Does libjulia support dynamic reinitialization?

Internals & Design
1

I need a dynamic Julia re-initialization but I guess it’s not supported or there is a bug in the libjulia because in the example below variable x keeps it’s previous value after second jl_init call.

#include <julia.h>
#include <stdio.h>

int64_t getX() {
  jl_value_t *x = jl_eval_string("x");
  return jl_unbox_int64(x);
}

int main(int argc, char *argv[]) {

  jl_init();

  jl_eval_string("x::Int64 = 19");

  printf("x: %d\n", getX());

  jl_atexit_hook(0);

  jl_init();

  jl_eval_string("x=x+1");

  printf("x: %d\n", getX());

  jl_atexit_hook(0);

  return 0;
}

Output:
x: 19
x: 20

2

Have you considered dynamically loading libjulia.so and then unloading the shared library via dlopen and then dlclose?

@GunnarFarneback has an example here:

I’m not completely sure this is supported, but this would be my best guess.

1 Like
3

I have considered to use dlopen/dlclose but it would be better to have more convenient option to work with the library. Anyway thank you for example, it can be useful for me.

4

This is more developed if you want to look into dynamically loading libjulia: GitHub - GunnarFarneback/DynamicallyLoadedEmbedding.jl: Embed Julia with dynamical loading of libjulia at runtime.

5

Unfortunately dynamic library loading/unloading gives the same result :frowning_face:

#include <stdint.h>
#include <stdio.h>
#include <windows.h>

#define JULIA_LIB                                                              \
  "Julia-1.9.4\\bin\\libjulia."    \
  "dll"

HMODULE libjulia;

#define JL_NOTSAFEPOINT

typedef struct _jl_value_t jl_value_t;
typedef struct _jl_sym_t jl_sym_t;
typedef struct _jl_module_t jl_module_t;
typedef jl_value_t jl_function_t;

static void (*jl_init)(void);
static void (*jl_atexit_hook)(int);
static jl_value_t *(*jl_eval_string)(const char *);
static int64_t (*jl_unbox_int64)(jl_value_t *v) JL_NOTSAFEPOINT;

static void *load_function(const char *name, int *success) {
  void *p = GetProcAddress(libjulia, name);

  if (!p) {
    fprintf(stderr, "%s not found in libjulia.\n", name);
    *success = 0;
  }

  return p;
}

void julia_init() {
  libjulia = LoadLibrary(JULIA_LIB);
  if (libjulia == NULL) {
    fprintf(stderr, "libjulia isn't found.\n");
    exit(1);
  }
  int success = 1;
  jl_init = load_function("jl_init", &success);
  jl_atexit_hook = load_function("jl_atexit_hook", &success);
  jl_eval_string = load_function("jl_eval_string", &success);
  jl_unbox_int64 = load_function("jl_unbox_int64", &success);

  if (!success) {
    fprintf(stderr, "libjulia intialization failed.\n");
  }

  jl_init();
}

void julia_deinit() {
  jl_atexit_hook(0);
  BOOL res = FreeLibrary(libjulia);
  if (res == FALSE) {
    fprintf(stderr, "libjulia library unloading failure.\n");
  }
}

int64_t getX() {
  jl_value_t *x = jl_eval_string("x");
  return jl_unbox_int64(x);
}

int main(int argc, char *argv[]) {

  julia_init();

  jl_eval_string("x::Int64 = 19");

  printf("x: %lld\n", getX());

  julia_deinit();

  julia_init();

  jl_eval_string("x=x+1");

  printf("x: %lld\n", getX());

  julia_deinit();

  return 0;
}

x: 19
x: 20