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Some info on this: https://github.com/python/asyncio/issues/282#issuecomment-155957235 Long story short, Future implemented in C can speedup some asyncio code up to 25%.
I'm attaching a patch with a WIP implementation. There are some failing assertions deep in GC, which I need to track down. 'Future.remove_done_callback' still needs to be properly implemented.

We should really try to get this into 3.6.
--Guido (mobile)

I'm working on this. Some bugs are fixed, but doesn't pass tests for now.
https://github.com/methane/cpython/pull/5 

Passing all tests now.
Yury, could you explain what the comment "This isn't a Future class; it's a BaseFuture" means?
Should it be "_futures.Future" or "_futures.BaseFuture"?

Should I send pull request to github.com/python/asyncio?
Or should I post patch here?

> I'm working on this. Some bugs are fixed, but doesn't pass tests for now.
Thanks a lot! I couldn't find time to finish this myself. I can definitely help you and review the patch once it's ready.
> Yury, could you explain what the comment "This isn't a Future class; it's a BaseFuture" means?
Unfortunately I don't remember :(
> Should I send pull request to github.com/python/asyncio?
Or should I post patch here?
Please post it here. AFAIK we haven't yet transitioned to the GitHub.

OK. Here is current version.

In my patch, test_asyncio runs against C version Future.
I saw how test_json tests against C version and pure Python version.
But test_asyncio is more larger than test_json.
Before working on it, could someone give me idea to run whole test_asyncio
with and without C version Future easily?
And, which is master repository of asyncio? github? or hg.python.org?
If github, can I send separated pull request changing test_asyncio after
this patch is merged?

> Before working on it, could someone give me idea to run whole test_asyncio
with and without C version Future easily?
asyncio uses loop.create_future() to create sockets. I'd suggest you to create two base test classes: one that monkeypatches loop.create_future to return pure python Future in its setUp method; an another, that makes create_future to return a C version of the Future.
The derive some unittests from those base classes (which will effectively double the number of tests).
> And, which is master repository of asyncio? github? or hg.python.org?
If github, can I send separated pull request changing test_asyncio after
this patch is merged?
The master repo for asyncio is github, but since the C version won't be a part of asyncio (it will be checked in only in CPython source tree), I think it's fine to continue the work here, on bugs.python.org.

Thanks. I'll working on test_asyncio in next few days.

> asyncio uses loop.create_future() to create sockets. I'd suggest you to create two base test classes: one that monkeypatches loop.create_future to return pure python Future in its setUp method; an another, that makes create_future to return a C version of the Future.
windows_events.py has some classes extends futures.Future.
Task extends Future.
There are some `isinstance(future, futures.Future)`.
So monkeypatching `baseevent.create_future` seems not enough.
I want a way to completely reload asyncio and test_asyncio packages with and without C future.

THe guys developing uvloop say their implementation is already quite fast [1]. Is it worth integrating it?
[1] https://github.com/MagicStack/uvloop 

Yes. Most people will use vanilla asyncio anyways.

Yury, could you review this before 3.6a4?

> Yury, could you review this before 3.6a4?
Left a couple of comments; the important one -- Future.__await__ (and Future.__iter__) should always return a *new* instance of a generator-like object (tied to the Future object).

See also a discussion on Python-Dev about rewriting contextlib.contextmanager in C: https://mail.python.org/pipermail/python-dev/2016-August/thread.html#145786 .
What parts of Future are performance critical? Maybe it is worth to implement in C only the most critical code.

> What parts of Future are performance critical? Maybe it is worth to implement in C only the most critical code.
Basically everything. Contrary to @contextmanager, Futures are the building blocks of asyncio, so instantiation + awaiting on them + setting results must be fast.
To cover instantiation, I want to add a freelist for Futures, so this basically requires them to be implemented in C (and it's not a lot of C code actually).

I'd also think about implementing asyncio.Handle in C (with a freelist).

> Left a couple of comments; the important one -- Future.__await__ (and Future.__iter__) should always return a *new* instance of a generator-like object (tied to the Future object).
Implementing full behavior of generator seems difficult to me.
I'll implement minimum implementation in next patch.

> Implementing full behavior of generator seems difficult to me.
I'll implement minimum implementation in next patch.
Sure, but you have to implement send() and throw().

Implemented FutureIter

There are only two weeks until 3.6 beta.
Yury, could you review this again?
Or should I implement freelist before review?
Implementing freelist may be easy, but measuring the effect of freelist from
realistic application is not easy.

The actual _futures module appears missing from your latest patch -- what's up with that?

Oh, I'm sorry.
I usually working on git, and convert git diff to hg diff when posting patch.
I've used `patch -p1` instead of `hg import --no-edit` to apply git patch into hg workdir.
I wonder if Rietveld accepts git diff format...

Thanks! I can't review the whole thing, but I patched it in and tried running the asyncio/examples/crawl.py example, like so:
$ ~/src/cpython36/python.exe examples/crawl.py xkcd.com -q
Exception RuntimeError('yield was used instead of yield from in task <Task pending coro=<Crawler.fetch() running at examples/crawl.py:778>> with <Future pending cb=[_chain_future.<locals>._call_check_cancel() at /Users/guido/src/cpython36/Lib/asyncio/futures.py:472]>',) for ('xkcd.com', 80)
ERROR:asyncio:Task exception was never retrieved
future: <Task finished coro=<Crawler.fetch() done, defined at examples/crawl.py:769> exception=RuntimeError('yield was used instead of yield from in task <Task pending coro=<Crawler.fetch() running at examples/crawl.py:778>> with <Future pending cb=[_chain_future.<locals>._call_check_cancel() at /Users/guido/src/cpython36/Lib/asyncio/futures.py:472]>',)>
Traceback (most recent call last):
 File "/Users/guido/src/cpython36/Lib/asyncio/tasks.py", line 241, in _step
 result = coro.throw(exc)
 File "examples/crawl.py", line 778, in fetch
 yield from fetcher.fetch() # Fetcher gonna fetch.
 File "examples/crawl.py", line 507, in fetch
 yield from self.request.connect()
 File "examples/crawl.py", line 315, in connect
 self.port, self.ssl)
 File "examples/crawl.py", line 143, in get_connection
 ipaddrs = yield from self.loop.getaddrinfo(host, port)
RuntimeError: yield was used instead of yield from in task <Task pending coro=<Crawler.fetch() running at examples/crawl.py:778>> with <Future pending cb=[_chain_future.<locals>._call_check_cancel() at /Users/guido/src/cpython36/Lib/asyncio/futures.py:472]>
*** Report ***
http://xkcd.com no response object
Finished 0 urls in 0.041 secs (max_tasks=100) (0.000 urls/sec/task)
Todo: 0
Busy: 1
Done: 0
Date: Sat Sep 10 21:50:08 2016 local time
Traceback (most recent call last):
 File "examples/crawl.py", line 864, in <module>
 main()
 File "examples/crawl.py", line 852, in main
 loop.run_until_complete(crawler.crawl()) # Crawler gonna crawl.
 File "/Users/guido/src/cpython36/Lib/asyncio/base_events.py", line 438, in run_until_complete
 return future.result()
 File "/Users/guido/src/cpython36/Lib/asyncio/tasks.py", line 241, in _step
 result = coro.throw(exc)
 File "examples/crawl.py", line 766, in crawl
 yield from self.termination.wait()
 File "/Users/guido/src/cpython36/Lib/asyncio/locks.py", line 326, in wait
 yield from fut
RuntimeError: yield was used instead of yield from in task <Task pending coro=<Crawler.crawl() running at examples/crawl.py:766> cb=[_run_until_complete_cb() at /Users/guido/src/cpython36/Lib/asyncio/base_events.py:164]> with <Future pending>
Without your diff, that works, and the output includes this line:
Finished 1786 urls in 7.105 secs (max_tasks=100) (2.514 urls/sec/task)

Sorry, again. fixed.
Now this passes `./python -m test.test_asyncio`

Yury: What do you think of the code? How solid is it? (The issue I found was due to my own very recent changes to _blocking.)
Ned: Is it better to do this in 3.6b1 or to wait for 3.6b2?

> Yury: What do you think of the code? How solid is it? (The issue I found was due to my own very recent changes to _blocking.)
The code looks fine, I can fix the remaining nits myself. I've left a couple of comments in review.
> Ned: Is it better to do this in 3.6b1 or to wait for 3.6b2?
TBH it would be way more convenient if we could push this into b2. I can push this on Tuesday without rushing things, and we'll have plenty of time to watch buildbots etc.

Yeah, let's do this in 3.6b2.

This change touches a lot of files and affect both the unix* and Windows build processes so, yeah, I think it's too risky to go in to b1. Let's get it in as soon as possible after b1.

INADA, would you be able to address my last review comments? Also, I'm wondering what if we could implement __del__ and __repr__ in C too, so that we could drop BaseFuture class?

I'm working on fixing points you commented. Wait a minute.
Implementing __del__ and __repr__ in C is bit hard task to me.
I can't do it in this week. (maybe I can't do it in this month too.)
On Thu, Sep 15, 2016 at 7:37 AM, Yury Selivanov <report@bugs.python.org> wrote:
>
> Yury Selivanov added the comment:
>
> INADA, would you be able to address my last review comments? Also, I'm wondering what if we could implement __del__ and __repr__ in C too, so that we could drop BaseFuture class?
>
> ----------
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue26081>
> _______________________________________

> Implementing __del__ and __repr__ in C is bit hard task to me.
> I can't do it in this week. (maybe I can't do it in this month too.)
NP. I'll take a look myself after you upload the next iteration of the patch...

This is the patch.
And git branch is here https://github.com/methane/cpython/pull/5 

The most recent patch segfaults... Will try to debug.

INADA, would you be able to take a look?

FutureIter_throw is wrong, maybe.
Removing FutureIter_send and FutureIter_throw from FutureIter_methods solves the segv and test passed.

fixed

fastfuture3-wip.patch is work in progress implementation of
implementing __repr__ and __del__ in C.
I post it to avoid duplicated works.
Known TODOs:
* Support overriding Future._repr_info()
* Fix __del__ is not called (Research how tp_del, tp_finalize, and tp_deallocate works)
I hope I have enough time to finish in next week, but I'm not sure.

Fixed overriding Future._repr_info().
But I failed to implement overridable Future.__del__ in C yet.
(FYI, fastfuture2.patch passes tests by mix-in __del__ and __repr__)

Now I understand tp_dealloc, tp_finalize and subtype_dealloc.
Attached patch passes tests.

I quickly looked over the patch and I think it's good. If anything we still have time to hunt down any bugs or even revert this before 3.6 final.
INADA, feel free to commit it before Monday to 3.6 and default branches.

I've committed the patch with trivial fixes (adding curly braces to if statements).
And I'm sorry, I committed with wrong issue number.
https://hg.python.org/cpython/rev/678424183b38 (3.6)
https://hg.python.org/cpython/rev/f8815001a390 (default)
I fixed NEWS entry already.

I close this issue for now.
Further improvements can be new issue.

Thank you, INADA! Next task -- optimize asyncio.Task in C in 3.7. Another 10-15% performance improvement.

I mean another optimization possibility.

How about changing module name?
_asyncio_speedup for example.

Yes, I think it's a good idea.

This patch introduced multiple refleaks in test_asyncgen.

New changeset 345904bd0456 by Yury Selivanov in branch '3.6':
Issue #26081: Fix refleak in _asyncio.Future.__iter__().throw.
https://hg.python.org/cpython/rev/345904bd0456
New changeset b977775aa07d by Yury Selivanov in branch 'default':
Merge 3.6 (issue #26081)
https://hg.python.org/cpython/rev/b977775aa07d