PROPOSAL: Skip Run-Mode For Tasks

A proposal for a configuration to “skip” tasks in order to resolve the issue of skipping families or cycles of tasks which are not yet present in the pool or which have non-uniform required outputs by utilising broadcast task matching.

This is effectively an automated solution to calling cylc set --output=skip which allows tasks to be “selected” according to broadcast rules opening up a wider range of use cases.


Sometimes users may wish to “skip” one or more tasks in order to short circuit a graph.

With Cylc 7 they would do something like:

# skip a family
cylc reset <wid> '<family-id>.*' -s succeeded
# skip a cycle
cylc reset <wid> '*.<cycle>' -s succeeded

However, at Cylc 8 tasks cannot be “selected” by globs in this way as globs apply only to the pool and Cylc 7 style reset is not permitted.

Note: Resetting to “waiting” use cases are catered for by cylc trigger --flow=new.


  1. A new task run mode called “skip” to sit alongside the existing “live” and “simulation” modes. The implementation would follow the same code-pathway as simulation mode. I.E. it would fake submission and execution, but yield real outputs into the workflow.

  2. The “skip” mode would be configured by [runtime][<namespace>][skip] to separate it from [runtime][<namespace>][simulation]. The valid configurations would be:

    • outputs - Define the outputs to be generated when this task runs in skip mode.
      • By default, all required outputs will be generated plus succeeded if success is optional.
      • The outputs submitted and started are always produced and do not need to be defined in outputs.
      • If outputs is specified and does not include either succeeded or failed then succeeded will be produced.
    • disable task event handlers - Disable the event handlers which would normally be called on task lifecycle events. By default event handers will be turned off.

    The skip mode will not support simulation mode configurations such as speedup factor which are not relevant to this functionality.

  3. The run mode should be controlled by a new task configuration [runtime][<namespace>]run mode with the default being live. As a runtime configuration, this can be defined in the workflow for development / testing purposes or set by cylc broadcast.

    If the run mode is set to simulation or skip in the workflow configuration, then cylc validate and cylc lint should produce a warning (similar to development features in other languages / systems).


    # run plotting tasks in skip mode (i.e. turn it off)
    cylc broadcast -n plotting -p '*' -s 'run mode=skip'
    # run debugging tasks in live mode (i.e. turn them on)
    cylc broadcast -n DEBUG -p '*' -s 'run mode=live'
  4. The cylc set --out option should accept the skip value which should set the outputs defined in [runtime][<namespace>][skip]outputs. The skip keyword should not be allowed in custom outputs.

  5. Tasks with run mode = skip will continue to abide by the is_held flag as normal.

  6. Force-triggering a task will not override the run mode.

  7. [Extension] The configured run mode should be made available as a task attribute so that the UI’s can display skip/simulation mode tasks with a task modifier (the held and runahead “badges” are task modifiers).

    The order of precedence for this modifier should be bellow the held and runahead states, but above queued.


    Task(is_held=True, run_mode='skip') => is_held modifier
    Task(is_runahead=True, run_mode='simulation') => runahead modifier
    Task(is_queued=True, run_mode='skip') => skip modifier
  8. [Extension] When tasks are run in skip mode, the prerequisites which correspond to the outputs they generate should be marked as satisfied by skip mode rather than satisfied naturally for provenance reasons.

    For the purpose of cylc remove logic, satisfied by skip mode should be treated the same as satisfied naturally.