First command output latency: output visible after command ends #2262
Description
I noticed that the first command wasn't showing in emacs when compiling until it finished & I was assuming it was an emacs issue.
As far as I understand [0] is the same command as [1] but showing when it started running?
The issue is that when ninja is spawned as a subprocess, I don't see any feedback until the first command has finished. When Just running ninja in the terminal though, I get immediate feedback.
It's also noticeable when redirecting to a file. The first command [0] cmd.. will not get written to the file, while everything else does.
ninja > out: first command[0]not shownninja | tee out: again[0]not writtenunbuffer ninja >out:[0]gets written
The issue also appears when running ninja -v. With this even when running the command in the terminal, we won't get the first command written to the stdout until it finishes