I have a problem for which Reactive Extensions seems particularly well suited. I have an event source that creates events in short bursts with relatively long idle periods in between. I would like to group those events in batches where (ideally) each burst of events would end up in one batch. Using RxJava, is there a good way to do this? Observable.buffer(Observable) or Observable.buffer(Func0) seem promising, but it might be possible to do using Observable.window() or Observable.groupByUntil().
Here is code that seems to work for a debounced buffer:
import java.util.List;
import java.util.concurrent.TimeUnit;
import rx.Observable;
import rx.Subscriber;
import rx.schedulers.Schedulers;
public class DebounceBuffer {
public static void main(String args[]) {
// see all bursts in a single sequence
// intermittentBursts().toBlocking().forEach(System.out::println);
// debounce to the last value in each burst
// intermittentBursts().debounce(10, TimeUnit.MILLISECONDS).toBlocking().forEach(System.out::println);
/* The following will emit a buffered list as it is debounced */
// first we multicast the stream ... using refCount so it handles the subscribe/unsubscribe
Observable<Integer> burstStream = intermittentBursts().publish().refCount();
// then we get the debounced version
Observable<Integer> debounced = burstStream.debounce(10, TimeUnit.MILLISECONDS);
// then the buffered one that uses the debounced stream to demark window start/stop
Observable<List<Integer>> buffered = burstStream.buffer(debounced);
// then we subscribe to the buffered stream so it does what we want
buffered.take(20).toBlocking().forEach(System.out::println);
}
public static Observable<Integer> intermittentBursts() {
return Observable.create((Subscriber<? super Integer> s) -> {
while (!s.isUnsubscribed()) {
// burst some number of items
for (int i = 0; i < Math.random() * 20; i++) {
s.onNext(i);
}
try {
// sleep for a random amount of time
Thread.sleep((long) (Math.random() * 1000));
} catch (Exception e) {
// do nothing
}
}
}).subscribeOn(Schedulers.newThread()); // use newThread since we are using sleep to block
}
}
It emits the following:
[0, 1, 2, 3, 4, 5, 6, 7]
[0, 1, 2, 3, 4, 5]
[0, 1, 2, 3, 4, 5, 6, 7, 8]
[0, 1]
[0, 1, 2, 3, 4, 5]
[0, 1, 2]
[0, 1, 2, 3, 4, 5, 6, 7]
[0, 1, 2, 3, 4, 5, 6, 7, 8]
[0, 1, 2, 3, 4, 5, 6]
[0, 1, 2]
[0, 1, 2, 3, 4, 5, 6, 7, 8]
[0, 1, 2, 3, 4]
[0, 1, 2, 3]
[0, 1, 2, 3, 4, 5, 6, 7, 8]
[0, 1, 2, 3, 4, 5, 6, 7]
[0, 1, 2, 3, 4, 5, 6, 7, 8]
[0, 1, 2, 3]
[0]
[0, 1, 2]
[0]