title: Launch concurrent.futures.ProcessPoolExecutor with initialization?
body: <p>I'm planning to use <code>concurrent.futures.ProcessPoolExecutor</code> to parallelize execution of functions. According to the <a href="https://docs.python.org/3/library/concurrent.futures.html" rel="noreferrer">documentation</a>, its <code>executor</code> object can only accept a simple function in <code>map</code>. My actual situation involves initialization (loading of data) prior to execution of the 'to-be-parallelized' function. How do I arrange that?</p>
  
  <p>The 'to-be-parallelized' function is called in an iteration for many times. I don't want it to be re-initialized each time.</p>
  
  <p>In other words, there's an <code>init</code> function that produces some output to this tbp function. Each child should have its own copy of that output, because the function depended on that.</p>