Does the Rx subscriber get disposed when OnCompleted is called?

We use an implementation of an observable command - ObservableCommand<T> in our view models not only to wire the actions of controls defined in the XAML but to allow the other interested parties to be notified when the command has executed.

We were wondering what happens when the observable command is disposed, does the OnCompleted method for the subscribers get called and importantly are the subscribers disposed?

Our observable command has an implementation similar to this:

   1:   

   2:  public class ObservableCommand<T> : ICommand, IObservable<T>

   3:  {

   4:      private readonly Subject<T> _subj = new Subject<T>();

   5:   

   6:      public void Execute(object parameter)

   7:      {

   8:          _subj.OnNext((T)parameter);

   9:      }

  10:   

  11:      public bool CanExecute(object parameter)

  12:      {

  13:          return true;

  14:      }

  15:   

  16:      public event EventHandler CanExecuteChanged;

  17:   

  18:      public IDisposable Subscribe(IObserver<T> observer)

  19:      {

  20:          return _subj.Subscribe(observer);

  21:      }

  22:  }

To test question I used a simple class which generates numbers, this exposes 2 methods one to set up a subscription and the other to shut down the under lying stream, this wouldn't be any good for 'real' code but will do for a test:

   1:  public class NumberGenerator

   2:  {

   3:      private readonly TimeSpan _interval = TimeSpan.FromMilliseconds(500);

   4:      private IObserver<int> _stream;

   5:   

   6:      public IObservable<int> Generate()

   7:      {

   8:          var number = 42;

   9:   

  10:          return Observable.Create<int>(o =>

  11:          {

  12:              _stream = o;

  13:              return Observable.Timer(DateTime.Now.Add(_interval), _interval)

  14:              .Subscribe(l =>

  15:              {

  16:                  var currentNumber = number;

  17:                  number = number + 1;

  18:   

  19:                  _stream.OnNext(currentNumber);

  20:              });

  21:          });

  22:      }

  23:   

  24:      public void Complete()

  25:      {

  26:          _stream.OnCompleted();

  27:      }

  28:  }

This was then tested with following program, notice I pass in an Action<T> for the completed action to the Subscribe method:

   1:  internal class Program

   2:  {

   3:      private IObservable<long> _underlying;

   4:   

   5:      private static void Main(string[] args)

   6:      {

   7:          var generator = new NumberGenerator();

   8:   

   9:          var disposable = generator.Generate()

  10:              .Subscribe(n => Console.WriteLine("Number: " + n), () => Console.WriteLine("Completed..."));

  11:   

  12:          Console.ReadLine();

  13:   

  14:          generator.Complete();

  15:   

  16:          Console.ReadLine();

  17:      }

  18:  }

It sets up a subscription on a background thread, the generator then starts producing values every couple of seconds (on another background thread). These are recieved and outputted to the console. Whilst this is happening the main thread is blocked by the first call Console.ReadLine method. Once the enter key is pressed the the internal under lying stream in the generator is shut down and hopefully the OnCompleted method will be called for the subscriber and output "Completed..."

Did OnCompleted get called?

Yes...

So the title question is 'Does the Rx subscriber get disposed when OnComplete is called?'

Yes...

To check this lets look inside the returned IDisposable for the test program:

Debugging the app with a breakpoint on the second Console.ReadLine method, you can see the disposable local variable has been disposed:

So when the under lying stream in Rx is shutdown then all of the subscribers will have their OnCompleted methods called and will be disposed of automatically - perfect!