Demonstration of how stacktraces can be limited in async programming

Scratch.java

/*
 * Copyright (c) 2011-2019 Pivotal Software Inc, All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.time.LocalTime;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

import reactor.core.publisher.Flux;
import reactor.core.publisher.Hooks;
import reactor.core.publisher.Mono;
import reactor.core.scheduler.Schedulers;

class Scratch {

	public static void main(String[] args) {
		try { imperative(); System.out.println("RE RUN imperative()"); } catch (Exception t) { t.printStackTrace();}
		try { reactive(); System.out.println("RE RUN reactive()"); } catch (Exception t) { t.printStackTrace();}
		try { reactiveNoSubscribeOn(); System.out.println("RE RUN reactiveNoSubscribeOn()"); } catch (Exception t) { t.printStackTrace();}
		try { log(); System.out.println("RE RUN log()"); } catch (Exception t) { t.printStackTrace();}
		try { hook(); System.out.println("RE RUN hook()"); } catch (Exception t) { t.printStackTrace();}
		try { checkpoint(); System.out.println("RE RUN checkpoint()"); } catch (Exception t) { t.printStackTrace();}

		System.exit(0);
	}

	private static void imperative() throws ExecutionException, InterruptedException {
		final ScheduledExecutorService executor =
				Executors.newSingleThreadScheduledExecutor();

		int seconds = LocalTime.now().getSecond();
		List<Integer> source;
		if (seconds % 2 == 0) {
			source = IntStream.range(1, 11).boxed().collect(Collectors.toList());
		}
		else if (seconds % 3 == 0) {
			source = IntStream.range(0, 4).boxed().collect(Collectors.toList());
		}
		else {
			source = Arrays.asList(1, 2, 3, 4);
		}

		executor.submit(() -> source.get(5))  //line 76
		        .get();
	}

	private static void reactive() {
		int seconds = LocalTime.now().getSecond();
		Mono<Integer> source;
		if (seconds % 2 == 0) {
			source = Flux.range(1, 10)
			             .elementAt(5);
		}
		else if (seconds % 3 == 0) {
			source = Flux.range(0, 4)
			             .elementAt(5);
		}
		else {
			source = Flux.just(1, 2, 3, 4)
			             .elementAt(5);
		}

		source.subscribeOn(Schedulers.parallel())
		      .block(); //line 97
	}

	private static void reactiveNoSubscribeOn() {
		int seconds = LocalTime.now().getSecond();
		Mono<Integer> source;
		if (seconds % 2 == 0) {
			source = Flux.range(1, 10)
			             .elementAt(5);
		}
		else if (seconds % 3 == 0) {
			source = Flux.range(0, 4)
			             .elementAt(5);
		}
		else {
			source = Flux.just(1, 2, 3, 4)
			             .elementAt(5);
		}

		source.block(); //line 116
	}

	private static void log() {
		int seconds = LocalTime.now().getSecond();
		Mono<Integer> source;
		if (seconds % 2 == 0) {
			source = Flux.range(1, 10)
			             .elementAt(5)
			             .log("source A");
		}
		else if (seconds % 3 == 0) {
			source = Flux.range(0, 4)
			             .elementAt(5)
			             .log("source B");
		}
		else {
			source = Flux.just(1, 2, 3, 4)
			             .elementAt(5)
			             .log("source C");
		}

		source.block(); //line 138
	}


	private static void hook() {
		Hooks.onOperatorDebug();
		try {
			int seconds = LocalTime.now().getSecond();
			Mono<Integer> source;
			if (seconds % 2 == 0) {
				source = Flux.range(1, 10)
				             .elementAt(5); //line 149
			}
			else if (seconds % 3 == 0) {
				source = Flux.range(0, 4)
				             .elementAt(5); //line 153
			}
			else {
				source = Flux.just(1, 2, 3, 4)
				             .elementAt(5); //line 157
			}

			source.block(); //line 160
		}
		finally {
			Hooks.resetOnOperatorDebug();
		}
	}

	private static void checkpoint() {
		int seconds = LocalTime.now().getSecond();
		Mono<Integer> source;
		if (seconds % 2 == 0) {
			source = Flux.range(1, 10)
			             .elementAt(5)
			             .checkpoint("source range(1,10)");
		}
		else if (seconds % 3 == 0) {
			source = Flux.range(0, 4)
			             .elementAt(5)
			             .checkpoint("source range(0,4)");
		}
		else {
			source = Flux.just(1, 2, 3, 4)
			             .elementAt(5)
			             .checkpoint("source just(1,2,3,4)");
		}

		source.block(); //line 186
	}
}