2.6, 3.0, and truly independent intepreters

VanL van.lindberg at gmail.com
Thu Oct 30 18:39:49 CET 2008


Jesse Noller wrote:

> Even luminaries such as Brian Goetz and many, many others have pointed
> out that threading, as it exists today is fundamentally difficult to
> get right. Ergo the "renaissance" (read: echo chamber) towards
> Erlang-style concurrency.

I think this is slightly missing what Andy is saying. Andy is trying
something that would look much more like Erlang-style concurrency than
classic threads - "green processes" to use someone else's term.

AFAIK, Erlang "processes" aren't really processes at the OS level.
Instead, they are named processes because they only communicate through
message passing. When multiple "processes" are running in the same
os-level-multi-threaded interpreter, the interpreter cheats to make the
message passing fast.

I think Andy is thinking along the same lines. With a Python
subinterpreter per thread, he is suggesting intra-process message
passing as a way to get concurrency.

Its actually not too far from what he is doing already, but he is
fighting OS-level shared library semantics to do it. Instead, if Python
supported a per-subinterpreter GIL and per-subinterpreter state, then
you could theoretically get to a good place:
	
- You only initialize subinterpreters if you need them, so
single-process Python doesn't pay a large (any?) penalty
- Intra-process message passing can be fast, but still has the
no-shared-state benefits of the Erlang concurrency model
- There are fewer changes to the Python core, because the GIL doesn't go
away

No, this isn't whole-hog free threading (or safe threading), there are
restrictions that go along with this model - but there would be benefits.




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