[Stackless] Multi-CPU Actor Based Python

Jeff Senn senn at maya.com
Tue Nov 18 20:58:10 CET 2008

On Nov 18, 2008, at 11:32 AM, Timothy Baldridge wrote:

> Because all information for an object is contained in that object
> (including message queues, and data). We could remove all locks from
> the list objects, as the internal object tasklet will be the only
> object modifying the code. These queues are the only parts that would
> need to be locked, and those can be created via CAS operations, we
> could take out 90% of the locks in Python.

Hm.  Are you forgetting that "objects" in Python are all by reference.
And therefore it is pretty much impossible to "contain" them.

Imagine I create a message:

   msg = [ [1,2], [3,4] ]  # Notice msg is a reference to a tree of 7  

Then I pass this message to 2 different tasks running in parallel
and they both do something like:

   del msg[0][1]

What happens in the absence of a lock (the GIL) on msg[0]?

One solution, of course, is to deep copy all messages whenever they
cross a "boundary"...  which will very quickly become a rat hole...
and you might as well simply run a separate python interpreter
per-thread and pickle/unpickle all the messages moving between
them...  probably not what you had in mind...

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