分布式锁实现

需要JAVA Spring Cloud大型企业分布式微服务云构建的B2B2C电子商务平台源码：壹零叁八柒柒肆六二六

基于Consul的分布式锁主要利用Key/Value存储API中的acquire和release操作来实现。acquire和release操作是类似Check-And-Set的操作：

acquire操作只有当锁不存在持有者时才会返回true，并且set设置的Value值，同时执行操作的session会持有对该Key的锁，否则就返回false release操作则是使用指定的session来释放某个Key的锁，如果指定的session无效，那么会返回false，否则就会set设置Value值，并返回true

基本流程

具体实现

public class Lock {private static final String prefix = "lock/";  // 同步锁参数前缀private ConsulClient consulClient;private String sessionName;private String sessionId = null;private String lockKey;/**** @param consulClient* @param sessionName   同步锁的session名称* @param lockKey       同步锁在consul的KV存储中的Key路径，会自动增加prefix前缀，方便归类查询*/public Lock(ConsulClient consulClient, String sessionName, String lockKey) {this.consulClient = consulClient;this.sessionName = sessionName;this.lockKey = prefix + lockKey;}/*** 获取同步锁** @param block     是否阻塞，直到获取到锁为止* @return*/public Boolean lock(boolean block) {if (sessionId != null) {throw new RuntimeException(sessionId + " - Already locked!");}sessionId = createSession(sessionName);while(true) {PutParams putParams = new PutParams();putParams.setAcquireSession(sessionId);if(consulClient.setKVValue(lockKey, "lock:" + LocalDateTime.now(), putParams).getValue()) {return true;} else if(block) {continue;} else {return false;}}}/*** 释放同步锁** @return*/public Boolean unlock() {PutParams putParams = new PutParams();putParams.setReleaseSession(sessionId);boolean result = consulClient.setKVValue(lockKey, "unlock:" + LocalDateTime.now(), putParams).getValue();consulClient.sessionDestroy(sessionId, null);return result;}/*** 创建session* @param sessionName* @return*/private String createSession(String sessionName) {NewSession newSession = new NewSession();newSession.setName(sessionName);return consulClient.sessionCreate(newSession, null).getValue();}}
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单元测试 下面单元测试的逻辑：通过线程的方式来模拟不同的分布式服务来竞争锁。多个处理线程同时以阻塞方式来申请分布式锁，当处理线程获得锁之后，Sleep一段随机事件，以模拟处理业务逻辑，处理完毕之后释放锁。

public class TestLock {private Logger logger = Logger.getLogger(getClass());@Testpublic void testLock() throws Exception  {new Thread(new LockRunner(1)).start();new Thread(new LockRunner(2)).start();new Thread(new LockRunner(3)).start();new Thread(new LockRunner(4)).start();new Thread(new LockRunner(5)).start();Thread.sleep(200000L);}class LockRunner implements Runnable {private Logger logger = Logger.getLogger(getClass());private int flag;public LockRunner(int flag) {this.flag = flag;}@Overridepublic void run() {Lock lock = new Lock(new ConsulClient(), "lock-session", "lock-key");try {if (lock.lock(true)) {logger.info("Thread " + flag + " start!");Thread.sleep(new Random().nextInt(3000L));logger.info("Thread " + flag + " end!");}} catch (Exception e) {e.printStackTrace();} finally {lock.unlock();}}}}
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单元测试执行结果如下：

2017-04-12 21:28:09,698 INFO  [Thread-0] LockRunner - Thread 1 start!
2017-04-12 21:28:12,717 INFO  [Thread-0] LockRunner - Thread 1 end!
2017-04-12 21:28:13,219 INFO  [Thread-2] LockRunner - Thread 3 start!
2017-04-12 21:28:15,672 INFO  [Thread-2] LockRunner - Thread 3 end!
2017-04-12 21:28:15,735 INFO  [Thread-1] LockRunner - Thread 2 start!
2017-04-12 21:28:17,788 INFO  [Thread-1] LockRunner - Thread 2 end!
2017-04-12 21:28:18,249 INFO  [Thread-4] LockRunner - Thread 5 start!
2017-04-12 21:28:19,573 INFO  [Thread-4] LockRunner - Thread 5 end!
2017-04-12 21:28:19,757 INFO  [Thread-3] LockRunner - Thread 4 start!
2017-04-12 21:28:21,353 INFO  [Thread-3] LockRunner - Thread 4 end!
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从测试结果我们可以看到，通过分布式锁的形式来控制并发时，多个同步操作只会有一个操作能够被执行，其他操作只有在等锁释放之后才有机会去执行，所以通过这样的分布式锁，我们可以控制共享资源同时只能被一个操作进行执行，以保障数据处理时的分布式并发问题。

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