// assumptions:
// -pingSource() stays constant within a stack frame (so you can cache it)
// -all changes happen with tempSetPingSource
// -multiple threads can share a PingSource
static PingSource pingSource() {
  ret pingSource_tl()!;
}

static PingSource pingSource(Thread thread) {
  ret pingSource_tl().get(thread);
}

Began life as a copy of #1033339