janet_pcall_callback_snippet.c

static JanetFunction *global_cb = NULL;

Janet register_callback(int32_t argc, Janet *argv) {
  janet_fixarity(argc, 1);
  JanetFunction *cb = janet_getfunciton(argv, 0);
  global_cb = cb;
  // Make sure the callback is not garbage collected while waiting
  janet_gcroot(argv[0]);
  return janet_wrap_nil();
}

void some_cb_handler(void) {
  int32_t argc = 1;
  Janet argv[1];
  argv[0] = janet_ckeywordv("some-arg");
  Janet return_value;
  JanetFiber *fiber_used = NULL;
  JanetSignal signal = janet_pcall(global_cb, argc, argv, &return_value, &fiber_used);
  if (signal != JANET_SIGNAL_OK) {
    janet_stacktrace(fiber_used, return_value);
  } else {
    // Everything went well, use return value as you want. The fiber fiber_used should be dead, though.
  }
}