[Serve] Make handle serializable (#22473)

python/ray/serve/handle.py

@@ -169,14 +169,19 @@ async def remote(self, *args, **kwargs):
     def __repr__(self):
         return f"{self.__class__.__name__}" f"(deployment='{self.deployment_name}')"
 
+    @classmethod
+    def _deserialize(cls, kwargs):
+        """Required for this class's __reduce__ method to be picklable."""
+        return cls(**kwargs)
+
     def __reduce__(self):
         serialized_data = {
             "controller_handle": self.controller_handle,
             "deployment_name": self.deployment_name,
             "handle_options": self.handle_options,
             "_internal_pickled_http_request": self._pickled_http_request,
         }
-        return lambda kwargs: RayServeHandle(**kwargs), (serialized_data,)
+        return RayServeHandle._deserialize, (serialized_data,)
 
     def __getattr__(self, name):
         return self.options(method_name=name)
@@ -228,4 +233,4 @@ def __reduce__(self):
             "handle_options": self.handle_options,
             "_internal_pickled_http_request": self._pickled_http_request,
         }
-        return lambda kwargs: RayServeSyncHandle(**kwargs), (serialized_data,)
+        return RayServeSyncHandle._deserialize, (serialized_data,)

python/ray/serve/tests/test_handle.py

@@ -46,6 +46,31 @@ def task(handle):
     assert ray.get(result_ref) == "hello"
 
 
+def test_handle_serializable_in_deployment_init(serve_instance):
+    """Test that a handle can be passed into a constructor (#22110)"""
+
+    @serve.deployment
+    class RayServer1:
+        def __init__(self):
+            pass
+
+        def __call__(self, *args):
+            return {"count": self.count}
+
+    @serve.deployment
+    class RayServer2:
+        def __init__(self, handle):
+            self.handle = handle
+
+        def __call__(self, *args):
+            return {"count": self.count}
+
+    RayServer1.deploy()
+    for sync in [True, False]:
+        rs1_handle = RayServer1.get_handle(sync=sync)
+        RayServer2.deploy(rs1_handle)
+
+
 def test_sync_handle_in_thread(serve_instance):
     @serve.deployment
     def f():