[Placement Group] Support Placement Group state table. (#10090)

* Done.

* Addressed code review.

* Linting.

* Fix lint.

* Fix lint.

* Fix a test.

* Lint.

* Add a lint sleep to test.

* Fix the lint issue.

* Fixed doc build error.

python/ray/tests/test_placement_group.py

@@ -219,6 +219,47 @@ def test_placement_group_hang(ray_start_cluster):
     assert "CPU_group_" in list(resources.keys())[0], resources
 
 
+def test_placement_group_table(ray_start_cluster):
+    @ray.remote(num_cpus=2)
+    class Actor(object):
+        def __init__(self):
+            self.n = 0
+
+        def value(self):
+            return self.n
+
+    cluster = ray_start_cluster
+    num_nodes = 2
+    for _ in range(num_nodes):
+        cluster.add_node(num_cpus=4)
+    ray.init(address=cluster.address)
+
+    # Originally placement group creation should be pending because
+    # there are no resources.
+    name = "name"
+    strategy = "PACK"
+    bundles = [{"CPU": 2, "GPU": 1}, {"CPU": 2}]
+    placement_group_id = ray.experimental.placement_group(
+        name=name, strategy=strategy, bundles=bundles)
+    result = ray.experimental.placement_group_table(placement_group_id)
+    assert result["name"] == name
+    assert result["strategy"] == strategy
+    for i in range(len(bundles)):
+        assert bundles[i] == result["bundles"][i]
+    assert result["state"] == "PENDING"
+
+    # Now the placement group should be scheduled.
+    cluster.add_node(num_cpus=5, num_gpus=1)
+    cluster.wait_for_nodes()
+    actor_1 = Actor.options(
+        placement_group_id=placement_group_id,
+        placement_group_bundle_index=0).remote()
+    ray.get(actor_1.value.remote())
+
+    result = ray.experimental.placement_group_table(placement_group_id)
+    assert result["state"] == "ALIVE"
+
+
 def test_cuda_visible_devices(ray_start_cluster):
     @ray.remote(num_gpus=1)
     def f():