A case for extending task dependencies

Abstract

Tasks offer a natural mechanism to express asynchronous operations in OpenMP as well as to express parallel patterns with dynamic sizes and shapes. Since the release of OpenMP 4 task dependencies have made an already flexible tool practical in many more situations. Even so, while tasks can be made asynchronous with respect to the encountering thread, there are no mechanisms to tie an OpenMP task into a truly asynchronous operation outside of OpenMP without blocking an OpenMP thread. Additionally, producer/consumer parallel patterns, or more generally pipeline parallel patterns, suffer from the lack of a convenient and efficient point-to-point synchronization and data passing mechanism. This paper presents a set of extensions, leveraging the task and dependency mechanisms, that can help users and implementers tie tasks into other asynchronous systems and more naturally express pipeline parallelism while decreasing the overhead of passing data between otherwise small tasks by as much as 80 %.