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

* 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