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

Florian Weimer
2024-05-02T09:52:12Z

* Christian Brauner:

> Unless I'm missing something the question here is PID (as in TGID aka
> thread-group leader id gotten via getpid()) vs TID (thread specific id
> gotten via gettid()). You want the thread-specific id as you want to
> interact with the futex state of a specific thread not the thread-group
> leader.
>
> Aside from that TIDs are subject to the same race conditions that PIDs
> are. They are allocated from the same pool (see alloc_pid()).

For most mutex types (but not robust mutexes), it is undefined in
userspace if a thread exits while it has locked a mutex. Such a usage
condition would ensure that the race doesn't happen, I believe.

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.

Thanks,
Florian