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From Daryl Olander <dolan...@gmail.com>
Subject Re: Page Flow Runtime Control Container Design
Date Fri, 20 Jan 2006 00:53:24 GMT
In thinking about Eddie and Rich's objections, I've decided to provide the
Control Container as an abstraction.  It should actually be an pluggable
interceptor that sits inside the synchronized blocks.  I will abstract the
Container into a bean that could be configured (eventually) through Spring
and an interface defining the containers contract.  I will place the object
on Thread Local so that it can be accessed within a page flow for
programatic use (Eddie's concern).  It will also be possible in the future
for a "portal" to provide an implementation that can optimize for their use
cases (space/time tradeoff) and/or implement a different symantic (Rich's
concern).

BTW, I haven't verified this, but I believe in thinking about it, we never
cleared controls out of the CCC once they were added so we were leaking all
controls in page flows instances beyond the life of the instance.  In
addition, I would guess this also made the unique id's unstable within
instance of the same page flow.  I'm going to verify this, but I suspect
this is a side affect of the current implementation.

On 1/19/06, Daryl Olander <dolander@gmail.com> wrote:
>
> Is there an easy way to tell how big an object is?  (The space is mostly
> in the Bean base classes that are part of Java.Beans)
>
> On 1/19/06, Rich Feit < richfeit@gmail.com> wrote:
> >
> > Ah right, it's not just for requests that go to shared flows.  Well, I
> > think this will all work.  My biggest concern is the space requirements
> > of the CCC, multiplied if this happens in a portal.  It's just something
> > we should look at.  Do we know how big the CCC will be?
> >
> > Daryl Olander wrote:
> > > No, because you have to get access to the "shared flow" lock before
> > you can
> > > enter user code in onCreate, action invocation and JSP
> > rendering.  Thus the
> > > statement that we have serialization points for multiple threads
> > within a
> > > session.
> > >
> > > On 1/19/06, Rich Feit <richfeit@gmail.com> wrote:
> > >
> > >> OK... one other thing: is there still a hole here for direct access
> > to
> > >> the shared flow through a reference in the page flow?
> > >>
> > >> Daryl Olander wrote:
> > >>
> > >>> On 1/19/06, Rich Feit <richfeit@gmail.com> wrote:
> > >>>
> > >>>
> > >>>> I can't tell the difference between this and Daryl's option #2,
so
> > I
> > >>>> guess I agree with both of you.  :)
> > >>>>
> > >>>> Daryl, I have just a few questions:
> > >>>>     1) The Lock object is session-scoped, right?
> > >>>>
> > >>>>
> > >>> Right...
> > >>>
> > >>>     2) Are you saying that you'd call the CCC's begin/end-context
> > >>>
> > >>>
> > >>>> methods around *every* point that runs user code?  So within a
> > given
> > >>>> request, you'd potentially do this around onCreate(), the action
> > >>>> invocation, and JSP rendering?
> > >>>>
> > >>>>
> > >>> Exactly...These are the three points where we do this.  For the
> > average
> > >>> request, it would be just the action invocation and JSP rendering.
> > >>>
> > >>> Eddie O'Neil wrote:
> > >>>
> > >>>
> > >>>>>   Hm...this is a tricky issue.  I'd actually go a different
route
> > and
> > >>>>> do two things:
> > >>>>>
> > >>>>> 1) only create the CCC for each page flow in the presence of
> > @Control
> > >>>>> annotations
> > >>>>> 2) explain how to write code to create a CCC and drive it through
> > its
> > >>>>>
> > >>>>>
> > >>>> lifecycle
> > >>>>
> > >>>>
> > >>>>> This is how the JUnit test container works for Controls --
you can
> > use
> > >>>>> the ControlsTestCase base class or write code that calls utilities
> >
> > >>>>> that provide the CCC and drive it through its lifecycle.
> > >>>>>
> > >>>>>   Seems like this provides the best of both worlds -- uses
> > metadata to
> > >>>>> decide when controls are used but gives application developers
a
> > way
> > >>>>> to use controls programmatically without having a Controls-related
> > API
> > >>>>> exposed on the Page Flow base class.
> > >>>>>
> > >>>>>   Yes, there's a compatibility issue *if* you used JPF from
1.0and
> > >>>>> declared controls programmatically, but that's probably not
very
> > >>>>> common.
> > >>>>>
> > >>>>> Eddie
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>> On 1/19/06, Daryl Olander <dolander@gmail.com> wrote:
> > >>>>>
> > >>>>>
> > >>>>>
> > >>>>>> So it turns out, there is indeed a test that creates a
control
> > >>>>>> programmatically in a page flow.  This seems to leave us
with two
> > >>>>>> alternatives
> > >>>>>> 1) we always create the CCC for every page flow
> > >>>>>> 2) we add an ensureControlContainerContextExists() API
(to the
> > base
> > >>>>>> PageFlowController) to make sure that it is created and
> > initialized.
> > >>>>>>
> > >>>>>> I lean toward 2 because I think this use case is rare.
 It is a
> > >>>>>>
> > >>>>>>
> > >>>> backward
> > >>>>
> > >>>>
> > >>>>>> compatibility issue with our 1.0 release.
> > >>>>>>
> > >>>>>> Thoughts?
> > >>>>>>
> > >>>>>> On 1/18/06, Daryl Olander < dolander@gmail.com> wrote:
> > >>>>>>
> > >>>>>>
> > >>>>>>
> > >>>>>>> This mail summarizes the proposed design for the Control
> > container
> > >>>>>>> implementation inside of the page flow runtime.  It
is a summary
> > of
> > >>>>>>>
> > >>>>>>>
> > >>>> the
> > >>>>
> > >>>>
> > >>>>>>> previous threads on this subject.  I'm currently in
the process
> > of
> > >>>>>>> implementing this solution and believe it solves the
sets of
> > issues
> > >>>>>>>
> > >>>>>>>
> > >>>> brought
> > >>>>
> > >>>>
> > >>>>>>> up in those emails.  I would really like review of
this solution
> > and
> > >>>>>>> comments/questions so we can be sure this works.
> > >>>>>>>
> > >>>>>>> There are two basic requirements of the Control container
> > >>>>>>> 1) All controls have only a single thread in them at
a time
> > (Single
> > >>>>>>> Threaded)
> > >>>>>>> 2) The resources a control may acquire are only used
for a
> > single
> > >>>>>>> request.  It is ok if the resources are acquired more
than once
> > for
> > >>>>>>>
> > >> a
> > >>
> > >>>> single
> > >>>>
> > >>>>
> > >>>>>>> request.
> > >>>>>>>
> > >>>>>>> In today's implementation, both of these requirements
are
> > violated
> > >>>>>>>
> > >> by
> > >>
> > >>>>>>> standard page flows and shared flows (and global app).
 These
> > issues
> > >>>>>>>
> > >>>>>>>
> > >>>> are
> > >>>>
> > >>>>
> > >>>>>>> summarized in the previous threads on this subject.
> > >>>>>>>
> > >>>>>>> The proposed solution is this,
> > >>>>>>>
> > >>>>>>> For a standard page flow (normal page flow, singleton
page flow
> > and
> > >>>>>>>
> > >>>>>>>
> > >>>> nested
> > >>>>
> > >>>>
> > >>>>>>> page flow), they have a ControlContainerContext (CCC)
for the
> > >>>>>>>
> > >> controls
> > >>
> > >>>> that
> > >>>>
> > >>>>
> > >>>>>>> they contain.  The CCC is only allocated if the page
flow
> > contains a
> > >>>>>>> control.  We will have to probably add an API someplace
to
> > create
> > >>>>>>>
> > >> this
> > >>
> > >>>> if a
> > >>>>
> > >>>>
> > >>>>>>> user wants to create a control programmatically.
> > >>>>>>>
> > >>>>>>> For all Shared flows and global app, they will share
a single
> > CCC.
> > >>>>>>>
> > >>>>>>> During a request, there are three possible synchronization
> > points
> > >>>>>>>
> > >>>>>>>
> > >>>> where
> > >>>>
> > >>>>
> > >>>>>>> user code can run and call methods on controls
> > >>>>>>> 1) during onCreate when a page flow is created
> > >>>>>>> 2) during the beforeAction/Action/afterAction cycle
> > >>>>>>> 3) during JSP rendering
> > >>>>>>>
> > >>>>>>> During any of these, code may access a shared flow
and interact
> > with
> > >>>>>>> controls. For most page flow requests only 2 and 3
are run.
> > >>>>>>>
> > >>>>>>> For a the standard page flows, these synchronization
points
> > create a
> > >>>>>>> single threaded model.  For the standard page flow
CCC, we will
> > run
> > >>>>>>>
> > >>>>>>>
> > >>>> the
> > >>>>
> > >>>>
> > >>>>>>> beginContext, endContext events which activate the
resource
> > >>>>>>>
> > >>>>>>>
> > >>>> lifecycle.  This
> > >>>>
> > >>>>
> > >>>>>>> is sufficient to guarantee 1 and 2.
> > >>>>>>>
> > >>>>>>> For shared flows, we still have issues if multiple
threads are
> > >>>>>>>
> > >> running
> > >>
> > >>>>>>> through the session.  To solve this we will do this,
> > >>>>>>> 1)  We will create a single Lock object that must be
obtained in
> > the
> > >>>>>>> synchronization points before we can proceed.
> > >>>>>>> 2) Once the lock is obtained, we will run beginContext
on the
> > shared
> > >>>>>>>
> > >>>>>>>
> > >>>> flows
> > >>>>
> > >>>>
> > >>>>>>> CCC.
> > >>>>>>> 3) We will run the normal user code
> > >>>>>>> 4) We will then run the endContext on the shared flows
CCC
> > >>>>>>> 5) We will release the lock
> > >>>>>>>
> > >>>>>>> Rich, please verify this will work...
> > >>>>>>>
> > >>>>>>> The result of this, is that we will serialize threads
within a
> > >>>>>>>
> > >> session
> > >>
> > >>>>>>> through these synchronization points.  The result is
that shared
> > >>>>>>>
> > >> flows
> > >>
> > >>>> will
> > >>>>
> > >>>>
> > >>>>>>> become single threaded (requirement 1 above) and because
we run
> > the
> > >>>>>>> beginContext/endContext that satisfies 2 above.
> > >>>>>>>
> > >>>>>>> There is a bit more overhead to this solution because
there will
> > >>>>>>>
> > >>>>>>>
> > >>>> typically
> > >>>>
> > >>>>
> > >>>>>>> be two CCC objects active at one time.  Deep nesting
and
> > singletons
> > >>>>>>>
> > >>>>>>>
> > >>>> will add
> > >>>>
> > >>>>
> > >>>>>>> more.  The CCC is only created for page flows that
have
> > >>>>>>>
> > >> controls.  The
> > >>
> > >>>>>>> benefits is that the CCC objects match the lifetime
of the
> > controls
> > >>>>>>>
> > >>>>>>>
> > >>>> that
> > >>>>
> > >>>>
> > >>>>>>> they contain.
> > >>>>>>>
> > >>>>>>> Please review this and send comments.
> > >>>>>>>
> > >>>>>>> Thanks
> > >>>>>>>
> > >>>>>>> Daryl
> > >>>>>>>
> > >>>>>>>
> > >>>>>>>
> > >>>>>>>
> > >>>>>>>
> > >>>>>>>
> > >>>>>
> > >>>
> > >
> > >
> >
>
>

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