ParallelWorkItemDispatcher
ParallelWorkItemDispatcher handles execution of work items by
queuing them for worker threads to process.
Enumerates all the Queues supported by the dispatcher
Enumerates all the shifts supported by the dispatcher
Construct a ParallelWorkItemDispatcher
Cancel the ongoing run completely.
If no run is in process, the call has no effect.
Dispatch a single work item for execution. The first
work item dispatched is saved as the top-level
work item and used when stopping the run.
Start execution, setting the top level work,
enqueuing it and starting a shift to execute it.