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  • Automated Error Reporting in .NET Reflector - harnessing the most powerful test rig in existence

    - by Alex.Davies
    I know a testing system that will find more bugs than all the unit testing, integration testing, and QA you could possibly do. And the chances are you're not using it. It's called your users. It's a cliché that you should test so that you find your bugs rather than your users. Of course you should. But it's also a cliché that no software is ever shipped bug-free. Lost cause? No, opportunity! I think .NET Reflector 6 is pretty stable. In fact I know exactly how stable it is, because some (surprisingly high) proportion of its users tell me every time it crashes: If they press "Send Error Report", I get: And then I fix it. As a rough guess, while a standard stack trace is enough to fix a problem 30% of the time, having all those local variables in the stack trace means I can fix it about 80% of the time. How does this all happen? Did it take ages to code this swish system? Nope, it was one checkbox in SmartAssembly. It adds some clever code to your assembly to capture local variables every time an exception is thrown, and to ask your user to report it to you, with a variety of other useful information. Of course not all bugs show up as exceptions. But if you get used to knowing that SmartAssembly will tell you when an exception happens, you begin to change your coding style. Now, as long as an exception gets thrown in any situation you don't expect, you'll fix it if it ever happens. You'll start throwing exceptions liberally, and stop having to think about whether tiny edge cases are possible, as long as they throw an exception if they happen.

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  • C# async and actors

    - by Alex.Davies
    If you read my last post about async, you might be wondering what drove me to write such odd code in the first place. The short answer is that .NET Demon is written using NAct Actors. Actors are an old idea, which I believe deserve a renaissance under C# 5. The idea is to isolate each stateful object so that only one thread has access to its state at any point in time. That much should be familiar, it's equivalent to traditional lock-based synchronization. The different part is that actors pass "messages" to each other rather than calling a method and waiting for it to return. By doing that, each thread can only ever be holding one lock. This completely eliminates deadlocks, my least favourite concurrency problem. Most people who use actors take this quite literally, and there are plenty of frameworks which help you to create message classes and loops which can receive the messages, inspect what type of message they are, and process them accordingly. But I write C# for a reason. Do I really have to choose between using actors and everything I love about object orientation in C#? Type safety Interfaces Inheritance Generics As it turns out, no. You don't need to choose between messages and method calls. A method call makes a perfectly good message, as long as you don't wait for it to return. This is where asynchonous methods come in. I have used NAct for a while to wrap my objects in a proxy layer. As long as I followed the rule that methods must always return void, NAct queued up the call for later, and immediately released my thread. When I needed to get information out of other actors, I could use EventHandlers and callbacks (continuation passing style, for any CS geeks reading), and NAct would call me back in my isolated thread without blocking the actor that raised the event. Using callbacks looks horrible though. To remind you: m_BuildControl.FilterEnabledForBuilding(    projects,    enabledProjects = m_OutOfDateProjectFinder.FilterNeedsBuilding(        enabledProjects,             newDirtyProjects =             {                 ....... Which is why I'm really happy that NAct now supports async methods. Now, methods are allowed to return Task rather than just void. I can await those methods, and C# 5 will turn the rest of my method into a continuation for me. NAct will run the other method in the other actor's context, but will make sure that when my method resumes, we're back in my context. Neither actor was ever blocked waiting for the other one. Apart from when they were actually busy doing something, they were responsive to concurrent messages from other sources. To be fair, you could use async methods with lock statements to achieve exactly the same thing, but it's ugly. Here's a realistic example of an object that has a queue of data that gets passed to another object to be processed: class QueueProcessor {    private readonly ItemProcessor m_ItemProcessor = ...     private readonly object m_Sync = new object();    private Queue<object> m_DataQueue = ...    private List<object> m_Results = ...     public async Task ProcessOne() {         object data = null;         lock (m_Sync)         {             data = m_DataQueue.Dequeue();         }         var processedData = await m_ItemProcessor.ProcessData(data); lock (m_Sync)         {             m_Results.Add(processedData);         }     } } We needed to write two lock blocks, one to get the data to process, one to store the result. The worrying part is how easily we could have forgotten one of the locks. Compare that to the version using NAct: class QueueProcessorActor : IActor { private readonly ItemProcessor m_ItemProcessor = ... private Queue<object> m_DataQueue = ... private List<object> m_Results = ... public async Task ProcessOne()     {         // We are an actor, it's always thread-safe to access our private fields         var data = m_DataQueue.Dequeue();         var processedData = await m_ItemProcessor.ProcessData(data);         m_Results.Add(processedData);     } } You don't have to explicitly lock anywhere, NAct ensures that your code will only ever run on one thread, because it's an actor. Either way, async is definitely better than traditional synchronous code. Here's a diagram of what a typical synchronous implementation might do: The left side shows what is running on the thread that has the lock required to access the QueueProcessor's data. The red section is where that lock is held, but doesn't need to be. Contrast that with the async version we wrote above: Here, the lock is released in the middle. The QueueProcessor is free to do something else. Most importantly, even if the ItemProcessor sometimes calls the QueueProcessor, they can never deadlock waiting for each other. So I thoroughly recommend you use async for all code that has to wait a while for things. And if you find yourself writing lots of lock statements, think about using actors as well. Using actors and async together really takes the misery out of concurrent programming.

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  • A better way to do concurrent programming

    - by Alex.Davies
    Programming to take advantage of multicore processors is hard. If you let multiple threads access the same memory, bad things happen. To avoid this, you use the lock keyword, but if you use that in the wrong way, your code deadlocks. It's all a nightmare. Luckily, there's a better way - Actors. They're really easy to think about. They're really safe (if you follow a couple of simple rules). And high-performance, type-safe actors are now available for .NET by using this open-source library: http://code.google.com/p/n-act/ Have a look at the site for details. I'll blog with more reasons to use actors and tips and tricks to get the best parallelism from them soon.

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  • Accessing Repositories from Domain

    - by Paul T Davies
    Say we have a task logging system, when a task is logged, the user specifies a category and the task defaults to a status of 'Outstanding'. Assume in this instance that Category and Status have to be implemented as entities. Normally I would do this: Application Layer: public class TaskService { //... public void Add(Guid categoryId, string description) { var category = _categoryRepository.GetById(categoryId); var status = _statusRepository.GetById(Constants.Status.OutstandingId); var task = Task.Create(category, status, description); _taskRepository.Save(task); } } Entity: public class Task { //... public static void Create(Category category, Status status, string description) { return new Task { Category = category, Status = status, Description = descrtiption }; } } I do it like this because I am consistently told that entities should not access the repositories, but it would make much more sense to me if I did this: Entity: public class Task { //... public static void Create(Category category, string description) { return new Task { Category = category, Status = _statusRepository.GetById(Constants.Status.OutstandingId), Description = descrtiption }; } } The status repository is dependecy injected anyway, so there is no real dependency, and this feels more to me thike it is the domain that is making thedecision that a task defaults to outstanding. The previous version feels like it is the application layeer making that decision. Any why are repository contracts often in the domain if this should not be a posibility? Here is a more extreme example, here the domain decides urgency: Entity: public class Task { //... public static void Create(Category category, string description) { var task = new Task { Category = category, Status = _statusRepository.GetById(Constants.Status.OutstandingId), Description = descrtiption }; if(someCondition) { if(someValue > anotherValue) { task.Urgency = _urgencyRepository.GetById (Constants.Urgency.UrgentId); } else { task.Urgency = _urgencyRepository.GetById (Constants.Urgency.SemiUrgentId); } } else { task.Urgency = _urgencyRepository.GetById (Constants.Urgency.NotId); } return task; } } There is no way you would want to pass in all possible versions of Urgency, and no way you would want to calculate this business logic in the application layer, so surely this would be the most appropriate way? So is this a valid reason to access repositories from the domain?

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  • Is it bad practice for services to share a database in SOA?

    - by Paul T Davies
    I have recently been reading Hohpe and Woolf's Enterprise Integration Patterns, some of Thomas Erl's books on SOA and watching various videos and podcasts by Udi Dahan et al. on CQRS and Event Driven systems. Systems in my place of work suffer from high coupling. Although each system theoretically has its own database, there is a lot of joining between them. In practice this means there is one huge database that all systems use. For example, there is one table of customer data. Much of what I've read seems to suggest denormalising data so that each system uses only its database, and any updates to one system are propagated to all the others using messaging. I thought this was one of the ways of enforcing the boundaries in SOA - each service should have its own database, but then I read this: http://stackoverflow.com/questions/4019902/soa-joining-data-across-multiple-services and it suggests this is the wrong thing to do. Segregating the databases does seem like a good way of decoupling systems, but now I'm a bit confused. Is this a good route to take? Is it ever recommended that you should segregate a database on, say an SOA service, an DDD Bounded context, an application, etc?

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  • What modern design pattern / software engineering books for Java SE 6 do you recommend ?

    - by Scott Davies
    Hi, I am very familiar with Java 6 SE language features and am now looking for modern books that cover design patterns in Java for beginners as well as software engineering books that discuss architectures, algorithms and best practices in Java coding (sort of like the Effective C# books). I am aware of the classic GoF design patterns book, however, I'd like a more modern reference that takes advantage of the features of Java 6 SE. What books would you recommend ? Thanks, Scott

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  • .NET Demon support for VS 11 dark theme

    - by Alex.Davies
    I'm pleased to announce that .NET Demon will be shipping simultaneously with Visual Studio 11, whenever it ends up being released. That means we're going to make sure that a version of .NET Demon is released very near to the Visual Studio 11 final release which supports the new version of VS fully. The interesting part of this support is going to be the new dark theme of VS, which I'm looking forward to using. I'm told dark colours reduce eye strain for developers. It's important that extensions like .NET Demon switch to a dark theme when the rest of the IDE changes, or the dark theme will look silly. Unfortunately, none of my favourite extensions look right in the dark theme yet, so even though I use Visual Studio 11 beta for my day-to-day development already, I can't use the dark theme. Luckily .NET Demon uses WPF throughout, and the team at Microsoft are helping us to use the WPF Style system to make it easy for me to implement the support without having to add colour attributes to all the controls manually. We should have dark theme support in .NET Demon in the next month or so.

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  • OSB and Ubuntu 10.04 - Too Many Open Files

    - by jeff.x.davies
    When installing the latest Oracle Service Bus (11gR1PS3) onto my Ubuntu 10.04 system, the Eclipse IDE was complaining about there being too many open files. The Oracle Service Bus and the Oracle Enterprise Pack for Eclipse (aka OEPE) do make use of ALOT of files. By default, Ubuntu will restrict each user to 1024 open files. A much more realistic number for OSB development is 4096. Changing the file limit in Ubuntu is fairly simple (if arcane). You will need to modify two different files and then restart your server. First, you need to modify the limits.conf file as the root user. Open a terminal window and enter the following command: sudo gedit /etc/security/limits.conf Add the following 2 lines to the file. The asterisk simply means that the rule will apply to all users. * soft nofile 4096 * hard nofile 4096 Save your changes and close gedit. The second file to change is the common-session file. Use the following command: sudo gedit /etc/pam.d/common-session Add the following line: session required pam_limits.so Save the file and exit gedit. Restart your machine. You shouldn't have any more problems with too many open files anymore.

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  • Would a multitouch capable PC allow me to do Android development simulating the touch UI without an Android device ?

    - by Scott Davies
    Hi, I recently purchased a Samsung Galaxy Tab as a reference implementation (phone and first gen Android tablet), of Android 2.x for app development. I have noticed a slew of Android 3.0 slates being talked about at CES 2011 (Motorola XOOM, etc.). If I had a multitouch PC with the Android SDK/Emulator on it, would this allow me to more closely approximate device simulation by allowing user input via the multitouch screen ? Would it work via touch just like Windows 7 recognizes touch as mouse style input ? Has anyone done this ? Thanks, Scott

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  • AsyncBridge? Async on .NET 4.0 using VS11

    - by Alex.Davies
    I've just found something quite cool. It's a code snippet that lets you use the real VS 11 C#5 compiler to write code that uses the async and await keywords, but to target .NET 4.0. It was published by Daniel Grunwald (from SharpDevelop).That means I can stop using the Async CTP for VS2010, which is not at all supported anymore, and a pain to install if you have windows updates turned on. Obviously I couldn't ask all my users to install .NET 4.5 beta, but .NET Demon is a VS 2010 extension, so we already have .NET 4.0. At the time of writing, VS11 is in beta still, but hopefully it's stable enough for my team to use!I would have written the code myself, but I had the wrong impression that the C# 5 beta compiler only looked in mscorlib for the helper classes it needs to implement async methods. Turns out you can provide them yourself. You can get the code here: https://gist.github.com/1961087You just add it to your project, and the compiler will apparently pick it up and use it to implement async/await. I'm at my parents' place for Easter without access to a machine with VS 11 to try it out. Let me know whether you get it to work!This reminds me of LINQBridge, which let us use C# 3 LINQ, but only require .NET 2. We should stick up a webpage to explain, with a nice easy dll, put it in nuget, and call it AsyncBridge.If you were really enthusiastic, you could re-implement the skeleton of the Task Parallel Library against .NET 2 to use async/await without even requiring .NET 4. Our usage stats suggest that practically everyone that uses Red Gate tools already has .NET 4 installed though, so I don't think I'll go to the effort.

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  • C# 5: At last, async without the pain

    - by Alex.Davies
    For me, the best feature in Visual Studio 11 is the async and await keywords that come with C# 5. I am a big fan of asynchronous programming: it frees up resources, in particular the thread that a piece of code needs to run in. That lets that thread run something else, while waiting for your long-running operation to complete. That's really important if that thread is the UI thread, or if it's holding a lock because it accesses some data structure. Before C# 5, I think I was about the only person in the world who really cared about asynchronous programming. The trouble was that you had to go to extreme lengths to make code asynchronous. I would forever be writing methods that, instead of returning a value, accepted an extra argument that is a "continuation". Then, when calling the method, I'd have to pass a lambda in to it, which contained all the stuff that needed to happen after the method finished. Here is a real snippet of code that is in .NET Demon: m_BuildControl.FilterEnabledForBuilding(     projects,     enabledProjects = m_OutOfDateProjectFinder.FilterNeedsBuilding(         enabledProjects,         newDirtyProjects =         {             // Mark any currently broken projects as dirty             newDirtyProjects.UnionWith(m_BrokenProjects);             // Copy what we found into the set of dirty things             m_DirtyProjects = newDirtyProjects;             RunSomeBuilds();         })); It's just obtuse. Who puts a lambda inside a lambda like that? Well, me obviously. But surely enabledProjects should just be the return value of FilterEnabledForBuilding? And newDirtyProjects should just be the return value of FilterNeedsBuilding? C# 5 async/await lets you write asynchronous code without it looking so stupid. Here's what I plan to change that code to, once we upgrade to VS 11: var enabledProjects = await m_BuildControl.FilterEnabledForBuilding(projects); var newDirtyProjects = await m_OutOfDateProjectFinder.FilterNeedsBuilding(enabledProjects); // Mark any currently broken projects as dirty newDirtyProjects.UnionWith(m_BrokenProjects); // Copy what we found into the set of dirty things m_DirtyProjects = newDirtyProjects; RunSomeBuilds(); Much easier to read! But how is this the same code? If we were on the UI thread, doesn't the UI thread have to block while FilterEnabledForBuilding runs? No, it doesn't, and that's the magic of the await keyword! It cuts your method up into its constituent pieces, much like I did manually with lambdas before. When you run it, only the piece up to the first await actually runs. The rest is passed to FilterEnabledForBuilding as a continuation, which will get called back whenever that method is finished. In the meantime, our thread returns, and can go back to making the UI responsive, or whatever else threads do in their spare time. This is actually a massive simplification, and if you're interested in all the gory details, and speed hacks that the await keyword actually does for you, I recommend Jon Skeet's blog posts about it.

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  • Object oriented wrapper around a dll

    - by Tom Davies
    So, I'm writing a C# managed wrapper around a native dll. The dll contains several hundred functions. In most cases, the first argument to each function is an opaque handle to a type internal to the dll. So, an obvious starting point for defining some classes in the wrapper would be to define classes corresponding to each of these opaque types, with each instance holding and managing the opaque handle (passed to its constructor) Things are a little awkward when dealing with callbacks from the dll. Naturally, the callback handlers in my wrapper have to be static, but the callbacks arguments invariable contain an opaque handle. In order to get from the static callback back to an object instance, I've created a static dictionary in each class, associating handles with class instances. In the constructor of each class, an entry is put into the dictionary, and this entry is then removed in the Destructors. When I receive a callback, I can then consult the dictionary to retrieve the class instance corresponding to the opaque reference. Are there any obvious flaws to this? Something that seems to be a problem is that the existence static dictionary means that the garbage collector will not act on my class instances that are otherwise unreachable. As they are never garbage collected, they never get removed from the dictionary, so the dictionary grows. It seems I might have to manually dispose of my objects, which is something absolutely would like to avoid. Can anyone suggest a good design that allows me to avoid having to do this?

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  • An experiment: unlimited free trial

    - by Alex.Davies
    The .NET Demon team have just implemented an experiment that is quite a break from Red Gate's normal business model. Instead of the tool expiring after the trial period, it now continues to work, but with a new message that appears after the tool has saved you a certain amount of time. The rationale is that a user that stops using .NET Demon because the trial expired isn't doing anyone any good. We'd much rather people continue using it forever, as long as everyone that finds it useful and can afford it still pays for it. Hopefully the message appearing is annoying enough to achieve that, but not for people to uninstall it. It's true that many companies have tried it before with mixed results, but we have a secret weapon. The perfect nag message? The neat thing for .NET Demon is that we can easily measure exactly how much time .NET Demon has saved you, in terms of unnecessary project builds that Visual Studio would have done. When you press F5, the message shows you the time saved, and then makes you wait a shorter time before starting your application. Confronted with the truth about how amazing .NET Demon is, who can do anything but buy it? The real secret though, is that while you wait, .NET Demon gives you entertainment, in the form of a picture of a cute kitten. I've only had time to embed one kitten so far, but the eventual aim is for a random different kitten to appear each time. The psychological health benefits of a dose of kittens in the daily life of the developer are obvious. My only concern is that people will complain after paying for .NET Demon that the kittens are gone.

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  • A new tool in beta: Conflict Alert

    - by Alex Davies
    You know that manual merges are a real pain? Well, I’ve just released a Visual Studio extension that makes manual merges a thing of the past. No source control system can automatically merge two edits to the same line of code. Conflict Alert solves this by warning you that you are heading down a path that will cause a manual merge later down the line. You choose whether you want to carry on, or talk to your teammate and find out what they are doing. Have you ever warned your teammates that you are doing a big refactor, and that they should ‘keep out of class X’? Conflict Alert tells them for you automatically by highlighting the sections of code that you have edited.   It doesn’t need to connect to your source control system, so it works no matter which you use. Its a first release, and I hope it is useful. Any feedback would be gratefully received. Grab a teammate and try it now.

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  • An experiment: unlimited free trial

    - by Alex.Davies
    The .NET Demon team have just implemented an experiment that is quite a break from Red Gate's normal business model. Instead of the tool expiring after the trial period, it now continues to work, but with a new message that appears after the tool has saved you a certain amount of time. The rationale is that a user that stops using .NET Demon because the trial expired isn't doing anyone any good. We'd much rather people continue using it forever, as long as everyone that finds it useful and can afford it still pays for it. Hopefully the message appearing is annoying enough to achieve that, but not for people to uninstall it. It's true that many companies have tried it before with mixed results, but we have a secret weapon. The perfect nag message? The neat thing for .NET Demon is that we can easily measure exactly how much time .NET Demon has saved you, in terms of unnecessary project builds that Visual Studio would have done. When you press F5, the message shows you the time saved, and then makes you wait a shorter time before starting your application. Confronted with the truth about how amazing .NET Demon is, who can do anything but buy it? The real secret though, is that while you wait, .NET Demon gives you entertainment, in the form of a picture of a cute kitten. I've only had time to embed one kitten so far, but the eventual aim is for a random different kitten to appear each time. The psychological health benefits of a dose of kittens in the daily life of the developer are obvious. My only concern is that people will complain after paying for .NET Demon that the kittens are gone.

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  • Latest update to Ubuntu 13.10 broke Intel graphics drivers

    - by James Davies
    I'm running a copy of Ubuntu 13.10 on an i7-4771 w/ Intel HD4600 Graphics using a Dell Ultrasharp 1440p monitor via Displayport. Up until today this configuration has been working perfectly, however the latest update appears to have broken my graphics configuration, and xorg is now refusing to go above 1280p resolution. Running xrandr it appears the driver incorrectly thinks my monitor is plugged into the HDMI port and is detecting a max resolution of 1920x1200 instead of 2560x1440. (It's actually plugged in via Displayport). Based on the apt history.log, the latest update was for the kernel. I'm presuming the issue is that the official Intel driver hasn't been updated to support this version? Is there any way to resolve this, or will I need to upgrade to 14.10 to get the latest driver from Intel? Start-Date: 2014-05-28 11:30:57 Commandline: aptdaemon role='role-commit-packages' sender=':1.473' Install: linux-image-extra-3.11.0-22-generic:amd64 (3.11.0-22.38), linux-image-3.11.0-22-generic:amd64 (3.11.0-22.38), linux-headers-3.11.0-22:amd64 (3.11.0-22.38), linux-headers-3.11.0-22-generic:amd64 (3.11.0-22.38)

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  • An experiment: unlimited free trial

    - by Alex Davies
    The .NET Demon team have just implemented an experiment that is quite a break from Red Gate’s normal business model. Instead of the tool expiring after the trial period, it now continues to work, but with a new message that appears after the tool has saved you a certain amount of time. The rationale is that a user that stops using .NET Demon because the trial expired isn’t doing anyone any good. We’d much rather people continue using it forever, as long as everyone that finds it useful and can afford it still pays for it. Hopefully the message appearing is annoying enough to achieve that, but not for people to uninstall it. It’s true that many companies have tried it before with mixed results, but we have a secret weapon. The perfect nag message? The neat thing for .NET Demon is that we can easily measure exactly how much time .NET Demon has saved you, in terms of unnecessary project builds that Visual Studio would have done. When you press F5, the message shows you the time saved, and then makes you wait a shorter time before starting your application. Confronted with the truth about how amazing .NET Demon is, who can do anything but buy it? The real secret though, is that while you wait, .NET Demon gives you entertainment, in the form of a picture of a cute kitten. I’ve only had time to embed one kitten so far, but the eventual aim is for a random different kitten to appear each time. The psychological health benefits of a dose of kittens in the daily life of the developer are obvious. My only concern is that people will complain after paying for .NET Demon that the kittens are gone.

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  • What programming language(s) could I develop this app with for an iPhone

    - by Keon Davies
    The app I'm thinking of making would be little similar to fruit ninja. The app/ game would involve different types of animals flying straight at and you have to choose the right item to catch the animal before he gets to you. For example to capture a fish you would have to select the net and then click on the fish to capture it. Also I would like to have a leader board too. Which programming language(s) could I use to develop what I just described?

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  • You can step over await

    - by Alex Davies
    I’ve just found the coolest feature of VS 2012 by far. I thought that being able to silence an exception from the “exception was thrown” popup was awesome, and the “reload all” button when a project file changes is amazing, but this is way beyond all of that. You can step over awaits when you debug your code!! With F10!!! Ok, so that may not sound such a big deal. You can step over ifs and whiles and no-one is celebrating. But await is different. await actually stops your method, signs up to be notified when a Task is finished,  returns, and resumes your method at some indeterminate point in the future. You could even end up continuing on a completely different thread. All that happens, and all I have to do is press F10. I used to have to painstakingly set a breakpoint on the first line of my callback before stepping over any asynchronous method. Even when we started using async, my mouse would instinctively click the margin every time I wanted to go past an await. And the times I was driven insane by my breakpoint getting hit by some other path of execution I don’t care about. I think this might have been introduced in the VS11 Beta, I’m pretty sure I tried it in the Async CTP in VS2010 and it didn’t work. Now it does! Woop!

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  • My book is released – Async in C# 5

    - by Alex Davies
    I’m pleased to announce that my book “Async in C# 5″ has been published by O’Reilly! http://oreil.ly/QQBjO3 If you want to know about how to use async, and whether it’s important for your code, I thoroughly recommend reading it. It’s the best book about the subject I’ve ever written. In fact it’s probably the best book I’ve written full stop. I may have only written one book. It also has a very fetching parrot on the cover, which would make a very good addition to your bookshelf.

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  • Should business services cross bounded contexts?

    - by Paul T Davies
    Firstly, I am following the convention that a bounded context is synonymous to a department, or possibly one department has 1 to many bounded contexts. We have a client consultancy department that has a Documentation Service. Documents are stored in the Document Store Service (which is where all documents in the company are stored - it is a utility service), and the Documentation Service stores information about that document (a business service). As it was designed for the client consultancy, it is information relevant to them. Now health and safety need somewhere to store information about a document. This is different information to client consultancy, but I have been instructed to extend the existing service to account for this extra information. I feel this service is now crossing a bounded context. My worry is that all departments will eventually store there information in here and the service will become bloated, trying to be all things to all departments. Each document record will only store a subset of the information because it will only belong to one department. It will get worse when different departments want to store the same information but refer to it in a diferent ways, or when two departments want to store different information that they refer to in the same way. In my understanding, this is exactly the reason for bounded contexts. I feel each department should have it's own business service for information about a document, but use the same utility service to actually store the document. What would be the correct approach?

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  • Is this a violation of the Liskov Substitution Principle?

    - by Paul T Davies
    Say we have a list of Task entities, and a ProjectTask sub type. Tasks can be closed at any time, except ProjectTasks which cannot be closed once they have a status of Started. The UI should ensure the option to close a started ProjectTask is never available, but some safeguards are present in the domain: public class Task { public Status Status { get; set; } public virtual void Close() { Status = Status.Closed; } } public ProjectTask : Task { public override void Close() { if (Status == Status.Started) throw new Exception("Cannot close a started Project Task"); base.Close(); } } Now when calling Close() on a Task, there is a chance the call will fail if it is a ProjectTask with the started status, when it wouldn't if it was a base Task. But this is the business requirements. It should fail. Can this be regarded as a violation?

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  • RemoveHandler Issues with Custom Events

    - by Jeff Certain
    This is a case of things being more complicated that I thought they should be. Since it took a while to figure this one out, I thought it was worth explaining and putting all of the pieces to the answer in one spot. Let me set the stage. Architecturally, I have the notion of generic producers and consumers. These put items onto, and remove items from, a queue. This provides a generic, thread-safe mechanism to load balance the creation and processing of work items in our application. Part of the IProducer(Of T) interface is: 1: Public Interface IProducer(Of T) 2: Event ItemProduced(ByVal sender As IProducer(Of T), ByVal item As T) 3: Event ProductionComplete(ByVal sender As IProducer(Of T)) 4: End Interface Nothing sinister there, is there? In order to simplify our developers’ lives, I wrapped the queue with some functionality to manage the produces and consumers. Since the developer can specify the number of producers and consumers that are spun up, the queue code manages adding event handlers as the producers and consumers are instantiated. Now, we’ve been having some memory leaks and, in order to eliminate the possibility that this was caused by weak references to event handles, I wanted to remove them. This is where it got dicey. My first attempt looked like this: 1: For Each producer As P In Producers 2: RemoveHandler producer.ItemProduced, AddressOf ItemProducedHandler 3: RemoveHandler producer.ProductionComplete, AddressOf ProductionCompleteHandler 4: producer.Dispose() 5: Next What you can’t see in my posted code are the warnings this caused. The 'AddressOf' expression has no effect in this context because the method argument to 'AddressOf' requires a relaxed conversion to the delegate type of the event. Assign the 'AddressOf' expression to a variable, and use the variable to add or remove the method as the handler.  Now, what on earth does that mean? Well, a quick Bing search uncovered a whole bunch of talk about delegates. The first solution I found just changed all parameters in the event handler to Object. Sorry, but no. I used generics precisely because I wanted type safety, not because I wanted to use Object. More searching. Eventually, I found this forum post, where Jeff Shan revealed a missing piece of the puzzle. The other revelation came from Lian_ZA in this post. However, these two only hinted at the solution. Trying some of what they suggested led to finally getting an invalid cast exception that revealed the existence of ItemProducedEventHandler. Hold on a minute! I didn’t create that delegate. There’s nothing even close to that name in my code… except the ItemProduced event in the interface. Could it be? Naaaaah. Hmmm…. Well, as it turns out, there is a delegate created by the compiler for each event. By explicitly creating a delegate that refers to the method in question, implicitly cast to the generated delegate type, I was able to remove the handlers: 1: For Each producer As P In Producers 2: Dim _itemProducedHandler As IProducer(Of T).ItemProducedEventHandler = AddressOf ItemProducedHandler 3: RemoveHandler producer.ItemProduced, _itemProducedHandler 4:  5: Dim _productionCompleteHandler As IProducer(Of T).ProductionCompleteEventHandler = AddressOf ProductionCompleteHandler 6: RemoveHandler producer.ProductionComplete, _productionCompleteHandler 7: producer.Dispose() 8: Next That’s “all” it took to finally be able to remove the event handlers and maintain type-safe code. Hopefully, this will save you the same challenges I had in trying to figure out how to fix this issue!

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  • Uninstall Apache using make

    - by Jeff
    I installed httpd using make. But i cant find any remove/uninstall method in README or INSTALL files. Also, i searched the http://apache.org docs. There also there is no mention of uninstalling using make. Actually, i didnt pass the PREFIX value, and it got installed into /usr/local/apache/. Is it fine? Where would it be installed by sudo apt-get install apache2? Thanks, Jeff p.s.I am using Ubuntu 9.10

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  • Silverlight Cream for November 21, 2011 -- #1171

    - by Dave Campbell
    In this Issue: Colin Eberhardt, Sumit Dutta, Morten Nielsen, Jesse Liberty, Jeff Blankenburg(-2-), Brian Noyes, and Tony Champion. Above the Fold: Silverlight: "PV Basics : Client-side Collections" Tony Champion WP7: "Pushpin Clustering with the Windows Phone 7 Bing Map control" Colin Eberhardt Shoutouts: Michael Palermo's latest Desert Mountain Developers is up Michael Washington's latest Visual Studio #LightSwitch Daily is up From SilverlightCream.com: Pushpin Clustering with the Windows Phone 7 Bing Map control Colin Eberhardt is back discussing Pushpins for a BingMaps app on WP7 and provides a utility class that clusters pushpins, allowing you to render 1000s of pins on an app ... all the explanation and all the code Part 22 - Windows Phone 7 - Tile Push Notification Part 22 in Sumit Dutta's WP7 series is about Tile Push Notification... nice tutorial with all the code listed Correctly displaying your current location Morten Nielsen demonstrates formatting the information from the GPS on your WP7 into something intelligible and useful Spiking the Pomodoro Timer Jesse Liberty put up a quick and dirty version of a Pomodoro timer for WP7.1 to explore the technical challenges of the Full Stack Phase 2 he's cranking up 31 Days of Mango | Day #11: Network Jeff Blankenburg's Number 10 in his 31 Days quest of WP7.1 is about the NetworkInformation namespace which gives you all sorts of info on the user's device network connection availability, type, etc. 31 Days of Mango | Day #11: Live Tiles Jeff Blankenburg takes off on Live Tiles for Day 11... big topic for a 1 day post, but he takes off on it... updating and Live Tiles too Working with Prism 4 Part 2: MVVM Basics and Commands Brian Noyes has part 2 of his Prism/MVVM series up at SilverlightShow... very nice tutorial on the basics of getting a view and viewmodel up, and setting up an ICommand to launch an Edit View... plus the code to peruse. PV Basics : Client-side Collections Tony Champion is startig a series on Silverlight 5 and Pivot Viewer... First up is some basics in dealing with the control in SL5 and talking about Client-side Collections... great informative tutorial and all the code Stay in the 'Light! Twitter SilverlightNews | Twitter WynApse | WynApse.com | Tagged Posts | SilverlightCream Join me @ SilverlightCream | Phoenix Silverlight User Group Technorati Tags: Silverlight    Silverlight 3    Silverlight 4    Windows Phone MIX10

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