Groups   183 of 99+      julia-users › call compiled Julia image from multiple threads in Cpp 3 posts by 2 authors      Igor Cerovsky    Oct 6   Hello,  Calling compiled Julia 0.5 code from Cpp  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?     Yichao Yu    Oct 6    You cannot initialize the runtime multiple times and we don't support  unmanaged threads at the moment.   Ref https:  github.com JuliaLang julia issues 17573   It's planned but since the threading support itself is still very  experimental this does not currently have high priority.       Igor Cerovsky    Oct 7   Thanks for quick answer.  Is there a best practice to achieve similar behavior - calling compiled Julia code in parallel?