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Re: Asynchronous event loop brainstorm at FSF 30

From: Christopher Allan Webber
Subject: Re: Asynchronous event loop brainstorm at FSF 30
Date: Sun, 04 Oct 2015 10:19:03 -0500

Amirouche Boubekki writes:

> Héllo,
> Please excuse my layman question in advance.
> I find the idea awesome to work on asynchronous framework for Guile.
> Le 2015-10-04 00:29, Christopher Allan Webber a écrit:
>> So David Thompson, Mark Weaver, Andrew Engelbrecht and I sat down to
>> talk over how we might go about an asynchronous event loop in Guile 
>> that
>> might be fairly extensible.  Here are some of what we discussed, in
>> bullet points:
>>  - General idea is to do something coroutine based.
> IUC coroutine takes advantage of the ability to pause the execution of 
> given procedure A to run a blocking operation B and execute some other 
> procedure C while the blocking operation B is running. At some point, 
> when the blocking operation B is finished, and C is finished, A restarts 
> where it left.

Sort of, I'm not sure that "blocking" needs to be tossed in there.
We're interested in as much nonblocking behavior as possible.

Coroutines in this case basically means functions that can be suspended
and then woken up again when whatever asynchronous code they rely on has
completed (possibly receiving a value from that as well).

>>  - This would be like asyncio or node.js, asynchronous but *not* OS
>>    thread based (it's too much work to make much of Guile fit around
>>    that for now)
>>  - If you really need to maximize your multiple cores, you can do
>>    multiple processes with message passing anyway
> Does it mean that there will be one event loop per thread per process ?


>>  - So what we really need is a nice API for how to do coroutines, write
>>    asynchronous code, and work with some event loop with a scheduler
>>  - Probably a good way to start on this would be to use libuv (or is it
>>    libev?) and prototype this.  It's not clear if that's a good long
>>    term approach (eg, I think it doesn't work on the HURD for those who
>>    care about that, and Guix certainly does)
> In asyncio the event loop can be swapped the default event loop is pure 
> python. You mean that the first version will use libuv (libuv is the 
> nodejs eventloop, formely based on libev).

Right, I think that modeling the event loop in an abstract way is a
strong idea.  One nice feature is that the asyncio event loop can be
swapped out... thus, it's possible to use the default event loop, a GTK
event loop, or twisted, or whatever, IIRC

>>  - Binary/custom ports could be a nice means of abstraction for this
>> So, that's our thoughts, maybe someone or one of us or maybe even *you*
>> will be inspired to start from here?
> I don't want to make promises (pun on punpose) but I find this proposal 
> really interesting.

Great!  And good pun :)

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