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namespace DigitalRuby.SimpleCache;
/// <summary>
/// Distributed cache item
/// </summary>
public readonly struct DistributedCacheItem
{
/// <summary>
/// The item bytes or null if no item found
/// </summary>
public byte[]? Bytes { get; init; }
/// <summary>
/// The item expiration relative to now or null if none
/// </summary>
public TimeSpan? Expiry { get; init; }
/// <summary>
/// Whether there is an item
/// </summary>
[MemberNotNullWhen(true, nameof(Bytes))]
[MemberNotNullWhen(true, nameof(Expiry))]
public bool HasValue => Bytes is not null && Expiry is not null;
}
/// <summary>
/// Distributed cache interface
/// </summary>
public interface IDistributedCache
{
/// <summary>
/// Attempt to get an item from the cache
/// </summary>
/// <param name="key">Key</param>
/// <param name="cancelToken">Cancel token</param>
/// <returns>Task that returns the item</returns>
Task<DistributedCacheItem> GetAsync(string key, CancellationToken cancelToken = default);
/// <summary>
/// Set an item in the cache
/// </summary>
/// <param name="key">Key</param>
/// <param name="item">Item</param>
/// <param name="cancelToken">Cancel token</param>
/// <returns>Task</returns>
Task SetAsync(string key, DistributedCacheItem item, CancellationToken cancelToken = default);
/// <summary>
/// Delete an item from the cache
/// </summary>
/// <param name="key">Key</param>
/// <param name="cancelToken">Cancel token</param>
/// <returns>Task</returns>
Task DeleteAsync(string key, CancellationToken cancelToken = default);
/// <summary>
/// Key change event, get notified if a key changes outside of this machine
/// </summary>
event Action<string>? KeyChanged;
}
/// <summary>
/// Null distributed cache that no-ops everything
/// </summary>
public sealed class NullDistributedCache : IDistributedCache, IDistributedLockFactory
{
#pragma warning disable CS0067 // never used
/// <inheritdoc />
public event Action<string>? KeyChanged;
#pragma warning restore
/// <inheritdoc />
public Task DeleteAsync(string key, CancellationToken cancelToken = default)
{
return Task.CompletedTask;
}
/// <inheritdoc />
public Task<DistributedCacheItem> GetAsync(string key, CancellationToken cancelToken = default)
{
return Task.FromResult<DistributedCacheItem>(new DistributedCacheItem());
}
/// <inheritdoc />
public Task SetAsync(string key, DistributedCacheItem item, CancellationToken cancelToken = default)
{
return Task.CompletedTask;
}
/// <inheritdoc />
public Task<IAsyncDisposable?> TryAcquireLockAsync(string key, TimeSpan lockTime, TimeSpan timeout, CancellationToken cancelToken)
{
return Task.FromResult<IAsyncDisposable?>(new DistributedMemoryCache.FakeDistributedLock());
}
}
/// <summary>
/// Distributed cache but all in memory (for testing)
/// </summary>
/// <remarks>
/// Constructor
/// </remarks>
/// <param name="clock">Clock</param>
public sealed class DistributedMemoryCache(TimeProvider clock) : IDistributedCache, IDistributedLockFactory
{
private readonly TimeProvider clock = clock;
internal sealed class FakeDistributedLock : IAsyncDisposable
{
public ValueTask DisposeAsync()
{
return new();
}
}
private readonly ConcurrentDictionary<string, (DateTimeOffset, byte[])> items = new();
/// <inheritdoc />
public event Action<string>? KeyChanged;
/// <inheritdoc />
public Task DeleteAsync(string key, CancellationToken cancelToken = default)
{
if (items.TryRemove(key, out _))
{
KeyChanged?.Invoke(key);
}
return Task.CompletedTask;
}
/// <inheritdoc />
public Task<DistributedCacheItem> GetAsync(string key, CancellationToken cancelToken = default)
{
if (items.TryGetValue(key, out var item) && item.Item1 > clock.GetUtcNow())
{
return Task.FromResult(new DistributedCacheItem { Bytes = item.Item2, Expiry = item.Item1 - clock.GetUtcNow() });
}
return Task.FromResult<DistributedCacheItem>(default);
}
/// <inheritdoc />
public Task SetAsync(string key, DistributedCacheItem item, CancellationToken cancelToken = default)
{
if (item.Bytes is not null)
{
DateTimeOffset expire = clock.GetUtcNow() + item.Expiry ?? throw new ArgumentException("Null expiry not allowed");
items[key] = new(expire, item.Bytes);
}
return Task.CompletedTask;
}
/// <inheritdoc />
public Task<IAsyncDisposable?> TryAcquireLockAsync(string key, TimeSpan lockTime, TimeSpan timeout, CancellationToken cancelToken)
{
if (items.TryAdd(key, new()))
{
return Task.FromResult<IAsyncDisposable?>(new FakeDistributedLock());
}
return Task.FromResult<IAsyncDisposable?>(null);
}
}
/// <summary>
/// Distributed redis cache
/// </summary>
public sealed class DistributedRedisCache : BackgroundService, IDistributedCache, IDistributedLockFactory
{
private static readonly TimeSpan oneMinute = TimeSpan.FromMinutes(1.0);
private readonly IConnectionMultiplexer connectionMultiplexer;
private readonly string keyPrefix;
private readonly ILogger<DistributedRedisCache> logger;
private ISubscriber? changeQueue;
/// <summary>
/// Constructor
/// </summary>
/// <param name="options">Options</param>
/// <param name="connectionMultiplexer">Connection multiplexer</param>
/// <param name="logger">Logger</param>
public DistributedRedisCache(DistributedRedisCacheOptions options,
IConnectionMultiplexer connectionMultiplexer,
ILogger<DistributedRedisCache> logger)
{
this.keyPrefix = string.IsNullOrWhiteSpace(options.KeyPrefix) ? string.Empty : options.KeyPrefix + ":";
this.connectionMultiplexer = connectionMultiplexer;
this.logger = logger;
// if we get a connection multiplexer that hasn't connected properly, log an error
if (!connectionMultiplexer.IsConnected)
{
logger.LogError("Connection multiplexer has failed to connect");
}
}
/// <inheritdoc />
public Task DeleteAsync(string key, CancellationToken cancelToken = default)
{
return PerformOperation(async () =>
{
await connectionMultiplexer.GetDatabase().KeyDeleteAsync(key);
logger.LogDebug("Redis cache deleted {key}", key);
return true;
});
}
/// <inheritdoc />
public Task<DistributedCacheItem> GetAsync(string key, CancellationToken cancelToken = default)
{
return PerformOperation(async () =>
{
var item = await connectionMultiplexer.GetDatabase().StringGetWithExpiryAsync(key);
if (item.Value.HasValue)
{
logger.LogDebug("Redis cache hit {key}", key);
return new DistributedCacheItem { Bytes = item.Value, Expiry = item.Expiry };
}
logger.LogDebug("Redis cache miss {key}", key);
return default;
});
}
/// <inheritdoc />
public Task SetAsync(string key, DistributedCacheItem item, CancellationToken cancelToken = default)
{
if (!item.HasValue)
{
throw new ArgumentException("Cannot add a null item or null expiration to redis cache, key: " + key);
}
return PerformOperation(async () =>
{
await connectionMultiplexer.GetDatabase().StringSetAsync(key, item.Bytes, expiry: item.Expiry);
logger.LogDebug("Redis cache set {key}", key);
return true;
});
}
/// <inheritdoc />
public event Action<string>? KeyChanged;
private async Task<T?> PerformOperation<T>(Func<Task<T>> operation)
{
T? returnValue = default;
await PerformOperationInternal(async () => returnValue = await operation());
return returnValue;
}
private async Task PerformOperationInternal(Func<Task> operation)
{
try
{
await operation();
}
catch (RedisCommandException ex)
{
// handle replica going down and then coming back alive
if (ex.Message.Contains("replica", StringComparison.OrdinalIgnoreCase))
{
logger.LogError(ex, "Command failure on replica, re-init connection multiplexer and trying again...");
connectionMultiplexer.Configure();
RegisterChangeQueue();
await operation();
return;
}
// some other error, fail
throw;
}
}
private void RegisterChangeQueue()
{
try
{
const string keyspace = "__keyspace@0__:";
var queue = changeQueue;
changeQueue = null;
queue?.UnsubscribeAll();
var namespaceForSubscribe = $"{keyspace}{keyPrefix}*";
var namespaceForSubscribeFlushAll = $"{keyspace}__flushall__*";
queue = connectionMultiplexer.GetSubscriber();
#pragma warning disable CS0618 // Type or member is obsolete
queue.Subscribe(namespaceForSubscribe, (channel, value) =>
{
string key = channel.ToString()[keyspace.Length..];
KeyChanged?.Invoke(key);
});
queue.Subscribe(namespaceForSubscribeFlushAll, (channel, value) =>
{
if (value == "set")
{
string key = channel.ToString()[keyspace.Length..];
KeyChanged?.Invoke(key);
}
});
#pragma warning restore CS0618 // Type or member is obsolete
changeQueue = queue;
}
catch (Exception ex)
{
logger.LogError(ex, "Error registering change queue");
}
}
private class DistributedLock(IConnectionMultiplexer connection, string lockKey, string lockToken) : IAsyncDisposable
{
private readonly IConnectionMultiplexer connection = connection;
private readonly string lockKey = lockKey;
private readonly string lockToken = lockToken;
public async ValueTask DisposeAsync()
{
await connection.GetDatabase().LockReleaseAsync(lockKey, lockToken);
}
}
private static readonly TimeSpan distributedLockSleepTime = TimeSpan.FromMilliseconds(100.0);
/// <inheritdoc />
public async Task<IAsyncDisposable?> TryAcquireLockAsync(string key, TimeSpan lockTime, TimeSpan timeout, CancellationToken cancelToken)
{
var db = connectionMultiplexer.GetDatabase();
Stopwatch timer = Stopwatch.StartNew();
string lockKey = "DistributedLock_" + key;
string lockToken = Guid.NewGuid().ToString("N");
lockTime = lockTime.Ticks == 0 ? oneMinute : lockTime;
do
{
if (await db.LockTakeAsync(lockKey, lockToken, lockTime))
{
logger.LogDebug("Acquired redis cache distributed lock {lockKey}", lockKey);
return new DistributedLock(connectionMultiplexer, lockKey, lockToken);
}
if (timeout > distributedLockSleepTime)
{
await Task.Delay(distributedLockSleepTime, cancelToken);
}
}
while (!cancelToken.IsCancellationRequested && timer.Elapsed < timeout);
return null;
}
/// <inheritdoc />
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
while (!stoppingToken.IsCancellationRequested)
{
// make sure pub/sub is up
if (changeQueue is null)
{
RegisterChangeQueue();
}
await Task.Delay(10000, stoppingToken);
}
}
}
/// <summary>
/// Distributed redis cache options
/// </summary>
public sealed class DistributedRedisCacheOptions
{
/// <summary>
/// Key prefix
/// </summary>
public string KeyPrefix { get; set; } = string.Empty;
}
/// <summary>
/// Interface for distributed locks
/// </summary>
public interface IDistributedLockFactory
{
/// <summary>
/// Attempt to acquire a distributed lock
/// </summary>
/// <param name="key">Lock key</param>
/// <param name="lockTime">Duration to hold the lock before it auto-expires. Set this to the maximum possible duration you think your code might hold the lock. Default is 1 minute.</param>
/// <param name="timeout">Time out to acquire the lock or default to only make one attempt to acquire the lock</param>
/// <param name="cancelToken">Cancel token</param>
/// <returns>The lock or null if the lock could not be acquired</returns>
Task<IAsyncDisposable?> TryAcquireLockAsync(string key, TimeSpan lockTime = default, TimeSpan timeout = default, CancellationToken cancelToken = default);
}
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