Two-way variable implementation in the job submission end-point. Where
Flamenco v2 did the variable replacement in the add-on, this has now
been moved to the Manager itself. The only thing the add-on needs to
pass is its platform, so that the right values can be recognised.
This also implements two-way replacement when tasks are handed out, such
that the `{jobs}` value gets replaced to a value suitable for the
Worker's platform as well.
Add a `sleep_repeats: 1` setting to `debug-job-echo.sh`. It doesn't change
the behaviour of the job, but it does make it visible that this setting
exists, and that it can be used to generate a large number of tasks.
Worker and Manager implementation of the "may-I-kee-running" protocol.
While running tasks, the Worker will ask the Manager periodically
whether it's still allowed to keep running that task. This allows the
Manager to abort commands on Workers when:
- the Worker should go to another state (typically 'asleep' or
'shutdown'),
- the task changed status from 'active' to something non-runnable
(typically 'canceled' when the job as a whole is canceled).
- the task has been assigned to a different Worker. This can happen when
a Worker loses its connection to its Manager, resulting in a task
timeout (not yet implemented) after which the task can be assigned to
another Worker. If then the connectivity is restored, the first Worker
should abort (last-assigned Worker wins).
