Exponential retry

gistfile1.txt

import lombok.extern.slf4j.Slf4j;
import reactor.core.Disposable;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import reactor.util.retry.Retry;

import java.time.Duration;
import java.util.List;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.stream.IntStream;

@Slf4j
public class BackoffRetry {
    private static final Duration CHECK_INTERVAL = Duration.ofMillis(500);

    public static void main(String[] args) {
        Disposable subscription = Flux.interval(CHECK_INTERVAL)
                .doOnSubscribe((s) -> log.info("Scheduled check every {}", CHECK_INTERVAL))
                .log(log.getName(), Level.FINEST)
                .concatMap((i) -> checkAllInstances(i))
                .retryWhen(Retry.backoff(Long.MAX_VALUE, Duration.ofSeconds(1))
                        .doBeforeRetry((s) -> log.warn("Unexpected error in status check. Retries {} / {}",
                                s.totalRetries(),
                                s.totalRetriesInARow(),
                                s.failure())))
                .subscribe();
        try {
            TimeUnit.HOURS.sleep(2);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }

    }

    private static Mono<Void> checkAllInstances(Long tick) {
        log.info("running check {}", tick);
        List<Integer> items = IntStream.range(0, 5).boxed().toList();

        return Flux.fromIterable(items).flatMap(idx -> {
            log.info("flatMap {}", idx);
            return randomlySlowMono(0.1);
        }).then();

    }

    private static Mono<Void> randomlySlowMono(double slowProbability) {
        if (ThreadLocalRandom.current().nextDouble() <= slowProbability) {
            return Mono.just("slow response")
                    .delayElement(CHECK_INTERVAL.plus(Duration.ofMillis(100)))
                    .then();
        } else {
            return Mono.empty();
        }
    }
}