Sample code for stackoverflow question

SinkTests.java

import lombok.RequiredArgsConstructor;
import org.junit.jupiter.api.Test;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Sinks;
import reactor.core.scheduler.Schedulers;

import java.util.function.Function;

public class SinkTests {

    @RequiredArgsConstructor
    class Emitter {
        private static final Sinks.EmitFailureHandler emitFailureHandler = (signalType, emitResult) -> {
            System.out.println(signalType + " -> " + emitResult);
            return false;
        };
        private final Sinks.Many<String> sink;

        private static void sleep(int dekaSeconds) {
            try {
                Thread.sleep(100 * dekaSeconds);
            } catch (InterruptedException ex) {
                System.out.println(ex);
            }
        }

        public void emit(String str) {
            sink.emitNext(str, emitFailureHandler);
        }

        public void emitAndSleep(String str, int dekaSeconds) {
            sink.emitNext(str, emitFailureHandler);
            sleep(dekaSeconds);
        }

        public void emitComplete() {
            sink.emitComplete(emitFailureHandler);
        }
    }

    @Test
    public void replay() {
        // there is "synchronization" between clients
        //final Sinks.Many<String> sink = Sinks.many().replay().limit(1, Duration.ZERO);
        final Sinks.Many<String> sink = Sinks.many().multicast().onBackpressureBuffer(5);
        
        final Function<Sinks.Many<String>, Flux> getFlux = (Sinks.Many<String> snk) ->
                snk.asFlux()
                        .subscribeOn(Schedulers.newSingle("asdf"))
                        .onBackpressureBuffer(6);


        final Emitter s = new Emitter(sink);
        s.emitAndSleep("nula", 10);
        //getFlux.apply(sink).subscribe(x -> System.out.println("Consumer 0: " + x));
        s.emit("jedna");
        s.emitAndSleep("dva", 10);

        getFlux.apply(sink).subscribe(x -> {
            Emitter.sleep(4);
            System.out.println("Consumer 1: " + x);
        });
        s.emitAndSleep("tri", 10);

        getFlux.apply(sink).subscribe(x -> {
            Emitter.sleep(9);
            System.out.println(" SLOW er 2: " + x);
        });
        s.emitAndSleep("štyri", 10);
        for (int i = 1; i < 18; i++) s.emitAndSleep("rýchlo " + i, 1);

        Emitter.sleep(1);
        s.emitComplete();
    }
}