Multithreading Conflicts

Question

I have my c# form running two threads one thread listens for data to come in and the other is processing the data so i can use it. for some reason once the process thread starts the listen thread isn't executed any more.

Thread th1 = new Thread(new ThreadStart(zeroMQConn.Listen));
th1.Start();
Thread th2 = new Thread(() => ProcessData(zeroMQConn));
th2.Start();

when i debug this it starts the th1 goes into it and then th2 starts and it never goes back to th1 and my data comes back null.

public void Listen()
    {
        while (true)
        {
            try
            {
                byte[] zmqBuffer = new byte[102400];
                int messageLength;
                lockForZMQ.EnterWriteLock();
                messageLength = socket.Receive(zmqBuffer);
                lockForZMQ.ExitWriteLock();
                byte[] message = new byte[messageLength];
                Buffer.BlockCopy(zmqBuffer, 0, message, 0, messageLength);
                PriceBookData priceBook = PriceBookData.CreateBuilder().MergeFrom(message).Build();
                double Type = priceBook.GetPb(0).QuoteType;
                if (Type == 0.0)
                {
                    lockForList.EnterWriteLock();
                    CachedBidBooks = priceBook;
                    lockForList.ExitWriteLock();
                }
                else
                {
                    lockForList.EnterWriteLock();
                    CachedAskBooks = priceBook;
                    lockForList.ExitWriteLock();
                }
            }
            catch (ZmqException ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }

 public void ProcessData(object connection)
    {
        while (true)
        {
            priceBookData = ((ZeroMQClass)connection).GetPriceBook();
        }

    }

 public List<PriceBookData> GetPriceBook()
    {
        List<PriceBookData> AskAndBid = new List<PriceBookData>();
        lockForList.EnterWriteLock();
        if (CachedAskBooks != null && CachedBidBooks != null)
        {
            AskAndBid.Add(CachedBidBooks);
            AskAndBid.Add(CachedAskBooks);
            CachedBidBooks = null;
            CachedAskBooks = null;
            lockForList.ExitWriteLock();
            return AskAndBid;
        }
        lockForList.ExitWriteLock();
        return null;
    }

Answer 1

What you have here is a producer-consumer model, but you aren't properly synchronizing them. The problem is that rather than some sort of buffer or collection of data that's ready to be processed, you have a single variable, and you completely synchronize access to that variable. This means that the producer can't ever be working while the consumer is working.

The BlockingCollection<T> is a fantastic class whenever dealing with producer/consumer queues.

var queue = new BlockingCollection<PriceBookData>();

Task.Factory.StartNew(() =>
{
    while (true)
    {
        byte[] zmqBuffer = new byte[102400];
        int messageLength;
        socket.Receive(zmqBuffer);
        byte[] message = new byte[messageLength];
        Buffer.BlockCopy(zmqBuffer, 0, message, 0, messageLength);
        PriceBookData priceBook = PriceBookData.CreateBuilder().MergeFrom(message).Build();
        double Type = priceBook.GetPb(0).QuoteType;
        queue.Add(priceBook);
    }
}, TaskCreationOptions.LongRunning);

Task.Factory.StartNew(() =>
{
    foreach (var item in queue.GetConsumingEnumerable())
    {
        //do stuff with item
    }
}, TaskCreationOptions.LongRunning);