libthread_db thread handles

[Daniel Jacobowitz <drow at mvista dot com>]

On Tue, Jan 14, 2003 at 02:32:59PM -0800, Michael Snyder wrote:
> Daniel Jacobowitz wrote:
> > 
> > On Mon, Jan 13, 2003 at 04:04:20PM -0800, Michael Snyder wrote:
> > > Daniel Jacobowitz wrote:
> 
> > > > For instance, I'd like to know if I
> > > > can safely cache the thread handles across resumes; if I could, this
> > > > would be much much much much easier to do efficiently.  We could get
> > > > the thread handle and LWP when the thread is created, and then hold the
> > > > thread handle, and optionally hold the LWP.  I am pretty sure this is
> > > > safe given glibc, but I don't know in general.
> > >
> > > I think in general not.
> > 
> > Hmm.  The Solaris documentation suggests that this is valid; I have no
> > way to check whether it actually is, and there is no explicit
> > description of the lifetime of a thread handle, but it doesn't describe
> > them as being of limited life.  It's a handle to "the thread object"
> > itself.
> 
> Dan, 
> 
> I passed your question along to Ulrich Drepper, and he says that, 
> if by "thread handle" you mean the th_unique value, then yes, 
> those are persistant until the thread exits.  If you mean the
> td_thrhandle_t value, though, then no, they are not persistant.
> They are allocated by libthread-db as needed, then thrown away.

Eh?  I'm a little thick-headed; Ulrich, could you explain to me what
you mean?

First of all, libthread_db doesn't necessarily create the
td_thrhandle_t; they're allocated by the caller of libthread_db, for
map_id2thr and map_lwp2thr.  The iterators create them and then throw
them away, of course.

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?

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer