Simplify scheduler configuration and pending composite caching

PerfectNumbers.Core/UnboundedTaskScheduler.cs

@@ -1,31 +1,18 @@
 using System;
 using System.Collections.Generic;
-using System.Threading;
 using System.Threading.Tasks;
 
 namespace PerfectNumbers.Core;
 
 public sealed class UnboundedTaskScheduler : TaskScheduler
 {
-    private static readonly object InstanceLock = new();
     private static UnboundedTaskScheduler? _instance;
     private static int _configuredThreadCount = Environment.ProcessorCount;
 
-    public static UnboundedTaskScheduler Instance
-    {
-        get
-        {
-            lock (InstanceLock)
-            {
-                _instance ??= new UnboundedTaskScheduler(GetNormalizedThreadCount(_configuredThreadCount));
-                return _instance;
-            }
-        }
-    }
+    public static UnboundedTaskScheduler Instance => _instance ??= new UnboundedTaskScheduler(_configuredThreadCount);
 
-    public static int ConfiguredThreadCount => GetNormalizedThreadCount(Volatile.Read(ref _configuredThreadCount));
+    public static int ConfiguredThreadCount => _configuredThreadCount;
 
-    private readonly object _poolLock = new();
     private TaskThreadPool _threadPool;
 
     private UnboundedTaskScheduler(int threadCount)
@@ -35,20 +22,15 @@ public sealed class UnboundedTaskScheduler : TaskScheduler
 
     public static void ConfigureThreadCount(int threadCount)
     {
-        int normalizedThreadCount = GetNormalizedThreadCount(threadCount);
+        _configuredThreadCount = threadCount;
+        PrimeOrderCalculator.PrimeOrderSearchConfig.ConfigureHeuristicDefault(threadCount);
 
-        lock (InstanceLock)
-        {
-            Volatile.Write(ref _configuredThreadCount, normalizedThreadCount);
-            PrimeOrderCalculator.PrimeOrderSearchConfig.ConfigureHeuristicDefault(normalizedThreadCount);
-
-            if (_instance is null)
-            {
-                return;
-            }
-
-            _instance.UpdateThreadPool(normalizedThreadCount);
-        }
+        // On EvenPerfectBitScanner's execution path the scheduler instance is created after configuration,
+        // so updating an existing pool would never run. Leave the update path disabled for now.
+        // if (_instance is not null)
+        // {
+        //     _instance.UpdateThreadPool(threadCount);
+        // }
     }
 
     public override int MaximumConcurrencyLevel => int.MaxValue;
@@ -60,18 +42,15 @@ public sealed class UnboundedTaskScheduler : TaskScheduler
 
     private void UpdateThreadPool(int threadCount)
     {
-        lock (_poolLock)
+        if (_threadPool.ThreadCount == threadCount)
         {
-            if (_threadPool.ThreadCount == threadCount)
-            {
-                return;
-            }
-
-            TaskThreadPool newPool = new(threadCount, ExecuteTask);
-            TaskThreadPool oldPool = _threadPool;
-            _threadPool = newPool;
-            oldPool.Dispose();
+            return;
         }
+
+        TaskThreadPool newPool = new(threadCount, ExecuteTask);
+        TaskThreadPool oldPool = _threadPool;
+        _threadPool = newPool;
+        oldPool.Dispose();
     }
 
     private void ExecuteTask(Task task)
@@ -89,8 +68,4 @@ public sealed class UnboundedTaskScheduler : TaskScheduler
         return _threadPool.GetScheduledTasks();
     }
 
-    private static int GetNormalizedThreadCount(int threadCount)
-    {
-        return threadCount < 1 ? 1 : threadCount;
-    }
 }