Float maxsize is treated as infinity in asyncio.Queue

[vajrasky]

BPO	21723
Nosy	@gvanrossum, @vstinner, @1st1, @ajdavis, @vajrasky
Files	asyncio_queue_accept_handles_maxsize.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 2014-06-17.22:07:42.845>
created_at = <Date 2014-06-11.15:59:54.939>
labels = ['type-bug', 'expert-asyncio']
title = 'Float maxsize is treated as infinity in asyncio.Queue'
updated_at = <Date 2014-06-17.22:44:52.861>
user = 'https://github.com/vajrasky'

bugs.python.org fields:

activity = <Date 2014-06-17.22:44:52.861>
actor = 'emptysquare'
assignee = 'none'
closed = True
closed_date = <Date 2014-06-17.22:07:42.845>
closer = 'vstinner'
components = ['asyncio']
creation = <Date 2014-06-11.15:59:54.939>
creator = 'vajrasky'
dependencies = []
files = ['35574']
hgrepos = []
issue_num = 21723
keywords = ['patch']
message_count = 8.0
messages = ['220280', '220283', '220289', '220360', '220840', '220899', '220906', '220907']
nosy_count = 6.0
nosy_names = ['gvanrossum', 'vstinner', 'python-dev', 'yselivanov', 'emptysquare', 'vajrasky']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue21723'
versions = ['Python 3.5']

[vajrasky]

import asyncio

loop = asyncio.get_event_loop()
q = asyncio.Queue(maxsize=1.2, loop=loop)
q.put_nowait(1)
q.put_nowait(1)
q.put_nowait(1)
q.put_nowait(1)
q.put_nowait(1)
.... and so on

It seems counter intuitive for my innocent eyes. As comparison with the traditional queue:

import queue
q = queue.Queue(maxsize=1.2)
q.put(1)
q.put(1)
q.put(1) -> blocking

Here is the patch to make the behaviour consistent with its sibling.

[vstinner]

It looks strange to use a float as maxsize. I suggest to raise a TypeError in the constructor if the type is not int, or maybe to cast maxsize parameter to an int.

[1st1]

FWIW, this can also be resolved by fixing Queue.full to do "self.qsize() >= self._maxsize" instead of "self.qsize() == self._maxsize".

I generally don't like implicit casts as they break duck typing.

[vajrasky]

"It looks strange to use a float as maxsize." => It is. But the float could be coming programmatically. Float value interpreted as infinity could give a shock for some people.

"maybe to cast maxsize parameter to an int." => ceiling or flooring?

[gvanrossum]

The patch looks fine to me.

[python-dev]

New changeset ccfc13183fea by Victor Stinner in branch '3.4':
Issue bpo-21723: asyncio.Queue: support any type of number (ex: float) for the
http://hg.python.org/cpython/rev/ccfc13183fea

New changeset a2f115bfa513 by Victor Stinner in branch 'default':
(Merge 3.4) Issue bpo-21723: asyncio.Queue: support any type of number (ex: float)
http://hg.python.org/cpython/rev/a2f115bfa513

[vstinner]

Thanks Vajrasky, I aplied your patch.

[vstinner]

Change also pushed to Tulip (changeset 3a392e5328c0).