DistributedIdGenerator.java

/**
 * Copyright 2016 Yahoo Inc.
 *
 * Licensed 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 com.yahoo.pulsar.broker.service;

import java.util.concurrent.atomic.AtomicLong;

import org.apache.bookkeeper.util.ZkUtils;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException.NodeExistsException;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Generate unique ids across multiple nodes.
 * <p>
 * Each node has an instance of this class and uses the same z-node. At startup each node gets assigned a unique id,
 * using ZK sequential nodes.
 * <p>
 * After that, each node can just use a local counter and combine, the application prefix, its own instance id and with
 * the counter incremental value to obtain a globally unique id.
 */
public class DistributedIdGenerator {

    private final String prefix;
    private final int generatorInstanceId;
    private final AtomicLong counter;

    /**
     *
     * @param zk
     * @param path
     *            path of the z-node used to track the generators ids
     * @param prefix
     *            prefix to prepend to the generated id. Having a unique prefix can make the id globally unique
     * @throws Exception
     */
    public DistributedIdGenerator(ZooKeeper zk, String path, String prefix) throws Exception {
        this.prefix = prefix;
        this.counter = new AtomicLong(0);

        // Create base path if it doesn't exist
        if (zk.exists(path, false) == null) {
            try {
                ZkUtils.createFullPathOptimistic(zk, path, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,
                        CreateMode.PERSISTENT);
            } catch (NodeExistsException e) {
                // Ok
            }
        }

        // Create an ephemeral sequential z-node that will have a name containing a unique number. We'll use this number
        // as a prefix for all the generated ids, in addition to the specified prefix.
        String createdPath = zk.create(path + "/-", new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,
                CreateMode.EPHEMERAL_SEQUENTIAL);

        // Parse the sequential z-node name and extract the unique number
        String[] parts = createdPath.split("/");
        String name = parts[parts.length - 1].replace('-', ' ').trim();

        this.generatorInstanceId = Integer.parseInt(name);
        log.info("Created sequential node at {} -- Generator Id is {}-{}", createdPath, prefix, generatorInstanceId);
    }

    public String getNextId() {
        return String.format("%s-%d-%d", prefix, generatorInstanceId, counter.getAndIncrement());
    }

    private static final Logger log = LoggerFactory.getLogger(DistributedIdGenerator.class);
}