fnmatch.py can appear in tracemalloc diffs

[pitrou]

BPO	21952
Nosy	@pitrou, @vstinner, @serhiy-storchaka

^{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 = <Date 2021-12-06.16:21:43.530>
created_at = <Date 2014-07-10.19:36:07.100>
labels = ['type-bug', 'library']
title = 'fnmatch.py can appear in tracemalloc diffs'
updated_at = <Date 2021-12-06.16:21:43.529>
user = 'https://github.com/pitrou'

bugs.python.org fields:

activity = <Date 2021-12-06.16:21:43.529>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2021-12-06.16:21:43.530>
closer = 'vstinner'
components = ['Library (Lib)']
creation = <Date 2014-07-10.19:36:07.100>
creator = 'pitrou'
dependencies = []
files = []
hgrepos = []
issue_num = 21952
keywords = []
message_count = 4.0
messages = ['222692', '222696', '246722', '407829']
nosy_count = 3.0
nosy_names = ['pitrou', 'vstinner', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue21952'
versions = ['Python 3.4', 'Python 3.5']

[pitrou]

When using some filters and comparing snapshots, fnmatch will appear in the statistic diffs, e.g.:

/home/antoine/34/lib/python3.4/fnmatch.py:70: size=824 B (+64 B), count=2 (+1), average=412 B
eeleak.py:37: size=2512 B (+0 B), count=3 (+0), average=837 B
/home/antoine/llvmpy/llvm/ee.py:109: size=976 B (+0 B), count=2 (+0), average=488 B
/home/antoine/llvmpy/llvm/core.py:401: size=904 B (+0 B), count=2 (+0), average=452 B
/home/antoine/34/lib/python3.4/sre_compile.py:488: size=856 B (+0 B), count=1 (+0), average=856 B

Perhaps it would be nice to manually cache the compiled re pattern, instead of going through fnmatch's lru_cache thing which seems to make reports less robust.

[vstinner]

When using some filters and comparing snapshots, fnmatch will appear in the statistic diffs, e.g.:

During the design of the tracemalloc module (PEP-454), it was decided to not filter traces in the C module, but filter traces on a snapshot object. The reason is to keep the C module simple. To debug, you can analyze snapshots on a fast machine.

Can you try to filter traces?

snapshot = snapshot.filter_traces(Filter(False, tracemalloc.__file__))

In you case, the top frame is in the fnmatch module, so you probably need to trace more than one thread (ex: tracemalloc.start(10)) and apply the filter on all frames, not only on the top frame:

snapshot = snapshot.filter_traces(Filter(False, tracemalloc.__file__, all_frames=True))

You can also ignore fnmatch & sre_compile modules (blacklist, exclusive filters), or only keep traces of the directory /home/antoine/llvmpy/llvm/ (whitelist, an inclusive filter).

Perhaps it would be nice to manually cache the compiled re pattern, instead of going through fnmatch's lru_cache thing which seems to make reports less robust.

Ah, interesting point. Would you be interested to work on that?

I tried to use tracemalloc to detect memory leaks in test.regrtest, but it's very difficult to get a reliable output. See the issue bpo-19816.

[serhiy-storchaka]

In 3.5+ lru_cache() is implemented in C. Is this issue still actual?

[vstinner]

Exposing internal caches in tracemalloc is not a bug but a deliberate choice. It's easy to write your own filters to ignore selected files (or even specific functions if you can locate them by line nubmers).