Use "spawn" multiprocessing start method (#1279)

workaround https://bugs.python.org/issue6721

Fixes #1278

patroni/__init__.py

@@ -176,6 +176,13 @@ def fatal(string, *args):
     sys.exit(1)
 
 
+def use_spawn_start_method():
+    if sys.version_info >= (3, 4):
+        # The default, forking, method is not a good idea in a multithreaded process: https://bugs.python.org/issue6721
+        import multiprocessing
+        multiprocessing.set_start_method('spawn')
+
+
 def check_psycopg2():
     min_psycopg2 = (2, 5, 4)
     min_psycopg2_str = '.'.join(map(str, min_psycopg2))
@@ -198,6 +205,7 @@ def check_psycopg2():
 
 
 def main():
+    use_spawn_start_method()
     check_psycopg2()
     if os.getpid() != 1:
         return patroni_main()

tests/test_patroni.py

@@ -83,6 +83,7 @@ class TestPatroni(unittest.TestCase):
 
     @patch('os.getpid')
     @patch('multiprocessing.Process')
+    @patch('patroni.use_spawn_start_method', Mock())
     @patch('patroni.patroni_main', Mock())
     def test_patroni_main(self, mock_process, mock_getpid):
         mock_getpid.return_value = 2