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Fix for bug 30378 regressed SysLogHandler by making it resolve addresses at initialization instead of in .emit() #82535
Description
| BPO | 38354 |
|---|---|
| Nosy | @vsajip, @ngie-eign, @iritkatriel |
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 2019-10-02.21:32:12.533>
labels = ['type-bug', 'library', '3.9', '3.10', '3.11']
title = 'Fix for bug 30378 regressed SysLogHandler by making it resolve addresses at initialization instead of in `.emit()`'
updated_at = <Date 2021-10-18.23:26:10.897>
user = 'https://github.com/ngie-eign'bugs.python.org fields:
activity = <Date 2021-10-18.23:26:10.897>
actor = 'iritkatriel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-10-02.21:32:12.533>
creator = 'ngie'
dependencies = []
files = []
hgrepos = []
issue_num = 38354
keywords = []
message_count = 4.0
messages = ['353775', '353780', '353907', '404247']
nosy_count = 4.0
nosy_names = ['vinay.sajip', 'ngie', 'calcheng', 'iritkatriel']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38354'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']Linked PRs
- gh-82535: Ignore address resolution failure in SysLogHandler constructor #154504
- [3.15] gh-82535: Ignore address resolution failure in SysLogHandler constructor (GH-154504) #155457
- [3.14] gh-82535: Ignore address resolution failure in SysLogHandler constructor (GH-154504) #155458
- [3.13] gh-82535: Ignore address resolution failure in SysLogHandler constructor (GH-154504) #155459
Activity
ngie-eign commentedon Oct 2, 2019
The change made for bug 30378 caused a regression in our code by making
lookups for SysLogHandler addresses at init time, instead of making them more lazy. Example:
This is exacerbated by the fact that a lot of code the organization I work for (and to be honest, I have written in the past) initializes global loggers once at import time. If the SysLogHandler is added to the global logger and the DNS resolution isn't possible (/etc/hosts is empty on Unix or does not contain the entry, and DNS out is to lunch), it will fall on its face at initialization time.
There needs to be a more graceful way of initializing loggers like this, or a way of delaying the host resolution, so it fails gracefully and doesn't crash the entire program (restoring the previous behavior).
Example: SMTPHandler doesn't do name resolution until it calls emit, which seems like a much more logical place to do the operation (especially since DNS records can change or become invalid).
[-]Fix for bug 30378 regressed SysLogHandler[/-][+]Fix for bug 30378 regressed SysLogHandler by making it resolve addresses at initialization instead of in `.emit()`[/+]ngie-eign commentedon Oct 2, 2019
Capturing more context here, based on internal discussion: other handlers are doing address resolution in
emit()(HTTPHandler, SMTPHandler), which is expensive. In order for SysLogHandler to not regress behavior and not become expensive, performance-wise, it would probably be best to usefunctools.lru_cache(), using the address and a timeout as the key when resolving the addresses to avoid always doing address resolutions, e.g., DNS lookups: https://docs.python.org/3/library/functools.html#functools.lru_cache .vsajip commentedon Oct 4, 2019
This could perhaps be handled by just swallowing errors in the constructor (as is done for Unix sockets, for example) and trying to connect in emit() if there is no connection.
Not sure I want to go down the caching route - it complicates things for what is a rare use case, plus raises the question of allowing configurable timeouts for the cache, etc.
This seems a rare use case, so I have things that have a higher priority on my list of things to do, but I'll certainly review a patch to address this.
iritkatriel commentedon Oct 18, 2021
Reproduced on 3.11.
Changing type because crash typically refers to segfault or hang in the interpreter rather than a valid exception.
serhiy-storchaka commentedon Jul 22, 2026
This would conflict with #126400. How to resolve this conflict?
serhiy-storchaka commentedon Jul 22, 2026
On other hand, if swallow only socket.gaierror, not OSError, it no longer conflicts.
PR #154504 does this. How to target it? Should it be backported?
gh-82535: Ignore address resolution failure in SysLogHandler construc…
pythongh-82535: Ignore address resolution failure in SysLogHandler co…
[3.13] gh-82535: Ignore address resolution failure in SysLogHandler c…
[3.15] gh-82535: Ignore address resolution failure in SysLogHandler c…
[3.14] gh-82535: Ignore address resolution failure in SysLogHandler c…