[cdi-dev] Enhancing SPI to support async operation for contexts

Thu Feb 19 12:44:18 EST 2015

Okay, so request scope is not associated with web requests, but with
"invocation chains". I thought so because session scope is associated with
web requests and Weld is backing it's request scope implementation with
request attributes.

So the SPI has a need for dispatching async work in new threads, at it's
best with most common scopes (application, session and request) being
active?

Application does not seem to be a problem. Request is always a new context
per thread. The question is, whether session scope is propagated to newly
spawned threads, when using this SPI? Afaik it's currently only active
during web requests. From an implementation point of view it could be
tricky to disassociate current session scope impls from servlet session
lifecycle. On the other side: from a user point of view it would be nice,
if I dispatch work via some SPI, the processing of work is done in the same
"user context".

2015-02-19 18:18 GMT+01:00 Romain Manni-Bucau <rmannibucau at gmail.com>:

> today request scope = thread scope and we can't help on it. I recall
> having said web scopes should stay aligned on web behavior but answer
> was quite clear: this is not what is in the spec (at least in
> intention term) which is fine but today request scope is also used in
> batches for thread scope behaviors so too late to change. Servlet spec
> can have its own web scope now which would allow to fix this and go
> ahead.
>
>
> Romain Manni-Bucau
> @rmannibucau
> http://www.tomitribe.com
> http://rmannibucau.wordpress.com
> https://github.com/rmannibucau
>
>
> 2015-02-19 18:13 GMT+01:00 Sven Linstaedt <sven.linstaedt at gmail.com>:
> > The question remains: Does CDI has to make sure, request scope implies
> > single threaded access, because most existing applications are not aware
> of
> > possible threading issues for request scoped beans?
> >
> > I do not think so. Afaik the same problem has affected session scoped
> beans
> > before servlet 3.0, but application developers are hopefully more aware
> of
> > it.
> >
> > 2015-02-19 17:52 GMT+01:00 Romain Manni-Bucau <rmannibucau at gmail.com>:
> >>
> >> @Mark: for the container usage only but nothing prevents you to use it
> >> elsewhere at your own risk
> >>
> >>
> >> Romain Manni-Bucau
> >> @rmannibucau
> >> http://www.tomitribe.com
> >> http://rmannibucau.wordpress.com
> >> https://github.com/rmannibucau
> >>
> >>
> >> 2015-02-19 17:40 GMT+01:00 Mark Struberg <struberg at yahoo.de>:
> >> > Even in Servlets-3.0 a ‚Request‘ is only attached to exactly one
> single
> >> > thread AT THE SAME TIME afaik.
> >> >
> >> > So they can switch a Request from one thread to another one, but there
> >> > is always just a single one accessing it at the same time. At least
> that is
> >> > what I did understand.
> >> >
> >> > LieGrue,
> >> > strub
> >> >
> >> >
> >> >> Am 19.02.2015 um 17:33 schrieb Sven Linstaedt
> >> >> <sven.linstaedt at gmail.com>:
> >> >>
> >> >> Hi,
> >> >>
> >> >> and sorry for spontaneously dropping in. Just to clarify some
> personal
> >> >> questions/assumptions:
> >> >>
> >> >> 1. Regarding threading the current spec only states that "A context
> may
> >> >> be associated with one or more threads".
> >> >>
> >> >> 2. It is nowhere stated that @RequestScoped beans are inherently
> thread
> >> >> safe. Thread safety was implied from the servlet spec, because the
> scope
> >> >> backing container (ServletRequest#attributes) was executed single
> threaded.
> >> >>
> >> >> 3. With Servlet 3.0 the same ServletRequest#attributes is available
> for
> >> >> access from multiple threads via  ServletRequest#startAsync(), so
> containing
> >> >> objects may have a need for synchronization.
> >> >>
> >> >> 4. Why does CDI 2.0 has to care about thread safety of @RequestScoped
> >> >> beans? If the application is for some reason setting the request in
> async
> >> >> mode, the application must also ensure, it's containing and accessed
> beans
> >> >> are thread safe.
> >> >>
> >> >>
> >> >> Best regards
> >> >> Sven
> >> >>
> >> >> 2015-02-19 11:22 GMT+01:00 Romain Manni-Bucau <rmannibucau at gmail.com
> >:
> >> >> Hi
> >> >>
> >> >> I'm +1 for it but it needs important changes (= surely new contexts).
> >> >> Typically we can't change today @RequestScoped (which has no link
> with
> >> >> a request but only with a thread!).
> >> >>
> >> >> So we could have @RequestScoped (~ @ThreadLocalScoped) and
> >> >> @InheritedRequestScoped which would be a real request scope (but not
> >> >> an InheritedThreadLocal please)
> >> >>
> >> >> For the request it makes a lot of sense since you need to stay thread
> >> >> safe even accross threads (servlet spec) and avoids to be forced to
> >> >> use message passing which - even if a good pattern - adds boilerplate
> >> >> code for simple async needs.
> >> >>
> >> >> For JAXRS I dont know since it is really suspend/resume semantic so
> >> >> request scope maybe doesnt makes much sense here (there is a break in
> >> >> the flow).
> >> >>
> >> >>
> >> >>
> >> >> Romain Manni-Bucau
> >> >> @rmannibucau
> >> >> http://www.tomitribe.com
> >> >> http://rmannibucau.wordpress.com
> >> >> https://github.com/rmannibucau
> >> >>
> >> >>
> >> >> 2015-02-19 10:32 GMT+01:00 Antoine Sabot-Durand
> >> >> <antoine at sabot-durand.net>:
> >> >> > Hi All,
> >> >> >
> >> >> > Beyond the asynchronous event case, shouldn’t we provide a way for
> >> >> > user to launch async treatments in CDI with the possibility to
> keep the
> >> >> > existing contexts at the moment of async operation launch?
> >> >> > Today servlet or JAX-RS spec support async call without the loss of
> >> >> > request for instance. Shouldn’t we think to something like that?
> >> >> >
> >> >> > Thanks for your input on that point.
> >> >> >
> >> >> > Antoine
> >> >> >
> >> >> >
> >> >> >
> >> >> >
> >> >> >
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