bpo-19675: Terminate processes if construction of a pool is failing. (GH-5614)

1 files changed, 43 insertions, 0 deletions

diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py
index dc59e9f..7993fcb 100644
--- a/Lib/test/_test_multiprocessing.py
+++ b/Lib/test/_test_multiprocessing.py
@@ -3,6 +3,7 @@
 #
 
 import unittest
+import unittest.mock
 import queue as pyqueue
 import contextlib
 import time
@@ -4635,6 +4636,48 @@ class TestSimpleQueue(unittest.TestCase):
         proc.join()
 
 
+class TestPoolNotLeakOnFailure(unittest.TestCase):
+
+    def test_release_unused_processes(self):
+        # Issue #19675: During pool creation, if we can't create a process,
+        # don't leak already created ones.
+        will_fail_in = 3
+        forked_processes = []
+
+        class FailingForkProcess:
+            def __init__(self, **kwargs):
+                self.name = 'Fake Process'
+                self.exitcode = None
+                self.state = None
+                forked_processes.append(self)
+
+            def start(self):
+                nonlocal will_fail_in
+                if will_fail_in <= 0:
+                    raise OSError("Manually induced OSError")
+                will_fail_in -= 1
+                self.state = 'started'
+
+            def terminate(self):
+                self.state = 'stopping'
+
+            def join(self):
+                if self.state == 'stopping':
+                    self.state = 'stopped'
+
+            def is_alive(self):
+                return self.state == 'started' or self.state == 'stopping'
+
+        with self.assertRaisesRegex(OSError, 'Manually induced OSError'):
+            p = multiprocessing.pool.Pool(5, context=unittest.mock.MagicMock(
+                Process=FailingForkProcess))
+            p.close()
+            p.join()
+        self.assertFalse(
+            any(process.is_alive() for process in forked_processes))
+
+
+
 class MiscTestCase(unittest.TestCase):
     def test__all__(self):
         # Just make sure names in blacklist are excluded