python · gpshead · Nov 9, 2024 · Nov 7, 2024 · Nov 7, 2024 · Nov 8, 2024
@@ -174,6 +174,8 @@ def main(listener_fd, alive_r, preload, main_path=None, sys_path=None):
                 spawn.import_main_path(main_path)
             finally:
                 del process.current_process()._inheriting
+        if sys_path is not None:
+            sys.path[:] = sys_path
         for modname in preload:
             try:
                 __import__(modname)

diff --git a/Lib/test/test_multiprocessing_forkserver/test_forkserver_main.py b/Lib/test/test_multiprocessing_forkserver/test_forkserver_main.py
@@ -0,0 +1,57 @@
+import os
+import sys
+import unittest
+from unittest import mock
+
+from multiprocessing import forkserver
+
+
+class TestForkserverMain(unittest.TestCase):
+
+    def setUp(self):
+        self._orig_sys_path = list(sys.path)
+
+    def tearDown(self):
+        sys.path[:] = self._orig_sys_path
+
+    @mock.patch("multiprocessing.process.current_process")
+    @mock.patch("multiprocessing.spawn.import_main_path")
+    @mock.patch("multiprocessing.util._close_stdin")
+    def test_preload_kwargs(
+        self,
+        mock_close_stdin,
+        mock_import_main_path,
+        mock_current_process,
+    ):
+        # Very much a whitebox test of the first stanza of main before
+        # we start diddling with file descriptors and pipes.
+        mock_close_stdin.side_effect = RuntimeError("stop test")
+        self.assertNotIn(
+            "colorsys",
+            sys.modules.keys(),
+            msg="Thie test requires a module that has not yet been imported.",
+        )
+
+        with self.assertRaisesRegex(RuntimeError, "stop test"):
+            forkserver.main(None, None, ["sys", "colorsys"])
+        mock_current_process.assert_not_called()
+        mock_import_main_path.assert_not_called()
+        self.assertIn("colorsys", sys.modules.keys())
+        self.assertEqual(sys.path, self._orig_sys_path)  # unmodified
+
+        del sys.modules["colorsys"]  # unimport
+        fake_path = os.path.dirname(__file__)
+        with self.assertRaisesRegex(RuntimeError, "stop test"):
+            forkserver.main(None, None, ["sys", "colorsys"], sys_path=[fake_path])
+        self.assertEqual(
+            sys.path, [fake_path], msg="sys.path should have been overridden"
+        )
+        self.assertNotIn(
+            "colorsys",
+            sys.modules.keys(),
+            msg="import of colorsys should have failed with unusual sys.path",
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/Misc/NEWS.d/next/Library/2024-11-07-01-40-11.gh-issue-117378.o9O5uM.rst b/Misc/NEWS.d/next/Library/2024-11-07-01-40-11.gh-issue-117378.o9O5uM.rst
@@ -0,0 +1,11 @@
+Fixed the :mod:`multiprocessing` ``"forkserver"`` start method forkserver
+process was to correctly inherit the parent's :data:`sys.path` during the
+importing of :func:`multiprocessing.set_forkserver_preload` modules in the
+same manner as :data:`sys.path` is configured when executing work items in
+the worker processes.
+
+This bug could cause some forkserver module preloading to silently fail to
+be preloaded, leading to a performance degration in child processes due to
+additional repeated work.  It could also have led to a side effect of ``""``
+still being in :data:`sys.path` during forkserver preload imports instead of
+the absolute path of the directory that workers see.