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 */ package nl.gridline.zieook.workflow.scheduler; import java.io.IOException; import java.nio.ByteBuffer; import java.util.ArrayList; import java.util.Collections; import java.util.HashMap; import java.util.List; import java.util.Map; import nl.gridline.zieook.exceptions.DistrQueueException; import nl.gridline.zieook.tasks.ZieOokTask; import nl.gridline.zieook.workflow.model.QueueItem; import nl.gridline.zieook.workflow.model.ZooKeeperElement; import nl.gridline.zieook.workflow.model.ZooKeeperState; import org.apache.zookeeper.KeeperException; import org.apache.zookeeper.WatchedEvent; import org.apache.zookeeper.Watcher; import org.apache.zookeeper.ZooKeeper; import org.apache.zookeeper.data.Stat; import org.slf4j.Logger; import org.slf4j.LoggerFactory; /** * [purpose] * <p /> * Project zieook-backend-workflow<br /> * ZkQueue.java created 15 dec. 2010 * <p /> * Copyright, all rights reserved 2010 GridLine Amsterdam * @author <a href="mailto:job@gridline.nl">Job</a> * @version $Revision$, $Date$ */ public class ZieOokScheduler implements Watcher { public static final String ZIEOOK_QUEUE = "/gridline/zieook/queue"; private static final Logger LOG = LoggerFactory.getLogger(ZieOokScheduler.class); private ZooKeeper zk; private DistributedQueue dq; /** * Creates a ZieOok distributed scheduler * Tasks put on the queue will only be executed once, independently of the amount of instances running * @param connectString comma separated host:port pairs, each corresponding to a zk server. e.g. * "127.0.0.1:3000,127.0.0.1:3001,127.0.0.1:3002" If the optional chroot suffix is used the example would * look like: "127.0.0.1:3000,127.0.0.1:3001,127.0.0.1:3002/app/a" where the client would be rooted at * "/app/a" and all paths would be relative to this root - ie getting/setting/etc... "/foo/bar" would * result in operations being run on "/app/a/foo/bar" (from the server perspective). * @param sessionTimeout session timeout in milliseconds * @throws InterruptedException * @throws KeeperException * @throws DistrQueueException * @throws Exception */ public ZieOokScheduler(String connectString, int retries, int sessionTimeout) throws KeeperException, InterruptedException, DistrQueueException { try { LOG.info("creating zookeeper connection to <" + connectString + ">"); // create zookeeper instance: zk = new ZooKeeper(connectString, sessionTimeout, this); // create distributed queue instance: dq = new DistributedQueue(zk, ZIEOOK_QUEUE, null); LOG.info("zookeeper instance created"); } catch (IOException e) { throw new DistrQueueException("failed to itialize zookeeper queue", e); } } public ZooKeeper getZooKeeper() { return zk; } private ZooKeeperElement getTree(String path) { String element = path.substring(path.lastIndexOf('/')); ZooKeeperElement result = new ZooKeeperElement(element); try { List<String> children = zk.getChildren(path, false); if (children != null && children.size() > 0) { Collections.sort(children); for (String child : children) { LOG.debug("getting path: <{}/{}>", path, child); result.getChildren().add(getTree(path + "/" + child)); } } else { Stat nodeStat = new Stat(); byte[] data = zk.getData(path, false, nodeStat); if (data != null) { ByteBuffer buf = ByteBuffer.wrap(data); result.setValue(buf.getLong()); } } } catch (KeeperException e) { LOG.error("failed to get tree", e); } catch (InterruptedException e) { LOG.error("failed to get tree", e); } return result; } public ZooKeeperState getState() { ZooKeeperState result = new ZooKeeperState(); result.setState(zk.getState().toString()); result.setTree(getTree("/gridline")); return result; } /** * shutdown the scheduler */ public void shutdown() { LOG.info("closing down zookeeper connection"); try { zk.close(); } catch (InterruptedException e) { LOG.info("zookeeper shutdown interrupted", e); } } /** * Offers an id to be released at a certain time in the future, or immediately if the release time < current time * @param release time in milliseconds from epoch * @param id an id * @return true if succefully offered * @throws KeeperException * @throws InterruptedException */ public boolean offer(long release, long id) throws KeeperException, InterruptedException { if (id != -1) { return dq.offer(new QueueItem(release, id)); } else { return false; } } /** * Returns the next task-id when available of the task that needs to be executed,it will wait forever * @return task id or -1 if failed * @throws InterruptedException */ public long poll() throws InterruptedException { return poll(-1); } /** * Returns the next task-id when available of the task that needs to be executed, it will wait for <tt>timeout</tt> * milliseconds * @param timeout milliseconds to wait. * @return task id or -1 if failed * @throws InterruptedException */ public long poll(long timeout) throws InterruptedException { long time = System.currentTimeMillis(); try { QueueItem item = dq.take(timeout); time = System.currentTimeMillis() - time; if (item != null) { LOG.debug("found: {} in {}ms", item.getId(), time); return item.getId(); } } catch (KeeperException e) { LOG.error("failed to poll item", e); } catch (IOException e) { LOG.error("failed to poll item", e); } return -1; } public List<Long> getScheduled(long start, long end, int size) throws InterruptedException, KeeperException { List<Long> result = new ArrayList<Long>(size); List<QueueItem> scheduled = dq.getScheduled(); for (QueueItem i : scheduled) { // handle timeout: if (i.getTimeout() > start && i.getTimeout() < end) { result.add(i.getId()); // handle max-size: if (size == result.size()) { break; } } } return result; } @Override public void process(WatchedEvent event) { // nothing to do... LOG.info(event.toString()); } /** * Retrieve the list of active task progresses. In case of an error an empty map is returned. * @return */ public Map<Long, Long> getActiveTasks() { try { return ZieOokTask.getProgress(zk); } catch (KeeperException e) { LOG.error("failed to retrieve progress for any task", e); } catch (InterruptedException e) { LOG.error("failed to retrieve progress for any task - maybe we're shutting down", e); } return new HashMap<Long, Long>(0); } /** * Retrieve the list of active task messages * @return * @throws KeeperException * @throws InterruptedException */ public Map<Long, String> getMessage() { try { return ZieOokTask.getMessages(zk); } catch (KeeperException e) { LOG.error("failed to retrieve messages for any task", e); } catch (InterruptedException e) { LOG.error("failed to retrieve messages for any task - maybe we're shutting down", e); } return new HashMap<Long, String>(0); } }