[det]tdebugclass property of a thread set by thread_create/3
or set_thread/2.
This implies loading the graphical tracer and switching the thread to
debug mode using debug/0.
New threads created inherit their debug mode from the thread that
created them.
Thread classes have been introduced in SWI-Prolog 10.0.2/10.1.5. This
allows for more selective debugging as well as ensuring debugging works
in newly created threads. For example, the HTTP server creates all its worker
threads in the class http. Using query below, we
reliable make sure spy points are trapped in HTTP handler threads,
regardless of whether the worker existed or is lazily created and
regardless of whether the user switched to
nodebug mode while tracing a previous event (see
debug_reset_from_class/0).
?- tdebug(http).