[Python-Dev] Importance of "async" keyword

[R. David Murray]

On Sat, 27 Jun 2015 01:10:33 +1000, Chris Angelico <rosuav at gmail.com> wrote:
> The way I'm seeing it, coroutines are like cooperatively-switched
> threads; you don't have to worry about certain operations being
> interrupted (particularly low-level ones like refcount changes or list
> growth), but any time you hit an 'await', you have to assume a context
> switch. That's all very well, but I'm not sure it's that big a problem
> to accept that any call could context-switch; atomicity is already a
> concern in other cases, which is why we have principles like EAFP
> rather than LBYL.

Read Glyph's article, it explains why:

https://glyph.twistedmatrix.com/2014/02/unyielding.html

> There's clearly some benefit to being able to assume that certain
> operations are uninterruptible (because there's no 'await' anywhere in
> them), but are they truly so? Signals can already interrupt something
> _anywhere_:

Yes, and you could have an out of memory error anywhere in your program
as well.  (Don't do things in your signal handlers, set a flag.)  But
that doesn't change the stuff Glyph talks about (and Guido talks about)
about *reasoning* about your code.

I did my best to avoid using threads, and never invested the time and
effort in Twisted.  But I love programming with asyncio for highly
concurrent applications.  It fits in my brain :)

--David