title: Multi-threading writing to multiple distributed tables in a DolphinDB database
body: <p>I tried to conduct concurrent writes in DolphinDB and set <code>enableChunkGranularityConfig = true</code>. I have three tables, <code>oq</code>, <code>mk</code>, <code>ts</code>, all under the <code>1db3tb</code> database. I want to write data to these tables and test the concurrent performance. How to write a dos command to conduct concurrent writes?</p>
  <p>I created a dos file as follows, but it seems still single-threaded. How can I append data to the tables at the same time?
  <code>tableObj1.append!(t1)</code>
  <code>tableObj2.append!(t2)</code>
  <code>tableObj3.append!(t3)</code></p>