OTS — Handling multiple resource registrations

he specification for register_resource does not define what should happen if a
resource is registered twice in the same transaction (page 1-22 of the
Transaction Services chapter).

On page 1-44 (In "Example of a Recoverable Server"), we finally get the words
"before registering the Resource, the object must check whether it has already
been registered for the same transaction." What this has to do with the example
is a complete mystery, as the example code immediately following this doesn't do
anything remotely like this.

The text I was quoting before goes on to opine that "This is done using the
hash_transaction and is_same_transaction operations on the current Coordinator
to compare a list of saved coordinators representing currently active
transactions". An interesting idea, but not good enough. What if another object
registers this resource?

The string of words that I have quoted above also fails to mention exactly what
will happen if a resource is registered twice in the same transaction.

I propose that the specification of register resource should actually specify
what the behaviour of the operation is, without requiring examples 22 pages
later to vaguely describe the error handling as an afterthought.

Finally, I would suggest that the only object that has the global knowledge
necessary to make this determination is the transaction itself. Therefore the
test for repeated registration must be in register_resource itself. What is left
to determine is if this is an error or (better) if the registration is silently
ignored.

Duplicate of #3600, close issue