/// <summary>
/// Add/update an entry in the cache
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="key">Key used to locate value in the cache</param>
/// <param name="value"></param>
/// <param name="ttl"></param>
public void Set <T>(string key, T value, TimeSpan ttl)
{
// parameter validation
if (string.IsNullOrWhiteSpace(key))
{
throw new ArgumentNullException(nameof(key));
}
if (value == null)
{
throw new ArgumentNullException(nameof(value));
}
if (ttl.TotalSeconds < 1)
{
throw new ArgumentNullException(nameof(ttl));
}
// Get the current timestamp before we do anything else. Decrement it by one so any sync messages processed during
// this method call will force an immediate expiration of the key's hash slot
var timestamp = Stopwatch.GetTimestamp() - 1;
var keyHashSlot = HashSlotCalculator.CalculateHashSlot(key);
byte[] serializedData = null;
// Serialize the data and write to Redis
using (MemoryStream ms = new MemoryStream())
{
_serializationProvider.Serialize <T>(ms, value);
serializedData = ms.ToArray();
}
// Execute the Redis SET and PUBLISH operations in one round trip using Lua
// (Could use StackExchange.Redis batch here, instead)
string luaScript = @"
redis.call('SET', KEYS[1], ARGV[1], 'EX', ARGV[2])
redis.call('PUBLISH', ARGV[3], ARGV[4])
";
var scriptArgs = new RedisValue[4];
scriptArgs[0] = serializedData;
scriptArgs[1] = ttl.TotalSeconds;
scriptArgs[2] = SYNC_CHANNEL_NAME;
scriptArgs[3] = DataSyncMessage.Create(_instanceId, keyHashSlot).Serialize();
_redisDb.ScriptEvaluate(luaScript, new RedisKey[] { key }, scriptArgs);
// Update the in-process cache
_inProcessCache.Set(key, new LocalCacheEntry <T>(keyHashSlot, timestamp, value), DateTimeOffset.UtcNow.Add(ttl));
}
/// <summary>
/// Message handler for hash key invalidation messages
/// </summary>
/// <param name="channel">Redis pub/sub channel name</param>
/// <param name="message">Pub/sub message</param>
private void DataSynchronizationMessageHandler(RedisChannel channel, RedisValue message)
{
// Early out, if channel name doesn't match our sync channel
if (string.Compare(channel, SYNC_CHANNEL_NAME, StringComparison.InvariantCultureIgnoreCase) != 0)
{
return;
}
// otherwise, deserialize the message
var dataSyncMessage = DataSyncMessage.Deserialize(message);
// and update the appropriate _lastUpdated element with the current timestamp
// Invalidate.Exchange() would make more sense here, but the lock statement
// makes the purpose more evident for an example
lock (_lastUpdated)
{
_lastUpdated[dataSyncMessage.KeyHashSlot] = Stopwatch.GetTimestamp();
}
}