# Program has different results when ran in REPL and from Nsight compute

**URL:** <https://discourse.julialang.org/t/program-has-different-results-when-ran-in-repl-and-from-nsight-compute/100817>\
**Category:** GPU\
**Created:** [June 25, 2023, 6:48pm UTC](https://discourse.julialang.org/t/program-has-different-results-when-ran-in-repl-and-from-nsight-compute/100817 "2023-06-25T18:48:24Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Zentrik](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/zentrik/32/35409_2.png) [@Zentrik](https://discourse.julialang.org/u/Zentrik)\
**Post date:** [June 25, 2023, 6:48pm UTC](https://discourse.julialang.org/t/program-has-different-results-when-ran-in-repl-and-from-nsight-compute/100817/1 "2023-06-25T18:48:24Z")

</div>

```julia
index = CuArray{UInt32}([1])
function ker(index)
    i = (blockIdx().x - Int32(1)) * blockDim().x + threadIdx().x
    @cuprintln "i: " i
    @cuprintln "index: " index[]
    @cuprintln "old_index: " index[] += 1

    return nothing
end
@cuda threads=1 blocks=1 ker(index)

```

In the REPL this prints

```julia
i: 1
index: 1
old_index: 2

```

whereas in nsight compute it prints

```julia
i: 1
index: 1
old_index: 2
i: 1
index: 2
old_index: 3
i: 1
index: 3
old_index: 4
i: 1
index: 4
old_index: 5
i: 1
index: 5
old_index: 6
i: 1
index: 6
old_index: 7
i: 1
index: 7
old_index: 8
i: 1
index: 8
old_index: 9
i: 1
index: 9
old_index: 10
i: 1
index: 10
old_index: 11
i: 1
index: 11
old_index: 12
i: 1
index: 12
old_index: 13
i: 1
index: 13
old_index: 14
i: 1
index: 14
old_index: 15
i: 1
index: 15
old_index: 16
i: 1
index: 16
old_index: 17
i: 1
index: 17
old_index: 18
i: 1
index: 18
old_index: 19
i: 1
index: 19
old_index: 20
i: 1
index: 20
old_index: 21
i: 1
index: 21
old_index: 22
i: 1
index: 22
old_index: 23
i: 1
index: 23
old_index: 24
i: 1
index: 24
old_index: 25
i: 1
index: 25
old_index: 26
i: 1
index: 26
old_index: 27
i: 1
index: 27
old_index: 28
i: 1
index: 28
old_index: 29
i: 1
index: 29
old_index: 30
i: 1
index: 30
old_index: 31
i: 1
index: 31
old_index: 32
i: 1
index: 32
old_index: 33
i: 1
index: 33
old_index: 34
i: 1
index: 34
old_index: 35
i: 1
index: 35
old_index: 36
i: 1
index: 36
old_index: 37
i: 1
index: 37
old_index: 38
i: 1
index: 38
old_index: 39
i: 1
index: 39
old_index: 40
i: 1
index: 40
old_index: 41
i: 1
index: 41
old_index: 42
i: 1
index: 42
old_index: 43
i: 1
index: 43
old_index: 44
i: 1
index: 44
old_index: 45

```

It seems nsight compute reruns the kernel many times which causes the `index` variable to be wrong.  
Is there a way to fix this as I’m using `index` to index into data and it’s causing out of bounds errors in nsight compute. If it matters I’m stuck on Nsight compute version 2019.5.1 as I’m using a gtx 1070.

---

<div class="post-metadata">

**Author:** ![Zentrik](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/zentrik/32/35409_2.png) [@Zentrik](https://discourse.julialang.org/u/Zentrik)\
**Post date:** [June 25, 2023, 7:03pm UTC](https://discourse.julialang.org/t/program-has-different-results-when-ran-in-repl-and-from-nsight-compute/100817/2 "2023-06-25T19:03:17Z")

</div>

Doing

```julia
index = CuArray{UInt32}([1])
function ker(index)
    i = (blockIdx().x - Int32(1)) * blockDim().x + threadIdx().x
    if i == 1
        index[] = 1
    end
    @cuprintln "i: " i
    @cuprintln "index: " index[]
    @cuprintln "old_index: " index[] += 1

    return nothing
end
@cuda threads=1 blocks=1 ker(index)

```

Seems to work even with multiple threads.

EDIT: the `i == 1` branch sometimes doesn’t execute first, i.e. `i = 2` might run before so this will give incorrect results.