[tune] Fix syncer=None not disabling trial-to-driver syncing (#20418)

python/ray/tune/syncer.py

@@ -556,8 +556,8 @@ def detect_cluster_syncer(
 
     sync_config = sync_config or SyncConfig()
 
-    if bool(sync_config.upload_dir):
-        # No sync to driver for cloud checkpointing
+    if bool(sync_config.upload_dir) or sync_config.syncer is None:
+        # No sync to driver for cloud checkpointing or if manually disabled
         return False
 
     _syncer = sync_config.syncer

python/ray/tune/tests/test_sync.py

@@ -17,8 +17,10 @@ from ray.rllib import _register_all
 from ray import tune
 from ray.tune.integration.docker import DockerSyncer
 from ray.tune.integration.kubernetes import KubernetesSyncer
+from ray.tune.sync_client import NOOP
 from ray.tune.syncer import (CommandBasedClient, detect_cluster_syncer,
-                             get_cloud_sync_client)
+                             get_cloud_sync_client, SyncerCallback)
+from ray.tune.utils.callback import create_default_callbacks
 
 
 class TestSyncFunctionality(unittest.TestCase):
@@ -404,6 +406,34 @@ class TestSyncFunctionality(unittest.TestCase):
                 tune.SyncConfig(syncer=DockerSyncer), kubernetes_file)
             self.assertTrue(issubclass(syncer, DockerSyncer))
 
+    @patch("ray.tune.syncer.log_sync_template",
+           lambda: "rsync {source} {target}")
+    def testNoSyncToDriver(self):
+        """Test that sync to driver is disabled"""
+
+        class _Trial:
+            def __init__(self, id, logdir):
+                self.id = id,
+                self.logdir = logdir
+
+        trial = _Trial("0", "some_dir")
+
+        sync_config = tune.SyncConfig(syncer=None)
+
+        # Create syncer callbacks
+        callbacks = create_default_callbacks([], sync_config, loggers=None)
+        syncer_callback = callbacks[-1]
+
+        # Sanity check that we got the syncer callback
+        self.assertTrue(isinstance(syncer_callback, SyncerCallback))
+
+        # Sync function should be false (no sync to driver)
+        self.assertEquals(syncer_callback._sync_function, False)
+
+        # Sync to driver is disabled, so this should be no-op
+        trial_syncer = syncer_callback._get_trial_syncer(trial)
+        self.assertEquals(trial_syncer.sync_client, NOOP)
+
 
 if __name__ == "__main__":
     import pytest