Cache by-type lookups in DefaultListableBeanFactory

Prior to this change, by-type lookups using DLBF#getBeanNamesForType
required traversal of all bean definitions within the bean factory
in order to inspect their bean class for assignability to the target
type. These operations are comparatively expensive and when there are a
large number of beans registered within the container coupled with a
large number of by-type lookups at runtime, the performance impact can
be severe. The test introduced here demonstrates such a scenario clearly.

This performance problem is likely to manifest in large Spring-based
applications using non-singleton beans, particularly request-scoped
beans that may be created and wired many thousands of times per second.

This commit introduces a simple ConcurrentHashMap-based caching strategy
for by-type lookups; container-wide assignability checks happen only
once on the first by-type lookup and are afterwards cached by type
with the values in the map being an array of all bean names assignable
to that type. This means that at runtime when creating and autowiring
non-singleton beans, the cost of by-type lookups is reduced to that of
ConcurrentHashMap#get.

Issue: SPR-6870

spring-beans/src/main/java/org/springframework/beans/factory/support/DefaultListableBeanFactory.java

@@ -92,6 +92,7 @@ import org.springframework.util.StringUtils;
  * @author Juergen Hoeller
  * @author Sam Brannen
  * @author Costin Leau
+ * @author Chris Beams
  * @since 16 April 2001
  * @see StaticListableBeanFactory
  * @see PropertiesBeanDefinitionReader
@@ -135,6 +136,12 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 	/** Map of bean definition objects, keyed by bean name */
 	private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>();
 
+	/** Map of singleton bean names keyed by bean class */
+	private final Map<Class<?>, String[]> singletonBeanNamesByType = new ConcurrentHashMap<Class<?>, String[]>();
+
+	/** Map of non-singleton bean names keyed by bean class */
+	private final Map<Class<?>, String[]> nonSingletonBeanNamesByType = new ConcurrentHashMap<Class<?>, String[]>();
+
 	/** List of bean definition names, in registration order */
 	private final List<String> beanDefinitionNames = new ArrayList<String>();
 
@@ -301,6 +308,21 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 	}
 
 	public String[] getBeanNamesForType(Class<?> type, boolean includeNonSingletons, boolean allowEagerInit) {
+		if (type == null || !allowEagerInit) {
+			return this.doGetBeanNamesForType(type, includeNonSingletons, allowEagerInit);
+		}
+		Map<Class<?>, String[]> cache = includeNonSingletons ?
+				this.nonSingletonBeanNamesByType : this.singletonBeanNamesByType;
+		String[] resolvedBeanNames = cache.get(type);
+		if (resolvedBeanNames != null) {
+			return resolvedBeanNames;
+		}
+		resolvedBeanNames = this.doGetBeanNamesForType(type, includeNonSingletons, allowEagerInit);
+		cache.put(type, resolvedBeanNames);
+		return resolvedBeanNames;
+	}
+
+	private String[] doGetBeanNamesForType(Class<?> type, boolean includeNonSingletons, boolean allowEagerInit) {
 		List<String> result = new ArrayList<String>();
 
 		// Check all bean definitions.
@@ -671,6 +693,10 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 			destroySingleton(beanName);
 		}
 
+		// Remove any assumptions about by-type mappings
+		this.singletonBeanNamesByType.clear();
+		this.nonSingletonBeanNamesByType.clear();
+
 		// Reset all bean definitions that have the given bean as parent (recursively).
 		for (String bdName : this.beanDefinitionNames) {
 			if (!beanName.equals(bdName)) {