    001    // Copyright 2006, 2007, 2008, 2009, 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.internal.services;
    016
    017    import org.apache.tapestry5.SymbolConstants;
    018    import org.apache.tapestry5.internal.util.Holder;
    019    import org.apache.tapestry5.ioc.Invokable;
    020    import org.apache.tapestry5.ioc.annotations.IntermediateType;
    021    import org.apache.tapestry5.ioc.annotations.Symbol;
    022    import org.apache.tapestry5.ioc.internal.util.ConcurrentBarrier;
    023    import org.apache.tapestry5.ioc.util.TimeInterval;
    024    import org.apache.tapestry5.services.*;
    025
    026    import java.io.IOException;
    027    import java.util.concurrent.TimeUnit;
    028
    029    /**
    030     * Implements a barrier that periodically asks the {@link org.apache.tapestry5.services.UpdateListenerHub} to check for
    031     * updates to files. The UpdateListenerHub is invoked from a write method, meaning that when it is called, all other
    032     * threads will be blocked.
    033     */
    034    public class CheckForUpdatesFilter implements RequestFilter
    035    {
    036        private final long checkInterval;
    037
    038        private final long updateTimeout;
    039
    040        private final UpdateListenerHub updateListenerHub;
    041
    042        private final ConcurrentBarrier barrier = new ConcurrentBarrier();
    043
    044        private final Runnable checker = new Runnable()
    045        {
    046            public void run()
    047            {
    048                // On a race condition, multiple threads may hit this method briefly. If we've
    049                // already done a check, don't run it again.
    050
    051                if (System.currentTimeMillis() - lastCheck >= checkInterval)
    052                {
    053
    054                    // Fire the update event which will force a number of checks and then
    055                    // corresponding invalidation events.
    056
    057                    updateListenerHub.fireCheckForUpdates();
    058
    059                    lastCheck = System.currentTimeMillis();
    060                }
    061            }
    062        };
    063
    064        private long lastCheck = 0;
    065
    066        /**
    067         * @param updateListenerHub
    068         *            invoked, at intervals, to spur the process of detecting changes
    069         * @param checkInterval
    070         *            interval, in milliseconds, between checks
    071         * @param updateTimeout
    072         *            time, in milliseconds, to wait to obtain update lock.
    073         */
    074        public CheckForUpdatesFilter(UpdateListenerHub updateListenerHub,
    075
    076        @Symbol(SymbolConstants.FILE_CHECK_INTERVAL)
    077        @IntermediateType(TimeInterval.class)
    078        long checkInterval,
    079
    080        @Symbol(SymbolConstants.FILE_CHECK_UPDATE_TIMEOUT)
    081        @IntermediateType(TimeInterval.class)
    082        long updateTimeout)
    083        {
    084            this.updateListenerHub = updateListenerHub;
    085            this.checkInterval = checkInterval;
    086            this.updateTimeout = updateTimeout;
    087        }
    088
    089        public boolean service(final Request request, final Response response, final RequestHandler handler)
    090                throws IOException
    091        {
    092            final Holder<IOException> exceptionHolder = new Holder<IOException>();
    093
    094            Invokable<Boolean> invokable = new Invokable<Boolean>()
    095            {
    096                public Boolean invoke()
    097                {
    098                    if (System.currentTimeMillis() - lastCheck >= checkInterval)
    099                        barrier.tryWithWrite(checker, updateTimeout, TimeUnit.MILLISECONDS);
    100
    101                    // And, now, back to code within the read lock.
    102
    103                    try
    104                    {
    105                        return handler.service(request, response);
    106                    }
    107                    catch (IOException ex)
    108                    {
    109                        exceptionHolder.put(ex);
    110                        return false;
    111                    }
    112                }
    113            };
    114
    115            // Obtain a read lock while handling the request. This will not impair parallel operations, except when a file
    116            // check
    117            // is needed (the exclusive write lock will block threads attempting to get a read lock).
    118
    119            boolean result = barrier.withRead(invokable);
    120
    121            if (exceptionHolder.hasValue())
    122                throw exceptionHolder.get();
    123
    124            return result;
    125        }
    126    }