Sunday, June 5, 2011

Rx v.1.0.10425–Breaking changes!

For those that follow Rx, many will have noticed a new drop was made available in late April 2011. This was interesting for numerous reasons:

  1. I believe that it was the first drop since the Rx team move off of the dev labs site and on to the Microsoft Data site
  2. They have supplied two downloads, Supported and Experimental
  3. It is available via Nuget
  4. It broke most of the sample code of this blog
  5. ...It has massive breaking changes !

The first thing I noticed was that only the more recent frameworks were in the “supported” release i.e. .NET 4, Silverlight 4 and Windows Phone. Next, when you open up the install directory (which has moved, again) the files are different to previous releases.

This is a comparison of the location and files of the old v.s. new version (.NET 4 target):

C:\Program Files\Microsoft Cloud Programmability\Reactive Extensions\v1.0.2856.0\Net4

C:\Program Files\Microsoft Reactive Extensions SDK\v1.0.10425\Binaries\.NETFramework\v4.0

Note the files names are named System.Reactive instead of hijacking the existing BCL namespaces such as System, System.IO, System.Linq etc. Here are a list of the old and new Namespaces found in the Rx libraries with the count of the Types in each namespace.

C:\Program Files\Microsoft Cloud Programmability\Reactive Extensions\v1.0.2856.0\Net4
System                         6
System.Collections.Generic     21
System.Concurrency             14
System.Diagnostics             1
System.Disposables             8
System.IO                      1
System.Joins                   34
System.Linq                    13
System.Reactive.Testing        4
System.Reactive.Testing.Mocks  10
System.Threading.Tasks         1
System.Web                     1
System.Windows.Forms           1
System.Windows.Threading       1

C:\Program Files\Microsoft Reactive Extensions SDK\v1.0.10425\Binaries\.NETFramework\v4.0
Microsoft.Reactive.Testing     7
System                         1
System.Reactive                10
System.Reactive.Concurrency    16
System.Reactive.Disposables    9
System.Reactive.Joins          34
System.Reactive.Linq           8
System.Reactive.Subjects       8
System.Reactive.Threading.Tasks 1

Summary of impact

Here is a quick list of the changes that have affected the code from the samples off this blog

Unit has been moved to System.Reactive. I imagine to prevent any conflicts with FSharp’s Unit?

EventLoopScheduler no longer has a constructor that takes a string for the name of the thread, it instead takes a function to act as a Thread Factory so you can use that to specify a name for the thread instead.

Similar methods have been collapsed to overloads. For example; BufferWithTime, BufferWithCount & BufferTimeOrCount are all just Buffer with various overloads. Same goes for WindowWithTime, WIndowWithCount & WindowTimeOrCount. GenerateWithTime is now just an overload of Generate. CreateWithDisposable is now just an overload of Create.

Potentially confusing names have been adjusted. I must admit, I found AsyncSubject and odd name, and also found it odd that Prune was the method you would use to transform an existing observable to one that exhibited AsynchSubject behaviour. The new version of this is the far more appropriately named TakeLast(int). Obviously just pass a value of 1 to get the old semantics of Prune.

The Run method has now been renamed the more obvious (well to new comers) ForEach. It is a bit of an enumerable construct, but that is cool.

My big problem has been the disappearance of the IsEmpty extension method. So I had a long think about this and have decided that you can replace it by creating your own extension method that looks like this

public static class ObservableExtensions
  //Is missing now the System.Interactive has been dropped
  public static IObservable<bool> IsEmpty<T>(this IObservable<T> source)
    return source.Materialize()
        .Select(n => n.Kind == NotificationKind.OnCompleted
                      || n.Kind == NotificationKind.OnError);

For even more details, check out the forum post that has the summary release notes and allsorts of rants about what has changed and what is causing problems for other (+ some helpful tips).

This change is not one that you can just take and expect all to be well. However assuming that you can just update some references and add the missing extensions to you own library, you could be fine.

Changes to TestScheduler

The real problems come from the big changes to the testing part of Rx. This appears to have undergone a complete change and most of my existing code does not work. This looks like a big and possibly welcome change to the TestScheduler.

Problems with the previous TestScheduler

There were some fundamental problems with the TestScheduler as it was. There were problems with running it to a specific point in time if there were not any actions scheduled for that point in time. For example, the old TestScheduler would allow you to request that it run to say 5seconds. If there were no actions scheduled, then the clock would not actually advance. You could then Schedule an action to happen at 3Seconds (effectively in the past) and then call Run and it would execute the actions. Hmmm.

TestScheduler scheduler = new TestScheduler();
scheduler.Schedule(()=>{Console.WriteLine("Running at 1seconds");}, TimeSpan.FromSeconds(1));
scheduler.RunTo( scheduler.FromTimeSpan(TimeSpan.FromSeconds(5)));
//The next line is scheduled in the past and somehow this all works!
scheduler.Schedule(()=>{Console.WriteLine("Running at 3seconds");}, TimeSpan.FromSeconds(3));

There also seemed to be a lack of functionality for running to a relative point in time. I have used these extension methods to work around this shortcoming.

public static class TestSchedulerExtensions
  /// <summary>
  /// Runs the scheduler from now to the given TimeSpan. Advances relative to it's <c>Now</c> value.
  /// </summary>
  public static void RunNext(this TestScheduler scheduler, TimeSpan interval)
    var tickInterval = scheduler.FromTimeSpan(interval);
    scheduler.RunTo(scheduler.Ticks + tickInterval + 1);

  public static void RunTo(this TestScheduler scheduler, TimeSpan interval)
    var tickInterval = scheduler.FromTimeSpan(interval);

  public static void Step(this TestScheduler scheduler)
    scheduler.RunTo(scheduler.Ticks + 1);

  /// <summary>
  /// Provides a fluent interface so that you can write<c>7.Seconds()</c> instead of <c>TimeSpan.FromSeconds(7)</c>.
  /// </summary>
  /// <param name="seconds">A number of seconds</param>
  /// <returns>Returns a System.TimeSpan to represents the specified number of seconds.</returns>
  public static TimeSpan Seconds(this int seconds)
    return TimeSpan.FromSeconds(seconds);

However on initial inspection of the new TestScheduler there appears to be features that support running to an absolute or relative time. It looks like that the Post on testing Rx will need a re-write Sad smile

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1 comment:

DaveG said...

Thanks for such a useful post. I just started digging into Rx over the weekend, and thought I was going crazy because so many examples I tried to understand were broken. Your summary puts it all into perspective.