Thanks, yeah. For what it's worth, partly what led me to even leave this comment is that when he wrote "the code above is broken", I stared at it, and for the life of me I couldn't see why it was broken. Because, of course, the code was lying: there was no mention of leases or timeouts. Having a "lease" suddenly pulled out of nowhere really felt like a fast one being pulled on me (and really unfairly so!), hence I decided I'd actually leave the comment and question what the basis for this hidden time bomb even was in the first place?! If the code had said leaseLock(filename, timeout), I think the bug would've been glaringly obvious, and far fewer people would've been surprised by looking at the code.

Also for what it's worth, I can guess what some of the answers might be. For example, it's possible you'd need very precise timing facilities that aren't always available, in order to be able to guarantee high throughput with correctness (like Google Spanner's). Or it might be that doing so requires a trade-off between availability and partition-tolerance that in some applications isn't justified. But I'm curious what the answer actually is, rather than just (semi-)random guesses as to what it could be.