Skip to main content

Proper initialize/dispose with WCF and MEF

Initialization and disposing of services in a WCF application is a bit of a hassle to control when running on an IIS instance, since the application starts and stops every now and then based on server requests. It doesnt make it easier when using an IOC, as in our case MEF.

To have total control of the startup and shutdown events we began with adding a service factory to all our WCF services.

<%@ ServiceHost Language="C#" Debug="true" Service="WcfService" Factory="CustomServiceHostFactory" %>

When ever the application gets woke up by a request to any of the services, the service factory will be used to instantiate the service. This means we can add any logic to these methods to have full control of the WCF application initialization. Here is what a service factory class could look like. (Composition is a static class containing a reference to the MEF container)

public class CustomServiceHostFactory : ServiceHostFactory
{
    private static readonly object SynchronizationContext = new object();

    public CustomServiceHostFactory ()
    {
        ApplicationInitialize();
    }

    protected override ServiceHost CreateServiceHost(Type serviceType, Uri[] baseAddresses)
    {
        var serviceHost = base.CreateServiceHost(serviceType, baseAddresses);
        serviceHost.Opened += (s, a) => ApplicationStarted();
        serviceHost.Closed += (s, a) => ApplicationDispose();
        return serviceHost;
    }

    private void ApplicationInitialize()
    {
        if (Composition.Container != null) return;

        lock (SynchronizationContext)
        {
            if (Composition.Container == null)
            {
                // Initialize container
                Composition.Initialize();
            }
        }
    }

    private void ApplicationStarted()
    {
        // Do anything after application has been started
    }

    private void ApplicationDispose()
    {
        lock (SynchronizationContext)
        {
            if (Composition.Container != null)
                Composition.Dispose();
        }
    }
}

Since there are more than one service running we have to make sure the factory is thread safe and only does the initialization and disposing once. You should also note the order in which the methods are executed. The initialization are done in the constructor, but if you want something done when initialization is completed you should use the ServiceHost.Opened event, which is accessible by overriding the CreateServiceHost method.

Comments

Popular posts from this blog

The Cornball goes to Brunch with Chaplin

Lately I've been working pretty hard on different projects but not really stumbling upon anything blogworthy. The most recent project is quite interesting though, a single page, touch friendly, web application using the latest and greatest technologies. We've ended up with using Brunch with Chaplin, which is a very neat way of setting up a Backbone based single page web project with Brunch and Chaplin.

Aside from this, I have my own little project that has lived on for almost 15 years already, The Cornball. From being a plain Windows application written i C an Win32 API, it has been ported to .NET using WPF, and is currently a Silverlight application hosted on Windows Azure.

I could not find a better time to reanimate this project and create a new web based version, touch friendly, super optimized, awesome in any way. So I did... So please follow my journey at Github. It's going to take a while, I assure you, but I already have some ground work done.

Meanwhile, check out …

Binding a HTML-formatted string to a WPF WebBrowser control

Sometimes there is a need to display a HTML formatted string in a WPF application. There are a couple of ways to do this, but the most stright forward is to use a WebBrowser control and the NavigateToString method.

This approach has one big flaw, you cannot use binding to a string out of the box, but I found a great solution through Stack Overflow which adds a bindable property to the  WebBrowser control using  NavigateToString.

The following class is all that is needed to add that behavior. A new depencency property named Html is introduced to the  WebBrowser and the proper change action is performed in the OnHtmlChanged method.

public class BrowserBehavior { public static readonly DependencyProperty HtmlProperty = DependencyProperty.RegisterAttached( "Html", typeof(string), typeof(BrowserBehavior), new FrameworkPropertyMetadata(OnHtmlChanged)); [AttachedPropertyBrowsableForType(typeof(WebBrowser))] public static string GetHtml(WebBrowser browser) { …

Using Bootstrap Tooltip to show Parsley validation errors

I'm currently working on a web application using a variety of different frameworks, such as Backbone for the back-end, Bootstrap for the front-end and Parsley for client side form validation. Parsley is a really powerful validation toolkit, but it takes some tweaking to make it blend with the Bootstrap front-end. Fortunately this is a one time fix, which can be re-used all over our project.

Since there will be some custom options in our Parsley object, we can't use the default parsley-validate attribute on the form. Instead we have to initialize the validation with the jQuery syntax:

$('#my-form').parsley(parsleyOptions);
The options are were the magic happens, and in our case we have a global options object that our forms use to get the same experience all over the application. Here's what it looks like:

var parsleyOptions = {  // Sets success and error class to Bootstrap class names  successClass: 'has-success',  errorClass: 'has-error',  // Bo…