# Metal throws ERROR: Exception handler triggered on unmanaged thread

**URL:** https://discourse.julialang.org/t/metal-throws-error-exception-handler-triggered-on-unmanaged-thread/97727
**Category:** Performance
**Tags:** gpu, apple, metaljl
**Created:** [April 21, 2023, 12:31am UTC](https://discourse.julialang.org/t/metal-throws-error-exception-handler-triggered-on-unmanaged-thread/97727 "2023-04-21T00:31:45Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![pitsianis](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pitsianis/32/26588_2.png) [@pitsianis](https://discourse.julialang.org/u/pitsianis)
#### Post date: [April 21, 2023, 12:31am UTC](https://discourse.julialang.org/t/metal-throws-error-exception-handler-triggered-on-unmanaged-thread/97727/1 "2023-04-21T00:31:45Z")

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This is my very first try to use the M2 GPU using the 1.9-rc2 aa64. The following implements a straight forward imperative bitonic sort. However, when running from the REPL, from time to time, it throws

```julia
ERROR: Exception handler triggered on unmanaged thread.
[56040] signal (10.1): Bus error: 10
in expression starting at REPL[4]:1
unknown function (ip: 0x2bbe70208)
MTLDispatchListApply at /System/Library/Frameworks/Metal.framework/Versions/A/Metal (unknown line)
Allocations: 27896731 (Pool: 27862763; Big: 33968); GC: 44

```

But so far I did not see the error when running it from the terminal, `julia1.9 --project=. mbitonic.jl `

Any hints or help appreciated 😉

```julia
using Random, ThreadsX, Metal

function vxchange!(a, jj, kk)
  i = thread_position_in_grid_1d()-1

  ij = i ⊻ jj
  if ij > i
    if (i & kk) == 0 && a[i + 1] > a[ij + 1]
      a[i + 1], a[ij + 1] = a[ij + 1], a[i + 1]
    end
    if (i & kk) != 0 && a[i + 1] < a[ij + 1]
      a[i + 1], a[ij + 1] = a[ij + 1], a[i + 1]
    end
  end
  nothing
end
 
function pibitonic!(a)
  n = length(a)
  q = Int(log2(n))
  for k = 1:q
    kk = 1 << k
    for j = k-1:-1:0
      jj = 1 << j
      @metal threads=2^10 groups=n ÷ 2^10 vxchange!(a, jj, kk)
    end
  end
  nothing
end
 
function test(n)
  a = rand(Float32,n)
  b = MtlArray(copy(a))

  @time ThreadsX.sort!(a)
  @time pibitonic!(b)

  @assert Array(b) == a
end

for i=1:5
  test(2^24)
end

```

---

<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: [April 21, 2023, 7:02am UTC](https://discourse.julialang.org/t/metal-throws-error-exception-handler-triggered-on-unmanaged-thread/97727/2 "2023-04-21T07:02:23Z")

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Known issue on 1.9, [Sporadic `ERROR: Exception handler triggered on unmanaged thread.` · Issue #138 · JuliaGPU/Metal.jl · GitHub](https://github.com/JuliaGPU/Metal.jl/issues/138). Best to use 1.8 for the time being.

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<div class="post-metadata">

### Author: ![pitsianis](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/pitsianis/32/26588_2.png) [@pitsianis](https://discourse.julialang.org/u/pitsianis)
#### Post date: [April 21, 2023, 3:07pm UTC](https://discourse.julialang.org/t/metal-throws-error-exception-handler-triggered-on-unmanaged-thread/97727/3 "2023-04-21T15:07:49Z")

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Interestingly, `ThreadsX.sort!` is substantially slower with `1.8.5` intel compared to `1.9-rc2` native.  
@tkf might be interested in this observation.