Scheduling contract algorithms on multiple processors

Anytime algorithms offer a tradeoff between computation time and the quality of the result returned. They can be divided into two classes: contract algorithms, for which the total run time must be specified in advance, and interruptible algorithms, which can be queried at any time for a solution. An interruptible algorithm can be constructed from a contract algorithm by repeatedly activating the contract algorithm with increasing run times. The acceleration ratio of a run-time schedule is a worst-case measure of how inefficient the constructed interruptible algorithm is compared to the contract algorithm. The smallest acceleration ratio achievable on a single processor is known. Using multiple processors, smaller acceleration ratios are possible. In this paper, we provide a schedule for m processors and prove that it is optimal for all m. Our results provide general guidelines for the use of parallel processors in the design of real-time systems.