Replace cache lockers with production-ready sp_getapplock and SETNX implementations

src/ActionCache.csproj

@@ -52,6 +52,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.Azure.Cosmos" Version="3.46.1" />
+    <PackageReference Include="Microsoft.Data.SqlClient" Version="5.2.2" />
     <PackageReference Include="Microsoft.Extensions.Caching.StackExchangeRedis" Version="$(_TargetVersion)" />
     <PackageReference Include="Microsoft.Extensions.Caching.SqlServer" Version="$(_TargetVersion)" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />

src/Common/Concurrency/Locks/NullCacheLock.cs

@@ -12,5 +12,6 @@ public class NullCacheLock : CacheLock
     /// <param name="resource">The resource name associated with this lock.</param>
     public NullCacheLock(string resource) : base(resource)
     {
+        IsAcquired = true;
     }
 }

src/Memory/Extensions/Internal/IMemoryCacheExtensions.cs

@@ -59,7 +59,7 @@ internal static void SetKey(this IMemoryCache cache, Namespace @namespace, strin
         var keys = cache.GetKeys(@namespace, entryOptions);
         if (keys.TryAdd(key, entryOptions.AbsoluteExpiration))
         {
-            cache.Set(key, keys, entryOptions);
+            cache.Set(@namespace, keys, entryOptions);
         }
     }
 

src/Memory/MemoryActionCache.cs

@@ -1,5 +1,5 @@
 using ActionCache.Common.Caching;
-using ActionCache.Common.Concurrency;
+using ActionCache.Common.Concurrency.Locks;
 using ActionCache.Memory.Extensions.Internal;
 using ActionCache.Utilities;
 using Microsoft.Extensions.Caching.Memory;
@@ -10,7 +10,7 @@
 /// <summary>
 /// Represents a memory action cache implementation.
 /// </summary>
-public class MemoryActionCache : ActionCacheBase<SemaphoreSlimLock>
+public class MemoryActionCache : ActionCacheBase<NullCacheLock>
 {
     /// <summary>
     /// A memory cache implementation.
@@ -31,7 +31,7 @@
     public MemoryActionCache(
         IMemoryCache cache,
         CancellationTokenSource cancellationTokenSource,
-        ActionCacheContext<SemaphoreSlimLock> context
+        ActionCacheContext<NullCacheLock> context
     ) : base(context)
     {
         Cache = cache;
@@ -55,15 +55,15 @@
     /// </summary>
     /// <param name="key">The key of the cache entry.</param>
     /// <returns>The cached value or null if not found.</returns> 
     public override Task<TValue> GetAsync<TValue>(string key) =>
         Task.FromResult(Cache.Get<TValue>(Namespace.Create(key)));
 
     /// <summary>
     /// Asynchronously sets a value in the cache.
     /// </summary>
     /// <param name="key">The cache key to set the value for.</param>
     /// <param name="value">The value to set in the cache.</param>
     public override Task SetAsync<TValue>(string key, TValue value)
     {
         var entryOptions = CreateEntryOptions();
         Cache.Set(Namespace.Create(key), value, entryOptions);

src/Memory/MemoryActionCacheFactory.cs

@@ -1,6 +1,7 @@
 using ActionCache.Common;
 using ActionCache.Common.Caching;
 using ActionCache.Common.Concurrency;
+using ActionCache.Common.Concurrency.Locks;
 using ActionCache.Utilities;
 using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.Options;
@@ -45,15 +46,12 @@ IActionCacheRefreshProvider refreshProvider
     {
         if (ExpirationTokens.TryGetOrAdd(@namespace, out var expirationTokenSource))
         {
-            var context = new ActionCacheContext<SemaphoreSlimLock>
+            var context = new ActionCacheContext<NullCacheLock>
             {
                 Namespace = @namespace,
                 EntryOptions = EntryOptions,
                 RefreshProvider = RefreshProvider,
-                CacheLocker = new SemaphoreSlimLocker(
-                    EntryOptions.LockDuration, 
-                    EntryOptions.LockTimeout
-                )
+                CacheLocker = new NullCacheLocker()
             };
 
             return new MemoryActionCache(Cache, expirationTokenSource, context);
@@ -69,7 +67,7 @@ IActionCacheRefreshProvider refreshProvider
     {
         if (ExpirationTokens.TryGetOrAdd(@namespace, out var expirationTokenSource))
         {
-            var context = new ActionCacheContext<SemaphoreSlimLock>
+            var context = new ActionCacheContext<NullCacheLock>
             {
                 Namespace = @namespace,
                 EntryOptions = new ActionCacheEntryOptions
@@ -78,10 +76,7 @@ IActionCacheRefreshProvider refreshProvider
                     SlidingExpiration = slidingExpiration
                 },
                 RefreshProvider = RefreshProvider,
-                CacheLocker = new SemaphoreSlimLocker(
-                    EntryOptions.LockDuration, 
-                    EntryOptions.LockTimeout
-                )
+                CacheLocker = new NullCacheLocker()
             };
 
             return new MemoryActionCache(Cache, expirationTokenSource, context);

src/Redis/Concurrency/Locks/RedisCacheLock.cs

@@ -0,0 +1,31 @@
+using ActionCache.Common.Concurrency;
+
+namespace ActionCache.Redis.Concurrency.Locks;
+
+/// <summary>
+/// Represents a Redis-backed distributed lock acquired via SET NX PX.
+/// Holds the lock key and a unique fencing token used by the release script
+/// to ensure only the owner can release the lock.
+/// </summary>
+public class RedisCacheLock : CacheLock
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="RedisCacheLock"/> class.
+    /// </summary>
+    /// <param name="resource">The logical resource being locked (used to build <see cref="Key"/>).</param>
+    /// <param name="lockDuration">How long the lock is held in Redis (TTL on the key).</param>
+    /// <param name="lockTimeout">Maximum time the locker will poll before giving up.</param>
+    public RedisCacheLock(string resource, TimeSpan lockDuration, TimeSpan lockTimeout) : base(resource)
+    {
+        Duration = lockDuration;
+        Timeout = lockTimeout;
+        Key = $"Lock:{resource}";
+        Token = Guid.NewGuid().ToString("N");
+    }
+
+    /// <summary>Redis key under which the lock is stored.</summary>
+    public string Key { get; }
+
+    /// <summary>Unique fencing token stored as the Redis value; used by the release script.</summary>
+    public string Token { get; }
+}