# Error compiling package using JavaCall

**URL:** <https://discourse.julialang.org/t/error-compiling-package-using-javacall/96779>\
**Category:** General Usage\
**Tags:** packages, precompilation\
**Created:** [March 29, 2023, 1:05pm UTC](https://discourse.julialang.org/t/error-compiling-package-using-javacall/96779 "2023-03-29T13:05:18Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![bvanderbeek](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bvanderbeek/32/48135_2.png) [@bvanderbeek](https://discourse.julialang.org/u/bvanderbeek)\
**Post date:** [March 29, 2023, 1:05pm UTC](https://discourse.julialang.org/t/error-compiling-package-using-javacall/96779/1 "2023-03-29T13:05:18Z")

</div>

I’m trying to build a package that is dependent on the JavaCall package. The JavaCall package has some known issues with Mac which can be avoided by setting the environment variable ‘JULIA\_COPY\_STACKS=yes’ and starting Julia using the command-line flag ‘julia --handle-signals=no’.

After doing so, on a Mac I can start the JVM from within Julia without error using ‘JavaCall.init()’. The problem is, if ‘JavaCall.init()’ is called in my package, I get a segmentation fault upon loading the package via ‘using MyPackageWithJavaCall’. I’m wondering if when compiling the package Julia is unaware of the ‘–handle-signals=no’ or if one can force the package to be compiled with this flag.

Below is a minimal working example of a package that produces this segmentation fault and the particular error stack I get. Any help on this would be greatly appreciated!!

Simple Package

```julia
module JavaTest

# Dependencies
using JavaCall

# Check for required environment variable required for JavaCall
if ~haskey(ENV,"JULIA_COPY_STACKS")
    error("Environment variable 'JULIA_COPY_STACKS=yes' is required for JavaCall package but is not defined.")
else
    if ~(ENV["JULIA_COPY_STACKS"] == "yes")
        error("Environment variable 'JULIA_COPY_STACKS=yes' is required for JavaCall package but is not defined.")
    end
end

# Initialise Java Virtual Machine--SEGMENTATION FAULT HERE
JavaCall.init()

greet() = print("Hello World!")

end

```

And the error

```julia
using JavaTest
[Info: Precompiling JavaTest [40cc168c-4df6-4a30-87ce-9a1cad52c5d0]

signal (11): Segmentation fault: 11
in expression starting at /Users/bvanderbeek/research/software/JuliaProjects/JavaTest/src/JavaTest.jl:16
unknown function (ip: 0x16090651b)
Allocations: 729607 (Pool: 729209; Big: 398); GC: 1
ERROR: Failed to precompile JavaTest [40cc168c-4df6-4a30-87ce-9a1cad52c5d0] to /Users/bvanderbeek/.julia/compiled/v1.8/JavaTest/jl_7kXmSn.
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:35
 [2] compilecache(pkg::Base.PkgId, path::String, internal_stderr::IO, internal_stdout::IO, keep_loaded_modules::Bool)
   @ Base ./loading.jl:1705
 [3] compilecache
   @ ./loading.jl:1649 [inlined]
 [4] _require(pkg::Base.PkgId)
   @ Base ./loading.jl:1337
 [5] _require_prelocked(uuidkey::Base.PkgId)
   @ Base ./loading.jl:1200
 [6] macro expansion
   @ ./loading.jl:1180 [inlined]
 [7] macro expansion
   @ ./lock.jl:223 [inlined]
 [8] require(into::Module, mod::Symbol)
   @ Base ./loading.jl:1144

```

---

<div class="post-metadata">

**Author:** ![mkitti](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mkitti/32/12459_2.png) [@mkitti](https://discourse.julialang.org/u/mkitti)\
**Post date:** [March 29, 2023, 1:09pm UTC](https://discourse.julialang.org/t/error-compiling-package-using-javacall/96779/2 "2023-03-29T13:09:12Z")

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You should call `JavaCall.init()` within your module’s ` __init__ `.

```julia
module JavaTest

# Dependencies
using JavaCall

function __init__ ()

# Check for required environment variable required for JavaCall
if ~haskey(ENV,"JULIA_COPY_STACKS")
    error("Environment variable 'JULIA_COPY_STACKS=yes' is required for JavaCall package but is not defined.")
else
    if ~(ENV["JULIA_COPY_STACKS"] == "yes")
        error("Environment variable 'JULIA_COPY_STACKS=yes' is required for JavaCall package but is not defined.")
    end
end

# Initialise Java Virtual Machine--SEGMENTATION FAULT HERE
JavaCall.init()

end

greet() = print("Hello World!")

end

```

---

<div class="post-metadata">

**Author:** ![bvanderbeek](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bvanderbeek/32/48135_2.png) [@bvanderbeek](https://discourse.julialang.org/u/bvanderbeek)\
**Post date:** [March 29, 2023, 1:39pm UTC](https://discourse.julialang.org/t/error-compiling-package-using-javacall/96779/3 "2023-03-29T13:39:51Z")

</div>

@mkitti Well that was easy! Appreciate the quick help as I just started writing Julia packages.

---

<div class="post-metadata">

**Author:** ![mkitti](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mkitti/32/12459_2.png) [@mkitti](https://discourse.julialang.org/u/mkitti)\
**Post date:** [March 29, 2023, 1:47pm UTC](https://discourse.julialang.org/t/error-compiling-package-using-javacall/96779/4 "2023-03-29T13:47:43Z")

</div>

Some basics… anything at the top level of the module will be executed once at “precompile” time. This will not change until you precompile the package by changing or `touch`ing it.

Anything involving external code or pointers, you probably want to do during ` __init__ ()`. ` __init__ ()` runs when you use `using` or `import`.