High CPU usage

[listeningwing]

using mmap for performance.

[masatake]

A pull request with the results of benchmarks is welcome.
I don't think the ideas improve the performance that can be measured with time command.

a. Nice or renice commands may be what you want (if you use GNU/Linux).

b. If you use glibc, you can ask fopen to use mmap internally by specifying m. See https://sourceware.org/glibc/manual/2.40/html_node/Opening-Streams.html . However, I don't expect any performance improvement because in most cases, ctags accesses input files sequentially. The buffering mechanism behind fopen and fgetc may work as if we use mmap for sequential access.

Unlike ctags, readtags accesses tag files randomly. So mmap may improve the performance. I already added m flag to open. universal-ctags/libreadtags@c0f0107

[masatake]

An article read(2) vs mmap(2) の迷信 written in Japanese helps us think about the b.