Pools renamed to FixedCapacityPools. Other fixed capacity collections added. Queues, concurrent queues and standard stacks replaced with fixed capacity stacks. MethodImplOptions.AggressiveInlining and .AggressiveOptimization added to simple methods and getters / setters. Variables optimized in few places.

PerfectNumbers.Core/ConcurrentFixedCapacityStack.cs

@@ -0,0 +1,77 @@
+using System.Runtime.CompilerServices;
+
+namespace PerfectNumbers.Core;
+
+public sealed class ConcurrentFixedCapacityStack<T>(int capacity)
+{
+	private static readonly FixedCapacityArrayPool<T> _arrayPool = FixedCapacityPools<T>.ExclusiveArray;
+
+	private readonly T[] _items = _arrayPool.Rent(capacity);
+	private readonly int _capacity = capacity;
+
+	private int _count = 0;
+	public int Count
+	{
+		[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+		get => Volatile.Read(ref _count);
+	}
+
+	public int Capacity
+	{
+		[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+		get => _capacity;
+	}
+
+	[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+	public void Clear() => Interlocked.Exchange(ref _count, 0);
+
+	[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+	public T? Pop() => TryPop(out T? item) ? item : default;
+
+	[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+	public bool TryPop(out T? item)
+	{
+		while (true)
+		{
+			int observed = Volatile.Read(ref _count);
+			if (observed == 0)
+			{
+				item = default;
+				return false;
+			}
+
+			int next = observed - 1;
+			if (Interlocked.CompareExchange(ref _count, next, observed) == observed)
+			{
+				item = _items[next];
+				return true;
+			}
+		}
+	}
+
+	[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+	public void Push(T item)
+	{
+		int next = Interlocked.Increment(ref _count);
+		if (next <= _capacity)
+		{
+			_items[next - 1] = item;
+			return;
+		}
+
+		Interlocked.Decrement(ref _count);
+		throw new InvalidOperationException("Stack is full.");
+	}
+
+	[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+	public static void Return(in T[] items) => _arrayPool.Return(items);
+
+	[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+	public T[] ToArray()
+	{
+		int count = Volatile.Read(ref _count);
+		T[] result = _arrayPool.Rent(count);
+		Array.Copy(_items, result, count);
+		return result;
+	}
+}