Issue #15101: Make pool finalizer avoid joining current thread.

Lib/multiprocessing/pool.py

@@ -496,7 +496,8 @@ class Pool(object):
         # We must wait for the worker handler to exit before terminating
         # workers because we don't want workers to be restarted behind our back.
         debug('joining worker handler')
-        worker_handler.join()
+        if threading.current_thread() is not worker_handler:
+            worker_handler.join()
 
         # Terminate workers which haven't already finished.
         if pool and hasattr(pool[0], 'terminate'):
@@ -506,10 +507,12 @@ class Pool(object):
                     p.terminate()
 
         debug('joining task handler')
-        task_handler.join()
+        if threading.current_thread() is not task_handler:
+            task_handler.join()
 
         debug('joining result handler')
-        result_handler.join()
+        if threading.current_thread() is not result_handler:
+            result_handler.join()
 
         if pool and hasattr(pool[0], 'terminate'):
             debug('joining pool workers')

Misc/NEWS

@@ -29,6 +29,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #15101: Make pool finalizer avoid joining current thread.
+
 - Issue #14657: The frozen instance of importlib used for bootstrap is now
   also the module imported as importlib._bootstrap.