Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.pinterest.terrapin.controller; import com.google.common.annotations.VisibleForTesting; import com.google.common.collect.Lists; import com.google.common.collect.Maps; import com.google.common.collect.Sets; import com.pinterest.terrapin.Constants; import com.pinterest.terrapin.zookeeper.ViewInfo; import com.pinterest.terrapin.zookeeper.ZooKeeperManager; import com.twitter.ostrich.stats.Stats; import org.apache.helix.NotificationContext; import org.apache.helix.model.ExternalView; import org.apache.helix.spectator.RoutingTableProvider; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import java.util.List; import java.util.Map; import java.util.Set; /** * This class adds a batching abstraction on top of the RoutingTable provider to batch updates * to the client view by time. It writes out external views every 15 seconds. */ public class TerrapinRoutingTableProvider extends RoutingTableProvider { private static final Logger LOG = LoggerFactory.getLogger(TerrapinRoutingTableProvider.class); static class ViewInfoRecord { public ViewInfo viewInfo; public boolean drained; } private final ZooKeeperManager zkManager; private Map<String, ViewInfoRecord> viewInfoRecordMap; private volatile boolean isRunning; private Thread thread; class ViewSyncRunnable implements Runnable { @Override public void run() { isRunning = true; while (isRunning) { try { List<ViewInfo> viewInfoList = Lists.newArrayList(); synchronized (viewInfoRecordMap) { for (Map.Entry<String, ViewInfoRecord> entry : viewInfoRecordMap.entrySet()) { if (!entry.getValue().drained) { viewInfoList.add(entry.getValue().viewInfo); entry.getValue().drained = true; } } } for (ViewInfo viewInfo : viewInfoList) { try { zkManager.setViewInfo(viewInfo); } catch (Exception e) { LOG.error("Exception while syncing " + viewInfo.getResource(), e); Stats.incr("compressed-view-sync-errors"); } } try { Thread.sleep(Constants.VIEW_INFO_REFRESH_INTERVAL_SECONDS_DEFAULT * 1000); } catch (InterruptedException e) { LOG.info("Interrupted."); } } catch (Throwable t) { LOG.info("Got exception in view syncer thread", t); } } } } public TerrapinRoutingTableProvider(ZooKeeperManager zkManager, List<String> resourceList) { this.zkManager = zkManager; this.viewInfoRecordMap = Maps.newHashMapWithExpectedSize(resourceList.size()); // Initialize the view info with what we have in zookeeper to avoid double writes. for (String resource : resourceList) { ViewInfo viewInfo = this.zkManager.getViewInfo(resource); if (viewInfo != null) { ViewInfoRecord viewInfoRecord = new ViewInfoRecord(); viewInfoRecord.drained = true; viewInfoRecord.viewInfo = viewInfo; this.viewInfoRecordMap.put(resource, viewInfoRecord); } else { LOG.error("Compressed view is null on startup for " + resource); Stats.incr("compressed-view-init-errors"); } } } public void start() { this.thread = new Thread(new ViewSyncRunnable()); this.thread.setName("sync-external-view-thread"); this.thread.start(); } @VisibleForTesting public void updateExternalView(List<ExternalView> externalViewList) { Set<String> resourceSet = Sets.newHashSetWithExpectedSize(externalViewList.size()); synchronized (viewInfoRecordMap) { for (ExternalView externalView : externalViewList) { if (externalView == null) { continue; } String resource = externalView.getResourceName(); resourceSet.add(resource); ViewInfoRecord record = viewInfoRecordMap.get(resource); ViewInfoRecord newRecord = new ViewInfoRecord(); newRecord.viewInfo = new ViewInfo(externalView); if (record != null) { // Only put stuff to be drained if the new external view does not equal the // previous external view. if (newRecord.viewInfo.equals(record.viewInfo)) continue; } newRecord.drained = false; viewInfoRecordMap.put(resource, newRecord); } // Finally remove any deleted external views from the map. Set<String> resourcesToRemove = Sets.newHashSetWithExpectedSize(viewInfoRecordMap.size()); for (String resource : viewInfoRecordMap.keySet()) { if (!resourceSet.contains(resource)) { resourcesToRemove.add(resource); } } for (String resource : resourcesToRemove) { this.viewInfoRecordMap.remove(resource); } } } @Override public void onExternalViewChange(List<ExternalView> externalViewList, NotificationContext context) { super.onExternalViewChange(externalViewList, context); updateExternalView(externalViewList); } public void shutdown() { this.isRunning = false; this.thread.interrupt(); } }