Further Scheduling

In this section we will quickly run through some of the more advanced features of Cylc’s scheduling logic.


So far we have written dependencies like foo => bar. This is, in fact, shorthand for foo:succeed => bar. It means that the task bar will run once foo has finished successfully. If foo were to fail then bar would not run. We will talk more about these task states in the Runtime Section.

We refer to the :succeed descriptor as a qualifier. There are qualifiers for different task states e.g:

When the task has started running.
When the task finishes if it fails (produces non-zero return code).
When the task has completed (either succeeded or failed).

It is also possible to create your own custom qualifiers to handle events within your code (custom outputs).

For more information see the Cylc User Guide.

Clock Triggers

In Cylc, cycle points are just labels. Tasks are triggered when their dependencies are met irrespective of the cycle they are in, but we can force cycles to wait for a particular time before running using clock triggers. This is necessary for certain operational and monitoring systems.

For example in the following suite the cycle 2000-01-01T12Z will wait until 11:00 on the 1st of January 2000 before running:

    initial cycle point = 2000-01-01T00Z
    [[special tasks]]
        clock-trigger = daily(-PT1H)
             graph = daily  # "daily" will run, at the earliest, one hour
                            # before midday.


See the Clock Triggered Tasks tutorial for more information.

Alternative Calendars

By default Cylc uses the Gregorian calendar for datetime cycling, but Cylc also supports the 360-day calendar (12 months of 30 days each in a year).

    cycling mode = 360day

For more information see the Cylc User Guide.