[Help wanted] Support loading ort format models using mmap on non-Windows platforms

[csukuangfj]

See #211
for how to get ort format models from onnx format.

See also https://github.com/moonshine-ai/moonshine/blob/main/core/ort-utils/ort-utils.cpp#L35
for how to use mmap

int ort_session_from_path(const OrtApi *ort_api, OrtEnv *env,
                          OrtSessionOptions *session_options, const char *path,
                          OrtSession **session, const char **mmapped_data,
                          size_t *mmapped_data_size) {
  std::string cpp_path(path);
  if (cpp_path.find(".ort") != std::string::npos) {
    int fd = open(path, O_RDONLY);
    if (fd == -1) {
      fprintf(stderr, "Failed to open memory map file %s at %s:%d\n", path,
              __FILE__, __LINE__);
      return -1;
    }
    struct stat st;
    if (fstat(fd, &st) == -1) {
      fprintf(stderr, "Failed to get file size for %s at %s:%d\n", path,
              __FILE__, __LINE__);
      return -1;
    }
    *mmapped_data = static_cast<const char *>(
        mmap(nullptr, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0));
    if (*mmapped_data == MAP_FAILED) {
      fprintf(stderr, "Failed to memory map file %s at %s:%d\n", path, __FILE__,
              __LINE__);
      return -1;
    }
    *mmapped_data_size = st.st_size;
    close(fd);
    RETURN_ON_ORT_ERROR(ort_api, ort_api->CreateSessionFromArray(
                                     env, *mmapped_data, *mmapped_data_size,
                                     session_options, session));
  } else {
    if (!std::filesystem::exists(path)) {
      fprintf(stderr, "Model directory '%s' does not exist at %s:%d\n", path,
              __FILE__, __LINE__);
      return -1;
    }
    RETURN_ON_ORT_ERROR(
        ort_api, ort_api->CreateSession(env, path, session_options, session));
    *mmapped_data = nullptr;
    *mmapped_data_size = 0;
  }
  return 0;
}

We need to update our code to initialize sessions using mmap on non-Windows platforms when users provide ort format models.

Help from the community is appreciated.

---

See also

• Switched to ORT files for the web to save space moonshine-ai/moonshine#69