public void waitForFirstPut() throws InterruptedException {
      // wait until put thread actually puts some data
      while (isAlive() && numPutsFinished == 0) {
        checkNoError();
        Thread.sleep(50);
      }
    }
Block calling thread until this instance of PutThread has put at least one row.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestHRegion.java