bpo-46391: Library multiprocess leaks named resources.

Author: XD Trol

Lib/multiprocessing/context.py

@@ -223,6 +223,10 @@ class Process(process.BaseProcess):
     def _Popen(process_obj):
         return _default_context.get_context().Process._Popen(process_obj)
 
+    @staticmethod
+    def _bootstrap_util():
+        return _default_context.get_context().Process._bootstrap_util()
+
 class DefaultContext(BaseContext):
     Process = Process
 
@@ -283,6 +287,11 @@ def _Popen(process_obj):
             from .popen_spawn_posix import Popen
             return Popen(process_obj)
 
+        @staticmethod
+        def _bootstrap_util():
+            # Process is spawned, no need to bootstrap util.
+            pass
+
     class ForkServerProcess(process.BaseProcess):
         _start_method = 'forkserver'
         @staticmethod
@@ -326,6 +335,11 @@ def _Popen(process_obj):
             from .popen_spawn_win32 import Popen
             return Popen(process_obj)
 
+        @staticmethod
+        def _bootstrap_util():
+            # Process is spawned, no need to bootstrap util.
+            pass
+
     class SpawnContext(BaseContext):
         _name = 'spawn'
         Process = SpawnProcess

Lib/multiprocessing/process.py

@@ -304,8 +304,7 @@ def _bootstrap(self, parent_sentinel=None):
             if threading._HAVE_THREAD_NATIVE_ID:
                 threading.main_thread()._set_native_id()
             try:
-                util._finalizer_registry.clear()
-                util._run_after_forkers()
+                self._bootstrap_util()
             finally:
                 # delay finalization of the old process object until after
                 # _run_after_forkers() is executed
@@ -336,6 +335,13 @@ def _bootstrap(self, parent_sentinel=None):
 
         return exitcode
 
+    @staticmethod
+    def _bootstrap_util():
+        from . import util
+        util._finalizer_registry.clear()
+        util._run_after_forkers()
+
+
 #
 # We subclass bytes to avoid accidental transmission of auth keys over network
 #

Lib/test/_test_multiprocessing.py

@@ -5706,6 +5706,41 @@ def test_namespace(self):
         self.run_worker(self._test_namespace, o)
 
 
+class TestNamedResource(unittest.TestCase):
+
+    def test_global_named_resource_spawn(self):
+        #
+        # Check that global named resources in main module
+        # will not leak by a subprocess, in spawn context.
+        #
+        import tempfile as tf
+        py = tf.NamedTemporaryFile('w', delete=False)
+        try:
+            py.write('''if 1:
+                import multiprocessing as mp
+
+                ctx = mp.get_context('spawn')
+
+                global_resource = ctx.Semaphore()
+
+                def submain(): pass
+
+                if __name__ == '__main__':
+                    p = ctx.Process(target=submain)
+                    p.start()
+                    p.join()
+            ''')
+            py.close()
+
+            p = subprocess.run([sys.executable, py.name],
+                               stderr=subprocess.PIPE,
+                               text=True)
+
+            self.assertNotRegex(p.stderr, 'resource_tracker: There appear to be .* leaked')
+        finally:
+            os.unlink(py.name)
+
+
 class MiscTestCase(unittest.TestCase):
     def test__all__(self):
         # Just make sure names in not_exported are excluded

Misc/NEWS.d/next/Library/2022-01-16-03-09-58.bpo-46391.LZUzDI.rst

@@ -0,0 +1,2 @@
+Fix that Library multiprocess leaks named resources when global named
+resources are used in the main module in spawn context.