使用zookeeper實現分布式共享鎖
分布式系統中經常需要協調多進程，多個jvm，或者多臺機器之間的同步問題，得益于zookeeper，實現了一個分布式的共享鎖，方便在多臺服務器之間競爭資源時，來協調各系統之間的協作和同步。
package com.concurrent;
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;
/**
DistributedLock lock = null;
try {
lock = new DistributedLock("127.0.0.1:2182","test");
lock.lock();
//do something...
} catch (Exception e) {
e.printStackTrace();
}
finally {
if(lock != null)
lock.unlock();
}
* @author xueliang
*
*/
public class DistributedLock implements Lock, Watcher{
private ZooKeeper zk;
private String root = "/locks";//根
private String lockName;//競爭資源的標志
private String waitNode;//等待前一個鎖
private String myZnode;//當前鎖
private CountDownLatch latch;//計數器
private int sessionTimeout = 30000;
private List<Exception> exception = new ArrayList<Exception>();
/**
* 創建分布式鎖,使用前請確認config配置的zookeeper服務可用
* @param config 127.0.0.1:2181
* @param lockName 競爭資源標志,lockName中不能包含單詞lock
*/
public DistributedLock(String config, String lockName){
this.lockName = lockName;
// 創建一個與服務器的連接
try {
zk = new ZooKeeper(config, sessionTimeout, this);
Stat stat = zk.exists(root, false);
if(stat == null){
// 創建根節點
zk.create(root, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT);
}
} catch (IOException e) {
exception.add(e);
} catch (KeeperException e) {
exception.add(e);
} catch (InterruptedException e) {
exception.add(e);
}
}
/**
* zookeeper節點的監視器
*/
public void process(WatchedEvent event) {
if(this.latch != null) {
this.latch.countDown();
}
}
public void lock() {
if(exception.size() > 0){
throw new LockException(exception.get(0));
}
try {
if(this.tryLock()){
System.out.println("Thread " + Thread.currentThread().getId() + " " +myZnode + " get lock true");
return;
}
else{
waitForLock(waitNode, sessionTimeout);//等待鎖
}
} catch (KeeperException e) {
throw new LockException(e);
} catch (InterruptedException e) {
throw new LockException(e);
}
}
public boolean tryLock() {
try {
String splitStr = "_lock_";
if(lockName.contains(splitStr))
throw new LockException("lockName can not contains \\u000B");
//創建臨時子節點
myZnode = zk.create(root + "/" + lockName + splitStr, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.EPHEMERAL_SEQUENTIAL);
System.out.println(myZnode + " is created ");
//取出所有子節點
List<String> subNodes = zk.getChildren(root, false);
//取出所有lockName的鎖
List<String> lockObjNodes = new ArrayList<String>();
for (String node : subNodes) {
String _node = node.split(splitStr)[0];
if(_node.equals(lockName)){
lockObjNodes.add(node);
}
}
Collections.sort(lockObjNodes);
System.out.println(myZnode + "==" + lockObjNodes.get(0));
if(myZnode.equals(root+"/"+lockObjNodes.get(0))){
//如果是最小的節點,則表示取得鎖
return true;
}
//如果不是最小的節點，找到比自己小1的節點
String subMyZnode = myZnode.substring(myZnode.lastIndexOf("/") + 1);
waitNode = lockObjNodes.get(Collections.binarySearch(lockObjNodes, subMyZnode) - 1);
} catch (KeeperException e) {
throw new LockException(e);
} catch (InterruptedException e) {
throw new LockException(e);
}
return false;
}
public boolean tryLock(long time, TimeUnit unit) {
try {
if(this.tryLock()){
return true;
}
return waitForLock(waitNode,time);
} catch (Exception e) {
e.printStackTrace();
}
return false;
}
private boolean waitForLock(String lower, long waitTime) throws InterruptedException, KeeperException {
Stat stat = zk.exists(root + "/" + lower,true);
//判斷比自己小一個數的節點是否存在,如果不存在則無需等待鎖,同時注冊監聽
if(stat != null){
System.out.println("Thread " + Thread.currentThread().getId() + " waiting for " + root + "/" + lower);
this.latch = new CountDownLatch(1);
this.latch.await(waitTime, TimeUnit.MILLISECONDS);
this.latch = null;
}
return true;
}
public void unlock() {
try {
System.out.println("unlock " + myZnode);
zk.delete(myZnode,-1);
myZnode = null;
zk.close();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
}
}
public void lockInterruptibly() throws InterruptedException {
this.lock();
}
public Condition newCondition() {
return null;
}
public class LockException extends RuntimeException {
private static final long serialVersionUID = 1L;
public LockException(String e){
super(e);
}
public LockException(Exception e){
super(e);
}
}
} 多線程的并發測試要復雜很多，下面是一個使用CountDownLatch實現的并發測試工具，可以簡單模擬一些并發場景
package com.concurrent;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicInteger;
/**
ConcurrentTask[] task = new ConcurrentTask[5];
for(int i=0;i<task.length;i++){
task[i] = new ConcurrentTask(){
public void run() {
System.out.println("==============");
}};
}
new ConcurrentTest(task);
* @author xueliang
*
*/
public class ConcurrentTest {
private CountDownLatch startSignal = new CountDownLatch(1);//開始閥門
private CountDownLatch doneSignal = null;//結束閥門
private CopyOnWriteArrayList<Long> list = new CopyOnWriteArrayList<Long>();
private AtomicInteger err = new AtomicInteger();//原子遞增
private ConcurrentTask[] task = null;
public ConcurrentTest(ConcurrentTask... task){
this.task = task;
if(task == null){
System.out.println("task can not null");
System.exit(1);
}
doneSignal = new CountDownLatch(task.length);
start();
}
/**
* @param args
* @throws ClassNotFoundException
*/
private void start(){
//創建線程，并將所有線程等待在閥門處
createThread();
//打開閥門
startSignal.countDown();//遞減鎖存器的計數，如果計數到達零，則釋放所有等待的線程
try {
doneSignal.await();//等待所有線程都執行完畢
} catch (InterruptedException e) {
e.printStackTrace();
}
//計算執行時間
getExeTime();
}
/**
* 初始化所有線程，并在閥門處等待
*/
private void createThread() {
long len = doneSignal.getCount();
for (int i = 0; i < len; i++) {
final int j = i;
new Thread(new Runnable(){
public void run() {
try {
startSignal.await();//使當前線程在鎖存器倒計數至零之前一直等待
long start = System.currentTimeMillis();
task[j].run();
long end = (System.currentTimeMillis() - start);
list.add(end);
} catch (Exception e) {
err.getAndIncrement();//相當于err++
}
doneSignal.countDown();
}
}).start();
}
}
/**
* 計算平均響應時間
*/
private void getExeTime() {
int size = list.size();
List<Long> _list = new ArrayList<Long>(size);
_list.addAll(list);
Collections.sort(_list);
long min = _list.get(0);
long max = _list.get(size-1);
long sum = 0L;
for (Long t : _list) {
sum += t;
}
long avg = sum/size;
System.out.println("min: " + min);
System.out.println("max: " + max);
System.out.println("avg: " + avg);
System.out.println("err: " + err.get());
}
public interface ConcurrentTask {
void run();
}
} 下面使用這個工具來測試一下我們的分布式共享鎖
package com.concurrent;
import com.concurrent.ConcurrentTest.ConcurrentTask;
public class ZkTest {
public static void main(String[] args) {
Runnable task1 = new Runnable(){
public void run() {
DistributedLock lock = null;
try {
lock = new DistributedLock("127.0.0.1:2182","test1");
//lock = new DistributedLock("127.0.0.1:2182","test2");
lock.lock();
Thread.sleep(3000);
System.out.println("===Thread " + Thread.currentThread().getId() + " running");
} catch (Exception e) {
e.printStackTrace();
}
finally {
if(lock != null)
lock.unlock();
}
}
};
new Thread(task1).start();
try {
Thread.sleep(1000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
ConcurrentTask[] tasks = new ConcurrentTask[10];
for(int i=0;i<tasks.length;i++){
ConcurrentTask task3 = new ConcurrentTask(){
public void run() {
DistributedLock lock = null;
try {
lock = new DistributedLock("127.0.0.1:2183","test2");
lock.lock();
System.out.println("Thread " + Thread.currentThread().getId() + " running");
} catch (Exception e) {
e.printStackTrace();
}
finally {
lock.unlock();
}
}
};
tasks[i] = task3;
}
new ConcurrentTest(tasks);
}
} 測試結果： /locks/test1_lock_0000004356 is created /locks/test1_lock_0000004356==test1_lock_0000004356 Thread 8 /locks/test1_lock_0000004356 get lock true /locks/test2_lock_0000004357 is created /locks/test2_lock_0000004359 is created /locks/test2_lock_0000004358 is created /locks/test2_lock_0000004363 is created /locks/test2_lock_0000004361 is created /locks/test2_lock_0000004360 is created /locks/test2_lock_0000004362 is created /locks/test2_lock_0000004366 is created /locks/test2_lock_0000004365 is created /locks/test2_lock_0000004364 is created /locks/test2_lock_0000004357==test2_lock_0000004357 Thread 14 /locks/test2_lock_0000004357 get lock true Thread 14 running unlock /locks/test2_lock_0000004357 /locks/test2_lock_0000004358==test2_lock_0000004357 /locks/test2_lock_0000004361==test2_lock_0000004357 /locks/test2_lock_0000004359==test2_lock_0000004357 /locks/test2_lock_0000004362==test2_lock_0000004357 Thread 12 waiting for /locks/test2_lock_0000004360 /locks/test2_lock_0000004366==test2_lock_0000004357 Thread 18 waiting for /locks/test2_lock_0000004357 /locks/test2_lock_0000004363==test2_lock_0000004357 Thread 18 running unlock /locks/test2_lock_0000004358 Thread 13 waiting for /locks/test2_lock_0000004362 /locks/test2_lock_0000004365==test2_lock_0000004358 Thread 16 waiting for /locks/test2_lock_0000004361 Thread 19 waiting for /locks/test2_lock_0000004358 /locks/test2_lock_0000004360==test2_lock_0000004358 Thread 15 waiting for /locks/test2_lock_0000004365 /locks/test2_lock_0000004364==test2_lock_0000004358 Thread 11 waiting for /locks/test2_lock_0000004364 Thread 20 waiting for /locks/test2_lock_0000004359 Thread 19 running unlock /locks/test2_lock_0000004359 Thread 17 waiting for /locks/test2_lock_0000004363 Thread 20 running unlock /locks/test2_lock_0000004360 Thread 12 running unlock /locks/test2_lock_0000004361 Thread 16 running unlock /locks/test2_lock_0000004362 Thread 13 running unlock /locks/test2_lock_0000004363 Thread 17 running unlock /locks/test2_lock_0000004364 Thread 11 running unlock /locks/test2_lock_0000004365 Thread 15 running unlock /locks/test2_lock_0000004366 min: 506 max: 1481 avg: 968 err: 0 ===Thread 8 running unlock /locks/test1_lock_0000004356
關于zookeeper的很好的文章：
https://www.ibm.com/developerworks/cn/opensource/os-cn-zookeeper/
這個分布式共享鎖就是參考這篇文章實現的。
來自：http://my.oschina.net/shenxueliang/blog/135865
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