SMPPEX.ESME.Sync.pdus

You're seeing just the function pdus, go back to SMPPEX.ESME.Sync module for more information.
Link to this function

pdus(esme, timeout \\ 5000)

View Source

Specs

pdus(esme :: pid(), timeout()) :: [awaited()]

A nonblocking version of wait_for_pdus/2.

The difference is that it always immediately returns a list of items(maybe empty) and never returns :timeout or :stop.