Rate limit asyncio actor (#6242)

python/ray/async_compat.py

@@ -0,0 +1,13 @@
+"""
+This file should only be imported from Python 3.
+It will raise SyntaxError when importing from Python 2.
+"""
+
+
+def sync_to_async(func):
+    """Convert a blocking function to async function"""
+
+    async def wrapper(*args, **kwargs):
+        return func(*args, **kwargs)
+
+    return wrapper