# Non-intuitive difference of copyto! between CuArray and Array

**URL:** <https://discourse.julialang.org/t/non-intuitive-difference-of-copyto-between-cuarray-and-array/119904>\
**Category:** GPU\
**Tags:** question, bug, interface\
**Created:** [September 26, 2024, 9:42am UTC](https://discourse.julialang.org/t/non-intuitive-difference-of-copyto-between-cuarray-and-array/119904 "2024-09-26T09:42:51Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![0samuraiE](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/0samuraie/32/209825_2.png) [@0samuraiE](https://discourse.julialang.org/u/0samuraiE)\
**Post date:** [September 26, 2024, 9:42am UTC](https://discourse.julialang.org/t/non-intuitive-difference-of-copyto-between-cuarray-and-array/119904/1 "2024-09-26T09:42:51Z")

</div>

Hi all. I trapped an error when using `copyto!` to `CuArray.`  
Error is

```julia
ERROR: CUDA error: invalid argument (code 1, ERROR_INVALID_VALUE)
Stacktrace:
  [1] throw_api_error(res::CUDA.cudaError_enum)
    @ CUDA ~/.julia/packages/CUDA/Tl08O/lib/cudadrv/libcuda.jl:30
  [2] check
    @ ~/.julia/packages/CUDA/Tl08O/lib/cudadrv/libcuda.jl:37 [inlined]
  [3] cuMemcpyDtoDAsync_v2
    @ ~/.julia/packages/CUDA/Tl08O/lib/utils/call.jl:34 [inlined]
  [4] unsafe_copyto!(dst::CuPtr{Float32}, src::CuPtr{Float32}, N::Int64; stream::CuStream, async::Bool)
    @ CUDA ~/.julia/packages/CUDA/Tl08O/lib/cudadrv/memory.jl:426
  [5] unsafe_copyto!
    @ ~/.julia/packages/CUDA/Tl08O/lib/cudadrv/memory.jl:420 [inlined]
  [6] (::CUDA.var"#1129#1130"{Float32, CuArray{…}, Int64, CuArray{…}, Int64, Int64})()
    @ CUDA ~/.julia/packages/CUDA/Tl08O/src/array.jl:577
  [7] #context!#990
    @ ~/.julia/packages/CUDA/Tl08O/lib/cudadrv/state.jl:168 [inlined]
  [8] context!
    @ ~/.julia/packages/CUDA/Tl08O/lib/cudadrv/state.jl:163 [inlined]
  [9] unsafe_copyto!(dest::CuArray{…}, doffs::Int64, src::CuArray{…}, soffs::Int64, n::Int64)
    @ CUDA ~/.julia/packages/CUDA/Tl08O/src/array.jl:575
 [10] copyto!
    @ ~/.julia/packages/CUDA/Tl08O/src/array.jl:517 [inlined]
 [11] copyto!(dest::CuArray{Float32, 1, CUDA.DeviceMemory}, src::CuArray{Float32, 2, CUDA.DeviceMemory})
    @ CUDA ~/.julia/packages/CUDA/Tl08O/src/array.jl:521
 [12] top-level scope
    @ ~/dev/MR/comm.jl:17
Some type information was truncated. Use `show(err)` to see complete types.

```

I believe this behavior is a bug because Array `copyto!` do not throw any error and I think it worked before.

```julia
using CUDA
A = CUDA.zeros(16)
B = CUDA.ones(8)
copyto!(A, B)
copyto!(B, A) # This throws error

A = zeros(16)
B = ones(8)
copyto!(A, B)
copyto!(B, A)

```

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<div class="post-metadata">

**Author:** ![0samuraiE](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/0samuraie/32/209825_2.png) [@0samuraiE](https://discourse.julialang.org/u/0samuraiE)\
**Post date:** [September 26, 2024, 9:54am UTC](https://discourse.julialang.org/t/non-intuitive-difference-of-copyto-between-cuarray-and-array/119904/2 "2024-09-26T09:54:46Z")

</div>

This will work. But still I wonder the difference.

```julia
using CUDA
A = CUDA.zeros(16)
B = CUDA.ones(8)
copyto!(A, B)
copyto!(B, @views A[1:min(length(A), length(B))])

A = zeros(4, 4)
B = ones(8)
copyto!(A, B)
copyto!(B, @views A[1:min(length(A), length(B))])

```

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<div class="post-metadata">

**Author:** ![maleadt](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/maleadt/32/10097_2.png) [@maleadt](https://discourse.julialang.org/u/maleadt)\
**Post date:** [September 26, 2024, 10:46am UTC](https://discourse.julialang.org/t/non-intuitive-difference-of-copyto-between-cuarray-and-array/119904/3 "2024-09-26T10:46:19Z")

</div>

> [@0samuraiE](#):
>
> I believe this behavior is a bug because Array `copyto!` do not throw any error and I think it worked before.

The behavior is working as intended, and errors with `Array` too:

```julia
julia> A = zeros(16);

julia> B = ones(8);

julia> copyto!(A, B);

julia> copyto!(B, A);
ERROR: BoundsError: attempt to access 8-element Vector{Float64} at index [1:16]

```

The fact that you’re getting an `ERROR_INVALID_VALUE` instead of a bounds error with CUDA.jl reveals that you’re running with `--check-bounds=no`, which is the problem here.

---

<div class="post-metadata">

**Author:** ![0samuraiE](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/0samuraie/32/209825_2.png) [@0samuraiE](https://discourse.julialang.org/u/0samuraiE)\
**Post date:** [September 26, 2024, 2:43pm UTC](https://discourse.julialang.org/t/non-intuitive-difference-of-copyto-between-cuarray-and-array/119904/4 "2024-09-26T14:43:01Z")

</div>

Thank you and I’m sorry for being so weird.