Thread_POSIX.cpp shouldn't convert thread IDs to long

[arrowd]

According to the POSIX standard returning value of pthread_self() is opaque and can't be casted to long. See NOTES section of pthread_self(3) and pthread_equal(3) man pages.

The code of ThreadImpl::currentOsTidImpl() causes compilation to fail on FreeBSD with

poco/Foundation/src/Thread_POSIX.cpp:326:12: error: cannot initialize return object of type 'long' with an rvalue of type 'pthread_t' (aka 'pthread *')
    return ::pthread_self();
           ^~~~~~~~~~~~~~~~

On the other hand, the method is called currentOsTidImpl and on Linux it calls gettid() syscall. If this method is intended to return kernel thread identifier, then the #else case shouldn't call pthread_self() and instead have #error Implement this for your OS. I'm happy to prepare a pull request if my analysis is right.

[aleks-f]

@arrowd I think there should be a warning and return 0; discarding any OS except Linux and MacOS over this is a too harsh measure
/cc @obiltschnig

[neotron]

On FreeBSD specifically you can add a case using this:

return ::pthread_getthreadid_np();

defined in <pthread_np.h>

[arrowd]

The point is that an ID returned from pthread_* isn't the same thing as an ID returned by gettid(). So if the Linux case uses gettid, then all other cases can't use phtread_*.

[neotron]

I do agree pthread_self() shouldn't be used as a numerical thread id since it's not intended to be used that way. pthread_getthreadid_np() on the other hand does return the unique numerical id of the thread.

[arrowd]

It is still a different thing compared to gettid. FreeBSD case should use thr_self() here.

[neotron]

I was not aware of the thr_self() method. That said when testing both they seem to return the same value, at least in my test case:

*** thr_self=101298, getthreadid=101298

thr_self() seems like the better option given that it better matches the Linux version, and returns a long rather than int (in the unlikely case thread id would exceed a signed int).

https://github.com/freebsd/freebsd-src/blob/d4a80d21b3d32a2de02d1820cc1f38dba1f127cb/sys/kern/kern_thr.c#L297
https://github.com/freebsd/freebsd-src/blob/d4a80d21b3d32a2de02d1820cc1f38dba1f127cb/lib/libthr/thread/thr_getthreadid_np.c#L51

[github-actions]

This issue is stale because it has been open for 365 days with no activity.