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這篇文章將為大家詳細講解有關ZooKeeper中怎樣實現分布式鎖，文章內容質量較高，因此小編分享給大家做個參考，希望大家閱讀完這篇文章后對相關知識有一定的了解。
在zookeeper指定節點（locks）下創建臨時順序節點node_n
獲取locks下所有子節點children
對子節點按節點自增序號從小到大排序
判斷本節點是不是第一個子節點，若是，則獲取鎖；若不是，則監聽比該節點小的那個節點的刪除事件
若監聽事件生效，則回到第二步重新進行判斷，直到獲取到鎖。
下面就具體使用java和zookeeper實現分布式鎖，操作zookeeper使用的是apache提供的zookeeper的包。
通過實現Watch接口，實現process(WatchedEvent event) 方法來實施監控，使CountDownLatch來完成監控，在等待鎖的時候使用CountDownLatch來計數，等到后進行countDown，停止等待，繼續運行。
以下整體流程基本與上述描述流程一致，只是在監聽的時候使用的是CountDownLatch來監聽前一個節點。
import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;
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;
/**
* Created by liuyang on 2017/4/20.
*/
public class DistributedLock implements Lock, Watcher {
//Zk對象操作
private ZooKeeper zk = null;
// 根節點
private String ROOT_LOCK = "/locks";
// 競爭的資源
private String lockName;
// 等待的前一個鎖
private String WAIT_LOCK;
// 當前鎖
private String CURRENT_LOCK;
// 計數器
private CountDownLatch countDownLatch;
private int sessionTimeout = 30000;
private List<Exception> exceptionList = new ArrayList<Exception>();
/**
* 配置分布式鎖
* @param config 連接的url
* @param lockName 競爭資源
*/
public DistributedLock(String config, String lockName) {
this.lockName = lockName;
try {
// 連接zookeeper
zk = new ZooKeeper(config, sessionTimeout, this);
Stat stat = zk.exists(ROOT_LOCK, false);
if (stat == null) {
// 如果根節點不存在，則創建根節點
zk.create(ROOT_LOCK, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE,
CreateMode.PERSISTENT);
}
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
}
}
// 節點監視器
public void process(WatchedEvent event) {
if (this.countDownLatch != null) {
this.countDownLatch.countDown();
}
}
public void lock() {
if (exceptionList.size() > 0) {
throw new LockException(exceptionList.get(0));
}
try {
if (this.tryLock()) {
System.out.println(Thread.currentThread().getName() + " " + lockName
+ "獲得了鎖");
return;
} else {
// 等待鎖
waitForLock(WAIT_LOCK, sessionTimeout);
}
} catch (InterruptedException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
}
}
public boolean tryLock() {
try {
String splitStr = "_lock_";
if (lockName.contains(splitStr)) {
throw new LockException("鎖名有誤");
}
// 創建臨時有序節點
CURRENT_LOCK = zk.create(ROOT_LOCK + "/" + lockName + splitStr,
new byte[0],ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
System.out.println(CURRENT_LOCK + " 已經創建");
// 取所有子節點
List<String> subNodes = zk.getChildren(ROOT_LOCK, false);
// 取出所有lockName的鎖
List<String> lockObjects = new ArrayList<String>();
for (String node : subNodes) {
String _node = node.split(splitStr)[0];
if (_node.equals(lockName)) {
lockObjects.add(node);
}
}
Collections.sort(lockObjects);
System.out.println(Thread.currentThread().getName() + " 的鎖是 "
+CURRENT_LOCK);
// 若當前節點為最小節點，則獲取鎖成功
if (CURRENT_LOCK.equals(ROOT_LOCK + "/" + lockObjects.get(0))) {
return true;
}
// 若不是最小節點，則找到自己的前一個節點
String prevNode = CURRENT_LOCK.substring(CURRENT_LOCK.lastIndexOf("/")+ 1);
WAIT_LOCK = lockObjects.get(Collections.binarySearch(lockObjects, prevNode) - 1)
} catch (InterruptedException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
}
return false;
}
public boolean tryLock(long timeout, TimeUnit unit) {
try {
if (this.tryLock()) {
return true;
}
return waitForLock(WAIT_LOCK, timeout);
} catch (Exception e) {
e.printStackTrace();
}
return false;
}
// 等待鎖
private boolean waitForLock(String prev, long waitTime) throws KeeperException, InterruptedException {
Stat stat = zk.exists(ROOT_LOCK + "/" + prev, true);
if (stat != null) {
System.out.println(Thread.currentThread().getName() + "等待鎖 " + ROOT_LOCK + "/" + prev);
this.countDownLatch = new CountDownLatch(1);
// 計數等待，若等到前一個節點消失，則precess中進行countDown，停止等待，獲取鎖
this.countDownLatch.await(waitTime, TimeUnit.MILLISECONDS);
this.countDownLatch = null;
System.out.println(Thread.currentThread().getName() + " 等到了鎖");
}
return true;
}
public void unlock() {
try {
System.out.println("釋放鎖 " + CURRENT_LOCK);
zk.delete(CURRENT_LOCK, -1);
CURRENT_LOCK = null;
zk.close();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (KeeperException e) {
e.printStackTrace();
}
}
public Condition newCondition() {
return null;
}
public void lockInterruptibly() throws InterruptedException {
this.lock();
}
public class LockException extends RuntimeException {
private static final long serialVersionUID = 1L;
public LockException(String e){
super(e);
}
public LockException(Exception e){
super(e);
}
}
}public class Test {
static int n = 500;
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("127.0.0.1:2181", "test1");
lock.lock();
secskill();
System.out.println(Thread.currentThread().getName() + "正在運行");
} finally {
if (lock != null) {
lock.unlock();
}
}
}
};
for (int i = 0; i < 10; i++) {
Thread t = new Thread(runnable);
t.start();
}
}
}
關于ZooKeeper中怎樣實現分布式鎖就分享到這里了，希望以上內容可以對大家有一定的幫助，可以學到更多知識。如果覺得文章不錯，可以把它分享出去讓更多的人看到。
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