xargs -P "$(nproc)" --process-slot-var=s sh -c 'grep X "$@" >>/tmp/g.$s' d0
cat /tmp/g.*
You can also cobble together that second style with a custom config setup wherein a command is given $s and responds with some host names and there might be an `ssh` in front of the `grep`, for example. That `d0` argument (for $0) is a bit janky and there can be shell quoting issues, of course. But then again, you may not have hostile filenames/whatever. Remote loadavg adaptation might be nice, but then again, maybe you control all the remotes. Similarly, I could not get back-to-back executions of the EPOCHREALTIME thing closer than 250 microseconds. So, collision basically will not happen even though it probably could in theory.