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 org.apache.hadoop.hbase.procedure; import java.io.Closeable; import java.io.IOException; import java.util.List; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.hbase.zookeeper.ZKUtil; import org.apache.hadoop.hbase.zookeeper.ZooKeeperListener; import org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher; import org.apache.zookeeper.KeeperException; /** * This is a shared ZooKeeper-based znode management utils for distributed procedure. All znode * operations should go through the provided methods in coordinators and members. * * Layout of nodes in ZK is * /hbase/[op name]/acquired/ * [op instance] - op data/ * /[nodes that have acquired] * /reached/ * [op instance]/ * /[nodes that have completed] * /abort/ * [op instance] - failure data * * NOTE: while acquired and completed are znode dirs, abort is actually just a znode. * * Assumption here that procedure names are unique */ @InterfaceAudience.Private public abstract class ZKProcedureUtil extends ZooKeeperListener implements Closeable { private static final Log LOG = LogFactory.getLog(ZKProcedureUtil.class); public static final String ACQUIRED_BARRIER_ZNODE_DEFAULT = "acquired"; public static final String REACHED_BARRIER_ZNODE_DEFAULT = "reached"; public static final String ABORT_ZNODE_DEFAULT = "abort"; public final String baseZNode; protected final String acquiredZnode; protected final String reachedZnode; protected final String abortZnode; /** * Top-level watcher/controller for procedures across the cluster. * <p> * On instantiation, this ensures the procedure znodes exist. This however requires the passed in * watcher has been started. * @param watcher watcher for the cluster ZK. Owned by <tt>this</tt> and closed via * {@link #close()} * @param procDescription name of the znode describing the procedure to run * @throws KeeperException when the procedure znodes cannot be created */ public ZKProcedureUtil(ZooKeeperWatcher watcher, String procDescription) throws KeeperException { super(watcher); // make sure we are listening for events watcher.registerListener(this); // setup paths for the zknodes used in procedures this.baseZNode = ZKUtil.joinZNode(watcher.baseZNode, procDescription); acquiredZnode = ZKUtil.joinZNode(baseZNode, ACQUIRED_BARRIER_ZNODE_DEFAULT); reachedZnode = ZKUtil.joinZNode(baseZNode, REACHED_BARRIER_ZNODE_DEFAULT); abortZnode = ZKUtil.joinZNode(baseZNode, ABORT_ZNODE_DEFAULT); // first make sure all the ZK nodes exist // make sure all the parents exist (sometimes not the case in tests) ZKUtil.createWithParents(watcher, acquiredZnode); // regular create because all the parents exist ZKUtil.createAndFailSilent(watcher, reachedZnode); ZKUtil.createAndFailSilent(watcher, abortZnode); } @Override public void close() throws IOException { // the watcher is passed from either Master or Region Server // watcher.close() will be called by the owner so no need to call close() here } public String getAcquiredBarrierNode(String opInstanceName) { return ZKProcedureUtil.getAcquireBarrierNode(this, opInstanceName); } public String getReachedBarrierNode(String opInstanceName) { return ZKProcedureUtil.getReachedBarrierNode(this, opInstanceName); } public String getAbortZNode(String opInstanceName) { return ZKProcedureUtil.getAbortNode(this, opInstanceName); } public String getAbortZnode() { return abortZnode; } public String getBaseZnode() { return baseZNode; } public String getAcquiredBarrier() { return acquiredZnode; } /** * Get the full znode path for the node used by the coordinator to trigger a global barrier * acquire on each subprocedure. * @param controller controller running the procedure * @param opInstanceName name of the running procedure instance (not the procedure description). * @return full znode path to the prepare barrier/start node */ public static String getAcquireBarrierNode(ZKProcedureUtil controller, String opInstanceName) { return ZKUtil.joinZNode(controller.acquiredZnode, opInstanceName); } /** * Get the full znode path for the node used by the coordinator to trigger a global barrier * execution and release on each subprocedure. * @param controller controller running the procedure * @param opInstanceName name of the running procedure instance (not the procedure description). * @return full znode path to the commit barrier */ public static String getReachedBarrierNode(ZKProcedureUtil controller, String opInstanceName) { return ZKUtil.joinZNode(controller.reachedZnode, opInstanceName); } /** * Get the full znode path for the node used by the coordinator or member to trigger an abort * of the global barrier acquisition or execution in subprocedures. * @param controller controller running the procedure * @param opInstanceName name of the running procedure instance (not the procedure description). * @return full znode path to the abort znode */ public static String getAbortNode(ZKProcedureUtil controller, String opInstanceName) { return ZKUtil.joinZNode(controller.abortZnode, opInstanceName); } public ZooKeeperWatcher getWatcher() { return watcher; } /** * Is this a procedure related znode path? * * TODO: this is not strict, can return true if had name just starts with same prefix but is * different zdir. * * @return true if starts with baseZnode */ boolean isInProcedurePath(String path) { return path.startsWith(baseZNode); } /** * Is this the exact procedure barrier acquired znode */ boolean isAcquiredNode(String path) { return path.equals(acquiredZnode); } /** * Is this in the procedure barrier acquired znode path */ boolean isAcquiredPathNode(String path) { return path.startsWith(this.acquiredZnode) && !path.equals(acquiredZnode); } /** * Is this the exact procedure barrier reached znode */ boolean isReachedNode(String path) { return path.equals(reachedZnode); } /** * Is this in the procedure barrier reached znode path */ boolean isReachedPathNode(String path) { return path.startsWith(this.reachedZnode) && !path.equals(reachedZnode); } /** * Is this in the procedure barrier abort znode path */ boolean isAbortNode(String path) { return path.equals(abortZnode); } /** * Is this in the procedure barrier abort znode path */ public boolean isAbortPathNode(String path) { return path.startsWith(this.abortZnode) && !path.equals(abortZnode); } // -------------------------------------------------------------------------- // internal debugging methods // -------------------------------------------------------------------------- /** * Recursively print the current state of ZK (non-transactional) * @param root name of the root directory in zk to print * @throws KeeperException */ void logZKTree(String root) { if (!LOG.isDebugEnabled()) return; LOG.debug("Current zk system:"); String prefix = "|-"; LOG.debug(prefix + root); try { logZKTree(root, prefix); } catch (KeeperException e) { throw new RuntimeException(e); } } /** * Helper method to print the current state of the ZK tree. * @see #logZKTree(String) * @throws KeeperException if an unexpected exception occurs */ protected void logZKTree(String root, String prefix) throws KeeperException { List<String> children = ZKUtil.listChildrenNoWatch(watcher, root); if (children == null) return; for (String child : children) { LOG.debug(prefix + child); String node = ZKUtil.joinZNode(root.equals("/") ? "" : root, child); logZKTree(node, prefix + "---"); } } public void clearChildZNodes() throws KeeperException { // TODO This is potentially racy since not atomic. update when we support zk that has multi LOG.info("Clearing all procedure znodes: " + acquiredZnode + " " + reachedZnode + " " + abortZnode); // If the coordinator was shutdown mid-procedure, then we are going to lose // an procedure that was previously started by cleaning out all the previous state. Its much // harder to figure out how to keep an procedure going and the subject of HBASE-5487. ZKUtil.deleteChildrenRecursively(watcher, acquiredZnode); ZKUtil.deleteChildrenRecursively(watcher, reachedZnode); ZKUtil.deleteChildrenRecursively(watcher, abortZnode); } public void clearZNodes(String procedureName) throws KeeperException { // TODO This is potentially racy since not atomic. update when we support zk that has multi LOG.info("Clearing all znodes for procedure " + procedureName + "including nodes " + acquiredZnode + " " + reachedZnode + " " + abortZnode); ZKUtil.deleteNodeRecursively(watcher, getAcquiredBarrierNode(procedureName)); ZKUtil.deleteNodeRecursively(watcher, getReachedBarrierNode(procedureName)); ZKUtil.deleteNodeRecursively(watcher, getAbortZNode(procedureName)); } }