process: add nice() function
The nice function allows us to fine-tune the process to meet desired scheduling behavior. If our process needs less schedule time because it is a long-running one, we can increase the nice value and cause the scheduler to select the process not so often.
If desired, here's the technical documentation: http://man7.org/linux/man-pages/man2/nice.2.html
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines