/**
   * Wait for the region servers to report in.
   * We will wait until one of this condition is met:
   *  - the master is stopped
   *  - the 'hbase.master.wait.on.regionservers.maxtostart' number of
   *    region servers is reached
   *  - the 'hbase.master.wait.on.regionservers.mintostart' is reached AND
   *   there have been no new region server in for
   *      'hbase.master.wait.on.regionservers.interval' time AND
   *   the 'hbase.master.wait.on.regionservers.timeout' is reached
   *
   * @throws InterruptedException
   */
  public void waitForRegionServers(MonitoredTask status)
  throws InterruptedException {
    final long interval = this.master.getConfiguration().
      getLong(WAIT_ON_REGIONSERVERS_INTERVAL, 1500);
    final long timeout = this.master.getConfiguration().
      getLong(WAIT_ON_REGIONSERVERS_TIMEOUT, 4500);
    int minToStart = this.master.getConfiguration().
      getInt(WAIT_ON_REGIONSERVERS_MINTOSTART, 1);
    if (minToStart < 1) {
      LOG.warn(String.format(
        "The value of '%s' (%d) can not be less than 1, ignoring.",
        WAIT_ON_REGIONSERVERS_MINTOSTART, minToStart));
      minToStart = 1;
    }
    int maxToStart = this.master.getConfiguration().
      getInt(WAIT_ON_REGIONSERVERS_MAXTOSTART, Integer.MAX_VALUE);
    if (maxToStart < minToStart) {
        LOG.warn(String.format(
            "The value of '%s' (%d) is set less than '%s' (%d), ignoring.",
            WAIT_ON_REGIONSERVERS_MAXTOSTART, maxToStart,
            WAIT_ON_REGIONSERVERS_MINTOSTART, minToStart));
        maxToStart = Integer.MAX_VALUE;
    }

    long now =  System.currentTimeMillis();
    final long startTime = now;
    long slept = 0;
    long lastLogTime = 0;
    long lastCountChange = startTime;
    int count = countOfRegionServers();
    int oldCount = 0;
    while (
      !this.master.isStopped() &&
        count < maxToStart &&
        (lastCountChange+interval > now || timeout > slept || count < minToStart)
      ){

      // Log some info at every interval time or if there is a change
      if (oldCount != count || lastLogTime+interval < now){
        lastLogTime = now;
        String msg =
          "Waiting for region servers count to settle; currently"+
            " checked in " + count + ", slept for " + slept + " ms," +
            " expecting minimum of " + minToStart + ", maximum of "+ maxToStart+
            ", timeout of "+timeout+" ms, interval of "+interval+" ms.";
        LOG.info(msg);
        status.setStatus(msg);
      }

      // We sleep for some time
      final long sleepTime = 50;
      Thread.sleep(sleepTime);
      now =  System.currentTimeMillis();
      slept = now - startTime;

      oldCount = count;
      count = countOfRegionServers();
      if (count != oldCount) {
        lastCountChange = now;
      }
    }

    LOG.info("Finished waiting for region servers count to settle;" +
      " checked in " + count + ", slept for " + slept + " ms," +
      " expecting minimum of " + minToStart + ", maximum of "+ maxToStart+","+
      " master is "+ (this.master.isStopped() ? "stopped.": "running.")
    );
  }