# Julia crashes when using a @cfunction from another module
**URL:** https://discourse.julialang.org/t/julia-crashes-when-using-a-cfunction-from-another-module/98576
**Category:** General Usage
**Tags:** ccall, interoperability, c
**Created:** [May 9, 2023, 9:01pm UTC](https://discourse.julialang.org/t/julia-crashes-when-using-a-cfunction-from-another-module/98576 "2023-05-09T21:01:07Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@heyx3](https://discourse.julialang.org/u/heyx3)
#### Post date: [May 9, 2023, 9:01pm UTC](https://discourse.julialang.org/t/julia-crashes-when-using-a-cfunction-from-another-module/98576/1 "2023-05-09T21:01:07Z")
I’m trying to define some Julia callbacks to give to a C library, but hit some strange crashes when those functions are invoked. In an attempt to pin down the problem I have created a very simple project which still crashes Julia.
This happens in both 1.7.2 and 1.8.5.
The buggy module is defined like this:
```julia
module bug_ccall
@noinline get_value(i::Int64)::Int64 = i * 27
const GET_VALUE = @cfunction(get_value, Int64, (Int64, ))
pretend_c_call(i) = ccall(GET_VALUE, Int64, (Int64, ), Int64(i))
println("While compiling module: ", pretend_c_call(2))
end # module
```
When I compile this module, I get the expected printout:
> While compiling module: 54
However, when I invoke the ccall from outside the module, I get a crash:
```julia
PS C:\Users\manni\Documents\tep\bug_ccall> julia --project=. -e 'using bug_ccall; println(:outside_the_module_, bug_ccall.pretend_c_call(4))'
While compiling module: 54
Please submit a bug report with steps to reproduce this fault, and any error messages that follow (in their entirety). Thanks.
Exception: EXCEPTION_ACCESS_VIOLATION at 0x5ece0ac0 -- unknown function (ip: 000000005ece0ac0)
in expression starting at none:1
unknown function (ip: 000000005ece0ac0)
Allocations: 2723 (Pool: 2712; Big: 11); GC: 0
```
Am I misunderstanding something? What is the correct way to use a `@cfunction` from another module?
---
### Author:  [@GunnarFarneback](https://discourse.julialang.org/u/GunnarFarneback)
#### Post date: [May 9, 2023, 9:19pm UTC](https://discourse.julialang.org/t/julia-crashes-when-using-a-cfunction-from-another-module/98576/2 "2023-05-09T21:19:01Z")
I don’t have the picture fully clear but it seems possible that your module gets precompiled and stores a pointer to your `@cfunction`, which is stale when you load the module the next time. If this is the case the solution is to instead create the pointer in the module’s ` __init__ ` function. See [Modules · The Julia Language](https://docs.julialang.org/en/v1/manual/modules/#Module-initialization-and-precompilation) and the docstring for ` __init__ `.
---
### Author:  [@heyx3](https://discourse.julialang.org/u/heyx3)
#### Post date: [May 9, 2023, 9:32pm UTC](https://discourse.julialang.org/t/julia-crashes-when-using-a-cfunction-from-another-module/98576/3 "2023-05-09T21:32:37Z")
Thank you, this did it! Here is the fixed code, that doesn’t crash:
```julia
module bug_ccall
@noinline get_value(i::Int64)::Int64 = i * 27
const GET_VALUE = Ref{Ptr{Cvoid}}()
function __init__ ()
GET_VALUE[] = @cfunction(get_value, Int64, (Int64, ))
end
make_c_call(i) = ccall(GET_VALUE[], Int64, (Int64, ), Int64(i))
end # module
...
> julia --project=. -e 'using bug_ccall; println(bug_ccall.make_c_call(5))'
135
```
The call during compilation crashes, but that makes sense because ` __init__ ()` hasn’t been called yet.
Now I just have to port this change into my real project.