perf(runtime): remove callback count allocation

Author: ReubenBond

src/Orleans.Core/Messaging/StripedCallbackDictionary.cs

@@ -113,6 +113,12 @@ public int Count
     /// Counts items matching a predicate across all stripes.
     /// </summary>
     public int CountWhere(Func<TValue, bool> predicate)
+        => CountWhere(predicate, static (value, predicate) => predicate(value));
+
+    /// <summary>
+    /// Counts items matching a predicate across all stripes.
+    /// </summary>
+    public int CountWhere<TState>(TState state, Func<TValue, TState, bool> predicate)
     {
         int count = 0;
         foreach (var stripe in _stripes)
@@ -121,7 +127,7 @@ public int CountWhere(Func<TValue, bool> predicate)
             {
                 foreach (var value in stripe.Dictionary.Values)
                 {
-                    if (predicate(value))
+                    if (predicate(value, state))
                     {
                         count++;
                     }

src/Orleans.Runtime/Core/InsideRuntimeClient.cs

@@ -616,7 +616,9 @@ public void Participate(ISiloLifecycle lifecycle)
         }
 
         public int GetRunningRequestsCount(GrainInterfaceType grainInterfaceType)
-            => this.callbacks.CountWhere(c => c.Message.InterfaceType == grainInterfaceType);
+            => this.callbacks.CountWhere(
+                grainInterfaceType,
+                static (callback, grainInterfaceType) => callback.Message.InterfaceType == grainInterfaceType);
 
         private async Task MonitorCallbackExpiry()
         {

test/Orleans.Runtime.Tests/StripedCallbackDictionaryTests.cs

@@ -9,6 +9,7 @@ namespace Tester;
 public class StripedCallbackDictionaryTests
 {
     private static readonly Action<int, object?> EmptyVisitor = static (_, _) => { };
+    private static readonly Func<int, int, bool> MatchValue = static (value, expected) => value == expected;
 
     [Fact]
     public void CorrelationIdsDistributeAcrossStripesAtOverflowAndWithStride()
@@ -142,4 +143,19 @@ public void EmptyVisitorDoesNotAllocate()
 
         Assert.Equal(0, allocated);
     }
+
+    [Fact]
+    public void StatefulCountDoesNotAllocate()
+    {
+        var dictionary = new StripedCallbackDictionary<int>();
+        Assert.True(dictionary.TryAdd(new CorrelationId(42), 42));
+        Assert.Equal(1, dictionary.CountWhere(42, MatchValue));
+
+        var allocatedBefore = GC.GetAllocatedBytesForCurrentThread();
+        var count = dictionary.CountWhere(42, MatchValue);
+        var allocated = GC.GetAllocatedBytesForCurrentThread() - allocatedBefore;
+
+        Assert.Equal(1, count);
+        Assert.Equal(0, allocated);
+    }
 }