I don't think this is an awkward fit. There's no reason it should be Mutex<CustomerBankAccount> it can be Mutex<MyTransferToken> or indeed Mutex<()> if you're r

I don't think this is an awkward fit. There's no reason it should be Mutex<CustomerBankAccount> it can be Mutex<MyTransferToken> or indeed Mutex<()> if you're really sure you don't actually want to lock any data. One piece of advice I'd suggest is, write APIs which take that MyTransferToken to signify that you must take the lock before calling them, it can be a unit type (a Zero Size type, a struct with no members) at the start if you like, but I suspect you'll find that across several functions which take that MyTransferToken you realise actually the data I was going to put in a separate parameter is really always accompanying that token, and so it might as well go inside the the MyTransferToken and before you know it your unit type that was just to ensure correct locking is in fact an object with important data protected by the lock.