More than one interpreter per process?

[Graham Dumpleton]

On Dec 19, 2:37 am, sturlamolden <sturlamol... at yahoo.no> wrote:
> On 18 Des, 10:24, Roger Binns <rog... at rogerbinns.com> wrote:
>
> > You can.  Have a look at mod_python andmod_wsgiwhich does exactly
> > this.  But extension modules that use the simplified GIL api don't work
> > with them (well, if at all).
>
> mod_python implements use Py_NewInterpreter() to create sub-
> interpreters. They all share the same GIL. The GIL is declared static
> in ceval.c, and shared for the whole process. But ok, if
> PyEval_AquireLock() would take a pointer to a 'sub-GIL', sub-
> interpreters could run concurrent on SMPs. But it would require a
> separate thread scheduler in each subprocess.

In current versions of Python it is possible for multiple sub
interpreters to access the same instance of a Python object which is
notionally independent of any particular interpreter. In other words,
sharing of objects exists between sub interpreters. If you remove the
global GIL and make it per sub interpreter then you would loose this
ability. This may have an impact of some third party C extension
modules, or in embedded systems, which are able to cache simple Python
data objects for use in multiple sub interpreters so that memory usage
is reduced.

Graham