Question on multiple Python users in one application

[Loren Wilton]

> From: "Paul Rubin" <no.email at nospam.invalid>
> I don't think Python threads are the answer.  You want a separate
> interpreter per user, which is annoying to do with CPython.  Do you have
> concrete performance expectations about the sharing of data between
> interpreter sessions?  Those old mainframes were very slow compared to
> today's machines, even counting Python's interpretation overhead.

Without separate context it sounds like Python threads are moderately 
useless except in special circumstances, and this certainly isn't one of 
those circumstances.

As for performance, especially with shared data, it is an interesting 
question, but one not easily answered at the moment. The VM does a lot of 
interesting JIT type stuff, so gets performance that easily exceeds the most 
recent hardware implementation of the machine, which was only made a few 
years ago. Yes, a raw PC can do things faster (obviously). But people like 
the mainframe environment for the same reason people like Python over C: it 
does what they want, easier. They are willing to pay some performance for 
this -- but only some. They still have network response times to meet and 
need to get the monthend batch processing done before midnight.

In our case, shared data is no slower to access than process-unique data. 
Well, maybe a little slower if you have to acquire and release a lock, 
because that takes a few nanoseconds or so. So I'd prefer that Python shared 
data access was not a lot slower than non-shared access. My impression is 
that all data is in a common heap, so a lock is required to access anything. 
I'd think that makes all data access equally slow or equally fast.

I haven't found much data on multiple separate interpreters within a single 
process space.

What exactly do you get that is unique to each interpreter? Separate heaps? 
Seperate GC locks? Separate process threads? I would guess maybe separate 
builtins.

Does multiple interpreters make it harder to share data between the 
interpreters?

        Loren