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From Daryl Olander <>
Subject Re: Multiple Threads inside a Page Flow instance?
Date Mon, 16 Jan 2006 20:28:35 GMT
Let me see if I understand this,

Looks like there are a few thing that synchronize on the current page flow:
1) The onCreate is synchronized
2) The beginAction, Action, afterAction
3) The JSP rendering

(There may be others but these are the important ones)

So outside of these synchronized sections, we create things like the
ServletBeanContext that has reference to the request and response.  Further,
the resource events can occur in any of the three spots above, but we can
swap threads through this:

1) Thread 1 executes 1
2) Thread 2 executes 1 and 2
3) Thread 1 executes 2 and 3
4) Thread 2 executes 3

As far as I can tell, the result is that any resources acquired in the
onAcquire() method will then be used by both threads until one of them hits
the uninitializeControls method and frees the contexts.

Does this agree with your understanding?

On 1/16/06, Rich Feit <> wrote:
> Hey Daryl,
> We should never allow two threads into user code at the same time,
> although you could potentially get into a situation where you're
> interleaving calls to actions and property getters.  We synchronize the
> page rendering on the controller instance; see PageFlowPageFilter:284.
> Let me know if you see any issues with this, though.
> Rich
> Daryl Olander wrote:
> >Rich, I'd love some confirmation of the following if you can,
> >
> >I'm in the process of looking at some issue with the BeanContext and
> Control
> >use in NetUI and I have a question about threading.  I believe that we
> make
> >the statement that PageFlow are single threaded.  The issue is that I
> >believe we in fact allow more than one thread into a page flow.  Here is
> an
> >example of where I think it can happen.
> >
> >If you have a set of frames on a page, all making requests to the same
> page
> >flow, they will serialize access to the actions in the page flow.  When
> the
> >first thread finishes the action and forwards to a JSP, the second thread
> is
> >allowed access to the page flow.  This is the reason we say things are
> >single threaded.  The problem is that if the JSP takes a while to run and
> it
> >databinds to properties on the page flow you can have multiple threads
> >running through the page flow.  The first thread is calling property
> getters
> >while rendering the JSP and the second thread is running an action.  This
> is
> >actually not uncommon if the property being accessed calls a control that
> >accesses an external resource like a database.
> >
> >Rich, can you comment on this?  Is there something else that prevents
> >multiple threads from entering a page flow?
> >
> >
> >

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