关于spring ioc容器的问题

private Object resolveReference(String argName, RuntimeBeanReference ref) {
		if (this.beanFactory.logger.isTraceEnabled()) {
			this.beanFactory.logger.trace("Resolving reference from property " + argName + " in bean '" +
					this.beanName + "' to bean '" + ref.getBeanName() + "'");
		}
		try {
			if (ref.isToParent()) {
				if (this.beanFactory.getParentBeanFactory() == null) {
					throw new BeanCreationException(
							this.beanDefinition.getResourceDescription(), this.beanName,
							"Can't resolve reference to bean '" + ref.getBeanName() +
							"' in parent factory: no parent factory available");
				}
				return this.beanFactory.getParentBeanFactory().getBean(ref.getBeanName());
			}
			else {
				Object bean = this.beanFactory.getBean(ref.getBeanName());
				if (this.beanDefinition.isSingleton()) {
					this.beanFactory.registerDependentBean(ref.getBeanName(), this.beanName);
				}
				return bean;
			}
		}
		catch (BeansException ex) {
			throw new BeanCreationException(
					this.beanDefinition.getResourceDescription(), this.beanName,
					"Cannot resolve reference to bean '" + ref.getBeanName() + "' while setting " + argName, ex);
		}
	}

			if (this.beanDefinition.isSingleton()) {
					this.beanFactory.registerDependentBean(ref.getBeanName(), this.beanName);
				}
				return bean;
			}

/**
	 * Add the given bean to the list of disposable beans in this factory,
	 * registering its DisposableBean interface and/or the given destroy method
	 * to be called on factory shutdown (if applicable). Only applies to singletons.
	 * <p>Also registers bean as dependent on other beans, according to the
	 * "depends-on" configuration in the bean definition.
	 * @param beanName the name of the bean
	 * @param bean the bean instance
	 * @param mbd the bean definition for the bean
	 * @see RootBeanDefinition#isSingleton
	 * @see RootBeanDefinition#getDependsOn
	 * @see #registerDisposableBean
	 * @see #registerDependentBean
	 */
	protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {
		if (mbd.isSingleton() && requiresDestruction(bean, mbd)) {
			// Register a DisposableBean implementation that performs all destruction
			// work for the given bean: DestructionAwareBeanPostProcessors,
			// DisposableBean interface, custom destroy method.
			registerDisposableBean(beanName,
					new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors()));

			// Register bean as dependent on other beans, if necessary,
			// for correct shutdown order.
			String[] dependsOn = mbd.getDependsOn();
			if (dependsOn != null) {
				for (int i = 0; i < dependsOn.length; i++) {
					registerDependentBean(dependsOn[i], beanName);
				}
			}
		}
	}

	protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {
		if (mbd.isSingleton() && requiresDestruction(bean, mbd)) {
			// Register a DisposableBean implementation that performs all destruction
			// work for the given bean: DestructionAwareBeanPostProcessors,
			// DisposableBean interface, custom destroy method.
			registerDisposableBean(beanName,
					new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors()));

			// Register bean as dependent on other beans, if necessary,
			// for correct shutdown order.
			String[] dependsOn = mbd.getDependsOn();
			if (dependsOn != null) {
				for (int i = 0; i < dependsOn.length; i++) {
					registerDependentBean(dependsOn[i], beanName);
				}
			}
		}
	}

	public void registerDependentBean(String beanName, String dependentBeanName) {
		synchronized (this.dependentBeanMap) {
			Set dependencies = (Set) this.dependentBeanMap.get(beanName);
			if (dependencies == null) {
				dependencies = CollectionFactory.createLinkedSetIfPossible(8);
				this.dependentBeanMap.put(beanName, dependencies);
			}
			dependencies.add(dependentBeanName);
		}
	}