HybridCache : implement the tag expiration feature

eng/MSBuild/LegacySupport.props

@@ -23,7 +23,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)\..\..\src\LegacySupport\CallerAttributes\*.cs" LinkBase="LegacySupport\CallerAttributes" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(InjectSkipLocalsInitAttributeOnLegacy)' == 'true' AND ('$(TargetFramework)' == 'net462' or '$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'netcoreapp3.1')">
+  <ItemGroup Condition="'$(InjectSkipLocalsInitAttributeOnLegacy)' == 'true' AND ('$(TargetFramework)' == 'net462' or '$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'netstandard2.1' or '$(TargetFramework)' == 'netcoreapp3.1')">
     <Compile Include="$(MSBuildThisFileDirectory)\..\..\src\LegacySupport\SkipLocalsInitAttribute\*.cs" LinkBase="LegacySupport\SkipLocalsInitAttribute" />
   </ItemGroup>
 

src/Libraries/Microsoft.Extensions.Caching.Hybrid/Internal/BufferChunk.cs

@@ -15,20 +15,23 @@ namespace Microsoft.Extensions.Caching.Hybrid.Internal;
 internal readonly struct BufferChunk
 {
     private const int FlagReturnToPool = (1 << 31);
-
     private readonly int _lengthAndPoolFlag;
 
-    public byte[]? Array { get; } // null for default
+    public byte[]? OversizedArray { get; } // null for default
+
+    public bool HasValue => OversizedArray is not null;
 
+    public int Offset { get; }
     public int Length => _lengthAndPoolFlag & ~FlagReturnToPool;
 
     public bool ReturnToPool => (_lengthAndPoolFlag & FlagReturnToPool) != 0;
 
     public BufferChunk(byte[] array)
     {
         Debug.Assert(array is not null, "expected valid array input");
-        Array = array;
+        OversizedArray = array;
         _lengthAndPoolFlag = array!.Length;
+        Offset = 0;
 
         // assume not pooled, if exact-sized
         // (we don't expect array.Length to be negative; we're really just saying
@@ -39,11 +42,12 @@ public BufferChunk(byte[] array)
         Debug.Assert(Length == array.Length, "array length not respected");
     }
 
-    public BufferChunk(byte[] array, int length, bool returnToPool)
+    public BufferChunk(byte[] array, int offset, int length, bool returnToPool)
     {
         Debug.Assert(array is not null, "expected valid array input");
         Debug.Assert(length >= 0, "expected valid length");
-        Array = array;
+        OversizedArray = array;
+        Offset = offset;
         _lengthAndPoolFlag = length | (returnToPool ? FlagReturnToPool : 0);
         Debug.Assert(ReturnToPool == returnToPool, "return-to-pool not respected");
         Debug.Assert(Length == length, "length not respected");
@@ -58,7 +62,7 @@ public byte[] ToArray()
         }
 
         var copy = new byte[length];
-        Buffer.BlockCopy(Array!, 0, copy, 0, length);
+        Buffer.BlockCopy(OversizedArray!, Offset, copy, 0, length);
         return copy;
 
         // Note on nullability of Array; the usage here is that a non-null array
@@ -73,15 +77,19 @@ internal void RecycleIfAppropriate()
     {
         if (ReturnToPool)
         {
-            ArrayPool<byte>.Shared.Return(Array!);
+            ArrayPool<byte>.Shared.Return(OversizedArray!);
         }
 
         Unsafe.AsRef(in this) = default; // anti foot-shotgun double-return guard; not 100%, but worth doing
-        Debug.Assert(Array is null && !ReturnToPool, "expected clean slate after recycle");
+        Debug.Assert(OversizedArray is null && !ReturnToPool, "expected clean slate after recycle");
     }
 
+    internal ArraySegment<byte> AsArraySegment() => Length == 0 ? default! : new(OversizedArray!, Offset, Length);
+
+    internal ReadOnlySpan<byte> AsSpan() => Length == 0 ? default : new(OversizedArray!, Offset, Length);
+
     // get the data as a ROS; for note on null-logic of Array!, see comment in ToArray
-    internal ReadOnlySequence<byte> AsSequence() => Length == 0 ? default : new ReadOnlySequence<byte>(Array!, 0, Length);
+    internal ReadOnlySequence<byte> AsSequence() => Length == 0 ? default : new ReadOnlySequence<byte>(OversizedArray!, Offset, Length);
 
     internal BufferChunk DoNotReturnToPool()
     {

src/Libraries/Microsoft.Extensions.Caching.Hybrid/Internal/DefaultHybridCache.CacheItem.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Diagnostics;
+using System.Runtime.CompilerServices;
 using System.Threading;
 using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.Logging;
@@ -13,10 +14,22 @@ internal partial class DefaultHybridCache
 {
     internal abstract class CacheItem
     {
+        private readonly long _creationTimestamp;
+
+        protected CacheItem(long creationTimestamp, TagSet tags)
+        {
+            Tags = tags;
+            _creationTimestamp = creationTimestamp;
+        }
+
         private int _refCount = 1; // the number of pending operations against this cache item
 
         public abstract bool DebugIsImmutable { get; }
 
+        public long CreationTimestamp => _creationTimestamp;
+
+        public TagSet Tags { get; }
+
         // Note: the ref count is the number of callers anticipating this value at any given time. Initially,
         // it is one for a simple "get the value" flow, but if another call joins with us, it'll be incremented.
         // If either cancels, it will get decremented, with the entire flow being cancelled if it ever becomes
@@ -27,6 +40,9 @@ internal abstract class CacheItem
 
         internal int RefCount => Volatile.Read(ref _refCount);
 
+        internal void UnsafeSetCreationTimestamp(long timestamp)
+            => Unsafe.AsRef(in _creationTimestamp) = timestamp;
+
         internal static readonly PostEvictionDelegate SharedOnEviction = static (key, value, reason, state) =>
         {
             if (value is CacheItem item)
@@ -88,6 +104,11 @@ protected virtual void OnFinalRelease() // any required release semantics
 
     internal abstract class CacheItem<T> : CacheItem
     {
+        protected CacheItem(long creationTimestamp, TagSet tags)
+            : base(creationTimestamp, tags)
+        {
+        }
+
         public abstract bool TryGetSize(out long size);
 
         // Attempt to get a value that was *not* previously reserved.
@@ -112,6 +133,7 @@ public T GetReservedValue(ILogger log)
             static void Throw() => throw new ObjectDisposedException("The cache item has been recycled before the value was obtained");
         }
 
-        internal static CacheItem<T> Create() => ImmutableTypeCache<T>.IsImmutable ? new ImmutableCacheItem<T>() : new MutableCacheItem<T>();
+        internal static CacheItem<T> Create(long creationTimestamp, TagSet tags) => ImmutableTypeCache<T>.IsImmutable
+            ? new ImmutableCacheItem<T>(creationTimestamp, tags) : new MutableCacheItem<T>(creationTimestamp, tags);
     }
 }

src/Libraries/Microsoft.Extensions.Caching.Hybrid/Internal/DefaultHybridCache.Debug.cs

@@ -47,14 +47,13 @@ internal void DebugOnlyIncrementOutstandingBuffers()
     }
 #endif
 
-    private partial class MutableCacheItem<T>
+    internal partial class MutableCacheItem<T>
     {
 #if DEBUG
         private DefaultHybridCache? _cache; // for buffer-tracking - only needed in DEBUG
 #endif
 
         [Conditional("DEBUG")]
-        [SuppressMessage("Performance", "CA1822:Mark members as static", Justification = "Instance state used in debug")]
         internal void DebugOnlyTrackBuffer(DefaultHybridCache cache)
         {
 #if DEBUG
@@ -63,18 +62,21 @@ internal void DebugOnlyTrackBuffer(DefaultHybridCache cache)
             {
                 _cache?.DebugOnlyIncrementOutstandingBuffers();
             }
+#else
+            _ = this; // dummy just to prevent CA1822, never hit
 #endif
         }
 
         [Conditional("DEBUG")]
-        [SuppressMessage("Performance", "CA1822:Mark members as static", Justification = "Instance state used in debug")]
         private void DebugOnlyDecrementOutstandingBuffers()
         {
 #if DEBUG
             if (_buffer.ReturnToPool)
             {
                 _cache?.DebugOnlyDecrementOutstandingBuffers();
             }
+#else
+            _ = this; // dummy just to prevent CA1822, never hit
 #endif
         }
     }

src/Libraries/Microsoft.Extensions.Caching.Hybrid/Internal/DefaultHybridCache.ImmutableCacheItem.cs

@@ -8,10 +8,15 @@ namespace Microsoft.Extensions.Caching.Hybrid.Internal;
 
 internal partial class DefaultHybridCache
 {
-    private sealed class ImmutableCacheItem<T> : CacheItem<T> // used to hold types that do not require defensive copies
+    internal sealed class ImmutableCacheItem<T> : CacheItem<T> // used to hold types that do not require defensive copies
     {
         private static ImmutableCacheItem<T>? _sharedDefault;
 
+        public ImmutableCacheItem(long creationTimestamp, TagSet tags)
+            : base(creationTimestamp, tags)
+        {
+        }
+
         private T _value = default!; // deferred until SetValue
 
         public long Size { get; private set; } = -1;
@@ -25,7 +30,7 @@ public static ImmutableCacheItem<T> GetReservedShared()
             ImmutableCacheItem<T>? obj = Volatile.Read(ref _sharedDefault);
             if (obj is null || !obj.TryReserve())
             {
-                obj = new();
+                obj = new(0, TagSet.Empty); // timestamp doesn't matter - not used in L1/L2
                 _ = obj.TryReserve(); // this is reliable on a new instance
                 Volatile.Write(ref _sharedDefault, obj);
             }