Copy

Copy#

2026-03-13

3 min read time

Applies to Linux

#include <raft/core/copy.hpp>

namespace raft

template<typename DstType, typename SrcType>
detail::mdspan_copyable_not_with_kernel_t<DstType, SrcType> copy(
resources const &res,
DstType &&dst,
SrcType &&src
)#

Copy data from one mdspan to another with the same extents.

This function copies data from one mdspan to another, regardless of whether or not the mdspans have the same layout, memory type (host/device/managed) or data type. So long as it is possible to convert the data type from source to destination, and the extents are equal, this function should be able to perform the copy.

This header does not include the custom kernel used for copying data between completely arbitrary mdspans on device. For arbitrary copies of this kind, #include <raft/core/copy.cuh> instead. Specializations of this function that require the custom kernel will be SFINAE-omitted when this header is used instead of copy.cuh. This header does support device-to-device copies that can be performed with cuBLAS or a straightforward cudaMemcpy. Any necessary device operations will be stream-ordered via the CUDA stream provided by the raft::resources argument.

Limitations: Currently this function does not support copying directly between two arbitrary mdspans on different CUDA devices. It is assumed that the caller sets the correct CUDA device. Furthermore, host-to-host copies that require a transformation of the underlying memory layout are currently not performant, although they are supported.

Note that when copying to an mdspan with a non-unique layout (i.e. the same underlying memory is addressed by different element indexes), the source data must contain non-unique values for every non-unique destination element. If this is not the case, the behavior is undefined. Some copies to non-unique layouts which are well-defined will nevertheless fail with an exception to avoid race conditions in the underlying copy.

Template Parameters:

  • DstType – An mdspan type for the destination container.

  • SrcType – An mdspan type for the source container

Parameters:

  • res – raft::resources used to provide a stream for copies involving the device.

  • dst – The destination mdspan.

  • src – The source mdspan.

RAFT_NON_CUDA_COPY_IMPLEMENTED#