[Python-Dev] Sandboxed Threads in Python (original) (raw)

Adam Olsen rhamph at gmail.com
Sat Oct 8 14:29:25 CEST 2005

On 10/7/05, Phillip J. Eby <pje at telecommunity.com> wrote:

At 07:17 PM 10/7/2005 -0600, Adam Olsen wrote: >On 10/7/05, Phillip J. Eby <pje at telecommunity.com> wrote: > > Note that implementing a root-based GC for Python is non-trivial, since > > extension modules can store pointers to PyObjects anywhere they > > like. Further, many Python objects don't even support being tracked by the > > current cycle collector. > > > > So, changing this would probably require a lot of C extensions to be > > rewritten to support the needed API changes for the new garbage collection > > strategy. > >They only need to be rewritten if you want them to provide an >immutable type that can be transferred between sandboxes.

No. You're missing my point. If they are able to reference these objects, then the garbage collector has to know about it, or else it can't know when to reclaim them. Ergo, these objects will leak, or else extensions will crash when they refer to the deallocated memory. In other words, you can't handwave the whole problem away by assuming "a garbage collector". The garbage collector has to actually be able to work, and you haven't specified how it can work without changing the C API.

Unfortunately the rammifications of your original statement didn't set in until well after I sent my reply. You are right, it does make it impossible without changing the C API, so that much of the idea is dead.

I wonder if it would be possible to use a wrapper around the immutable type instead.. something to ponder anyway.

>I was aware that weakrefs needed some special handling (I just forgot >to mention it), but I didn't know it was used by subclassing. >Unfortunately I don't know what purpose it serves so I can't >contemplate how to deal with it.

It allows changes to a supertype's C-level slots to propagate to subclasses.

I see. Well, I would have required the supertype to be immutable, so there couldn't be any changes to the C-level slots.

-- Adam Olsen, aka Rhamphoryncus

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