static void Main(string[] args)
        {
            var stop=new Stopwatch();
            var ths=new List<Thread>();
            long times = 0, maxTimes = 5000000;

            var ulist=new List<int>();
            ulist.AddRange(Enumerable.Range(1, 1000));

#if M
            //ImmutableList<int> list=ImmutableList<int>.Empty;
            //var builder=list.ToBuilder();
            //builder.AddRange(Enumerable.Range(1,1000));
            //list = builder.ToImmutable();
            stop.Start();
            for (int i = 0; i < 50; i++)
            {
                var i1 = i;
                var th=new Thread(() =>
                {
                    while (true)
                    {
                        if (Interlocked.Read(ref times) >= maxTimes)
                        {
                            stop.Stop();
                            //list = builder.ToImmutable();
                            Console.WriteLine("times:" + stop.ElapsedMilliseconds / 1000.0 + " length:" + ulist.Count);
                            return;
                        }
                        //builder.Add(i1);
                        //builder.Remove(i1);
                        var dic=new Dictionary<int,int>();
                        int prev = 0;
                        foreach (var i2 in ulist)
                        {
                            if (i2 - prev != 1)
                            {
                                throw new Exception("unsaft");
                            }
                            dic.Add(i2, 0);
                            prev = i2;
                        }
                        dic.Clear();
                        dic = null;
                        Interlocked.Increment(ref times);
                        //Console.WriteLine(Interlocked.Read(ref times));
                    }
                    
                });
                th.Start();
                ths.Add(th);
            }

#endif
            Console.Read();
        }