Called when a repeat callback fails by throwing an exception. There will
be one call to this method for each exception thrown during a repeat
operation (e.g. a chunk).
There is no need to re-throw the exception here - that will be done by
the enclosing framework.
Called once at the start of a complete batch, before any items are
processed. Implementers can use this method to acquire any resources that
might be needed during processing. Implementers can halt the current
operation by setting the complete flag on the context. To halt all
enclosing batches (the whole job), the would need to use the parent