fix: support zero sized allocation

cuda_core/cuda/core/_memory/_legacy.py

@@ -46,8 +46,11 @@ def allocate(self, size, stream=None) -> Buffer:
             from cuda.core._stream import default_stream
 
             stream = default_stream()
-        err, ptr = driver.cuMemAllocHost(size)
-        raise_if_driver_error(err)
+        if size:
+            err, ptr = driver.cuMemAllocHost(size)
+            raise_if_driver_error(err)
+        else:
+            ptr = 0
         return Buffer._init(ptr, size, self, stream)
 
     def deallocate(self, ptr: DevicePointerT, size, stream):
@@ -64,8 +67,10 @@ def deallocate(self, ptr: DevicePointerT, size, stream):
         """
         if stream is not None:
             stream.sync()
-        (err,) = driver.cuMemFreeHost(ptr)
-        raise_if_driver_error(err)
+
+        if size:
+            (err,) = driver.cuMemFreeHost(ptr)
+            raise_if_driver_error(err)
 
     @property
     def is_device_accessible(self) -> bool:
@@ -96,15 +101,19 @@ def allocate(self, size, stream=None) -> Buffer:
             from cuda.core._stream import default_stream
 
             stream = default_stream()
-        err, ptr = driver.cuMemAlloc(size)
-        raise_if_driver_error(err)
+        if size:
+            err, ptr = driver.cuMemAlloc(size)
+            raise_if_driver_error(err)
+        else:
+            ptr = 0
         return Buffer._init(ptr, size, self, stream)
 
     def deallocate(self, ptr, size, stream):
         if stream is not None:
             stream.sync()
-        (err,) = driver.cuMemFree(ptr)
-        raise_if_driver_error(err)
+        if size:
+            (err,) = driver.cuMemFree(ptr)
+            raise_if_driver_error(err)
 
     @property
     def is_device_accessible(self) -> bool:

cuda_core/tests/test_device.py

@@ -47,6 +47,16 @@ def test_device_alloc(deinit_cuda):
     assert buffer.device_id == int(device)
 
 
+def test_device_alloc_zero_bytes(deinit_cuda):
+    device = Device()
+    device.set_current()
+    buffer = device.allocate(0)
+    device.sync()
+    assert buffer.handle >= 0
+    assert buffer.size == 0
+    assert buffer.device_id == int(device)
+
+
 def test_device_id(deinit_cuda):
     for device in Device.get_all_devices():
         device.set_current()

cuda_core/tests/test_graph_mem.py

@@ -182,6 +182,23 @@ def test_graph_alloc_with_output(mempool_device, mode):
     assert compare_buffer_to_constant(out, 6)
 
 
+@pytest.mark.parametrize("mode", ["global", "thread_local", "relaxed"])
+def test_graph_mem_alloc_zero(mempool_device, mode):
+    device = mempool_device
+    gb = device.create_graph_builder().begin_building(mode)
+    stream = device.create_stream()
+    gmr = GraphMemoryResource(device)
+    buffer = gmr.allocate(0, stream=gb)
+    graph = gb.end_building().complete()
+    graph.upload(stream)
+    graph.launch(stream)
+    stream.sync()
+
+    assert buffer.handle >= 0
+    assert buffer.size == 0
+    assert buffer.device_id == int(device)
+
+
 @pytest.mark.parametrize("mode", ["global", "thread_local", "relaxed"])
 def test_graph_mem_set_attributes(mempool_device, mode):
     device = mempool_device

cuda_core/tests/test_memory.py

@@ -1240,3 +1240,28 @@ def test_graph_memory_resource_object(init_cuda):
     # These objects are interned.
     assert gmr1 is gmr2 is gmr3
     assert gmr1 == gmr2 == gmr3
+
+
+def test_memory_resource_alloc_zero_bytes(init_cuda, memory_resource_factory):
+    MR, MROps = memory_resource_factory
+
+    device = Device()
+    device.set_current()
+
+    if MR is DeviceMemoryResource and not device.properties.memory_pools_supported:
+        pytest.skip("Device does not support mempool operations")
+    elif MR is PinnedMemoryResource:
+        skip_if_pinned_memory_unsupported(device)
+        mr = MR()
+    elif MR is ManagedMemoryResource:
+        skip_if_managed_memory_unsupported(device)
+        mr = create_managed_memory_resource_or_skip(MROps(preferred_location=device.device_id))
+    else:
+        assert MR is DeviceMemoryResource
+        mr = MR(device)
+
+    buffer = mr.allocate(0)
+    device.sync()
+    assert buffer.handle >= 0
+    assert buffer.size == 0
+    assert buffer.device_id == mr.device_id