[Zope] Storing unpicklable objects

[Jim Fulton]

Li Dongfeng wrote:
> 
> Question: can we store an arbitrary python object
>  (created with external method)

Note that external methods are really not appropriate when
you have any kind of persistence issues involved.

>  in the ZOPE namespace
>  during the life of the current ZOPE server process?
>
> If the object is picklable, then we just assign it to an
> attribute of a folder. The object will survive pickling.
> 
> But if the object is not picklable, e.g., an open pipe,
> or an open file, then Zope does not allow it to be
> assigned to a normal attribute.

This is as it should be, since it makes to sense to
save an open pipe in a database. :)

> The solution I used now
> is to assign the object to an attribute with name starting
> with _v_, like _v_my_sub_process_pipe. Then the object
> can be saved, for some period of time, and can be used
> by other external methods(other than the one created it).
> But, after a while, the saved _v_ attribute simply dispears.
> I guess it has been saved to the ODB and then reloaded, but attributes
> with _v_ name prefix cannot survive pickling, so it is lost.

Right. You have another problem too: if you habe multiple
application threads, then two requests to the same logical
object may not get the same phisical object. So saving a value
in a _v_ attribute does not assure that you will get the value
the next time you access the same (logical) object, even if the
physical object is not removed from memory.
 
> Zope gurus: is there any way to allow saving of arbitrary
>  python object in the running Zope process? I only need
>  the object to live during the server process's life.

You might be better served to create a global registry of
pipes that is keyed on persistent object id and and protected by
a lock.  This registry might be in a module global variable
in a *product* module, *not* an external method file.
 
Jim

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