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On application responsiveness

Saturday, September 23rd, 2006

Dr. Dobb’s recently published an article on “Application Responsiveness” by Joe Duffy where he gives a very thorough treatment of threading issues in UIs. I felt that the discussion of the solutions was a bit light, but there was one solution missing that, in my opinion, is more important than all the rest.

The kinds of systems that I work on almost always have the client side being asynchronously updated by events published by a server. If there’s one thing I’ve learned, its that threading is a HARD problem. What makes it hard is that it adds another dimension to the complexity of the system. Which is why I’ll do almost anything to have the code that I’m looking at behave single-threaded.

The solution involved first separating out classes that will be touched by only one thread. This means that all view classes (in MVC terms) will be accessed only on the control thread. Secondly, classes that receive information asynchronously from the server will only run on the background thread. Classes in the model (in MVC terms) will not be thread-aware, therefore it is the responsibility of other classes to interact with the model in a thread-safe manner. All other classes, like the controllers (in MVC terms) will be run on both/multiple threads. Despite the need to marshal a call from the background thread to the foreground one (which has been done to death), these controllers have state that needs to be protected.

Enter the ContextBoundObject. This framework class enables you to quite simply put a [Synchronization] attribute on a class that inherits from it, and voila, its thread safe. Not only that, but it will share a single lock with all the other objects that inherit from ContextBoundObject, as long as they’re in the same Synchronization Domain. Don’t worry, it’s easy. Just have a single object that is also a ContextBoundObject be the one that causes all others to be created. If you’re using a container like spring, then the first object would be that which asks spring to initialize.

OK, so technologically – you’re all set. But doing the design according to the constraints mentioned above isn’t trivial. Especially when it comes to the Model objects. But believe me, it’s much easier than an endless hunt after deadlocks and race conditions.

Posted in Development | No Comments »

MSMQ scale out question

Friday, September 15th, 2006

It appears that the questions are getting more concrete around my Autonomous Services article. This one comes from Eric who asks:

“Udi,

Your article caught my attention because we are currently trying to figure out the “infrastructure implementation” piece of the puzzle in an MSMQ cluster scenario. I didn’t understand the term “remote transactional reads”; can you describe it as it relates to this architecture?

The problem we’ve encountered is how do we make it easy for our ops team to just add/remove servers from the cluster, and have the load redistribute itself properly. MSMQ tied to virtual IPs by itself doesn’t seem smart enough. We’re toying with both HW load balancing, and/or some NLB/MOM/AppCenter interactions (with programming layers to make it work.)”

Eric, the current version of MSMQ lacks the remote transactional receive capability – meaning that if your “application” is trying to perform a “Receive” operation on a queue that is located on a remote machine in a transactional context, it will not work. The next version of MSMQ is supposed to “fix” this.

Why would you want such a feature? Well, if you put a single queue on a clustered server (for availability) and had many other servers using that queue as their input queue, you’d have the ability to add servers at runtime to handle increases in load. However, since the handling of a message from a queue often requires a transaction, the current version of MSMQ won’t support this out of the box.

What you could do is have some sort of dispatcher application that would send messages to the other servers. When a server would be ready to receive a message (not under heavy load), it could send the dispatcher a message saying just that. The dispatcher would store the return address (ResponseQueue) so that when a message would arrive, it could send that message to the server.

This scenario would have each server have its own input queue and be aware of the dispatcher. The dispatcher would not have to know about the other servers directly – it would just store the return addresses of the messages it receives. The result of this behavior would cause the messages to be sent transactionally to only one server, which would, in turn, transactionally receive the message from its local queue and process it.

I hope that answers your question Eric. If you’d like more information, feel free to follow up.

Posted in Autonomous Services, Development, MSMQ, Scalability | No Comments »

Re: Generics, Anonymous Methods, & Delegate inference

Wednesday, August 23rd, 2006

In my previous post .Net 2.0 Generics, Anonymous Methods, and Delegate inference bug I bemoaned the difference in behavior between anonymous methods and delegates.

When using plain old event handlers, it is perfectly acceptable to subscribe and unsubscribe by doing the following:

Commands.Open.Activated += new EventHandler<OpenEventArgs>(Open_Activated);
Commands.Open.Activated -= new EventHandler<OpenEventArgs>(Open_Activated);

Even though the delegate that you are removing is a different object than the one you subscribed with, since delegates are immutable they behave like value types so this works. However, with anonymous delegates this is apparently not the case (as my previous post showed). The following code is incorrect, even for the same object ‘f’:

Commands.Open.Activated += this.GetOpenPolylineCallbackFor(f);
Commands.Open.Activated -= this.GetOpenPolylineCallbackFor(f);

Considering that anonymous methods are syntactic sugar for regular delegates, and the whole variable promotion is handled by the compiler, it is unclear why anonymous methods behave differently.

Anyway, here’s the correct code – courtesy of Ayende Rahien:

private void RouteForm_OnNeedPolyline(object sender, EventArgs e)
{
IRouteForm f = sender as IRouteForm;
if (f == null) return;

  EventHandler<OpenEventArgs> openCallback = delegate(object sender, OpenEventArgs e)
  {
    Polyline p = e.Entity as Polyline;
    if (p != null)
      f.Polyline = p;

Commands.Open.Activated -= openCallback;
};

Commands.Open.Activated += openCallback;

Commands.New.Activate(this, new NewEventArgs(typeof(Polyline)));
}

Posted in Development | No Comments »

.Net 2.0 Generics, Anonymous Methods, and Delegate inference bug

Sunday, August 20th, 2006

I’m working on this system that allows the user to perform certain tasks on a map. For instance, building a route on the map is performed by quite simply clicking on the map to add waypoints. This action is done as a part of the RouteForm data entry – on the form there is a button that, when clicked, changes the map’s state to accept user input (the polyline map tool is selected). Of course, the user could have a number of these forms open at any time. Obviously, we’d need to route selected on the map to be passed back to the originating form, and not a different open RouteForm.

In this case, we’d have our RouteForm expose a “NeedPolyline” event. We wouldn’t want our forms or controlling logic (presenters) to be dependent on the map implementation, so we make heavy use of the command pattern to transfer data between them.

So, as a result of the “NeedPolyline” event raised by the RouteForm, the RouteController needs to communicate that it needs a new polyline to be created. This is done by activating the “New” command and passing “typeof(Polyline)” in the event args “EntityType” property. When the MapController gets called back on the command, it activates the relevant map tool. When the user finishes selecting the route on the map (signalled by a right click), the map controller needs to take the polyline from the map control and pass it back into the application. This is done by activating the “Open” command, and passing the polyline as a parameter to the event args. What the RouteController needs to do when its called back on that command is to pass the polyline back to the RouteForm that initiated the whole deal. Ay, there’s the rub.

Well, there’s an elegant solution that uses the new features of .net 2.0 to do just that, or so I thought. Here’s the code:

private void RouteForm_OnNeedPolyline(object sender, EventArgs e)
{
IRouteForm f = sender as IRouteForm;
if (f == null) return;

Commands.Open.Activated += this.GetOpenPolylineCallbackFor(f);
Commands.New.Activate(this, new NewEventArgs(typeof(Polyline)));
}

private EventHandler<OpenEventArgs> GetOpenPolylineCallbackFor(IRouteForm f)
{
  return delegate(object sender, OpenEventArgs e)
  {
    Polyline p = e.Entity as Polyline;
    if (p == null) return;

    f.Polyline = p;
    Commands.Open.Activated -= this.GetOpenPolylineCallbackFor(f);
  }
}

The nicest thing about the above code is that the management of which form requested the polyline is automatically handled – I don’t have to write any code that pipes the event back to the originating form. There’s only one eensy-weensy problem. Unsubscribing from the event doesn’t work – the code “Commands.Open.Activated -= this.GetOpenPolylineCallbackFor(f);” doesn’t do anything. In which case, only the first RouteForm works correctly, since the event is piped back to all forms ever opened.

Is this a bug? Well, it is in my book. I don’t get how the subscription can work while the inverse doesn’t. I know that there are workarounds – I’ve already implemented them and moved on. But I think that there’s a real missed opportunity here. This is the kind of code .net 2.0 is supposed to support – generic, concise, elegant.

I really hope that this gets rolled into SP1 of VS2005. I’d really hate to have to wait 3 years for a fix for this (re: VS2003 sp1).

Posted in Development | No Comments »

Polymorphism and the switch statement

Friday, August 4th, 2006

In my previous post, I contrivedly complained about how C# makes it hard for me to switch based on type. In the comments I got, rather quickly I might mention, Keith suggested the “replace switch statement with polymorphism” refactoring. While that refactoring is quite often what is needed when the switch is found in implementations of procedural business logic, the appropriate refactoring in this case is different.

First, some context. The code described was in an event handler for a specific command activation – the ‘new’ command. The command pattern is a common one in user interfaces so I won’t expound on it here. OK, so the user can via the menu or toolbar request to create a new entity. The menu, or toolbar, activate the ‘new’ command while passing along the type of entity to create in the EventArgs of the Activated event of the command.

The code shown in the previous post showed a single event handler that would decide based on the EntityType property of the event args what to do – open the customer form, order form, etc. What is needed is to perform the refactoring called (well, I call it): “replace switch statement in single event handler with multiple, specific type based event handlers”. I should probably find a better name for that 🙂

I’ll skip some of the interim steps and go directly to the generic solution. The new code would look more like this:

public class CommandHandler<T> where T : IEntity
{
  public CommandHandler()
  {
    NewCommand.Activated += delegate(object sender, EntityEventArgs e) {
      if (e.EntityType == typeof(T))
      {
        IView v = this.builder.Build<IEntityView<T>>();
        v.Show();
      }
    };
  }
}

and then you’d just instantiate a command handler for each entity type like so:

new CommandHandler<Customer>();
new CommandHandler<Order>();

and the forms would respectively implement IEntityView<Customer> and IEntityView<Order>. The builder that you use (I use Spring) would easily look up the type supporting that interface (you’d most probably only have one class like that in play) and instantiate it.

So, although in this case Microsoft does not make it easy to get the poorly designed code working, surprisingly they supply no guidance around this incredibly common Rich/Smart scenario – even in the CAB/Smart Client Factory. The solution is object oriented, generic, and results in less code. A winner all around.

What say you?

Posted in Development | No Comments »

Switch statement angst

Tuesday, August 1st, 2006

The C# compiler doesn’t like the following code:

public void NewCommandActivatedCallback(object sender, EntityTypeEventArgs e);
{
switch(e.EntityType)
{
case typeof(Customer): // open new customer form; break;
case typeof(Order): // open new order form; break;
//and so on
}
}

It doesn’t like the fact that the values of the case elements aren’t constant. Well, logically speaking they are constant. Is the following code that much different?

public void NewCommandActivatedCallback(object sender, EntityTypeEventArgs e);
{
switch(e.EntityType.Name)
{
case “Customer”: // open new customer form; break;
case “Order”: // open new order form; break;
//and so on
}
}

Well, yes. For starters, it compiles. It’s also uglier. And less maintainable. But, its semantically equivalent.

My wish for Orcas is FIX IT!!! God! We’ve been carrying this crap through 2.5 versions of .net. Enough already. Hell, roll it into SP1 of VS2003 or VS2005. It’s not like it’ll break any existing code.

OK, I feel better now. Move along now. Nothing to see here.

Posted in Development | No Comments »

Asynchronous Callback R Us

Saturday, July 1st, 2006

I’m sure a lot of people are familiar with the kind of asynchronous programming model supported by the .Net framework. The common API looks something like this:

public IAsyncResult BeginXXX (data, AsyncCallback callback, Object state);

The purpose of the “state” object is to allow you to put in some data that you’d like to get back with the callback. This is absolutely essential in the case where your code can fire off numerous asynchronous calls, and you need a way to differentiate one callback from another.

Which would result in client code looking like this:

public void OrderForm_onSubmitRequested(object sender, EventArgs e)
{
  IOrderForm f = (IOrderForm)sender;
  Order o = f.Order;
  this.ServiceAgent.BeginSubmitOrder(o, new AsyncCallback(this.SubmitOrderCompleted), f);
f.Visible = false;
}

But, in the “SubmitOrderSucceded” method, you’d have to do an ugly cast on the “IAsyncResult.AsyncState” property to get back your IOrderForm. And I’m sure everyone will agree with me on this, it’s a pretty clunky API.

Wouldn’t it be nicer to write code like this:

public void OrderForm_onSubmitRequested(object sender, EventArgs e)
{
  IOrderForm f = (IOrderForm)sender;
  Order o = f.Order;
  this.ServiceAgent.SubmitOrder(o).Completed += delegate(int errorCode)
  { this.SubmitOrderCompleted(errorCode, f); };
f.Visible = false;
}

Why is this nicer? Well, you get the method call separated from the callback declaration. Not to mention the nice code completion features of the IDE for events, which you don’t have for plain old delegates.

If you want to implement this kind of API in your own code, you need to do some anonymous delegate tricks yourself. It’s pretty amazing that you can get two sequential callstacks to communicate – since the method call, and the event subscription are really two separate calls.

But you’ll have to wait for the next post to see how it’s done… 🙂

Posted in Development | Comments Off on Asynchronous Callback R Us

Spring.net gets method injection!

Tuesday, June 27th, 2006

You might remember my previous post on Dependency Injection Woes where I bemoaned the issue of string naming as well as the lack of method injection. Well, it turns out that the latest version of Spring.net has just added method injection.

I just wanted to mention one not-so-small issue I have with method injection – it’s testability.

When using the IObjectBuilder I described in the previous post, when I wanted to test the class that needed to create a new instance of another object at runtime (it’s code looking like this: “this.builder.Build();”), I could do something like this (using NUnit.Mocks):

DynamicMock builderMock = new DynamicMock(typeof(IBuilder));
DynamicMock otherObjectMock = new DynamicMock(typeof(IOtherObject));

unitUnderTest.builder = builderMock.MockInstance as IBuilder;

builderMock.ExpectAndReturn(“Build”, otherObjectMock.MockInstance);

And I could embellish properties and such on the created object.

With method injection, in my tests I have to subclass the unit under test and override the method. While both styles work, and I think I like the way the production code comes out with method injection better, the added weight for testing is a drag.

The law of conservation of energy will apparently always apply.

Posted in Development | No Comments »

Careful how you inject those dependencies

Sunday, May 21st, 2006

When using dependency injection, you often find two different kinds of scenarios that are common – singleton and single-call, which match the lifetime of the objects being injected. If the object you’re currently working on needs a reference to a repository, the main form, or something like that, you’ll probably expose either a setter, or accept the reference in a constructor argument. This is the primary area where DI shines enabling lower levels of coupling between classes than before.

However, when your object needs to instantiate a new object at runtime the story changes slightly. For instance, you wouldn’t want your UI controller to have a reference to a concrete form so that you could better test it. However, there must be some other way to inject that dependency – neither a setter or a constructor argument.

In my opinion, this is no longer DI, but rather something of a deferred object construction. Instead of your code “newing” up the concrete class, you defer that to something else, the DI framework. Indeed, all the frameworks I’m aware of support this.

One of the most common ways this construction is done is for your code to ask for the object by name. Since the DI framework needs a way to identify objects/classes for wiring purposes, every object gets a name in the config file. So, in order to get a new instance of the customer form you would write code like this:

ICustomerForm f = springContext.GetObject(“CustomerForm”) as ICustomerForm;

Where, in the config file, CustomerForm is defined to be a single-call object, meaning that a new instance is created every time “GetObject” is called for it.

And this works great. So you go and implement all your UI controllers similarly. In fact, any place you need to create an object, you do the same – all your programmers do. And you all pat yourselves on the back what a fantastically loosely-coupled system you’ve created.

Until, one day, that very same code blows up. The call to GetObject returns null. You check the config file, the entry is there. You check that class file that it references, the Dlls are there. You check constructor parameters, and everything’s fine. You go and check it on a different machine and it works. Go back to the first machine, it doesn’t.

AAAAAARRRRRRRGGGGGGGHHHHHH!!!!

Hours later, somebody (maybe a tester) walks by and sees you peering at the config file looking for salvation. He comments “I thought the ‘f’ in Customerform was supposed to be uppercase”. You shout, and then cry, and laugh, some more crying, make the fix, and go home.

Hopefully, you reach the same conclusion that I did. Those strings are evil. The compiler does not check them. Neither do the unit tests. Chances are the acceptance tests don’t either. You must never embed a string in your source code which must be identical to some other string outside the source for the system to work. Alas, the string passed to “GetObject” is just such a string.

The solution is simple, once you’ve returned to the problem. Since the UI controller only knows about ICustomerForm, it must ask the DI framework to give it the object that implements ICustomerForm. That code knows nothing else, so it cannot ask for anything else. Since, by design, in a given deployment you will only have one object that fulfills the role of ICustomerForm, you’re all set.

Ay, there’s the rub.

In your design, the interfaces whose implementations you will need to be able to create in a single-call fashion must be such that they do not get used in different, single-call scenarios. Otherwise, when asking for the object who implements ICustomerForm, you could get several, but only one of them is correct (not that you can know at runtime which one). Therein is the constraint on the solution to the correct problem.

The code for spring.net, wrapped in IObjectBuilder, looks like this:

    public class Builder : IBuilder
    {
        #region IBuilder Members

        public object Build(Type interfaceType)
        {
            Spring.Context.IApplicationContext ctx = Spring.Context.Support.ContextRegistry.GetContext();

            System.Collections.IDictionary dict = ctx.GetObjectsOfType(interfaceType, true, false);

            System.Diagnostics.Debug.Assert(dict.Count == 1,
                "Should only be one type that implements " + interfaceType.FullName,
                "Types found: " + this.GetTypeNames(dict.Values));

            System.Collections.IDictionaryEnumerator de = dict.GetEnumerator();
            return (de.MoveNext() ? de.Value : null);
        }

        public InterfaceType Build<InterfaceType>() where InterfaceType : class
        {
            return this.Build(typeof(InterfaceType)) as InterfaceType;
        }

        #endregion

        private string GetTypeNames(System.Collections.ICollection iCollection)
        {
            StringBuilder sb = new StringBuilder();

            foreach (Type t in iCollection)
            { sb.Append(t.FullName); sb.Append(", "); }

            return sb.ToString();
        }
    }

Anyway, like the title says, careful with those injections. You wouldn’t want to introduce other, hidden (string-based) dependencies as a result of removing todays (class-based) ones.

Posted in Dependency Injection, Development | No Comments »

Logging as an Aspect – bad idea

Thursday, May 11th, 2006

Now that I have your attention, let me rephrase that. If all you want to log is what method was called and with what parameters, knock yourself out, go and use aspects (maybe like this).

But what about when something interesting happens and you want to log that? Something interesting, maybe some like this: as a result of his last purchase, customer Joe got upgrade to ‘preferred’ status. If anything, you’d like this information to be logged differently than all that other crap. The last thing we want with logging is to (re)create the needle in a haystack problem.

Posted in Development | Comments Off on Logging as an Aspect – bad idea

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“Udi delivered a 5 hour long workshop on SOA for aspiring architects in Norway. While keeping everyone awake and excited Udi gave us some great insights and really delivered on making complex software challenges simple. Truly the software simplist.”

Motty Cohen, SW Manager at KorenTec Technologies
“I know Udi very well from our mutual work at KorenTec. During the analysis and design of a complex, distributed C4I system - where the basic concepts of NServiceBus start to emerge - I gained a lot of "Udi's hours" so I can surely say that he is a professional, skilled architect with fresh ideas and unique perspective for solving complex architecture challenges. His ideas, concepts and parts of the artifacts are the basis of several state-of-the-art C4I systems that I was involved in their architecture design.”

Aaron Jensen, VP of Engineering at Eleutian Technology
“Awesome. Just awesome.

We’d been meaning to delve into messaging at Eleutian after multiple discussions with and blog posts from Greg Young and Udi Dahan in the past. We weren’t entirely sure where to start, how to start, what tools to use, how to use them, etc. Being able to sit in a room with Udi for an entire week while he described exactly how, why and what he does to tackle a massive enterprise system was invaluable to say the least.

We now have a much better direction and, more importantly, have the confidence we need to start introducing these powerful concepts into production at Eleutian.”

Gad Rosenthal, Department Manager at Retalix
“A thinking person. Brought fresh and valuable ideas that helped us in architecting our product. When recommending a solution he supports it with evidence and detail so you can successfully act based on it. Udi's support "comes on all levels" - As the solution architect through to the detailed class design. Trustworthy!”

Chris Bilson, Developer at Russell Investment Group
“I had the pleasure of attending a workshop Udi led at the Seattle ALT.NET conference in February 2009. I have been reading Udi's articles and listening to his podcasts for a long time and have always looked to him as a source of advice on software architecture.
When I actually met him and talked to him I was even more impressed. Not only is Udi an extremely likable person, he's got that rare gift of being able to explain complex concepts and ideas in a way that is easy to understand.
All the attendees of the workshop greatly appreciate the time he spent with us and the amazing insights into service oriented architecture he shared with us.”

Alexey Shestialtynov, Senior .Net Developer at Candidate Manager
“I met Udi at Candidate Manager where he was brought in part-time as a consultant to help the company make its flagship product more scalable. For me, even after 30 years in software development, working with Udi was a great learning experience. I simply love his fresh ideas and architecture insights.
As we all know it is not enough to be armed with best tools and technologies to be successful in software - there is still human factor involved. When, as it happens, the project got in trouble, management asked Udi to step into a leadership role and bring it back on track. This he did in the span of a month. I can only wish that things had been done this way from the very beginning.
I look forward to working with Udi again in the future.”

Christopher Bennage, President at Blue Spire Consulting, Inc.
“My company was hired to be the primary development team for a large scale and highly distributed application. Since these are not necessarily everyday requirements, we wanted to bring in some additional expertise. We chose Udi because of his blogging, podcasting, and speaking. We asked him to to review our architectural strategy as well as the overall viability of project.
I was very impressed, as Udi demonstrated a broad understanding of the sorts of problems we would face. His advice was honest and unbiased and very pragmatic. Whenever I questioned him on particular points, he was able to backup his opinion with real life examples. I was also impressed with his clarity and precision. He was very careful to untangle the meaning of words that might be overloaded or otherwise confusing. While Udi's hourly rate may not be the cheapest, the ROI is undoubtedly a deal. I would highly recommend consulting with Udi.”

Robert Lewkovich, Product / Development Manager at Eggs Overnight
“Udi's advice and consulting were a huge time saver for the project I'm responsible for. The $ spent were well worth it and provided me with a more complete understanding of nServiceBus and most importantly in helping make the correct architectural decisions earlier thereby reducing later, and more expensive, rework.”

Ray Houston, Director of Development at TOPAZ Technologies
“Udi's SOA class made me smart - it was awesome.

The class was very well put together. The materials were clear and concise and Udi did a fantastic job presenting it. It was a good mixture of lecture, coding, and question and answer. I fully expected that I would be taking notes like crazy, but it was so well laid out that the only thing I wrote down the entire course was what I wanted for lunch. Udi provided us with all the lecture materials and everyone has access to all of the samples which are in the nServiceBus trunk.

Now I know why Udi is the "Software Simplist." I was amazed to find that all the code and solutions were indeed very simple. The patterns that Udi presented keep things simple by isolating complexity so that it doesn't creep into your day to day code. The domain code looks the same if it's running in a single process or if it's running in 100 processes.”

Ian Cooper, Team Lead at Beazley
“Udi is one of the leaders in the .Net development community, one of the truly smart guys who do not just get best architectural practice well enough to educate others but drives innovation. Udi consistently challenges my thinking in ways that make me better at what I do.”

Liron Levy, Team Leader at Rafael
“I've met Udi when I worked as a team leader in Rafael. One of the most senior managers there knew Udi because he was doing superb architecture job in another Rafael project and he recommended bringing him on board to help the project I was leading.
Udi brought with him fresh solutions and invaluable deep architecture insights. He is an authority on SOA (service oriented architecture) and this was a tremendous help in our project.
On the personal level - Udi is a great communicator and can persuade even the most difficult audiences (I was part of such an audience myself..) by bringing sound explanations that draw on his extensive knowledge in the software business. Working with Udi was a great learning experience for me, and I'll be happy to work with him again in the future.”

Adam Dymitruk, Director of IT at Apara Systems
“I met Udi for the first time at DevTeach in Montreal back in early 2007. While Udi is usually involved in SOA subjects, his knowledge spans all of a software development company's concerns. I would not hesitate to recommend Udi for any company that needs excellent leadership, mentoring, problem solving, application of patterns, implementation of methodologies and straight out solution development.
There are very few people in the world that are as dedicated to their craft as Udi is to his. At ALT.NET Seattle, Udi explained many core ideas about SOA. The team that I brought with me found his workshop and other talks the highlight of the event and provided the most value to us and our organization. I am thrilled to have the opportunity to recommend him.”

Eytan Michaeli, CTO Korentec
“Udi was responsible for a major project in the company, and as a chief architect designed a complex multi server C4I system with many innovations and excellent performance.”

Carl Kenne, .Net Consultant at Dotway AB
“Udi's session "DDD in Enterprise apps" was truly an eye opener. Udi has a great ability to explain complex enterprise designs in a very comprehensive and inspiring way. I've seen several sessions on both DDD and SOA in the past, but Udi puts it in a completly new perspective and makes us understand what it's all really about. If you ever have a chance to see any of Udi's sessions in the future, take it!”

Avi Nehama, R&D Project Manager at Retalix
“Not only that Udi is a briliant software architecture consultant, he also has remarkable abilities to present complex ideas in a simple and concise manner, and...
always with a smile. Udi is indeed a top-league professional!”

Ben Scheirman, Lead Developer at CenterPoint Energy
“Udi is one of those rare people who not only deeply understands SOA and domain driven design, but also eloquently conveys that in an easy to grasp way. He is patient, polite, and easy to talk to. I'm extremely glad I came to his workshop on SOA.”

Scott C. Reynolds, Director of Software Engineering at CBLPath
“Udi is consistently advancing the state of thought in software architecture, service orientation, and domain modeling.
His mastery of the technologies and techniques is second to none, but he pairs that with a singular ability to listen and communicate effectively with all parties, technical and non, to help people arrive at context-appropriate solutions. Every time I have worked with Udi, or attended a talk of his, or just had a conversation with him I have come away from it enriched with new understanding about the ideas discussed.”

Evgeny-Hen Osipow, Head of R&D at PCLine
“Udi has helped PCLine on projects by implementing architectural blueprints demonstrating the value of simple design and code.”

Rhys Campbell, Owner at Artemis West
“For many years I have been following the works of Udi. His explanation of often complex design and architectural concepts are so cleanly broken down that even the most junior of architects can begin to understand these concepts. These concepts however tend to typify the "real world" problems we face daily so even the most experienced software expert will find himself in an "Aha!" moment when following Udi teachings.
It was a pleasure to finally meet Udi in Seattle Alt.Net OpenSpaces 2008, where I was pleasantly surprised at how down-to-earth and approachable he was. His depth and breadth of software knowledge also became apparent when discussion with his peers quickly dove deep in to the problems we current face. If given the opportunity to work with or recommend Udi I would quickly take that chance. When I think .Net Architecture, I think Udi.”

Sverre Hundeide, Senior Consultant at Objectware
“Udi had been hired to present the third LEAP master class in Oslo. He is an well known international expert on enterprise software architecture and design, and is the author of the open source messaging framework nServiceBus. The entire class was based on discussion and interaction with the audience, and the only Power Point slide used was the one showing the agenda.
He started out with sketching a naive traditional n-tier application (big ball of mud), and based on suggestions from the audience we explored different solutions which might improve the solution. Whatever suggestions we threw at him, he always had a thoroughly considered answer describing pros and cons with the suggested solution. He obviously has a lot of experience with real world enterprise SOA applications.”

Raphaël Wouters, Owner/Managing Partner at Medinternals
“I attended Udi's excellent course 'Advanced Distributed System Design with SOA and DDD' at Skillsmatter. Few people can truly claim such a high skill and expertise level, present it using a pragmatic, concrete no-nonsense approach and still stay reachable.”

Nimrod Peleg, Lab Engineer at Technion IIT
“One of the best programmers and software engineer I've ever met, creative, knows how to design and implemet, very collaborative and finally - the applications he designed implemeted work for many years without any problems!”

Jose Manuel Beas
“When I attended Udi's SOA Workshop, then it suddenly changed my view of what Service Oriented Architectures were all about. Udi explained complex concepts very clearly and created a very productive discussion environment where all the attendees could learn a lot. I strongly recommend hiring Udi.”

Daniel Jin, Senior Lead Developer at PJM Interconnection
“Udi is one of the top SOA guru in the .NET space. He is always eager to help others by sharing his knowledge and experiences. His blog articles often offer deep insights and is a invaluable resource. I highly recommend him.”

Pasi Taive, Chief Architect at Tieto
“I attended both of Udi's "UI Composition Key to SOA Success" and "DDD in Enterprise Apps" sessions and they were exceptionally good. I will definitely participate in his sessions again. Udi is a great presenter and has the ability to explain complex issues in a manner that everyone understands.”

Eran Sagi, Software Architect at HP
“So far, I heard about Service Oriented architecture all over. Everyone mentions it – the big buzz word. But, when I actually asked someone for what does it really mean, no one managed to give me a complete satisfied answer. Finally in his excellent course “Advanced Distributed Systems”, I got the answers I was looking for. Udi went over the different motivations (principles) of Services Oriented, explained them well one by one, and showed how each one could be technically addressed using NService bus. In his course, Udi also explain the way of thinking when coming to design a Service Oriented system. What are the questions you need to ask yourself in order to shape your system, place the logic in the right places for best Service Oriented system.

I would recommend this course for any architect or developer who deals with distributed system, but not only. In my work we do not have a real distributed system, but one PC which host both the UI application and the different services inside, all communicating via WCF. I found that many of the architecture principles and motivations of SOA apply for our system as well. Enough that you have SW partitioned into components and most of the principles becomes relevant to you as well. Bottom line – an excellent course recommended to any SW Architect, or any developer dealing with distributed system.”

Consult with Udi

Guest Authored Books

Article: The Enterprise Service Bus and Your SOA

97 Things Every Software Architect Should Know

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