[cdi-dev] Destroying beans from an interceptor
Jozef Hartinger
jharting at redhat.com
Fri Nov 14 04:46:50 EST 2014
On 11/14/2014 09:14 AM, Mark Struberg wrote:
> I did not say it cannot work but that it is not guaranteed to work. It's just totally up to implementation details of the container and your actual situation. Basically it's non-portable at best.
>
>
> E.g. consider the case that you are NOT the outermost interceptor but there are 2 other decorators and interceptors. The decorators will probably not hurt much as they are defined to be called _after_ interceptors. But if there is an interceptor in addition to yours then you will probably kill em and after returning from the chain you might end up in a dead bean (the other interceptor).
You are right Mark but I think this is not a problem of whether you call
AlterableContext.destroy() from within an interceptor or not. This is a
more general problem of destroying instances. Say you have an
intercepted @ApplicationScoped bean Foo. Thread 1 is calling an
intercepted method and is currently in the middle of the interceptor
chain. Thread 2 calls AlterableContext.destroy(Foo) in a Servlet (not
from an interceptor!). Foo is destroyed together with its interceptors
by Thread 2. Thread 1 finds itself executing a dead interceptor chain
for a destroyed bean.
>
> There are just so many things which can go wrong. Even though I like the general idea what you like to do with that interceptor. But I suggest you probably use another trick. Every CDI bean must (as per the interceptors spec) support 'self-interception'. Means you only need to add an @AroundInvoke method and do the re-setup of your CONNECTION inside your @ApplicationScoped bean (with full access to the underlying business infrastructure).
>
>
> This is fundamentally different to your approach as I do not ditch the whole service but only fix the thing which broke in it.
>
>
> LieGrue,
> strub
>
>
>
> On Thursday, 13 November 2014, 16:28, arjan tijms <arjan.tijms at gmail.com> wrote:
>> Hi,
>>
>> On Wednesday, November 12, 2014, Jozef Hartinger <jharting at redhat.com> wrote:
>>
>> Hi Arjan,
>>> there is a bug in Weld (WELD-1785) preventing this from working which is going to be fixed in the next release. What you are doing should work IMO as long as the interceptor does not call any other methods on the target instance.
>>
>> That's great to hear really.
>>
>>
>> I'm slightly confused through why Mark thinks this cannot really work, while you say it should.
>>
>>
>> Is there something in the spec that may need to be clarified here? Ie some words about what an interceptor is at least allowed to do and what is definitely not allowed?
>>
>>
>>
>> In addition it must count with the target instance being destroyed within the instance.destroy() call.
>>
>>
>> Sorry, I don't fully follow this. You mean something must be counted?
>>
>>
>>> Perhaps a nicer way of doing this would be:
>>>
>>> @Inject
>>> @Intercepted
>>> private Bean<?> bean;
>>>
>>> Context context = manager.getContext(bean.getScope());
>>> if (!(context instanceof AlterableContext)) {
>>> throw new IllegalStateException("Context does not support removal of instances");
>>> }
>>> AlterableContext alterableContext = AlterableContext.class.cast(context);
>>> alterableContext.destroy(bean);
>>
>> I tried something close to that as well, just used the bean manager to resolve a Bean from the target object. Thanks for the suggestion!
>>
>>
>> Kind regards,
>> Arjan
>>
>>
>>
>>
>>> On 11/10/2014 02:59 PM, arjan tijms wrote:
>>>
>>> Hi,
>>>> I wonder if it would be allowed according to the CDI spec to destroy a
>>>> bean instance from within an interceptor.
>>>>
>>>> To test this (on Weld) I used the following code:
>>>>
>>>> @Interceptor
>>>> @DestroyOnError
>>>> @Priority(APPLICATION)
>>>> public class DestroyOnErrorInterceptor implements Serializable {
>>>>
>>>> private static final long serialVersionUID = 1L;
>>>>
>>>> @AroundInvoke
>>>> public Object tryInvoke(InvocationContext ctx) throws Exception {
>>>>
>>>> try {
>>>> return ctx.proceed();
>>>> } catch (Exception e) {
>>>> destroy(ctx.getMethod().getDeclaringClass());
>>>> throw e;
>>>> }
>>>> }
>>>>
>>>> private <T> void destroy(Class<T> clazz) {
>>>> Instance<T> instance = CDI.current().select(clazz);
>>>> instance.destroy(instance.get());
>>>> }
>>>>
>>>> }
>>>>
>>>>
>>>> When I use this interceptor on a SessionScoped bean:
>>>>
>>>> @SessionScoped
>>>> public class TestBean implements Serializable {
>>>>
>>>> private static final long serialVersionUID = 1L;
>>>>
>>>> @DestroyOnError
>>>> public void test() {
>>>> throw new IllegalStateException();
>>>> }
>>>> }
>>>>
>>>> And then inject said bean in say a Servlet and call the test() method,
>>>> destruction of the bean happens partially, but as soon as Weld tried
>>>> to invocate a preDestroy method, it goes through the bean proxy again,
>>>> detects that "the" interceptor handler is already active, promptly
>>>> skips its attempt to call a preDestroy method and then to add insult
>>>> to injury tries to call a "proceed" method which is always null and
>>>> thus throws a NPE.
>>>>
>>>> (this happens in
>>>> org.jboss.weld.bean.proxy.CombinedInterceptorAndDecoratorStackMethodHandler.invoke)
>>>>
>>>> I tried some alternative methods to destroy the bean such as:
>>>>
>>>>
>>>> Bean<T> bean = resolve(beanManager, beanClass);
>>>>
>>>> AlterableContext context = (AlterableContext)
>>>> beanManager.getContext(bean.getScope());
>>>> context.destroy(bean);
>>>>
>>>> with resolve being:
>>>>
>>>> public static <T> Bean<T> resolve(BeanManager beanManager, Class<T> beanClass) {
>>>> Set<Bean<?>> beans = beanManager.getBeans(beanClass);
>>>>
>>>> for (Bean<?> bean : beans) {
>>>> if (bean.getBeanClass() == beanClass) {
>>>> return (Bean<T>)
>>>> beanManager.resolve(Collections.<Bean<?>>singleton(bean));
>>>> }
>>>> }
>>>>
>>>> return (Bean<T>) beanManager.resolve(beans);
>>>> }
>>>>
>>>> But this resulted in the same problem.
>>>>
>>>> Any idea?
>>>>
>>>> Kind regards,
>>>> Arjan Tijms
>>>> _______________________________________________
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>>>> cdi-dev at lists.jboss.org
>>>> https://lists.jboss.org/mailman/listinfo/cdi-dev
>>>>
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>>>>
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