What are the differences between librt and libeio for asynchronous I/O, and why would I choose one over the other?

I really want to put more in the body to explain the question… but the title really covers it all. As far as I can suss, librt is more “official” (it’s a standard part of libc?), but I also remember seeing that Node.js uses libeio. Which should I spend more time looking int开发者_运维问答o? What about portability? How different are their APIs?

(I’d appreciate it if somebody with ≥1,500 rep could add the tags “libeio” and “librt” to this question, as I cannot.)

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libeio wraps standard calls in threads, and handles a large swath of the common system calls.

librt only has a few calls -- read and write, but not, for example, stat.