C#

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public class ConcurrentList<T> : IList<T>
{
    #region Fields

    private IList<T> _internalList;

    private readonly object lockObject = new object();

    #endregion

    #region ctor

    public ConcurrentList()
    {
        _internalList = new List<T>();
    }

    public ConcurrentList(int capacity)
    {
        _internalList = new List<T>(capacity);
    }

    public ConcurrentList(IEnumerable<T> list)
    {
        _internalList = list.ToList();
    }

    #endregion

    public T this[int index]
    {
        get
        {
            return LockInternalListAndGet(l => l[index]);
        }

        set
        {
            LockInternalListAndCommand(l => l[index] = value);
        }
    }

    public int Count
    {
        get
        {
            return LockInternalListAndQuery(l => l.Count());
        }
    }

    public bool IsReadOnly => false;

    public void Add(T item)
    {
        LockInternalListAndCommand(l => l.Add(item));
    }

    public void Clear()
    {
        LockInternalListAndCommand(l => l.Clear());
    }

    public bool Contains(T item)
    {
        return LockInternalListAndQuery(l => l.Contains(item));
    }

    public void CopyTo(T[] array, int arrayIndex)
    {
        LockInternalListAndCommand(l => l.CopyTo(array, arrayIndex));
    }

    public IEnumerator<T> GetEnumerator()
    {
        return LockInternalListAndQuery(l => l.GetEnumerator());
    }

    public int IndexOf(T item)
    {
        return LockInternalListAndQuery(l => l.IndexOf(item));
    }

    public void Insert(int index, T item)
    {
        LockInternalListAndCommand(l => l.Insert(index, item));
    }

    public bool Remove(T item)
    {
        return LockInternalListAndQuery(l => l.Remove(item));
    }

    public void RemoveAt(int index)
    {
        LockInternalListAndCommand(l => l.RemoveAt(index));
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return LockInternalListAndQuery(l => l.GetEnumerator());

    }

    #region Utilities

    protected virtual  void LockInternalListAndCommand(Action<IList<T>> action)
    {
        lock (lockObject)
        {
            action(_internalList);
        }
    }

    protected virtual T LockInternalListAndGet(Func<IList<T>, T> func)
    {
        lock (lockObject)
        {
            return func(_internalList);
        }
    }

    protected virtual TObject LockInternalListAndQuery<TObject>(Func<IList<T>, TObject> query)
    {
        lock (lockObject)
        {
            return query(_internalList);
        }
    }

    #endregion
}