Removing the FrameProxyObject workaround (#751)

Adding testing of cudf dataframe copy, which fails prior to rapidsai/cudf#9397

#### UPDATE: This PR now handles the jit-unspill failures we have been seeing with cudf v21.12.

Some background, when we introduced `ProxyObject`, cudf was using `cudf._lib.table.Table` as the base class for all frame-like objects (dataframes, series, etc). `Table` was implemented in cython so our proxy object had to derive from `Table` in order to support cython functions. The result was to use the class `FrameProxyObject` as a workaround:
```python
    # In order to support the cuDF API implemented in Cython, we inherit from
    # `cudf._lib.table.Table`, which is the base class of Index, Series, and
    # Dataframes in cuDF.
    # Notice, the order of base classes matters. Since ProxyObject is the first
    # base class, ProxyObject.__init__() is called on creation, which doesn't
    # define the Table._data and Table._index attributes. Thus, accessing
    # FrameProxyObject._data and FrameProxyObject._index is pass-through to
    # ProxyObejct.__getattr__(), which is what we want.
    class FrameProxyObject(ProxyObject, cudf._lib.table.Table):
        pass
```
Now that cudf uses `Frame`, a pure Python class, we don't need this workaround anymore. In fact, using `FrameProxyObject` triggers some infinite recursion errors when used together with v21.12+

cc. @randerzander

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

Approvers:
  - Peter Andreas Entschev (https://github.com/pentschev)

URL: #751

dask_cuda/proxify_device_objects.py

@@ -225,38 +225,19 @@ def proxify_device_object_python_dict(
 def _register_cudf():
     import cudf
 
-    try:
-        # In v21.12, cuDF removed Table in favor of Frame as base class
-        from cudf._lib.table import Table as Frame
-    except ImportError:
-        from cudf.core.frame import Frame
-
-    # In order to support the cuDF API implemented in Cython, we inherit from
-    # `cudf.core.frame.Frame`, which is the base class of Index, Series, and
-    # Dataframes in cuDF.
-    # Notice, the order of base classes matters. Since ProxyObject is the first
-    # base class, ProxyObject.__init__() is called on creation, which doesn't
-    # define the Frame._data and Frame._index attributes. Thus, accessing
-    # FrameProxyObject._data and FrameProxyObject._index is pass-through to
-    # ProxyObejct.__getattr__(), which is what we want.
-    class FrameProxyObject(ProxyObject, Frame):
-        pass
-
     @dispatch.register(cudf.DataFrame)
     @dispatch.register(cudf.Series)
     @dispatch.register(cudf.BaseIndex)
     def proxify_device_object_cudf_dataframe(
         obj, proxied_id_to_proxy, found_proxies, excl_proxies
     ):
-        return proxify(
-            obj, proxied_id_to_proxy, found_proxies, subclass=FrameProxyObject
-        )
+        return proxify(obj, proxied_id_to_proxy, found_proxies)
 
     try:
         from dask.array.dispatch import percentile_lookup
 
         from dask_cudf.backends import percentile_cudf
 
-        percentile_lookup.register(FrameProxyObject, percentile_cudf)
+        percentile_lookup.register(ProxyObject, percentile_cudf)
     except ImportError:
         pass

dask_cuda/tests/test_proxify_host_file.py

@@ -181,7 +181,7 @@ def task(x):
         assert isinstance(x, cudf.DataFrame)
         if jit_unspill:
             # Check that `x` is a proxy object and the proxied DataFrame is serialized
-            assert "FrameProxyObject" in str(type(x))
+            assert "ProxyObject" in str(type(x))
             assert x._obj_pxy["serializer"] == "dask"
         else:
             assert type(x) == cudf.DataFrame

dask_cuda/tests/test_proxy.py

@@ -285,7 +285,7 @@ def task(x):
         assert isinstance(x, cudf.DataFrame)
         if jit_unspill:
             # Check that `x` is a proxy object and the proxied DataFrame is serialized
-            assert "FrameProxyObject" in str(type(x))
+            assert "ProxyObject" in str(type(x))
             assert x._obj_pxy["serializer"] == "dask"
         else:
             assert type(x) == cudf.DataFrame
@@ -569,3 +569,18 @@ def test_array_ufucn_proxified_object(np_func):
     actual = np_func(proxy_obj, np_array)
 
     assert_series_equal(expected.to_pandas(), actual.to_pandas())
+
+
+def test_cudf_copy():
+    cudf = pytest.importorskip("cudf")
+    df = cudf.DataFrame({"A": range(10)})
+    df = proxify_device_objects(df)
+    cpy = df.copy()
+    assert_frame_equal(cpy.to_pandas(), df.to_pandas())
+
+
+def test_cudf_fillna():
+    cudf = pytest.importorskip("cudf")
+    df = cudf.DataFrame({"A": range(10)})
+    df = proxify_device_objects(df)
+    df = df.fillna(0)