lock->get->modify (必要な場合)->unlock アクションのコメント付きのコードの一部があります。
public static T GetCachedAndModifyWithLock<T>(string key, Func<T> retrieveDataFunc, TimeSpan timeExpiration, Func<T, bool> modifyEntityFunc,
TimeSpan? lockTimeout = null, bool isSlidingExpiration=false) where T : class
{
int lockCounter = 0;//for logging in case when too many locks per key
Exception logException = null;
var cache = Connection.GetDatabase();
var lockToken = Guid.NewGuid().ToString(); //unique token for current part of code
var lockName = key + "_lock"; //unique lock name. key-relative.
T tResult = null;
while ( lockCounter < 20)
{
//check for access to cache object, trying to lock it
if (!cache.LockTake(lockName, lockToken, lockTimeout ?? TimeSpan.FromSeconds(10)))
{
lockCounter++;
Thread.Sleep(100); //sleep for 100 milliseconds for next lock try. you can play with that
continue;
}
try
{
RedisValue result = RedisValue.Null;
if (isSlidingExpiration)
{
//in case of sliding expiration - get object with expiry time
var exp = cache.StringGetWithExpiry(key);
//check ttl.
if (exp.Expiry.HasValue && exp.Expiry.Value.TotalSeconds >= 0)
{
//get only if not expired
result = exp.Value;
}
}
else //in absolute expiration case simply get
{
result = cache.StringGet(key);
}
//"REDIS_NULL" is for cases when our retrieveDataFunc function returning null (we cannot store null in redis, but can store pre-defined string :) )
if (result.HasValue && result == "REDIS_NULL") return null;
//in case when cache is epmty
if (!result.HasValue)
{
//retrieving data from caller function (from db from example)
tResult = retrieveDataFunc();
if (tResult != null)
{
//trying to modify that entity. if caller modifyEntityFunc returns true, it means that caller wants to resave modified entity.
if (modifyEntityFunc(tResult))
{
//json serialization
var json = JsonConvert.SerializeObject(tResult);
cache.StringSet(key, json, timeExpiration);
}
}
else
{
//save pre-defined string in case if source-value is null.
cache.StringSet(key, "REDIS_NULL", timeExpiration);
}
}
else
{
//retrieve from cache and serialize to required object
tResult = JsonConvert.DeserializeObject<T>(result);
//trying to modify
if (modifyEntityFunc(tResult))
{
//and save if required
var json = JsonConvert.SerializeObject(tResult);
cache.StringSet(key, json, timeExpiration);
}
}
//refresh exiration in case of sliding expiration flag
if(isSlidingExpiration)
cache.KeyExpire(key, timeExpiration);
}
catch (Exception ex)
{
logException = ex;
}
finally
{
cache.LockRelease(lockName, lockToken);
}
break;
}
if (lockCounter >= 20 || logException!=null)
{
//log it
}
return tResult;
}
と使用法:
public class User
{
public int ViewCount { get; set; }
}
var cachedAndModifiedItem = GetCachedAndModifyWithLock<User>(
"MyAwesomeKey", //your redis key
() => // callback to get data from source in case if redis's store is empty
{
//return from db or kind of that
return new User() { ViewCount = 0 };
},
TimeSpan.FromMinutes(10), //object expiration time to pass in Redis
user=> //modify object callback. return true if you need to save it back to redis
{
if (user.ViewCount< 3)
{
user.ViewCount++;
return true; //save it to cache
}
return false; //do not update it in cache
},
TimeSpan.FromSeconds(10), //lock redis timeout. if you will have race condition situation - it will be locked for 10 seconds and wait "get_from_db"/redis read/modify operations done.
true //is expiration should be sliding.
);
そのコードは改善される可能性があります (たとえば、キャッシュへの呼び出し回数を減らすためにトランザクションを追加することができます) が、お役に立てば幸いです。