jax-ml/jax · error · ValueError

Mock topology must be of the form "<number-of-slices> x <num

Error message

Mock topology must be of the form "<number-of-slices> x <number-of-hosts-per-slice> x <number-of-devices-per-host>".

What it means

Error "Mock topology must be of the form "<number-of-slices> x <number-of-hosts-per-slice> x <number-of-devices-per-host>"." thrown in jax-ml/jax.

Source

Thrown at jax/_src/xla_bridge.py:372

      num_nodes=distributed.global_state.num_processes,
      collectives=collectives,
      num_devices=num_devices,
      get_local_topology_timeout_minutes=cpu_get_local_topology_timeout_minutes.value,
      get_global_topology_timeout_minutes=cpu_get_global_topology_timeout_minutes.value,
      transfer_server_factory=_make_transfer_server_factory(),
  )


register_backend_factory(
    "cpu", make_cpu_client, priority=0, fail_quietly=False
)

def get_num_nodes_from_gpu_topology(topology: str) -> int:
    try:
      slices_str, hosts_per_slice_str, _ = topology.split("x", 2)
      return int(slices_str) * int(hosts_per_slice_str)
    except (IndexError, ValueError):
      raise ValueError('Mock topology must be of the form '
                       '"<number-of-slices> x <number-of-hosts-per-slice> x '
                       '<number-of-devices-per-host>".')

# TODO(phawkins,skyewm): switch TPU plugin to use the PJRT plugin mechanism,
# and then fail loudly on initialization failure.
register_backend_factory(
  'tpu', partial(tpu_client_timer_callback, timer_secs=60.0), priority=300,
  fail_quietly=True)


def _get_pjrt_plugin_names_and_library_paths(
    plugins_from_env: str,
) -> dict[str, str]:
  """Gets the names and library paths of PJRT plugins to load from env var.

  Args:
    plugins_from_env: plugin name and paths from env var. It is in the format
      of 'name1:path1,name2:path2' ('name1;path1,name2;path2' for windows).

View on GitHub (pinned to 1e1c6a8fc0)

When it happens

Trigger: Thrown at jax/_src/xla_bridge.py:372 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of jax-ml/jax@1e1c6a8fc0 (2026-08-27). Data as JSON: /api/errors/d4d30f0b6f62c344. Report an issue: GitHub.