Working with interruptible tasks

When a task has at least two incoming links, one of which constrains the start of the task and one of which constrains the finish of the task, it is possible that the dates that are calculated during a reschedule may be contradictory. For example, a Start-to-Start relationship between two tasks may want to start the successor activity before the Finish-to-Finish relationship will allow for, as illustrated below:

Normally, the reschedule will not change the relationship between these two tasks, meaning that the Start-to-Start relationship is not accurately portrayed in the project. To get around this problem, you can designate tasks such as task B in this example - which have at least two incoming links, one of which constrains the start of the task and one of which constrains the finish of the task - as interruptible tasks. Interruptible tasks are those that are able to start earlier and in which work can be interrupted at some point before the finish of the task. If task B in this example is an interruptible task, rescheduling the project will result in the following:

Monitoring the consumption of interruptible tasks

You can use the Buffer consumption field to monitor the way in which the durations of interruptible tasks change during reschedules. You do this in the same way as you use the field to monitor the consumption of buffer tasks.

Filtering for interruptible and potentially interruptible tasks

You can use the Constraints and buffers page of the Filter Wizard to filter for interruptible tasks, and also for potentially interruptible tasks, ie those tasks that have at least two incoming links, one of which constrains the start of the task and one of which constrains the finish of the task. If task B in the illustrations above had not already been designated as an interruptible task, it would be identified by the Filter Wizard as a potentially interruptible task, as it is an ideal candidate for conversion into a an interruptible task. Once you have filtered for potentially interruptible tasks you can mark them as interruptible as required.