linker error for JACK symbols on macOS

[pri-yan-shu]

While compiling libremidi with JACK backend on macOS, build fails with error:

Undefined symbols for architecture x86_64:
  "_jack_get_cycle_times", referenced from:
      libremidi::midi_in_jack::process(unsigned int) in liblibremidi.a[3](midi_in.cpp.o)
  "_jack_ringbuffer_create", referenced from:
      libremidi::midi_out_jack_queued::midi_out_jack_queued(libremidi::output_configuration&&, libremidi::jack_output_configuration&&) in liblibremidi.a[4](midi_out.cpp.o)
  "_jack_ringbuffer_free", referenced from:
      libremidi::jack_queue::~jack_queue() in liblibremidi.a[4](midi_out.cpp.o)
      libremidi::midi_out_jack_queued::~midi_out_jack_queued() in liblibremidi.a[4](midi_out.cpp.o)
  "_jack_ringbuffer_peek", referenced from:
      libremidi::jack_queue::read(void*) const in liblibremidi.a[4](midi_out.cpp.o)
  "_jack_ringbuffer_read", referenced from:
      libremidi::jack_queue::read(void*) const in liblibremidi.a[4](midi_out.cpp.o)
  "_jack_ringbuffer_read_advance", referenced from:
      libremidi::jack_queue::read(void*) const in liblibremidi.a[4](midi_out.cpp.o)
      libremidi::jack_queue::read(void*) const in liblibremidi.a[4](midi_out.cpp.o)
  "_jack_ringbuffer_read_space", referenced from:
      libremidi::jack_queue::read(void*) const in liblibremidi.a[4](midi_out.cpp.o)
  "_jack_ringbuffer_write", referenced from:
      libremidi::midi_out_jack_queued::send_message(unsigned char const*, unsigned long) in liblibremidi.a[4](midi_out.cpp.o)
      libremidi::midi_out_jack_queued::send_message(unsigned char const*, unsigned long) in liblibremidi.a[4](midi_out.cpp.o)
  "_jack_ringbuffer_write_space", referenced from:
      libremidi::midi_out_jack_queued::midi_out_jack_queued(libremidi::output_configuration&&, libremidi::jack_output_configuration&&) in liblibremidi.a[4](midi_out.cpp.o)
      libremidi::midi_out_jack_queued::send_message(unsigned char const*, unsigned long) in liblibremidi.a[4](midi_out.cpp.o)
ld: symbol(s) not found for architecture x86_64
c++: error: linker command failed with exit code 1 (use -v to see invocation)

Similarly android builds fail with error: (I didn't see any reference of JACK supporting android, so maybe it is a build configuration issue here)

ld.lld: error: undefined symbol: jack_ringbuffer_create
>>> referenced by helpers.hpp:266 (/home/runner/work/mixxx/mixxx/lib/libremidi-5.4.3/include/libremidi/backends/jack/helpers.hpp:266)
>>>               midi_out.cpp.o:(libremidi::midi_out_jack_queued::midi_out_jack_queued(libremidi::output_configuration&&, libremidi::jack_output_configuration&&)) in archive lib/libremidi-5.4.3/liblibremidi.a

ld.lld: error: undefined symbol: jack_ringbuffer_write_space
>>> referenced by helpers.hpp:267 (/home/runner/work/mixxx/mixxx/lib/libremidi-5.4.3/include/libremidi/backends/jack/helpers.hpp:267)
>>>               midi_out.cpp.o:(libremidi::midi_out_jack_queued::midi_out_jack_queued(libremidi::output_configuration&&, libremidi::jack_output_configuration&&)) in archive lib/libremidi-5.4.3/liblibremidi.a
...

Any help?

[jcelerier]

hello, how are you building ? are you passing -ljack to your link line in some way ?

[pri-yan-shu]

It is a CMake project. I added libremidi dependency as:

if(LIBREMIDI)
...
  add_subdirectory(lib/readerwriterqueue-1.0.7)
  add_subdirectory(lib/libremidi-5.4.3)

  target_link_libraries(libremidi PUBLIC readerwriterqueue)
  target_link_libraries(project PUBLIC libremidi)
...
endif()

Similar error is observed while building on Windows as well. A project mainainer suggested that macOS error might be due to building statically on macOS.

The project also uses PortAudio which also links JACK, and the maintainer pointed to a CMake snippet:

    if(PortAudio_IS_STATIC)
      find_package(JACK)
      if(JACK_FOUND)
        set_property(
          TARGET PortAudio::PortAudio
          APPEND
          PROPERTY INTERFACE_LINK_LIBRARIES JACK::jack
        )
      endif()

I try to replicate it with libremidi in place of PortAudio, but CMake fails with:

CMake Error at CMakeLists.txt:3706 (set_property):
  The link interface of target "libremidi" contains:

    JACK::jack

  but the target was not found.

[jcelerier]

I think JACK::jack is a CMake target created by portaudio:

https://github.com/PortAudio/portaudio/blob/8f97a5ca6aa6ecf6c85246977be22f313c329849/cmake/modules/FindJACK.cmake#L65

For libremidi, if you cannot use weakjack for dynamic linking, I'd do a

find_library(JACK_LIBRARIES NAMES jack)

before add_subdirectory(libremidi). And then target_link_libraries(your_app PRIVATE jack)
That said with JACK (and actually any system dependency which is not ultra-basic such as glibc), by far what I recommend is to link with it dynamically at run-time (e.g. with dlopen), through weakjack, and not at link-time with -ljack.
Otherwise people that use your software will need to install jack for it to open.

[jcelerier]

since this is related to MIXXX, I'd really recommend to go that way.
That said weakjack is a bit of a PITA as a header, I will likely replace it with a simpler built-in solution.

[jcelerier]

I implemented a change which will enforce going through dynamically-loaded libjack and fix this issue (or rather, turn it into a run-time one which you can check with if(libremidi::jack_backend::available()) and show or hide the JACK backend to your users depending on the answer

[pri-yan-shu]

Thanks a lot for the help. The builds run fine now.

[jcelerier]

Can you try with my PR #201 too ?

[pri-yan-shu]

I did build with that PR. Windows and macOS x64 and arm64 builds succeed now.

[jcelerier]

ok great! does it work too?

[pri-yan-shu]

From limited testing, it works fine. I couldn't specifically test the JACK backend, I tried looking at the examples but I encountered some issues beyond my understanding. Also I can only test for linux. If I encounter any issues I'll make sure to ask for help.

[jcelerier]

alright :) I'll merge and fix any issue that may crop up