private final CountDownLatch startLatch = new CountDownLatch(1);
    private final CountDownLatch stopLatch = new CountDownLatch(1);

    private volatile boolean running = false;

    @Override
    public @Nullable Void call() throws InterruptedException {
      running = true;
      startLatch.countDown();
      stopLatch.await();
      running = false;
      return null;
    }

		return
	}

	p.append(prog, cond, true)
}

func (p *Parser) patch() {
	for _, patch := range p.toPatch {
		targetProg := p.labels[patch.label]
		if targetProg == nil {
			p.errorf("undefined label %s", patch.label)
			return
		}
		p.branch(patch.addr, targetProg)
	}
	p.toPatch = p.toPatch[:0]
}

func (p *Parser) branch(addr *obj.Addr, target *obj.Prog) {
	*addr = obj.Addr{

	input         []lex.Token
	inputPos      int
	pendingLabels []string // Labels to attach to next instruction.
	labels        map[string]*obj.Prog
	toPatch       []Patch
	addr          []obj.Addr
	arch          *arch.Arch
	ctxt          *obj.Link
	firstProg     *obj.Prog
	lastProg      *obj.Prog
	dataAddr      map[string]int64 // Most recent address for DATA for this symbol.