Apache ZooKeeper Server Source Code

Apache ZooKeeper is an open-source server which enables highly reliable distributed coordination.

Apache ZooKeeper Server Source Code files are provided in the source packge (apache-zookeeper-3.7.0.tar.gz). You can download it at Apache ZooKeeper Website.

You can also browse Apache ZooKeeper Server Source Code below:

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 * 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,
 * See the License for the specific language governing permissions and
 * limitations under the License.

package org.apache.zookeeper.server;

import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import java.io.IOException;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import org.apache.jute.InputArchive;
import org.apache.jute.OutputArchive;
import org.apache.jute.Record;
import org.apache.zookeeper.data.Stat;
import org.apache.zookeeper.data.StatPersisted;

 * This class contains the data for a node in the data tree.
 * <p>
 * A data node contains a reference to its parent, a byte array as its data, an
 * array of ACLs, a stat object, and a set of its children's paths.
@SuppressFBWarnings({"EI_EXPOSE_REP", "EI_EXPOSE_REP2"})
public class DataNode implements Record {

    // the digest value of this node, calculated from path, data and stat
    private volatile long digest;

    // indicate if the digest of this node is up to date or not, used to
    // optimize the performance.
    volatile boolean digestCached;

    /** the data for this datanode */
    byte[] data;

     * the acl map long for this datanode. the datatree has the map
    Long acl;

     * the stat for this node that is persisted to disk.
    public StatPersisted stat;

     * the list of children for this node. note that the list of children string
     * does not contain the parent path -- just the last part of the path. This
     * should be synchronized on except deserializing (for speed up issues).
    private Set<String> children = null;

    private static final Set<String> EMPTY_SET = Collections.emptySet();

     * default constructor for the datanode
    DataNode() {
        // default constructor

     * create a DataNode with parent, data, acls and stat
     * @param data
     *            the data to be set
     * @param acl
     *            the acls for this node
     * @param stat
     *            the stat for this node.
    public DataNode(byte[] data, Long acl, StatPersisted stat) {
        this.data = data;
        this.acl = acl;
        this.stat = stat;

     * Method that inserts a child into the children set
     * @param child
     *            to be inserted
     * @return true if this set did not already contain the specified element
    public synchronized boolean addChild(String child) {
        if (children == null) {
            // let's be conservative on the typical number of children
            children = new HashSet<String>(8);
        return children.add(child);

     * Method that removes a child from the children set
     * @param child
     * @return true if this set contained the specified element
    public synchronized boolean removeChild(String child) {
        if (children == null) {
            return false;
        return children.remove(child);

     * convenience method for setting the children for this datanode
     * @param children
    public synchronized void setChildren(HashSet<String> children) {
        this.children = children;

     * convenience methods to get the children
     * @return the children of this datanode. If the datanode has no children, empty
     *         set is returned
    public synchronized Set<String> getChildren() {
        if (children == null) {
            return EMPTY_SET;

        return Collections.unmodifiableSet(children);

    public synchronized void copyStat(Stat to) {
        to.setDataLength(data == null ? 0 : data.length);
        int numChildren = 0;
        if (this.children != null) {
            numChildren = children.size();
        // when we do the Cversion we need to translate from the count of the creates
        // to the count of the changes (v3 semantics)
        // for every create there is a delete except for the children still present
        to.setCversion(stat.getCversion() * 2 - numChildren);

    private static long getClientEphemeralOwner(StatPersisted stat) {
        EphemeralType ephemeralType = EphemeralType.get(stat.getEphemeralOwner());
        if (ephemeralType != EphemeralType.NORMAL) {
            return 0;
        return stat.getEphemeralOwner();

    public synchronized void deserialize(InputArchive archive, String tag) throws IOException {
        data = archive.readBuffer("data");
        acl = archive.readLong("acl");
        stat = new StatPersisted();
        stat.deserialize(archive, "statpersisted");

    public synchronized void serialize(OutputArchive archive, String tag) throws IOException {
        archive.startRecord(this, "node");
        archive.writeBuffer(data, "data");
        archive.writeLong(acl, "acl");
        stat.serialize(archive, "statpersisted");
        archive.endRecord(this, "node");

    public boolean isDigestCached() {
        return digestCached;

    public void setDigestCached(boolean digestCached) {
        this.digestCached = digestCached;

    public long getDigest() {
        return digest;

    public void setDigest(long digest) {
        this.digest = digest;

    public synchronized byte[] getData() {
        return data;




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2018-10-18, 28903👍, 1💬