string-hash | Get the hash of a string | Hashing library

I have two functions, scheduleScan() and scan().

scan() calls scheduleScan() when there's nothing else to do except scheduling a new scan, so scheduleScan() can schedule a scan(). But there's a problem, some jobs run twice.

I want to make sure that only one job is being processed at any given time. How can I achieve that? I believe it has something to do with done(), (it was in scan(), removed now) but I couldn't come up with a solution.

Bull version: 3.12.1

Important late edit: scan() calls another functions and they may or may not call other functions, but they're all sync functions, so they only call a function when their own jobs are completed, there is only one way forward. At the end of the "tree", I call it, the last function calls scheduleScan(), but there can't be two simultaneous jobs running. Every single job starts at scan(), by the way, and they end with scheduleScan(stock, period, milliseconds, 'called by file.js')