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From "Leonardo Uribe (JIRA)" <>
Subject [jira] [Commented] (MYFACES-3664) JSF View Pooling (going beyond JSF Stateless Mode)
Date Fri, 06 Dec 2013 23:03:35 GMT


Leonardo Uribe commented on MYFACES-3664:

I have updated the patch to 2.2.x branch and I also did a full and exhaustive review of the
solution. I took some time, but finally the code is ready to be committed.

To enable the view pool, org.apache.myfaces.CACHE_EL_EXPRESSIONS must be set to "alwaysRecompile".
It can be initialized using web config parameters or as a faces-config-extension. 

At the end, the view pool gives an small improvement in cpu when the page is rendered, but
it reduce the amount of created objects. In ajax requests the difference is noticeable, specially
in large views where the time spent building the view is more than the time spent rendering
the ajax response.

If no objections, I'll commit the solution proposed soon on 2.2.x branch.

> JSF View Pooling (going beyond JSF Stateless Mode)
> --------------------------------------------------
>                 Key: MYFACES-3664
>                 URL:
>             Project: MyFaces Core
>          Issue Type: New Feature
>          Components: JSR-344
>            Reporter: Leonardo Uribe
>            Assignee: Leonardo Uribe
>         Attachments: myfacesStatelessMode-12-view-pool.patch, myfacesStatelessMode-6-view-pool.patch,
> 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:
> 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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