This document presents an addition proposed for a future version of the SYCL Specification. The goal of this proposal is to reduce the complexity and verbosity of using SYCL for programmers.
Queues in SYCL are out-of-order by default. SYCL constructs directed acyclic graphs to ensure tasks are properly ordered based on their data dependences. However, many programs only require linear DAGs. The overheads of constructing and managing DAGs are unnecessary for this class of program. The ordered_queue class exists to serve this class of programs by providing simple in-order semantics. ordered_queue otherwise functions identically to the normal SYCL queue. Due to the simpler semantics and task dependences of an in-order queue, additional programming simplifications are also possible.
link:ordered_queue.h[role=include]Since ordered_queue has simpler in-order semantics, programmers do not need to specify dependences between tasks by building DAGs based on data dependences. Command group scope for tasks submitted to ordered_queue only needs to contain kernel definitions or explicit memory operations in order to define valid execution. Consequently, the single_task and parallel_for APIs, normally used on the command group handler class, are available directly on the ordered_queue class.