由于RedLock算法是建立在多个相互独立的redis之上的（为了区分可以叫做Redisson node），所以在编码之中也是获取多个锁的实例以组成一个RedLock。
Redisson实现RedLock源码分析 @Override public boolean tryLock(long waitTime, long leaseTime, TimeUnit unit) throws InterruptedException { long newLeaseTime = -1; if (leaseTime != -1) { if (waitTime == -1) { newLeaseTime = unit.toMillis(leaseTime); } else { newLeaseTime = unit.toMillis(waitTime)*2; } } long time = System.currentTimeMillis(); long remainTime = -1; if (waitTime != -1) { remainTime = unit.toMillis(waitTime); } long lockWaitTime = calcLockWaitTime(remainTime); /** * 1. 允许加锁失败节点个数限制（N-(N/2+1)） */ int failedLocksLimit = failedLocksLimit(); List<RLock> acquiredLocks = new ArrayList<>(locks.size()); /** * 2. 遍历所有节点通过EVAL命令执行lua加锁 */ for (ListIterator<RLock> iterator = locks.listIterator(); iterator.hasNext();) { RLock lock = iterator.next(); boolean lockAcquired; /** * 3.对节点尝试加锁，使用的就是RedissonLock.tryLock() */ try { if (waitTime == -1 && leaseTime == -1) { lockAcquired = lock.tryLock(); } else { long awaitTime = Math.min(lockWaitTime, remainTime); lockAcquired = lock.tryLock(awaitTime, newLeaseTime, TimeUnit.MILLISECONDS); } } catch (RedisResponseTimeoutException e) { // 如果抛出这类异常，为了防止加锁成功，但是响应失败，需要解锁所有节点 unlockInner(Arrays.asList(lock)); lockAcquired = false; } catch (Exception e) { // 抛出异常表示获取锁失败 lockAcquired = false; } if (lockAcquired) { /** *4. 如果获取到锁则添加到已获取锁集合中 */ acquiredLocks.add(lock); } else { /** * 5. 计算已经申请锁失败的节点是否已经到达 允许加锁失败节点个数限制 （N-(N/2+1)） * 如果已经到达， 就认定最终申请锁失败，则没有必要继续从后面的节点申请了 * 因为 Redlock 算法要求至少N/2+1 个节点都加锁成功，才算最终的锁申请成功 */ if (locks.size() - acquiredLocks.size() == failedLocksLimit()) { break; } if (failedLocksLimit == 0) { unlockInner(acquiredLocks); if (waitTime == -1) { return false; } failedLocksLimit = failedLocksLimit(); acquiredLocks.clear(); // reset iterator while (iterator.hasPrevious()) { iterator.previous(); } } else { failedLocksLimit--; } } /** * 6.计算 目前从各个节点获取锁已经消耗的总时间，如果已经等于最大等待时间， * 则认定最终申请锁失败，返回false */ if (remainTime != -1) { remainTime -= System.currentTimeMillis() - time; time = System.currentTimeMillis(); if (remainTime <= 0) { unlockInner(acquiredLocks); return false; } } } if (leaseTime != -1) { List<RFuture<Boolean>> futures = new ArrayList<>(acquiredLocks.size()); for (RLock rLock : acquiredLocks) { RFuture<Boolean> future = ((RedissonLock) rLock).expireAsync(unit.toMillis(leaseTime), TimeUnit.MILLISECONDS); futures.add(future); } for (RFuture<Boolean> rFuture : futures) { rFuture.syncUninterruptibly(); } } /** * 7.如果逻辑正常执行完则认为最终申请锁成功，返回true */ return true; }