I just tested my implementation from a few months ago (I was running macOS26 at the time) and it looks like it was simply a bug. I of course need to run way more tests but it looks like macOS27 is behaving correctly and I can run both a pcap and a NWEthernetChannel controller at the same time. Let's see after more tests!

I think it's exclusive by design (at least it's what I understood from Matt Mora), so I didn't really insist when I tested it 6 months ago. Since I still have the code implemented, I'll give it a try with macOS27 then. It would be way better than using pcap library (or the too limited AVBFramework).

Hi Arno, I would advise against using NWEthernetChannel as it will "eat" all the AVTP-C frames (I tried implementing it), which means no other controller on the same computer will be able to work properly (including macOS embedded controller).

Thank you very much, that confirms what I suspected. On windows, one can use the _SH_DENYRD flag when calling open and this locks the file so any other process using any available file opening method will be prevented access to it. I was merely looking for a similar functionality on macOS. I need to prevent any other process (using any open method that's not under my control) from accessing a file until I'm done with what I want to do with it. I guess my best option would be chmod then.