SLAB - Reactive Event Sourcing

In the previous post we saw how we can use ETW events generated using EventSource using PerfView. We can also use these events in our application using EventListener. This is another new abstract type provided in .net framework 4.5. The abstract member is OnEventWritten() method. Additionally, it has a virtual method OnEventSourceCreated(). Below is a custom event listener. Here we are overriding the two members. We are just writing the debug messages when these methods are called. During development, debug messages can be seen in the Visual Studio's Debug Output window.


The listener's OnEventWritten method is called when EventSource writes an event. But before that we need to specify what level of events we are interested in from the EventSource. This is called Enabling the events where listener is specified with the EventSource and EventLevel.

You can notice OnEventSourceCreated and OnEventWritten being used by the logs in the Output window. The above code wold result the following logs:



Semantic Logging Application Block
Semantic Logging Application Block is provided in Enterprise Library 6 for supporting structured logging. It enhances EventSource to support logging events in SQL Server and Azure tables. Like other application blocks, this is also available as a Nuget package.



SLAB provides custom implementation of EventListener. The listener is Rx's IObservable. This is named as ObservableEventListener. Since this implements IObservable, it allows subscriptions from Event sinks. The sinks are IObserver (s) to observe on these event listeners.



The application block also provides a specialization of EventSource. This is named as SemanticLoggingEventSource.



In-Process Vs Out-Process
SLAB can be used in-process or out-process. We can use the Nuget package to use the libraries for using it in process. For out of process, it is hosted as a windows service. The service installer is available as a separate download. In the previous post, we discussed how we can use out-process logging with SLAB.

Event Text Formatter
SLAB supports JSON and XML based text formatting. The types are available in Microsoft.Practices.EnterpriseLibrary.SemanticLogging.Formatters namespace available in Microsoft.Practices.EnterpriseLibrary.SemanticLogging assembly. The assembly is downloaded using EnterpriseLibrary.SemanticLogging nuget package.



Event Sinks & Factories
SLAB also provides Event Sinks and their factories. All of these event sinks are IObserver.



Let's install EnterpriseLibrary.SemanticLogging application block nuget package. The package should take care of all its dependencies installation as well, which is only comprised of Newtonsoft.Json package.



Let's also install Rx-Main nuget package for subscriptions using Reactive extensions based subscribers.



In the following code we are subscribing to ObservableEventListener. We can get the messages in the OnNext() method for the subscriber. Here we have also used OnCompleted() and OnError() of the subscriber.

Running the above code would result in the following output. Please notice that the messages being logged using the event source as provided to the listener. Since we are subscribing to the listener, we are getting those messages in OnNext(). Here we are just writing those messages to Debug Window.


Download

Semantic Out-Process Logging using Semantic Logging Application Block - File Sink

In this post, we are going to look how SLAB (Semantic Logging Application Block) can be used for out-process logging for ETW events. Pattern & Practices (P&P) team has provided support for out-process logging of ETW based logs using Semantic Log Service. The executable for the service can be downloaded from here: [ http://go.microsoft.com/fwlink/p/?LinkID=290903 ]. Let's copy the downloaded installer to the some folder.



Running the executable extracts the required files in the specified directory. Here we are specially interested in install-packages.ps, the power shell script to download the required nuget packages to the directory.



Let's run the power shell script. This would download the required nuget packages as follows:



It must be remembered that the Semantic Logging Service must run on the same machine as the source application emanating ETW events data. We need to update the configuration of the out-proc service to utilize the events. You can see that we have updated the event source definition to look for the specified events. Here we have used FlatFileSink. This would write the events data to the file specified. In the current example we are using SemanticETWLogs.log, which would be created in the same folder. Here we have also used the text formatter which would create header text. In the next post, we will be introducing what other text formatting options are available.


Now we can run the out-proc process to register and log the ETW events. The process can run as a Windows Service or Console application. For our example, let us run it as a console application. This requires -console switch to be used to run it. Please make sure that you are running this with a command prompt using the Administrative privileges, otherwise, the command results in a failure.



Now we simply need to run the source application. Since it is registering some events, the logs are available in the specified file. For my case the data is as follows:


Please make sure that your EventSource is decorated with the attribute to specify the ETW event expected by out-proc listener.


Download

Enterprise Library 6 is out!

Enterprise Library provides an excellent way to keep the cross-cutting concerns outside your main application code. Microsoft Pattern & Practices team released new version of Enterprise Library last week. This was released on 25th April and this is Version 6 of the library. Full version of the library and source code can be downloaded from Microsoft's Download Center.



The documentation can be downloaded directly form Pattern & Practices team's codeplex page. The documentation is still in preview version and is not updated on MSDN. Still this can be downloaded from the main page. In addition to the Enterprise Library documentation, it also includes the migration guide for migrating applications from Enterprise Library 5. You can also find the reference PDF for Unity Application Block version 3 which is provided as part of the new version of Enterprise Library.



List of Application Blocks in Enterprise Library 6
The library seems to be released with exciting new features in existing application block. It includes a new application block with the name Semantic Logging Application Block. Transient Fault Handling application Block seems to have been added from Azure Integration Pack for Enterprise Library 5. Enterprise Library 6 includes the following application blocks.

1. Data Access Application Block
2. Exception Handling Application Block
3. Logging Application Block
4. Policy Injection Application Block
5. Semantic Logging Application Block
6. Transient Fault Handling Application Block
7. Unity Application Block
8. Validation Application Block

As discussed above, Semantic Application Block is the newest in the list. This is supposed to be built on top of EventSource provided in .net framework 4.5 for structured logging. EventSource provides structured logging support for ETW events. Semantic Application Block is supposed to add support structured logging by specializing EventSource, where the logs can be sinked to Azure or SQL Server database.

There are other application blocks which used to be in Enterprise Library 5 and haven't been migrated over to EntLib6. They include the following:

1. Cryptography Application Block
2. Caching Application Block
3. Validation Application Block

Back in 2010, we did discuss about how we can use Validation Application Block in an MVVM based application.

Unity 3.0
The release also includes a new version of unity application block. This is version 3 of Unity. As we know Unity provides the support of Dependency Injection for .net applications. This is a container based approach to Inversion of Control. Unity 3 extends Dependency Injection Windows store Apps and deeper integration with ASP.net MVC and Web API.

Requirements for Enterprise Library 6
Enterprise Library 6 only works with .net framework 4.5 and .net for Windows Store Apps (for Unity and Transient fault handling application block. It cannot be used side by side with existing Enterprise Library 5 binaries. If you are still on .net framework 4.0, you will need to make a decision about migrating to .net framework 4.5 first before moving to the new version of the enterprise library.

Using Enterprise Library Application Blocks
You can download the list of the binaries from the link provided in download section to use enterprise library's application blocks in your code. Pattern & Practices team suggests using Nuget for this purpose. For ease of developers, Pattern & Practices team has provided these application blocks in the form of Nuget packages. These Nuget packages can be used individually as per the requirement. Just add the appropriate package to your project using Nuget



Still To Come
This is the view of the release from top. There are other minor improvements and updates which require more detailed discussions. I am planning a few posts about the updates in Enterprise Library 6. You might find me blogging about them next month. You can find release notes here.