public void awaitShutdown() {
        shutdown();
        var timeout = Duration.ofSeconds(30);
        try {
            if (!service.awaitTermination(timeout.toMillis(), TimeUnit.MILLISECONDS)) {
                log.log(Level.WARNING, "Maintainer " + name() + " failed to shutdown " +
                                       "within " + timeout);
            }
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }
Waits for shutdown to complete, calling {@link #shutdown} if this hasn't been done already.
vespajlib/src/main/java/com/yahoo/concurrent/maintenance/Maintainer.java