< Marvin> I am writing a unit test for a flow for prefect v3 Prefect Community #ask-marvin

<@ULVA73B9P> I am writing a unit test for a flow f...

Menekse Kuyu

10/01/2024, 10:16 AM

@Marvin I am writing a unit test for a flow for prefect v3. This test was used to written in v2 and used SequentialTaskRunner, now I migrated to v3 and it starts giving errors

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E                     File "/Users/.../site-packages/prefect/_internal/concurrency/cancellation.py", line 536, in cancel_sync_at
E                       with cancel_sync_after(timeout, name=name) as ctx:
E                   ResourceWarning: unclosed <socket.socket fd=27, family=2, type=1, proto=6, laddr=('127.0.0.1', 64935), raddr=('127.0.0.1', 8651)>

Marvin

10/01/2024, 10:16 AM

It seems that in Prefect 3,

SequentialTaskRunner

has been deprecated and the task execution system has undergone some changes. The error you are encountering is likely related to these changes. In Prefect 3, task runners like

ThreadPoolTaskRunner

DaskTaskRunner

, and

RayTaskRunner

are recommended for running tasks concurrently or in parallel. The main change is that task runners need to be explicitly configured and used with the

.submit()

method to enable concurrency or parallelism. Here's how you might adapt your unit test to use Prefect 3.x's `ThreadPoolTaskRunner`:

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python
from prefect import flow, task
from prefect.task_runners import ThreadPoolTaskRunner

@task
def example_task():
    # Your task implementation
    pass

@flow(task_runner=ThreadPoolTaskRunner())
def example_flow():
    example_task.submit()
    # or simply call example_task() if you don't require concurrency

# Now you can run your flow directly in your test
example_flow()

For more information on task runners in Prefect 3, you can refer to the Prefect 3 task runners documentation. If the issue persists, consider examining sockets management in your tasks, as the error message indicates potentially unclosed sockets. Ensure that any network connections or file handles are properly closed after use. Feel free to reach out if you have more questions!

Marvin

10/01/2024, 12:07 PM

The issue seems related to unclosed sockets, which might be caused by the way Prefect's concurrency mechanisms are used in your unit tests. Possible Resolution Steps: 1. Concurrency Handling in Tests: Ensure that you're properly handling socket connections in your tasks, especially if they involve network calls or multiprocessing. 2. Prefect Concurrency Contexts: Use the concurrency context manager to control the maximum number of concurrent operations. 3. Traceback Analysis: Rerun the specific test with detailed traceback information to pinpoint where the unclosed socket is initiated:

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bash
   PYTHONTRACEMALLOC=25 pytest path_to_your_test.py

4. Task Runner Update: Use Prefect’s recommended

ThreadPoolTaskRunner

for flows which do not require specific concurrency limitations. Here is how you can structure your flow with `ThreadPoolTaskRunner`:

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python
from prefect import flow, task
from prefect.task_runners import ThreadPoolTaskRunner

@task
def example_task():
    # Your task implementation
    pass

@flow(task_runner=ThreadPoolTaskRunner())
def example_flow():
    example_task.submit()

# Run your flow directly in your test
example_flow()

For further reading, you might find these resources useful: 1. Prefect’s global concurrency limits 2. Prefect’s troubleshooting guide These steps and resources should help identify and mitigate the

ResourceWarning

related to unclosed sockets in your unit tests with Prefect 3. If the issue persists, checking for proper resource clean-up in your tasks will be essential.

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