Improve BufferedReader.read1()

[pitrou]

BPO	13393
Nosy	@pitrou
Files	bufioread1.patch textioread.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 2011-11-18.23:58:10.779>
created_at = <Date 2011-11-13.04:15:01.118>
labels = ['library', 'expert-IO', 'performance']
title = 'Improve BufferedReader.read1()'
updated_at = <Date 2011-11-18.23:58:10.778>
user = 'https://github.com/pitrou'

bugs.python.org fields:

activity = <Date 2011-11-18.23:58:10.778>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2011-11-18.23:58:10.779>
closer = 'pitrou'
components = ['Library (Lib)', 'IO']
creation = <Date 2011-11-13.04:15:01.118>
creator = 'pitrou'
dependencies = []
files = ['23675', '23676']
hgrepos = []
issue_num = 13393
keywords = ['patch']
message_count = 4.0
messages = ['147549', '147740', '147924', '147925']
nosy_count = 4.0
nosy_names = ['pitrou', 'neologix', 'python-dev', 'sbt']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue13393'
versions = ['Python 3.3']

[pitrou]

The main current user of BufferedReader.read1() is TextIOWrapper. In this context, read1() is used to signal that we want to bypass binary buffering as much as possible, since TextIOWrapper does its own buffering. The current read1() implementation is therefore suboptimal: it copies data around, and limits the number of bytes that you're allowed to get in one call (even if the raw stream would satisfy more).

Attached patch improves read1() in this respect. Also, a separate modification of TextIOWrapper is needed to take advantage of it, which I will attach in another patch.

[python-dev]

New changeset 27bf3d0b8e5f by Antoine Pitrou in branch 'default':
Issue bpo-13393: BufferedReader.read1() now asks the full requested size to
http://hg.python.org/cpython/rev/27bf3d0b8e5f

[python-dev]

New changeset 76d414cc3e38 by Antoine Pitrou in branch 'default':
Issue bpo-13393: In TextIOWrapper.read(n), try to read n characters as
http://hg.python.org/cpython/rev/76d414cc3e38

[pitrou]

I've committed a slightly modified patch. Not a huge improvement, but makes sense nevertheless (and it's really short).