chore: import upstream snapshot with attribution

doc/source/cluster/doc_code/yarn/example.py

@@ -0,0 +1,50 @@
+import sys
+import time
+from collections import Counter
+
+import ray
+
+
+@ray.remote
+def get_host_name(x):
+    import platform
+    import time
+
+    time.sleep(0.01)
+    return x + (platform.node(),)
+
+
+def wait_for_nodes(expected):
+    # Wait for all nodes to join the cluster.
+    while True:
+        num_nodes = len(ray.nodes())
+        if num_nodes < expected:
+            print(
+                "{} nodes have joined so far, waiting for {} more.".format(
+                    num_nodes, expected - num_nodes
+                )
+            )
+            sys.stdout.flush()
+            time.sleep(1)
+        else:
+            break
+
+
+def main():
+    wait_for_nodes(4)
+
+    # Check that objects can be transferred from each node to each other node.
+    for i in range(10):
+        print("Iteration {}".format(i))
+        results = [get_host_name.remote(get_host_name.remote(())) for _ in range(100)]
+        print(Counter(ray.get(results)))
+        sys.stdout.flush()
+
+    print("Success!")
+    sys.stdout.flush()
+    time.sleep(20)
+
+
+if __name__ == "__main__":
+    ray.init(address="localhost:6379")
+    main()