.NET：如何并行的从集合中返还元素？

实现代码

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

namespace CSharpStudy.ParallelStudy
{
    class HowToReturnList
    {
        public static void Error_Test()
        {
            var list = Enumerable.Range(1, 1000);

            var results = new List<string>();
            Parallel.ForEach(list, (item) =>
            {
                results.Add("item:" + item);
            });

            Console.WriteLine(results.Count);
        }

        public static void Lock_Test()
        {
            var list = Enumerable.Range(1, 1000);

            var results = new List<string>();
            Parallel.ForEach(list, (item) =>
            {
                lock (results)
                {
                    results.Add("item:" + item);
                }
            });

            Console.WriteLine(results.Count);
        }

        public static void Concurrent_Collections_Test()
        {
            var list = Enumerable.Range(1, 1000);

            var results = new ConcurrentQueue<string>();
            Parallel.ForEach(list, (item) =>
            {
                lock (results)
                {
                    results.Enqueue("item:" + item);
                }
            });

            Console.WriteLine(results.Count);
        }

        public static void Task_Test()
        {
            var list = Enumerable.Range(1, 1000);

            var tasks = list.Select(item =>
            {
                return Task.Run<string>(() =>
                {
                    return "item:" + item;
                });
            }).ToArray();
            Task.WhenAll(tasks);

            Console.WriteLine(tasks.Select(x => x.Result).Count());
        }

        public static void PLinq_Test()
        {
            var list = Enumerable.Range(1, 1000);

            var results = list.AsParallel().Select(item => "item:" + item);

            Console.WriteLine(results.Count());
        }
    }
}