bpo-39360: Ensure all workers exit when finalizing a multiprocessing.…

…Pool

Lib/multiprocessing/pool.py

@@ -651,8 +651,6 @@ def close(self):
     def terminate(self):
         util.debug('terminating pool')
         self._state = TERMINATE
-        self._worker_handler._state = TERMINATE
-        self._change_notifier.put(None)
         self._terminate()
 
     def join(self):
@@ -683,6 +681,8 @@ def _terminate_pool(cls, taskqueue, inqueue, outqueue, pool, change_notifier,
         util.debug('finalizing pool')
 
         worker_handler._state = TERMINATE
+        change_notifier.put(None)
+
         task_handler._state = TERMINATE
 
         util.debug('helping task handler/workers to finish')

Lib/test/_test_multiprocessing.py

@@ -2780,6 +2780,21 @@ def test_pool_worker_lifetime_early_close(self):
         for (j, res) in enumerate(results):
             self.assertEqual(res.get(), sqr(j))
 
+    def test_pool_hang(self):
+        # tests cases against bpo-38744 and bpo-39360
+        cmd = '''if 1:
+            from multiprocessing import Pool
+            class A:
+                def init(self):
+                    self.pool = Pool(processes=1)
+            def do_something(x):
+                return x1
+            problem = A()
+            problem.pool.map(do_something, [1,2,3])
+        '''
+        rc, out, err = test.support.script_helper.assert_python_ok('-c', cmd)
+        self.assertEqual(rc, 0)
+
 #
 # Test of creating a customized manager class
 #

Misc/NEWS.d/next/Library/2020-03-15-05-41-05.bpo-39360.cmcU5p.rst

@@ -0,0 +1,2 @@
+Ensure all workers exit when finalizing a :class:`multiprocessing.Pool`.
+Patch by Batuhan Taskaya.