Support placement_group=None in PlacementGroupSchedulingStrategy

doc/source/ray-core/gotchas.rst

@@ -3,11 +3,11 @@
 Ray Gotchas
 ===========
 
-Ray sometimes has some aspects of its behavior that might catch 
-users off guard. There may be sound arguments for these design choices. 
+Ray sometimes has some aspects of its behavior that might catch
+users off guard. There may be sound arguments for these design choices.
 
-In particular, users think of Ray as running on their local machine, and 
-while this is mostly true, this doesn't work. 
+In particular, users think of Ray as running on their local machine, and
+while this is mostly true, this doesn't work.
 
 Environment variables are not passed from the driver to workers
 ---------------------------------------------------------------
@@ -39,9 +39,9 @@ Filenames work sometimes and not at other times
 -----------------------------------------------
 
 **Issue**: If you reference a file by name in a task or actor,
-it will sometimes work and sometimes fail. This is 
-because if the task or actor runs on the head node 
-of the cluster, it will work, but if the task or actor 
+it will sometimes work and sometimes fail. This is
+because if the task or actor runs on the head node
+of the cluster, it will work, but if the task or actor
 runs on another machine it won't.
 
 **Example**: Let's say we do the following command:
@@ -50,7 +50,7 @@ runs on another machine it won't.
 
 	% touch /tmp/foo.txt
 
-And I have this code: 
+And I have this code:
 
 .. code-block:: python
 
@@ -61,15 +61,15 @@ And I have this code:
   def check_file():
     foo_exists = os.path.exists("/tmp/foo.txt")
     print(f"Foo exists? {foo_exists}")
-  
+
   futures = []
-  for _ in range(1000): 
+  for _ in range(1000):
     futures.append(check_file.remote())
 
   ray.get(futures)
 
 
-then you will get a mix of True and False. If 
+then you will get a mix of True and False. If
 ``check_file()`` runs on the head node, or we're running
 locally it works. But if it runs on a worker node, it returns ``False``.
 
@@ -78,7 +78,7 @@ It's the same code after all.
 
 **Fix**
 
-- Use only shared paths for such applications -- e.g. if you are using a network file system you can use that, or the files can be on s3. 
+- Use only shared paths for such applications -- e.g. if you are using a network file system you can use that, or the files can be on s3.
 - Do not rely on file path consistency.
 
 
@@ -87,10 +87,10 @@ Placement groups are not composable
 -----------------------------------
 
 **Issue**: If you have a task that is called from something that runs in a placement
-group, the resources are never allocated and it hangs. 
+group, the resources are never allocated and it hangs.
 
 **Example**: You are using Ray Tune which creates placement groups, and you want to
-apply it to an objective function, but that objective function makes use 
+apply it to an objective function, but that objective function makes use
 of Ray Tasks itself, e.g.
 
 .. code-block:: python
@@ -111,18 +111,18 @@ of Ray Tasks itself, e.g.
   tuner = tune.Tuner(objective, param_space={"a": 1})
   tuner.fit()
 
-This will error with message: 
-ValueError: Cannot schedule create_task_that_uses_resources.<locals>.sample_task with the placement group 
+This will error with message:
+ValueError: Cannot schedule create_task_that_uses_resources.<locals>.sample_task with the placement group
 because the resource request {'CPU': 10} cannot fit into any bundles for the placement group, [{'CPU': 1.0}].
 
 **Expected behavior**: The above executes.
 
 **Fix**: In the ``@ray.remote`` declaration of tasks
 called by ``create_task_that_uses_resources()`` , include a
-``placement_group=None``.
+``scheduling_strategy=PlacementGroupSchedulingStrategy(placement_group=None)``.
 
 .. code-block:: diff
 
   def create_task_that_uses_resources():
-  +     @ray.remote(num_cpus=10, placement_group=None)
+  +     @ray.remote(num_cpus=10, scheduling_strategy=PlacementGroupSchedulingStrategy(placement_group=None))
   -     @ray.remote(num_cpus=10)

python/ray/tests/test_placement_group_2.py

@@ -18,11 +18,7 @@
 )
 from ray.util.client.ray_client_helpers import connect_to_client_or_not
 from ray.util.placement_group import get_current_placement_group
-
-try:
-    import pytest_timeout
-except ImportError:
-    pytest_timeout = None
+from ray.util.scheduling_strategies import PlacementGroupSchedulingStrategy
 
 
 @ray.remote
@@ -376,7 +372,11 @@ def schedule_nested_actor(self):
 
             def schedule_nested_actor_outside_pg(self):
                 # Don't use placement group.
-                actor = NestedActor.options(placement_group=None).remote()
+                actor = NestedActor.options(
+                    scheduling_strategy=PlacementGroupSchedulingStrategy(
+                        placement_group=None
+                    )
+                ).remote()
                 ray.get(actor.ready.remote())
                 self.actors.append(actor)
 

python/ray/tests/test_scheduling_2.py

@@ -244,16 +244,6 @@ def func():
 
         func.options(scheduling_strategy="XXX").remote()
 
-    with pytest.raises(ValueError):
-
-        @ray.remote
-        def func():
-            return 0
-
-        func.options(
-            scheduling_strategy=PlacementGroupSchedulingStrategy(placement_group=None)
-        ).remote()
-
 
 @pytest.mark.parametrize("connect_to_client", [True, False])
 def test_node_affinity_scheduling_strategy(

python/ray/util/scheduling_strategies.py

@@ -30,11 +30,6 @@ def __init__(
         placement_group_bundle_index: int = -1,
         placement_group_capture_child_tasks: Optional[bool] = None,
     ):
-        if placement_group is None:
-            raise ValueError(
-                "placement_group needs to be an instance of PlacementGroup"
-            )
-
         self.placement_group = placement_group
         self.placement_group_bundle_index = placement_group_bundle_index
         self.placement_group_capture_child_tasks = placement_group_capture_child_tasks