Concurrent transactions in different sessions by single user

I believe the transaction is stored as a session variable for the given user's context on the server. If you have two parallel sessions with the same user using transactions, the first call to submit_transaction() will proceed and delete the transaction id. If you call it a second time from the other session, it will likely fail as the transaction id has been removed by the first call. The only real solutions is to use the locking mechanism in the System.SystemInfo interface. The first session can acquire a lock and then perform it's transaction. The second session will attempt to acquire a lock and wait until one is available and then lock it's attempt at a transaction. I wrote about those interfaces in the article on Concurrent iControl Programming - https://devcentral.f5.com/articles/concurrent-icontrol-programming-explained.

The other option is to use multiple user accounts.