Redis分布式锁学习
最近研究了一下Redis分布锁，在github上搜了一下
就拿star最多的 https://github.com/KidFashion/redlock-cs来参考。。
但是相比Redisson(java的实现)有以下几点不足：
1.当一个资源解锁的时候，释放锁之后，其他之前等待的锁不能自动重试申请锁。
2.如果设置了一个超时时间，但是确实执行时间超过了超时时间，那么锁会被自动释放，原来持锁的客户端再次解锁的时候会出现问题
也要保证一旦一个客户端持锁，在客户端可用时不会被其他客户端解锁。
3.如果关键业务，可能需要重入场景，无法实现重入锁。
于是我仿照Redisson在c#的实现
测试一下：
TODO:接收事件去重新获取锁
public class RedisLock { #region Property //KEYS[1] ：需要加锁的key，这里需要是字符串类型。 //ARGV[1] ：锁的超时时间，防止死锁 //ARGV[2] ：锁的唯一标识 private const String LOCK_SCRIPT = @" if (redis.call('exists', KEYS[1]) == 0) then redis.call('hset', KEYS[1], ARGV[2], 1); redis.call('pexpire', KEYS[1], ARGV[1]); return nil; end; if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then redis.call('hincrby', KEYS[1], ARGV[2], 1); redis.call('pexpire', KEYS[1], ARGV[1]); return nil; end; return redis.call('pttl', KEYS[1]); "; //– KEYS[1] ：需要加锁的key，这里需要是字符串类型。 //– KEYS[2] ：redis消息的ChannelName,一个分布式锁对应唯一的一个channelName:“redisson_lock__channel__{” + getName() + “}” //– ARGV[1] ：reids消息体，这里只需要一个字节的标记就可以，主要标记redis的key已经解锁，再结合redis的Subscribe，能唤醒其他订阅解锁消息的客户端线程申请锁。 //– ARGV[2] ：锁的超时时间，防止死锁 //– ARGV[3] ：锁的唯一标识 private const String UN_LOCK_SCRIPT = @" if (redis.call('exists', KEYS[1]) == 0) then redis.call('publish', KEYS[2], ARGV[1]); return 1; end; if (redis.call('hexists', KEYS[1], ARGV[3]) == 0) then return nil; end; local counter = redis.call('hincrby', KEYS[1], ARGV[3], -1); if (counter > 0) then redis.call('pexpire', KEYS[1], ARGV[2]); return 0; else redis.call('del', KEYS[1]); redis.call('publish', KEYS[2], ARGV[1]); return 1; end; return nil; "; private const double ClockDriveFactor = 0.01; /// <summary> /// 默认的30秒过期时间 /// </summary> private readonly TimeSpan LeaseTimeSpan = new TimeSpan(0, 0, 30); private readonly ConcurrentDictionary<string, CancellationTokenSource> ExpirationRenewalMap = new ConcurrentDictionary<string, CancellationTokenSource>(); private readonly ConnectionMultiplexer Server; #endregion #region Constructor public RedisLock(ConnectionMultiplexer connection) { Server = connection; Server.PreserveAsyncOrder = false; } #endregion #region Public /// <summary> /// 加锁 /// </summary> /// <param name="resource">锁名</param> /// <param name="waitTimeSpan">如果没有锁成功,允许动重试申请锁的最大时长</param> /// <param name="leaseTimeSpan">如果锁成功,对于锁(key)的过期时间</param> /// <param name="lockObject">锁成功信息包装成对象返回</param> /// <returns>true:成功</returns> public bool TryLock(RedisKey resource, TimeSpan waitTimeSpan, TimeSpan leaseTimeSpan, out Lock lockObject) { lockObject = null; try { var startTime = DateTime.Now; var val = CreateUniqueLockId(); //申请锁，返回还剩余的锁过期时间 var ttl = tryAcquire(resource, val, leaseTimeSpan); var drift = Convert.ToInt32((waitTimeSpan.TotalMilliseconds * ClockDriveFactor) + 2); var validity_time = waitTimeSpan - (DateTime.Now - startTime) - new TimeSpan(0, 0, 0, 0, drift); // 如果为空，表示申请锁成功 if (ttl.IsNull) { lockObject = new Lock(resource, val, validity_time); //开始一个调度程序 ScheduleExpirationRenewal(leaseTimeSpan, lockObject); return true; } // 订阅监听redis消息 Subscriber(resource); startTime = DateTime.Now; while (true) { // 再次尝试一次申请锁 ttl = tryAcquire(resource, val, leaseTimeSpan); // 获得锁，返回 if (ttl.IsNull) { lockObject = new Lock(resource, val, validity_time); ScheduleExpirationRenewal(leaseTimeSpan, lockObject); return true; } drift = Convert.ToInt32((waitTimeSpan.TotalMilliseconds * ClockDriveFactor) + 2); validity_time = waitTimeSpan - (DateTime.Now - startTime) - new TimeSpan(0, 0, 0, 0, drift); if (validity_time.TotalMilliseconds < 0) { //说明已经超过了客户端设置的最大wait time，则直接返回false，取消订阅，不再继续申请锁了。 Console.WriteLine("已经超过了客户端设置的最大wait time,Thread ID:" + Thread.CurrentThread.ManagedThreadId); return false; } } } catch (Exception) { return false; } finally { // 无论是否获得锁,都要取消订阅解锁消息 UnSubscriber(resource); } } /// <summary> /// 解锁 /// </summary> /// <param name="lockObject">锁成功的返回对象</param> /// <returns></returns> public RedisResult UnLock(Lock lockObject) { if (lockObject == null) return null; CancelExpirationRenewal(lockObject); RedisKey[] key = { lockObject.Resource, GetChannelName(lockObject.Resource) }; RedisValue[] values = { Thread.CurrentThread.ManagedThreadId, 10000, lockObject.Value }; return Server.GetDatabase().ScriptEvaluate(UN_LOCK_SCRIPT, key, values); } #endregion #region Private private void Subscriber(RedisKey resource) { Console.WriteLine("Thread ID:" + Thread.CurrentThread.ManagedThreadId + " 订阅广播"); var aa = Thread.CurrentThread.ManagedThreadId; ISubscriber sub = Server.GetSubscriber(); sub.Subscribe(GetChannelName(resource), (channel, message) => { Console.WriteLine("Thread ID:" + aa + ",收到广播:Thread ID:" + message + " 已解锁"); }); } private void UnSubscriber(RedisKey resource) { ISubscriber sub = Server.GetSubscriber(); sub.Unsubscribe(GetChannelName(resource)); } private string GetChannelName(RedisKey resource) { return "redisson_lock__channel__{" + resource.ToString() + "}"; } private RedisResult tryAcquire(RedisKey resource, string value, TimeSpan? leaseTimeSpan) { if (leaseTimeSpan != null) { return LockInnerAsync(resource, leaseTimeSpan.Value, value); } else { return LockInnerAsync(resource, value); } } private RedisResult LockInnerAsync(RedisKey resource, TimeSpan waitTime, string threadId) { RedisKey[] key = { resource }; RedisValue[] values = { waitTime.TotalMilliseconds, threadId }; return Server.GetDatabase().ScriptEvaluate(LOCK_SCRIPT, key, values); } private RedisResult LockInnerAsync(RedisKey resource, string threadId) { var task = LockInnerAsync(resource, this.LeaseTimeSpan, threadId); return task; } protected static string CreateUniqueLockId() { return string.Concat(Guid.NewGuid().ToString(), Thread.CurrentThread.ManagedThreadId); } protected void setTimeOut(ElapsedEventHandler doWork, int time) { System.Timers.Timer timer = new System.Timers.Timer(); timer.Interval = time; timer.Elapsed += delegate (object s, ElapsedEventArgs args) { timer.Stop(); }; timer.Elapsed += doWork; timer.Start(); } protected CancellationTokenSource TaskTimeOut(Func<Lock, bool> action, Lock lockObj, int time) { var timeoutCancellationTokenSource = new CancellationTokenSource(); var task = Task.Run(() => { while (!timeoutCancellationTokenSource.IsCancellationRequested) { Thread.Sleep(time); if (action(lockObj)) { Console.WriteLine("锁:" + lockObj.Value + " 重置过期时间"); } } }, timeoutCancellationTokenSource.Token); return timeoutCancellationTokenSource; } private void ScheduleExpirationRenewal(TimeSpan leaseTimeSpan, Lock lockObject) { ScheduleExpirationRenewal((lockObj) => Server.GetDatabase().KeyExpire(lockObj.Resource, leaseTimeSpan), lockObject, Convert.ToInt32(leaseTimeSpan.TotalMilliseconds) / 3); } private void ScheduleExpirationRenewal(Func<Lock, bool> action, Lock lockObj, int time) { // 保证任务不会被重复创建 if (ExpirationRenewalMap.ContainsKey(lockObj.Resource)) { return; } var task = TaskTimeOut(action, lockObj, time); //如果已经存在，停止任务，也是为了在极端的并发情况下，保证任务不会被重复创建 if (!ExpirationRenewalMap.TryAdd(lockObj.Resource, task)) { task.Cancel(); } } private void CancelExpirationRenewal(Lock lockObj) { CancellationTokenSource task; if (ExpirationRenewalMap.TryRemove(lockObj.Resource, out task)) { if (task != null) { task.Cancel(); } } } #endregion }