watchman

nteracting with a file at the same time as something else mounted an equivalent path "over" the directory the file was originally in is nonzero. - It's been a few years since I fought with this, but aren't there edge cases here if the system clock goes backwards? IIRC the inode timestamp isn't monotonic--right? There are various strategies for detecting clock adjustment, of various reliability, that you could use here, if so. Just checking if the mtime-vs-system-clock diff is negative is a start. That covers the more common of the "vanishingly uncommon but I've still seen 'em" cases related to file modification detection. Whether you choose to cope with people messing with the file via utime(2) is up to you (past a point, it feels like coping with malicious misuse rather than edge cases). But since your code runs in a loop, you're well-positioned to do that (and detect drift/manipulations of the system clock): track a monotonic clock and use it to approximate the elapsed wall time between honker poller ticks (say it fast with an accent, and you get https://www.bbc.com/news/world-latin-america-11465127); if the timestamp reported by (f)stat(2) ever doesn't advance at the same rate, fall back to checksumming the file, or crashing or something. But this is well into the realm of abject paranoia by now. It's been a decade or so since I worked in this area, so some of that knowledge is likely stale; you probably know a lot more than I do after developing this library even before considering how out-of-date my knowledge might be. When I worked on this stuff, I remember that statx(2) was going to solve all the problems any day now, and then didn't. More relevant, I also remember that the lsyncd (https://github.com/lsyncd/lsyncd) and watchman (https://github.com/facebook/watchman) codebases were really good sources of "what didn't I think of" information in this area. But seriously, again, nice work! Those are nitpicks; this is awesome as-is!

ndard expected by developers was a very difficult systems problem with a ton of event ordering and cache invalidation concerns. (With EdenFS, in particular, I believe there was machine learning involved to detect prefetch patterns.) For smaller repos, it is much simpler to do linear scans. Since it is really fast on modern hardware anyway, it is also the right thing to do, following the maxim of doing the simplest thing that works.

uple of times for git as well but nothing has come of it so far [2]. [1] https://github.com/facebook/watchman [2] http://git.661346.n2.nabble.com/inotify-to-minimize-stat-cal...