[HACKERS] How to determine that a TransactionId is really aborted?

When sitting inside an extension, and given an arbitrary TransactionId, how can you determine that it aborted/crashed
*and*that no other active transaction thinks it is still running? 

I've tried to answer this question myself (against the 9.3 sources), and it seems like it's just:

{  TransactionId oldestXmin = GetOldestXmin (false, false);  TransactionId xid = 42;   if (TransactionIdPrecedes(xid,
oldestXmin)&&      !TransactionIdDidCommit(xid) &&      !TransactionIdIsInProgress(xid)) /* not even sure this is
necessary?*/  {     /* xid is aborted/crashed and no active transaction cares */  } 
}

Can anyone confirm or deny that this is correct?  I feel like it is correct, but I'm no expert.

Thanks so much for your time!

eric

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