分布式锁的实现方式和优缺点&Java代码实现
1、基于数据库
它的实现方式很简单,就是在数据库中创建一个lock表,申请锁就是向表中插入一行唯一关键字,数据库能够保证只有一个请求执行成功,也就是说这个请求申请到了锁,其他请求会报错说明没有申请到锁。释放锁就是在数据库中删除这一行数据。
分部式锁接口定义:
package com.zhi.util; /** * 分布式锁接口 * * @author 张远志 * @since 2020年5月3日11:38:27 * */ public interface DistributeLock { /** * 申请锁 * * @param key 锁关键字 * @param requestId 请求ID,主要用于校验,防止锁被误释放 * @return 是否成功申请锁 */ boolean lock(String key, String requestId); /** * 申请锁 * * @param key 锁关键字 * @param requestId 请求ID,主要用于校验,防止锁被误释放 * @param second 自动释放时间,防止系统崩溃后锁一直出于无法释放的状态 * @return 是否成功申请锁 */ boolean lock(String key, String requestId, Integer second); /** * 释放锁 * * @param key 锁关键字 * @param requestId 请求ID * @return */ boolean unlock(String key, String requestId); }
建表SQL:
CREATE TABLE `dis_lock` ( `id` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL, `content` varchar(20) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL, PRIMARY KEY (`id`) USING BTREE ) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci COMMENT = ‘分布式锁‘ ROW_FORMAT = Dynamic;
Java代码实现:
package com.zhi.util; import java.sql.Connection; import java.sql.PreparedStatement; import javax.sql.DataSource; import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; /** * 数据库实现分布式锁,数据库先创建好dis_lock表 * * @author 张远志 * @since 2020年5月3日12:05:22 * */ public class DatabaseLock implements DistributeLock { private static Logger logger = LogManager.getLogger(DatabaseLock.class); private final static String INSET = "insert dis_lock(id, content) values (?, ?)"; private final static String DELETE = "delete from dis_lock where id=? and content=?"; private DataSource dataSource; public DatabaseLock(DataSource dataSource) { this.dataSource = dataSource; } @Override public boolean lock(String key, String requestId) { try (Connection connection = dataSource.getConnection(); PreparedStatement statement = connection.prepareStatement(INSET);) { statement.setString(1, key); statement.setString(2, requestId); statement.execute(); return true; } catch (Exception e) { return false; } } @Override public boolean lock(String key, String requestId, Integer second) { if (second != null) { throw new RuntimeException("not suport expire time set"); } return lock(key, requestId); } @Override public boolean unlock(String key, String requestId) { try (Connection connection = dataSource.getConnection(); PreparedStatement statement = connection.prepareStatement(DELETE);) { statement.setString(1, key); statement.setString(2, requestId); statement.execute(); return statement.getUpdateCount() > 0; } catch (Exception e) { logger.error("释放锁出错", e); return false; } } }
2、基于缓存(redis)
使用redis做分布式锁,主要是因为redis作为高速缓存,它的存储速度非常快。另外redis可对记录设置过期时间,防止系统崩溃锁无法自动释放。
Java实现:
package com.zhi.util; import java.util.Collections; import redis.clients.jedis.Jedis; import redis.clients.jedis.JedisPool; import redis.clients.jedis.params.SetParams; /** * Redis分布式锁实现 * * @author 张远志 * @since 2020年5月3日11:45:56 * */ public class RedisLock implements DistributeLock { private JedisPool jedisPool; /** * 加锁成功标示 */ private static final String LOCK_SUCCESS = "OK"; /** * 解锁成功标示 */ private static final Long RELEASE_SUCCESS = 1L; public RedisLock(JedisPool jedisPool) { this.jedisPool = jedisPool; } @Override public boolean lock(String key, String requestId) { return lock(key, requestId, null); } @Override public boolean lock(String key, String requestId, Integer second) { try (Jedis jedis = jedisPool.getResource()) { String back = null; SetParams params = new SetParams(); params.nx(); // 若锁不存在才进行写操作 if (second != null) { params.ex(second); // 设置超时时间,单位秒 } back = jedis.set(key, requestId, params); return LOCK_SUCCESS.equals(back); } } @Override public boolean unlock(String key, String requestId) { try (Jedis jedis = jedisPool.getResource();) { String script = "if redis.call(‘get‘, KEYS[1]) == ARGV[1] then return redis.call(‘del‘, KEYS[1]) else return 0 end"; Object result = jedis.eval(script, Collections.singletonList(key), Collections.singletonList(requestId)); return RELEASE_SUCCESS.equals(result); } } }
3、基于zookeeper
package com.zhi.util; import org.apache.zookeeper.CreateMode; import org.apache.zookeeper.ZooDefs.Ids; import org.apache.zookeeper.data.Stat; import org.apache.zookeeper.ZooKeeper; /** * Zookeeper实现分布式锁 * * @author 张远志 * @since 2020年5月3日12:04:33 * */ public class ZookeeperLock implements DistributeLock { private ZooKeeper zooKeeper; /** * 一般锁单独放一个目录中,我这里简单加一个前缀 */ private static final String prefix = "/lock_"; public ZookeeperLock(ZooKeeper zooKeeper) { this.zooKeeper = zooKeeper; } @Override public boolean lock(String key, String requestId) { try { String path = getPath(key); Stat stat = zooKeeper.exists(path, false); if (stat != null) { // 节点已存在,锁已占用 return false; } // CreateMode.PERSISTENT表示数据将被持久化保存 zooKeeper.create(path, requestId.getBytes("UTF-8"), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); return true; } catch (Exception e) { return false; } } @Override public boolean lock(String key, String requestId, Integer second) { if (second != null) { throw new RuntimeException("not suport expire time set"); } return lock(key, requestId); } @Override public boolean unlock(String key, String requestId) { try { String path = getPath(key); Stat stat = new Stat(); byte[] bits = zooKeeper.getData(path, false, stat); String oKey = new String(bits, "UTF-8"); if (requestId.equals(oKey)) { // 比较拥有者是否一致 zooKeeper.delete(path, stat.getVersion()); // 删除指定版本数据 } else { throw new RuntimeException("不允许释放拥有者不是自己的锁"); } return true; } catch (Exception e) { return false; } } private String getPath(String key) { return prefix + key; } }
4、锁测试
package com.zhi.test; import java.util.Random; import java.util.concurrent.CountDownLatch; import org.apache.commons.dbcp2.BasicDataSource; import org.apache.commons.lang3.StringUtils; import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; import org.apache.zookeeper.WatchedEvent; import org.apache.zookeeper.Watcher; import org.apache.zookeeper.ZooKeeper; import org.junit.jupiter.api.MethodOrderer; import org.junit.jupiter.api.Order; import org.junit.jupiter.api.Test; import org.junit.jupiter.api.TestInstance; import org.junit.jupiter.api.TestInstance.Lifecycle; import org.junit.jupiter.api.TestMethodOrder; import com.zhi.util.DatabaseLock; import com.zhi.util.DistributeLock; import com.zhi.util.RedisLock; import com.zhi.util.ZookeeperLock; import redis.clients.jedis.JedisPool; import redis.clients.jedis.JedisPoolConfig; /** * 分布式锁测试 * * @author 张远志 * @since 2020年5月3日13:10:43 * */ @TestInstance(Lifecycle.PER_CLASS) @TestMethodOrder(MethodOrderer.OrderAnnotation.class) public class LockTest { private final Logger logger = LogManager.getLogger(this.getClass()); private static final String key = "test"; @Order(1) @Test public void test1() { logger.info("开始测试数据库(MySQL)分布式锁-----------------------------------------------"); BasicDataSource dataSource = new BasicDataSource(); dataSource.setUsername("root"); dataSource.setPassword("abc123"); dataSource.setUrl("jdbc:mysql://192.168.59.131:3306/zhi_test"); dataSource.setDriverClassName("com.mysql.cj.jdbc.Driver"); doJob(new DatabaseLock(dataSource)); } @Order(2) @Test public void test2() { logger.info("开始测试Redis分布式锁-----------------------------------------------"); JedisPoolConfig config = new JedisPoolConfig(); config.setMaxIdle(5); config.setTestOnBorrow(false); JedisPool jedisPool = new JedisPool(config, "192.168.59.131", 6379); doJob(new RedisLock(jedisPool)); } @Order(3) @Test public void test3() { logger.info("开始测试Zookeeper分布式锁-----------------------------------------------"); ZooKeeper zooKeeper = null; try { zooKeeper = new ZooKeeper("192.168.59.131:2181", 60000, new Watcher() { public void process(WatchedEvent event) { logger.info("事件类型:{},路径:{}", event.getType(), event.getPath()); } }); doJob(new ZookeeperLock(zooKeeper)); } catch (Exception e) { } finally { try { zooKeeper.close(); } catch (Exception e) { } } } private void doJob(DistributeLock locker) { int jobCount = 100; CountDownLatch latch = new CountDownLatch(jobCount); for (int i = 0; i < jobCount; i++) { new Worker(i, locker, latch).start(); } try { latch.await(); } catch (InterruptedException e) { } } class Worker extends Thread { private DistributeLock locker; private CountDownLatch latch; public Worker(int tNo, DistributeLock locker, CountDownLatch latch) { super("线程" + StringUtils.leftPad(String.valueOf(tNo), 3, "0")); this.locker = locker; this.latch = latch; } @Override public void run() { LockTest.doSleep(new Random().nextInt(20) * 1000); long startTime = System.currentTimeMillis(); if (locker.lock(key, getName())) { logger.info("{}申请到锁,申请动作耗时{}毫秒", getName(), System.currentTimeMillis() - startTime); LockTest.doSleep(1000); boolean flag = locker.unlock(key, getName()); logger.info("{}释放锁{}", getName(), flag ? "成功" : "失败"); } latch.countDown(); } } public static void doSleep(long millis) { try { Thread.sleep(millis); } catch (Exception e) { } } }
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