Function bound_parallel_pool 

pub fn bound_parallel_pool()

Build rayon’s process-wide pool before a library builds it, so its size is [LIBRARY_THREADS] rather than one worker per logical CPU: a library that first calls par_iter (a message layer’s group tree, a renderer, a text layout) builds that pool itself, and on a machine with hundreds of CPUs it then holds hundreds of idle threads for work that is a handful of items. Bulk work a person waits for goes through cpu_pool, which is sized per core on purpose.