Allow to retrieve ongoing exception handled by every threads

[jd]

BPO	41435
Nosy	@jd, @serhiy-storchaka
PRs	bpo-41435: Add sys._current_exceptions() function #21689

^{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 2020-11-02.20:54:45.715>
created_at = <Date 2020-07-29.15:39:46.446>
labels = ['interpreter-core', 'type-feature', '3.10']
title = 'Allow to retrieve ongoing exception handled by every threads'
updated_at = <Date 2020-11-02.20:54:45.715>
user = 'https://github.com/jd'

bugs.python.org fields:

activity = <Date 2020-11-02.20:54:45.715>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2020-11-02.20:54:45.715>
closer = 'serhiy.storchaka'
components = ['Interpreter Core']
creation = <Date 2020-07-29.15:39:46.446>
creator = 'jd'
dependencies = []
files = []
hgrepos = []
issue_num = 41435
keywords = ['patch']
message_count = 4.0
messages = ['374575', '374727', '374728', '380223']
nosy_count = 2.0
nosy_names = ['jd', 'serhiy.storchaka']
pr_nums = ['21689']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue41435'
versions = ['Python 3.10']

[jd]

In order to do statistical profiling on raised exception, having the ability to poll all the running threads for their currently handled exception would be fantastic.

There is an exposed function named sys._current_frames() that allows to list the current frame handled by CPython. Having an equivalent for sys._current_exceptions() that would return the content of sys.exc_info() for each running thread would solve the issue.

[serhiy-storchaka]

Would not be more useful to add a method to the Thread or frame object to obtain the topmost handled exception? Then you could iterate all threads or frames and obtain exceptions together with other useful information.

Note also that it omits exceptions in generators and coroutines.

[jd]

Adding to the thread object might be a good idea, but it does not work if you ever start threads with the low-level _thread API.
It's also a different design from the existing sys._current_frames.

Adding it on top of a frame is interesting though. I think internally it's more linked to the execution stack in a thread than to a frame, though.

[serhiy-storchaka]

New changeset 64366fa by Julien Danjou in branch 'master':
bpo-41435: Add sys._current_exceptions() function (GH-21689)
64366fa