Saturday, 29 September 2012

MEF and memory

For those of you that are coding in .NET today, chances are high that you are doing it in using composition through usually a container and using Inversion of Control (IoC). Many will use the Managed Extensibility Framework or MEF, for achieving IoC. MEF is not entirely a true IoC container, as the framework supports non-specific import and export of interfaces bound to implementation(s) using inheritors of ComposablePartCatalog such as AssemblyCatalog.

To download versions of MEF, visit the site http://mef.codeplex.com However, most of us will use the stable version of MEF available in .NET 4, situated in the System.ComponentModel.Composition namespace.

MEF is very easy to get started with and the concepts of importing and exporting parts are really great.
However, there is big flaw in MEF which is well known to its users and contributors, which is the way MEF handles memory. Without getting too much into detail, MEF will generally keep a reference to all parts in its container as long as the application or system is running. This results in a high and observable memory leak. To take an example, I have put together a downloadable solution at the end of this article which shows a way to avoid the memory leak. The test solution will be explained throughout this article with the most relevant parts underlined.

First off, the base of this test solution is not mine. I needed to get a sample of a WPF/MVVM/MEF/Prism solution where I could test out the concepts at home and googled for some simple demo project. I found one at the top, Prism 4 MEF application. It is available at the following URL:

Prism 4 MEF application:
http://www.codeproject.com/Articles/254120/Prism-4-MEF-Application

Code Project Open License terms:
http://www.codeproject.com/info/cpol10.aspx

I will understate that my sample is based on the solution written by Danny Siew from Wellington, New Zealand. Thanks to Danny Siew I could focus on finding a solution of the memory leak problem in MEF.

To verify that the memory leak was fixed with my solution, I downloaded the ANTS Memory Profiler from Red Gate. A trial can be downloaded at the following URL:
http://www.red-gate.com/products/dotnet-development/ants-memory-profiler/

Using the ANTS Memory Profiler, one can quickly identity the memory leak through MEF by profiling your application that is using MEF and witness that parts that are removed and is no longer used in the application are kept alive (that is, not disposed so memory resources can become available again). My main concern are the parts that are marked as CreationPolicy.NonShared. The other parts are usually the singletons, with CreationPolicy.Shared. These parts will have at most one instance and should live throughout the lifetime of the application and not become disposed before the container is disposed. It is though a huge issue that those parts that are marked as NonShared will not be dispoed before the container is dispose, because this means that the number of instances will be accumulated in memory. Clearly, not a desired behavior of MEF!

My solution is actually based upon the following discussion at the following thread on the MEF Codeplex site:
http://mef.codeplex.com/discussions/285445

Thanks to the user Palomino for this great tip:
http://www.codeplex.com/site/users/view/palomino

The strategy of Palomino is to create a CustomCatalog inheriting from the usual abstract base class ComposablePartCatalog in MEF. This class will detect when a part is requiring disposing. I have modified Palomino's code slightly, as it will deactivate the non-desired caching of the part in the CatalogExportProvider MEF uses if the part is marked as CreationPolicy.NonShared. This is how I mean the correct behavior should be. The singletons or shared parts should be disposed in the usual "MEF-way", that is when the container is disposed. The non-shared parts should be disposed when parts go out of scope for early release of resources. In no circumstances should MEF keep caching non-shared parts, as the chances for memory leak is 100%. The project manager of MEF, Glenn Block has created ExportFactory classes that are able to dispose parts on demand. This will be available in .NET 4.5 and a port has been made available at Glenn's Skydrive for download (consisting of a single DLL file) where the inherited MEF Bootstrapper can be adjusted to allow this dispose on demand. I spent some time testing out this ExportFactory class but using ANTS Memory Profiler I could not see the memory leak go away..

It is time present some code for how to avoid this memory leak problem in ANTS, since any real application or system out there using MEF today will have this huge memory leak problem and cause degraded performance and larger and larger memory footprint as the application is running.

Lets start off with this new custom catalog, for any reason of better naming, I decided to change as little of Palomino's code, so let's just call it CustomCatalog here too:



  public class CustomCatalog : ComposablePartCatalog
    {
        private readonly ComposablePartCatalog _innerCatalog;

        public CustomCatalog(ComposablePartCatalog catalog)
        {
            _innerCatalog = catalog;
        }

        public override IEnumerable<Tuple<ComposablePartDefinition, ExportDefinition>> GetExports(ImportDefinition definition)
        {
            var exports = _innerCatalog.GetExports(definition);
            return exports.Select(e => new Tuple<ComposablePartDefinition, ExportDefinition>(
                new CustomComposablePartDefinition(e.Item1), e.Item2));
        }

        public override IQueryable<ComposablePartDefinition> Parts
        {
            get
            {
                return _innerCatalog.Parts
                    .Select(p => new CustomComposablePartDefinition(p))
                    .AsQueryable();
            }
        }
    }
To explain this class in short terms, we pass in an inheritor of the abstract ComposablePartCatalog, such as AssemblyCatalog, in the constructor. Then we override the method GetExports and readonly property Parts. Instead of just returning the implementation of the passed in ComposablePartCatalog inheritor instance, a wrapping CustomComposablePartDefinition is used. This class will be presented next:
    public class CustomComposablePartDefinition : ComposablePartDefinition
    {
        private readonly ComposablePartDefinition _innerPartDefinition;

        public CustomComposablePartDefinition(ComposablePartDefinition innerPartDefinition)
        {
            _innerPartDefinition = innerPartDefinition;
        }

        public override ComposablePart CreatePart()
        {
            var innerPart = _innerPartDefinition.CreatePart();
            if (ReflectionModelServices.IsDisposalRequired(_innerPartDefinition) && 
                _innerPartDefinition.Metadata.ContainsKey(CompositionConstants.PartCreationPolicyMetadataName) && 
                (CreationPolicy)_innerPartDefinition.Metadata[CompositionConstants.PartCreationPolicyMetadataName] == CreationPolicy.NonShared)
            {
                return new NotDisposableComposablePart(innerPart);
            }
            return innerPart;
        }

        public override IEnumerable<ExportDefinition> ExportDefinitions
        {
            get { return _innerPartDefinition.ExportDefinitions; }
        }

        public override IEnumerable<ImportDefinition> ImportDefinitions
        {
            get { return _innerPartDefinition.ImportDefinitions; }
        }

        public override IDictionary<string, object> Metadata
        {
            get { return _innerPartDefinition.Metadata; }
        }

        public override string ToString()
        {
            return _innerPartDefinition.ToString();
        }
    }

The class CustomComposablePartDefinition shown above inherits from the usual ComposablePartDefinition and provides a custom functionlity for the case where the part is a NonShared part and requires disposing, which usually means the part implements IDisposable. This is the source of the memory leak, i.e. where MEF will keep its cached reference to the part in the CatalogExportProvider and stop the Garbace Collector (GC) from being able to dispose the part on a timely manner. The code for the NotDisposableComposablePart follows:
public class NotDisposableComposablePart : ComposablePart
    {

        private ComposablePart _composablePart; 

        public NotDisposableComposablePart(ComposablePart composablePart)
        {
            _composablePart = composablePart; 
        }

        public override IEnumerable<ExportDefinition> ExportDefinitions
        {
            get { return _composablePart.ExportDefinitions; }
        }

        public override object GetExportedValue(ExportDefinition definition)
        {
            return _composablePart.GetExportedValue(definition); 
        }

        public override IEnumerable<ImportDefinition> ImportDefinitions
        {
            get { return _composablePart.ImportDefinitions; }
        }

        public override void SetImport(ImportDefinition definition, IEnumerable<Export> exports)
        {
            _composablePart.SetImport(definition, exports); 
        }
    }
The NotDisposableComposablePart inherits from the base class ComposablePart. It does not implement IDisposable and will not therefore be cached by the ExportCatalogProvider of MEF. Hence, the memory leak would not occur anymore where the container keeps reference. By using the ANTS Memory Profiler I can verify this behavior. An example how of to adjust an AssemblyCatalog in the MEF Bootstrapper follows, using this CustomCatalog:
           var assemblyCatalog = new AssemblyCatalog(typeof(ItemViewModel).Assembly);
            this.AggregateCatalog.Catalogs.Add(new CustomCatalog(assemblyCatalog)); 
This wrapping of the CustomCatalog can be done not only for AssemblyCatalog and TypeCatalog and so on. Wherever a memory leak is shown in large scale in an application using MEF, the wrapping where one uses CustomCatalog is strongly recommended. The following image shows an image from the sample application, which I have adjusted some from Danny's sample on Code Project:

Here is a screenshot of the memory profiling application I use, ANTS Memory Profiler from Red Gate:

To evaluate this memory leak fix of MEF yourself, the sample solution is available for download at the following URL: Prism 4 MEF Sample with memory leak fix [Zip file, 4 MB download]


It is strange that Microsoft choose to have an instance retention policy where the disposing of parts are postponed until the disposing of the container, which is usually done when the application is exited. This actually allows a huge memory leak, especially for the NonShared parts. It is usual in say a WPF/MVVM/Prism/MEF scenario to add and remove view models and other types of instances and maintaining these parts in memory allows a great access to memory leak in a multitude of applications. If you use MEF today, do not be suprised that there are a lot of memory leaks in your managed coded application. Just because it is .NET and managed code does not mean memory leaks are not present, on the contrary side. Thanks to the great tips of Palomino, user at MEF Codeplex, and Danny Siew for providing an easy and great Prism 4 MEF starting solution. Evaluate the code. Make note that the necessary Prism and MEF DLL-s are added. In addition to .NET 4 (obviously), download Microsoft WPF Ribbon 4.0 from MSDN here:


Microsoft Ribbon 4.0 WPF I have compiled the solution in Visual Studio 2012 RC so you will find binaries in the bin folders also to start off the sample right away. Hopefully, this fix will patch MEF until MEF 2 is released. After reading a bit more about MEF 2, it seems they use ExportFactory and the early release or dispose of objects will be an opt in. It will be easier to wrap the different catalogs used with this CustomCatalog to at least try to fix the massive memory leak that MEF almost provides as default behavior. Feel free to comment this article if you have supplementary information. I have used MEF quite a lot in the last two years, but I have less deep knowledge of MEF. I wrote this article because I had to inspect if there really were workarounds of this central bug of MEF.. Happy coding!

Sunday, 16 September 2012

Testing WPF localization

WPF is a very powerful framework for rich clients, but it is not perfect. One major drawback is the support for localization. Despite localization being rather easy in framework such as ASP.NET, the process of localizing a WPF app is way too hard. The support for tools inside Visual Studio seems very poor. After googling around for suggestions, I went for the strategy of using a tool called LocBaml, which is actually a sample project inside the Windows SDK v7.1. After downloading this SDK I decided to take a short route and get an already compiled version available here: http://michaelsync.net/2010/03/01/locbaml-for-net-4-0
Reading Michael Sync blog article, a link for Locbaml.exe is available in the article linked above. I successfully used this Locbaml.exe file for testing out localization. So once we got this LocBaml tool, what is it? The Locbaml tool is a small tool for generating CSV files from a given project and generating up satellite assemblies that can be put into the subfolders of the bin\debug folder for the specified culture to localize. Locbaml got additional functionality, but this short article will not discuss them. Lets first start up with a simple GUI in WPF:
Edit the project file of the GUI and add the UICulture xml element in the .csproj file, given you implement in C#, or .vbproj for the VB developers out there.




E.g. set ui culture to english-american like this: <UICulture>en-US</UICulture> Continue, editing the AssemblyInfo.cs file and add the following:

[assembly:NeutralResourcesLanguage("en-US", UltimateResourceFallbackLocation.Satellite)]

Next up, create a new folder in the bin/debug folder. Create two folders for testing, I create here nb-NO for the Norwegian satellite assembly and the folder en-US for the English satellite asssembly file. If you compile now, it should be possible to see a satellite assembly in the bin/Debug folder and in the obj/x86 folder.


Continue with updating the xaml files of your project to have Uids The following command is to be used in the root folder of your project, use Visual Studio command prompt:

msbuild /t:updateuid TestWPFLocalization.csproj 
This will insert Uids on all the GUI elements and is another preparation step of the localization process for WPF. Sample XAML code follows showing these generated Uids:



Note the x:Uid attributes injected into each XAML element representing a visual state or control. To evaluate your progress of localizing a WPF application, see the official MSDN guide here:

http://msdn.microsoft.com/en-us/library/ms746621.aspx

The problem with the MSDN help article is - it does not work entirely. The part where Locbaml is run fails when running in the bin/Debug folder. I have instead followed the suggestions by Atul Gupta here:

http://www.infosysblogs.com/microsoft/2007/09/locbaml_to_localize_wpf_applic.html

So instead, we navigate to the obj/x86/Debug folder and first run this command:
locbaml /parse TestWPFLocalization.g.nb-NO.resources /out:TestW
PFLocalizationnb-NO.csv
Make note that it is the generate resources file in this folder we target when running the Locbaml command to generate the CSV file (comma-separated value). Sample content of the CSV file follows:

TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBlock_1:System.Windows.Controls.TextBlock.Text,Text,True,True,,Fornavn
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBlock_1:System.Windows.Controls.Grid.Row,None,False,True,,0
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBlock_1:System.Windows.Controls.Grid.Column,None,False,True,,0
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBox_1:System.Windows.Controls.TextBox.$Content,Text,True,True,,
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBox_1:System.Windows.Controls.Grid.Row,None,False,True,,0
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBox_1:System.Windows.Controls.Grid.Column,None,False,True,,1
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBlock_2:System.Windows.Controls.TextBlock.$Content,Text,True,True,,
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBlock_2:System.Windows.Controls.TextBlock.Text,Text,True,True,,Etternavn
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBlock_2:System.Windows.Controls.Grid.Row,None,False,True,,1
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBlock_2:System.Windows.Controls.Grid.Column,None,False,True,,0
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBox_2:System.Windows.Controls.TextBox.$Content,Text,True,True,,
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBox_2:System.Windows.Controls.Grid.Row,None,False,True,,1
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBox_2:System.Windows.Controls.Grid.Column,None,False,True,,1
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBlock_3:System.Windows.Controls.TextBlock.$Content,Text,True,True,,
TestWPFLocalization.g.nb-NO.resources:mainwindow.baml,TextBlock_3:System.Windows.Controls.TextBlock.Text,Text,True,True,,Alder

The sample csv file is manually translated into Norwegian as shown above. It is is possible to edit the csv file in Excel, but I just use notepad. However, editing in Excel will perhaps be safer, as one does not delete a comma as easy when viewing the csv file inside Excel. The only text to replace in this kind of CSV file is the last parameter for the value of the localized key, for the GUI elements that should be localized. Continuing, we need to generate a new satellite assembly with this translated CSV file. Using LocBaml again, we run the following command in the obj/x86/Debug folder:

locbaml.exe /generate TestWPFLocalization.resources.dll /trans:
TestWPFLocalizationnb-NO.csv /out:.. /cul:nb-NO 
The command above takes the .csv file and generates a satellite assembly in the folder in the parent folder, that is in the obj/x86 folder. I then move this file into the nb-NO folder in the bin/Debug folder. There are now two satellite assembly files in the two folders en-US and nb-NO. Consider adding these DLL files to your project, however they will quickly go out of date. A better strategy would be to create a post build step in MSBuild to generate all these satellite assemblies dynamically. To test out the localization, you probably will want to switch the culture while running the program. Since making Locbaml work in my demo took some time, especially since the MSDN article for Localization did not present a technique that actually worked, I decided to do the short path. Add some test code in the App.xaml.cs file constructor of the App class:
   
    /// 
    /// Interaction logic for App.xaml
    /// 
    public partial class App : Application
    {
        public App()
        {
            CultureInfo ci = new CultureInfo("nb-NO");
            Thread.CurrentThread.CurrentCulture = ci;
            Thread.CurrentThread.CurrentUICulture = ci; 
        }
    }


Note that the Thread.CurrentCulture is set to an instance of CultureInfo set up to Norwegian. Running the demo app again, we can see that the satellite assembly for the Norwegian culture is picked up, and the result is displayed in the GUI

Of course, a more complete article would also discuss more background information and present code for switching language while the application is running. I decided to keep this article short, as the usage of the tool LocBaml was kind of irritating me, as the way MSDN and Microsoft explains its usage did not work. It is strange that such a versatile and powerful GUI-centric framework as WPF is so hard to use when it comes to localization. It almost seems as the WPF development team forgot to include proper support for LocBaml. Hopefully, a future version of WPF will support Localization much better without all these manual steps necessary to get started when updating.

At the same time, once this process is done, one can see that it kind of works, it is however not good that it takes this much work to get started. How about using some naming convention for Resource dictionary files, such as the one used in ASP.NET? I hope Microsoft will come with better support for localization in the next WPF version. The worst part of this strategy is that is actually some kind of "one-time localization". When the GUI is changed, one must update the Uids and then run the LocBaml commands again and copy the new assembly files to the correct subfolder in Bin\Debug. It is though not that difficult to create a new MSBuild target and add the necessary Exec xml elements in the MSBuild project file to create fresh satellite assemblies. However, the developer must translate the CSV file which does not fit well into this strategy. The end result is that the LocBaml strategy mainly lends itself to developers localizing the application after development is done and the part of localizing the application remains (i.e the application GUI will not change much for a time).

Wednesday, 5 September 2012

Basic WCF operation interception

This article will present a basic implementation of WCF operation interception. The interception is possible by implementing two interfaces, IParameterInspector and IOperationBehavior. Strictly speaking, only the interface IOperationBehavior is required for this, but this sample will present the use of IParameterInspector interface also to intercept the operation before and after the call. The following code shows how to create a sample WCF operation interception as an attribute that can be applied on a target operation in a WCF service contract.

 public class SampleOperationBehaviorAttribute : Attribute, IOperationBehavior, IParameterInspector
    {

        public void AddBindingParameters(OperationDescription operationDescription, System.ServiceModel.Channels.BindingParameterCollection bindingParameters)
        {
        }

        public void ApplyClientBehavior(OperationDescription operationDescription, System.ServiceModel.Dispatcher.ClientOperation clientOperation)
        {
            clientOperation.ParameterInspectors.Add(this); 
        }

        public void ApplyDispatchBehavior(OperationDescription operationDescription, System.ServiceModel.Dispatcher.DispatchOperation dispatchOperation)
        {
            dispatchOperation.ParameterInspectors.Add(this);
        }

        public void Validate(OperationDescription operationDescription)
        {
        }

        public void AfterCall(string operationName, object[] outputs, object returnValue, object correlationState)
        {
            Debug.WriteLine(string.Format("After call of operation {0}", operationName));
        }

        public object BeforeCall(string operationName, object[] inputs)
        {
            Debug.WriteLine(string.Format("Before call of operation {0}", operationName));
            return null;
        }

    }

As the code above shows, inheriting from Attribute class allows using the code as an attribute on the target operation. Furthermore, implementing IOperationBehavior and IParameterInspector in the same class allows easy adding the parameterinspector instance in the ApplyDispatchBehavior and ApplyClientBehavior. Finally, the last step is attributing a target operation in the service contract. The sample service will then look for example like this:
 
    [ServiceContract]
    public interface IService1
    {

        [SampleOperationBehavior]
        [OperationContract]
        string GetData(int value);
     
    }