All sessions/connections to IS are handled by unique threads. File polling uses a thread for each file.
Generally, threading isn’t something you need to worry about.
That said, there are some configurations that can lead to trouble. For example, I once had a race condition and/or deadlock when processing fairly large EDI files. I had set the processing rule that handled each transaction set to be async. On occassion the process would fail. It’s been a while so I don’t recall the exact details but the way I had the processing set up the transaction sets rule needed to be sync.
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