High-level template for the task-based parallel wavefront pattern

Given the arrival of multicore processors, it has become a matter of urgency to introduce parallel programming into mainstream computing. In emerging applications, a class of computational problem that poses a challenge to the programmers is the wavefront pattern. A particular characteristic of this pattern is multi-dimensional streaming of the computations that must follow a dependence pattern. The modern software stack for multicore systems offers task-based programming libraries like TBB (Threading Building Blocks), that allow an execution model based on lightweight asynchronous tasks. We suggest that TBB provides useful features to improve the scalability of these kinds of codes but at the cost of leaving some low-level task management details to the programmer. In this paper, we discuss such low-level task management issues and incorporate them into a high-level TBB-based template. The goal of the template is to improve the programmer's productivity such that a nonexpert user can easily code complex wavefront problems without having to deal with task creation, synchronization or scheduling mechanisms. With our template, the user only has to specify a definition file with the wavefront dependence pattern and the function that each task has to execute. In addition, we describe our experience with the TBB template when coding four complex real wavefront problems. In these experiments, we found that the template implementations reduced the programming effort from 25% to 50% at a cost of increasing the overhead up to 5% when compared to manual implementations of the same problem.