skip-mode.rst

.. cylc-scope:: flow.cylc[runtime][<namespace>]

Skip Mode

.. versionadded:: 8.4.0

Skip mode is designed as an aid to workflow control:

• It allows creation of :term:`dummy tasks<dummy task>` as part of workflow design.
• It allows skipping of tasks in a running workflow using either: * cylc broadcast -s 'run mode = skip' (for when it is ready to run). This will work with any future task or family. * cylc set --out skip (to immediately skip). This only works with globs for active tasks. Otherwise task names must be explicit.

Note

Setting :cylc:conf:`run mode=skip` in your flow.cylc will lead to cylc validate returning a warning:

WARNING - The following tasks are set to run in skip mode:
  * example_task

This is designed to prevent users running a task in skip mode by mistake. If you are using skip mode deliberately then this can be ignored.

Task Outputs

Skip mode allows the user to specify which task outputs will be emitted using :cylc:conf:`[skip]outputs`.

By default:

• All required outputs will be generated.
• succeeded will be generated even if success is :term:`optional <optional output>`.
• If :cylc:conf:`[skip]outputs` is specified and does not include either succeeded or failed, then succeeded will still be generated.

The outputs submitted and started are always generated and do not need to be defined in outputs.

Task Event Handlers

By default task event handlers are disabled by skip mode, but they can be enabled using :cylc:conf:`[skip]disable task event handlers`.

Skip Mode Examples

Set task to succeeded

Scenario

We want to turn off a future task or cycle of a workflow. We don't want to set the outputs right now. But when it would have run we want to set it to succeed.

Broadcast :cylc:conf:`run mode` setting the value to skip.

# Set a single future task to run in skip mode:
cylc broadcast myworkflow// -p 4 -n mytask -s 'run mode = skip'

# Skip Cycle 4:
cylc broadcast myworkflow// -p 4 -n '*' -s 'run mode = skip'

# Skip mytask for all cycles:
cylc broadcast myworkflow// -n mytask -s 'run mode = skip'

Create a Graph Control Task

Scenario

We have a large family to large family trigger.

If we increase N, the number of dependencies being tracked by the scheduler is N^2.

In this scenario the addition of a skip-mode task between two families improves the efficiency of the Cylc scheduler.

.. seealso::

   This scenario is explained in detail in
   :ref:`EfficientInterFamilyTriggering`

Parameter Exclusion

Scenario

We want to skip a small number of tasks from a parameterized group of tasks:

[task parameters]
    # House number 13 doesn't actually exist on this street...
    house_number = 1..20

We can use skip mode to make sure that a parameter task always succeeds without running anything:

[runtime]
    [[post parcel<house_number>]]
        script = send letter
    [[post parcel<house_number=13>]]
        run mode = skip

.. cylc-scope::