| /** |
| * 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 org.apache.curator.framework.recipes.queue; |
| |
| import org.apache.curator.framework.CuratorFramework; |
| import org.apache.curator.utils.PathUtils; |
| import org.apache.curator.utils.ZKPaths; |
| import org.apache.zookeeper.CreateMode; |
| import org.apache.zookeeper.KeeperException; |
| import org.apache.zookeeper.WatchedEvent; |
| import org.apache.zookeeper.Watcher; |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| import java.util.Collections; |
| import java.util.List; |
| import java.util.NoSuchElementException; |
| import java.util.concurrent.CountDownLatch; |
| import java.util.concurrent.TimeUnit; |
| |
| /** |
| * <p> |
| * Drop in replacement for: org.apache.zookeeper.recipes.queue.DistributedQueue that is part of |
| * the ZooKeeper distribution |
| * </p> |
| * |
| * <p> |
| * This class is data compatible with the ZK version. i.e. it uses the same naming scheme so |
| * it can read from an existing queue |
| * </p> |
| */ |
| public class SimpleDistributedQueue |
| { |
| private final Logger log = LoggerFactory.getLogger(getClass()); |
| private final CuratorFramework client; |
| private final String path; |
| |
| private final String PREFIX = "qn-"; |
| |
| /** |
| * @param client the client |
| * @param path path to store queue nodes |
| */ |
| public SimpleDistributedQueue(CuratorFramework client, String path) |
| { |
| this.client = client; |
| this.path = PathUtils.validatePath(path); |
| } |
| |
| /** |
| * Return the head of the queue without modifying the queue. |
| * |
| * @return the data at the head of the queue. |
| * @throws Exception errors |
| * @throws NoSuchElementException if the queue is empty |
| */ |
| public byte[] element() throws Exception |
| { |
| byte[] bytes = internalElement(false, null); |
| if ( bytes == null ) |
| { |
| throw new NoSuchElementException(); |
| } |
| return bytes; |
| } |
| |
| /** |
| * Attempts to remove the head of the queue and return it. |
| * |
| * @return The former head of the queue |
| * @throws Exception errors |
| * @throws NoSuchElementException if the queue is empty |
| */ |
| public byte[] remove() throws Exception |
| { |
| byte[] bytes = internalElement(true, null); |
| if ( bytes == null ) |
| { |
| throw new NoSuchElementException(); |
| } |
| return bytes; |
| } |
| |
| /** |
| * Removes the head of the queue and returns it, blocks until it succeeds. |
| * |
| * @return The former head of the queue |
| * @throws Exception errors |
| */ |
| public byte[] take() throws Exception |
| { |
| return internalPoll(0, null); |
| } |
| |
| /** |
| * Inserts data into queue. |
| * |
| * @param data the data |
| * @return true if data was successfully added |
| * @throws Exception errors |
| */ |
| public boolean offer(byte[] data) throws Exception |
| { |
| String thisPath = ZKPaths.makePath(path, PREFIX); |
| client.create().creatingParentContainersIfNeeded().withMode(CreateMode.PERSISTENT_SEQUENTIAL).forPath(thisPath, data); |
| return true; |
| } |
| |
| /** |
| * Returns the data at the first element of the queue, or null if the queue is empty. |
| * |
| * @return data at the first element of the queue, or null. |
| * @throws Exception errors |
| */ |
| public byte[] peek() throws Exception |
| { |
| try |
| { |
| return element(); |
| } |
| catch ( NoSuchElementException e ) |
| { |
| return null; |
| } |
| } |
| |
| /** |
| * Retrieves and removes the head of this queue, waiting up to the |
| * specified wait time if necessary for an element to become available. |
| * |
| * @param timeout how long to wait before giving up, in units of |
| * <tt>unit</tt> |
| * @param unit a <tt>TimeUnit</tt> determining how to interpret the |
| * <tt>timeout</tt> parameter |
| * @return the head of this queue, or <tt>null</tt> if the |
| * specified waiting time elapses before an element is available |
| * @throws Exception errors |
| */ |
| public byte[] poll(long timeout, TimeUnit unit) throws Exception |
| { |
| return internalPoll(timeout, unit); |
| } |
| |
| /** |
| * Attempts to remove the head of the queue and return it. Returns null if the queue is empty. |
| * |
| * @return Head of the queue or null. |
| * @throws Exception errors |
| */ |
| public byte[] poll() throws Exception |
| { |
| try |
| { |
| return remove(); |
| } |
| catch ( NoSuchElementException e ) |
| { |
| return null; |
| } |
| } |
| |
| private byte[] internalPoll(long timeout, TimeUnit unit) throws Exception |
| { |
| ensurePath(); |
| |
| long startMs = System.currentTimeMillis(); |
| boolean hasTimeout = (unit != null); |
| long maxWaitMs = hasTimeout ? TimeUnit.MILLISECONDS.convert(timeout, unit) : Long.MAX_VALUE; |
| for(;;) |
| { |
| final CountDownLatch latch = new CountDownLatch(1); |
| Watcher watcher = new Watcher() |
| { |
| @Override |
| public void process(WatchedEvent event) |
| { |
| latch.countDown(); |
| } |
| }; |
| byte[] bytes = internalElement(true, watcher); |
| if ( bytes != null ) |
| { |
| return bytes; |
| } |
| |
| if ( hasTimeout ) |
| { |
| long elapsedMs = System.currentTimeMillis() - startMs; |
| long thisWaitMs = maxWaitMs - elapsedMs; |
| if ( thisWaitMs <= 0 ) |
| { |
| return null; |
| } |
| latch.await(thisWaitMs, TimeUnit.MILLISECONDS); |
| } |
| else |
| { |
| latch.await(); |
| } |
| } |
| } |
| |
| private void ensurePath() throws Exception |
| { |
| client.createContainers(path); |
| } |
| |
| private byte[] internalElement(boolean removeIt, Watcher watcher) throws Exception |
| { |
| ensurePath(); |
| |
| List<String> nodes; |
| try |
| { |
| nodes = (watcher != null) ? client.getChildren().usingWatcher(watcher).forPath(path) : client.getChildren().forPath(path); |
| } |
| catch ( KeeperException.NoNodeException dummy ) |
| { |
| return null; |
| } |
| Collections.sort(nodes); |
| |
| for ( String node : nodes ) |
| { |
| if ( !node.startsWith(PREFIX) ) |
| { |
| log.warn("Foreign node in queue path: " + node); |
| continue; |
| } |
| |
| String thisPath = ZKPaths.makePath(path, node); |
| try |
| { |
| byte[] bytes = client.getData().forPath(thisPath); |
| if ( removeIt ) |
| { |
| client.delete().forPath(thisPath); |
| } |
| return bytes; |
| } |
| catch ( KeeperException.NoNodeException ignore ) |
| { |
| //Another client removed the node first, try next |
| } |
| } |
| |
| return null; |
| } |
| } |