On 27 May 2017 at 03:30, Guido van Rossum email@example.com wrote:
On Fri, May 26, 2017 at 8:28 AM, Nick Coghlan firstname.lastname@example.org wrote:
[...] assuming the rest of idea works out well, we'd eventually like to move to a tiered model where the GIL becomes a read/write lock. Most code execution in subinterpreters would then only need a read lock on the GIL, and hence could happily execute code in parallel with other subinterpreters running on other cores.
Since the GIL protects refcounts and refcounts are probably the most frequently written item, I'm skeptical of this.
Likewise - hence my somewhat garbled attempt to explain that actually doing that would be contingent on the GILectomy folks figuring out some clever way to cope with the refcounts :)
By contrast, being able to reliably model Communicating Sequential Processes in Python without incurring any communications overhead though (ala goroutines)? Or doing the same with the Actor model (ala Erlang/BEAM processes)?
Those are *very* interesting language design concepts, and something where offering a compelling alternative to the current practices of emulating them with threads or coroutines pretty much requires the property of zero-copy ownership transfer.
But subinterpreters (which have independent sys.modules dicts) seem a poor match for that. It feels as if you're speculating about an entirely different language here, not named Python.
Ah, you're right - the types are all going to be separate as well, which means "cost of a deep copy" is the cheapest we're going to be able to get with this model. Anything better than that would require a more esoteric memory management architecture like the one in PyParallel.
I guess I'll have to scale back my hopes on that front to be closer to what Stephan described - even a deep copy equivalent is often going to be cheaper than a full serialise/transmit/deserialise cycle or some other form of inter-process communication.