private void awaitCountdown(CountDownLatch countDownLatch, long timeoutMs, AtomicReference<Exception> exception,
      String errMsg) throws Exception {
    if (!countDownLatch.await(timeoutMs, TimeUnit.MILLISECONDS)) {
      if (exception.get() == null) {
        exception.set(new Exception(errMsg));
      }
      throw exception.get();
    }
  }
Starts up an ambry server given a port number in localhost

@param port the port number over which ambry server needs to be started
@return the {@link SocketServer} referring to ambry's instance
@throws IOException
@throws InterruptedException
ambry-network/src/test/java/com/github/ambry/network/BlockingChannelConnectionPoolTest.java