    001    // Copyright 2006, 2007, 2008, 2010, 2011 The Apache Software Foundation
    002    //
    003    // Licensed under the Apache License, Version 2.0 (the "License");
    004    // you may not use this file except in compliance with the License.
    005    // You may obtain a copy of the License at
    006    //
    007    // http://www.apache.org/licenses/LICENSE-2.0
    008    //
    009    // Unless required by applicable law or agreed to in writing, software
    010    // distributed under the License is distributed on an "AS IS" BASIS,
    011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012    // See the License for the specific language governing permissions and
    013    // limitations under the License.
    014
    015    package org.apache.tapestry5.services;
    016
    017    import org.apache.tapestry5.ioc.ObjectLocator;
    018
    019    /**
    020     * Manages a set of {@link org.apache.tapestry5.services.UpdateListener}s. Periodically (say, every request during
    021     * development, or every minute or so during production), request processing is locked down so that only a single thread
    022     * is active, and the active thread invokes {@link #fireCheckForUpdates()}. Various services that are dependent on
    023     * external resource files (such as classes or template files) can check to see if any file they've used has changed. If
    024     * so, the service can invalidate its internal cache, or notify other services (typically via
    025     * {@link org.apache.tapestry5.services.InvalidationListener} that they should do the same.
    026     * <p>
    027     * Note that this interface has moved from module tapestry-core to tapestry-ioc, but has kept the same package (for
    028     * backwards compatibility reasons).
    029     * <p>
    030     * A <em>weak reference</em> to the listener is kept; this ensures that registering as a listener will not prevent a
    031     * listener instance from being reclaimed by the garbage collector (this is useful as proxies created by
    032     * {@link ObjectLocator#proxy(Class, Class)} may register as listeners, but still be ephemeral).
    033     * <p>
    034     * Starting in Tapestry 5.3, this services does <em>nothing</em> in production mode.
    035     *
    036     * @since 5.1.0.0
    037     */
    038    public interface UpdateListenerHub
    039    {
    040        /**
    041         * Adds a listener.
    042         */
    043        void addUpdateListener(UpdateListener listener);
    044
    045        /**
    046         * Invoked periodically to allow services to check if underlying state has changed. For example, a template file may
    047         * have changed. Listeners will typically notify applicable listeners of their own (they usually implement
    048         * {@link org.apache.tapestry5.services.InvalidationEventHub}) when such a change occurs.
    049         */
    050        void fireCheckForUpdates();
    051    }