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From "Leonardo Uribe (JIRA)" <...@myfaces.apache.org>
Subject [jira] [Created] (MYFACES-3664) JSF View Pooling (going beyond JSF Stateless Mode)
Date Mon, 17 Dec 2012 16:14:00 GMT
Leonardo Uribe created MYFACES-3664:
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             Summary: JSF View Pooling (going beyond JSF Stateless Mode)
                 Key: MYFACES-3664
                 URL: https://issues.apache.org/jira/browse/MYFACES-3664
             Project: MyFaces Core
          Issue Type: Bug
          Components: JSR-314
            Reporter: Leonardo Uribe
            Assignee: Leonardo Uribe


In the last months, I have been doing some investigations around "stateless JSF" ideas. The
intention is try to find ways to improve MyFaces Core performance as much as possible, without
lose all those nice features we all are used to.

In summary, the justification around stateless JSF is that, if it is possible to cut the build
view time from a request, there will be an improvement from both speed and memory perspective.
This is true, but only to some point, because the response time for a request is given by
the build view, validation/invoke application and render response time. 

To get to the same goal, without sacrifice JSF stateful behavior, other improvements has been
already done (cache EL expressions, cache ids, make tree structure lighter, ...). The idea
is cache that "stateless information" into a place where it can be reused effectively, which
in this case is inside Facelet abstract syntax tree (AST). This has worked well so far. The
side effects of enable these optimizations has been analysed, and there is a good understanding
about this.

In few words, the basic idea about stateless JSF as proposed originally by Rudi Simic in his
blog is this:

Mark the view as stateless using some attribute.
Use a pool of views, because views are not thread safe.
Before store the view in the pool, use a visitTree call to reset the fields.

Unfortunately, it was quickly found that the implementation proposed requires a better view
pool and try to reset the fields is not fail-safe, because the component tree also stores
more than just the input field values. Additionally, it doesn't provide a way to use it for
dynamic views.

Provide a thread safe implementation of UIComponent that can be reused across threads is not
a  good solution, because anyway there is some information that is inside UIComponent and
should be stored per thread, and precisely UIComponent is a place specifically designed to
store that information.

Based on the previous background, the big question is if a solution based on object pooling
pattern can be done effectively for a web framework like JSF. A good description of the technique
and its trade-off can be found at:

http://en.wikipedia.org/wiki/Object_pool_pattern 

In few words, the proposal is go "Beyond JSF Stateless Mode", and instead blame the state,
make it your friend. Let's just take advantage of the stateful nature of JSF to allow reuse
views fully or partially. 

How? 

- PSS algorithm can be used to check if a view has been modified or not, checking its state.
So, it can be used to check which components has state, and if it is possible to provide a
way to reset the state of a component to the initial state set by the first markInitialState(),
restore the state is possible.

-If the view cannot be reset fully, it is possible to use facelets refreshing algorithm and
reuse a view partially.

- Add some additional code to recover a view instance when it is discarded, and store it into
the view pool. This requires some changes over NavigationHandlerImpl, because it is not possible
to reuse a view and store it in the pool that is still on usage, so it is necessary to do
a "deferred navigation", changing the default ActionListenerImpl and ensure handleNavigation()
is called before end invoke application phase but outside the visitTree() call.

- In MyFaces there exists the concept of FaceletState. It is possible to use this concept
and cache even dynamic views, because each different FaceletState can identify an specific
view structure. 


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