[semidet]py_with_gil(:Goal)once(Goal) while holding the Phyton
GIL (Global Interpreter Lock). Note that all predicates that
interact with Python lock the GIL. This predicate is only required if we
wish to make multiple calls to Python while keeping the GIL. The GIL is
a
recursive lock and thus calling py_call/1,2
while holding the GIL does not deadlock.