TransientIO: Finishing task is mandatory. (#976)
Keep trying or throw:
Prone to StackOverFlowException is some very rare
scenario (if there is a long transaction going on
with the file).

Secondly, fixes the compiler issue where
map filename is the property of base executor
instead of a local variable.
Merge pull request #981 from am11/master

TransientIO: Finishing task is mandatory (#976)