libthread_db thread handles

[Roland McGrath]

> td_thrhandle_t is opaque; it is documented as opaque in <thread_db.h>. 
> I don't want to look at th_unique.  Can I rely on the fact that the contents
> of a td_thrhandle_t are stable and can be re-used if I save the
> td_thrhandle_t?

For the life of the td_thragent_t, yes.  That is, until there is a TD_DEATH
event for the thread.  Once you resume the LWP that stopped to report the
TD_DEATH event, any td_thrandle_t associated with the dying thread is
invalid (as you would expect).  Since the closest thing to a spec for
thread_db is the Solaris documentation, and that's vague, we can't quite
say that this is "part of the spec".  But in extant GNU/Linux
implementations it is certainly true, and I can't envision an
implementation in which it would not be true.