Simple and Integrated Heuristic Algorithms for Scheduling Tasks with Time and Resource Constraints

We consider the problem of scheduling a set of n tasks in a system having r resources. Each task has an arbitrary, but known, processing time and a deadline, and may request use of a number of resources. A resource can be used either in shared mode or exclusive mode. In this article, we study algorithms used for determining whether or not a set of tasks is schedulable in such a system, and if so, determining a schedule for it. This scheduling problem is known to be NPcomplete and hence we methodically study a set of heuristics that can be used by such an algorithm. Due to the complex-ity of the problem, simple heuristics do not perform satisfactorily. However, an algorithm that uses combina-tions of these simple heuristics works very well com-pared to an optimal algorithm that takes exponential time complexity. For the combination that performs the best, we also determine the scheduling costs as a function of the size of the task set scheduled. 1