# Preventing alternate and main task from running and inconsistent task status

**URL:** <https://cylc.discourse.group/t/preventing-alternate-and-main-task-from-running-and-inconsistent-task-status/1021>\
**Category:** Cylc Support\
**Created:** [September 17, 2024, 4:58am UTC](https://cylc.discourse.group/t/preventing-alternate-and-main-task-from-running-and-inconsistent-task-status/1021 "2024-09-17T04:58:15Z")\
**Posts on this page:** 1\
**Showing post:** 6

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**Author:** ![oliver.sanders](https://yyz2.discourse-cdn.com/free1/user_avatar/cylc.discourse.group/oliver.sanders/32/110_2.png) [@oliver.sanders](https://cylc.discourse.group/u/oliver.sanders)\
**Post date:** [September 17, 2024, 10:13am UTC](https://cylc.discourse.group/t/preventing-alternate-and-main-task-from-running-and-inconsistent-task-status/1021/6 "2024-09-17T10:13:27Z")

</div>

> Here is the link to the earlier post [Blocking a task being triggered if its recovery task is active - Cylc / Cylc Support - Cylc Workflow Engine](https://cylc.discourse.group/t/blocking-a-task-being-triggered-if-its-recovery-task-is-active/750)

Thanks, that’s useful.

If I understand correctly, you are worried that operators might manually trigger the `forecast` task whilst the `forecast_shortstep` task is running causing problems?

If so, I would recommend using a single `forecast` task and using `cylc broadcast` to toggle the shortstep behavior on and off. This is how we work at the MO.

Here’s an over-simplified example:

```cylc
[runtime]
    [[forecast]]
        script = my-model
        [[[environment]]]
            SHORTSTEP = false    

```

To turn shortstep on, issue a broadcast e.g:

```auto
$ cylc broadcast <workflow> -p <cycle> -n forecast -s '[environment]SHORTSTEP=true'

```

Any subsequent submission of this task will now run with `SHORTSTEP=true`.

You can automate this using “retry event handlers”. Here’s an example where the task will run with `SHORTSTEP=false` the first time, then all subsequent attempts will run with `SHORTSTEP=true":

```cylc
[runtime]
    [[forecast]]
        script = my-model
        execution retry delays = 4*PT1M
        [[[events]]]
            retry event handlers = cylc broadcast $CYLC_WORKFLOW_ID -p $CYLC_TASK_CYCLE_POINT -n $CYLC_TASK_NAME -s '[environment]SHORTSTEP=true'
        [[[environment]]]
            SHORTSTEP = false

```

It’s likely your example isn’t quite as simple as mine above:

- There might be multiple environment variables to change.
- You might need to extend the `execution time limit`.
- You want to retry three times _before_ falling back to shortstep.

To handle this extra complexity, you might want to move the logic into a short script (e.g. in the workflow’s `bin/` directory)

```cylc
# flow.cylc

[runtime]
    [[forecast]]
        script = my-model
        execution retry delays = 4*PT1M
        execution time limit = PT30M
        [[[events]]]
            retry event handlers = shortstep-handler %(workflow)s %(cycle)s %(task)s %(try_num)d
        [[[environment]]]
            SHORTSTEP = false

```

```bash
# bin/shortstep-handler

set -euo pipefail

WORKFLOW="$1"
CYCLE="$2"
TASK="$3"
TRY_NUM="$4"

if [[$TRY_NUM -gt 3]];
    # the task is on its third retry
    cylc broadcast "${WORKFLOW}" \
        -p "${CYCLE}" \
        -n "${TASK}" \
        -s '[environment]SHORTSTEP=true' \
        -s '[environment]FOO=bar' \
        -s 'execution time limit=PT1H'
fi

```

For a list of the `%(variable)s` available to event handlers (e.g. `retry event handlers`), see [task event template variables](https://cylc.github.io/cylc-doc/stable/html/user-guide/writing-workflows/runtime.html#task-event-template-variables).

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