selectors: raise an exception if the selector is closed

[vstinner]

BPO	23225
Nosy	@gvanrossum, @vstinner, @1st1, @Martiusweb
Files	close_selector.patch

^{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 2015-01-13.09:07:09.541>
created_at = <Date 2015-01-12.11:06:01.534>
labels = ['expert-asyncio']
title = 'selectors: raise an exception if the selector is closed'
updated_at = <Date 2015-01-13.09:07:09.541>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2015-01-13.09:07:09.541>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2015-01-13.09:07:09.541>
closer = 'vstinner'
components = ['asyncio']
creation = <Date 2015-01-12.11:06:01.534>
creator = 'vstinner'
dependencies = []
files = ['37682']
hgrepos = []
issue_num = 23225
keywords = ['patch']
message_count = 4.0
messages = ['233881', '233890', '233908', '233911']
nosy_count = 6.0
nosy_names = ['gvanrossum', 'vstinner', 'neologix', 'python-dev', 'yselivanov', 'martius']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue23225'
versions = ['Python 3.4', 'Python 3.5']

[vstinner]

I propose to raise a RuntimeError exception on operations of a selector when the selector is closed.

I'm not sure that RuntimeError is the most common exception:

• io and gzip raise ValueError
• asyncio raises RuntimeError (and selectors is "linked" to asyncio)
• multiprocessing raises OSError
• dbm.dumb raises dbm.dumb.error

This issue is related to the issue bpo-23209 which propopses to set the _map attribute to None when in the close() method.

[neologix]

RuntimeError sounds better to me (raising ValueError when no value is
provided, e.g. in select() sounds definitely strange).

[python-dev]

New changeset 1544bdc409be by Victor Stinner in branch '3.4':
Issue bpo-23209, bpo-23225: selectors.BaseSelector.close() now clears its internal
https://hg.python.org/cpython/rev/1544bdc409be

New changeset 6e7403bc906f by Victor Stinner in branch 'default':
Issue bpo-23209, bpo-23225: selectors.BaseSelector.get_key() now raises a
https://hg.python.org/cpython/rev/6e7403bc906f

[vstinner]

Oh, I forgot Python 3.4. Changing the behaviour of get_key() in a minor Python version (3.4.x) would break the compatibility. I used Martin Richard's patch for Python 3.4: raise a KeyError if the selector is closed.

I commit my change to Python 3.5 and Tulip.