I've ran into this before, and I've always wondered why programs don't just do this: when data gets added to a previously-empty output buffer, make the input non-blocking, and whenever a read comes back with EWOULDBLOCK, flush the output buffer and make the input blocking again. (Or in other words, always make sure the output buffer is flushed before waiting/going to sleep.) Wouldn't this fix the problem? Would it have any negative side effects?

Setting nonblocking takes effect on the file description rather than just the file descriptor. Meaning if your program crashes the description remains in nonblocking mode for the next program, which is not prepared to handle it.

Node.js sets stdin to nonblocking. This is great because it means copy and pasting a shell script containing an npm install into your shell will work, since the description is reset between each program by your terminal. But when those same lines are executed by the bash interpreter directly, processes after npm will randomly fail by failing to read from stdin with a return value they never expected to see. Ask me how I know