WeakHashtable.cs

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using System.Collections;
using System.Collections.Generic;
 
namespace System.ComponentModel;
 
internal sealed class WeakHashtable : Hashtable
{
    private sealed class WeakKeyComparer : IEqualityComparer
    {
        bool IEqualityComparer.Equals(object x, object y)
        {
            if (x == null)
            {
                return y == null;
            }
            if (y != null && x.GetHashCode() == y.GetHashCode())
            {
                if (x is WeakReference weakReference)
                {
                    if (!weakReference.IsAlive)
                    {
                        return false;
                    }
                    x = weakReference.Target;
                }
                if (y is WeakReference weakReference2)
                {
                    if (!weakReference2.IsAlive)
                    {
                        return false;
                    }
                    y = weakReference2.Target;
                }
                return x == y;
            }
            return false;
        }
 
        int IEqualityComparer.GetHashCode(object obj)
        {
            return obj.GetHashCode();
        }
    }
 
    private sealed class EqualityWeakReference : WeakReference
    {
        private readonly int _hashCode;
 
        internal EqualityWeakReference(object o)
            : base(o)
        {
            _hashCode = o.GetHashCode();
        }
 
        public override bool Equals(object o)
        {
            if (o?.GetHashCode() != _hashCode)
            {
                return false;
            }
            if (o == this || (IsAlive && o == Target))
            {
                return true;
            }
            return false;
        }
 
        public override int GetHashCode()
        {
            return _hashCode;
        }
    }
 
    private static readonly IEqualityComparer s_comparer = new WeakKeyComparer();
 
    private long _lastGlobalMem;
 
    private int _lastHashCount;
 
    internal WeakHashtable()
        : base(s_comparer)
    {
    }
 
    public void SetWeak(object key, object value)
    {
        ScavengeKeys();
        this[new EqualityWeakReference(key)] = value;
    }
 
    private void ScavengeKeys()
    {
        int count = Count;
        if (count == 0)
        {
            return;
        }
        if (_lastHashCount == 0)
        {
            _lastHashCount = count;
            return;
        }
        long totalMemory = GC.GetTotalMemory(forceFullCollection: false);
        if (_lastGlobalMem == 0L)
        {
            _lastGlobalMem = totalMemory;
            return;
        }
        float num = (float)(totalMemory - _lastGlobalMem) / (float)_lastGlobalMem;
        float num2 = (float)(count - _lastHashCount) / (float)_lastHashCount;
        if (num < 0f && num2 >= 0f)
        {
            List<object> list = null;
            foreach (object key in Keys)
            {
                if (key is WeakReference { IsAlive: false } weakReference)
                {
                    if (list == null)
                    {
                        list = new List<object>();
                    }
                    list.Add(weakReference);
                }
            }
            if (list != null)
            {
                foreach (object item in list)
                {
                    Remove(item);
                }
            }
        }
        _lastGlobalMem = totalMemory;
        _lastHashCount = count;
    }
}