Test of sizeof proxy object (#774)

Adding test of `sizeof` of `ProxyObject` motivated by rapidsai/cudf#9544, which change the `__sizeof__` semantic of cudf.  
As far as I can see, `ProxyObject` should continue working after rapidsai/cudf#9544 has been merged.

Authors:
  - Mads R. B. Kristensen (https://github.com/madsbk)

Approvers:
  - Benjamin Zaitlen (https://github.com/quasiben)

URL: #774

dask_cuda/proxy_object.py

@@ -513,7 +513,7 @@ def __class__(self):
 
     @_pxy_cache_wrapper("sizeof")
     def __sizeof__(self):
-        """Returns either the size of the proxied object
+        """Returns the size of the proxy object (serialized or not)
 
         Notice, we cache the result even though the size of proxied object
         when serialized or not serialized might slightly differ.
@@ -523,7 +523,7 @@ def __sizeof__(self):
             _, frames = pxy.obj
             return sum(map(distributed.utils.nbytes, frames))
         else:
-            return sizeof(self._pxy_deserialize())
+            return sizeof(pxy.obj)
 
     def __len__(self):
         pxy = self._pxy_get(copy=True)

dask_cuda/tests/test_proxy.py

@@ -10,6 +10,7 @@
 import dask
 import dask.array
 from dask.dataframe.core import has_parallel_type
+from dask.sizeof import sizeof
 from distributed import Client
 from distributed.protocol.serialize import deserialize, serialize
 
@@ -578,3 +579,32 @@ def test_cudf_fillna():
     df = cudf.DataFrame({"A": range(10)})
     df = proxify_device_objects(df)
     df = df.fillna(0)
+
+
+def test_sizeof_cupy():
+    cupy = pytest.importorskip("cupy")
+    cupy.cuda.set_allocator(None)
+    a = cupy.arange(1e7)
+    a_size = sizeof(a)
+    pxy = proxy_object.asproxy(a)
+    assert a_size == pytest.approx(sizeof(pxy))
+    pxy._pxy_serialize(serializers=("dask",))
+    assert a_size == pytest.approx(sizeof(pxy))
+    assert pxy._pxy_get().is_serialized()
+    pxy._pxy_cache = {}
+    assert a_size == pytest.approx(sizeof(pxy))
+    assert pxy._pxy_get().is_serialized()
+
+
+def test_sizeof_cudf():
+    cudf = pytest.importorskip("cudf")
+    a = cudf.datasets.timeseries().reset_index()
+    a_size = sizeof(a)
+    pxy = proxy_object.asproxy(a)
+    assert a_size == pytest.approx(sizeof(pxy))
+    pxy._pxy_serialize(serializers=("dask",))
+    assert a_size == pytest.approx(sizeof(pxy))
+    assert pxy._pxy_get().is_serialized()
+    pxy._pxy_cache = {}
+    assert a_size == pytest.approx(sizeof(pxy))
+    assert pxy._pxy_get().is_serialized()