druntime thread (from foreach parallel?) cleanup bug

[Steven Schveighoffer]

On Tuesday, 1 November 2022 at 18:18:45 UTC, Steven Schveighoffer 
wrote:
>
> Oh yeah, isDaemon detaches the thread from the GC. Don't do 
> that unless you know what you are doing.

As discussed on discord, this isn't actually true. All it does is 
prevent the thread from being joined before exiting the runtime.

What is *likely* happening is, the runtime shuts down. That 
thread is still running, but the D runtime is gone. So it 
eventually starts trying to do something (like let's say, access 
thread local storage), and it's gone. Hence the segfault.

-Steve