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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