Copilot commented on code in PR #50827:
URL: https://github.com/apache/arrow/pull/50827#discussion_r3730204633
##########
cpp/src/arrow/c/dlpack.cc:
##########
@@ -131,30 +155,34 @@ Result<DLDevice> ExportDevice(const
std::shared_ptr<Array>& arr) {
}
}
+namespace {
+
+template <typename DT>
struct TensorManagerCtx {
std::shared_ptr<Tensor> t;
std::vector<int64_t> strides;
std::vector<int64_t> shape;
- DLManagedTensor tensor;
+ DT tensor;
};
-Result<DLManagedTensor*> ExportTensor(const std::shared_ptr<Tensor>& t) {
+template <typename DT>
+Result<DT*> ExportTensorImpl(const std::shared_ptr<Tensor>& t) {
// Define the DLDataType struct
const DataType& type = *t->type();
ARROW_ASSIGN_OR_RAISE(auto dlpack_type, GetDLDataType(type));
// Define DLDevice struct
- ARROW_ASSIGN_OR_RAISE(auto device, ExportDevice(t))
+ ARROW_ASSIGN_OR_RAISE(auto device, ExportDevice(t));
// Create TensorManagerCtx that will serve as the owner of the
DLManagedTensor
- auto ctx = std::make_unique<TensorManagerCtx>();
+ auto ctx = std::make_unique<TensorManagerCtx<DT>>();
// Define the data pointer to the DLTensor
// If tensor is of length 0, data pointer should be NULL
if (t->size() == 0) {
- ctx->tensor.dl_tensor.data = NULL;
+ ctx->tensor.dl_tensor.data = nullptr;
} else {
- ctx->tensor.dl_tensor.data = t->raw_mutable_data();
+ ctx->tensor.dl_tensor.data = const_cast<uint8_t*>(t->raw_data());
}
Review Comment:
`ExportTensorImpl` now exports immutable tensors through the legacy
`DLManagedTensor` path by `const_cast`ing `raw_data()`. Because the legacy
DLPack struct has no read-only flag, consumers may legally write through
`DLTensor::data`, which would violate Arrow’s immutability contract for
non-mutable tensors/buffers. Consider rejecting immutable tensors for the
legacy API and requiring the versioned export (which can set
`DLPACK_FLAG_BITMASK_READ_ONLY`).
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