Repository navigation
Use scandir() to speed up the glob module #69782
Description
| BPO | 25596 |
|---|---|
| Nosy | @gvanrossum, @vstinner, @benhoyt, @xdegaye, @dimaqq, @serhiy-storchaka |
| Dependencies | |
| Files |
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
Show more details
GitHub fields:
assignee = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2016-09-07.11:10:52.544>
created_at = <Date 2015-11-10.11:18:07.859>
labels = ['type-feature', 'library']
title = 'Use scandir() to speed up the glob module'
updated_at = <Date 2016-09-07.11:10:52.543>
user = 'https://github.com/xdegaye'bugs.python.org fields:
activity = <Date 2016-09-07.11:10:52.543>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2016-09-07.11:10:52.544>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2015-11-10.11:18:07.859>
creator = 'xdegaye'
dependencies = ['16620', '25994']
files = ['40996', '40999', '41474', '41481', '41533', '41570', '41571', '41576', '41895']
hgrepos = []
issue_num = 25596
keywords = ['patch']
message_count = 30.0
messages = ['254440', '254449', '257347', '257354', '257403', '257421', '257423', '257424', '257456', '257655', '257659', '257758', '257912', '257930', '257938', '257947', '257953', '257954', '257958', '258009', '258015', '258016', '260098', '273912', '274611', '274612', '274696', '274770', '274783', '274794']
nosy_count = 7.0
nosy_names = ['gvanrossum', 'vstinner', 'benhoyt', 'xdegaye', 'python-dev', 'Dima.Tisnek', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue25596'
versions = ['Python 3.6']
Activity
xdegaye commentedon Nov 10, 2015
The glob module happily joins names of regular files together with os.path.join() or attempts to list the files contained into a regular file (sic). The same 'except os.error' statement is used to handle both these cases and the case of a non readable directory.
The attached patch makes the code more correct and easier to understand.
xdegaye commentedon Nov 10, 2015
This second patch rewrites the conditionals that decide whether to call _iglob() recursively, in a more natural way and without changing the behavior from the first patch.
Note that when 'dirname == pathname', then basename is empty and glob2() or glob1() are not called.
The patch also refactors the code with a new _listdir() function.
serhiy-storchaka commentedon Jan 2, 2016
In general the patch LGTM. It allows to speed up glob by 5-10% in warn test. But much more gain we can achieve by using os.scandir(). Here are results of microbenchmarks:
Yet one benefit is that iglob() now yields path names without the delay for reading the full content of a directory (see bpo-22167).
bitdancer commentedon Jan 2, 2016
I don't think it is a good idea to break backward compatibility here even if the globN are internal functions. Better would be to continue to have globN functions that support the existing API and emit deprecation warnings.
serhiy-storchaka commentedon Jan 3, 2016
I think so too. I just wanted someone to confirmed that it is not overcautiousness. For now glob1() is used only in one place in the stdlib (bpo-16620).
But there was other problem with previous patch, the same as with current implementation of os.walk() (bpo-25995). It makes glob to use a lot of file descriptors.
Updated patch lefts deprecated glob1() and glob2() and makes glob to consume all scandir iterator before starting to yield values (but the problem with fd leaks on non-refcounted implementations is still left, bpo-25994). This doesn't affect performance, but lefts the issue with delaying (bpo-22167).
xdegaye commentedon Jan 3, 2016
os.scandir() is called recursively in the last patch and the file descriptors are not closed until returning from the recursion.
The glob functions should fail explicitly when scandir() raises OSERROR with posix errno set to EMFILE (The process has too many files open), or even better, silently ignore only the PermissionError exception instead of ignoring OSERROR.
xdegaye commentedon Jan 3, 2016
I may be missing something, anyway here are few comments on the patch:
Is the call to entry.is_symlink() in _iterdir() necessary since is_dir() follows symlinks ?
If _iterdir() would yield the DirEntry instance instead of DirEntry.name, then _rlistdir() could use x.is_dir() to know whether it is correct to iterate over _rlistdir(x.path, dironly)
serhiy-storchaka commentedon Jan 3, 2016
No, os.scandir() is called non-recursively in _iterdir(), and since _iterdir() results are always accumulated in a list, a recursion starts only after exhausting the os.scandir() iterator and closing the file descriptor. We need first to resolve bpo-25994 to close the file descriptor explicitly.
Patched code passes existing tests. Do you have additional tests?
Ah, I thought is_dir() doesn't follow symlinks. Yes, now the call to entry.is_symlink() is not necessary.
Yes, but this can complicate the rest of the code. _rlistdir() is called with dironly=False only when the pattern ends with '**'. I'm not sure this is enough important case for optimization. In most cases '**' is used in the middle of the pattern, and all names yielded by _iterdir() are directory names (or broken symlinks).
xdegaye commentedon Jan 4, 2016
Right, I failed to note that point. And so, since the file descriptor opened by os.scandir() is closed within each call to recursive _rlistdir(), then my other comment about EMFILE does not stand as well.
vstinner commentedon Jan 6, 2016
Related issue: bpo-26032 "Use scandir() to speed up pathlib globbing".
gvanrossum commentedon Jan 6, 2016
(IOW once this patch has been applied maybe you can do the same for globbing in pathlib as requested in issue bpo-26032.)
xdegaye commentedon Jan 8, 2016
Adding a doc patch.
7 remaining items
[-]Use scandir() to speed the glob module[/-][+]Use scandir() to speed up the glob module[/+]benhoyt commentedon Jan 11, 2016
Nice! Good to see scandir() getting used to speed up other functions, functions that folks are using a ton already, like glob().
gvanrossum commentedon Jan 11, 2016
Looks like switching to scandir will also resolve http://bugs.python.org/issue22167 without further action.
serhiy-storchaka commentedon Jan 11, 2016
Not this version of the path. It accumulates all scandir results in a list before yielding values. Otherwise globbing will consume a lot of open file descriptors and could leak them (see bpo-25994, bpo-25995).
gvanrossum commentedon Jan 11, 2016
Oh well. Too bad. Never mind then.
serhiy-storchaka commentedon Feb 11, 2016
The patch is completed now. The with statement is used to avoid FD leaks.
dimaqq commentedon Aug 30, 2016
Who can review Serhiy's patch?
P.S. core of the patch seems good to me, but I'm not an expert on stdlib.
serhiy-storchaka commentedon Sep 6, 2016
I think the change in general is approved by GvR. If there are some implementation bugs, we can fix them later.
python-dev commentedon Sep 6, 2016
New changeset cb7ee9d9cddd by Serhiy Storchaka in branch 'default':
Issue bpo-25596: Optimized glob() and iglob() functions in the
https://hg.python.org/cpython/rev/cb7ee9d9cddd
gvanrossum commentedon Sep 7, 2016
Thanks Serhiy!
--Guido (mobile)
On Sep 6, 2016 12:35 PM, "Roundup Robot" <report@bugs.python.org> wrote:
python-dev commentedon Sep 7, 2016
New changeset 48e573e0a610 by Serhiy Storchaka in branch 'default':
Issue bpo-25596: Falls back to listdir in glob for bytes paths on Windows.
https://hg.python.org/cpython/rev/48e573e0a610
dimaqq commentedon Sep 7, 2016
@serhiy please comment the implications / limitations of the fallback on Windows.
Is it that scandir cannot handle bytes argument only?
If argument is unicode, but response set contains bytes paths, will that work?
serhiy-storchaka commentedon Sep 7, 2016
os.scandir() cannot handle bytes argument on Windows. If an argument is string, os.scandir() yields entries with string names, if an argument is bytes object, os.scandir() yields entries with bytes names. Opened bpo-27998 for adding support of bytes paths in os.scandir(). After this will be implemented, a workaround cb7ee9d9cddd can be reverted.