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Showing posts from 2012

IIS Worker Process Quits, Service Unavailable

Ran into one of those issue yesterday that I have come across almost 2 years back. My WCF service was hosted on IIS, and we were doing a few load tests, after a few rounds of requests no request went through and was in error.Tried browsing the WCF SVC file from IIS and got the message "Service Unavailable", went to the application pool section in IIS and noticed that the app pool running the WCF service has stopped. In a situation like this, I never try to just fix the issue but to see why the problem has come in the first place. Took a look at the event viewer and I could see a number of errors from ASP.NET and that the worker processor has quit. Took a look at the code and the code pointed out that their was a piece of code that runs on a separate thread and that thread throws an error due to a missing stored procedure in the database.
So why does the worker processor stop when there is an error?, by default, from .NET 2.0, if there is an unhandled exception, the worker proces…

Hosting WCF services on IIS or Windows Services?

There came one of those questions from the client whether to use II7 hosting or windows service hosting for WCF services. I tried recollecting a few points and thought of writing it down.
WCF applications can be hosted in 2 main ways- In a Windows service- On IIS 7 and aboveWhen WCF was first released, IIS 6 did not support hosting WCF applications that support Non-HTTP communication like Net.TCP or Net.MSMQ and developers had to rely on hosting these services on Windows Services.With the release of IIS 7, it was possible to deploy these Non-Http based applications also on IIS 7. Following are the benefits of using IIS 7 to host WCF applications
Less development effort
Hosting on Windows service, mandates the creating of a Windows service installer project on windows service and writing code to instantiate the service, whereas the service could just be hosted on IIS by creating an application on IIS, no further development is needed, just the service implementation is n…

MEF (Managed Extensibility Framework), .NET 4, Dependency Injection and Plug-in Development

Almost after .Net 4 was released I remember reading about MEF (Managed Extensibility Framework), this was a framework for developers to compose their application with required dependencies. At first this looks like the Unity Container used for dependency injection, but MEF is much more than a dependency container but there is nothing stopping you from using MEF as a dependency injector.I remember around 5 years back when I was in a project that created a framework that allows developers to plug-in there modules as WinForm screens. The developer would create a set of screens with the intended functionalities and the drop this component in the bin folder of the framework and then will move on to do some painful configurations for the framework to pick up the module. Dropping the component into the bin folder and doing a bit of configuration is all that s needed for the framework to pick up display the screens. Typically, the configurations would also contain metadata about the screen.Al…

Task based Asynchronous pattern, Async & Await and .NET 4.5

One of the key features in .Net 4.5 is to write asynchronous programs much easier. So if I was to write asynchronous programs in .Net 2.0/3.5, I would either follow the event based model or the callback based model. For an example, a synchronous method that does intensive work (say the DoWork()) can be made asynchronous by using the following patterns
1) Implementing the IAsyncResult pattern. in this implementation, 2 methods are exposed for the DoWork() synchronous method, the BeginDoWork() and the EndDoWork() method. The user will call the BeingDoWork() passing in the required parameters and a callback of the delegate type AsyncCallback(IAsyncResult). The BeginDoWork() will spawn a new thread a return control back to the user. Once work is completed in the spawned method, as a last step, it will call the inform the AsyncResult implementation, which in turns will call the EndDoWork() (which is the callback that was passed in to the BeginDoWork()).
2) Implementing the event pattern. Her…

REST Services with ASP.NET Web API

Sometimes back, ASP.NET MVC 4 beta was release, this comes with quite a lot of capabilities to create mobile web applications with HTML5, to new features on Razor etc..One of the milestones of this release is ASP.NET Web APIs, which allows developers to implement REST services. .NET 3.5/4.0 WCF provides us with the support of creating REST APIs using the webHttpBinding, however most of the features required to run the service needs the ASP.NET compatibility mode, this basically means the request to the REST service would first go through the ASP.NET pipeline, before being handed over to WCF. Then there was the WCF Web API, where Microsoft tried to re-define how REST services are created, but they opted in for moving REST support into ASP.NET and then to WCF, hence ASP.NET Web API, becomes the de facto technology for creating REST services. WCF WebHttpBinding would still exist, bu the recommendation is to to use Web APIs.
Implementing a Web API is simple, the steps involved are... 1) Cre…

Simple factory, Dependency Injection and Unity

Someone asked me the question whether a simple factory can be implemented using dependency injection container. The example he bought up is where a simple factory takes in a string and switches this string to return the correct instance of the object needed....I am talking about something like this.internalIWaterMarkProvider GetProvider(string fileExtension){IWaterMarkProvider provider = null;switch (fileExtension.ToLower()){case"pdf":provider = newPDFProvider();break;case".docx":provider = newWordProvider();

System.Runtime.Caching (.Net 4.0)

.Net 4.0 introduced the System.Runtime.Caching namespace, this made developers to make use of caching functionality independent of the cache found in the System.Web DLL.Caching using the System.Runtime.Caching provides an in memory cache but also allows developers to extend this with a different provider. For an example, you could have an implementation that could hold the items in memory but also persists it into the hard disk for the fear of cache eviction.
Adding an item into the cache is done this way...
//Get the default cache MemoryCache cache = MemoryCache.Default; //Add the itemcache.Add("MyKey","Nairooz Nilafdeen",DateTimeOffset.Now.AddMinutes(19));//Get the item from the cacheif (cache.Contains("MyKey")){Console.WriteLine(cache.Get("MyKey"));}
The caching namespace also allows you to set ChangeMonitors for the cache policy, for an example, you can specify that the cache needs to expire once a file changes or the database query changes.. You …