Textualize/textual · error · NoActiveWorker

There is no active worker in this task or thread.

Error message

There is no active worker in this task or thread.

What it means

NoActiveWorker raised by get_current_worker(): there is no worker associated with the current asyncio task or thread. Worker context is tracked via a contextvar/Local set only inside running worker callables, so calling this outside a worker has nothing to find.

Source

Thrown at src/textual/worker.py:77

class WorkerCancelled(WorkerError):
    """The worker was cancelled and did not complete."""


def get_current_worker() -> Worker:
    """Get the currently active worker.

    Raises:
        NoActiveWorker: If there is no active worker.

    Returns:
        A Worker instance.
    """
    try:
        return active_worker.get()
    except LookupError:
        raise NoActiveWorker(
            "There is no active worker in this task or thread."
        ) from None


class WorkerState(enum.Enum):
    """A description of the worker's current state."""

    PENDING = 1
    """Worker is initialized, but not running."""
    RUNNING = 2
    """Worker is running."""
    CANCELLED = 3
    """Worker is not running, and was cancelled."""
    ERROR = 4
    """Worker is not running, and exited with an error."""
    SUCCESS = 5
    """Worker is not running, and completed successfully."""

View on GitHub (pinned to 06dbeef4bb)

Solutions

1. Only call get_current_worker() inside code run via `self.run_worker(...)` / `@work` decorated methods.
2. Guard the call: try/except NoActiveWorker and fall back to non-worker behavior.
3. Pass the Worker instance explicitly to helpers instead of relying on ambient context.

Example fix

# before
worker = get_current_worker()
# after
from textual.worker import NoActiveWorker
try:
    worker = get_current_worker()
except NoActiveWorker:
    worker = None

from textual.worker import NoActiveWorker
try:
    worker = get_current_worker()
except NoActiveWorker:
    worker = None

from textual.worker import NoActiveWorker
try:
    get_current_worker().check_cancelled()
except NoActiveWorker:
    pass  # not running as a worker

When it happens

Trigger: Calling `get_current_worker()` from a regular async method, a button handler, `on_mount`, or a plain thread that was not started via run_worker/run_thread with the worker machinery.

Common situations: Shared helper functions used both inside worker functions and in normal app code; calling worker APIs like `worker.check_cancelled()` or progress updates outside a worker.

Related errors

• Can not create a worker from a non-async function unless `th
• App is not running
• The `call_from_thread` method must run in a different thread
• Unsupported attempt to run a thread worker
• Request to run a non-async function as an async worker

AI-assisted analysis of Textualize/textual@06dbeef4bb (2026-08-27). Data as JSON: /api/errors/88aa6ee5ec3930dd. Report an issue: GitHub.