[Python-ideas] yield from multiple iterables (was Re: The async API of the future: yield-from)

[Greg Ewing]

Guido van Rossum wrote:
> On Mon, Oct 22, 2012 at 8:55 AM, Steve Dower <Steve.Dower at microsoft.com> wrote:

>> Yes, but unless you run all subsequent code on the IOCP thread (thereby
>> blocking any more completions) you need to schedule it back to another thread.
>> This requires synchronization.

I think there's an assumption behind this whole async tasks discussion
that the tasks being scheduled are I/O bound. We're trying to overlap
CPU activity with I/O, and different I/O activities with each other.
We're *not* trying to achieve concurrency of CPU-bound tasks -- the
GIL prevents that anyway for pure Python code.

The whole Windows IOCP thing, on the other hand, seems to be geared
towards having a pool of threads, any of which can handle any I/O
operation. That's not helpful for us; when one of our tasks blocks
waiting for I/O, the completion of that I/O must wake up *that particular
task*, and it must be run using the same OS thread that was running
it before.

I gather that Windows provides a way of making an async I/O request
and specifying a callback for that request. If that's the case, do
we need to bother with an IOCP at all? Just have the callback wake
up the associated task directly.

-- 
Greg