void startPollAndWait() {
        try {
            synchronized (pollThread) {
                if ( ! pollThread.isAlive()) {
                    pollThread.start();
                }
                long before = pollCount;
                pollThread.notifyAll();
                while (pollCount <= before + 1) {
                    pollThread.notifyAll();
                    pollThread.wait();
                }
            }
        } catch (InterruptedException e) {}
    }
This class retrieves metrics from all nodes in the given config, usually all
nodes in a Vespa application.

@author gjoranv
metrics-proxy/src/main/java/ai/vespa/metricsproxy/http/application/ApplicationMetricsRetriever.java