[cdi-dev] Building EJB-like @Asynchronous via interceptor in CDI
arjan tijms
arjan.tijms at gmail.com
Sat Jan 17 07:11:11 EST 2015
Hi,
On Sat, Jan 17, 2015 at 11:05 AM, Antonio Goncalves <
antonio.goncalves at gmail.com> wrote:
> @arjan Your example is base on ManagedExecutorService from the Java EE
> Concurrency spec. That's one topic we've been wondering about : should the
> @Asynchronous interceptor go to the Java EE Concurrency spec or not ? But
> it looks like the spec might not be updated.
>
The example I showed here would IMHO best be placed in the Java EE
Concurrency spec. That would in my opinion be a perfect analogy to
@Transactional and JTA. As given, the interceptor uses CDI/Interceptors and
Concurrency, so theoretically it could also be put into a third spec.
Personally I would find it strange to put something in spec A, when it may
better belong in spec B, just because spec B is not updated. What's holding
the update of Java EE Concurrency back? If most of the EG members would be
of the opinion that an @Asynchronous interceptor belongs best in Java EE
Concurrency, then we can just update that spec, right?
I know that MR releases can be quite fast and agile process wise, while
still packing some punch. JTA 1.2 itself was just such an MR, and JASPIC
1.1 was too. I was somewhat involved with JASPIC 1.1 (as community member)
and I think the setup time was pretty fast. Mid feb 2013 we created the
JIRA issues, the MR draft was published early march 2013 and the release
was with EE 7 end may 2013.
If it would just be about putting a few interceptors formally in Java EE
Concurrency, then why not do such small update for it?
Kind regards,
Arjan
>
> Antonio
>
> On Sat, Jan 17, 2015 at 12:32 AM, arjan tijms <arjan.tijms at gmail.com>
> wrote:
>
>> Hi,
>>
>> On Fri, Jan 16, 2015 at 10:41 PM, Jozef Hartinger <jharting at redhat.com>
>> wrote:
>>
>>> Hi Arjan,
>>>
>>> I did some changes recently in Weld interceptors and this usecase now
>>> works smoothly. The code is not part of a release yet. See this test for a
>>> simple implementation of an @Async interceptor (basically the same as your
>>> initial attempt). Note that the chain is repeatable but at the same time it
>>> is not reset after dispatch to a different thread so you no longer need the
>>> ThreadLocal nor any other workaround.
>>>
>>
>> That's quite a coincidence, it's indeed rather similar ;)
>>
>> I wonder how it now works though, as the InvocationContext "ctx" does not
>> seem to be made aware that it's been dispatched to a different thread from
>> within the code. Does it use an internal thread local to keep state or so?
>>
>> I'll also try to see what this does on OWB. Do you think this is
>> something that should work, or just something that Weld happens to support
>> regardless of the spec?
>>
>> Kind regards,
>> Arjan
>>
>>
>>
>>
>>>
>>>
>>> https://github.com/weld/core/blob/master/tests-arquillian/src/test/java/org/jboss/weld/tests/interceptors/thread/async/AsyncInterceptor.java
>>>
>>> Jozef
>>>
>>>
>>> On 01/16/2015 06:17 PM, arjan tijms wrote:
>>>
>>> Hi,
>>>
>>> I'm attempting to emulate EJB's @Asynchronous in CDI using interceptors.
>>>
>>> Originally I had defined my interceptor as follows;
>>>
>>> @Interceptor
>>> @Asynchronous
>>> @Priority(APPLICATION)
>>> public class AsynchronousInterceptor implements Serializable {
>>>
>>> private static final long serialVersionUID = 1L;
>>>
>>> @Resource
>>> private ManagedExecutorService managedExecutorService;
>>>
>>> @AroundInvoke
>>> public Object submitAsync(InvocationContext ctx) throws Exception {
>>> return new FutureDelegator(managedExecutorService.submit( ()-> {
>>> return ctx.proceed(); } ));
>>> }
>>>
>>> }
>>>
>>> With FutureDelegator as follows:
>>>
>>> public class FutureDelegator implements Future<Object> {
>>>
>>> private Future<?> future;
>>>
>>> public FutureDelegator(Future<?> future) {
>>> this.future = future;
>>> }
>>>
>>> @Override
>>> public Object get() throws InterruptedException, ExecutionException {
>>> AsyncResult<?> asyncResult = (AsyncResult<?>) future.get();
>>> if (asyncResult == null) {
>>> return null;
>>> }
>>>
>>> return asyncResult.get();
>>> }
>>>
>>> @Override
>>> public Object get(long timeout, TimeUnit unit) throws
>>> InterruptedException, ExecutionException, TimeoutException {
>>> AsyncResult<?> asyncResult = (AsyncResult<?>)
>>> future.get(timeout, unit);
>>> if (asyncResult == null) {
>>> return null;
>>> }
>>>
>>> return asyncResult.get();
>>> }
>>>
>>> @Override
>>> public boolean cancel(boolean mayInterruptIfRunning) {
>>> return future.cancel(mayInterruptIfRunning);
>>> }
>>>
>>> @Override
>>> public boolean isCancelled() {
>>> return future.isCancelled();
>>> }
>>> @Override
>>> public boolean isDone() {
>>> return future.isDone();
>>> }
>>>
>>> }
>>>
>>> This of course didn't quite work, as the InvocationContext will be
>>> reset after the @AroundInvoke method returns, and an infinite intercept
>>> loop results (on Weld).
>>>
>>> I got it to work though on Weld by using a thread local check to break
>>> that loop:
>>>
>>> @Interceptor
>>> @Asynchronous
>>> @Priority(PLATFORM_BEFORE)
>>> public class AsynchronousInterceptor implements Serializable {
>>>
>>> private static final long serialVersionUID = 1L;
>>>
>>> @Resource
>>> private ManagedExecutorService managedExecutorService;
>>>
>>> private static final ThreadLocal<Boolean> asyncInvocation = new
>>> ThreadLocal<Boolean>();
>>>
>>> @AroundInvoke
>>> public synchronized Object submitAsync(InvocationContext ctx) throws
>>> Exception {
>>>
>>> if (TRUE.equals(asyncInvocation.get())) {
>>> return ctx.proceed();
>>> }
>>>
>>> return new FutureDelegator(managedExecutorService.submit( ()-> {
>>> try {
>>> asyncInvocation.set(TRUE);
>>> return ctx.proceed();
>>> } finally {
>>> asyncInvocation.remove();
>>> }
>>> }));
>>> }
>>>
>>> }
>>>
>>> But I've got a feeling this works just by chance and not because the
>>> workaround is so clever.
>>>
>>> What do you guys think, what would be the best way to support this
>>> with the current CDI version? Or would CDI/Interceptors need something like
>>> Servlet's async support, where the InvocationContext is put into async mode
>>> whereafter it "simply" allows an other thread to continue processing on it?
>>>
>>> Kind regards,
>>> Arjan Tijms
>>>
>>>
>>>
>>>
>>>
>>>
>>>
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>>>
>>>
>>>
>>
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>> intellectual property rights inherent in such information.
>>
>
>
>
> --
> Antonio Goncalves
> Software architect, Java Champion and Pluralsight author
>
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