Remove manual checkpoint() directory return value

Prior to this PR, a manual checkpoint() call returned the directory that the
checkpoint was written to.

This isn't really needed, so this PR removes it as part of removing cruft
around the checkpoint API, as part of refactoring towards pluggable
checkpointing.

The only use is in a test case, which this PR rewrites.

Author: benclifford

docs/userguide/workflows/checkpoints.rst

@@ -265,8 +265,7 @@ of the ``slow_double`` app.
     # Wait for the results
     [i.result() for i in d]
 
-    cpt_dir = dfk.checkpoint()
-    print(cpt_dir)  # Prints the checkpoint dir
+    dfk.checkpoint()
 
 
 Resuming from a checkpoint

parsl/dataflow/dflow.py

@@ -1267,7 +1267,7 @@ def cleanup(self) -> None:
         # should still see it.
         logger.info("DFK cleanup complete")
 
-    def checkpoint(self, tasks: Optional[Sequence[TaskRecord]] = None) -> str:
+    def checkpoint(self, tasks: Optional[Sequence[TaskRecord]] = None) -> None:
         """Checkpoint the dfk incrementally to a checkpoint file.
 
         When called, every task that has been completed yet not
@@ -1328,8 +1328,6 @@ def checkpoint(self, tasks: Optional[Sequence[TaskRecord]] = None) -> str:
             else:
                 logger.info("Done checkpointing {} tasks".format(count))
 
-            return checkpoint_dir
-
     @staticmethod
     def _log_std_streams(task_record: TaskRecord) -> None:
         tid = task_record['id']

parsl/tests/test_checkpointing/test_python_checkpoint_1.py

@@ -1,4 +1,5 @@
 import os
+from pathlib import Path
 
 import pytest
 
@@ -20,12 +21,14 @@ def uuid_app():
 
 
 @pytest.mark.local
-def test_initial_checkpoint_write():
+def test_initial_checkpoint_write() -> None:
     """1. Launch a few apps and write the checkpoint once a few have completed
     """
     uuid_app().result()
 
-    cpt_dir = parsl.dfk().checkpoint()
+    parsl.dfk().checkpoint()
 
-    cptpath = cpt_dir + '/tasks.pkl'
+    cpt_dir = Path(parsl.dfk().run_dir) / 'checkpoint'
+
+    cptpath = cpt_dir / 'tasks.pkl'
     assert os.path.exists(cptpath), f"Tasks checkpoint missing: {cptpath}"