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package eu.dnetlib.iis.common.lock;
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import java.util.Collections;
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import java.util.Map;
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import java.util.concurrent.Semaphore;
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import org.apache.hadoop.conf.Configuration;
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import org.apache.hadoop.ha.ZKFailoverController;
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import org.apache.log4j.Logger;
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import org.apache.zookeeper.CreateMode;
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import org.apache.zookeeper.KeeperException;
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import org.apache.zookeeper.WatchedEvent;
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import org.apache.zookeeper.Watcher;
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import org.apache.zookeeper.ZooDefs;
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import org.apache.zookeeper.ZooKeeper;
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import eu.dnetlib.iis.core.java.PortBindings;
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import eu.dnetlib.iis.core.java.porttype.PortType;
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/**
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* Zookeeper lock managing process.
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* Blocks until lock is released.
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* @author mhorst
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*
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*/
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public class LockManagingProcess implements eu.dnetlib.iis.core.java.Process {
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public static final String DEFAULT_ROOT_NODE = "/cache";
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public static final String NODE_SEPARATOR = "/";
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public static final String PARAM_ZK_SESSION_TIMEOUT = "zk_session_timeout";
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public static final String PARAM_ROOT_NODE = "root_node";
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public static final String PARAM_NODE_ID = "node_id";
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public static final String PARAM_LOCK_MODE = "mode";
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public static enum LockMode {
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obtain,
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release
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}
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public static final int DEFAULT_SESSION_TIMEOUT = 60000;
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public static final Logger log = Logger.getLogger(LockManagingProcess.class);
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@Override
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public Map<String, PortType> getInputPorts() {
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return Collections.emptyMap();
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}
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@Override
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public Map<String, PortType> getOutputPorts() {
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return Collections.emptyMap();
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}
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@Override
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public void run(PortBindings portBindings, Configuration conf,
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Map<String, String> parameters) throws Exception {
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if (!parameters.containsKey(PARAM_NODE_ID)) {
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throw new Exception("node id not provided!");
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}
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if (!parameters.containsKey(PARAM_LOCK_MODE)) {
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throw new Exception("lock mode not provided!");
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}
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String zkConnectionString = conf.get(
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ZKFailoverController.ZK_QUORUM_KEY);
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if (zkConnectionString==null || zkConnectionString.isEmpty()) {
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throw new Exception("zookeeper quorum is unknown, invalid " +
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ZKFailoverController.ZK_QUORUM_KEY +
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" property value: " + zkConnectionString);
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}
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int sessionTimeout;
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if (parameters.containsKey(PARAM_ZK_SESSION_TIMEOUT)) {
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sessionTimeout = Integer.valueOf(parameters.get(PARAM_ZK_SESSION_TIMEOUT));
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} else {
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sessionTimeout = DEFAULT_SESSION_TIMEOUT;
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}
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final ZooKeeper zk = new ZooKeeper(zkConnectionString, sessionTimeout, new Watcher() {
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@Override
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public void process(WatchedEvent event) {
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}
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});
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String rootNode = parameters.containsKey(PARAM_ROOT_NODE)?
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parameters.get(PARAM_ROOT_NODE):
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DEFAULT_ROOT_NODE;
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// initializing root node if does not exist
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if (zk.exists(rootNode, false)==null) {
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log.warn("initializing root node: " + rootNode);
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zk.create(rootNode,
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new byte[0],
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ZooDefs.Ids.OPEN_ACL_UNSAFE,
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CreateMode.PERSISTENT);
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log.warn("root node initialized");
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}
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final String nodePath = generatePath(
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parameters.get(PARAM_NODE_ID), rootNode);
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LockMode lockMode = LockMode.valueOf(parameters.get(PARAM_LOCK_MODE));
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final Semaphore semaphore = new Semaphore(1);
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semaphore.acquire();
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if (LockMode.obtain.equals(lockMode)) {
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log.warn("trying to obtain lock: " + nodePath);
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if (zk.exists(nodePath, new Watcher() {
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@Override
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public void process(WatchedEvent event) {
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if (Event.EventType.NodeDeleted == event.getType()) {
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log.warn(nodePath + " lock release detected");
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log.warn("creating new lock instance: " + nodePath + "...");
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try {
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zk.create(nodePath,
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new byte[0],
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ZooDefs.Ids.OPEN_ACL_UNSAFE,
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CreateMode.PERSISTENT);
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log.warn("lock" + nodePath + " created");
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semaphore.release();
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} catch (KeeperException e) {
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throw new RuntimeException(e);
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} catch (InterruptedException e) {
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throw new RuntimeException(e);
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}
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}
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}
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})==null) {
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log.warn("lock not found, creating new lock instance: " + nodePath);
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zk.create(nodePath, new byte[0],
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ZooDefs.Ids.OPEN_ACL_UNSAFE,
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CreateMode.PERSISTENT);
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log.warn("lock" + nodePath + " created");
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semaphore.release();
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} else {
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// waiting until node is removed by other lock manager
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log.warn("waiting until lock is released");
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long startTime = System.currentTimeMillis();
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semaphore.acquire();
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log.warn("lock released, waited for " +
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(System.currentTimeMillis()-startTime) + " ms");
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semaphore.release();
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}
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} else if (LockMode.release.equals(lockMode)) {
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log.warn("removing lock" + nodePath + "...");
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zk.delete(nodePath, -1);
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log.warn("lock" + nodePath + " removed");
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} else {
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throw new Exception("unsupported lock mode: " + lockMode);
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}
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}
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public static final String generatePath(String nodeId, String rootNode) {
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if (nodeId!=null) {
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return rootNode + NODE_SEPARATOR + nodeId.replace('/', '_');
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} else {
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return null;
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}
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}
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}
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