Thanks for your replay Corona688.

I found similar code in glibc (tls.h)...

Code:

/* Return the TCB address of the current thread.  */
# define THREAD_SELF                                   \
  ({ tcbhead_t *__tcb;                                  \
     __asm__ ("movl %%gs:%c1,%0" : "=r" (__tcb)                      \
          : "i" (offsetof (tcbhead_t, tcb)));                  \
     __tcb;})

Which I believe is accessing the Thread Control Block of the running thread which resides here in the gs register, specifically the offset containing the tcb address, I think.

This should result in a pretty quick, "inexpensive" and scalable operation then. Wondered if there was a chance that another thread could overwrite the register where this value is written before the calling thread retrieved it, (the volatile keyword isn't used) but I suppose this function would be useless if that was a possibility. This function must be thread safe, right?

Cheers,