Fix hang on rank zero only

Author: carmocca

pytorch_lightning/core/lightning.py

@@ -303,7 +303,7 @@ def log(
         add_dataloader_idx: bool = True,
         batch_size: Optional[int] = None,
         metric_attribute: Optional[str] = None,
-        rank_zero_only: Optional[bool] = None,
+        rank_zero_only: bool = False,
     ) -> None:
         """Log a key, value pair.
 
@@ -441,7 +441,7 @@ def log_dict(
         sync_dist_group: Optional[Any] = None,
         add_dataloader_idx: bool = True,
         batch_size: Optional[int] = None,
-        rank_zero_only: Optional[bool] = None,
+        rank_zero_only: bool = False,
     ) -> None:
         """Log a dictionary of values at once.
 

pytorch_lightning/trainer/connectors/logger_connector/result.py

@@ -616,8 +616,8 @@ def cpu(self) -> "ResultCollection":
 
     def sync(self) -> None:
         for result_metric in self.result_metrics:
-            if result_metric.is_tensor:
-                result_metric.sync()
+            if result_metric.is_tensor and not result_metric._is_synced:
+                result_metric.sync(should_sync=not result_metric.meta.sync.rank_zero_only)
 
     def unsync(self) -> None:
         for result_metric in self.result_metrics: