ActuatorSchedulePreemption

Task Preemption

Both LOW and LOW_PREEMPT priority Tasks can be preempted. LOW priority Tasks may be preempted by a conflicting HIGH priority Task before it starts. LOW_PREEMPT priority Tasks can be preempted by HIGH priority Tasks even after they start.

When a Task is preempted the ActuatorAgent will publish to "devices/actuators/schedule/response" with the following header:

#python
{
    'type': 'CANCEL_SCHEDULE',
    'requesterID': <Agent ID for the preempted Task>,
    'taskID': <Task ID for the preempted Task>
}

And the message (after parsing the json):

#python
{
    'result': 'PREEMPTED',
    'info': '',
    'data': 
    {
        'agentID': <Agent ID of preempting task>,
        'taskID': <Task ID of preempting task>
    }
}

Preemption Grace Time

If a LOW_PREEMPT priority Task is preempted while it is running the Task will be given a grace period to clean up before ending. For every device which has a current time slot the window of remaining time will be reduced to the grace time. At the end of the grace time the Task will finish. If the Task has no currently open time slots on any devices it will end immediately.