< Marvin> I m running the following code ```from prefect imp Prefect Community #ask-marvin

<@ULVA73B9P> I'm running the following code: ```fr...

Gavrie Philipson

02/03/2025, 11:24 AM

@Marvin I'm running the following code:

Copy code

from prefect import flow, task
from prefect.futures import wait

@task
def download_panel() -> None:
    raise RuntimeError("Download failed")

@task
def prepare_panel():
    logger.info("Preparing panel")

@flow
def glimpse_prep_workflow():
    task_download = download_panel.submit()
    task_prepare = prepare_panel.submit(wait_for=[task_download])

    wait([task_download, task_prepare])

When running this, I get the following output:

Copy code

Please wait for all submitted tasks to complete before exiting your flow by calling `.wait()` on the `PrefectFuture` returned from your `.submit()` calls.

Example:

from prefect import flow, task

@task
def say_hello(name):
    print(f"Hello, {name}!")

@flow
def example_flow():
    future = say_hello.submit(name="Marvin")
    future.wait()

example_flow()

Since I did call

wait

, the warning and example seem to be superfluous. Is this a bug in my code, or in Prefect's?

Marvin

02/03/2025, 11:24 AM

Your message was too long by 602 tokens...

Marvin

02/03/2025, 11:25 AM

Your message was too long by 222 tokens...

Marvin

02/03/2025, 11:26 AM

Your message was too long by 132 tokens...

Marvin

02/03/2025, 11:27 AM

Your message was too long by 79 tokens...

Marvin

02/03/2025, 11:27 AM

The warning you're encountering is related to how Prefect 3.x handles

PrefectFuture

objects. In Prefect 3.x, tasks submitted using

.submit()

return

PrefectFuture

objects, which need to be explicitly waited upon using

.wait()

.result()

. The warning is triggered when a

PrefectFuture

is garbage collected without being resolved, which can lead to task run failures if the flow exits prematurely. Here's what you need to know: 1. Explicit Waiting: Each

PrefectFuture

must be explicitly resolved using

.wait()

.result()

. Your code seems to be following this pattern, but the warning suggests that Prefect might not recognize it due to the order or manner of execution. 2. Ensure Proper Resolution: Make sure that the

wait()

method is called directly on each

PrefectFuture

object. It might be helpful to call

.wait()

directly on the future objects, rather than using the

wait

function from

prefect.futures

. 3. Potential Bug or Edge Case: If you are certain that your code is correctly waiting on all futures, this might be an edge case or bug in Prefect. It's worth checking the latest updates or issues on Prefect's GitHub repository for any related reports. For more information on handling

PrefectFuture

and resolving these warnings, refer to the Prefect 3.x documentation: - Task Runners and Prefect Futures If the problem persists, consider raising an issue with a detailed description and reproduction steps in the Prefect GitHub repository.

3 Views

Open in Slack

Previous Next