zookeeper 实现分布式锁

Posted 2021-01-28 newlangwen

 实现互斥锁

package com.zookeeper.lock;

import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

import org.I0Itec.zkclient.IZkDataListener;
import org.I0Itec.zkclient.ZkClient;
import org.I0Itec.zkclient.exception.ZkNoNodeException;

public class BaseDistributedLock {

    private final ZkClient client;
    private final String path;

    // zookeeper中locker节点的路径
    private final String basePath;
    private final String lockName;
    private static final Integer MAX_RETRY_COUNT = 10;

    public BaseDistributedLock(ZkClient client, String path, String lockName) {

        this.client = client;
        this.basePath = path;
        this.path = path.concat("/").concat(lockName);
        this.lockName = lockName;

    }

    private void deleteOurPath(String ourPath) throws Exception {
        client.delete(ourPath);
    }

    private String createLockNode(ZkClient client, String path)
            throws Exception {

        return client.createEphemeralSequential(path, null);
    }

    private boolean waitToLock(long startMillis, Long millisToWait,
            String ourPath) throws Exception {

        boolean haveTheLock = false;
        boolean doDelete = false;

        try {

            while (!haveTheLock) {
                // 获取lock节点下的所有节点
                List children = getSortedChildren();
                String sequenceNodeName = ourPath
                        .substring(basePath.length() + 1);

                // 获取当前节点的在所有节点列表中的位置
                int ourIndex = children.indexOf(sequenceNodeName);
                // 节点位置小于0,说明没有找到节点
                if (ourIndex < 0) {
                    throw new ZkNoNodeException("节点没有找到: " + sequenceNodeName);
                }

                // 节点位置大于0说明还有其他节点在当前的节点前面，就需要等待其他的节点都释放
                boolean isGetTheLock = ourIndex == 0;
                String pathToWatch = (String) (isGetTheLock ? null : children
                        .get(ourIndex - 1));

                if (isGetTheLock) {

                    haveTheLock = true;

                } else {

                    String previousSequencePath = basePath.concat("/").concat(
                            pathToWatch);
                    final CountDownLatch latch = new CountDownLatch(1);
                    final IZkDataListener previousListener = new IZkDataListener() {

                        public void handleDataDeleted(String dataPath)
                                throws Exception {
                            latch.countDown();
                        }

                        public void handleDataChange(String dataPath,
                                Object data) throws Exception {
                            // ignore
                        }
                    };

                    try {
                        // 如果节点不存在会出现异常
                        client.subscribeDataChanges(previousSequencePath,
                                previousListener);

                        if (millisToWait != null) {
                            millisToWait -= (System.currentTimeMillis() - startMillis);
                            startMillis = System.currentTimeMillis();
                            if (millisToWait <= 0) {
                                doDelete = true; // timed out - delete our node
                                break;
                            }

                            latch.await(millisToWait, TimeUnit.MICROSECONDS);
                        } else {
                            latch.await();
                        }
                    } catch (ZkNoNodeException e) {
                        // ignore
                    } finally {
                        client.unsubscribeDataChanges(previousSequencePath,
                                previousListener);
                    }

                }
            }
        } catch (Exception e) {
            // 发生异常需要删除节点
            doDelete = true;
            throw e;
        } finally {
            // 如果需要删除节点
            if (doDelete) {
                deleteOurPath(ourPath);
            }
        }
        return haveTheLock;
    }

    private String getLockNodeNumber(String str, String lockName) {
        int index = str.lastIndexOf(lockName);
        if (index >= 0) {
            index += lockName.length();
            return index <= str.length() ? str.substring(index) : "";
        }
        return str;
    }

    List<String> getSortedChildren() throws Exception {
        try {

            List<String> children = client.getChildren(basePath);
            Collections.sort(children, new Comparator<String>() {
                public int compare(String lhs, String rhs) {
                    return getLockNodeNumber(lhs, lockName).compareTo(
                            getLockNodeNumber(rhs, lockName));
                }
            });
            return children;

        } catch (ZkNoNodeException e) {

            client.createPersistent(basePath, true);
            return getSortedChildren();

        }
    }

    protected void releaseLock(String lockPath) throws Exception {
        deleteOurPath(lockPath);

    }

    protected String attemptLock(long time, TimeUnit unit) throws Exception {

        final long startMillis = System.currentTimeMillis();
        final Long millisToWait = (unit != null) ? unit.toMillis(time) : null;

        String ourPath = null;
        boolean hasTheLock = false;
        boolean isDone = false;
        int retryCount = 0;

        // 网络闪断需要重试一试
        while (!isDone) {
            isDone = true;

            try {
                ourPath = createLockNode(client, path);
                hasTheLock = waitToLock(startMillis, millisToWait, ourPath);
            } catch (ZkNoNodeException e) {
                if (retryCount++ < MAX_RETRY_COUNT) {
                    isDone = false;
                } else {
                    throw e;
                }
            }
        }
        if (hasTheLock) {
            return ourPath;
        }

        return null;
    }

}

View Code

接口类

package com.zookeeper.lock;

import java.util.concurrent.TimeUnit;

public interface DistributedLock {

    /** 获取锁，如果没有得到就等待 */
    public void acquire() throws Exception;

    /**
     * 获取锁，直到超时
     * 
     * @param time
     *            超时时间
     * @param unit
     *            参数的单位
     * @return 是否获取到锁
     * @throws Exception
     */
    public boolean acquire(long time, TimeUnit unit) throws Exception;

    /**
     * 释放锁
     * 
     * @throws Exception
     */
    public void release() throws Exception;

}

View Code

测试类

package com.zookeeper.lock;

import org.I0Itec.zkclient.ZkClient;
import org.I0Itec.zkclient.serialize.BytesPushThroughSerializer;

import coom.zookeeperdemo.lock.SimpleDistributedLockMutex;

public class TestDistributedLock {

    public static void main(String[] args) {

        final ZkClient zkClientExt1 = new ZkClient("192.168.1.105:2181",
                5000, 5000, new BytesPushThroughSerializer());
        final SimpleDistributedLockMutex mutex1 = new SimpleDistributedLockMutex(
                zkClientExt1, "/Mutex");

        final ZkClient zkClientExt2 = new ZkClient("192.168.1.105:2181",
                5000, 5000, new BytesPushThroughSerializer());
        final SimpleDistributedLockMutex mutex2 = new SimpleDistributedLockMutex(
                zkClientExt2, "/Mutex");

        try {
            mutex1.acquire();
            System.out.println("Client1 locked");
            Thread client2Thd = new Thread(new Runnable() {

                public void run() {
                    try {
                        mutex2.acquire();
                        System.out.println("Client2 locked");
                        mutex2.release();
                        System.out.println("Client2 released lock");

                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });
            client2Thd.start();
            Thread.sleep(5000);
            mutex1.release();
            System.out.println("Client1 released lock");

            client2Thd.join();

        } catch (Exception e) {

            e.printStackTrace();
        }

    }

}

View Code

 

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