接收缓存-重播操作员清除

Question

I am using the following code from here - looks like an issue to me in clearing the " Replay cache "

https://gist.github.com/leeoades/4115023

If I change the following call and code like this I see that there is bug in Replay ie it is never cleared. Can someone please help to rectify this ?

private Cache<string> GetCalculator()
    {
        var calculation = Observable.Create<string>(o =>
        {
            _calculationStartedCount++;

            return Observable.Timer(_calculationDuration, _testScheduler)
                             .Select(_ => "Hello World!" + _calculationStartedCount) // suffixed the string with count to test the behaviour of Replay clearing
                             .Subscribe(o);
        });

        return new Cache<string>(calculation);
    }

[Test]
    public void After_Calling_GetResult_Calling_ClearResult_and_GetResult_should_perform_calculation_again()
    {
        // ARRANGE
        var calculator = GetCalculator();

        calculator.GetValue().Subscribe();
        _testScheduler.Start();

        // ACT
        calculator.Clear();

        string result = null;
        calculator.GetValue().Subscribe(r => result = r);
        _testScheduler.Start();

        // ASSERT
        Assert.That(_calculationStartedCount, Is.EqualTo(2));
        Assert.That(result, Is.EqualTo("Hello World!2")); // always returns Hello World!1 and not Hello World!2
        Assert.IsNotNull(result);
    }

Answer 1

The problem is a subtle one. The source sequence Timer completes after it emits an event, which in turn calls OnCompleted on the internal ReplaySubject created by Replay . When a Subject completes it no longer accepts any new values even if a new Observable shows up.

When you resubscribe to the underlying Observable it executes again, but isn't able to restart the Subject , so your new Observer can only receive the most recent value before the ReplaySubject completed.

The simplest solution would probably just be to never let the source stream complete (untested):

    public Cache(IObservable<T> source)
    {
        //Not sure why you are wrapping this in an Observable.create
        _source = source.Concat(Observable.Never())
                            .Replay(1, Scheduler.Immediate);
    }