private void workerThreadError(Throwable t) {
    thrown.compareAndSet(null, t);
  }
When NUM_TABLES is specified, the function starts multiple worker threads which individually
start a LoadTestTool instance to load a table. Each table name is in format &lt;tn>_&lt;index>.
For example, "-tn test -num_tables 2" , table names will be "test_1", "test_2"
@throws IOException if one of the load tasks is unable to complete
hbase-diagnostics/src/main/java/org/apache/hadoop/hbase/util/LoadTestTool.java