[performance] Too many closed() checkings

[wojtekwalczak]

BPO	1407
Nosy	@gvanrossum, @amauryfa, @pitrou, @tiran, @benjaminp

^{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 2009-02-28.18:11:10.581>
created_at = <Date 2007-11-08.20:30:33.046>
labels = ['interpreter-core', 'library', 'performance']
title = '[performance] Too many closed() checkings'
updated_at = <Date 2009-02-28.18:11:10.580>
user = 'https://bugs.python.org/wojtekwalczak'

bugs.python.org fields:

activity = <Date 2009-02-28.18:11:10.580>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2009-02-28.18:11:10.581>
closer = 'pitrou'
components = ['Interpreter Core', 'Library (Lib)']
creation = <Date 2007-11-08.20:30:33.046>
creator = 'wojtekwalczak'
dependencies = []
files = []
hgrepos = []
issue_num = 1407
keywords = []
message_count = 7.0
messages = ['57275', '57276', '57320', '68151', '68157', '82926', '82932']
nosy_count = 6.0
nosy_names = ['gvanrossum', 'amaury.forgeotdarc', 'pitrou', 'christian.heimes', 'wojtekwalczak', 'benjamin.peterson']
pr_nums = []
priority = 'normal'
resolution = 'wont fix'
stage = None
status = 'closed'
superseder = None
type = 'resource usage'
url = 'https://bugs.python.org/issue1407'
versions = ['Python 3.0']

[wojtekwalczak]

For debugging reasons I have added a simple line to PyObject_Call()
function in Objects/abstract.c:
printf("%s.%s\n", func->ob_type->tp_name, PyEval_GetFuncName(func));
Now, after compiling python and running interpreter with simple
print() call I receive this:

Python 3.0a1 (py3k, Nov  6 2007, 19:25:33)
[GCC 4.1.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> print('!',end='')
builtin_function_or_method.print
method.write
function.write
function.closed
function.closed
builtin_function_or_method.ascii_encode
function.closed
function.closed
!method.write   # here it goes again for 'end' parameter
function.write
function.closed
function.closed
builtin_function_or_method.ascii_encode
function.closed
builtin_function_or_method.displayhook
>>>

Note that there can be something going on between one function.closed
and the next one, because not every piece of code gets called by
PyObject_Call(), but still - isn't it checking if stream is closed a
bit too often?

Regards,
Wojtek Walczak

[tiran]

The problem should be addressed after the last alpha during the
optimization and cleanup phase.

[gvanrossum]

To find out what really happens, use pdb to step through the example.
This gives much better insight than adding a printf() call to
PyObject_Call(). I've notice myself when stepping through I/O that there
are a lot of checks for closed -- this may have to do with the stacking
text -> buffer -> binary though. I've also noticed overridden isinstance
checks in abc.py being called, which surprised me slightly. I haven't
had time to look into this further though.

[pitrou]

Is this issue still valid?

[amauryfa]

I reproduce almost the same output.
"function.closed" often come in pair, because TextIOWrapper.closed is a
property which delegates to self.buffer.closed

I think that the first check in TextIOWrapper.write() is not necessary:
self.buffer.write(b) will also check for "self.buffer.closed", and there
is not much code in-between. The only side-effect is the decoder state.

[benjaminp]

Does io in C help with this?

[pitrou]

Closing, as I don't think there's any point trying to micro-optimize the
Python version.