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Date: Mon, 5 Nov 2012 01:07:40 -0800 (PST)
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Subject: Re: python destructor
From: Ferencik Ioan <ferenciki...@gmail.com>
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On Monday, November 5, 2012 8:51:00 AM UTC+2, Ferencik Ioan wrote:
> Hello there folks,
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> I have a bit of a special issue.
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> I'll start by disclosing myself for what i am doing. I am a postgraduate =
student and I really have good reasons to do what I am doing. At least i th=
ink so.
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> And not the issue.
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> I am building a python web service. This web service has some generic obj=
ects and I use a metaclass to customize the classes.=20
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> Second I use a non-conventional object oriented database, dybase=20
>=20
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> (http://www.garret.ru/dybase/doc/dybase.html#introduction)
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> Now these is a OODBMS claiming to support ACID transactions.
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> The instances of my objects are recursively organizing themselves into a =
hierarchical tree-like structure. When I make an instance of this object pe=
rsistent dybase actually can recursively save all tree structure.
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> Everything works well here.=20
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> I altered the main class situated at the root of my class hierarchy to ac=
tually store inside the__dict__ not the instances of its children but their=
 unique ID's. Then when I set a child attribute I create it and instead of =
being stored in the instance the child goes to a database index object. Thu=
s it becomes Universally addressable. The a parent retrieves the child it a=
ctually fetches it from the database.=20
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> In this way I ended up with very small objects.However these objects can =
regenerate the treelike structure as if they were storing there children in=
 the __dict__.
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> The issue is how to give the instances access to the database and properl=
y handle the opening and closing of the database.
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> It seems futile to me to actually open/close the connection through a con=
text. Because the database is a file it will issue an IO operation on every=
 attribute access and we all know __getattribute__ is used extremely often.
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> For this reason I thought the best way would be to wrap the dybase Storag=
e (main class) into a local storage version which would have __del__ method=
.
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> The local Storage is a new style class..it opens the DB file but the __de=
l__ is never called.
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> This is because the Storage class has at least 2 cyclic references.=20
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> So my Storage class never closes the database. I would like this class to=
 close the database when it is garbage collected.
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> The class is a Singleton FYI as well but this might not be relevant or ev=
en necessary.
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> So my question is:
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> what s the best way to force __del__ on a singleton that has cyclic refer=
ences. Should i use weakref and alter the original source? Is there a way i=
 can force a singleton to garbage collect itself?.
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> I am by no means a software engineer so i would appreciate any advice fro=
m some experts on the matter.
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> Thank you in advance.

Just in case somebody is interested:
Because my Storage is a singleton I registered the close() method with atex=
it from the Storage open().

This actually closes the connection. Not sure if this is feasible but it WO=
RKS!

I am using mod_wsgi in daemon mode so I have multithreading issues. If I co=
nfigure the mod_wsgi with one process dybase works correctly.
I have to override the Persistent.store() and make it thread safe using mul=
tiprocessing. This is for ANYONE who uses or plans to use dybase in a web e=
nvironment.