# What happens when exiting Julia after ccall is made?

**URL:** <https://discourse.julialang.org/t/what-happens-when-exiting-julia-after-ccall-is-made/9095>\
**Category:** New to Julia\
**Tags:** ccall\
**Created:** [February 15, 2018, 8:37pm UTC](https://discourse.julialang.org/t/what-happens-when-exiting-julia-after-ccall-is-made/9095 "2018-02-15T20:37:40Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![tk3369](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tk3369/32/2824_2.png) [@tk3369](https://discourse.julialang.org/u/tk3369)\
**Post date:** [February 15, 2018, 8:37pm UTC](https://discourse.julialang.org/t/what-happens-when-exiting-julia-after-ccall-is-made/9095/1 "2018-02-15T20:37:40Z")

</div>

I got into a strange situation where Julia would segfault when I exit from the REPL. It happens whenever I make any `ccall` to a C library function. This is a vendor package and I think it has some licensing-related code but why does it happen only at the time of exit?

So my question is: what does Julia do when it exits? Maybe it’s trying to unload the shared lib?

```julia
julia>

signal (11): Segmentation fault
while loading no file, in expression starting on line 0
_ZNSt8_Rb_treeISsSt4pairIKSsN5boost10shared_ptrI11rlm_licenseEEESt10_Select1stIS6_ESt4lessISsESaIS6_EE8_M_eraseEPSt13_Rb_tree_nodeIS6_E at /opt/fincad/lib/libfincad_suite_64_2017.so (unknown line)
_ZNSt8_Rb_treeISsSt4pairIKSsN5boost10shared_ptrI11rlm_licenseEEESt10_Select1stIS6_ESt4lessISsESaIS6_EE8_M_eraseEPSt13_Rb_tree_nodeIS6_E at /opt/fincad/lib/libfincad_suite_64_2017.so (unknown line)
_ZNSt8_Rb_treeISsSt4pairIKSsN5boost10shared_ptrI11rlm_licenseEEESt10_Select1stIS6_ESt4lessISsESaIS6_EE8_M_eraseEPSt13_Rb_tree_nodeIS6_E at /opt/fincad/lib/libfincad_suite_64_2017.so (unknown line)
_Z23fc_release_all_licensesv at /opt/fincad/lib/libfincad_suite_64_2017.so (unknown line)
_Z32fc_rlm_terminate_reprise_libraryv at /opt/fincad/lib/libfincad_suite_64_2017.so (unknown line)
unknown function (ip: 0x7f9d30f3fd0d)
pthread_once at /lib64/libpthread.so.0 (unknown line)
unknown function (ip: 0x7f9d314bba21)
unknown function (ip: 0x7f9d3029a75e)
unknown function (ip: 0x7f9d318ce480)
unknown function (ip: 0x7f9d813bfa68)
unknown function (ip: 0x7f9d8269595f)
Allocations: 1813374 (Pool: 1812168; Big: 1206); GC: 1
Segmentation fault

```

My version info:

```julia
Julia Version 0.6.2
Commit d386e40c17 (2017-12-13 18:08 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz
  WORD_SIZE: 64
  BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Haswell)
  LAPACK: libopenblas64_
  LIBM: libopenlibm
  LLVM: libLLVM-3.9.1 (ORCJIT, broadwell)

```

---

<div class="post-metadata">

**Author:** ![Keno](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/keno/32/285_2.png) [@Keno](https://discourse.julialang.org/u/Keno)\
**Post date:** [February 15, 2018, 8:48pm UTC](https://discourse.julialang.org/t/what-happens-when-exiting-julia-after-ccall-is-made/9095/2 "2018-02-15T20:48:06Z")

</div>

> [@tk3369](#):
>
> So my question is: what does Julia do when it exits? Maybe it’s trying to unload the shared lib?

The C standard library has an exit hook that shared libraries can register themselves for. Julia doesn’t do anything special here.

---

<div class="post-metadata">

**Author:** ![tk3369](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tk3369/32/2824_2.png) [@tk3369](https://discourse.julialang.org/u/tk3369)\
**Post date:** [February 15, 2018, 9:19pm UTC](https://discourse.julialang.org/t/what-happens-when-exiting-julia-after-ccall-is-made/9095/3 "2018-02-15T21:19:49Z")

</div>

Got a new MWE - just calling `dlopen` will trigger this exit-segfault behavior.

```julia
julia> Libdl.dlopen("/opt/fincad/lib/libfincad_suite_64_2017.so")
Ptr{Void} @0x0000000002e01cf0

julia>

signal (11): Segmentation fault
while loading no file, in expression starting on line 0
_ZNSt8_Rb_treeISsSt4pairIKSsN5boost10shared_ptrI11rlm_licenseEEESt10_Select1stIS6_ESt4lessISsESaIS6_EE8_M_eraseEPSt13_Rb_tree_nodeIS6_E at /opt/fincad/lib/libfincad_suite_64_2017.so (unknown line)
_ZNSt8_Rb_treeISsSt4pairIKSsN5boost10shared_ptrI11rlm_licenseEEESt10_Select1stIS6_ESt4lessISsESaIS6_EE8_M_eraseEPSt13_Rb_tree_nodeIS6_E at /opt/fincad/lib/libfincad_suite_64_2017.so (unknown line)
_ZNSt8_Rb_treeISsSt4pairIKSsN5boost10shared_ptrI11rlm_licenseEEESt10_Select1stIS6_ESt4lessISsESaIS6_EE8_M_eraseEPSt13_Rb_tree_nodeIS6_E at /opt/fincad/lib/libfincad_suite_64_2017.so (unknown line)
_Z23fc_release_all_licensesv at /opt/fincad/lib/libfincad_suite_64_2017.so (unknown line)
_Z32fc_rlm_terminate_reprise_libraryv at /opt/fincad/lib/libfincad_suite_64_2017.so (unknown line)
unknown function (ip: 0x7fecee03dd0d)
pthread_once at /lib64/libpthread.so.0 (unknown line)
unknown function (ip: 0x7fecee5b9a21)
unknown function (ip: 0x7feced39875e)
unknown function (ip: 0x7fecee9cc480)
unknown function (ip: 0x7fed4052fa68)
unknown function (ip: 0x7fed4180595f)
Allocations: 974017 (Pool: 972913; Big: 1104); GC: 0
Segmentation fault

```

---

<div class="post-metadata">

**Author:** ![tk3369](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tk3369/32/2824_2.png) [@tk3369](https://discourse.julialang.org/u/tk3369)\
**Post date:** [February 15, 2018, 9:31pm UTC](https://discourse.julialang.org/t/what-happens-when-exiting-julia-after-ccall-is-made/9095/4 "2018-02-15T21:31:00Z")

</div>

Looks like `Libdl.dlopen` ends up calling `dlopen`:

[https://github.com/JuliaLang/julia/blob/release-0.6/src/dlload.c#L145](https://github.com/JuliaLang/julia/blob/release-0.6/src/dlload.c#L145)

I could create a simple C program that does the same but that won’t crash on exit. Maybe it’s time for me to compile Julia from source to track it down 😅

```nohighlight
#include <stdlib.h>
#include <stdio.h>
#include <dlfcn.h>

int main(int argc, char **argv)
{
    void *handle;
    char *error;

    handle = dlopen("libfincad_suite_64_2017.so", RTLD_LAZY);
    if (!handle) {
        fprintf(stderr, "%s\n", dlerror());
        exit(EXIT_FAILURE);
    }

    printf("good\n");
}

```

---

<div class="post-metadata">

**Author:** ![ihnorton](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ihnorton/32/26_2.png) [@ihnorton](https://discourse.julialang.org/u/ihnorton)\
**Post date:** [February 17, 2018, 2:55pm UTC](https://discourse.julialang.org/t/what-happens-when-exiting-julia-after-ccall-is-made/9095/5 "2018-02-17T14:55:35Z")

</div>

One suggestion is to try running your C program vs julia caller with LD\_DEBUG and compare which shared libraries are pulled in.

---

<div class="post-metadata">

**Author:** ![tk3369](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tk3369/32/2824_2.png) [@tk3369](https://discourse.julialang.org/u/tk3369)\
**Post date:** [February 19, 2018, 1:01am UTC](https://discourse.julialang.org/t/what-happens-when-exiting-julia-after-ccall-is-made/9095/6 "2018-02-19T01:01:18Z")

</div>

It turns out that there’s a housekeeping function that I should call before exiting the application and that fixes the seg fault issue. Although I still don’t understand the difference between the Julia and C versions, I don’t have an immediate problem anymore. Thanks for the ideas!