Extension of the Runnable interface, adding special callbacks for long-running operations.
Task scheduler interface that abstracts the scheduling of <code>Runnables</code> based on different kinds of triggers.
Common interface for trigger objects that determine the next execution time of a task that they get associated with.
Context object encapsulating last execution times and last completion time of a given task.
General exception to be thrown on scheduling failures, such as the scheduler already having shut down.