GH-388: add non blocking sleeper

- fix (#388)
- add non blocking sleeper

src/main/java/org/springframework/retry/backoff/BackOffPolicyBuilder.java

@@ -158,7 +158,7 @@ public BackOffPolicyBuilder random(boolean random) {
 
 	/**
 	 * The {@link Sleeper} instance to be used to back off. Policies default to
-	 * {@link ThreadWaitSleeper}.
+	 * {@link NonBlockingSleeper}.
 	 * @param sleeper the {@link Sleeper} instance
 	 * @return this
 	 */

src/main/java/org/springframework/retry/backoff/ExponentialBackOffPolicy.java

@@ -95,7 +95,7 @@ public class ExponentialBackOffPolicy implements SleepingBackOffPolicy<Exponenti
 	 */
 	private Supplier<Double> multiplierSupplier;
 
-	private Sleeper sleeper = new ThreadWaitSleeper();
+	private Sleeper sleeper = new NonBlockingSleeper();
 
 	/**
 	 * Public setter for the {@link Sleeper} strategy.

src/main/java/org/springframework/retry/backoff/FixedBackOffPolicy.java

@@ -45,7 +45,7 @@ public class FixedBackOffPolicy extends StatelessBackOffPolicy implements Sleepi
 	 */
 	private Supplier<Long> backOffPeriod = () -> DEFAULT_BACK_OFF_PERIOD;
 
-	private Sleeper sleeper = new ThreadWaitSleeper();
+	private Sleeper sleeper = new NonBlockingSleeper();
 
 	public FixedBackOffPolicy withSleeper(Sleeper sleeper) {
 		FixedBackOffPolicy res = new FixedBackOffPolicy();
@@ -56,7 +56,7 @@ public FixedBackOffPolicy withSleeper(Sleeper sleeper) {
 
 	/**
 	 * Public setter for the {@link Sleeper} strategy.
-	 * @param sleeper the sleeper to set defaults to {@link ThreadWaitSleeper}.
+	 * @param sleeper the sleeper to set defaults to {@link NonBlockingSleeper}.
 	 */
 	public void setSleeper(Sleeper sleeper) {
 		this.sleeper = sleeper;

src/main/java/org/springframework/retry/backoff/NonBlockingSleeper.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2014 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.backoff;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Non-blocking {@link Sleeper} implementation that just sleep with specified
+ * backOffPeriod.
+ *
+ * @author Alireza Hakimrabet
+ */
+@SuppressWarnings("serial")
+public class NonBlockingSleeper implements Sleeper {
+
+	@Override
+	public void sleep(long backOffPeriod) throws InterruptedException {
+		CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
+			try {
+				TimeUnit.MILLISECONDS.sleep(backOffPeriod);
+			}
+			catch (InterruptedException e) {
+				Thread.currentThread().interrupt();
+				throw new RuntimeException("Unexpected exception", e);
+			}
+		});
+		future.join();
+	}
+
+}

src/main/java/org/springframework/retry/backoff/ThreadWaitSleeper.java

@@ -20,9 +20,11 @@
  * Simple {@link Sleeper} implementation that just blocks the current Thread with sleep
  * period.
  *
+ * @deprecated in favor of {@link NonBlockingSleeper}
  * @author Artem Bilan
  * @since 1.1
  */
+@Deprecated
 @SuppressWarnings("serial")
 public class ThreadWaitSleeper implements Sleeper {
 

src/main/java/org/springframework/retry/backoff/UniformRandomBackOffPolicy.java

@@ -53,7 +53,7 @@ public class UniformRandomBackOffPolicy extends StatelessBackOffPolicy
 
 	private final Random random = new Random(System.currentTimeMillis());
 
-	private Sleeper sleeper = new ThreadWaitSleeper();
+	private Sleeper sleeper = new NonBlockingSleeper();
 
 	public UniformRandomBackOffPolicy withSleeper(Sleeper sleeper) {
 		UniformRandomBackOffPolicy res = new UniformRandomBackOffPolicy();
@@ -65,7 +65,7 @@ public UniformRandomBackOffPolicy withSleeper(Sleeper sleeper) {
 
 	/**
 	 * Public setter for the {@link Sleeper} strategy.
-	 * @param sleeper the sleeper to set defaults to {@link ThreadWaitSleeper}.
+	 * @param sleeper the sleeper to set defaults to {@link NonBlockingSleeper}.
 	 */
 	public void setSleeper(Sleeper sleeper) {
 		this.sleeper = sleeper;

src/test/java/org/springframework/retry/backoff/NonBlockingSleeperTests.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2006-2023 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.backoff;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Alireza Hakimrabet
+ */
+public class NonBlockingSleeperTests {
+
+	@Test
+	public void testSingleBackOff() throws Exception {
+		long backOffPeriod = 50;
+		NonBlockingSleeper strategy = new NonBlockingSleeper();
+		long before = System.currentTimeMillis();
+		strategy.sleep(backOffPeriod);
+		long after = System.currentTimeMillis();
+		assertEqualsApprox(backOffPeriod, after - before, 25);
+	}
+
+	private void assertEqualsApprox(long desired, long actual, long variance) {
+		long lower = desired - variance;
+		long upper = desired + 2 * variance;
+		assertThat(lower).describedAs("Expected value to be between '%d' and '%d' but was '%d'", lower, upper, actual)
+			.isLessThanOrEqualTo(actual);
+	}
+
+}