
    each ArrayNotificationBuffer.

  - the instance lock of each ArrayNotificationBuffer controls access
    to the array of notifications, including its size, and to the
    dispose flag of the ArrayNotificationBuffer.  The wait/notify
    mechanism is used to indicate changes to the array.

  If both locks are held at the same time, the globalLock must be
  taken first.

  Since adding or removing a BufferListener to an MBean can involve
  calling user code, we are careful not to hold any locks while it is
  done.
 */
public class ArrayNotificationBuffer implements NotificationBuffer {
    private boolean disposed = false;

    // FACTORY STUFF, INCLUDING SHARING

    private static final Object globalLock = new Object();
    private static final
        HashMap<MBeanServer,ArrayNotificationBuffer> mbsToBuffer =
        new HashMap<MBeanServer,ArrayNotificationBuffer>(1);
    private final Collection<ShareBuffer> sharers = new HashSet<ShareBuffer>(1);

    public static NotificationBuffer getNotificationBuffer(
            MBeanServer mbs, Map env) {

        if (env == null)
            env = Collections.emptyMap();

        //Find out queue size
        int queueSize = EnvHelp.getNotifBufferSize(env);

        ArrayNotificationBuffer buf;
        boolean create;
        NotificationBuffer sharer;
        synchronized (globalLock) {
            buf = mbsToBuffer.get(mbs);
            create = (buf == null);
            if (create) {
                buf = new ArrayNotificationBuffer(mbs, queueSize);
                mbsToBuffer.put(mbs, buf);
            }
            sharer = buf.new ShareBuffer(queueSize);
        }
        /* We avoid holding any locks while calling createListeners.
         * This prevents possible deadlocks involving user code, but
         * does mean that a second ConnectorServer created and started
         * in this window will return before all the listeners are ready,
         * which could lead to surprising behaviour.  The alternative
         * would be to block the second ConnectorServer until the first
         * one has finished adding all the listeners, but that would then
         * be subject to deadlock.
         */
        if (create)
            buf.createListeners();
        return sharer;
    }

    /* Ensure that this buffer is no longer the one that will be returned by
     * getNotificationBuffer.  This method is idempotent - calling it more
     * than once has no effect beyond that of calling it once.
     */
    static void removeNotificationBuffer(MBeanServer mbs) {
        synchronized (globalLock) {
            mbsToBuffer.remove(mbs);
        }
    }

    void addSharer(ShareBuffer sharer) {
        synchronized (globalLock) {
            synchronized (this) {
                if (sharer.getSize() > queueSize)
                    resize(sharer.getSize());
            }
            sharers.add(sharer);
        }
    }

    private void removeSharer(ShareBuffer sharer) {
        boolean empty;
        synchronized (globalLock) {
            sharers.remove(sharer);
            empty = sharers.isEmpty();
            if (empty)
                removeNotificationBuffer(mBeanServer);
            else {
                int max = 0;
                for (ShareBuffer buf : sharers) {
                    int bufsize = buf.getSize();
                    if (bufsize > max)
                        max = bufsize;
                }
                if (max < queueSize)
                    resize(max);
            }
        }
        if (empty) {
            synchronized (this) {
                disposed = true;
                // Notify potential waiting fetchNotification call
                notifyAll();
            }
            destroyListeners();
        }
    }

    private synchronized void resize(int newSize) {
        if (newSize == queueSize)
            return;
        while (queue.size() > newSize)
            dropNotification();
        queue.resize(newSize);
        queueSize = newSize;
    }

    private class ShareBuffer implements NotificationBuffer {
        ShareBuffer(int size) {
            this.size = size;
            addSharer(this);
        }

        public NotificationResult
            fetchNotifications(NotificationBufferFilter filter,
                               long startSequenceNumber,
                               long timeout,
                               int maxNotifications)
                throws InterruptedException {
            NotificationBuffer buf = ArrayNotificationBuffer.this;
            return buf.fetchNotifications(filter, startSequenceNumber,
                                          timeout, maxNotifications);
        }

        public void dispose() {
            ArrayNotificationBuffer.this.removeSharer(this);
        }

        int getSize() {
            return size;
        }

        private final int size;
    }


    // ARRAYNOTIFICATIONBUFFER IMPLEMENTATION

    private ArrayNotificationBuffer(MBeanServer mbs, int queueSize) {
        if (logger.traceOn())
            logger.trace("Constructor", "queueSize=" + queueSize);

        if (mbs == null || queueSize < 1)
            throw new IllegalArgumentException("Bad args");

        this.mBeanServer = mbs;
        this.queueSize = queueSize;
        this.queue = new ArrayQueue<NamedNotification>(queueSize);
        this.earliestSequenceNumber = System.currentTimeMillis();
        this.nextSequenceNumber = this.earliestSequenceNumber;

        logger.trace("Constructor", "ends");
    }

    private synchronized boolean isDisposed() {
        return disposed;
    }

    // We no longer support calling this method from outside.
    // The JDK doesn't contain any such calls and users are not
    // supposed to be accessing this class.
    public void dispose() {
        throw new UnsupportedOperationException();
    }

    /**
     * <p>Fetch notifications that match the given listeners.</p>
     *
     * <p>The operation only considers notifications with a sequence
     * number at least <code>startSequenceNumber</code>.  It will take
     * no longer than <code>timeout</code>, and will return no more
     * than <code>maxNotifications</code> different notifications.</p>
     *
     * <p>If there are no notifications matching the criteria, the
     * operation will block until one arrives, subject to the
     * timeout.</p>
     *
     * @param filter an object that will add notifications to a
     * {@code List<TargetedNotification>} if they match the current
     * listeners with their filters.
     * @param startSequenceNumber the first sequence number to
     * consider.
     * @param timeout the maximum time to wait.  May be 0 to indicate
     * not to wait if there are no notifications.
     * @param maxNotifications the maximum number of notifications to
     * return.  May be 0 to indicate a wait for eligible notifications
     * that will return a usable <code>nextSequenceNumber</code>.  The
     * {@link TargetedNotification} array in the returned {@link
     * NotificationResult} may contain more than this number of
     * elements but will not contain more than this number of
     * different notifications.
     */
    public NotificationResult
        fetchNotifications(NotificationBufferFilter filter,
                           long startSequenceNumber,
                           long timeout,
                           int maxNotifications)
            throws InterruptedException {

        logger.trace("fetchNotifications", "starts");

        if (startSequenceNumber < 0 || isDisposed()) {
            synchronized(this) {
                return new NotificationResult(earliestSequenceNumber(),
                                              nextSequenceNumber(),
                                              new TargetedNotification[0]);
            }
        }

        // Check arg validity
        if (filter == null
            || startSequenceNumber < 0 || timeout < 0
            || maxNotifications < 0) {
            logger.trace("fetchNotifications", "Bad args");
            throw new IllegalArgumentException("Bad args to fetch");
        }

        if (logger.debugOn()) {
            logger.trace("fetchNotifications",
                  "filter=" + filter + "; startSeq=" +
                  startSequenceNumber + "; timeout=" + timeout +
                  "; max=" + maxNotifications);
        }

        if (startSequenceNumber > nextSequenceNumber()) {
            final String msg = "Start sequence number too big: " +
                startSequenceNumber + " > " + nextSequenceNumber();
            logger.trace("fetchNotifications", msg);
            throw new IllegalArgumentException(msg);
        }

        /* Determine the end time corresponding to the timeout value.
           Caller may legitimately supply Long.MAX_VALUE to indicate no
           timeout.  In that case the addition will overflow and produce
           a negative end time.  Set end time to Long.MAX_VALUE in that
           case.  We assume System.currentTimeMillis() is positive.  */
        long endTime = System.currentTimeMillis() + timeout;
        if (endTime < 0) // overflow
            endTime = Long.MAX_VALUE;

        if (logger.debugOn())
            logger.debug("fetchNotifications", "endTime=" + endTime);

        /* We set earliestSeq the first time through the loop.  If we
           set it here, notifications could be dropped before we
           started examining them, so earliestSeq might not correspond
           to the earliest notification we examined.  */
        long earliestSeq = -1;
        long nextSeq = startSequenceNumber;
        List<TargetedNotification> notifs =
            new ArrayList<TargetedNotification>();

        /* On exit from this loop, notifs, earliestSeq, and nextSeq must
           all be correct values for the returned NotificationResult.  */
        while (true) {
            logger.debug("fetchNotifications", "main loop starts");

            NamedNotification candidate;

            /* Get the next available notification regardless of filters,
               or wait for one to arrive if there is none.  */
            synchronized (this) {

                /* First time through.  The current earliestSequenceNumber
                   is the first one we could have examined.  */
                if (earliestSeq < 0) {
                    earliestSeq = earliestSequenceNumber();
                    if (logger.debugOn()) {
                        logger.debug("fetchNotifications",
                              "earliestSeq=" + earliestSeq);
                    }
                    if (nextSeq < earliestSeq) {
                        nextSeq = earliestSeq;
                        logger.debug("fetchNotifications",
                                     "nextSeq=earliestSeq");
                    }
                } else
                    earliestSeq = earliestSequenceNumber();

                /* If many notifications have been dropped since the
                   last time through, nextSeq could now be earlier
                   than the current earliest.  If so, notifications
                   may have been lost and we return now so the caller
                   can see this next time it calls.  */
                if (nextSeq < earliestSeq) {
                    logger.trace("fetchNotifications",
                          "nextSeq=" + nextSeq + " < " + "earliestSeq=" +
                          earliestSeq + " so may have lost notifs");
                    break;
                }

                if (nextSeq < nextSequenceNumber()) {
                    candidate = notificationAt(nextSeq);
                    if (logger.debugOn()) {
                        logger.debug("fetchNotifications", "candidate: " +
                                     candidate);
                        logger.debug("fetchNotifications", "nextSeq now " +
                                     nextSeq);
                    }
                } else {
                    /* nextSeq is the largest sequence number.  If we
                       already got notifications, return them now.
                       Otherwise wait for some to arrive, with
                       timeout.  */
                    if (notifs.size() > 0) {
                        logger.debug("fetchNotifications",
                              "no more notifs but have some so don't wait");
                        break;
                    }
                    long toWait = endTime - System.currentTimeMillis();
                    if (toWait <= 0) {
                        logger.debug("fetchNotifications", "timeout");
                        break;
                    }

                    /* dispose called */
                    if (isDisposed()) {
                        if (logger.debugOn())
                            logger.debug("fetchNotifications",
                                         "dispose callled, no wait");
                        return new NotificationResult(earliestSequenceNumber(),
                                                  nextSequenceNumber(),
                                                  new TargetedNotification[0]);
                    }

                    if (logger.debugOn())
                        logger.debug("fetchNotifications",
                                     "wait(" + toWait + ")");
                    wait(toWait);

                    continue;
                }
            }

            /* We have a candidate notification.  See if it matches
               our filters.  We do this outside the synchronized block
               so we don't hold up everyone accessing the buffer
               (including notification senders) while we evaluate
               potentially slow filters.  */
            ObjectName name = candidate.getObjectName();
            Notification notif = candidate.getNotification();
            List<TargetedNotification> matchedNotifs =
                new ArrayList<TargetedNotification>();
            logger.debug("fetchNotifications",
                         "applying filter to candidate");
            filter.apply(matchedNotifs, name, notif);

            if (matchedNotifs.size() > 0) {
                /* We only check the max size now, so that our
                   returned nextSeq is as large as possible.  This
                   prevents the caller from thinking it missed
                   interesting notifications when in fact we knew they
                   weren't.  */
                if (maxNotifications <= 0) {
                    logger.debug("fetchNotifications",
                                 "reached maxNotifications");
                    break;
                }
                --maxNotifications;
                if (logger.debugOn())
                    logger.debug("fetchNotifications", "add: " +
                                 matchedNotifs);
                notifs.addAll(matchedNotifs);
            }

            ++nextSeq;
        } // end while

        /* Construct and return the result.  */
        int nnotifs = notifs.size();
        TargetedNotification[] resultNotifs =
            new TargetedNotification[nnotifs];
        notifs.toArray(resultNotifs);
        NotificationResult nr =
            new NotificationResult(earliestSeq, nextSeq, resultNotifs);
        if (logger.debugOn())
            logger.debug("fetchNotifications", nr.toString());
        logger.trace("fetchNotifications", "ends");

        return nr;
    }

    synchronized long earliestSequenceNumber() {
        return earliestSequenceNumber;
    }

    synchronized long nextSequenceNumber() {
        return nextSequenceNumber;
    }

    synchronized void addNotification(NamedNotification notif) {
        if (logger.traceOn())
            logger.trace("addNotification", notif.toString());

        while (queue.size() >= queueSize) {
            dropNotification();
            if (logger.debugOn()) {
                logger.debug("addNotification",
                      "dropped oldest notif, earliestSeq=" +
                      earliestSequenceNumber);
            }
        }
        queue.add(notif);
        nextSequenceNumber++;
        if (logger.debugOn())
            logger.debug("addNotification", "nextSeq=" + nextSequenceNumber);
        notifyAll();
    }

    private void dropNotification() {
        queue.remove(0);
        earliestSequenceNumber++;
    }

    synchronized NamedNotification notificationAt(long seqNo) {
        long index = seqNo - earliestSequenceNumber;
        if (index < 0 || index > Integer.MAX_VALUE) {
            final String msg = "Bad sequence number: " + seqNo + " (earliest "
                + earliestSequenceNumber + ")";
            logger.trace("notificationAt", msg);
            throw new IllegalArgumentException(msg);
        }
        return queue.get((int) index);
    }

    private static class NamedNotification {
        NamedNotification(ObjectName sender, Notification notif) {
            this.sender = sender;
            this.notification = notif;
        }

        ObjectName getObjectName() {
            return sender;
        }

        Notification getNotification() {
            return notification;
        }

        public String toString() {
            return "NamedNotification(" + sender + ", " + notification + ")";
        }

        private final ObjectName sender;
        private final Notification notification;
    }

    /*
     * Add our listener to every NotificationBroadcaster MBean
     * currently in the MBean server and to every
     * NotificationBroadcaster later created.
     *
     * It would be really nice if we could just do
     * mbs.addNotificationListener(new ObjectName("*:*"), ...);
     * Definitely something for the next version of JMX.
     *
     * There is a nasty race condition that we must handle.  We
     * first register for MBean-creation notifications so we can add
     * listeners to new MBeans, then we query the existing MBeans to
     * add listeners to them.  The problem is that a new MBean could
     * arrive after we register for creations but before the query has
     * completed.  Then we could see the MBean both in the query and
     * in an MBean-creation notification, and we would end up
     * registering our listener twice.
     *
     * To solve this problem, we arrange for new MBeans that arrive
     * while the query is being done to be added to the Set createdDuringQuery
     * and we do not add a listener immediately.  When the query is done,
     * we atomically turn off the addition of new names to createdDuringQuery
     * and add all the names that were there to the result of the query.
     * Since we are dealing with Sets, the result is the same whether or not
     * the newly-created MBean was included in the query result.
     *
     * It is important not to hold any locks during the operation of adding
     * listeners to MBeans.  An MBean's addNotificationListener can be
     * arbitrary user code, and this could deadlock with any locks we hold
     * (see bug 6239400).  The corollary is that we must not do any operations
     * in this method or the methods it calls that require locks.
     */
    private void createListeners() {
        logger.debug("createListeners", "starts");

        synchronized (this) {
            createdDuringQuery = new HashSet<ObjectName>();
        }

        try {
            addNotificationListener(MBeanServerDelegate.DELEGATE_NAME,
                                    creationListener, creationFilter, null);
            logger.debug("createListeners", "added creationListener");
        } catch (Exception e) {
            final String msg = "Can't add listener to MBean server delegate: ";
            RuntimeException re = new IllegalArgumentException(msg + e);
            EnvHelp.initCause(re, e);
            logger.fine("createListeners", msg + e);
            logger.debug("createListeners", e);
            throw re;
        }

        /* Spec doesn't say whether Set returned by QueryNames can be modified
           so we clone it. */
        Set<ObjectName> names = queryNames(null, broadcasterQuery);
        names = new HashSet<ObjectName>(names);

        synchronized (this) {
            names.addAll(createdDuringQuery);
            createdDuringQuery = null;
        }

        for (ObjectName name : names)
            addBufferListener(name);
        logger.debug("createListeners", "ends");
    }

    private void addBufferListener(ObjectName name) {
        checkNoLocks();
        if (logger.debugOn())
            logger.debug("addBufferListener", name.toString());
        try {
            addNotificationListener(name, bufferListener, null, name);
        } catch (Exception e) {
            logger.trace("addBufferListener", e);
            /* This can happen if the MBean was unregistered just
               after the query.  Or user NotificationBroadcaster might
               throw unexpected exception.  */
        }
    }

    private void removeBufferListener(ObjectName name) {
        checkNoLocks();
        if (logger.debugOn())
            logger.debug("removeBufferListener", name.toString());
        try {
            removeNotificationListener(name, bufferListener);
        } catch (Exception e) {
            logger.trace("removeBufferListener", e);
        }
    }

    private void addNotificationListener(final ObjectName name,
                                         final NotificationListener listener,
                                         final NotificationFilter filter,
                                         final Object handback)
            throws Exception {
        try {
            AccessController.doPrivileged(new PrivilegedExceptionAction<Void>() {
                public Void run() throws InstanceNotFoundException {
                    mBeanServer.addNotificationListener(name,
                                                        listener,
                                                        filter,
                                                        handback);
                    return null;
                }
            });
        } catch (Exception e) {
            throw extractException(e);
        }
    }

    private void removeNotificationListener(final ObjectName name,
                                            final NotificationListener listener)
            throws Exception {
        try {
            AccessController.doPrivileged(new PrivilegedExceptionAction<Void>() {
                public Void run() throws Exception {
                    mBeanServer.removeNotificationListener(name, listener);
                    return null;
                }
            });
        } catch (Exception e) {
            throw extractException(e);
        }
    }

    private Set<ObjectName> queryNames(final ObjectName name,
                                       final QueryExp query) {
        PrivilegedAction<Set<ObjectName>> act =
            new PrivilegedAction<Set<ObjectName>>() {
                public Set<ObjectName> run() {
                    return mBeanServer.queryNames(name, query);
                }
            };
        try {
            return AccessController.doPrivileged(act);
        } catch (RuntimeException e) {
            logger.fine("queryNames", "Failed to query names: " + e);
            logger.debug("queryNames", e);
            throw e;
        }
    }

    private static boolean isInstanceOf(final MBeanServer mbs,
                                        final ObjectName name,
                                        final String className) {
        PrivilegedExceptionAction<Boolean> act =
            new PrivilegedExceptionAction<Boolean>() {
                public Boolean run() throws InstanceNotFoundException {
                    return mbs.isInstanceOf(name, className);
                }
            };
        try {
            return AccessController.doPrivileged(act);
        } catch (Exception e) {
            logger.fine("isInstanceOf", "failed: " + e);
            logger.debug("isInstanceOf", e);
            return false;
        }
    }

    /* This method must not be synchronized.  See the comment on the
     * createListeners method.
     *
     * The notification could arrive after our buffer has been destroyed
     * or even during its destruction.  So we always add our listener
     * (without synchronization), then we check if the buffer has been
     * destroyed and if so remove the listener we just added.
     */
    private void createdNotification(MBeanServerNotification n) {
        final String shouldEqual =
            MBeanServerNotification.REGISTRATION_NOTIFICATION;
        if (!n.getType().equals(shouldEqual)) {
            logger.warning("createNotification", "bad type: " + n.getType());
            return;
        }

        ObjectName name = n.getMBeanName();
        if (logger.debugOn())
            logger.debug("createdNotification", "for: " + name);

        synchronized (this) {
            if (createdDuringQuery != null) {
                createdDuringQuery.add(name);
                return;
            }
        }

        if (isInstanceOf(mBeanServer, name, broadcasterClass)) {
            addBufferListener(name);
            if (isDisposed())
                removeBufferListener(name);
        }
    }

    private class BufferListener implements NotificationListener {
        public void handleNotification(Notification notif, Object handback) {
            if (logger.debugOn()) {
                logger.debug("BufferListener.handleNotification",
                      "notif=" + notif + "; handback=" + handback);
            }
            ObjectName name = (ObjectName) handback;
            addNotification(new NamedNotification(name, notif));
        }
    }

    private final NotificationListener bufferListener = new BufferListener();

    private static class BroadcasterQuery
            extends QueryEval implements QueryExp {
        private static final long serialVersionUID = 7378487660587592048L;

        public boolean apply(final ObjectName name) {
            final MBeanServer mbs = QueryEval.getMBeanServer();
            return isInstanceOf(mbs, name, broadcasterClass);
        }
    }
    private static final QueryExp broadcasterQuery = new BroadcasterQuery();

    private static final NotificationFilter creationFilter;
    static {
        NotificationFilterSupport nfs = new NotificationFilterSupport();
        nfs.enableType(MBeanServerNotification.REGISTRATION_NOTIFICATION);
        creationFilter = nfs;
    }

    private final NotificationListener creationListener =
        new NotificationListener() {
            public void handleNotification(Notification notif,
                                           Object handback) {
                logger.debug("creationListener", "handleNotification called");
                createdNotification((MBeanServerNotification) notif);
            }
        };

    private void destroyListeners() {
        checkNoLocks();
        logger.debug("destroyListeners", "starts");
        try {
            removeNotificationListener(MBeanServerDelegate.DELEGATE_NAME,
                                       creationListener);
        } catch (Exception e) {
            logger.warning("remove listener from MBeanServer delegate", e);
        }
        Set<ObjectName> names = queryNames(null, broadcasterQuery);
        for (final ObjectName name : names) {
            if (logger.debugOn())
                logger.debug("destroyListeners",
                             "remove listener from " + name);
            removeBufferListener(name);
        }
        logger.debug("destroyListeners", "ends");
    }

    private void checkNoLocks() {
        if (Thread.holdsLock(this) || Thread.holdsLock(globalLock))
            logger.warning("checkNoLocks", "lock protocol violation");
    }

    /**
     * Iterate until we extract the real exception
     * from a stack of PrivilegedActionExceptions.
     */
    private static Exception extractException(Exception e) {
        while (e instanceof PrivilegedActionException) {
            e = ((PrivilegedActionException)e).getException();
        }
        return e;
    }

    private static final ClassLogger logger =
        new ClassLogger("javax.management.remote.misc",
                        "ArrayNotificationBuffer");

    private final MBeanServer mBeanServer;
    private final ArrayQueue<NamedNotification> queue;
    private int queueSize;
    private long earliestSequenceNumber;
    private long nextSequenceNumber;
    private Set<ObjectName> createdDuringQuery;

    static final String broadcasterClass =
        NotificationBroadcaster.class.getName();
}