Pipeliner
Pipeliner is a Rust library to help you create multithreaded work pipelines. You can choose how many threads each step of the pipeline uses to tune performance for I/O- or CPU-bound workloads.
The API docs contain code examples.
Links
Comparison with Rayon
Rayon is another Rust library for parallel computation. If you're doing purely CPU-bound work, you may want to try that out to see if it offers better performance.
Pipeliner, IMHO, offers a simpler interface. That simpler interface makes it easier to combine parts of a data pipeline that may be I/O-bound and CPU-bound. Usually in those cases, your bottleneck is I/O, not the speed of your parallel execution library, so having a nice API may be preferable.