During the implementation of the engine, we found a problem
with using errsvc.
Background:
------------------------
- Only 1 instance of errsvc exists in the name space
of the application and all modules and libraries it uses.
- Errors (instances of ErrorInfo) are stored in one single list called
_ERRORS
in errsvc.py.
- Engine is going to use errsvc to store exception(s) raised
by checkpoints' execute() method. Engine will use checkpoint name
as the mod_id for the ErrorInfo objects so application can
easily identify which checkpoint failed.
Problem:
-----------------
- If the application choose to execute the same checkpoint multiple
times, and all the execution failed, multiple ErrorInfo with the
same mod_id will be added to the list of errors. Application
can not easily figure out which ErrorInfo belongs to which
invocation of that same checkpoint.
Possible Solutions:
-------------------------------
1) engine.execute_checkpoint() will always call
errsvc.clear_error_list() before it executes any checkpoint.
This way, when execution completes, the errsvc
will only contain errors raised during that execution.
The problem with this approach is that
error messages in errsvc that's not stored by the engine prior
to the execution, and not dealt with by the app, will get lost.
2) engine.execute_checkpoint() will search the errsvc for
any error associated with the checkpoints it plans to execute,
and remove all those ErrorInfo. The problem with this approach
is that the application will loose information about the
previous exceptions, if they haven't dealt with them already.
3) Move the responsibility to the application to manage the
error list. They should either clear it or remove the ErrorInfo objects
they are not interested in. The engine.execute_checkpoint()
will simplely append to the error list, and return the list of
checkpoints names that failed.
Any other ideas?
Thanks,
--Karen
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