Introduce onRetryPolicyInterruption() callback in RetryListener

In RetryTemplate, if we encounter an InterruptedException while
sleeping for the configured back-off duration, we throw a
RetryException with the InterruptedException as the cause.

However, prior to this commit, that RetryException propagated to the
caller without notifying the registered RetryListener.

To address that, this commit introduces a new
onRetryPolicyInterruption() callback in RetryListener as a companion to
the existing onRetryPolicyExhaustion() callback.

Closes gh-35442

spring-core/src/main/java/org/springframework/core/retry/RetryListener.java

@@ -53,7 +53,7 @@ public interface RetryListener {
 	}
 
 	/**
-	 * Called every time a retry attempt fails.
+	 * Called after every failed retry attempt.
 	 * @param retryPolicy the {@link RetryPolicy}
 	 * @param retryable the {@link Retryable} operation
 	 * @param throwable the exception thrown by the {@code Retryable} operation
@@ -65,8 +65,9 @@ public interface RetryListener {
 	 * Called if the {@link RetryPolicy} is exhausted.
 	 * @param retryPolicy the {@code RetryPolicy}
 	 * @param retryable the {@code Retryable} operation
-	 * @param exception the resulting {@link RetryException}, including the last operation
-	 * exception as a cause and all earlier operation exceptions as suppressed exceptions
+	 * @param exception the resulting {@link RetryException}, with the last
+	 * exception thrown by the {@link Retryable} operation as the cause and any
+	 * exceptions from previous attempts as suppressed exceptions
 	 * @see RetryException#getCause()
 	 * @see RetryException#getSuppressed()
 	 * @see RetryException#getRetryCount()
@@ -74,4 +75,19 @@ public interface RetryListener {
 	default void onRetryPolicyExhaustion(RetryPolicy retryPolicy, Retryable<?> retryable, RetryException exception) {
 	}
 
+	/**
+	 * Called if an {@link InterruptedException} is encountered while
+	 * {@linkplain Thread#sleep(long) sleeping} between retry attempts.
+	 * @param retryPolicy the {@code RetryPolicy}
+	 * @param retryable the {@code Retryable} operation
+	 * @param exception the resulting {@link RetryException}, with the
+	 * {@code InterruptedException} as the cause and any exceptions from previous
+	 * retry attempts as suppressed exceptions
+	 * @see RetryException#getCause()
+	 * @see RetryException#getSuppressed()
+	 * @see RetryException#getRetryCount()
+	 */
+	default void onRetryPolicyInterruption(RetryPolicy retryPolicy, Retryable<?> retryable, RetryException exception) {
+	}
+
 }

spring-core/src/main/java/org/springframework/core/retry/RetryTemplate.java

@@ -168,6 +168,7 @@ public class RetryTemplate implements RetryOperations {
 							"Unable to back off for retryable operation '%s'".formatted(retryableName),
 							interruptedException);
 					exceptions.forEach(retryException::addSuppressed);
+					this.retryListener.onRetryPolicyInterruption(this.retryPolicy, retryable, retryException);
 					throw retryException;
 				}
 				logger.debug(() -> "Preparing to retry operation '%s'".formatted(retryableName));

spring-core/src/main/java/org/springframework/core/retry/support/CompositeRetryListener.java

@@ -29,13 +29,14 @@ import org.springframework.core.retry.Retryable;
 import org.springframework.util.Assert;
 
 /**
- * A composite implementation of the {@link RetryListener} interface.
- * Delegate listeners will be called in their registration order.
+ * A composite implementation of the {@link RetryListener} interface, which is
+ * used to compose multiple listeners within a {@link RetryTemplate}.
  *
- * <p>This class is used to compose multiple listeners within a {@link RetryTemplate}.
+ * <p>Delegate listeners will be called in their registration order.
  *
  * @author Mahmoud Ben Hassine
  * @author Juergen Hoeller
+ * @author Sam Brannen
  * @since 7.0
  */
 public class CompositeRetryListener implements RetryListener {
@@ -88,4 +89,9 @@ public class CompositeRetryListener implements RetryListener {
 		this.listeners.forEach(listener -> listener.onRetryPolicyExhaustion(retryPolicy, retryable, exception));
 	}
 
+	@Override
+	public void onRetryPolicyInterruption(RetryPolicy retryPolicy, Retryable<?> retryable, RetryException exception) {
+		this.listeners.forEach(listener -> listener.onRetryPolicyInterruption(retryPolicy, retryable, exception));
+	}
+
 }

spring-core/src/test/java/org/springframework/core/retry/RetryTemplateTests.java

@@ -30,8 +30,11 @@ import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments.ArgumentSet;
 import org.junit.jupiter.params.provider.FieldSource;
+import org.junit.platform.commons.util.ExceptionUtils;
 import org.mockito.InOrder;
 
+import org.springframework.util.backoff.BackOff;
+
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.junit.jupiter.params.provider.Arguments.argumentSet;
@@ -213,6 +216,36 @@ class RetryTemplateTests {
 		verifyNoMoreInteractions(retryListener);
 	}
 
+	@Test
+	void retryWithInterruptionDuringSleep() {
+		Exception exception = new RuntimeException("Boom!");
+		InterruptedException interruptedException = new InterruptedException();
+
+		// Simulates interruption during sleep:
+		BackOff backOff = () -> () -> {
+			throw ExceptionUtils.throwAsUncheckedException(interruptedException);
+		};
+
+		RetryPolicy retryPolicy = RetryPolicy.builder().backOff(backOff).build();
+		RetryTemplate retryTemplate = new RetryTemplate(retryPolicy);
+		retryTemplate.setRetryListener(retryListener);
+		Retryable<String> retryable = () -> {
+			throw exception;
+		};
+
+		assertThatExceptionOfType(RetryException.class)
+				.isThrownBy(() -> retryTemplate.execute(retryable))
+				.withMessageMatching("Unable to back off for retryable operation '.+?'")
+				.withCause(interruptedException)
+				.satisfies(throwable -> assertThat(throwable.getSuppressed()).containsExactly(exception))
+				// TODO Fix retry count for InterruptedException scenario.
+				// Retry count should actually be 0.
+				.satisfies(throwable -> assertThat(throwable.getRetryCount()).isEqualTo(1))
+				.satisfies(throwable -> inOrder.verify(retryListener).onRetryPolicyInterruption(retryPolicy, retryable, throwable));
+
+		verifyNoMoreInteractions(retryListener);
+	}
+
 	@Test
 	void retryWithFailingRetryableAndMultiplePredicates() {
 		var invocationCount = new AtomicInteger();

spring-core/src/test/java/org/springframework/core/retry/support/CompositeRetryListenerTests.java

@@ -92,4 +92,14 @@ class CompositeRetryListenerTests {
 		verify(listener3).onRetryPolicyExhaustion(retryPolicy, retryable, exception);
 	}
 
+	@Test
+	void onRetryPolicyInterruption() {
+		RetryException exception = new RetryException("", new Exception());
+		compositeRetryListener.onRetryPolicyInterruption(retryPolicy, retryable, exception);
+
+		verify(listener1).onRetryPolicyInterruption(retryPolicy, retryable, exception);
+		verify(listener2).onRetryPolicyInterruption(retryPolicy, retryable, exception);
+		verify(listener3).onRetryPolicyInterruption(retryPolicy, retryable, exception);
+	}
+
 }