[Python-Dev] Coroutines (PEP 342)
Phillip J. Eby
pje at telecommunity.com
Tue Nov 15 04:24:52 CET 2005
At 03:46 PM 11/14/2005 -0700, Bruce Eckel wrote:
>I just finished reading PEP 342, and it appears to follow Hoare's
>Communicating Sequential Processes (CSP) where a process is a
>coroutine, and the communicaion is via yield and send(). It seems that
>if you follow that form (and you don't seem forced to, pythonically),
>then synchronization is not an issue.
>What is not clear to me, and is not discussed in the PEP, is whether
>coroutines can be distributed among multiple processors.
If you were to write a trampoline that used multiple threads, *and* you
were using a Python implementation that supported multiple processors (e.g.
Jython, IronPython, ?), *and* that Python implementation supported PEP 342,
However, that just means the answer is, "if you can run Python code on
multiple processors, you can run Python code on multiple processors". PEP
342 itself has nothing to say about that issue, which exists independently
of the PEP.
So, the PEP doesn't address what you're asking about, because the GIL still
exists in CPython, and will continue to exist. Also, guaranteeing
encapsulation of the coroutines would be *hard*, because lots of Python
objects like modules, functions, and the like would be shared between more
than one coroutine, and so then the issue of locking raises its ugly head
> If that is or
>isn't possible I think it should be explained in the PEP, and I'd be
>interested in know about it here (and ideally why it would or wouldn't
The PEP is entirely unrelated (and entirely orthogonal) to whether a given
Python implementation can interpret Python code on multiple processors
The only difference between what PEP 342 does and what Twisted does today
is in syntax. PEP 342 just provides a syntax that lets you avoid writing
your code in CPS (continuation-passing style) with lots of callbacks.
PEP 342 is implemented in the current Python SVN HEAD, by the way, if you
want to experiment with the implementation.
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