arraynotificationbuffer.java

java1.6众多例子参考

     * 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() {
                public Object 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() {
                public Object 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 {
        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();
}