presto-main/src/main/java/io/prestosql/execution/scheduler/FileBasedNetworkTopology.java/FileBasedNetworkTopology/FileBasedNetworkTopology
class FileBasedNetworkTopology:    FileBasedNetworkTopology(File networkTopologyFile, Duration refreshPeriod, Ticker ticker)
    {
        this.networkTopologyFile = requireNonNull(networkTopologyFile, "networkTopologyFile is null");
        this.refreshPeriodNanos = requireNonNull(refreshPeriod, "refreshPeriodNanos is null").roundTo(NANOSECONDS);
        this.ticker = requireNonNull(ticker, "ticker is null");
        refreshTopology();
    }