static <A> A waitUntilVarSet(Var<A> v) ctex {
  synchronized(v) { while (!v.has()) v.wait(); ret v.get(); }
}

static <A> A waitUntilVarSet(Var<A> v, int timeout) ctex {
  synchronized(v) {
    long time = nanoTime();
    while (!v.has() && (nanoTime()-time) < timeout*900000)
      v.wait(timeout); // XXX-???
    ret v.get();
  }
}