question about implementing XA-ish functions

I'm trying to implement a function that has some XA like properties.

Is it possible to write a postgres extension function that fires when called within a pg transaction... however, the
actionsit takes need to be later committed or rolled back based on the containing transactions commital or not.  Not
havinglooked to deeply into this, I'm wondering if this is possible.  Naively, my first hookpoint would be something
like:

allocate something in the transactions memory context and register a cleanup.... do my work.

when the transaction memory context is cleaned up, my cleanup handler fires, I detect whether the txn was committed or
rolledbackand rightly mark my work as committed or rolled back. 

Thoughts?

--
Theo Schlossnagle
http://omniti.com/is/theo-schlossnagle
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