Don't use threads when max_workers=1

octodns/manager.py

@@ -6,7 +6,7 @@ from __future__ import absolute_import, division, print_function, \
     unicode_literals
 
 from StringIO import StringIO
-from concurrent.futures import ThreadPoolExecutor
+from concurrent.futures import Future, ThreadPoolExecutor
 from importlib import import_module
 from os import environ
 import logging
@@ -37,10 +37,21 @@ class _AggregateTarget(object):
         return True
 
 
+class MainThreadExecutor(object):
+
+    def submit(self, func, *args, **kwargs):
+        future = Future()
+        try:
+            future.set_result(func(*args, **kwargs))
+        except Exception as e:
+            future.set_exception(e)
+        return future
+
+
 class Manager(object):
     log = logging.getLogger('Manager')
 
-    def __init__(self, config_file):
+    def __init__(self, config_file, max_workers=None):
         self.log.info('__init__: config_file=%s', config_file)
 
         # Read our config file
@@ -48,8 +59,12 @@ class Manager(object):
             self.config = safe_load(fh, enforce_order=False)
 
         manager_config = self.config.get('manager', {})
-        max_workers = manager_config.get('max_workers', 4)
-        self._executor = ThreadPoolExecutor(max_workers=max_workers)
+        max_workers = manager_config.get('max_workers', 1) \
+            if max_workers is None else max_workers
+        if max_workers > 1:
+            self._executor = ThreadPoolExecutor(max_workers=max_workers)
+        else:
+            self._executor = MainThreadExecutor()
 
         self.log.debug('__init__:   configuring providers')
         self.providers = {}

tests/test_octodns_manager.py

@@ -115,6 +115,11 @@ class TestManager(TestCase):
                 .sync(dry_run=False, force=True)
             self.assertEquals(19, tc)
 
+            # Again with max_workers = 1
+            tc = Manager(get_config_filename('simple.yaml'), max_workers=1) \
+                .sync(dry_run=False, force=True)
+            self.assertEquals(19, tc)
+
     def test_eligible_targets(self):
         with TemporaryDirectory() as tmpdir:
             environ['YAML_TMP_DIR'] = tmpdir.dirname