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ctime: I don't think that word means what you think it means. #49970
Description
| BPO | 5720 |
|---|---|
| Nosy | @pitrou, @benjaminp, @ezio-melotti |
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
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GitHub fields:
assignee = None
closed_at = None
created_at = <Date 2009-04-07.21:57:48.223>
labels = ['library']
title = "ctime: I don't think that word means what you think it means."
updated_at = <Date 2013-08-23.23:55:49.251>
user = 'https://bugs.python.org/zooko'bugs.python.org fields:
activity = <Date 2013-08-23.23:55:49.251>
actor = "Zooko.Wilcox-O'Hearn"
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2009-04-07.21:57:48.223>
creator = 'zooko'
dependencies = []
files = []
hgrepos = []
issue_num = 5720
keywords = []
message_count = 11.0
messages = ['85750', '85987', '89336', '195477', '196050', '196052', '196056', '196058', '196059', '196060', '196061']
nosy_count = 5.0
nosy_names = ['zooko', 'pitrou', 'benjamin.peterson', 'ezio.melotti', "Zooko.Wilcox-O'Hearn"]
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue5720'
versions = ['Python 3.4']
Activity
zooko commentedon Apr 7, 2009
The stat module currently uses the "st_ctime" slot to hold two kinds
values which are semantically different but which are frequently
confused with one another. It chooses which kind of value to put in
there based on platform -- Windows gets the file creation time and all
other platforms get the "ctime". The only sane way to use this API is
then to switch on platform:
(That is an actual code snippet from the Allmydata-Tahoe project.)
Many or even most programmers incorrectly think that unix ctime is file
creation time, so instead of using the sane idiom above, they write the
following:
metadata["ctime"] = s.st_ctime
thus passing on the confusion to the users of their metadata, who may
not know on which platform this metadata was created. This is the
situation we have found ourselves in for the Allmydata-Tahoe project --
we now have a bunch of "ctime" values stored in our filesystem and no
way to tell which kind they were.
More and more filesystems such as ZFS and Macintosh apparently offer
creation time nowadays.
I propose the following changes:
(Windows, ZFS, Mac) which can do so.
That is hopefully not too controversial and we could proceed to do so
even if the next proposal gets bogged down:
ctime and never by any other value (even on Windows, where the unix
ctime *is* available even though nobody cares about it), and deprecate
the hopelessly ambiguous "st_ctime" field.
You may be interested in http://allmydata.org/trac/tahoe/ticket/628
("mtime" and "ctime": I don't think that word means what you think it
means.) where the Allmydata-Tahoe project is carefully unpicking the
mess we made for ourselves by confusing ctime with file-creation time.
pitrou commentedon Apr 15, 2009
Sounds like a good idea, perhaps you could launch a discussion on
python-dev?
zooko commentedon Jun 13, 2009
Okay, I posted to python-dev:
http://mail.python.org/pipermail/python-dev/2009-June/090021.html
ezio-melotti commentedon Aug 17, 2013
What was the outcome?
ZookoWilcox-OHearn commentedon Aug 23, 2013
Well, read the thread! http://mail.python.org/pipermail/python-dev/2009-June/090021.html
Basically just a couple of +1's, and a good suggestion to name it something clearer than "crtime".
Please fix it!
benjaminp commentedon Aug 23, 2013
I don't think we should hijack st_ctime. All the other members of the stat object correspond exactly to what you get back from the Unix stat() call. Let's not break that. How about just leaving st_ctime as it is and adding st_creationtime, which will have the nicer semantics?
ZookoWilcox-OHearn commentedon Aug 23, 2013
Benjamin Peterson: what do you mean "hijack ctime"? I don't think I — or anyone — has proposed anything that fits that description. Please be more specific. My proposal in http://bugs.python.org/issue5720#msg85750 does not break anything.
benjaminp commentedon Aug 23, 2013
Indeed, "hijacking" is a bit strong. I mean filling it with a value that is not in the underlying st_ctime field from stat() call.
ZookoWilcox-OHearn commentedon Aug 23, 2013
Benjamin: I'm sorry, I still don't understand. Do you think my proposal would involve setting something named "ctime" to contain a value that didn't come from the underlying stat "ctime"?
benjaminp commentedon Aug 23, 2013
You're quite right. I stupidly misread "crtime" as "ctime".
ZookoWilcox-OHearn commentedon Aug 23, 2013
Aha! Mystery solved. I wouldn't say that you were stupid — I would say that "crtime" is way too close to "ctime", and I strongly agree with the suggestion (http://mail.python.org/pipermail/python-dev/2009-June/090026.html) on the mailing list by Greg Ewing that we name the new thing something more obvious.