RxJava2 Exhaust Map - ignore (drop) incoming requests while work is in progress

ExhaustMapTransformer.java

import java.util.concurrent.atomic.AtomicBoolean;

import io.reactivex.Observable;
import io.reactivex.ObservableTransformer;
import io.reactivex.functions.Function;

class ExhaustMapTransformer<Upstream, Downstream> implements ObservableTransformer<Upstream, Downstream> {

    private final AtomicBoolean workInProgress = new AtomicBoolean(false);
    private final Function<Upstream, Observable<Downstream>> mapper;

    public ExhaustMapTransformer(Function<Upstream, Observable<Downstream>> mapper) {
        this.mapper = mapper;
    }

    @Override
    public Observable<Downstream> apply(Observable<Upstream> upstream) {
        return upstream.flatMap(t -> {
            if (workInProgress.compareAndSet(false, true)) {
                return mapper.apply(t)
                        .doOnTerminate(() -> workInProgress.set(false));
            } else {
                return Observable.empty();
            }
        });

    }
}