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.
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