Split events based on criteria and handle in order - project-reactor

Question

Having the following problem: given a list of events that have a partitionId property (0-10 for example), I'd like incoming events to be split according to the paritionId so that events with same partitionId are handled in order they're received.
With more or less even distribution, that would lead to 10 events (for each partition) being handled in parallel.
Besides creating 10 single-threaded dispatchers and sending the event to the right dispatcher, is there a way to accomplish the above using Project Reactor ?
Thanks.

Answer 1

The code below
splits source stream into partitions,
creates ParallelFlux, one "rail" per partition,
schedules "rails" into separate threads,
collects the results
Having dedicated thread for each partition guaranties its values are processed in original order.
#Test
public void partitioning() throws InterruptedException {
final int N = 10;
Flux<Integer> source = Flux.range(1, 10000).share();
// partition source into publishers
Publisher<Integer>[] publishers = new Publisher[N];
for (int i = 0; i < N; i++) {
final int idx = i;
publishers[idx] = source.filter(v -> v % N == idx);
}
// create ParallelFlux each 'rail' containing single partition
ParallelFlux.from(publishers)
// schedule partitions into different threads
.runOn(Schedulers.newParallel("proc", N))
// process each partition in its own thread, i.e. in order
.map(it -> {
String threadName = Thread.currentThread().getName();
Assert.assertEquals("proc-" + (it % 10 + 1), threadName);
return it;
})
// collect results on single 'rail'
.sequential()
// and on single thread called 'subscriber-1'
.publishOn(Schedulers.newSingle("subscriber"))
.subscribe(it -> {
String threadName = Thread.currentThread().getName();
Assert.assertEquals("subscriber-1", threadName);
});
Thread.sleep(1000);
}