Playground.cs

using System;
using System.Linq;
using System.Threading.Tasks;
using System.Collections.Generic;

namespace Playground
{
	class MainClass
	{
		public static void Main (string[] args)
		{
			Console.WriteLine ("Hello World!");
			var tester = new Tester ();
			foreach(var text in tester.dataList) {
				Console.WriteLine (text);
			}
		}
	}

	class Tester
	{
		private IList<string> _list = null;

		public IList<string> dataList {
			get {
				if (_list == null) {
					InitAsync ().Wait ();
				}
				return _list;
			}
		}

		public void Init ()
		{
			_list = Task.Run (async () => await GetListAsync ()).Result;
		}

		public async Task InitAsync ()
		{
			_list = await GetListAsync ();
		}

		public async Task<IList<string>> GetListAsync()
		{
			await Task.Delay (1000);
			return new List<string> { "Hello", "World" };
		}
	}
}