1.什么是分布式锁
一般的锁：一般我们说的锁是但进程多线程的锁，在多线程并发编程中，用于线程之间的数据同步，保护共享资源的访问
分布式锁：分布式锁指的是在分布式环境下，保护跨进程，跨主机，跨网络的共享资源，实现互斥访问，保证一致性
2.分布式锁的架构图
20160320214246073.png
3.分布式锁的算法流程
20160320221558695.png
package com.jike.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
*/
public boolean acquire(long time, TimeUnit unit) throws Exception;
/*
* 释放锁
*/
public void release() throws Exception;
}
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 ZkClientExt 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(ZkClientExt 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<String> 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 = isGetTheLock ? null : children.get(ourIndex - 1);
if ( isGetTheLock ){
haveTheLock = true;
}else{
/**
* 获取当前节点的次小的节点，并监听节点的变化
*/
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);
}
/**
* 尝试获取锁
* @param time
* @param unit
* @return
* @throws Exception
*/
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;
}
}
import org.I0Itec.zkclient.serialize.BytesPushThroughSerializer;
public class TestDistributedLock {
public static void main(String[] args) {
final ZkClientExt zkClientExt1 = new ZkClientExt("192.168.1.105:2181", 5000, 5000, new BytesPushThroughSerializer());
final SimpleDistributedLockMutex mutex1 = new SimpleDistributedLockMutex(zkClientExt1, "/Mutex");
final ZkClientExt zkClientExt2 = new ZkClientExt("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();
}
}
}
原文链接：https://blog.csdn.net/ZuoAnYinXiang/article/details/50938430
