[Python-ideas] non-blocking buffered I/O

Kristján Valur Jónsson kristjan at ccpgames.com
Tue Oct 30 17:11:40 CET 2012

> -----Original Message-----
> From: Python-ideas [mailto:python-ideas-
> bounces+kristjan=ccpgames.com at python.org] On Behalf Of Greg Ewing
> Sent: 30. október 2012 05:10
> To: python-ideas at python.org
> Subject: Re: [Python-ideas] non-blocking buffered I/O
> > From my point of view, IOCP fits in very well provided the callbacks
> > (which will run in the IOCP thread pool) are only used to unblock tasks.
> Is it really necessary to have a separate thread just to handle unblocking
> tasks? That thread will have very little to do, so it could just as well run the
> tasks too, couldn't it?

StacklessIO (which is an IOCP implementation for stackless) uses callbacks on an arbitrary thread (in practice a worker thread from window's own threadpool that it keeps for such things) to unblock tasklets.  You don't want to do any significant work on such a thread because it is used for other stuff by the system.

By the way:  We found that acquiring the GIL by a random external thread in response to the IOCP to wake up tasklets was incredibly expensive.  I spent a lot of effort figuring out why that is and found no real answer.  The mechanism we now use is to let the external worker thread schedule a "pending call" which is serviced by the main thread at the earliest opportunity.  Also, the main thread is interrupted if it is doing a sleep.  This is much more efficient.


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