Optimize asyncio.iscoroutine() and loop.create_task() for non-native coroutines

[1st1]

BPO	32357
Nosy	@asvetlov, @1st1
PRs	bpo-32357: Optimize asyncio.iscoroutine() for non-native coroutines #4915 bpo-32357: Fix tests in refleak mode #4989 bpo-32357: Use PySet_GET_SIZE macro in _is_coroutine() from _asynciomodule.c  #4990
Files	bench.py

^{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 2017-12-19.12:19:04.774>
created_at = <Date 2017-12-18.05:33:40.749>
labels = ['expert-asyncio', '3.7', 'performance']
title = 'Optimize asyncio.iscoroutine() and loop.create_task() for non-native coroutines'
updated_at = <Date 2017-12-23.20:06:48.846>
user = 'https://github.com/1st1'

bugs.python.org fields:

activity = <Date 2017-12-23.20:06:48.846>
actor = 'yselivanov'
assignee = 'none'
closed = True
closed_date = <Date 2017-12-19.12:19:04.774>
closer = 'yselivanov'
components = ['asyncio']
creation = <Date 2017-12-18.05:33:40.749>
creator = 'yselivanov'
dependencies = []
files = ['47337']
hgrepos = []
issue_num = 32357
keywords = ['patch']
message_count = 4.0
messages = ['308515', '308631', '308960', '308967']
nosy_count = 2.0
nosy_names = ['asvetlov', 'yselivanov']
pr_nums = ['4915', '4989', '4990']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue32357'
versions = ['Python 3.7']

[1st1]

asyncio.Task now uses asyncio.iscoroutine() to give a comprehensible error if a user creates a Task for a non-awaitable type.

The problem is that iscoroutine() is quite expensive for non-native coroutines (like the ones compiled with Cython), as it uses isinstance(obj, collections.abc.Coroutine) call. This makes 'loop.create_task(cython_coroutine)' 20% slower than 'loop.create_task(python_coroutine)'.

The PR adds a positive type cache to the iscoroutine() function and to the asyncio.Task C implementation. Both caches make 'loop.create_task()' equally fast for all kinds of coroutines.

[1st1]

New changeset a9d7e55 by Yury Selivanov in branch 'master':
bpo-32357: Optimize asyncio.iscoroutine() for non-native coroutines (bpo-4915)
a9d7e55

[1st1]

New changeset 558aa30 by Yury Selivanov in branch 'master':
bpo-32357: Fix tests in refleak mode (bpo-4989)
558aa30

[1st1]

New changeset 0f47fa2 by Yury Selivanov (Andrew Svetlov) in branch 'master':
bpo-32357: Use PySet_GET_SIZE macro in _is_coroutine() from _asynciomodule.c (bpo-4990)
0f47fa2