While working on the class-loader switching code, we have revisited an
issue with the way JCas objects work with respect to views.
Currently, for each view, there is a separate set of xxx_Type objects, a
separate set of "cached" cover objects (which are identical to other
view's objects, except that their _Type ref points to the instance for
this view).
This is there only (as far as we can see) to support
aJCasObject.addToIndexes() and removeFromIndexes() which uses this
information to pick the right "view" to use (remember that indexes are
held per view).
Besides inefficiency (replication of objects per view), there is another
side-effect. JCas Objects can, themselves, be extended by users to hold
additional information, other than what's in the CAS. The current
design would create new versions of these objects per view, so that
iterators over different views would get different instances. So
information set into one JCas object in one view would not be "visible"
to instances obtained by iterating using a different view's index. This
could be a documented "feature", or it could be a "bug".
Because current users seem to often use the aJCasObject.addToIndexes()
method, I want to retain that method, while getting the efficiencies and
fixing the "bug" (if we consider it a bug) above. To do this, we could
make this work as before *for sofa-unaware annotators, only* as
follows: Change the impl of addToIndexes and removeFromIndexes to
reference the "current-view".
Where to get the current-view? First, it needs to be accessable in
several contexts, including the main one (JCas use in an annotator),
but also any other places JCas can be used - which includes
(top-level) application code, call-back routines (which include a
handle to a CAS), and code in flow controllers (which have access to
a CAS). One way I can see to do this is to stick an object
identifying the current-view onto thread-local. Any other
suggestions appreciated....
For *sofa-aware* annotators, we could use this same approach, but might
want to give warnings as well.
-Marshall
