bpo-38707: Fix for multiprocessing.Process MainThread.native_id (GH-17088)
This PR implements a fix for `multiprocessing.Process` objects; the error occurs when Processes are created using either `fork` or `forkserver` as the `start_method`.
In these instances, the `MainThread` of the newly created `Process` object retains all attributes from its parent's `MainThread` object, including the `native_id` attribute. The resulting behavior is such that the new process' `MainThread` captures an incorrect/outdated `native_id` (the parent's instead of its own).
This change forces the Process object to update its `native_id` attribute during the bootstrap process.
cc @vstinner
https://bugs.python.org/issue38707
Automerge-Triggered-By: @pitrou
diff --git a/Lib/multiprocessing/process.py b/Lib/multiprocessing/process.py
index c62c826..be13c07 100644
--- a/Lib/multiprocessing/process.py
+++ b/Lib/multiprocessing/process.py
@@ -301,6 +301,8 @@
_current_process = self
_parent_process = _ParentProcess(
self._parent_name, self._parent_pid, parent_sentinel)
+ if threading._HAVE_THREAD_NATIVE_ID:
+ threading.main_thread()._set_native_id()
try:
util._finalizer_registry.clear()
util._run_after_forkers()
diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py
index f7bebc6..611291c 100644
--- a/Lib/test/_test_multiprocessing.py
+++ b/Lib/test/_test_multiprocessing.py
@@ -361,6 +361,28 @@
self.assertNotIn(p, self.active_children())
close_queue(q)
+ @unittest.skipUnless(threading._HAVE_THREAD_NATIVE_ID, "needs native_id")
+ def test_process_mainthread_native_id(self):
+ if self.TYPE == 'threads':
+ self.skipTest('test not appropriate for {}'.format(self.TYPE))
+
+ current_mainthread_native_id = threading.main_thread().native_id
+
+ q = self.Queue(1)
+ p = self.Process(target=self._test_process_mainthread_native_id, args=(q,))
+ p.start()
+
+ child_mainthread_native_id = q.get()
+ p.join()
+ close_queue(q)
+
+ self.assertNotEqual(current_mainthread_native_id, child_mainthread_native_id)
+
+ @classmethod
+ def _test_process_mainthread_native_id(cls, q):
+ mainthread_native_id = threading.main_thread().native_id
+ q.put(mainthread_native_id)
+
@classmethod
def _sleep_some(cls):
time.sleep(100)