[Geotools-devel] AbstractDataStore#getFeatureReader(Query query, Transaction transaction)

[Vitali D. <vi...@ar...>]

Hello.

Recently I debugged deadlock of UDIG waiting write access to 
ShapefileDataStore during commit of changes e.g. Obviously the deadlock 
is caused because of read locks in ShpFiles are not released properly. 
But the reason of that is my inconsistent state of UDIG trunk with 
GeoTools dependencies being used and ClassCastException in 
DiffFeatureReader#getIndexedFeatures().  So an exception is thrown 
during creation of FeatureReader hierarchy (in particular from 
AbstractDataStore#getFeatureReader() method) and application code has no 
way to close reader in case of caught failure because it does not have 
reader instance.  So in my case I faced with this situation because some 
GT dependencies were not updated after recent commit with changes. But 
in general the situation is worth to take into account more carefully.

The clear strategy is:
in case of long hierarchy of calls to create FeatureReader/FeatureWriter 
an exception may be thrown and caught only in application code. If some 
locking operations were done on deep level of hierarchy then unlocking 
through FeatureReader#close() is not available.  It's necessary at some 
point catch exception where there is a an access to already created 
FeatureReader (like AbstractDataStore#getFeatureReader(Query 
query,Transaction transaction)), close it properly in catch{} clause and 
safely re-throw an  exception to application level.


P.S. I follow GeoTools/UDIG trunk development not on a regular basis and 
I can be unaware about already existing "medicine", especially because 
of not always an up-to-date snapshot of trunk codebase . But as I 
remember this is a very old problem..

Vitali.