Scheduler

Consider the simulation of a robot that delivers parcels of mail between desks on a same floor. Each request comes at a random time. Parameters such that the origin and destination desks are ignored for the purpose of this exercise. Each request has priority and the amount of time or duration necessary for the delivery. The priority is 0 (bulk), 1 (regular), or 2 (express). The robot should deliver parcels in the order in which they arrive except for the priority. If the delivery of a parcel has not begun and the delivery of a new parcel with higher priority is requested, the new parcel will be delivered first.

Design, code, and test a simulation of the robot activities. Assume that delivery requests and delivery time are uniformly and randomly distributed. Use a Scheduler pattern to schedule concurrent requests to the robot.

Hints:

1. A difficulty of this exercise is to simulate the clients. Consider constructing a dozen or two threads that wake up at random times and request a delivery with a random priority and duration. Some (but not too many) requests should be overlapping.
2. The scheduler pattern is quite difficult. You may simplify the technique described in the textbook by hardcoding in the scheduler the scheduling order (this solution is less general, but it may ease understanding a difficult pattern).
3. Ideally you first code a solution that does not use a scheduler. The robot simply delivers parcels in the order in which they are requested, i.e., it ignores the priority. Then you add the scheduler.
4. The scheduler uses wait() and notify() to first prevent and then free the access to a resource. Could these be replaced by suspend() and resume()?