How to throttle event stream using RX?

Question

I want to effectively throttle an event stream, so that my delegate is called when the first event is received but then not for 1 second if subsequent events are received. A

Answer 1

Inspired by Bluelings answer I provide here a version that compiles with Reactive Extensions 2.2.5.

This particular version counts the number of samples and also provide the last sampled value. To do this the following class is used:

class Sample {

  public Sample(T lastValue, Int32 count) {
    LastValue = lastValue;
    Count = count;
  }

  public T LastValue { get; private set; }

  public Int32 Count { get; private set; }

}

Here is the operator:

public static IObservable> SampleResponsive(this IObservable source, TimeSpan interval, IScheduler scheduler = null) {
  if (source == null)
    throw new ArgumentNullException(nameof(source));
  return Observable.Create>(
    observer => {
      var gate = new Object();
      var lastSampleValue = default(T);
      var lastSampleTime = default(DateTime);
      var sampleCount = 0;
      var scheduledTask = new SerialDisposable();
      return new CompositeDisposable(
        source.Subscribe(
          value => {
            lock (gate) {
              var now = DateTime.UtcNow;
              var elapsed = now - lastSampleTime;
              if (elapsed >= interval) {
                observer.OnNext(new Sample(value, 1));
                lastSampleValue = value;
                lastSampleTime = now;
                sampleCount = 0;
              }
              else {
                if (scheduledTask.Disposable == null) {
                  scheduledTask.Disposable = (scheduler ?? Scheduler.Default).Schedule(
                    interval - elapsed,
                    () => {
                      lock (gate) {
                        if (sampleCount > 0) {
                          lastSampleTime = DateTime.UtcNow;
                          observer.OnNext(new Sample(lastSampleValue, sampleCount));
                          sampleCount = 0;
                        }
                        scheduledTask.Disposable = null;
                      }
                    }
                  );
                }
                lastSampleValue = value;
                sampleCount += 1;
              }
            }
          },
          error => {
            if (sampleCount > 0)
              observer.OnNext(new Sample(lastSampleValue, sampleCount));
            observer.OnError(error);
          },
          () => {
            if (sampleCount > 0)
              observer.OnNext(new Sample(lastSampleValue, sampleCount));
            observer.OnCompleted();
          }
        ),
        scheduledTask
      );
    }
  );
}