Add pickle/cloudpickle regression tests for cuda.core objects (#1810)

Adds parametrized roundtrip tests covering both pickle and cloudpickle
for Device, ObjectCode, IPCBufferDescriptor, and IPCEventDescriptor.
These tests guard against the Cython @classmethod identity issue fixed
in #1660 (cloudpickle fails when __reduce__ references a @classmethod).

Closes #1671

Made-with: Cursor

Author: Andy-Jost

cuda_core/tests/test_object_protocols.py

@@ -1,10 +1,11 @@
 # SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 """
-Tests for Python object protocols (__eq__, __hash__, __weakref__, __repr__).
+Tests for Python object protocols (__eq__, __hash__, __weakref__, __repr__, pickle).
 
 This module tests that core cuda.core classes properly implement standard Python
-object protocols for identity, hashing, weak references, and string representation.
+object protocols for identity, hashing, weak references, string representation,
+and serialization.
 """
 
 import itertools
@@ -15,7 +16,17 @@
 from helpers.graph_kernels import compile_common_kernels
 from helpers.misc import try_create_condition
 
-from cuda.core import Buffer, Device, Kernel, LaunchConfig, Program, Stream, system
+from cuda.core import (
+    Buffer,
+    Device,
+    DeviceMemoryResource,
+    DeviceMemoryResourceOptions,
+    Kernel,
+    LaunchConfig,
+    Program,
+    Stream,
+    system,
+)
 from cuda.core._graph._graphdef import GraphDef
 from cuda.core._program import _can_load_generated_ptx
 
@@ -208,6 +219,30 @@ def sample_kernel_alt(sample_object_code_alt):
     return sample_object_code_alt.get_kernel("test_kernel_alt")
 
 
+# =============================================================================
+# Fixtures - IPC samples (for pickle tests)
+# =============================================================================
+
+POOL_SIZE = 2097152
+
+
+@pytest.fixture
+def sample_ipc_buffer_descriptor(ipc_device):
+    """An IPCBufferDescriptor."""
+    options = DeviceMemoryResourceOptions(max_size=POOL_SIZE, ipc_enabled=True)
+    mr = DeviceMemoryResource(ipc_device, options=options)
+    buf = mr.allocate(64)
+    return buf.get_ipc_descriptor()
+
+
+@pytest.fixture
+def sample_ipc_event_descriptor(ipc_device):
+    """An IPCEventDescriptor."""
+    stream = ipc_device.create_stream()
+    e = stream.record(options={"ipc_enabled": True})
+    return e.get_ipc_descriptor()
+
+
 # =============================================================================
 # Fixtures - Graph types (GraphDef and GraphNode)
 # =============================================================================
@@ -606,6 +641,20 @@ def sample_switch_node_alt(sample_graphdef):
     ("sample_kernel", lambda k: Kernel.from_handle(int(k.handle))),
 ]
 
+# Types with __reduce__ support (pickle/cloudpickle).
+# Event, Buffer, and memory resources are excluded: Event only supports
+# IPC-based serialization via multiprocessing reduction; Buffer and memory
+# resource __reduce__ use a cross-process registry that doesn't support
+# same-process roundtrips.
+PICKLE_TYPES = [
+    "sample_device",
+    "sample_object_code_cubin",
+    "sample_ipc_buffer_descriptor",
+    "sample_ipc_event_descriptor",
+]
+
+PICKLE_MODULES = ["pickle", "cloudpickle"]
+
 # Derived type groupings for collection tests
 DICT_KEY_TYPES = sorted(set(HASH_TYPES) & set(EQ_TYPES))
 WEAK_KEY_TYPES = sorted(set(HASH_TYPES) & set(EQ_TYPES) & set(WEAKREF_TYPES))
@@ -796,3 +845,18 @@ def test_repr_format(fixture_name, pattern, request):
     obj = request.getfixturevalue(fixture_name)
     result = repr(obj)
     assert re.fullmatch(pattern, result)
+
+
+# =============================================================================
+# Pickle tests
+# =============================================================================
+
+
+@pytest.mark.parametrize("pickle_module", PICKLE_MODULES)
+@pytest.mark.parametrize("fixture_name", PICKLE_TYPES)
+def test_pickle_roundtrip(fixture_name, pickle_module, request):
+    """Object survives a pickle/cloudpickle roundtrip."""
+    mod = pytest.importorskip(pickle_module)
+    obj = request.getfixturevalue(fixture_name)
+    result = mod.loads(mod.dumps(obj))
+    assert type(result) is type(obj)