[julia-users] call compiled Julia image from multiple threads in C++

[Igor Cerovsky]

Hello,

Calling compiled Julia 0.5 code from C++ (MSVS15) from multiple threads a 
code that follows fails.

Consider following example under WIN using Julia 0.5:
#include <thread>
#include <iostream>
#include "julia.h"

//@Base.ccallable Int64 jl_foo(x::Int64) = (x + 1)

void TestJl()
{
  jl_options.compile_enabled = JL_OPTIONS_COMPILE_OFF;
  jl_options.startupfile = JL_OPTIONS_STARTUPFILE_OFF;
  jl_options.use_precompiled = JL_OPTIONS_USE_PRECOMPILED_YES;
  jl_init_with_image(NULL, "myJulia.dll");

  jl_function_t *func1 = jl_get_function(jl_main_module, "jl_foo");
  jl_value_t* in = jl_box_int64(1);
  jl_value_t* ret = NULL;
  JL_GC_PUSH2(&in, &ret);
  // use computation in Julia here ...
  ret = jl_call1(func1, in);
  std::cout << "returned: " << jl_unbox_int64(ret) << "\n";
  JL_GC_POP();

  jl_atexit_hook(0);
}

int main()
{
  std::vector<std::thread> threads;
  for (size_t i = 0; i < 5; ++i)
  {
    threads.emplace_back(std::thread{ TestJl });
  }

  for (size_t i = 0; i < threads.size(); ++i)
  {
    threads[i].join();
  }

  return 0;
}

Error message: ": for the -enable-tail-merge option: may only occur zero or 
one times!"

Single threaded version (just call TestJL()) as well 1thread-version (1 
thread in the for loop) works fine.

Please, can anyone give some hints/explanation, if calling code from 
compiled Julia is possible from multiple threads?