Listeners.cs

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using System.Collections.Generic;
 
namespace System.Data;
 
internal sealed class Listeners<TElem> where TElem : class
{
    internal delegate void Action<T1, T2, T3, T4>(T1 arg1, T2 arg2, T3 arg3, T4 arg4);
 
    internal delegate TResult Func<T1, TResult>(T1 arg1);
 
    private readonly List<TElem> _listeners;
 
    private readonly Func<TElem, bool> _filter;
 
    private readonly int _objectID;
 
    private int _listenerReaderCount;
 
    internal bool HasListeners => 0 < _listeners.Count;
 
    internal Listeners(int ObjectID, Func<TElem, bool> notifyFilter)
    {
        _listeners = new List<TElem>();
        _filter = notifyFilter;
        _objectID = ObjectID;
        _listenerReaderCount = 0;
    }
 
    internal void Add(TElem listener)
    {
        _listeners.Add(listener);
    }
 
    internal int IndexOfReference(TElem listener)
    {
        return Index.IndexOfReference(_listeners, listener);
    }
 
    internal void Remove(TElem listener)
    {
        int index = IndexOfReference(listener);
        _listeners[index] = null;
        if (_listenerReaderCount == 0)
        {
            _listeners.RemoveAt(index);
            _listeners.TrimExcess();
        }
    }
 
    internal void Notify<T1, T2, T3>(T1 arg1, T2 arg2, T3 arg3, Action<TElem, T1, T2, T3> action)
    {
        int count = _listeners.Count;
        if (0 >= count)
        {
            return;
        }
        int nullIndex = -1;
        _listenerReaderCount++;
        try
        {
            for (int i = 0; i < count; i++)
            {
                TElem arg4 = _listeners[i];
                if (_filter(arg4))
                {
                    action(arg4, arg1, arg2, arg3);
                    continue;
                }
                _listeners[i] = null;
                nullIndex = i;
            }
        }
        finally
        {
            _listenerReaderCount--;
        }
        if (_listenerReaderCount == 0)
        {
            RemoveNullListeners(nullIndex);
        }
    }
 
    private void RemoveNullListeners(int nullIndex)
    {
        int num = nullIndex;
        while (0 <= num)
        {
            if (_listeners[num] == null)
            {
                _listeners.RemoveAt(num);
            }
            num--;
        }
    }
}