TST add test for reused semtracker + CLN unused code

python · pitrou · Apr 24, 2019 · Jan 13, 2018 · Feb 24, 2018 · Apr 6, 2018
commit 87964fc80cfaf13fc82057c4a6ef24fbbefefec5
diff --git a/Lib/multiprocessing/semaphore_tracker.py b/Lib/multiprocessing/semaphore_tracker.py
@@ -95,6 +95,8 @@ def ensure_running(self):
     def _check_alive(self):
         '''Check for that the pipe has not been closed by sending a probe.'''
         try:
+            # We cannot use send here as it calls ensure_running, creating
+            # a cycle.
             os.write(self._fd, b'PROBE:0\n')
         except BrokenPipeError:
             return False

diff --git a/Lib/multiprocessing/spawn.py b/Lib/multiprocessing/spawn.py
@@ -178,12 +178,6 @@ def get_preparation_data(name):
         start_method=get_start_method(),
         )
 
-    if sys.platform != "win32":
-        # Pass the semaphore_tracker pid to avoid re-spawning it in every child
-        from . import semaphore_tracker
-        semaphore_tracker.ensure_running()
-        d['tracker_pid'] = semaphore_tracker._semaphore_tracker._pid
-
     # Figure out whether to initialise main in the subprocess as a module
     # or through direct execution (or to leave it alone entirely)
     main_module = sys.modules['__main__']
@@ -237,10 +231,6 @@ def prepare(data):
     if 'start_method' in data:
         set_start_method(data['start_method'], force=True)
 
-    if 'tracker_pid' in data:
-        from . import semaphore_tracker
-        semaphore_tracker._semaphore_tracker._pid = data["tracker_pid"]
-
     if 'init_main_from_name' in data:
         _fixup_main_from_name(data['init_main_from_name'])
     elif 'init_main_from_path' in data:

diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py
@@ -4895,6 +4895,33 @@ def test_semaphore_tracker_sigkill(self):
         # Uncatchable signal.
         self.check_semaphore_tracker_death(signal.SIGKILL, True)
 
+    @staticmethod
+    def _is_semaphore_tracker_reused(conn):
+        from multiprocessing.semaphore_tracker import _semaphore_tracker
+        _semaphore_tracker.ensure_running()
+        reused = _semaphore_tracker._pid is None
+        reused &= _semaphore_tracker._check_alive()
+        conn.send(reused)
+
+    def test_semaphore_tracker_reused(self):
+        from multiprocessing.semaphore_tracker import _semaphore_tracker
+        _semaphore_tracker.ensure_running()
+        pid = _semaphore_tracker._pid
+
+        ctx = multiprocessing.get_context("spawn")
+        r, w = ctx.Pipe(duplex=False)
+        p = ctx.Process(target=self._is_semaphore_tracker_reused,
+                        args=(w,))
+        p.start()
+        is_semaphore_tracker_reused = r.recv()
+
+        # Clean up
+        p.join()
+        w.close()
+        r.close()
+
+        self.assertTrue(is_semaphore_tracker_reused)
+
 
 class TestSimpleQueue(unittest.TestCase):