Angel \”Java\” Lopez on Blog

January 29, 2008

Grid Computing in the browser

Filed under: .NET, C Sharp, Grid Computing — ajlopez @ 9:35 am

Daniel Vaughan has published a very interesting project (LGPL license) at Codeproject:

Legion: Build your own virtual super computer with Silverlight

Daniel is one of the 40 CodeProject MVPs for 2008. He is a software developer based in Canberra Australia, and Prague in the Czech Republic. (Thanks to Arvindra Sehmi, that sends me the article’s link).

It’s a project that uses Silverlight, the new Microsoft technology that runs in the browser, exposing .NET framework to JavaScript and other languages (in the 2.0 version).

According to the CodeProject article:

Legion is a grid computing framework that uses the Silverlight CLR to execute user definable tasks. It provides grid-wide thread-safe operations for web clients. Client performance metrics, such as bandwidth and processor speed, may be used to tailor jobs. Also includes a WPF Manager application.

Recently, I posted about Agents in a grid. Legion puts the agent code inside the browser, using Silverlight as a host environment. The server implements a JsonGridService that is accesible via web services from client side. It serializes the results using JSON (JavaScript Object Notation). One example method from that web services (JsonGridService.asmx.cs):


[WebMethod] [ScriptMethod(ResponseFormat = ResponseFormat.Json)] public TaskDescriptor StartNewJob(Agent agent) { try { TaskDescriptor descriptor = GridManager.GetDescriptor(agent); return descriptor; } catch (Exception ex) { HandleException(ex.Message, agent, ex); } return null; }

An instance of TaskDescriptor has a Type and a Job. The Type is a string describing the full name of the class and assembly to load and run in the client. The compiled assembly must reside in the ClientBin directory in the web server application. Job instance is a bit more complex: it’s a message, containing an arbitrary object to process in the client.

The code to run in the browser must inherits from SlaveTask. The client obtains a TaskDescriptor, creates an object according to the Type in TaskDescriptor, and runs it:


static void LoadAndRunTask() { TaskDescriptor info = gridService.StartNewJob(CreateAgent()); if (!info.Enabled) { return; } log.Debug("LoadAndRunTask() for Job Id " + info.Job.Id); Type type = Type.GetType(info.TypeName, true, true); if (slaveTask != null) { /* Detach last task. */ slaveTask.Complete -= taskBase_Complete; slaveTask.ProgressChanged -= taskBase_ProgressChanged; } slaveTask = (SlaveTask)Activator.CreateInstance(type); slaveTask.Initialise(info); OnTaskChanged(EventArgs.Empty); slaveTask.Complete += taskBase_Complete; slaveTask.ProgressChanged += taskBase_ProgressChanged; Thread newThread= new Thread( delegate { slaveTask.RunInternal(); }); newThread.Priority = ThreadPriority.Lowest; newThread.Start(); // ThreadPool.QueueUserWorkItem( // delegate // { // slaveTask.RunInternal(); // } // ); progressTimer.Enabled = true; }

 Note the use of Type.GetType to load the type. Silverligth uses the ClientBin directory on server side as one of the source for assembly loading. That’s the trick. Activator.CreateInstance creates the instance of the SlaveTask, and a new thread is launched to run the RunInternal method on that instance (for some reason, Vaughan commented the code that used the ThreadPool; I guess that he prefers to manage the priority in code).

In the article, more artifacts are described, as a WPF application, the Legion Manager, that allows monitoring of the grid. But now, let’s examine some concepts and alternatives.

Gridifyng the browser

The great idea, from Vaughan, is to use the browser as a host application for grid node tasks. This idea allows the use of any machine as a grid node (altought Vaughan’s approach needs the support of Silverlight). In the following paragraph, we’ll back to basic, to analyze the full picture implied in this kind of solution.

In a grid computing application, we must resolve the following problems (I’m simplifying the scenario landscape: we could have inter node communications too):

- How to program the task to run (languages, technologies…)

One of the options to the first problem, is to use a specialized language, dedicated to grid computing. Another alternative is to use a main stream language and technology, like Java or .NET. An another one: use scripting/dynamic languages, now supported in Java 6 and in .NET DLR.

- How to inject code to the grid node

If the host node application is a browser, we can program in Java (applets reloaded!), or .NET (now with Silverlight), or even in Flash. To inject the code, the technology at browser can remotely load .jars or compiled assemblies, or it can receive string with source code in dynamic languages, and run it as is.

- How to send task data to the grid node

Well, the data can be serialized, JSON is one method, XML is another one. But, now, another question emerges: who is in charge in sending the data? The server can send the data, but this implies that the client has some listening method. Or the client can poll the server, asking for new task data to process. I don’t know if an Java applet can use a ServerSocket, or if a Silverlight code can open a listening socket. One option to explore, is to have a WCF duplex channel in Silverlight client. Today, the sure option is: the client poll the server. That is the way Legion works.

- How to send back result from the node to a server

This question is an easier one. The data is send using JSON, XML, any serialization technology, to a web service in the server.


Each year, the browser is a more powerful application. Gridifying the browser, using the browser execution capabilities, it’s a promising idea, that deserves more exploration. Security issues, serialization, and the decision about push/pull model on message, are the points to research in more detail.

The next time you open the browser, ask its name. It could be “Legion”…. ;-)

Angel “Java” Lopez


  1. Hi Angel,

    The reason why I didn’t use the Threadpool was because I needed to set the ThreadPriority of the thread.

    This is a nice review of Legion.

    Comment by Daniel Vaughan — February 1, 2008 @ 10:59 am

  2. [...] Grid Computing in the browser [...]

    Pingback by Programando en el browser: Smalltalk Web Toolkit - Angel "Java" Lopez — April 30, 2008 @ 10:19 am

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