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prefect.task_runs

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Classes

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TaskRunWaiter

A service used for waiting for a task run to finish.

This service listens for task run events and provides a way to wait for a specific task run to finish. This is useful for waiting for a task run to finish before continuing execution.

The service is a singleton and must be started before use. The service will automatically start when the first instance is created. A single websocket connection is used to listen for task run events.

The service can be used to wait for a task run to finish by calling TaskRunWaiter.wait_for_task_run with the task run ID to wait for. The method will return when the task run has finished or the timeout has elapsed.

The service will automatically stop when the Python process exits or when the global loop thread is stopped.

Example:

import asyncio
from uuid import uuid4

from prefect import task
from prefect.task_engine import run_task_async
from prefect.task_runs import TaskRunWaiter


@task
async def test_task():
    await asyncio.sleep(5)
    print("Done!")


async def main():
    task_run_id = uuid4()
    asyncio.create_task(run_task_async(task=test_task, task_run_id=task_run_id))

    await TaskRunWaiter.wait_for_task_run(task_run_id)
    print("Task run finished")


if __name__ == "__main__":
    asyncio.run(main())

Methods:

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start

start(self) -> None

Start the TaskRunWaiter service.

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stop

stop(self) -> None

Stop the TaskRunWaiter service.

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add_done_callback

add_done_callback(cls, task_run_id: uuid.UUID, callback: Callable[[], None]) -> None

Add a callback to be called when a task run finishes.

Args:

• task_run_id: The ID of the task run to wait for.
• callback: The callback to call when the task run finishes.

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instance

instance(cls) -> Self

Get the singleton instance of TaskRunWaiter.