AllocFreeConcurrentStack.cs

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using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
 
namespace System.Collections.Immutable;
 
internal static class AllocFreeConcurrentStack<T>
{
    private static readonly Type s_typeOfT = typeof(T);
 
    private static Stack<RefAsValueType<T>> ThreadLocalStack
    {
        get
        {
            Dictionary<Type, object> dictionary = AllocFreeConcurrentStack.t_stacks;
            if (dictionary == null)
            {
                dictionary = (AllocFreeConcurrentStack.t_stacks = new Dictionary<Type, object>());
            }
            if (!dictionary.TryGetValue(s_typeOfT, out var value))
            {
                value = new Stack<RefAsValueType<T>>(35);
                dictionary.Add(s_typeOfT, value);
            }
            return (Stack<RefAsValueType<T>>)value;
        }
    }
 
    public static void TryAdd(T item)
    {
        Stack<RefAsValueType<T>> threadLocalStack = ThreadLocalStack;
        if (threadLocalStack.Count < 35)
        {
            threadLocalStack.Push(new RefAsValueType<T>(item));
        }
    }
 
    public static bool TryTake([MaybeNullWhen(false)] out T item)
    {
        Stack<RefAsValueType<T>> threadLocalStack = ThreadLocalStack;
        if (threadLocalStack != null && threadLocalStack.Count > 0)
        {
            item = threadLocalStack.Pop().Value;
            return true;
        }
        item = default(T);
        return false;
    }
}
internal static class AllocFreeConcurrentStack
{
    [ThreadStatic]
    internal static Dictionary<Type, object>? t_stacks;
}