In this short code snippet, I want to show a simple technique for ensuring only one instance of your .NET application can run at a time.
The technique is below :
public partial class App : Application
private Mutex _mutex;
_mutex = new Mutex(true, @"Global\" + "MyUniqueWPFApplicationName", out aIsNewInstance);
if (aIsNewInstance) return;
MessageBox.Show("There is already an instance running.",
"Instance already running.",
What happens is that a Mutex is created when the application starts up and it is given a unique name, in this case, “MyUniqueWPFApplicationName“. If another instance of the application is started up and the Mutex is already created with that name, the application will shut down. You will also notice that there is a prefix to the name (Global\) that makes the unique name global to a sever running terminal services. If you leave off this prefix, then the mutex is considered local.
Even though all the code in contained in the article, I have received many requests for a Visual Studio project containing the code and all the unit tests that cover the test scenarios in the original article, so what I have done is open source the code on Codeplex. It seems many people have found this code useful, which is great, so I hope that by open sourcing it, more people will get use out of it.
In a previous article on async and await, I showed a very simple example of how to run some code asynchronously. Then in the 2nd article I showed an example of updating the user interface in the main thread from an async method.
The code below (from the previous article) would execute a long running task which in this case counts to 5,000,000. As the task was running, on a set interval, the UI would be updated. This effectively decoupled the running of the task from the updating of the UI. You could have the task update the UI every 10ms, or you could update every 5 seconds. It really depends on what you are trying to do.
public partial class Form1 : Form
private readonly SynchronizationContext synchronizationContext;
private DateTime previousTime = DateTime.Now;
synchronizationContext = SynchronizationContext.Current;
private async void ButtonClickHandlerAsync(object sender, EventArgs e)
button1.Enabled = false;
var count = 0;
await Task.Run(() =>
for (var i = 0; i <= 5000000; i++)
count = i;
label1.Text = @"Counter " + count;
button1.Enabled = true;
public void UpdateUI(int value)
var timeNow = DateTime.Now;
if ((DateTime.Now - previousTime).Milliseconds <= 50) return;
synchronizationContext.Post(new SendOrPostCallback(o =>
label1.Text = @"Counter " + (int)o;
previousTime = timeNow;
A reader on Reddit suggested that you can write this code in a much more succinct way as shown below. The code is much simpler to see what’s going on, but the behaviour is slightly different. In this example, the code similarly counts upto 5,000,000 and updates the UI label. The await statement here will correctly restore the synchronisation context to update the UI thread which means you don’t have to deal with it manually (I didn’t realise that at the time). To enable the asynchrony of the task in this example we need to have a Task.Delay(1) as we are not using any other asynchronous objects in .NET for file or DB access for example.
In this article I have collated a few training links about the AutoMapper Library. I will keep adding to this page as I find other useful free resources. If you have any videos or articles that you feel would be useful here then please let me know in the comments and I will add them to the post. I would like it to be an archive of good material.
In a previous article on async and await, I showed a very simple example of how to run some code asynchronously. In this article, I want to take this a little further with another example.
I have recently had to go and maintain an old c# Winforms application (yes I know winforms is a little old and considered the new vb6 but the application works and still provides value) that needed some new features adding. The problem with this application is that is feels a little sluggish for the user and constantly locks up, or gives the impression that it has crashed which means users have been trying to kill the application when really, it is processing a lot of work and the UI has become unresponsive.
Whilst I was in the code base, I wanted to try and improve some of this unresponsiveness by moving code out into tasks and asynchronously updating the UI. In this article I will cover how to do this.
Example of Unresponsive Application
First lets start with a small example. Below is a screen shot of a very simple winforms app. It doesn’t really do much. When you load it up, you press the button and the application counts to 5,000,000. I want this count to be displayed on the screen.
public partial class Form1 : Form
private void ButtonClickHandler(object sender, EventArgs e)
for (var i = 0; i <= 5000000; i++)
label1.Text = @"Counter = " + i;
In the code above, when you click the button in the application it calls the ButtonClickHandler which starts a count to 5,000,000. Inside the for loop we also try to update the text on the label to tell the user how far the count has got.
I was talking with a colleague the other day about all the extra things I do outside of work, like recording my pluralsight course, writing for my blog, a simple educational game I am writing plus my other little open source projects I maintain. He asked the question, “How do you fit it all in?”.
It’s a great question, because I am a Dad to 2 children, plus a husband, and I work a full-time day job, so how do I fit it all in working on these projects and keeping my skills up to date. The rest of this post explains what I do.
Everyday I commute to work. This involves a 15 minute walk to the train station, 45 minutes on the train, and then another 20 minutes walk from the train station to the office. A lot of people would think that I am mad doing this everyday, but I wouldn’t give up this time for anything.
When I am walking to and from train stations I normally listen to podcasts like DotNetRocks,HelloWorld. These podcasts give you loads of new information and ideas, plus they are entertaining. Also, the walking is good exercise. I don’t go to the gym, but 35 minutes brisk walking everyday keeps me fit.
In this article I want to give a simple example for how to use the async await keywords in C# to create asynchronous background tasks.
Writing multi-threaded or asynchronous code has traditionally always been very hard to get right but is something that is needed to help keep our applications responsive and to avoid performance bottlenecks. C# 5 introduced a simplified model for doing asynchronous programming with the introduction of 2 new keywords, async and await.
If you specify that a method is an asynchronous method by using an async modifier, you enable the following two capabilities.
The marked async method can use the await keyword to designate suspension points. The await operator tells the compiler that the async method can’t continue past that point until the awaited asynchronous process is complete. In the meantime, control returns to the caller of the async method. The suspension of an async method at an await expression doesn’t constitute an exit from the method, and finally blocks don’t run.
The marked async method can itself be awaited by methods that call it.
An async method typically contains one or more occurrences of an await operator, but the absence of await expressions doesn’t cause a compiler error. If an async method doesn’t use an await operator to mark a suspension point, the method executes as a synchronous method does, despite the async modifier. The compiler issues a warning for such methods.
Asynchrony is essential for activities that are potentially blocking, such as when your application accesses the web or a file system. Access to a web resource, for example, is sometimes slow or delayed. If such an activity is blocked within a synchronous process, the entire application must wait. In an asynchronous process, the application can continue with other work that doesn’t depend on the web resource until the potentially blocking task finishes.
In this article I want to talk a little about Password Based Key Derivation Functions and their use in .NET. A Password Based Key Derivation Function or PBKDF2 as it is known, is a way to encode passwords as an alternative to hashing functions which are susceptible to rainbow table attacks.
For this article though I am going to try a different method of explaining it. I am going to talk about this subject and do a little code demo by video. Yes, you have to suffer my voice and video editing. This video was actually recoded back in June, and the astute amongst you will notice that this looks very much like a Pluralsight video. Well, it is, kind of. This is one of my audition videos that I had to produce to become a Pluralsight author.
I was very pleased with the result seeing as it was my first time recording and editing a video / code demo, and Pluralsight were gracious enough to give me permission to post the video on my blog, but minus the Pluralsight branding, as it is not an official video of theirs.
Now that I have the video recording bug, plus I have paid for all the software and hardware etc, I may do more of these along side my Pluralsight courses.
The other day Microsoft announced their new version of Windows, called Windows 10. If you want to try this yourself then you can download the preview from here. This is of-course a very early preview, but the new features so far include:
The return of the Start Menu: It’s back by popular demand. It’s a funny one, as this is what has caused so much fuss with Windows 8. I got around the problem by just installing Start 8, but some people really did get upset.
Task View and virtual workspaces : I am surprised it has taken this long to get virtual workspaces. I flit between Windows and Linux and this has always been something I really like in the gnome derivative Linux front ends.
Snap Assist : A new Snap Assist feature also helps users work out which way is best to snap apps to. You can snap windows into new screens and tile Windows.
Command Prompt Keyboard Short-cuts : you can now paste directly into the command prompt. FINALLY!!
Home Location: The latest windows explorer has a handy home location as the default view in explorer.
Continuum : Continuum is an on-the-fly mode for 2 in 1 devices that can automatically change mode if it detects there is suddenly no keyboard attached. So, for example, a back button appears to help you navigate the Desktop with touch if the keyboard is removed.
Windows 10 Universal Apps : Windows 10 will also usher in a new app model – Universal Windows apps. Windows Universal apps are the new name for Metro apps/Modern apps/Windows Store apps. Windows 10 will be able to run on all devices from phones to servers and there will be a single app store across the lot.
I downloaded the ISO image last night and started installing it into VMWare Workstation. The installation looked very familiar to that of Windows 8 and was pretty painless. I was up and running within 20 minutes.
The basic look and feel is similar to Windows 8 also, but as you can see in the screen shot below, the Start Menu is back and it represents a hybrid between the original Windows 7 start button and the Windows 8 Modern UI live tiles. On first impressions I like it. I need to play around with it more to configure it to my liking, but on first impressions I think I can easily get used to it.
My personal favourite new feature is the new virtual workspaces. Whilst many other operating systems have had this for ages, it is nice to finally get this in Windows. I like the idea of running my software development applications in 1 workspace and productivity apps on another if I am working on a single screen, or laptop.
My first impressions are that Microsoft are on the right track with Windows 10. They have learnt a lot of hard lessons from Windows 8, so I hope that this new version, once it finally gets released, will be their new killer operating system like Windows 7 was. I have only played with it for half an hour so far as it was quite late in the evening once I got it installed, but I will have a longer play and do a longer post about it.
Lots has been written about the benefits of Agile methodologies and Scrum for the development team. Articles about the agile manifesto and scrum have encouraged developers to think about iterations, user stories, backlog items and delivering value with rapid defect feedback, but at the end of the day, what’s in it for your business?
In this article I am going to think from the businesses point of view. What’s in it for your business? They don’t really care about iterations, continuous delivery, unit tests and all the other good stuff us developers love. They care about their business and competitive advantage. Especially if there is a danger of a young start-up being disruptive and stealing market share from under your feet.