fix: support zero-sized arrays as input to StridedMemoryView.from_cuda_array_interface (#1397)

* test: add failing test case for zero-sized array input to `StridedMemoryView.from_cuda_array_interface`

* fix: only pluck out device id if the data buffer pointer coming from CAI is valid

* chore: set zero-sized array device to the current device

* docs: add note about changes

* docs: clarify

Author: cpcloud

cuda_core/cuda/core/_memoryview.pyx

@@ -582,10 +582,13 @@ cpdef StridedMemoryView view_as_cai(obj, stream_ptr, view=None):
     buf.dl_tensor = NULL
     buf.ptr, buf.readonly = cai_data["data"]
     buf.is_device_accessible = True
-    buf.device_id = handle_return(
-        driver.cuPointerGetAttribute(
-            driver.CUpointer_attribute.CU_POINTER_ATTRIBUTE_DEVICE_ORDINAL,
-            buf.ptr))
+    if buf.ptr != 0:
+        buf.device_id = handle_return(
+            driver.cuPointerGetAttribute(
+                driver.CUpointer_attribute.CU_POINTER_ATTRIBUTE_DEVICE_ORDINAL,
+                buf.ptr))
+    else:
+        buf.device_id = handle_return(driver.cuCtxGetDevice())
 
     cdef intptr_t producer_s, consumer_s
     stream_ptr = int(stream_ptr)

cuda_core/docs/source/release/0.5.0-notes.rst

@@ -61,6 +61,7 @@ None.
 Fixes and enhancements
 ----------------------
 
+- Zero-size arrays are now supported as inputs when constructing ``StridedMemoryView``.
 - Most CUDA resources can be hashed now.
 - Python ``bool`` objects are now converted to C++ ``bool`` type when passed as kernel arguments (previously converted to ``int``).
 - Restored v0.3.x :class:`MemoryResource` behaviors and missing MR attributes for backward compatibility.

cuda_core/tests/test_utils.py

@@ -413,3 +413,23 @@ def test_view_sliced_external_negative_offset(stride_order, view_as):
     assert sliced_view._layout.itemsize == a_sliced.itemsize == layout.itemsize
     assert sliced_view.shape == a_sliced.shape
     assert sliced_view._layout.strides_in_bytes == a_sliced.strides
+
+
+@pytest.mark.parametrize(
+    "api",
+    [
+        StridedMemoryView.from_dlpack,
+        StridedMemoryView.from_cuda_array_interface,
+    ],
+)
+@pytest.mark.parametrize("shape", [(0,), (0, 0), (0, 0, 0)])
+@pytest.mark.parametrize("dtype", [np.int64, np.uint8, np.float64])
+def test_view_zero_size_array(api, shape, dtype):
+    cp = pytest.importorskip("cupy")
+
+    x = cp.empty(shape, dtype=dtype)
+    smv = api(x, stream_ptr=0)
+
+    assert smv.size == 0
+    assert smv.shape == shape
+    assert smv.dtype == np.dtype(dtype)