Refactoring code with a lot of "locks" to more lock-free code

Question

Upd thanks to Matthew Watson for noticing and note that I plan to port my code to c++-linux so I prefer "platform-independent" code

My trading application is almost lock-free. The code below is the only place where I do use locks. Let me start with the code, it's pretty long but don't worry there are a lot of repeating parts so it's simple. I prefer to add all "repeating" parts to better demonstrate how my things work:

Task.Factory.StartNew(() =>
{
    while (true)
    {
        Iterate();
    }
}, TaskCreationOptions.LongRunning);

private void Iterate()
{
    bool marketDataUpdated = false;

    lock (ordersToRegisterLock)
    {
        if (ordersToRegister.Count > 0)
        {
            marketDataUpdated = true;
            while (ordersToRegister.Count > 0)
            {
                Order order = ordersToRegister.Dequeue();
                // Stage1, Process
            }
        }
    }

    lock (aggrUpdatesLock)
    {
        if (aggrUpdates.Count > 0)
        {
            marketDataUpdated = true;
            while (!aggrUpdates.IsNullOrEmpty())
            {
                var entry = aggrUpdates.Dequeue();
                // Stage1, Process
            }
        }
    }

    lock (commonUpdatesLock)
    {
        if (commonUpdates.Count > 0)
        {
            marketDataUpdated = true;
            while (!commonUpdates.IsNullOrEmpty())
            {
                var entry = commonUpdates.Dequeue();
                // Stage1, Process
            }
        }
    }

    lock (infoUpdatesLock)
    {
        if (infoUpdates.Count > 0)
        {
            marketDataUpdated = true;
            while (!infoUpdates.IsNullOrEmpty())
            {
                var entry = infoUpdates.Dequeue();
                // Stage1, Process
            }
        }
    }

    lock (tradeUpdatesLock)
    {
        if (tradeUpdates.Count > 0)
        {
            marketDataUpdated = true;
            while (!tradeUpdates.IsNullOrEmpty())
            {
                var entry = tradeUpdates.Dequeue();
                // Stage1, Process
            }    

        }
    }

    if (marketDataUpdated)
    {
        // Stage2 !
        // make a lot of work. expensive operation. recalculate strategies, place orders etc.
    }
}

private readonly Queue<Order> ordersToRegister = new Queue<Order>();
private readonly object ordersToRegisterLock = new object();

private readonly Queue<AggrEntry> aggrUpdates = new Queue<AggrEntry>();
private readonly object aggrUpdatesLock = new object();

private readonly Queue<CommonEntry> commonUpdates = new Queue<CommonEntry>();
private readonly object commonUpdatesLock = new object();

private readonly Queue<InfoEntry> infoUpdates = new Queue<InfoEntry>();
private readonly object infoUpdatesLock = new object();

private readonly Queue<TradeEntry> tradeUpdates = new Queue<TradeEntry>();
private readonly object tradeUpdatesLock = new object();


    public void RegistorOrder(object sender, Gate.RegisterOrderArgs e)
    {
        lock (ordersToRegisterLock)
        {
            ordersToRegister.Enqueue(e.order);
        }
    }

    public void TradeUpdated(object sender, Gate.TradeArgs e)
    {
        lock (tradeUpdatesLock)
        {
            foreach (var entry in e.entries)
            {
                tradeUpdates.Enqueue(entry);
            }
        }
    }

    public void InfoUpdated(object sender, Gate.InfoArgs e)
    {
        lock (infoUpdatesLock)
        {
            foreach (var entry in e.entries)
            {
                infoUpdates.Enqueue(entry);
            }
        }
    }

    public void CommonUpdated(object sender, Gate.CommonArgs e)
    {
        lock (commonUpdatesLock)
        {
            foreach (var entry in e.entries)
            {
                commonUpdates.Enqueue(entry);
            }
        }
    }

    public void AggrUpdated(object sender, Gate.AggrArgs e)
    {
        lock (aggrUpdatesLock)
        {
            foreach (var entry in e.entries)
            {
                aggrUpdates.Enqueue(entry);
            }
        }
    }

In my code I have two stages. Stage1 is update stage and Stage2 is working stage. I need to switch between these two stages as fast as possible, like that:

• any updates? no
• any updates? no
• any updated? yes, order updated! apply update, do Stage2
• any updates? no
• any updates? yes, order need to be registered! apply update, do Stage2
• any updates? yes, trade occured, apply update, do Stage2

In Stage2 I should not update, but should keep "collecting" updates so I can apply they later.

And important thing - this is very latency-critical code so I agree to "spent" one core for having minimal latency! So when any update occure I need to process it asap and perform Stage2.

So I hope now it's clear what I need to achieve and it's clear how I have implemented that. Now it's time to discuss how good my code is. I do see several potential problems:

• a lot of locks! can it be replaced with some "lock-free" code? spinlock with CAS or something?
• occupy 100% of CPU core, can I save some CPU resources without affecting latency?
• can/should I tell .NET to use "dedicated" core (set task affinity?) to avoid extra "switch"?
• I add to Queues from one thread and I read Queues from another thread. Could it be a problem? If adding and reading to a Queue is volatile? Is it possible that my reading thread will not see update from a Queue because cache-update problem?

Any suggestions how to improve what I wrote are welcome, thanks!

upd partly solved - as I understand I better to replace queries to lock-free (likely ring-buffer based?) queries.. i think i will use c++ version of disruptor later. Also I've used this article http://www.umbraworks.net/bl0g/rebuildall/2010/03/08/Running_NET_threads_on_selected_processor_cores and replaced Task with a Thread running on the "fixed" core, however i'm still using "busy-spin", probably I should use something smarter?

Answer 1

With the code below, you are no longer locked during "stage 1" processing:

Task.Factory.StartNew(() =>
{
    while (true)
    {
        Iterate();
    }
}, TaskCreationOptions.LongRunning);


private void Iterate()
{
    bool marketDataUpdated = false;

    foreach (Order order in ordersToRegister)
    {
        marketDataUpdated = true;
        // Stage1, Process
    }

    foreach (var entry in aggrUpdates)
    {
        marketDataUpdated = true;
        // Stage1, Process
    }

    foreach (var entry in commonUpdates)
    {
        marketDataUpdated = true;
        // Stage1, Process
    }

    foreach (var entry in infoUpdates)
    {
        marketDataUpdated = true;
        // Stage1, Process
    }

    foreach (var entry in tradeUpdates)
    {
        marketDataUpdated = true;
        // Stage1, Process
    }

    if (marketDataUpdated)
    {
        // Stage2 !
        // make a lot of work. expensive operation. recalculate strategies, place orders etc.
    }
}

private readonly ConcurrentQueue<Order> ordersToRegister = new ConcurrentQueue<Order>();

private readonly ConcurrentQueue<AggrEntry> aggrUpdates = new ConcurrentQueue<AggrEntry>();

private readonly ConcurrentQueue<CommonEntry> commonUpdates = new ConcurrentQueue<CommonEntry>();

private readonly ConcurrentQueue<InfoEntry> infoUpdates = new ConcurrentQueue<InfoEntry>();

private readonly ConcurrentQueue<TradeEntry> tradeUpdates = new ConcurrentQueue<TradeEntry>();

    public void RegistorOrder(object sender, Gate.RegisterOrderArgs e)
    {
        ordersToRegister.Enqueue(e.order);
    }

    public void TradeUpdated(object sender, Gate.TradeArgs e)
    {
        foreach (var entry in e.entries)
        {
            tradeUpdates.Enqueue(entry);
        }
    }

    public void InfoUpdated(object sender, Gate.InfoArgs e)
    {
        foreach (var entry in e.entries)
        {
            infoUpdates.Enqueue(entry);
        }
    }

    public void CommonUpdated(object sender, Gate.CommonArgs e)
    {
        foreach (var entry in e.entries)
        {
            commonUpdates.Enqueue(entry);
        }
    }

    public void AggrUpdated(object sender, Gate.AggrArgs e)
    {
        foreach (var entry in e.entries)
        {
            aggrUpdates.Enqueue(entry);
        }
    }

Answer 2

Here is an approach that might be more portable. Hope it helps.

public class SafeQueue<T> : Queue<T>
{
    public T SafeDequeue()
    {
        lock (this)
        {
            return (Count > 0) ? Dequeue() : null;
        }
    }

    public void SafeEnqueue(T entry)
    {
        lock (this)
        {
            Enqueue(entry);
        }
    }
}

Task.Factory.StartNew(() =>
{
    while (true)
    {
        Iterate();
    }
}, TaskCreationOptions.LongRunning);


private void Iterate()
{
    bool marketDataUpdated = false;

    while ((Order order = ordersToRegister.SafeDequeue()) != null)
    {
        marketDataUpdated = true;
        // Stage1, Process
    }

    while ((var entry = aggrUpdates.SafeDequeue()) != null)
    {
        marketDataUpdated = true;
        // Stage1, Process
    }

    while ((var entry = commonUpdates.SafeDequeue()) != null)
    {
        marketDataUpdated = true;
        // Stage1, Process
    }

    while ((var entry = infoUpdates.SafeDequeue()) != null)
    {
        marketDataUpdated = true;
        // Stage1, Process
    }

    while ((var entry = tradeUpdates.SafeDequeue()) != null)
    {
        marketDataUpdated = true;
        // Stage1, Process
    }

    if (marketDataUpdated)
    {
        // Stage2 !
        // make a lot of work. expensive operation. recalculate strategies, place orders etc.
    }
}

private readonly SafeQueue<Order> ordersToRegister = new SafeQueue<Order>();

private readonly SafeQueue<AggrEntry> aggrUpdates = new SafeQueue<AggrEntry>();

private readonly SafeQueue<CommonEntry> commonUpdates = new SafeQueue<CommonEntry>();

private readonly SafeQueue<InfoEntry> infoUpdates = new SafeQueue<InfoEntry>();

private readonly SafeQueue<TradeEntry> tradeUpdates = new SafeQueue<TradeEntry>();

    public void RegistorOrder(object sender, Gate.RegisterOrderArgs e)
    {
        ordersToRegister.SafeEnqueue(e.order);
    }

    public void TradeUpdated(object sender, Gate.TradeArgs e)
    {
        foreach (var entry in e.entries)
        {
            tradeUpdates.SafeEnqueue(entry);
        }
    }

    public void InfoUpdated(object sender, Gate.InfoArgs e)
    {
        foreach (var entry in e.entries)
        {
            infoUpdates.SafeEnqueue(entry);
        }
    }

    public void CommonUpdated(object sender, Gate.CommonArgs e)
    {
        foreach (var entry in e.entries)
        {
            commonUpdates.SafeEnqueue(entry);
        }
    }

    public void AggrUpdated(object sender, Gate.AggrArgs e)
    {
        foreach (var entry in e.entries)
        {
            aggrUpdates.SafeEnqueue(entry);
        }
    }