@Marvin i would like to use as example the following: from prefect import task, flow from prefect.states import Completed, Failed @task def always_fails_task(): raise ValueError("I fail successfully") @task def always_succeeds_task(): print("I'm fail safe!") return "success" @flow def always_succeeds_flow(): x = always_fails_task.submit() y = always_succeeds_task.submit() if y.result() == "success": return Completed(message="I am happy with this result") else: return Failed(message="How did this happen!?") if name == "__main__": always_succeeds_flow() in particular this feature if y.result() == "success": return Completed(message="") and bring it in my code: @task def run_uploader(uploader: Uploader): uploader.load() @flow async def single_asset_uploader(asset_id: str) -> None: data_contract = get_data_contract(asset_id) uploaders = get_uploaders_from_data_contract(data_contract, datetime) upload_tasks = run_uploader.map(uploaders) await create_ok_file(wait_for=upload_tasks, data_contract=data_contract) in particular when one of task go in the statis creashed, i would like to force the status to Failed

In Prefect, handling the states of tasks and flows can vary slightly depending on the version you're using, so it's good to get a grip on how these operate. For both Prefect 2.x and 3.x, you can manually set the flow run state based on the task states. If any task ends in a failed state, you can explicitly mark the flow run as failed. Let's explore how you can modify your code to handle this: ### Prefect 3.x In Prefect 3.x, you might handle task or flow state directly by checking the state of the tasks. Here's a simplified approach of what you could use:

python
from prefect import task, flow
from prefect.states import Completed, Failed, State

@task
def run_uploader(uploader):
    uploader.load()

@flow
async def single_asset_uploader(asset_id: str):
    data_contract = get_data_contract(asset_id)
    uploaders = get_uploaders_from_data_contract(data_contract, datetime)
    upload_tasks = run_uploader.map(uploaders)
    
    # Check if any task failed
    if any(task.state.is_failed() for task in upload_tasks):
        return Failed(message="One or more tasks failed.")
    
    await create_ok_file(wait_for=upload_tasks, data_contract=data_contract)
    return Completed(message="All tasks completed successfully.")

This code assumes you're using Prefect 3.x. The

task.state.is_failed()

is a way to explicitly check if any task has failed. ### Additional Resources: - Prefect 3.x handles terminal state determination, and the flow's return value directly impacts whether it is considered

Completed

,

Failed

, or

Crashed

. For more details, see the Prefect 3.x manage states documentation and Prefect 3.x upgrade guide. - Prefect 2.x also allows a combination of states and the final state of the flow run depends on the resolution of these states. Relevant 2.x documentation includes concepts of flows and strategies during migration to Prefect 3.0. If you're not running a specific Prefect version, these examples give a general idea of how you can manage states and ensure failure is properly handled in your workflows.

i'm using prefect 2, could you please provide me a code that works with prefect 2?

To handle the task failure in Prefect 2.x and ensure that the flow returns a

Failed

state if any task fails, you can check the states of the tasks directly and use the

return_state

parameter to manage flow results. Here's how you can achieve that:

python
from prefect import task, flow
from prefect.engine.state import Completed, Failed
from prefect.tasks.controlflow import merge

@task
def run_uploader(uploader):
    uploader.load()

@flow
def single_asset_uploader(asset_id: str):
    data_contract = get_data_contract(asset_id)
    uploaders = get_uploaders_from_data_contract(data_contract, datetime)
    
    # Run uploader tasks and collect their results
    upload_tasks = [run_uploader.submit(uploader) for uploader in uploaders]
    
    # Check if any task failed
    task_states = [task.wait().state for task in upload_tasks]
    if any(state.is_failed() for state in task_states):
        return Failed(message="One or more tasks failed while uploading.")
    
    create_ok_file(data_contract=data_contract)
    return Completed(message="All tasks completed successfully.")

if __name__ == "__main__":
    single_asset_uploader("your_asset_id")

### Key Points 1. State Management: We capture each task's state using

.wait().state

and check if any task failed using

state.is_failed()

. 2. Return State: The flow manually returns a

Failed

state if any of the task states indicate a failure. For more details about using states in Prefect 2.x, you can refer to the Prefect 2.x flow concepts documentation. I hope this helps your flow run like a well-oiled machine... or at least as close as we can get in the thrilling world of asynchronous task management!

@Marvin is it not possible to mark the task itself as failed when the task crash. My focus is when a task go in the sttaus crashed to make it failed, so the retry mechanism could work

In Prefect 2.x, tasks can have retry mechanisms built in. When a task encounters what Prefect considers a "crash" (such as a network timeout or infrastructure issue), this isn't automatically treated as a "failed" state but can be managed to activate retries. ### Handling Crashes with Retries in Prefect 2.x To handle crashes, you can use Prefect's retry functionality, which by default handles retries if exceptions are raised. You can specify the retry mechanism at the task level. Here's an example with custom retry behavior:

python
from prefect import task, flow

@task(retries=3, retry_delay_seconds=10)
def run_uploader(uploader):
    if isinstance(uploader, SomeFailureCondition):  # Assuming you know the failure condition
        raise Exception("Simulating a crash!")
    uploader.load()

@flow
def single_asset_uploader(asset_id: str):
    data_contract = get_data_contract(asset_id)
    uploaders = get_uploaders_from_data_contract(data_contract, datetime)
    upload_tasks = [run_uploader.submit(uploader) for uploader in uploaders]

    # Wait for tasks to complete and check states, but retries happen automatically
    for task in upload_tasks:
        task.wait()  # Or handle the future object for more control if needed

if __name__ == "__main__":
    single_asset_uploader("your_asset_id")

### Explanation: - Retries Setup: We set up the task with

retries=3

to allow up to three retries upon encountering an exception or crash-like behavior. - Delay Between Retries: The

retry_delay_seconds=10

sets a 10-second delay between each retry attempt. ### Additional Pointers: - For tasks to be retried automatically on failure, ensure that exceptions are properly raised. - If specific crash situations need different handling, consider using a custom

retry_condition_fn

. If more specific criteria are involved in identifying a task status as "crashed" or if you want to ensure retries only in certain failed scenarios, check out the relevant Prefect 2.x task concepts documentation for guidance on setting global retry configurations or using custom retry conditions. And remember, even in the chaos of managing retries, there's always room for a bit of zen and order in your task scheduling!

the problem is that i do not know waht will be the problem of a crash and tehe proble is that the retry mechanidm works for failed task/flow not work with crash task/failed, for this i would like to impement something that when thet task run_uploader enter in crashed state we force the failed status

To handle "crashed" tasks in Prefect 2.x and convert them to a "failed" state to activate the retry mechanism, you can use Prefect's state change hooks. These hooks allow you to define custom behavior when a task transitions between states. Here's a strategy you can use to achieve this: ### Define a State Change Hook You can define a state change hook that triggers when a task enters a "crashed" state and converts it to "failed." This can activate Prefect's retry mechanism, as retries typically rely on a task's failed state.

python
from prefect import task, flow
from prefect.engine.state import Crashed, Failed
from prefect.engine.signals import FAIL

def state_handler(obj, old_state, new_state):
    # Check if the task has transitioned into a Crashed state
    if isinstance(new_state, Crashed):
        # Force the state to Failed to allow retrials
        return Failed("Task transitioned from Crashed to Failed.")

@task(state_handlers=[state_handler], retries=3, retry_delay_seconds=10)
def run_uploader(uploader):
    uploader.load()

@flow
def single_asset_uploader(asset_id: str):
    data_contract = get_data_contract(asset_id)
    uploaders = get_uploaders_from_data_contract(data_contract, datetime)
    upload_tasks = [run_uploader.submit(uploader) for uploader in uploaders]

    for task in upload_tasks:
        task.wait()

if __name__ == "__main__":
    single_asset_uploader("your_asset_id")

### Explanation - State Handler: The

state_handler

function checks if a task enters a

Crashed

state. If it does, it transitions to

Failed

, which allows for retry attempts. - Retries: The task retry logic is configured using the

retries

parameter to allow retries when the task state is "failed". ### Resources Refer to the Prefect 2.x state change hooks documentation for more details about managing state transitions. By converting "crashed" states to "failed," you can leverage Prefect's built-in retry mechanism, ensuring tasks get the chance to execute successfully despite transient issues—much like getting up again after accidentally "crashing" into a metaphorical wall.

@Marvin l'unica è fare che quando il subflow va in carshed, marchiamo tale subflow in failed --> implementami il codice:

@flow(flow_run_name=generate_flow_run_name, on_crashed=)
async def single_asset_uploader(asset_id: str, schedule_id: int = 1, datetime = datetime.now()) -> None:
    logger = get_run_logger()

    <http://logger.info|logger.info>(f"Load data contract for asset '{asset_id}'")
    data_contract = get_data_contract(asset_id)

    <http://logger.info|logger.info>(f"Remove file .ok asset '{asset_id}'")
    await remove_ok_file(data_contract)

    <http://logger.info|logger.info>(f"Import file from DataDock to DataGateway")
    await data_dock_to_data_gateway(data_contract, schedule_id)

    <http://logger.info|logger.info>(f"Upload asset to destinations")
    uploaders = get_uploaders_from_data_contract(data_contract, datetime)

    <http://logger.info|logger.info>(f"Run uploaders tasks")
    upload_tasks = run_uploader.map(uploaders)

    <http://logger.info|logger.info>(f"Creation file .ok asset '{asset_id}'")
    await create_ok_file(wait_for=upload_tasks, data_contract=data_contract)

To handle a

crashed

subflow by marking it as

failed

in Prefect 2.x, you can use a state change hook. This hook allows you to execute custom logic when your flow transitions to a

crashed

state. By doing so, you can programmatically change its state to

failed

. Here's how you can implement this logic in your flow:

python
from prefect import flow
from prefect.engine.state import Crashed, Failed
from prefect import get_run_logger

async def custom_crash_handler(flow, flow_run, state):
    # Check if the flow has transitioned into a Crashed state
    if isinstance(state, Crashed):
        logger = get_run_logger()
        logger.warning("Flow run crashed, marking as failed.")
        return Failed("Flow transitioned from Crashed to Failed.")

@flow(flow_run_name=generate_flow_run_name, on_crashed=custom_crash_handler)
async def single_asset_uploader(asset_id: str, schedule_id: int = 1, datetime=datetime.now()) -> None:
    logger = get_run_logger()

    <http://logger.info|logger.info>(f"Load data contract for asset '{asset_id}'")
    data_contract = get_data_contract(asset_id)

    <http://logger.info|logger.info>(f"Remove file .ok asset '{asset_id}'")
    await remove_ok_file(data_contract)

    <http://logger.info|logger.info>("Import file from DataDock to DataGateway")
    await data_dock_to_data_gateway(data_contract, schedule_id)

    <http://logger.info|logger.info>("Upload asset to destinations")
    uploaders = get_uploaders_from_data_contract(data_contract, datetime)

    <http://logger.info|logger.info>("Run uploaders tasks")
    upload_tasks = run_uploader.map(uploaders)

    <http://logger.info|logger.info>(f"Creation file .ok asset '{asset_id}'")
    await create_ok_file(wait_for=upload_tasks, data_contract=data_contract)

### Key Points: - Custom Crash Handler: The

custom_crash_handler

function checks the flow's state. If the state is

Crashed

, it logs a warning and modifies the state to

Failed

. This allows any retry logic configured for failures to kick in. - on_crashed Parameter: This parameter sets the hook to be used when the flow crashes. This approach ensures that if your subflow enters a

crashed

state, it is converted to

failed

, enabling any further logic tied to failed states, such as retries, to execute effectively. For more nuanced details on managing state transitions, check out the Prefect 2.x state change hooks documentation.