Java分布式鎖的三種實(shí)現(xiàn)方案

更新時(shí)間：2017年01月20日 09:24:40 作者：本杰明警官

本文主要介紹了Java分布式鎖的三種實(shí)現(xiàn)方案。具有一定的參考價(jià)值，下面跟著小編一起來(lái)看下吧

方案一：數(shù)據(jù)庫(kù)樂觀鎖

樂觀鎖通常實(shí)現(xiàn)基于數(shù)據(jù)版本(version)的記錄機(jī)制實(shí)現(xiàn)的，比如有一張紅包表（t_bonus），有一個(gè)字段(left_count)記錄禮物的剩余個(gè)數(shù)，用戶每領(lǐng)取一個(gè)獎(jiǎng)品，對(duì)應(yīng)的left_count減1，在并發(fā)的情況下如何要保證left_count不為負(fù)數(shù)，樂觀鎖的實(shí)現(xiàn)方式為在紅包表上添加一個(gè)版本號(hào)字段（version），默認(rèn)為0。

異常實(shí)現(xiàn)流程

-- 可能會(huì)發(fā)生的異常情況
-- 線程1查詢，當(dāng)前l(fā)eft_count為1，則有記錄
select * from t_bonus where id = 10001 and left_count > 0

-- 線程2查詢，當(dāng)前l(fā)eft_count為1，也有記錄
select * from t_bonus where id = 10001 and left_count > 0

-- 線程1完成領(lǐng)取記錄，修改left_count為0,
update t_bonus set left_count = left_count - 1 where id = 10001

-- 線程2完成領(lǐng)取記錄，修改left_count為-1，產(chǎn)生臟數(shù)據(jù)
update t_bonus set left_count = left_count - 1 where id = 10001

通過(guò)樂觀鎖實(shí)現(xiàn)

-- 添加版本號(hào)控制字段
ALTER TABLE table ADD COLUMN version INT DEFAULT '0' NOT NULL AFTER t_bonus;

-- 線程1查詢，當(dāng)前l(fā)eft_count為1，則有記錄，當(dāng)前版本號(hào)為1234
select left_count, version from t_bonus where id = 10001 and left_count > 0

-- 線程2查詢，當(dāng)前l(fā)eft_count為1，有記錄，當(dāng)前版本號(hào)為1234
select left_count, version from t_bonus where id = 10001 and left_count > 0

-- 線程1,更新完成后當(dāng)前的version為1235，update狀態(tài)為1，更新成功
update t_bonus set version = 1235, left_count = left_count-1 where id = 10001 and version = 1234

-- 線程2,更新由于當(dāng)前的version為1235，udpate狀態(tài)為0，更新失敗，再針對(duì)相關(guān)業(yè)務(wù)做異常處理
update t_bonus set version = 1235, left_count = left_count-1 where id = 10001 and version = 1234

方案二：基于Redis的分布式鎖

SETNX命令（SET if Not eXists）\
語(yǔ)法：SETNX key value\
功能：原子性操作，當(dāng)且僅當(dāng) key 不存在，將 key 的值設(shè)為 value ，并返回1；若給定的 key 已經(jīng)存在，則 SETNX 不做任何動(dòng)作，并返回0。\
Expire命令\
語(yǔ)法：expire(key, expireTime)\
功能：key設(shè)置過(guò)期時(shí)間\
GETSET命令\
語(yǔ)法：GETSET key value\
功能：將給定 key 的值設(shè)為 value ，并返回 key 的舊值 (old value)，當(dāng) key 存在但不是字符串類型時(shí)，返回一個(gè)錯(cuò)誤，當(dāng)key不存在時(shí)，返回nil。\
GET命令\
語(yǔ)法：GET key\
功能：返回 key 所關(guān)聯(lián)的字符串值，如果 key 不存在那么返回特殊值 nil 。\
DEL命令\
語(yǔ)法：DEL key [KEY …]\
功能：刪除給定的一個(gè)或多個(gè) key ,不存在的 key 會(huì)被忽略。

第一種：使用redis的setnx()、expire()方法，用于分布式鎖

setnx(lockkey, 1) 如果返回0，則說(shuō)明占位失敗；如果返回1，則說(shuō)明占位成功
expire()命令對(duì)lockkey設(shè)置超時(shí)時(shí)間，為的是避免死鎖問題。
執(zhí)行完業(yè)務(wù)代碼后，可以通過(guò)delete命令刪除key。

這個(gè)方案其實(shí)是可以解決日常工作中的需求的，但從技術(shù)方案的探討上來(lái)說(shuō)，可能還有一些可以完善的地方。比如，如果在第一步setnx執(zhí)行成功后，在expire()命令執(zhí)行成功前，發(fā)生了宕機(jī)的現(xiàn)象，那么就依然會(huì)出現(xiàn)死鎖的問題

第二種：使用redis的setnx()、get()、getset()方法，用于分布式鎖，解決死鎖問題

setnx(lockkey, 當(dāng)前時(shí)間+過(guò)期超時(shí)時(shí)間) ，如果返回1，則獲取鎖成功；如果返回0則沒有獲取到鎖，轉(zhuǎn)向2。
get(lockkey)獲取值oldExpireTime ，并將這個(gè)value值與當(dāng)前的系統(tǒng)時(shí)間進(jìn)行比較，如果小于當(dāng)前系統(tǒng)時(shí)間，則認(rèn)為這個(gè)鎖已經(jīng)超時(shí)，可以允許別的請(qǐng)求重新獲取，轉(zhuǎn)向3。
計(jì)算newExpireTime=當(dāng)前時(shí)間+過(guò)期超時(shí)時(shí)間，然后getset(lockkey, newExpireTime) 會(huì)返回當(dāng)前l(fā)ockkey的值currentExpireTime。
判斷currentExpireTime與oldExpireTime 是否相等，如果相等，說(shuō)明當(dāng)前getset設(shè)置成功，獲取到了鎖。如果不相等，說(shuō)明這個(gè)鎖又被別的請(qǐng)求獲取走了，那么當(dāng)前請(qǐng)求可以直接返回失敗，或者繼續(xù)重試。
在獲取到鎖之后，當(dāng)前線程可以開始自己的業(yè)務(wù)處理，當(dāng)處理完畢后，比較自己的處理時(shí)間和對(duì)于鎖設(shè)置的超時(shí)時(shí)間，如果小于鎖設(shè)置的超時(shí)時(shí)間，則直接執(zhí)行delete釋放鎖；如果大于鎖設(shè)置的超時(shí)時(shí)間，則不需要再鎖進(jìn)行處理。

import cn.com.tpig.cache.redis.RedisService;
import cn.com.tpig.utils.SpringUtils;
/**
 * Created by IDEA
 * User: shma1664
 * Date: 2016-08-16 14:01
 * Desc: redis分布式鎖
 */
public final class RedisLockUtil {
 private static final int defaultExpire = 60;
 private RedisLockUtil() {
 //
 }
 /**
 * 加鎖
 * @param key redis key
 * @param expire 過(guò)期時(shí)間，單位秒
 * @return true:加鎖成功，false，加鎖失敗
 */
 public static boolean lock(String key, int expire) {
 RedisService redisService = SpringUtils.getBean(RedisService.class);
 long status = redisService.setnx(key, "1");

 if(status == 1) {
 redisService.expire(key, expire);
 return true;
 }
 return false;
 }
 public static boolean lock(String key) {
 return lock2(key, defaultExpire);
 }
 /**
 * 加鎖
 * @param key redis key
 * @param expire 過(guò)期時(shí)間，單位秒
 * @return true:加鎖成功，false，加鎖失敗
 */
 public static boolean lock2(String key, int expire) {
 RedisService redisService = SpringUtils.getBean(RedisService.class);
 long value = System.currentTimeMillis() + expire;
 long status = redisService.setnx(key, String.valueOf(value));
 if(status == 1) {
 return true;
 }
 long oldExpireTime = Long.parseLong(redisService.get(key, "0"));
 if(oldExpireTime < System.currentTimeMillis()) {
 //超時(shí)
 long newExpireTime = System.currentTimeMillis() + expire;
 long currentExpireTime = Long.parseLong(redisService.getSet(key, String.valueOf(newExpireTime)));
 if(currentExpireTime == oldExpireTime) {
 return true;
 }
 }
 return false;
 }
 public static void unLock1(String key) {
 RedisService redisService = SpringUtils.getBean(RedisService.class);
 redisService.del(key);
 }
 public static void unLock2(String key) { 
 RedisService redisService = SpringUtils.getBean(RedisService.class); 
 long oldExpireTime = Long.parseLong(redisService.get(key, "0")); 
 if(oldExpireTime > System.currentTimeMillis()) { 
 redisService.del(key); 
 }
 }
}

public void drawRedPacket(long userId) {
 String key = "draw.redpacket.userid:" + userId;
 boolean lock = RedisLockUtil.lock2(key, 60);
 if(lock) {
 try {
 //領(lǐng)取操作
 } finally {
 //釋放鎖
 RedisLockUtil.unLock(key);
 }
 } else {
 new RuntimeException("重復(fù)領(lǐng)取獎(jiǎng)勵(lì)");
 }
}

Spring AOP基于注解方式和SpEL實(shí)現(xiàn)開箱即用的redis分布式鎖策略

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
 * RUNTIME
 * 定義注解
 * 編譯器將把注釋記錄在類文件中，在運(yùn)行時(shí) VM 將保留注釋，因此可以反射性地讀取。
 * @author shma1664
 *
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface RedisLockable {
 String[] key() default "";
 long expiration() default 60;
}

import javax.annotation.Resource;
import java.lang.reflect.Method;
import com.autohome.api.dealer.util.cache.RedisClient;
import com.google.common.base.Joiner;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.Signature;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.expression.EvaluationContext;
import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;
import org.springframework.stereotype.Component;
/**
 * Created by IDEA
 * User: mashaohua
 * Date: 2016-09-28 18:08
 * Desc:
 */
@Aspect
@Component
public class RedisLockAop {
 @Resource
 private RedisClient redisClient;
 @Pointcut("execution(* com.autohome.api.dealer.tuan.service.*.*(..))")
 public void pointcut(){}
 @Around("pointcut()")
 public Object doAround(ProceedingJoinPoint point) throws Throwable{
 Signature signature = point.getSignature();
 MethodSignature methodSignature = (MethodSignature) signature;
 Method method = methodSignature.getMethod();
 String targetName = point.getTarget().getClass().getName();
 String methodName = point.getSignature().getName();
 Object[] arguments = point.getArgs();
 if (method != null && method.isAnnotationPresent(RedisLockable.class)) {
 RedisLockable redisLock = method.getAnnotation(RedisLockable.class);
 long expire = redisLock.expiration();
 String redisKey = getLockKey(targetName, methodName, redisLock.key(), arguments);
 boolean isLock = RedisLockUtil.lock2(redisKey, expire);
 if(!isLock) {
 try {
 return point.proceed();
 } finally {
 unLock2(redisKey);
 }
 } else {
 throw new RuntimeException("您的操作太頻繁，請(qǐng)稍后再試");
 }
 }
 return point.proceed();
 }
 private String getLockKey(String targetName, String methodName, String[] keys, Object[] arguments) {
 StringBuilder sb = new StringBuilder();
 sb.append("lock.").append(targetName).append(".").append(methodName);
 if(keys != null) {
 String keyStr = Joiner.on(".").skipNulls().join(keys);
 String[] parameters = ReflectParamNames.getNames(targetName, methodName);
 ExpressionParser parser = new SpelExpressionParser();
 Expression expression = parser.parseExpression(keyStr);
 EvaluationContext context = new StandardEvaluationContext();
 int length = parameters.length;
 if (length > 0) {
 for (int i = 0; i < length; i++) {
 context.setVariable(parameters[i], arguments[i]);
 }
 }
 String keysValue = expression.getValue(context, String.class);
 sb.append("#").append(keysValue);
 }
 return sb.toString();
 }

<!-- https://mvnrepository.com/artifact/javassist/javassist -->
<dependency>
 <groupId>org.javassist</groupId>
 <artifactId>javassist</artifactId>
 <version>3.18.1-GA</version>
</dependency>

import javassist.*;
import javassist.bytecode.CodeAttribute;
import javassist.bytecode.LocalVariableAttribute;
import javassist.bytecode.MethodInfo;
import org.apache.log4j.Logger;
/**
 * Created by IDEA
 * User: mashaohua
 * Date: 2016-09-28 18:39
 * Desc:
 */
public class ReflectParamNames {
 private static Logger log = Logger.getLogger(ReflectParamNames.class);
 private static ClassPool pool = ClassPool.getDefault();
 static{
 ClassClassPath classPath = new ClassClassPath(ReflectParamNames.class);
 pool.insertClassPath(classPath);
 }
 public static String[] getNames(String className,String methodName) {
 CtClass cc = null;
 try {
 cc = pool.get(className);
 CtMethod cm = cc.getDeclaredMethod(methodName);
 // 使用javaassist的反射方法獲取方法的參數(shù)名
 MethodInfo methodInfo = cm.getMethodInfo();
 CodeAttribute codeAttribute = methodInfo.getCodeAttribute();
 LocalVariableAttribute attr = (LocalVariableAttribute) codeAttribute.getAttribute(LocalVariableAttribute.tag);
 if (attr == null) return new String[0];
 int begin = 0;
 String[] paramNames = new String[cm.getParameterTypes().length];
 int count = 0;
 int pos = Modifier.isStatic(cm.getModifiers()) ? 0 : 1;
 for (int i = 0; i < attr.tableLength(); i++){
 // 為什么 加這個(gè)判斷，發(fā)現(xiàn)在windows 跟linux執(zhí)行時(shí)，參數(shù)順序不一致，通過(guò)觀察，實(shí)際的參數(shù)是從this后面開始的
 if (attr.variableName(i).equals("this")){
 begin = i;
 break;
 }
 }
 for (int i = begin+1; i <= begin+paramNames.length; i++){
 paramNames[count] = attr.variableName(i);
 count++;
 }
 return paramNames;
 } catch (Exception e) {
 e.printStackTrace();
 }finally{
 try {
 if(cc != null) cc.detach();
 } catch (Exception e2) {
 log.error(e2.getMessage());
 }
 }
 return new String[0];
 }
}

在需要使用分布式鎖的地方添加注解

/**
 * 抽獎(jiǎng)接口
 * 添加redis分布式鎖保證一個(gè)訂單只有一個(gè)請(qǐng)求處理，防止用戶刷禮物，支持SpEL表達(dá)式
 * redisLockKey：lock.com.autohome.api.dealer.tuan.service.impl.drawBonus#orderId
 * @param orderId 訂單id
 * @return 抽中的獎(jiǎng)品信息
 */
@RedisLockable(key = {"#orderId"}, expiration = 120)
@Override
public BonusConvertBean drawBonus(Integer orderId) throws BonusException{
 // 業(yè)務(wù)邏輯
}

第三種方案：基于Zookeeper的分布式鎖

利用節(jié)點(diǎn)名稱的唯一性來(lái)實(shí)現(xiàn)獨(dú)占鎖

ZooKeeper機(jī)制規(guī)定同一個(gè)目錄下只能有一個(gè)唯一的文件名，zookeeper上的一個(gè)znode看作是一把鎖，通過(guò)createznode的方式來(lái)實(shí)現(xiàn)。所有客戶端都去創(chuàng)建/lock/${lock_name}_lock節(jié)點(diǎn)，最終成功創(chuàng)建的那個(gè)客戶端也即擁有了這把鎖，創(chuàng)建失敗的可以選擇監(jiān)聽繼續(xù)等待，還是放棄拋出異常實(shí)現(xiàn)獨(dú)占鎖。
package com.shma.example.zookeeper.lock;

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.*;
import org.apache.zookeeper.data.Stat;
/**
 * Created by IDEA
 * User: mashaohua
 * Date: 2016-09-30 16:09
 * Desc:
 */
public class ZookeeperLock implements Lock, Watcher {
 private ZooKeeper zk;
 private String root = "/locks";//根
 private String lockName;//競(jìng)爭(zhēng)資源的標(biāo)志
 private String myZnode;//當(dāng)前鎖
 private int sessionTimeout = 30000;
 private List<Exception> exception = new ArrayList<Exception>();
 /**
 * 創(chuàng)建分布式鎖,使用前請(qǐng)確認(rèn)config配置的zookeeper服務(wù)可用
 * @param config 127.0.0.1:2181
 * @param lockName 競(jìng)爭(zhēng)資源標(biāo)志,lockName中不能包含單詞lock
 */
 public ZookeeperLock(String config, String lockName){
 this.lockName = lockName;
 // 創(chuàng)建一個(gè)與服務(wù)器的連接
 try {
 zk = new ZooKeeper(config, sessionTimeout, this);
 Stat stat = zk.exists(root, false);
 if(stat == null){
 // 創(chuàng)建根節(jié)點(diǎn)
 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);
 }
 }
 @Override
 public void lock() {
 if(exception.size() > 0){
 throw new LockException(exception.get(0));
 }
 if(!tryLock()) {
 throw new LockException("您的操作太頻繁，請(qǐng)稍后再試");
 }
 }
 @Override
 public void lockInterruptibly() throws InterruptedException {
 this.lock();
 }
 @Override
 public boolean tryLock() {
 try {
 myZnode = zk.create(root + "/" + lockName, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
 return true;
 } catch (KeeperException e) {
 e.printStackTrace();
 } catch (InterruptedException e) {
 e.printStackTrace();
 }
 return false;
 }
 @Override
 public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
 return tryLock();
 }
 @Override
 public void unlock() {
 try {
 zk.delete(myZnode, -1);
 myZnode = null;
 zk.close();
 } catch (InterruptedException e) {
 e.printStackTrace();
 } catch (KeeperException e) {
 e.printStackTrace();
 }
 }
 @Override
 public Condition newCondition() {
 return null;
 }
 @Override
 public void process(WatchedEvent watchedEvent) {
 //
 }
}

ZookeeperLock lock = null;
try {
 lock = new ZookeeperLock("127.0.0.1:2182","test1");
 lock.lock();
 //業(yè)務(wù)邏輯處理
} catch (LockException e) {
 throw e;
} finally {
 if(lock != null)
 lock.unlock();
}

利用臨時(shí)順序節(jié)點(diǎn)控制時(shí)序?qū)崿F(xiàn)

/lock已經(jīng)預(yù)先存在，所有客戶端在它下面創(chuàng)建臨時(shí)順序編號(hào)目錄節(jié)點(diǎn)，和選master一樣，編號(hào)最小的獲得鎖，用完刪除，依次方便。\

算法思路：對(duì)于加鎖操作，可以讓所有客戶端都去/lock目錄下創(chuàng)建臨時(shí)順序節(jié)點(diǎn)，如果創(chuàng)建的客戶端發(fā)現(xiàn)自身創(chuàng)建節(jié)點(diǎn)序列號(hào)是/lock/目錄下最小的節(jié)點(diǎn)，則獲得鎖。否則，監(jiān)視比自己創(chuàng)建節(jié)點(diǎn)的序列號(hào)小的節(jié)點(diǎn)（比自己創(chuàng)建的節(jié)點(diǎn)小的最大節(jié)點(diǎn)），進(jìn)入等待。

對(duì)于解鎖操作，只需要將自身創(chuàng)建的節(jié)點(diǎn)刪除即可。

package com.shma.example.zookeeper.lock;
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;
/**
 * Created by IDEA
 * User: mashaohua
 * Date: 2016-09-30 16:09
 * Desc:
 */
public class DistributedLock implements Lock, Watcher{
 private ZooKeeper zk;
 private String root = "/locks";//根
 private String lockName;//競(jìng)爭(zhēng)資源的標(biāo)志
 private String waitNode;//等待前一個(gè)鎖
 private String myZnode;//當(dāng)前鎖
 private CountDownLatch latch;//計(jì)數(shù)器
 private int sessionTimeout = 30000;
 private List<Exception> exception = new ArrayList<Exception>();
 /**
 * 創(chuàng)建分布式鎖,使用前請(qǐng)確認(rèn)config配置的zookeeper服務(wù)可用
 * @param config 127.0.0.1:2181
 * @param lockName 競(jìng)爭(zhēng)資源標(biāo)志,lockName中不能包含單詞lock
 */
 public DistributedLock(String config, String lockName){
 this.lockName = lockName;
 // 創(chuàng)建一個(gè)與服務(wù)器的連接
 try {
 zk = new ZooKeeper(config, sessionTimeout, this);
 Stat stat = zk.exists(root, false);
 if(stat == null){
 // 創(chuàng)建根節(jié)點(diǎn)
 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(jié)點(diǎn)的監(jiān)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(chuàng)建臨時(shí)子節(jié)點(diǎn)
 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(jié)點(diǎn)
 List<String> subNodes = zk.getChildren(root, false);
 //取出所有l(wèi)ockName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(jié)點(diǎn),則表示取得鎖
 return true;
 }
 //如果不是最小的節(jié)點(diǎn)，找到比自己小1的節(jié)點(diǎn)
 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(gè)數(shù)的節(jié)點(diǎn)是否存在,如果不存在則無(wú)需等待鎖,同時(shí)注冊(cè)監(jiān)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);
 }
 }
}

以上就是本文的全部?jī)?nèi)容，希望本文的內(nèi)容對(duì)大家的學(xué)習(xí)或者工作能帶來(lái)一定的幫助，同時(shí)也希望多多支持腳本之家！

您可能感興趣的文章: