Re: RFC: A way to get a TID from a pthread_t handler

[Florian Weimer <fweimer@redhat.com>]

* Trevor Gross via Libc-help:

> It seems like there isn't a good way to get the thread ID from a
> pthread_t. If you are within the thread then you can call gettid(),
> but there is no public API to get a spawned thread's TID after calling
> pthread_create().
>
> This value is stored in the pthread, so a new public function could
> just be a basic getter:
>
>     pid_t pthread_gettid(pthread_t threadid)
>     {
>       struct pthread *pd = (struct pthread *) threadid;
>       return pd->tid;
>     }
>
> Would an addition like this likely get accepted? Or is there anything
> overlooked about an easier way to recover the spawned thread's TID?

We should probably make a copy of the TID inside pthread_create and
return that from pthread_gettid, instead of pd->tid that might be
cleared by the kernel upon thread exit.  This way, pthread_gettid
remains valid until pthread_join is called.

Thanks,
Florian