Fix #6803: Disable parallel build on macOS and py38+

CHANGES

@@ -7,6 +7,9 @@ Dependencies
 Incompatible changes
 --------------------
 
+* #6803: For security reason of python, parallel mode is disabled on macOS and
+  Python3.8+
+
 Deprecated
 ----------
 
@@ -19,6 +22,7 @@ Bugs fixed
 * #6776: LaTeX: 2019-10-01 LaTeX release breaks :file:`sphinxcyrillic.sty`
 * #6815: i18n: French, Hindi, Japanese and Korean translation messages has been
   broken
+* #6803: parallel build causes AttributeError on macOS and Python3.8
 
 Testing
 --------

sphinx/application.py

@@ -12,6 +12,7 @@
 
 import os
 import pickle
+import platform
 import sys
 import warnings
 from collections import deque
@@ -199,6 +200,12 @@ class Sphinx:
         # say hello to the world
         logger.info(bold(__('Running Sphinx v%s') % sphinx.__display_version__))
 
+        # notice for parallel build on macOS and py38+
+        if sys.version_info > (3, 8) and platform.system() == 'Darwin' and parallel > 1:
+            logger.info(bold(__("For security reason, parallel mode is disabled on macOS and "
+                                "python3.8 and above.  For more details, please read "
+                                "https://github.com/sphinx-doc/sphinx/issues/6803")))
+
         # status code for command-line application
         self.statuscode = 0
 

sphinx/util/parallel.py

@@ -9,6 +9,8 @@
 """
 
 import os
+import platform
+import sys
 import time
 import traceback
 from math import sqrt
@@ -26,7 +28,12 @@ logger = logging.getLogger(__name__)
 
 
 # our parallel functionality only works for the forking Process
-parallel_available = multiprocessing and (os.name == 'posix')
+#
+# Note: "fork" is not recommended on macOS and py38+.
+#       see https://bugs.python.org/issue33725
+parallel_available = (multiprocessing and
+                      (os.name == 'posix') and
+                      not (sys.version_info > (3, 8) and platform.system() == 'Darwin'))
 
 
 class SerialTasks:

tests/test_util_logging.py

@@ -10,6 +10,8 @@
 
 import codecs
 import os
+import platform
+import sys
 
 import pytest
 from docutils import nodes
@@ -276,6 +278,8 @@ def test_colored_logs(app, status, warning):
 
 
 @pytest.mark.xfail(os.name != 'posix', reason="Not working on windows")
+@pytest.mark.xfail(platform.system() == 'Darwin' and sys.version_info > (3, 8),
+                   reason="Not working on macOS and py38")
 def test_logging_in_ParallelTasks(app, status, warning):
     logging.setup(app, status, warning)
     logger = logging.getLogger(__name__)