[issue16853] add a Selector to the select module

[Charles-François Natali]

Charles-François Natali added the comment:

> Guido van Rossum added the comment:
> Can you try again with the failing assert replaced with this?
>
> 	self.assertTrue(0.018 <= t2-t0 <= 0.028, t2-t0)
>
> That should be a better way to check that code works.

I'm still getting - less frequent - failures:
"""
======================================================================
FAIL: test_run_until_complete_timeout (events_test.SelectEventLoopTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "tests/events_test.py", line 194, in test_run_until_complete_timeout
    self.assertTrue(0.018 <= t2-t0 <= 0.028, t2-t0)
AssertionError: False is not true : 0.029771103999337356

----------------------------------------------------------------------
"""

Looking at strace output:
11:00:47.383145 select(4, [3], [], [], {0, 9765}) = 0 (Timeout) <0.015713>

select() takes an extra 5ms (15ms instead of 10ms).

5ms is quite low for a GPOS (the typical quantum is around 4ms for
250Hz timer, and on my machine I have high-resolution timers
configured but probably a crappy hardware).

I'd suggest increasing the timeouts (especially when Tulip gets
merged, it'll likely fail on many buildbots).

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue16853>
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