EmptyEnumerable.cs

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using System.Collections.Generic;
 
namespace System.Linq.Parallel;
 
internal sealed class EmptyEnumerable<T> : ParallelQuery<T>
{
    private static volatile EmptyEnumerable<T> s_instance;
 
    private static volatile EmptyEnumerator<T> s_enumeratorInstance;
 
    internal static EmptyEnumerable<T> Instance
    {
        get
        {
            if (s_instance == null)
            {
                s_instance = new EmptyEnumerable<T>();
            }
            return s_instance;
        }
    }
 
    private EmptyEnumerable()
        : base(QuerySettings.Empty)
    {
    }
 
    public override IEnumerator<T> GetEnumerator()
    {
        if (s_enumeratorInstance == null)
        {
            s_enumeratorInstance = new EmptyEnumerator<T>();
        }
        return s_enumeratorInstance;
    }
}