AFP: Almost Functional Programming in C#: Part 2

using System;
using System.Collections.Generic;
using System.Threading;

namespace StockTest
{
    public class FakeConnection
    {
        class RandomPrice
        {
            public readonly string StockId;
            Random _rnd;
            double _price;

            public RandomPrice(string stockId)
            {
                StockId = stockId;
                _rnd = new Random();
                _price = 50.0;
            }

            public PriceUpdate GenerateFakePriceUpdate()
            {
                int direction = _rnd.Next(3);
                switch (direction) {
                    case 0:
                        _price = Math.Round(Math.Max(_price - 0.1, 10.0), 1);
                        break;
                    case 1:
                        _price = Math.Round(Math.Min(_price + 0.1, 100.0), 1);
                        break;
                }
                return new PriceUpdate(StockId, _price * 0.9, _price);
            }
        }

        List<RandomPrice> _fakeConnections = new List<RandomPrice>();
        Action<PriceUpdate> _callback;
        Thread _thread;
        volatile bool _stop;

        public void Start(Action<PriceUpdate> callback)
        {
            _callback = callback;
            _thread = new Thread(ThreadProc);
            _thread.Start();
        }

        public void Stop()
        {
            if (_thread != null) {
                _stop = true;
                _thread.Join();
            }
        }

        void ThreadProc()
        {
            var rnd = new Random();
            while (!_stop) {
                try {
                    var update = new PriceUpdate();
                    bool updateExists = false;
                    lock (_fakeConnections) {
                        if (_fakeConnections.Count > 0) {
                            var stock = _fakeConnections[rnd.Next(_fakeConnections.Count)];
                            update = stock.GenerateFakePriceUpdate();
                            updateExists = true;
                        }
                    }
                    if (updateExists)
                        _callback(update);
                } catch (Exception ex) {
                    Console.WriteLine("FakeConnection callback failed: {0}", ex.Message);
                }
                Thread.Sleep(100);
            }
        }

        public void Subscribe(string stockId)
        {
            lock (_fakeConnections) {
                _fakeConnections.Add(new RandomPrice(stockId));
            }
        }

        public void Unsubscribe(string stockId)
        {
            lock (_fakeConnections) {
                _fakeConnections.RemoveAll(x => x.StockId == stockId);
            }
        }
    }
}