fix(samples): respect CUDA_VISIBLE_DEVICES in multi-GPU cuda.core samples

cuda_core/tests/example_tests/test_sample_verification.py

@@ -99,6 +99,20 @@ def test_unsupported_core_sample_paths_return_waiver(
     assert len(waiver_returns) == 1
 
 
+@pytest.mark.parametrize("sample_name", ("simpleP2P", "simpleMultiGpu", "multiGPUGradientAverage"))
+@pytest.mark.agent_authored(model="gpt-6")
+def test_multi_gpu_samples_count_cuda_visible_devices(sample_name: str) -> None:
+    sample_path = REPO_ROOT / "samples" / "cuda_core" / sample_name / f"{sample_name}.py"
+    tree = ast.parse(sample_path.read_text(encoding="utf-8"), filename=str(sample_path))
+    expected_count = ast.parse("len(Device.get_all_devices())", mode="eval").body
+
+    assert any(ast.dump(node) == ast.dump(expected_count) for node in ast.walk(tree))
+    assert not any(
+        isinstance(node, ast.Call) and isinstance(node.func, ast.Attribute) and node.func.attr == "get_num_devices"
+        for node in ast.walk(tree)
+    )
+
+
 @pytest.mark.agent_authored(model="gpt-5")
 def test_verify_array_result_or_raise_enforces_match(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.syspath_prepend(str(UTILITIES_DIR))

samples/cuda_core/multiGPUGradientAverage/multiGPUGradientAverage.py

@@ -77,7 +77,6 @@
         Program,
         ProgramOptions,
         launch,
-        system,
     )
 except ImportError as e:
     print(f"Error: Required package not found: {e}")
@@ -103,7 +102,7 @@ def init_device(rank: int):
     tuple[Device, Stream]
         CUDA device object and stream object.
     """
-    num_gpus = system.get_num_devices()
+    num_gpus = len(Device.get_all_devices())
     if num_gpus == 0:
         raise RuntimeError("No CUDA devices available")
 

samples/cuda_core/simpleMultiGpu/README.md

@@ -33,7 +33,7 @@ input buffers, so the kernels see fully-materialized data.
 
 ### From `cuda.core`
 
-- `system.get_num_devices()` - count of visible CUDA devices
+- `len(Device.get_all_devices())` - count of devices visible to the CUDA runtime, respecting `CUDA_VISIBLE_DEVICES`
 - `Device(device_id)` / `Device.set_current()` - select and activate a device
 - `Device.create_stream()` - create a `cuda.core` stream on the current device
 - `Device.create_stream(adaptor)` - wrap a foreign stream via the `__cuda_stream__` protocol

samples/cuda_core/simpleMultiGpu/simpleMultiGpu.py

@@ -55,7 +55,7 @@
 try:
     import cupy as cp
 
-    from cuda.core import Device, LaunchConfig, Program, ProgramOptions, launch, system
+    from cuda.core import Device, LaunchConfig, Program, ProgramOptions, launch
 except ImportError as e:
     print(f"Error: Required package not found: {e}")
     print("Please install from requirements.txt:")
@@ -117,7 +117,7 @@ def _compile(device, source):
 
 
 def main():
-    num_devices = system.get_num_devices()
+    num_devices = len(Device.get_all_devices())
     if num_devices < 2:
         print(
             f"This sample requires at least 2 CUDA-capable devices (found {num_devices}). Waiving.",

samples/cuda_core/simpleP2P/README.md

@@ -6,7 +6,7 @@ This sample demonstrates peer-to-peer (P2P) memory access between multiple GPUs
 
 ## What you will learn
 
-- How to detect multiple CUDA-capable GPUs using `system.get_num_devices()` and `Device(id)`
+- How to detect CUDA-visible GPUs using `len(Device.get_all_devices())` and `Device(id)`
 - How to check P2P capability between GPU pairs using `device.can_access_peer()`
 - How to enable and disable peer access using `DeviceMemoryResource.peer_accessible_by`
 - How to allocate device memory on specific GPUs using `DeviceMemoryResource`
@@ -26,8 +26,7 @@ This sample demonstrates peer-to-peer (P2P) memory access between multiple GPUs
 ## Key APIs
 
 **From cuda.core:**
-- `system` – Pre-instantiated singleton for system-level CUDA information
-- `system.get_num_devices()` – Get number of CUDA-capable devices
+- `Device.get_all_devices()` – Get the CUDA-visible devices, respecting `CUDA_VISIBLE_DEVICES`
 - `Device(id)` – Get specific CUDA device handle
 - `device.can_access_peer(peer)` – Check if this device can access peer device memory
 - `device.set_current()` – Set active device for subsequent operations

samples/cuda_core/simpleP2P/simpleP2P.py

@@ -45,7 +45,6 @@
         Program,
         ProgramOptions,
         launch,
-        system,
     )
 except ImportError as e:
     print(f"Error: Required package not found: {e}")
@@ -99,8 +98,8 @@ def run(num_elements=1024 * 1024 * 16):
 
     # Check for multiple GPUs
     print("\nChecking for multiple GPUs...")
-    num_devices = system.get_num_devices()
-    print(f"CUDA-capable device count: {num_devices}")
+    num_devices = len(Device.get_all_devices())
+    print(f"CUDA-visible device count: {num_devices}")
 
     if num_devices < 2:
         print("Two or more GPUs with Peer-to-Peer access capability are required, waiving this sample.")