public RedisLock(RedisClient redisClient, string key, TimeSpan?timeOut)
{
this.redisClient = redisClient;
this.key = key;
ExecExtensions.RetryUntilTrue(
() =>
{
//This pattern is taken from the redis command for SETNX http://redis.io/commands/setnx
//Calculate a unix time for when the lock should expire
TimeSpan realSpan = timeOut ?? new TimeSpan(365, 0, 0, 0); //if nothing is passed in the timeout hold for a year
DateTime expireTime = DateTime.UtcNow.Add(realSpan);
string lockString = (expireTime.ToUnixTimeMs() + 1).ToString();
//Try to set the lock, if it does not exist this will succeed and the lock is obtained
var nx = redisClient.SetEntryIfNotExists(key, lockString);
if (nx)
{
return(true);
}
//If we've gotten here then a key for the lock is present. This could be because the lock is
//correctly acquired or it could be because a client that had acquired the lock crashed (or didn't release it properly).
//Therefore we need to get the value of the lock to see when it should expire
string lockExpireString = redisClient.Get <string>(key);
long lockExpireTime;
if (!long.TryParse(lockExpireString, out lockExpireTime))
{
return(false);
}
//If the expire time is greater than the current time then we can't let the lock go yet
if (lockExpireTime > DateTime.UtcNow.ToUnixTimeMs())
{
return(false);
}
//If the expire time is less than the current time then it wasn't released properly and we can attempt to
//acquire the lock. This is done by setting the lock to our timeout string AND checking to make sure
//that what is returned is the old timeout string in order to account for a possible race condition.
return(redisClient.GetAndSetEntry(key, lockString) == lockExpireString);
},
timeOut
);
}
public RedisLock(RedisClient redisClient, string key, TimeSpan? timeOut)
{
this.redisClient = redisClient;
this.key = key;
ExecExtensions.RetryUntilTrue(
() =>
{
//This pattern is taken from the redis command for SETNX http://redis.io/commands/setnx
//Calculate a unix time for when the lock should expire
TimeSpan realSpan = timeOut ?? new TimeSpan(365, 0, 0, 0); //if nothing is passed in the timeout hold for a year
DateTime expireTime = DateTime.UtcNow.Add(realSpan);
string lockString = (expireTime.ToUnixTimeMs() + 1).ToString();
//Try to set the lock, if it does not exist this will succeed and the lock is obtained
var nx = redisClient.SetEntryIfNotExists(key, lockString);
if (nx)
return true;
//If we've gotten here then a key for the lock is present. This could be because the lock is
//correctly acquired or it could be because a client that had acquired the lock crashed (or didn't release it properly).
//Therefore we need to get the value of the lock to see when it should expire
string lockExpireString = redisClient.Get<string>(key);
long lockExpireTime;
if (!long.TryParse(lockExpireString, out lockExpireTime))
return false;
//If the expire time is greater than the current time then we can't let the lock go yet
if (lockExpireTime > DateTime.UtcNow.ToUnixTimeMs())
return false;
//If the expire time is less than the current time then it wasn't released properly and we can attempt to
//acquire the lock. This is done by setting the lock to our timeout string AND checking to make sure
//that what is returned is the old timeout string in order to account for a possible race condition.
return redisClient.GetAndSetEntry(key, lockString) == lockExpireString;
},
timeOut
);
}
