Detailed Implementation of the Solution class

A Solution object contains a a mutation object, a combinatorial object (CO) - permutation, subset, or partition - and its costs, computed by the specified objective functions. Each combinatorial object has a reference count which is manipulated by the Solution class to know when to copy, commit, and discard the combinatorial object.

Since the system is time sensitive, generation of Solution objects are stopped by a monitoring object when the system meets a time constraint (e.g. reporting constraint, or deadline constraint). If the system meets the reporting constraint, the search that requests a solution to be generated must satisfy this constraint by reporting and then ask the monitoring object to lift the block. To ease a specific search (e.g. simulated annealing) to deal with these activities, they are handled in a BasicSearch class from which a specific search is derived. If the system meets the deadline constraint, it will stop.

The Solution class generate solutions in three distinct manners, which account for all the need of a typical local-search heuristic. Assuming time constraints have been satisfied,

1. generate random solution:
   • increment the new CO reference count (which was 0).
   • set mutation attribute to NoOp.
   • compute costs via user-defined objective functions.

2. generate a copy of a solution
   • increment the new object reference count.
   • set mutation attribute to the same as the one from which it is copied.
   • compute costs.

3. generate a random neighbor of a solution. This is where the real work is achieved, carefully. When we want to create a random mutation of a Solution object A,
   • if it is not a mutated object, then simply create a random mutation whose CO is pointed to A whose reference count is consequently incremented.
   • if it is a mutated object, then first its mutated CO must be committed before a new random mutation is created. Things must be handled properly in both cases where the count is greater than 1 or not.

Deletion of a Solution object occurs only if the deleted object is the sole possessor of the CO. Otherwise, the CO's reference count is decremented.

In Assignment of a Solution object, the object to be assigned to decrements its reference count and delete the CO if its no longer being referred to, before incrementing and pointing to the new referenced CO.