[RxJava 2.2.21]: throttleFirst does not switch thread to the default computation thread while throttleLast does switch thread to the default computation thread

[TonyTangAndroid]

sample repo to reproduce the issue: I have this pull request TonyTangAndroid/HelloRxJava#8 here to demonstrate that item through throttleFirst will remain to be the upstream thread main while item through throttleLast will be switched to the RxComputationThreadPool-2. This comes to me as a surprise.

Expectation : I had used throttleLast and learned that throttleLast will switch the thread to Computation thread pool. Hence, I made assumption that throttleFirst will also do the same.

Actual : item through throttleFirst will remain to be the upstream thread main.

[akarnokd]

The Javadoc clearly states.

This differs from throttleLast(long, java.util.concurrent.TimeUnit) in that this only tracks passage of time whereas throttleLast ticks at scheduled intervals.