jax-ml/jax · error · ValueError

Must signal an int32 value, but got {value_aval.dtype}

Error message

Must signal an int32 value, but got {value_aval.dtype}

What it means

semaphore_signal requires the increment value to be an int32; the abstract eval rejects any other dtype.

Source

Thrown at jax/_src/pallas/primitives.py:1030

  )


@semaphore_signal_p.def_effectful_abstract_eval
def _semaphore_signal_abstract_eval(
    *avals,
    args_tree,
    device_id_type: DeviceIdType,
):
  (
      sem_aval,
      sem_transforms_avals,
      value_aval,
      device_id_aval,
      core_index_aval,
  ) = tree_util.tree_unflatten(args_tree, avals)
  check_sem_avals(sem_aval, sem_transforms_avals, "signal")
  if value_aval.dtype != jnp.dtype("int32"):
    raise ValueError(f"Must signal an int32 value, but got {value_aval.dtype}")
  effs: set[effects.Effect] = {sem_effect}
  if device_id_aval is not None:
    device_id_flat_avals = tree_util.tree_leaves(device_id_aval)
    for aval in device_id_flat_avals:
      if aval.dtype != jnp.dtype("int32"):
        raise ValueError(
            f"`device_id`s must be an int32 value, but got {aval.dtype}"
        )
    if device_id_type is DeviceIdType.MESH and isinstance(device_id_aval, dict):
      for k in device_id_aval:
        if not isinstance(k, tuple):
          k = (k,)
        for k_ in k:
          effs.add(jax_core.NamedAxisEffect(k_))
    else:
      effs.add(pallas_core.comms_effect)
  return [], effs

View on GitHub (pinned to 1e1c6a8fc0)

Solutions

Cast the value: semaphore_signal(sem, value.astype(jnp.int32))
Ensure the increment is produced as int32 from the start (e.g., jnp.int32(1))

Example fix

// before
semaphore_signal(sem, jnp.float32(1.0))
// after
semaphore_signal(sem, jnp.int32(1))

Defensive patterns

Strategy: validation

Validate before calling

assert value_aval.dtype == jnp.dtype('int32'), f"signal value must be int32, got {value_aval.dtype}"

Prevention

Always cast semaphore increments to jnp.int32
Avoid float counters in semaphore logic

When it happens

Trigger: Calling semaphore_signal(sem, value) where value is not int32 — e.g., a Python int traced as int32 is fine, but a float32 array or int64 constant is rejected.

Common situations: Passing jnp.float32 counters or int64 (default for large Python ints on some platforms) increments; computing the increment in a different dtype inside the kernel.

Related errors

AI-assisted analysis of jax-ml/jax@1e1c6a8fc0 (2026-08-27). Data as JSON: /api/errors/8a976e0235190f53. Report an issue: GitHub.