bpo-36780: Add wait_at_exit to ThreadPoolExecutor.shutdown.

Author: hniksic

Doc/library/concurrent.futures.rst

@@ -159,6 +159,23 @@ And::
    .. versionchanged:: 3.7
       Added the *initializer* and *initargs* arguments.
 
+    .. method:: shutdown(wait=True, wait_at_exit=True)
+
+       Like :meth:`Executor.shutdown`, with the additional option to
+       suppress waiting for running futures at Python exit.
+
+       Normally, this method waits for all submitted jobs to finish
+       before returning. Specifying ``wait=False`` makes the method
+       return immediately, but when the Python process is about to
+       exit, it will still wait for the remaining futures to complete.
+
+       Specifying ``False`` for *wait_at_exit* inhibits waiting at
+       process exit.  It is typically used along with ``wait=False``,
+       so ``shutdown(wait=False, wait_at_exit=False)`` abandons the
+       executor and its futures.  This is useful when the submitted
+       jobs are possibly stuck, and waiting for them would make the
+       process hang.
+
 
 .. _threadpoolexecutor-example:
 

Lib/concurrent/futures/thread.py

@@ -211,11 +211,14 @@ def _initializer_failed(self):
                 if work_item is not None:
                     work_item.future.set_exception(BrokenThreadPool(self._broken))
 
-    def shutdown(self, wait=True):
+    def shutdown(self, wait=True, wait_at_exit=True):
         with self._shutdown_lock:
             self._shutdown = True
             self._work_queue.put(None)
         if wait:
             for t in self._threads:
                 t.join()
+        if not wait_at_exit:
+            for t in self._threads:
+                _threads_queues.pop(t, None)
     shutdown.__doc__ = _base.Executor.shutdown.__doc__