title: Is safe concurrent.futures.ThreadPoolExecutor in python?
body: <p>for a func that is not supported async, i will use the thread.
  it seems inefficient to create a new thread every time,
  i try to create a thread pool, and use it repeatedly while a program is running.</p>
  <p>i kwnow that even if an error occurs by executing some func in thread &quot;A&quot;, thread &quot;A&quot; can execute a different func.</p>
  <p>however, what happens if the first func uses a global variable, and this affects the next func?</p>
  <p>or, is there a case where 4 threads were created, but one died for some error and only three threads were used repeatedly?(except deadlock)</p>
  <p>if such problem above accurs,
  is there a way to check the problem and refresh the thread of the thread pool?</p>