Description

   This routine obtains and returns the thread sequence number
   for the thread identified by the thread object specified in the
   thread argument.

   The thread sequence number provides a unique identifier for each
   existing thread. A thread's thread sequence number is never
   reused while the thread exists, but can be reused after the
   thread terminates. The debugger interfaces use this sequence
   number to identify each thread in commands and in display output.

   The result of calling this routine is undefined if the thread
   argument does not specify a valid thread object.