jax-ml/jax · error · nb::value_error

get_topology_for_devices requires >= 1 devices.

Error message

get_topology_for_devices requires >= 1 devices.

What it means

Constructing a topology from a device list is only meaningful with at least one device; an empty list gives no client or platform to derive the topology from, so the binding validates input and throws.

Source

Thrown at jaxlib/jax.cc:621

           const absl::flat_hash_map<std::string, xla::PjRtValueType>& options)
            -> std::shared_ptr<xla::ifrt::Topology> {
          if (c_api.name() == nullptr ||
              std::string_view(c_api.name()) != "pjrt_c_api") {
            throw nb::value_error(
                "Argument to get_c_api_topology was not a pjrt_c_api capsule.");
          }
          if (c_api.data() == nullptr) {
            throw nb::value_error(
                "Argument to get_c_api_topology contained a null pointer.");
          }
          return std::make_shared<xla::ifrt::PjRtTopology>(xla::ValueOrThrow(
              xla::GetCApiTopology(static_cast<const PJRT_Api*>(c_api.data()),
                                   topology_name, options)));
        });
  m.def("get_topology_for_devices",
        [](const std::vector<nb_class_ptr<PyDevice>>& py_devices) {
          if (py_devices.empty()) {
            throw nb::value_error(
                "get_topology_for_devices requires >= 1 devices.");
          }
          auto client = py_devices[0]->client();
          absl::InlinedVector<xla::ifrt::Device*, 1> ifrt_devices;
          ifrt_devices.reserve(py_devices.size());
          for (const auto& py_device : py_devices) {
            if (py_device->client().get() != client.get()) {
              throw nb::value_error(
                  "devices passed to get_topology_for_devices come from "
                  "different clients.");
            }
            ifrt_devices.push_back(py_device->device());
          }
          xla::ifrt::DeviceListRef device_list = xla::ValueOrThrow(
              client->ifrt_client()->MakeDeviceList(ifrt_devices));
          return xla::ValueOrThrow(
              client->ifrt_client()->GetTopologyForDevices(device_list));
        });

View on GitHub (pinned to 1e1c6a8fc0)

Solutions

1. Check the list is non-empty before calling; debug why it's empty
2. Verify process/device slicing logic in multi-process jax jobs

Example fix

# before
jaxlib.get_topology_for_devices(my_devices)
# after
assert my_devices, 'no devices assigned to this process'
jaxlib.get_topology_for_devices(my_devices)

assert devices, 'need >= 1 device'

def has_devices(devs) -> bool:
    return len(devs) > 0

When it happens

Trigger: jaxlib.get_topology_for_devices([]) — typically because the devices list was built from an empty slice, wrong device filter, or a filtering bug.

Common situations: Multi-process code slicing jax.devices() per process and accidentally producing an empty list (e.g. wrong process index).

Related errors

• Argument to get_c_api_topology was not a pjrt_c_api capsule.
• {full_name} must be a pytree prefix with bool leaves or a tu
• The devices() method was called on {self._error_repr()}.{sel
• Axes mentioned in `manual_axis_type` field of ShapedArray sh
• varying and unreduced cannot have common mesh axes. Got vary

AI-assisted analysis of jax-ml/jax@1e1c6a8fc0 (2026-08-27). Data as JSON: /api/errors/24c67eb18303d389. Report an issue: GitHub.