I'm extremely surprised that creating 2k threads makes mac os reboot. Sure that's a lot for one application but not a totally crazy amount.
So I bumped it up to 20,000, thinking that would probably work as well: the computer immediately crashed and rebooted. I didn't even get the "kernel panic" screen, it just died (this is on a 2018 mac mini with a 3.2 Ghz Core i7). When it turned back on, this was the first line of the error message:
Panic(CPU 0, time 1921358616513346): NMIPI for unresponsive processor: TLB flush timeout, TLB state:0x0
Weird. I really thought that this wouldn't be an issue at all. And: if it was an issue, that the OS would be able to handle it and kill the process or something, not kernel panic.
If you have any more OSes laying around to run the test on, I’d be interested to hear how well windows and Linux handle the same thing.
Because on the face of it this seems like a serious bug in the OS. I’m only used to seeing this sort of thing with bad drivers
2000 threads does nothing - everything's still responsive, and the process is shown as using 0% of the CPU.
16,000 threads uses ~30% of a core, with a ~136MB RSS. The system still handles it fine, though, and everything stays responsive.
At 20,000 the program panics when spawning threads, with the message "failed to set up alternative stack guard page" due to EWOULDBLOCK. I'm not sure exactly what limit it's hitting, though.
That’s the sort of thing I expect - the OS starves the program, not the other way around.
Not that 2k threads is really that high; but it's probably high enough to break something.
But if you run below the explicit limit, but above the implicit limit of whatever continues to work, it's not surprising to me that the OS just freaked out.
You could report it to Apple, but their reporting process is pretty opaque, especially if you're not a registered developer (because why would you be, if you're just using mac os because you like the desktop environment, or whatever). Who knows if they'll fix it, but it's not worth making a big deal over, because you weren't really wanting to run 2k threads on mac os anyway, because it would suck, even if it did work.
From the other message on the thread; it looks like too many threads is causing a watchdog timer to fail, leading to the panic.
Like, can I just start 20k threads in WebAssembly and reboot anyone who visits my site?
Obviously I'd expect the browser to guard against that... but I expected the OS to as well, so my expectations may be way off!
But probably not on Windows 9x, maybe not even on NT4 (although, NT4 was pretty solid), and I wouldn't expect good results on Linux or a BSD from 2000 either.
But macos has lowered my expectations. It's a mash of FreeBSD from the turn of the century, with Mach from earlier, and whatever stuff they've fiddled with since then, plus a nice UI layer. They don't regularly pull in updates from FreeBSD, and the killed their server line (which was mediocre at best anyway), so when it panics if you do something weird, it's not unexpected.