[REVIEW] Change ways to access ptr in Buffer

docs/cudf/source/developer_guide/library_design.md

@@ -236,13 +236,11 @@ Spilling consists of two components:
   - A spill manager that tracks all instances of `SpillableBuffer` and spills them on demand.
 A global spill manager is used throughout cudf when spilling is enabled, which makes `as_buffer()` return `SpillableBuffer` instead of the default `Buffer` instances.
 
-Accessing `Buffer.ptr`, we get the device memory pointer of the buffer. This is unproblematic in the case of `Buffer` but what happens when accessing `SpillableBuffer.ptr`, which might have spilled its device memory. In this case, `SpillableBuffer` needs to unspill the memory before returning its device memory pointer. Furthermore, while this device memory pointer is being used (or could be used), `SpillableBuffer`  cannot spill its memory back to host memory because doing so would invalidate the device pointer.
+Accessing `Buffer.get_ptr(...)`, we get the device memory pointer of the buffer. This is unproblematic in the case of `Buffer` but what happens when accessing `SpillableBuffer.get_ptr(...)`, which might have spilled its device memory. In this case, `SpillableBuffer` needs to unspill the memory before returning its device memory pointer. Furthermore, while this device memory pointer is being used (or could be used), `SpillableBuffer` cannot spill its memory back to host memory because doing so would invalidate the device pointer.
 
 To address this, we mark the `SpillableBuffer` as unspillable, we say that the buffer has been _exposed_. This can either be permanent if the device pointer is exposed to external projects or temporary while `libcudf` accesses the device memory.
 
-The `SpillableBuffer.get_ptr()` returns the device pointer of the buffer memory just like `.ptr` but if given an instance of `SpillLock`, the buffer is only unspillable as long as the instance of `SpillLock` is alive.
-
-For convenience, one can use the decorator/context `acquire_spill_lock` to associate a `SpillLock` with a lifetime bound to the context automatically.
+The `SpillableBuffer.get_ptr(...)` returns the device pointer of the buffer memory but if called within an `acquire_spill_lock` decorator/context, the buffer is only marked unspillable while running within the decorator/context.
 
 #### Statistics
 cuDF supports spilling statistics, which can be very useful for performance profiling and to identify code that renders buffers unspillable.

python/cudf/cudf/_lib/column.pyi

@@ -52,8 +52,6 @@ class Column:
     @property
     def base_mask(self) -> Optional[Buffer]: ...
     @property
-    def base_mask_ptr(self) -> int: ...
-    @property
     def mask(self) -> Optional[Buffer]: ...
     @property
     def mask_ptr(self) -> int: ...

python/cudf/cudf/_lib/column.pyx

@@ -101,7 +101,7 @@ cdef class Column:
         if self.data is None:
             return 0
         else:
-            return self.data.ptr
+            return self.data.get_ptr(mode="write")
 
     def set_base_data(self, value):
         if value is not None and not isinstance(value, Buffer):
@@ -124,13 +124,6 @@ cdef class Column:
     def base_mask(self):
         return self._base_mask
 
-    @property
-    def base_mask_ptr(self):
-        if self.base_mask is None:
-            return 0
-        else:
-            return self.base_mask.ptr
-
     @property
     def mask(self):
         if self._mask is None:
@@ -145,7 +138,7 @@ cdef class Column:
         if self.mask is None:
             return 0
         else:
-            return self.mask.ptr
+            return self.mask.get_ptr(mode="write")
 
     def set_base_mask(self, value):
         """
@@ -206,7 +199,7 @@ cdef class Column:
         elif hasattr(value, "__cuda_array_interface__"):
             if value.__cuda_array_interface__["typestr"] not in ("|i1", "|u1"):
                 if isinstance(value, Column):
-                    value = value.data_array_view
+                    value = value.data_array_view(mode="write")
                 value = cp.asarray(value).view('|u1')
             mask = as_buffer(value)
             if mask.size < required_num_bytes:
@@ -329,10 +322,10 @@ cdef class Column:
 
         if col.base_data is None:
             data = NULL
-        elif isinstance(col.base_data, SpillableBuffer):
-            data = <void*><uintptr_t>(col.base_data).get_ptr()
         else:
-            data = <void*><uintptr_t>(col.base_data.ptr)
+            data = <void*><uintptr_t>(col.base_data.get_ptr(
+                mode="write")
+            )
 
         cdef Column child_column
         if col.base_children:
@@ -341,7 +334,9 @@ cdef class Column:
 
         cdef libcudf_types.bitmask_type* mask
         if self.nullable:
-            mask = <libcudf_types.bitmask_type*><uintptr_t>(self.base_mask_ptr)
+            mask = <libcudf_types.bitmask_type*><uintptr_t>(
+                self.base_mask.get_ptr(mode="write")
+            )
         else:
             mask = NULL
 
@@ -387,10 +382,8 @@ cdef class Column:
 
         if col.base_data is None:
             data = NULL
-        elif isinstance(col.base_data, SpillableBuffer):
-            data = <void*><uintptr_t>(col.base_data).get_ptr()
         else:
-            data = <void*><uintptr_t>(col.base_data.ptr)
+            data = <void*><uintptr_t>(col.base_data.get_ptr(mode="read"))
 
         cdef Column child_column
         if col.base_children:
@@ -399,7 +392,9 @@ cdef class Column:
 
         cdef libcudf_types.bitmask_type* mask
         if self.nullable:
-            mask = <libcudf_types.bitmask_type*><uintptr_t>(self.base_mask_ptr)
+            mask = <libcudf_types.bitmask_type*><uintptr_t>(
+                self.base_mask.get_ptr(mode="read")
+            )
         else:
             mask = NULL
 
@@ -549,7 +544,8 @@ cdef class Column:
                             f"{data_owner} is spilled, which invalidates "
                             f"the exposed data_ptr ({hex(data_ptr)})"
                         )
-                    data_owner.ptr  # accessing the pointer marks it exposed.
+                    # accessing the pointer marks it exposed permanently.
+                    data_owner.mark_exposed()
         else:
             data = as_buffer(
                 rmm.DeviceBuffer(ptr=data_ptr, size=0)

python/cudf/cudf/_lib/copying.pyx

@@ -1,4 +1,4 @@
-# Copyright (c) 2020-2022, NVIDIA CORPORATION.
+# Copyright (c) 2020-2023, NVIDIA CORPORATION.
 
 import pickle
 
@@ -765,7 +765,7 @@ cdef class _CPackedColumns:
         gpu_data = Buffer.deserialize(header["data"], frames)
 
         dbuf = DeviceBuffer(
-            ptr=gpu_data.ptr,
+            ptr=gpu_data.get_ptr(mode="write"),
             size=gpu_data.nbytes
         )
 

python/cudf/cudf/_lib/transform.pyx

@@ -62,7 +62,9 @@ def mask_to_bools(object mask_buffer, size_type begin_bit, size_type end_bit):
     if not isinstance(mask_buffer, cudf.core.buffer.Buffer):
         raise TypeError("mask_buffer is not an instance of "
                         "cudf.core.buffer.Buffer")
-    cdef bitmask_type* bit_mask = <bitmask_type*><uintptr_t>(mask_buffer.ptr)
+    cdef bitmask_type* bit_mask = <bitmask_type*><uintptr_t>(
+        mask_buffer.get_ptr(mode="read")
+    )
 
     cdef unique_ptr[column] result
     with nogil:

python/cudf/cudf/core/buffer/buffer.py

@@ -176,7 +176,9 @@ def _getitem(self, offset: int, size: int) -> Buffer:
         """
         return self._from_device_memory(
             cuda_array_interface_wrapper(
-                ptr=self.ptr + offset, size=size, owner=self.owner
+                ptr=self.get_ptr(mode="read") + offset,
+                size=size,
+                owner=self.owner,
             )
         )
 
@@ -202,11 +204,6 @@ def nbytes(self) -> int:
         """Size of the buffer in bytes."""
         return self._size
 
-    @property
-    def ptr(self) -> int:
-        """Device pointer to the start of the buffer."""
-        return self._ptr
-
     @property
     def owner(self) -> Any:
         """Object owning the memory of the buffer."""
@@ -215,18 +212,74 @@ def owner(self) -> Any:
     @property
     def __cuda_array_interface__(self) -> Mapping:
         """Implementation of the CUDA Array Interface."""
+        return self._get_cuda_array_interface(readonly=False)
+
+    def _get_cuda_array_interface(self, readonly=False):
+        """Helper function to create a CUDA Array Interface.
+
+        Parameters
+        ----------
+        readonly : bool, default False
+            If True, returns a CUDA Array Interface with
+            readonly flag set to True.
+            If False, returns a CUDA Array Interface with
+            readonly flag set to False.
+
+        Returns
+        -------
+        dict
+        """
         return {
-            "data": (self.ptr, False),
+            "data": (
+                self.get_ptr(mode="read" if readonly else "write"),
+                readonly,
+            ),
             "shape": (self.size,),
             "strides": None,
             "typestr": "|u1",
             "version": 0,
         }
 
+    @property
+    def _readonly_proxy_cai_obj(self):
+        """
+        Returns a proxy object with a read-only CUDA Array Interface.
+        """
+        return cuda_array_interface_wrapper(
+            ptr=self.get_ptr(mode="read"),
+            size=self.size,
+            owner=self,
+            readonly=True,
+            typestr="|u1",
+            version=0,
+        )
+
+    def get_ptr(self, *, mode) -> int:
+        """Device pointer to the start of the buffer.
+
+        Parameters
+        ----------
+        mode : str
+            Supported values are {"read", "write"}
+            If "write", the data pointed to may be modified
+            by the caller. If "read", the data pointed to
+            must not be modified by the caller.
+            Failure to fulfill this contract will cause
+            incorrect behavior.
+
+
+        See Also
+        --------
+        SpillableBuffer.get_ptr
+        """
+        return self._ptr
+
     def memoryview(self) -> memoryview:
         """Read-only access to the buffer through host memory."""
         host_buf = host_memory_allocation(self.size)
-        rmm._lib.device_buffer.copy_ptr_to_host(self.ptr, host_buf)
+        rmm._lib.device_buffer.copy_ptr_to_host(
+            self.get_ptr(mode="read"), host_buf
+        )
         return memoryview(host_buf).toreadonly()
 
     def serialize(self) -> Tuple[dict, list]:

python/cudf/cudf/core/buffer/spillable_buffer.py

@@ -145,7 +145,7 @@ def __len__(self):
 
     def __getitem__(self, i):
         if i == 0:
-            return self._buf.ptr
+            return self._buf.get_ptr(mode="write")
         elif i == 1:
             return False
         raise IndexError("tuple index out of range")
@@ -359,7 +359,7 @@ def spill_lock(self, spill_lock: SpillLock) -> None:
             self.spill(target="gpu")
             self._spill_locks.add(spill_lock)
 
-    def get_ptr(self) -> int:
+    def get_ptr(self, *, mode) -> int:
         """Get a device pointer to the memory of the buffer.
 
         If this is called within an `acquire_spill_lock` context,
@@ -369,8 +369,8 @@ def get_ptr(self) -> int:
         If this is *not* called within a `acquire_spill_lock` context,
         this buffer is marked as unspillable permanently.
 
-        Return
-        ------
+        Returns
+        -------
         int
             The device pointer as an integer
         """
@@ -409,18 +409,6 @@ def memory_info(self) -> Tuple[int, int, str]:
             ).__array_interface__["data"][0]
         return (ptr, self.nbytes, self._ptr_desc["type"])
 
-    @property
-    def ptr(self) -> int:
-        """Access the memory directly
-
-        Notice, this will mark the buffer as "exposed" and make
-        it unspillable permanently.
-
-        Consider using `.get_ptr()` instead.
-        """
-        self.mark_exposed()
-        return self._ptr
-
     @property
     def owner(self) -> Any:
         return self._owner
@@ -559,12 +547,12 @@ def __init__(self, base: SpillableBuffer, offset: int, size: int) -> None:
         self._owner = base
         self.lock = base.lock
 
-    @property
-    def ptr(self) -> int:
-        return self._base.ptr + self._offset
-
-    def get_ptr(self) -> int:
-        return self._base.get_ptr() + self._offset
+    def get_ptr(self, *, mode) -> int:
+        """
+        A passthrough method to `SpillableBuffer.get_ptr`
+        with factoring in the `offset`.
+        """
+        return self._base.get_ptr(mode=mode) + self._offset
 
     def _getitem(self, offset: int, size: int) -> Buffer:
         return SpillableBufferSlice(

python/cudf/cudf/core/column/categorical.py

@@ -956,9 +956,10 @@ def clip(self, lo: ScalarLike, hi: ScalarLike) -> "column.ColumnBase":
             self.astype(self.categories.dtype).clip(lo, hi).astype(self.dtype)
         )
 
-    @property
-    def data_array_view(self) -> cuda.devicearray.DeviceNDArray:
-        return self.codes.data_array_view
+    def data_array_view(
+        self, *, mode="write"
+    ) -> cuda.devicearray.DeviceNDArray:
+        return self.codes.data_array_view(mode=mode)
 
     def unique(self, preserve_order=False) -> CategoricalColumn:
         codes = self.as_numerical.unique(preserve_order=preserve_order)