Presenting AjGroups: Finite Groups Library

I was writing a C# class library to manage finite groups. A group is a set G of elements with a defined binary operation *, where:

a * b  is in G    (closure)

a * (b * c) = (a * b) * c        (associative)

a * a’ = e     (inverse and identity)

a * e = e * a   (identity)

The solution code is in my AjCodeKata Google Project, under trunk/AjGroups:

The key interfaces are:

IElement has a method Multiply, that receives another IElement and returns the result IElement. IElement.Order is the number of elements to be multiplied to get the identity:

a * a * a ….. * a = e

IGroup.Elements is the collection of IElements that are the elements of the group. IGroup.Order is the count of elements.

There are two implementations of that interfaces: one based on permutations, another based on named elements (such “a”, “e”) and a table describing their multiplications.

There are methods to:

- Get the subgroups of a group
- Get the normal subgroups of a group
- Answer if two groups are isomorphic

I followed TDD ideas during development. All tests in green:

Good code coverage:

I should make some refactoring, but the project is taking form. I will write posts describing the permutation implementation, and the abstract elements implementation.

Keep tuned!

Angel “Java” Lopez
http://www.ajlopez.com
http://twitter.com/ajlopez

Azure: Multithreads in Worker Role, an example

In my previous post, I implemented a simple worker role, consuming and producing numbers from/to a queue. Now, I have a new app:

The worker role implements the generation of a Collatz sequence. See:

http://mathworld.wolfram.com/CollatzProblem.html
http://en.wikipedia.org/wiki/Collatz_conjecture
http://www.ericr.nl/wondrous/

You can download the solution from my AjCodeKatas Google project. The code is at:

http://code.google.com/p/ajcodekatas/source/browse/#svn/trunk/Azure/AzureCollatz

The initial page is simple:

The number range is send to the queue:

protected void btnProcess_Click(object sender, EventArgs e)
{
    int from = Convert.ToInt32(txtFromNumber.Text);
    int to = Convert.ToInt32(txtToNumber.Text);
    for (int k=from; k<=to; k++) 
    {
        CloudQueueMessage msg = new CloudQueueMessage(k.ToString());
        WebRole.Instance.NumbersQueue.AddMessage(msg);
    }
}

The worker role gets each of these message, and calculates the Collatz sequence:
 
I added a new feature in Azure.Library: a MessageProcessor that can consumes message from a queue, in its own thread:
public MessageProcessor(CloudQueue queue, Func<CloudQueueMessage, bool> process)
{
    this.queue = queue;
    this.process = process;
}
public void Start()
{
    Thread thread = new Thread(new ThreadStart(this.Run));
    thread.Start();
}
public void Run()
{
    while (true)
    {
        try
        {
            CloudQueueMessage msg = this.queue.GetMessage();
            if (this.ProcessMessage(msg))
                this.queue.DeleteMessage(msg);
        }
        catch (Exception ex)
        {
            Trace.WriteLine(ex.Message, "Error");
        }
    }
}
public virtual bool ProcessMessage(CloudQueueMessage msg)
{
    if (msg != null && this.process != null)
        return this.process(msg);
    Trace.WriteLine("Working", "Information");
    Thread.Sleep(10000);
    return false;
}

Then, the worker role is launching a fixed number (12) of MessageProcessor. In this way, each instance is dedicated to process many message. I guess that this is not needed in this example. But it was an easy “proof of concept” to test the idea. Part of Run method in worker role;
QueueUtilities qutil = new QueueUtilities(account);
CloudQueue queue = qutil.CreateQueueIfNotExists("numbers");
CloudQueueClient qclient = account.CreateCloudQueueClient();
for (int k=0; k<11; k++) 
{
    CloudQueue q = qclient.GetQueueReference("numbers");
    MessageProcessor p = new MessageProcessor(q, this.ProcessMessage);
    p.Start();
}
MessageProcessor processor = new MessageProcessor(queue, this.ProcessMessage);
processor.Run();

The ProcessMessage is in charge of the real work:
private bool ProcessMessage(CloudQueueMessage msg)
{
    int number = Convert.ToInt32(msg.AsString);
    List<int> numbers = new List<int>() { number };
    while (number > 1)
    {
        if ((number % 2) == 0)
        {
            number = number / 2;
            numbers.Add(number);
        }
        else
        {
            number = number * 3 + 1;
            numbers.Add(number);
        }
    }
    StringBuilder builder = new StringBuilder();
    builder.Append("Result:");
    foreach (int n in numbers)
    {
        builder.Append(" ");
        builder.Append(n);
    }
    Trace.WriteLine(builder.ToString(), "Information");
    return true;
}

The code of this example is in my 
Next steps: more distributed apps (genetic algorithm, web crawler…)
Keep tuned!
Angel “Java” Lopez

  
http://www.ajlopez.com 
http://twitter.com/ajlopez
	

Azure: a simple application

This is my first post here, about Azure programming. An easy start: an application with one web role, and one worker role:

You can download the solution from my AjCodeKatas Google project. The code is at:

http://code.google.com/p/ajcodekatas/source/browse/#svn/trunk/Azure/AzureNumbers

In the initial web page you can enter a number to process:

If you send the number 10, this data is send to a queue:

protected void btnProcess_Click(object sender, EventArgs e)
{
    int number = Convert.ToInt32(txtNumber.Text);
    CloudQueueMessage msg = new CloudQueueMessage(number.ToString());
    WebRole.NumbersQueue.AddMessage(msg);
}

The worker role is reading the queue. It decrements the number, and if the result is still positive, it is reinjected in the queue:
        public override void Run()
        {
            // This is a sample worker implementation. Replace with your logic.
            Trace.WriteLine("NumberWorkerRole entry point called", "Information");
            CloudStorageAccount account = CloudStorageAccount.FromConfigurationSetting("DataConnectionString");
            QueueUtilities qutil = new QueueUtilities(account);
            CloudQueue queue = qutil.CreateQueueIfNotExists("numbers");
            while (true)
            {
                CloudQueueMessage msg = queue.GetMessage();
                if (msg != null)
                {
                    int number = Convert.ToInt32(msg.AsString);
                    Trace.WriteLine(string.Format("Processing number: {0}", number), "Information");
                    number--;
                    if (number > 0)
                    {
                        CloudQueueMessage newmsg = new CloudQueueMessage(number.ToString());
                        queue.AddMessage(newmsg);
                    }
                    queue.DeleteMessage(msg);
                }
                else
                {
                    Thread.Sleep(10000);
                    Trace.WriteLine("Working", "Information");
                }
            }
        }

You can see the output at Development Fabric UI:
 
Note the use of AzureLibrary to create a Queue:
        public CloudQueue CreateQueueIfNotExists(string queuename)
        {
            CloudQueueClient queueStorage = this.account.CreateCloudQueueClient();
            CloudQueue queue = queueStorage.GetQueueReference(queuename);
            
            Trace.WriteLine("Creating queue...", "Information");
            Boolean queuecreated = false;
            while (queuecreated == false)
            {
                try
                {
                    queue.CreateIfNotExist();
                    queuecreated = true;
                }
                catch (StorageClientException e)
                {
                    if (e.ErrorCode == StorageErrorCode.TransportError)
                    {
                        Trace.TraceError(string.Format("Connect failure! The most likely reason is that the local " +
                            "Development Storage tool is not running or your storage account configuration is incorrect. " +
                            "Message: '{0}'", e.Message));
                        System.Threading.Thread.Sleep(5000);
                    }
                    else
                    {
                        throw;
                    }
                }
            }
            return queue;
        }

I borrowed part of this code from Azure SDK samples.
Next steps to explore: 
- Add instrumentation to worker role

  
- Use more instances, and generate more message (an explosion-like pattern) 
- Add multithreading support in the worker role 
- Example using table and blob storage
And the big ones:
- Inject and run AjSharp (or AjTalk) code at worker roles

  
- Implements a distributed application using roles (distributed genetic algorithm, distributed fractal or ray-tracer, montecarlo simulation, etc…)
Keep tuned!
Angel “Java” Lopez

  
http://www.ajlopez.com 
http://twitter.com/ajlopez