Update BaseContext.freeze_support instead of override it

Author: aisk

Lib/multiprocessing/context.py

@@ -145,9 +145,18 @@ def freeze_support(self):
         '''Check whether this is a fake forked process in a frozen executable.
         If so then run code specified by commandline and exit.
         '''
-        if self.get_start_method() == 'spawn' and getattr(sys, 'frozen', False):
-            from .spawn import freeze_support
-            freeze_support()
+        if not getattr(sys, 'frozen', False):
+            return
+
+        # GH-135726: allow_none=True prevents this "get" call from setting the
+        # default context as the selected one as a side-effect.
+        method = self.get_start_method(allow_none=True) \
+                 or _default_context.get_start_method(allow_none=True)
+        if method != "spawn":
+            return
+
+        from .spawn import freeze_support
+        freeze_support()
 
     def get_logger(self):
         '''Return package logger -- if it does not already exist then
@@ -266,17 +275,6 @@ def get_all_start_methods(self):
         )
         return start_method_names
 
-    def freeze_support(self):
-        '''Check whether this is a fake forked process in a frozen executable.
-        If so then run code specified by commandline and exit.
-        '''
-        start_method = self.get_start_method(allow_none=True)
-        if start_method is None:
-            start_method = self._default_context.get_start_method()
-        if start_method == 'spawn' and getattr(sys, 'frozen', False):
-            from .spawn import freeze_support
-            freeze_support()
-
 
 #
 # Context types for fixed start method

Lib/test/_test_multiprocessing.py

@@ -5823,6 +5823,13 @@ def test_context(self):
             self.assertRaises(ValueError, ctx.set_start_method, None)
             self.check_context(ctx)
 
+    def test_freeze_support_side_effect(self):
+        # GH-135726: freeze_support() should not set the start method
+        # as a side-feect,
+        multiprocessing.set_start_method(None, force=True)
+        multiprocessing.freeze_support()
+        self.assertIsNone(multiprocessing.get_start_method(allow_none=True))
+
     def test_context_check_module_types(self):
         try:
             ctx = multiprocessing.get_context('forkserver')