Redlock

为什么需要分布式锁？ 单机锁的局限： // ❌ 单机环境有效 synchronized (this) { // 扣减库存 } // ❌ 分布式环境失效 // 服务器1和服务器2的锁互不影响 分布式锁特性： 互斥性：同一时刻只有一个客户端持有锁 安全性：只有持锁者能释放锁 可用性：高可用，避免死锁 性能：加锁解锁快速 方案演进 V1：基础版（SETNX + EXPIRE） public boolean lock(String key, String value, long expireSeconds) { Boolean success = redis.opsForValue().setIfAbsent(key, value); if (Boolean.TRUE.equals(success)) { redis.expire(key, expireSeconds, TimeUnit.SECONDS); return true; } return false; } // ❌ 问题：SETNX和EXPIRE不是原子操作 // 如果SETNX成功后宕机，锁永不过期 V2：原子操作版（SET NX EX） public boolean lock(String key, String value, long expireSeconds) { Boolean success = redis.opsForValue() .setIfAbsent(key, value, expireSeconds, TimeUnit.SECONDS); return Boolean.TRUE.equals(success); } public void unlock(String key) { redis.delete(key); } // ❌ 问题：可能释放别人的锁 // 线程A持锁超时，锁自动释放 // 线程B获得锁 // 线程A执行完，删除了线程B的锁 V3：安全释放版（Lua脚本） public class DistributedLock { @Autowired private RedisTemplate<String, String> redis; private static final String UNLOCK_SCRIPT = "if redis.call('GET', KEYS[1]) == ARGV[1] then " + " return redis.call('DEL', KEYS[1]) " + "else " + " return 0 " + "end"; // 加锁 public boolean lock(String key, String requestId, long expireSeconds) { Boolean success = redis.opsForValue() .setIfAbsent(key, requestId, expireSeconds, TimeUnit.SECONDS); return Boolean.TRUE.equals(success); } // 安全解锁 public boolean unlock(String key, String requestId) { Long result = redis.execute( RedisScript.of(UNLOCK_SCRIPT, Long.class), Collections.singletonList(key), requestId ); return result != null && result == 1; } } // ✅ 优势：原子性校验和删除 // ❌ 问题：业务执行时间超过锁过期时间 V4：自动续期版（看门狗） @Component public class RedisLockWithWatchdog { @Autowired private RedisTemplate<String, String> redis; private static final long DEFAULT_EXPIRE_SECONDS = 30; private static final long RENEW_INTERVAL_SECONDS = 10; private final Map<String, ScheduledFuture<?>> renewTasks = new ConcurrentHashMap<>(); private final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1); public boolean lock(String key, String requestId) { Boolean success = redis.opsForValue() .setIfAbsent(key, requestId, DEFAULT_EXPIRE_SECONDS, TimeUnit.SECONDS); if (Boolean.TRUE.equals(success)) { // 启动续期任务 startRenewTask(key, requestId); return true; } return false; } private void startRenewTask(String key, String requestId) { ScheduledFuture<?> task = scheduler.scheduleAtFixedRate(() -> { try { String value = redis.opsForValue().get(key); if (requestId.equals(value)) { redis.expire(key, DEFAULT_EXPIRE_SECONDS, TimeUnit.SECONDS); log.debug("锁续期成功: {}", key); } else { // 锁已被他人持有，停止续期 stopRenewTask(key); } } catch (Exception e) { log.error("锁续期失败", e); } }, RENEW_INTERVAL_SECONDS, RENEW_INTERVAL_SECONDS, TimeUnit.SECONDS); renewTasks.put(key, task); } public boolean unlock(String key, String requestId) { stopRenewTask(key); String script = "if redis.call('GET', KEYS[1]) == ARGV[1] then " + " return redis.call('DEL', KEYS[1]) " + "else " + " return 0 " + "end"; Long result = redis.execute( RedisScript.of(script, Long.class), Collections.singletonList(key), requestId ); return result != null && result == 1; } private void stopRenewTask(String key) { ScheduledFuture<?> task = renewTasks.remove(key); if (task != null) { task.cancel(false); } } } 实战案例 案例1：库存扣减 @Service public class StockService { @Autowired private RedisLockWithWatchdog redisLock; @Autowired private RedisTemplate<String, Object> redis; public boolean deductStock(String productId, int quantity) { String lockKey = "lock:stock:" + productId; String requestId = UUID.randomUUID().toString(); try { // 尝试获取锁（超时3秒） if (!tryLock(lockKey, requestId, 3000)) { return false; // 获取锁失败 } // 检查库存 Integer stock = (Integer) redis.opsForValue().get("stock:" + productId); if (stock == null || stock < quantity) { return false; // 库存不足 } // 扣减库存 redis.opsForValue().decrement("stock:" + productId, quantity); return true; } finally { // 释放锁 redisLock.unlock(lockKey, requestId); } } private boolean tryLock(String key, String requestId, long timeoutMs) { long startTime = System.currentTimeMillis(); while (System.currentTimeMillis() - startTime < timeoutMs) { if (redisLock.lock(key, requestId)) { return true; } try { Thread.sleep(50); // 等待50ms后重试 } catch (InterruptedException e) { Thread.currentThread().interrupt(); return false; } } return false; } } 案例2：订单防重 @Service public class OrderService { @Autowired private RedisLockWithWatchdog redisLock; public String createOrder(OrderRequest request) { String lockKey = "lock:order:" + request.getUserId() + ":" + request.getOrderNo(); String requestId = UUID.randomUUID().toString(); try { if (!redisLock.lock(lockKey, requestId)) { throw new BusinessException("订单正在处理中，请勿重复提交"); } // 创建订单逻辑 Order order = new Order(); order.setOrderNo(request.getOrderNo()); // ... 保存订单 return order.getOrderNo(); } finally { redisLock.unlock(lockKey, requestId); } } } 案例3：定时任务防重 @Component public class ScheduledTaskWithLock { @Autowired private RedisLockWithWatchdog redisLock; @Scheduled(cron = "0 */5 * * * ?") // 每5分钟执行 public void syncData() { String lockKey = "lock:task:sync_data"; String requestId = UUID.randomUUID().toString(); if (!redisLock.lock(lockKey, requestId)) { log.info("其他节点正在执行同步任务，跳过"); return; } try { log.info("开始执行同步任务"); // 执行同步逻辑 doSync(); } finally { redisLock.unlock(lockKey, requestId); } } private void doSync() { // 同步逻辑 } } Redlock算法（多Redis实例） 问题：单Redis实例有单点故障风险 ...