gh-104090: Add exit code to multiprocessing ResourceTracker (GH-115410)

This builds on https://github.com/python/cpython/pull/106807, which adds
a return code to ResourceTracker, to make future debugging easier.
Testing this “in situ” proved difficult, since the global ResourceTracker is
involved in test infrastructure. So, the tests here create a new instance and
feed it fake data.

---------

Co-authored-by: Yonatan Bitton <yonatan.bitton@perception-point.io>
Co-authored-by: Yonatan Bitton <bityob@gmail.com>
Co-authored-by: Antoine Pitrou <antoine@python.org>

Lib/multiprocessing/resource_tracker.py

@@ -29,8 +29,12 @@ __all__ = ['ensure_running', 'register', 'unregister']
 _HAVE_SIGMASK = hasattr(signal, 'pthread_sigmask')
 _IGNORED_SIGNALS = (signal.SIGINT, signal.SIGTERM)
 
+def cleanup_noop(name):
+    raise RuntimeError('noop should never be registered or cleaned up')
+
 _CLEANUP_FUNCS = {
-    'noop': lambda: None,
+    'noop': cleanup_noop,
+    'dummy': lambda name: None,  # Dummy resource used in tests
 }
 
 if os.name == 'posix':
@@ -61,6 +65,7 @@ class ResourceTracker(object):
         self._lock = threading.RLock()
         self._fd = None
         self._pid = None
+        self._exitcode = None
 
     def _reentrant_call_error(self):
         # gh-109629: this happens if an explicit call to the ResourceTracker
@@ -84,9 +89,16 @@ class ResourceTracker(object):
             os.close(self._fd)
             self._fd = None
 
-            os.waitpid(self._pid, 0)
+            _, status = os.waitpid(self._pid, 0)
+
             self._pid = None
 
+            try:
+                self._exitcode = os.waitstatus_to_exitcode(status)
+            except ValueError:
+                # os.waitstatus_to_exitcode may raise an exception for invalid values
+                self._exitcode = None
+
     def getfd(self):
         self.ensure_running()
         return self._fd
@@ -119,6 +131,7 @@ class ResourceTracker(object):
                     pass
                 self._fd = None
                 self._pid = None
+                self._exitcode = None
 
                 warnings.warn('resource_tracker: process died unexpectedly, '
                               'relaunching.  Some resources might leak.')
@@ -221,6 +234,8 @@ def main(fd):
             pass
 
     cache = {rtype: set() for rtype in _CLEANUP_FUNCS.keys()}
+    exit_code = 0
+
     try:
         # keep track of registered/unregistered resources
         with open(fd, 'rb') as f:
@@ -242,6 +257,7 @@ def main(fd):
                     else:
                         raise RuntimeError('unrecognized command %r' % cmd)
                 except Exception:
+                    exit_code = 3
                     try:
                         sys.excepthook(*sys.exc_info())
                     except:
@@ -251,10 +267,17 @@ def main(fd):
         for rtype, rtype_cache in cache.items():
             if rtype_cache:
                 try:
-                    warnings.warn(
-                        f'resource_tracker: There appear to be {len(rtype_cache)} '
-                        f'leaked {rtype} objects to clean up at shutdown: {rtype_cache}'
-                    )
+                    exit_code = 1
+                    if rtype == 'dummy':
+                        # The test 'dummy' resource is expected to leak.
+                        # We skip the warning (and *only* the warning) for it.
+                        pass
+                    else:
+                        warnings.warn(
+                            f'resource_tracker: There appear to be '
+                            f'{len(rtype_cache)} leaked {rtype} objects to '
+                            f'clean up at shutdown: {rtype_cache}'
+                        )
                 except Exception:
                     pass
             for name in rtype_cache:
@@ -265,6 +288,9 @@ def main(fd):
                     try:
                         _CLEANUP_FUNCS[rtype](name)
                     except Exception as e:
+                        exit_code = 2
                         warnings.warn('resource_tracker: %r: %s' % (name, e))
                 finally:
                     pass
+
+        sys.exit(exit_code)

Lib/test/_test_multiprocessing.py

@@ -5609,8 +5609,9 @@ class TestResourceTracker(unittest.TestCase):
         '''
         for rtype in resource_tracker._CLEANUP_FUNCS:
             with self.subTest(rtype=rtype):
-                if rtype == "noop":
+                if rtype in ("noop", "dummy"):
                     # Artefact resource type used by the resource_tracker
+                    # or tests
                     continue
                 r, w = os.pipe()
                 p = subprocess.Popen([sys.executable,
@@ -5730,6 +5731,38 @@ class TestResourceTracker(unittest.TestCase):
         with self.assertRaises(ValueError):
             resource_tracker.register(too_long_name_resource, rtype)
 
+    def _test_resource_tracker_leak_resources(self, cleanup):
+        # We use a separate instance for testing, since the main global
+        # _resource_tracker may be used to watch test infrastructure.
+        from multiprocessing.resource_tracker import ResourceTracker
+        tracker = ResourceTracker()
+        tracker.ensure_running()
+        self.assertTrue(tracker._check_alive())
+
+        self.assertIsNone(tracker._exitcode)
+        tracker.register('somename', 'dummy')
+        if cleanup:
+            tracker.unregister('somename', 'dummy')
+            expected_exit_code = 0
+        else:
+            expected_exit_code = 1
+
+        self.assertTrue(tracker._check_alive())
+        self.assertIsNone(tracker._exitcode)
+        tracker._stop()
+        self.assertEqual(tracker._exitcode, expected_exit_code)
+
+    def test_resource_tracker_exit_code(self):
+        """
+        Test the exit code of the resource tracker.
+
+        If no leaked resources were found, exit code should be 0, otherwise 1
+        """
+        for cleanup in [True, False]:
+            with self.subTest(cleanup=cleanup):
+                self._test_resource_tracker_leak_resources(
+                    cleanup=cleanup,
+                )
 
 class TestSimpleQueue(unittest.TestCase):
 

Lib/test/test_concurrent_futures/test_init.py

@@ -3,6 +3,7 @@ import logging
 import queue
 import time
 import unittest
+import sys
 from concurrent.futures._base import BrokenExecutor
 from logging.handlers import QueueHandler
 
@@ -109,6 +110,31 @@ create_executor_tests(globals(), InitializerMixin)
 create_executor_tests(globals(), FailingInitializerMixin)
 
 
+@unittest.skipIf(sys.platform == "win32", "Resource Tracker doesn't run on Windows")
+class FailingInitializerResourcesTest(unittest.TestCase):
+    """
+    Source: https://github.com/python/cpython/issues/104090
+    """
+
+    def _test(self, test_class):
+        runner = unittest.TextTestRunner()
+        runner.run(test_class('test_initializer'))
+
+        # GH-104090:
+        # Stop resource tracker manually now, so we can verify there are not leaked resources by checking
+        # the process exit code
+        from multiprocessing.resource_tracker import _resource_tracker
+        _resource_tracker._stop()
+
+        self.assertEqual(_resource_tracker._exitcode, 0)
+
+    def test_spawn(self):
+        self._test(ProcessPoolSpawnFailingInitializerTest)
+
+    def test_forkserver(self):
+        self._test(ProcessPoolForkserverFailingInitializerTest)
+
+
 def setUpModule():
     setup_module()
 

Misc/NEWS.d/next/Core and Builtins/2023-07-16-15-02-47.gh-issue-104090.oMjNa9.rst

@@ -0,0 +1,2 @@
+The multiprocessing resource tracker now exits with non-zero status code if a resource
+leak was detected. It still exits with status code 0 otherwise.