分布式锁含义：分布式锁是指在多个***进程***中对A资源进行访问控制。需要保证多个进程访问A资源时必须是有序访问，不能同时访问。
使用zookeeper实现分布式锁的原理：
- 创建一个持久化节点例如：/lock
- 进程1在/lock下面创建临时有序节点
- 获得/lock下所有临时有序节点，取出最小序号的节点minNode，判断minNode和进程1创建的临时节点是否一样
- 如果相同，则进程1获得锁
- 如果不相同，监控前一个节点的删除事件，并且创建一个CountDownLatch等待CountDownLatch的wait变为0，
- 一旦wait为0，表示进程1获得锁
- 锁使用完毕后，需要进行释放操作，删除当前临时有序节点
package com.app.lock.zookeeper;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
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.ZooDefs;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.Stat;
/**
* @Author: chao.zhu
* @Email: [email protected]
* @CreateDate: 2018/07/25
* @Version: 1.0
*/
public class DistributedLock implements Lock, Watcher {
private ZooKeeper zooKeeper;
private String current_lock;
private String wait_lock;
private static String PATH = "/lock";
private CountDownLatch countDownLatch;
private Integer session_timeout = 5000;
private String lockName;
public DistributedLock(String connection,String lockName){
try {
zooKeeper = new ZooKeeper(connection, 5000, this);
this.lockName = lockName;
Stat stat = zooKeeper.exists(PATH,false);
if(stat == null){
zooKeeper.create(PATH,"".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT);
}
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
}
}
@Override
public void lock() {
if(tryLock()){
System.out.println(Thread.currentThread().getName()+"get lock："+current_lock);
}else{
try {
waitForLock(wait_lock,session_timeout);
// //添加对上一个节点的监控，watch为true
// Stat stat = zooKeeper.exists(PATH+"/"+wait_lock,true);
// if(stat != null){
// countDownLatch = new CountDownLatch(1);
// countDownLatch.await(session_timeout,TimeUnit.MICROSECONDS);
// countDownLatch = null;
// System.out.println(Thread.currentThread().getName()+"get lock："+current_lock);
// }
}catch (Exception e){
e.printStackTrace();
}
}
}
private boolean waitForLock(String prev, long waitTime) throws KeeperException, InterruptedException {
Stat stat = zooKeeper.exists(PATH + "/" + prev, true);
if (stat != null) {
System.out.println(Thread.currentThread().getName() + "等待锁 " + PATH + "/" + prev);
this.countDownLatch = new CountDownLatch(1);
// 计数等待，若等到前一个节点消失，则precess中进行countDown，停止等待，获取锁
this.countDownLatch.await(waitTime, TimeUnit.MILLISECONDS);
this.countDownLatch = null;
System.out.println(Thread.currentThread().getName() + " 等到了锁");
}
// //添加对上一个节点的监控，watch为true
// Stat stat = zooKeeper.exists(PATH+"/"+wait_lock,true);
// if(stat != null){
// countDownLatch = new CountDownLatch(1);
// countDownLatch.await(session_timeout,TimeUnit.MICROSECONDS);
// countDownLatch = null;
// System.out.println(Thread.currentThread().getName()+"get lock："+current_lock);
// }
return true;
}
@Override
public boolean tryLock() {
try {
String splitStr = "_lock_";
//先创建一个临时有序节点
current_lock = zooKeeper.create(PATH+"/"+lockName+splitStr,"".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.EPHEMERAL_SEQUENTIAL);
//获得PATH下面的所有节点
List<String> childList = zooKeeper.getChildren(PATH,false);
List<String> lockObjects = new ArrayList<String>();
for (String node : childList) {
String _node = node.split(splitStr)[0];
if (_node.equals(lockName)) {
lockObjects.add(node);
}
}
//对子节点进行排序
Collections.sort(lockObjects);
//获取最小的节点
//如果节点相同，那么当前节点就获得了锁
if (current_lock.equals(PATH + "/" + lockObjects.get(0))) {
return true;
}
//不相同的话，获得前一个节点，初始化阻塞线程对象
String prevNode = current_lock.substring(current_lock.lastIndexOf("/") + 1);
wait_lock = lockObjects.get(Collections.binarySearch(lockObjects, prevNode) - 1);
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
return false;
}
@Override
public void unlock() {
try {
zooKeeper.delete(current_lock,-1);
System.out.println(Thread.currentThread().getName()+"unlock :"+current_lock);
current_lock = null;
zooKeeper.close();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
}
}
@Override
public void process(WatchedEvent watchedEvent) {
if(countDownLatch != null){
countDownLatch.countDown();
}
}
@Override
public void lockInterruptibly() throws InterruptedException {
}
@Override
public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
return false;
}
@Override
public Condition newCondition() {
return null;
}
}
package com.app.lock.zookeeper;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
/**
* @Author: chao.zhu
* @Email: [email protected]
* @CreateDate: 2018/07/25
* @Version: 1.0
*/
public class Test {
static int n = 500;
private static final String ZK_CONNECTION = "127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183";
public static void secskill() {
System.out.println(--n);
}
public static void main(String[] args) {
Runnable runnable = new Runnable() {
public void run() {
DistributedLock lock = null;
try {
lock = new DistributedLock(ZK_CONNECTION, "test1");
lock.lock();
secskill();
// System.out.println(Thread.currentThread().getName() + "正在运行");
} finally {
if (lock != null) {
lock.unlock();
}
}
}
};
for (int i = 0; i < 10; i++) {
Thread t = new Thread(runnable);
t.start();
}
}
}
/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/bin/java "-javaagent:/Applications/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=51835:/Applications/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/lib/tools.jar:/Users/zhuchao/workspace_my_git/zookeepertest02/target/classes:/Users/zhuchao/maven_repository/repository/org/apache/zookeeper/zookeeper/3.4.6/zookeeper-3.4.6.jar:/Users/zhuchao/maven_repository/repository/org/slf4j/slf4j-api/1.6.1/slf4j-api-1.6.1.jar:/Users/zhuchao/maven_repository/repository/org/slf4j/slf4j-log4j12/1.6.1/slf4j-log4j12-1.6.1.jar:/Users/zhuchao/maven_repository/repository/log4j/log4j/1.2.16/log4j-1.2.16.jar:/Users/zhuchao/maven_repository/repository/jline/jline/0.9.94/jline-0.9.94.jar:/Users/zhuchao/maven_repository/repository/junit/junit/3.8.1/junit-3.8.1.jar:/Users/zhuchao/maven_repository/repository/io/netty/netty/3.7.0.Final/netty-3.7.0.Final.jar:/Users/zhuchao/maven_repository/repository/org/apache/commons/commons-lang3/3.7/commons-lang3-3.7.jar:/Users/zhuchao/maven_repository/repository/com/alibaba/fastjson/1.2.37/fastjson-1.2.37.jar:/Users/zhuchao/maven_repository/repository/com/101tec/zkclient/0.10/zkclient-0.10.jar com.app.lock.zookeeper.Test
objc[7082]: Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/bin/java (0x10e9934c0) and /Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/libinstrument.dylib (0x1101bc4e0). One of the two will be used. Which one is undefined.
log4j:WARN No appenders could be found for logger (org.apache.zookeeper.ZooKeeper).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Thread-8等待锁 /lock/test1_lock_0000000139
Thread-6等待锁 /lock/test1_lock_0000000138
Thread-0get lock：/lock/test1_lock_0000000137
499
Thread-1等待锁 /lock/test1_lock_0000000141
Thread-9等待锁 /lock/test1_lock_0000000137
Thread-4等待锁 /lock/test1_lock_0000000140
Thread-5等待锁 /lock/test1_lock_0000000143
Thread-3等待锁 /lock/test1_lock_0000000144
Thread-2等待锁 /lock/test1_lock_0000000142
Thread-0unlock :/lock/test1_lock_0000000137
Thread-9 等到了锁
498
Thread-9unlock :/lock/test1_lock_0000000138
Thread-6 等到了锁
497
Thread-8 等到了锁
496
Thread-6unlock :/lock/test1_lock_0000000139
Thread-4 等到了锁
495
Thread-8unlock :/lock/test1_lock_0000000140
Thread-1 等到了锁
494
Thread-4unlock :/lock/test1_lock_0000000141
Thread-1unlock :/lock/test1_lock_0000000142
Thread-2 等到了锁
493
Thread-5 等到了锁
492
Thread-2unlock :/lock/test1_lock_0000000143
Thread-3 等到了锁
491
Thread-5unlock :/lock/test1_lock_0000000144
Thread-3unlock :/lock/test1_lock_0000000145
490
Thread-7unlock :/lock/test1_lock_0000000146
Process finished with exit code 0
纸上得来终觉浅，绝知此事要躬行