AMQP-226 Fix Exponential Back Off

Previously, for stateful environments,the
multiplier had no effect and the backoff
policy always slept for the initial interval.

AMQP-226 Polishing

Using AttributeAccessor interface instead of concrete
RetryContextSupport.

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2012 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.
@@ -16,6 +16,8 @@
 
 package org.springframework.retry.backoff;
 
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
 import org.springframework.retry.RetryContext;
 import org.springframework.util.ClassUtils;
 
@@ -35,9 +37,11 @@
  * 
  * @author Rob Harrop
  * @author Dave Syer
+ * @author Gary Russell
  */
 public class ExponentialBackOffPolicy implements BackOffPolicy {
 
+	protected final Log logger = LogFactory.getLog(this.getClass());
 	/**
 	 * The default 'initialInterval' value - 100 millisecs. Coupled with the
 	 * default 'multiplier' value this gives a useful initial spread of pauses
@@ -151,7 +155,11 @@ public BackOffContext start(RetryContext context) {
 	public void backOff(BackOffContext backOffContext) throws BackOffInterruptedException {
 		ExponentialBackOffContext context = (ExponentialBackOffContext) backOffContext;
 		try {
-			sleeper.sleep(context.getSleepAndIncrement());
+			long sleepTime = context.getSleepAndIncrement();
+			if (logger.isDebugEnabled()) {
+				logger.debug("Sleeping for " + sleepTime);
+			}
+			sleeper.sleep(sleepTime);
 		}
 		catch (InterruptedException e) {
 			throw new BackOffInterruptedException("Thread interrupted while sleeping", e);

src/main/java/org/springframework/retry/support/RetryTemplate.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2012 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.
@@ -23,6 +23,7 @@
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.springframework.core.AttributeAccessor;
 import org.springframework.retry.ExhaustedRetryException;
 import org.springframework.retry.RecoveryCallback;
 import org.springframework.retry.RetryCallback;
@@ -67,6 +68,7 @@
  * 
  * @author Rob Harrop
  * @author Dave Syer
+ * @author Gary Russell
  */
 public class RetryTemplate implements RetryOperations {
 
@@ -220,8 +222,22 @@ protected <T> T doExecute(RetryCallback<T> retryCallback, RecoveryCallback<T> re
 				throw new TerminatedRetryException("Retry terminated abnormally by interceptor before first attempt");
 			}
 
-			// Start the backoff context...
-			BackOffContext backOffContext = backOffPolicy.start(context);
+			// Get or Start the backoff context...
+			BackOffContext backOffContext = null;
+			AttributeAccessor attributeAccessor = null;
+			if (context instanceof AttributeAccessor) {
+				attributeAccessor = (AttributeAccessor) context;
+				Object resource = attributeAccessor.getAttribute("backOffContext");
+				if (resource instanceof BackOffContext) {
+					backOffContext = (BackOffContext) resource;
+				}
+			}
+			if (backOffContext == null) {
+				backOffContext = backOffPolicy.start(context);
+				if (attributeAccessor != null && backOffContext != null) {
+					attributeAccessor.setAttribute("backOffContext", backOffContext);
+				}
+			}
 
 			/*
 			 * We allow the whole loop to be skipped if the policy or context

src/test/java/org/springframework/retry/policy/StatefulRetryIntegrationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007 the original author or authors.
+ * Copyright 2006-2012 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.
@@ -22,18 +22,23 @@
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
+import java.util.ArrayList;
 import java.util.Collections;
+import java.util.List;
 
 import org.junit.Test;
 import org.springframework.retry.ExhaustedRetryException;
+import org.springframework.retry.RecoveryCallback;
 import org.springframework.retry.RetryCallback;
 import org.springframework.retry.RetryContext;
 import org.springframework.retry.RetryState;
+import org.springframework.retry.backoff.ExponentialBackOffPolicy;
 import org.springframework.retry.support.DefaultRetryState;
 import org.springframework.retry.support.RetryTemplate;
 
 /**
  * @author Dave Syer
+ * @author Gary Russell
  * 
  */
 public class StatefulRetryIntegrationTests {
@@ -114,6 +119,38 @@ public void testExternalRetryWithSuccessOnRetry() throws Exception {
 		assertEquals("bar", result);
 	}
 
+	@Test
+	public void testExponentialBackOffIsExponential() throws Exception {
+		ExponentialBackOffPolicy policy = new ExponentialBackOffPolicy();
+		policy.setInitialInterval(100);
+		policy.setMultiplier(1.5);
+		RetryTemplate template = new RetryTemplate();
+		template.setBackOffPolicy(policy);
+		final List<Long> times = new ArrayList<Long>();
+		RetryState retryState = new DefaultRetryState("bar");
+		for (int i = 0; i < 3; i++) {
+			try {
+				template.execute(new RetryCallback<String>() {
+					public String doWithRetry(RetryContext context) throws Exception {
+						times.add(System.currentTimeMillis());
+						throw new Exception("Fail");
+					}
+				}, new RecoveryCallback<String>() {
+					public String recover(RetryContext context)
+							throws Exception {
+						return null;
+					}
+				}, retryState);
+			}
+			catch (Exception e) {
+				assertTrue(e.getMessage().equals("Fail"));
+			}
+		}
+		assertEquals(3, times.size());
+		assertTrue(times.get(1) - times.get(0) >= 100);
+		assertTrue(times.get(2) - times.get(1) >= 150);
+	}
+
 	/**
 	 * @author Dave Syer
 	 *