net.killa.kept.KeptLock.java Source code

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Here is the source code for net.killa.kept.KeptLock.java

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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,
 * 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 net.killa.kept;

import java.lang.management.ManagementFactory;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.EventType;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.ACL;
import org.apache.zookeeper.data.Stat;

/**
 * A Java {@link Lock} that is kept synchronized amongst a {@link ZooKeeper}
 * cluster.
 */
public class KeptLock implements Lock {
    private final ZooKeeper keeper;
    private final String znode;
    private final List<ACL> acl;

    /**
     * Construct a KeptLock.
     * 
     * @param keeper
     *            A {@link ZooKeeper} that is synchronized with
     * 
     * @param znode
     *            A {@link String} containing the znode that will serve as a
     *            lock
     * 
     * @param acl
     *            A {@link List} of {@link ACL} containing the access control
     *            lists for node creation
     */
    public KeptLock(ZooKeeper keeper, String znode, List<ACL> acl) {
        this.keeper = keeper;

        this.znode = znode;
        this.acl = acl;
    }

    private boolean lockIt(long t, TimeUnit tu) throws KeeperException, InterruptedException {
        final CountDownLatch latch = new CountDownLatch(1);

        // convert the given time to milliseconds and add it to the current time
        long last = System.currentTimeMillis() + TimeUnit.MILLISECONDS.convert(t, tu);
        do {
            if (this.keeper.exists(this.znode, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    if (event.getType() == EventType.NodeDeleted)
                        latch.countDown();
                    else if (event.getType() == EventType.NodeCreated)
                        ; // ignore it
                    else
                        throw new RuntimeException("unexpected event type" + event.getType());
                }
            }) != null) {
                if (!latch.await(t, tu))
                    try {
                        this.keeper.create(this.znode, ManagementFactory.getRuntimeMXBean().getName().getBytes(),
                                this.acl, CreateMode.EPHEMERAL);

                        return true;
                    } catch (KeeperException.NodeExistsException e) {
                        // ignore it
                    } catch (KeeperException e) {
                        throw e;
                    }
                else
                    return false;
            } else {
                try {
                    this.keeper.create(this.znode, ManagementFactory.getRuntimeMXBean().getName().getBytes(),
                            this.acl, CreateMode.EPHEMERAL);

                    return true;
                } catch (KeeperException.NodeExistsException e) {
                    // ignore it
                } catch (KeeperException e) {
                    throw e;
                }
            }
        } while (System.currentTimeMillis() < last);

        return false;
    }

    /** {@inheritDoc} */
    @Override
    public void lock() {
        // sleep until the client is unlocked. if interrupted, eat the exception
        try {
            this.lockIt(Long.MAX_VALUE, TimeUnit.DAYS);
        } catch (KeeperException e) {
            throw new RuntimeException("KeeperException caught", e);
        } catch (InterruptedException e) {
            // eat it
        }
    }

    /** {@inheritDoc} */
    @Override
    public void lockInterruptibly() throws InterruptedException {
        // sleep until the client is unlocked. if interrupted, just pass the
        // exception
        try {
            this.lockIt(Long.MAX_VALUE, TimeUnit.DAYS);
        } catch (KeeperException e) {
            throw new RuntimeException("KeeperException caught", e);
        }
    }

    /** {@inheritDoc} */
    @Override
    public Condition newCondition() {
        // we don't support conditions.... yet?
        throw new UnsupportedOperationException();
    }

    /** {@inheritDoc} */
    @Override
    public boolean tryLock() {
        try {
            return this.lockIt(0, TimeUnit.MICROSECONDS);
        } catch (KeeperException e) {
            throw new RuntimeException("KeeperException caught", e);
        } catch (InterruptedException e) {
            throw new RuntimeException("InterruptedException caught", e);
        }
    }

    /** {@inheritDoc} */
    @Override
    public boolean tryLock(long t, TimeUnit tu) throws InterruptedException {
        try {
            return this.lockIt(t, tu);
        } catch (KeeperException e) {
            throw new RuntimeException("KeeperException caught", e);
        }
    }

    /** {@inheritDoc} */
    @Override
    public void unlock() {
        // check if we are already locked, throw an exception if so
        try {
            Stat stat;
            if ((stat = this.keeper.exists(this.znode, false)) == null)
                throw new IllegalStateException("already unlocked");

            this.keeper.delete(this.znode, stat.getVersion());
        } catch (KeeperException e) {
            throw new RuntimeException("KeeperException caught", e);
        } catch (InterruptedException e) {
            throw new RuntimeException("InterruptedException caught", e);
        }
    }
}