org.springframework.retry.support.RetrySimulator Maven / Gradle / Ivy

/*
 * Copyright 2006-2022 the original author or authors.
 *
 * 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
 *
 *      https://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.
 */

package org.springframework.retry.support;

import java.util.ArrayList;
import java.util.List;

import org.springframework.retry.RetryCallback;
import org.springframework.retry.RetryContext;
import org.springframework.retry.RetryPolicy;
import org.springframework.retry.backoff.Sleeper;
import org.springframework.retry.backoff.SleepingBackOffPolicy;

/**
 * A {@link RetrySimulator} is a tool for exercising retry + backoff operations.
 *
 * When calibrating a set of retry + backoff pairs, it is useful to know the behaviour of
 * the retry for various scenarios.
 *
 * Things you may want to know: - Does a 'maxInterval' of 5000 ms in my backoff even
 * matter? (This is often the case when retry counts are low -- so why set the max
 * interval at something that cannot be achieved?) - What are the typical sleep durations
 * for threads in a retry - What was the longest sleep duration for any retry sequence
 *
 * The simulator provides this information by executing a retry + backoff pair until
 * failure (that is all retries are exhausted). The information about each retry is
 * provided as part of the {@link RetrySimulation}.
 *
 * Note that the impetus for this class was to expose the timings which are possible with
 * {@link org.springframework.retry.backoff.ExponentialRandomBackOffPolicy}, which
 * provides random values and must be looked at over a series of trials.
 *
 * @author Jon Travis
 */
public class RetrySimulator {

	private final SleepingBackOffPolicy backOffPolicy;

	private final RetryPolicy retryPolicy;

	public RetrySimulator(SleepingBackOffPolicy backOffPolicy, RetryPolicy retryPolicy) {
		this.backOffPolicy = backOffPolicy;
		this.retryPolicy = retryPolicy;
	}

	/**
	 * Execute the simulator for a give # of iterations.
	 * @param numSimulations Number of simulations to run
	 * @return the outcome of all simulations
	 */
	public RetrySimulation executeSimulation(int numSimulations) {
		RetrySimulation simulation = new RetrySimulation();

		for (int i = 0; i < numSimulations; i++) {
			simulation.addSequence(executeSingleSimulation());
		}
		return simulation;
	}

	/**
	 * Execute a single simulation
	 * @return The sleeps which occurred within the single simulation.
	 */
	public List executeSingleSimulation() {
		StealingSleeper stealingSleeper = new StealingSleeper();
		SleepingBackOffPolicy stealingBackoff = backOffPolicy.withSleeper(stealingSleeper);

		RetryTemplate template = new RetryTemplate();
		template.setBackOffPolicy(stealingBackoff);
		template.setRetryPolicy(retryPolicy);

		try {
			template.execute(new FailingRetryCallback());
		}
		catch (FailingRetryException e) {

		}
		catch (Throwable e) {
			throw new RuntimeException("Unexpected exception", e);
		}

		return stealingSleeper.getSleeps();
	}

	static class FailingRetryCallback implements RetryCallback {

		public Object doWithRetry(RetryContext context) throws Exception {
			throw new FailingRetryException();
		}

	}

	@SuppressWarnings("serial")
	static class FailingRetryException extends Exception {

	}

	@SuppressWarnings("serial")
	static class StealingSleeper implements Sleeper {

		private final List sleeps = new ArrayList<>();

		public void sleep(long backOffPeriod) throws InterruptedException {
			sleeps.add(backOffPeriod);
		}

		public List getSleeps() {
			return sleeps;
		}

	}

}