Porting Decision Tree Building and Pruning Algorithms to Multicore using FastFlow

The whole computer hardware industry embraced multicores. For these machines, the extreme optimisation of sequential algorithms is no longer sufficient to squeeze the real machine power, which can be only exploited via thread-level parallelism. Decision tree algorithms exhibit natural concurrency that makes them suitable to be parallelised. This paper presents an approach for easy-yet-efficient porting of an implementation of the C4.5 algorithm on multicores. The approach is based on the FastFlow parallel programming environment. The strength of our porting consists in minimal changes to the original sequential code. In addition to the tree building algorithm, we consider also the so far unaddressed problem of parallelising the error-based pruning with grafting algorithm of C4.5. We devise lower bounds for the forms of parallelisations adopted, and achieve performances close to such bounds