On 05Apr2012 21:07, Zooko Wilcox-O'Hearn <zo...@zooko.com> wrote: | On Thu, Apr 5, 2012 at 7:14 PM, Greg Ewing <greg.ew...@canterbury.ac.nz> wrote: | > This is the strict mathematical meaning of the word "monotonic", | > but the way it's used in relation to OS clocks, it seems to mean rather | > more than that. | | Yep. As far as I can tell, nobody has a use for an unsteady, monotonic clock.
Well, not for a wildly unsteady monotonic clock. | There seem to be two groups of people: | 1. Those who think that "monotonic clock" means a clock that never | goes backwards. I will always fall into this category. | These people are in the majority. After all, that's | what the word "monotonic" means ¹ . However, a clock which guarantees | *only* this is useless. Sure. I wouldn't have much use for a clock that was only monotonic, but the word "clock" implies a bit more all on its own, so I am undisturbed. | 2. Those who think that "monotonic clock" means a clock that never | jumps, and that runs at a rate approximating the rate of real time. If they're calling it "monotonic" on that basis alone, they are wrong. Pure and simple. | This is a very useful kind of clock to have! It is what C++ now calls | a "steady clock". It is what all the major operating systems provide. Sure. So _call_ it a steady clock! | The people in class 1 are more correct, technically, and far more | numerous, but the concept from 1 is a useless concept that should be | forgotten. | | So before proceeding, we should mutually agree that we have no | interest in implementing a clock of type 1. It wouldn't serve anyone's | use case (correct me if I'm wrong!) and the major operating systems | don't offer such a thing anyway. Bah! They are not disjoint sets of clocks! Linux' CLOCK_MONOTONIC_RAW is both type 1 and type 2. | Then, if we all agree to stop thinking about that first concept, then | we need to agree whether we're all going to use the word "monotonic | clock" to refer to the second concept, No. | or if we're going to use a | different word (such as "steady clock") to refer to the second | concept. I would prefer the latter, as it will relieve us of the need | to repeatedly explain to newcomers: "That word doesn't mean what you | think it means.". Yes. Resorting to The Princess Bride to resolve bad terminology is only funny in a movie, and should be a Big Clue that the term is either being misused or too badly understood. | The main reason to use the word "monotonic clock" to refer to the | second concept is that POSIX does so, but since Mac OS X, Solaris, | Windows, and C++ have all avoided following POSIX's mistake, I think | Python should too. No. If it is not monotonic, DO NOT CALL IT monotonic. Call it steady, perhaps, if it _is_ steady (within some threshold of course). But CLOCK_MONOTONIC_RAW is type 1 and 2, and is thus a "steady monotonic" clock. Probably a good choice for both. We can argue about what characteristics a useful clock has. And we can argue about what characteristics the various OS clocks possess. But please DO NOT invent a new and misleading meaning for a well defined word. "monotonic" alone is such a word, and means just one thing. "monotonic clock" means _more_, but isn't always a requirement; "steady clock" seems more commonly wanted. Except of course that some participants say "steady clock" is a nonsensical term. -- Cameron Simpson <c...@zip.com.au> DoD#743 http://www.cskk.ezoshosting.com/cs/ Politics, n. Strife of interests masquerading as a contest of principles. - Ambrose Bierce, _The_Devil's_Dictionary_ _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
