Re: [RFC PATCH 0/1] Add FUTEX_SPIN operation

* Christian Brauner:

quoted

From a glibc perspective, we typically cannot use long-term file
descriptors (that are kept open across function calls) because some
applications do not expect them, or even close them behind our back.

Yeah, good point. Note, I suggested it as an extension not as a
replacement for the TID. I still think it would be a useful extension in
general.

Applications will need a way to determine when it is safe to close the
pidfd, though.  If we automate this in glibc (in the same way we handle
thread stack deallocation for example), I think we are essentially back
to square one, except that pidfd collisions are much more likely than
TID collisions, especially on systems that have adjusted kernel.pid_max.
(File descriptor allocation is designed to maximize collisions, after
all.)

Thanks,
Florian