eval.c:9347
static rb_thread_t
rb_thread_alloc(klass)
    VALUE klass;
{
    rb_thread_t th;
    struct RVarmap *vars;

    THREAD_ALLOC(th);
    th->thread = Data_Wrap_Struct(klass, thread_mark, thread_free, th);

    for (vars = th->dyna_vars; vars; vars = vars->next) {
	if (FL_TEST(vars, DVAR_DONT_RECYCLE)) break;
	FL_SET(vars, DVAR_DONT_RECYCLE);
    }
    return th;
}
