Comment by rdtsc | Hacker News Reader

Comment by rdtsc | Hacker News Reader

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I wouldn't look at that. That is 5 years old, and that was a different Diesel framework.

Ok, same name (a cool one, I must admit), and I think same group of people. But, it did concurrency differently. It used to be a yield based API. Which, funny enough, is like Guido's latest Tulip/Async.IO approach. And it seems me they (Diesel) decided against it, and I 100% agree. Having yields in the library code, aside from demos and small examples, doesn't work very well.

I think Diesel creators came to their approach from a practical standpoint. And I think Guido (and other proponents of async yield based IO) came from a purist/theoretical approach. We'll see what will happen in the future. It is hard to tell. But I don't see yields everywhere as a good thing. Just like I don't see callbacks or deferreds everywhere as a good way to do concurrency.

greenlet (the base module gevent and eventlet are based on it) is probably the best thing that happened to Python in its recent history. It is really unfortunate it wasn't adopted as the main concurrency mechanism in the latest version.

"yield from" isn't available on Python 2.7, maybe that's why they switched?

That would have helped a lot, yeah. Also, dealing with exceptions in an intuitive way when you have a "fake" stack you're managing yourself is a drag. The performance of of managing your own stack also sucks.

But probably the biggest practical issue is there is a terrible, common silent mistake pattern, that bit us over and over again:

    self.do_something_async() # it's a generator

What you really wanted to do was to `yield` this so the reactorish element in the frame above you consumes it. Instead, you created a NOOP generator that is never consumed, so whatever work you thought you did, silently.. does nothing.

Anyway, I think `yield from` helps you get around some of this stuff, but I haven't been keeping up with tulip. Which is probably kind of silly since Guido works like 50 feet away from me.

Btw, hi Donovan. :-)

What was tulip (and is now asyncio in 3.4) has a debug flag that you can enable to detect if a coroutine is scheduled but never called.

More info here: https://docs.python.org/3/library/asyncio-dev.html#detect-co...

Thanks for the tip, that's really useful info.

Hi Jamie. That's some really interesting insight, thanks! I'm toying with generators in javascript now and I can see forgetting the yield being an issue. The other reply to your comment seems to suggest there is a solution though, I'll have to look into that.

Greenlet giving great exception stacks sure is nice, and greenlet's performance is REALLY nice.

(Can you believe it has been almost 10 years??)

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