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Executor.map does not submit futures until iter.next() is called #55986

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brianquinlan opened this issue Apr 6, 2011 · 7 comments
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Executor.map does not submit futures until iter.next() is called #55986

brianquinlan opened this issue Apr 6, 2011 · 7 comments
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@brianquinlan
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stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@brianquinlan
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BPO 11777
Nosy @brianquinlan, @merwok

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 = 'https://github.com/brianquinlan'
closed_at = <Date 2011-04-07.22:33:02.566>
created_at = <Date 2011-04-06.01:16:35.236>
labels = ['type-bug', 'library']
title = 'Executor.map does not submit futures until iter.next() is called'
updated_at = <Date 2011-04-21.15:28:48.978>
user = 'https://github.com/brianquinlan'

bugs.python.org fields:

activity = <Date 2011-04-21.15:28:48.978>
actor = 'eric.araujo'
assignee = 'bquinlan'
closed = True
closed_date = <Date 2011-04-07.22:33:02.566>
closer = 'bquinlan'
components = ['Library (Lib)']
creation = <Date 2011-04-06.01:16:35.236>
creator = 'bquinlan'
dependencies = []
files = []
hgrepos = []
issue_num = 11777
keywords = []
message_count = 7.0
messages = ['133104', '133107', '133108', '133196', '133197', '133270', '134223']
nosy_count = 4.0
nosy_names = ['bquinlan', 'eric.araujo', 'ysj.ray', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue11777'
versions = ['Python 3.3']
@brianquinlan
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from concurrent import futures

with futures.ThreadPoolExecutor(max_workers=5) as e:
  e.map(print, range(10))

# No output

@brianquinlan brianquinlan self-assigned this Apr 6, 2011
@brianquinlan brianquinlan added stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error labels Apr 6, 2011
@ysjray
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ysjray mannequin commented Apr 6, 2011

Isn't this the supposed behavior?

@brianquinlan
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I think that it surprising behavior, especially considering that asking for the *first* element in the iterator causes *all* of the futures to be created.

@ysjray
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ysjray mannequin commented Apr 7, 2011

Got it. Seems the behavior is not consist with the Executor.map() function:

"The returned iterator raises a TimeoutError if __next__() is called and the result isn't available after timeout seconds from ***the original call to map()***"

@brianquinlan
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Nice catch. I hadn't noticed that the docs are lying :-)

@python-dev
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python-dev mannequin commented Apr 7, 2011

New changeset 126353bc7e94 by Brian Quinlan in branch 'default':
Issue bpo-11777: Executor.map does not submit futures until iter.next() is called
http://hg.python.org/cpython/rev/126353bc7e94

@merwok
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merwok commented Apr 21, 2011

Just a bystander remark: when you use present in the commit message and Misc/NEWS entry (like in “Executor.map does not submit futures until iter.next() is called”), I don’t know whether it is the behavior being fixed (“X used to do Y”) or the new, correct behavior (“X now does Z”).

@ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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