Function UserSelectedBackend

cpp/src/arrow/memory_pool.cc:104–136

Return the MemoryPoolBackend selected by the user through the ARROW_DEFAULT_MEMORY_POOL environment variable, if any.

// Return the MemoryPoolBackend selected by the user through the
// ARROW_DEFAULT_MEMORY_POOL environment variable, if any.
std::optional<MemoryPoolBackend> UserSelectedBackend() {
  static auto user_selected_backend = []() -> std::optional<MemoryPoolBackend> {
    auto unsupported_backend = [](const std::string& name) {
      std::vector<std::string> supported;
      for (const auto backend : SupportedBackends()) {
        supported.push_back(std::string("'") + backend.name + "'");
      }
      ARROW_LOG(WARNING) << "Unsupported backend '" << name << "' specified in "
                         << kDefaultBackendEnvVar << " (supported backends are "
                         << internal::JoinStrings(supported, ", ") << ")";
    };

    auto maybe_name = internal::GetEnvVar(kDefaultBackendEnvVar);
    if (!maybe_name.ok()) {
      return {};
    }
    const auto name = *std::move(maybe_name);
    if (name.empty()) {
      // An empty environment variable is considered missing
      return {};
    }
    const auto found = std::find_if(
        SupportedBackends().begin(), SupportedBackends().end(),
        [&](const SupportedBackend& backend) { return name == backend.name; });
    if (found != SupportedBackends().end()) {
      return found->backend;
    }
    unsupported_backend(name);
    return {};
  }();

  return user_selected_backend;
}

MemoryPoolBackend DefaultBackend() {
  auto backend = UserSelectedBackend();