[cdi-dev] @ThreadScoped?

Reza Rahman reza_rahman at lycos.com
Sun Mar 20 14:23:02 EDT 2016 

As discussed elsewhere in this EG, even in the most pessimistic reading of the current spec, all that would be needed is a flag on the existing annotation. It's not out of the question at all.

> On Mar 20, 2016, at 1:36 PM, Manfred Riem <mnriem at gmail.com> wrote:
> 
> Why is changing @RequestScoped out of the question? 
> 
> From my perspective when an AsyncContext is started the request is still there. 
> 
> It is just being served by a different thread.
> 
> Certainly there is a need to work with the Servlet EG to figure out how to transfer “ownership” to the AsyncContext.
> 
> Anyway my 2 cents
> 
> Thanks!
> 
> Kind regards,
> Manfred Riem
> 
>> On Mar 19, 2016, at 3:35 PM, Stephan Knitelius <stephan at knitelius.com> wrote:
>> 
>> I would certainly agree with the assertion that in general it's not advisable to execute a request with multiple threads and that usually single threaded execution is sufficient.
>> 
>> However I don't think ignoring it is an option. Concurrent operations can be launched even from CDI beans. Yet we don't properly support context propagation nor a context spanning all threads launched from a request.
>> 
>> I know that changing @requestScoped is probably out of the question, but at least we should consider adding a new context spanning all threads and defining a logical solution for context propagation that can be explained to the end user.
>> 
>> 
>> 
>>> On Fr., 11. März 2016 at 17:17, Mark Struberg <struberg at yahoo.de> wrote:
>>> Yes, but certain things in EE are assumed to be handled on a single thread. And if you run on a servr then this is really not a blocker most times. If I get many paralllel requests hitting my box then I do not need async handling _that_ often. The whole overhead for setting up the new thread, etc often heavily exceeds the benefits.
>>> So I would not put too much energy into it…
>>> 
>>> LieGrue,
>>> strub
>>> 
>>> > Am 11.03.2016 um 15:44 schrieb Reza Rahman <reza_rahman at lycos.com>:
>>> >
>>> > This is essentially in keeping with the minimalist nature of the EE concurrency JSR. I believe most of it is left to vendors to do the right thing for users. May be a good idea is this language can be tightened up.
>>> >
>>> >> On Mar 11, 2016, at 6:01 AM, Mark Struberg <struberg at yahoo.de> wrote:
>>> >> E
>>> >> From the servlet spec:
>>> >>
>>> >> „Java Enterprise Edition features such as Section 15.2.2, “Web Application Environment” on page 15-174 and Section 15.3.1, “Propagation of Security Identity in EJBTM Calls” on page 15-176 are available only to threads executing the initial request or when the request is dispatched to the container via the AsyncContext.dispatch method. Java Enterprise Edition features may be available to other threads operating directly on the response object via the AsyncContext.start(Runnable) method.“
>>> >>
>>> >> check „available only to threads executing the initial request“
>>> >>
>>> >> Also if you look at the servlet AsyncContext then all the wording is written as MAY and not as MUST.
>>> >>
>>> >> LieGrue,
>>> >> strub
>>> >>
>>> >>
>>> >>> Am 10.03.2016 um 19:52 schrieb Romain Manni-Bucau <rmannibucau at gmail.com>:
>>> >>>
>>> >>> Hi Mark,
>>> >>>
>>> >>> think 2.3.3.4 states the opposite.
>>> >>>
>>> >>>
>>> >>> Romain Manni-Bucau
>>> >>> @rmannibucau |  Blog | Github | LinkedIn | Tomitriber
>>> >>>
>>> >>> 2016-03-10 19:43 GMT+01:00 Mark Struberg <struberg at yahoo.de>:
>>> >>> Back from JavaLand conference, so sorry for not kicking in earlier.
>>> >>>
>>> >>> I not quite get the argumentation chain. It’s that all triggered by async servlet requests? And isn’t the servlet spec also saying that all the request param etc may max be assigned to a single thread AT A TIME!
>>> >>>
>>> >>> Means that it might not be on multiple threads in parallel, but the data is allowed to get moved from one thread to another (disapearing from the first one), right?
>>> >>> Would really need to dig into the wording of the async servlets spec again, maybe has this in the back of his head?
>>> >>>
>>> >>> LieGrue,
>>> >>> strub
>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>> >>>> Am 08.03.2016 um 14:43 schrieb Romain Manni-Bucau <rmannibucau at gmail.com>:
>>> >>>>
>>> >>>> Hi guys,
>>> >>>>
>>> >>>> following request scope thread and to center the discussion on the thread safety part: do we work on this?
>>> >>>>
>>> >>>> Background: @RequestScoped is often used as a ThreadLocal instance solution. A lot of SE or Batch implementations rely on it from what I saw as well as async implementations reusing existing business logic with this thread safety constraint.
>>> >>>>
>>> >>>> Proposal: providing a @ThreadScoped implementation is cheap for CDI and implemenation and would avoid the headache we can have with @RequestScoped. Will also remove the quite dark side of the spec regarding servlet request and request scope since now we would have a more natural solution for all of these situation so @RequestScoped goals wouldn't collide as much.
>>> >>>>
>>> >>>> Questions:
>>> >>>> - is it automatically started as request scoped is (JMS, @Async, ...)? Alternative could be some configuration in beans.xml (merged accross the app):
>>> >>>>
>>> >>>> <beans>
>>> >>>> <scopes>
>>> >>>>   <thread>
>>> >>>>     <active>JMS</active>
>>> >>>>     <active>ASYNCHONOUS</active>
>>> >>>>   </thread>
>>> >>>> </scopes>
>>> >>>> </beans>
>>> >>>>
>>> >>>> - start/stop API (this is typically an API the user should be able to control for its own threads)
>>> >>>> - CDI 2.*0*?
>>> >>>>
>>> >>>> wdyt?
>>> >>>>
>>> >>>> Romain Manni-Bucau
>>> >>>> @rmannibucau |  Blog | Github | LinkedIn | Tomitriber
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>>> >>>
>>> >>>
>>> >>
>>> >>
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