For those curious, this implementation is based on a recent line of research called "heartbeat scheduling" which amortizes the overheads of creating parallelism, essentially accomplishing a kind of dynamic automatic granularity control.

Related papers:

(2018) Heartbeat Scheduling: Provable Efficiency for Nested Parallelism. https://www.andrew.cmu.edu/user/mrainey/papers/heartbeat.pdf

(2021) Task Parallel Assembly Language for Uncompromising Parallelism. https://users.cs.northwestern.edu/~simonec/files/Research/pa...

(2024) Compiling Loop-Based Nested Parallelism for Irregular Workloads. https://users.cs.northwestern.edu/~simonec/files/Research/pa...

(2024) Automatic Parallelism Management. https://www.cs.cmu.edu/~swestric/24/popl24-par-manage.pdf