private void checkForErrors() throws IOException {
    Throwable thrown = this.thrown.get();
    if (thrown == null) return;
    if (thrown instanceof IOException) {
      throw (IOException) thrown;
    } else {
      throw new RuntimeException(thrown);
    }
  }
Check for errors in the writer threads. If any is found, rethrow it.
hbase-diagnostics/src/main/java/org/apache/hadoop/hbase/util/LoadTestTool.java