Re: how to get rid of BTreeContainer as global variable

> On Sep 7, 2016, at 06:56, Sanjay Rao <[email protected]> wrote:
> 
> Hi,
> 
> I am using multiple objects of BTreeContainer (zope.app.container.btree.BTreeContainer) to store global mapping data in my application.

(Note that the code has moved to simply zope.container.btree.BTreeContainer. The zope.app.container.btree name is simply a backwards compatibility alias, new code should use zope.container.btree directly.)

> Now with new ZODB(4.4) and ZEO(4.3),  my application randomly throws following Error
> 
> ConnectionStateError: Shouldn't load state for baton.tpd.variants.VariantsRegistry 0x043155 when the connection is closed
> 
> 
> If I replace BTreeContainer with OOBTree, Is it a safe bet to get rid of this problem ?

No. They're both persistent object types.

This problem occurs when using *any* persistent object outside the scope of its connection. This was discussed in some detail in an email on Aug 24:

> Note, however, that that connection is not necessarily safe to use or associated with the current thread. If you have a bug in your code that allows a persistent object to leak between threads or outlive a transaction boundary when the connection is closed, you can run into trouble. A faulty cache, for example, can produce this situation, leaving you with ConnectionStateErrors: 
> 
> py>> import ZODB, ZODB.DemoStorage, persistent, transaction 
> py>> db = ZODB.DB(ZODB.DemoStorage.DemoStorage()) 
> py>> conn = db.open() 
> py>> plist = persistent.list.PersistentList() 
> py>> conn.root()['key'] = plist 
> # Note that there is no connection yet 
> py>> plist._p_jar 
> # After commit we have a connection 
> py>> transaction.commit() 
> py>> plist._p_jar 
> <Connection at 10728bf30> 
> # But we still have it after the connection is closed 
> py>> conn.close() 
> py>> plist._p_jar 
> <Connection at 10728bf30> 
> # And it is useless 
> py>> plist.thing 
> Traceback (most recent call last): 
>   ... 
> ConnectionStateError: Shouldn't load state for persistent.list.PersistentList 0x316490b7e11981b6 when the connection is closed 
> py>> plist._p_jar.root() 
> Traceback (most recent call last): 
>   ... 
> ConnectionStateError: The database connection is closed 
> 
> So I guess I'm just saying, be careful about the lifetime of your persistent objects.

Other than a faulty cache, trying to use persistent objects as module globals, or passing them up through WSGI middleware or pyramid tweens that are "above" the connection/transaction management can cause this type of error.

I think you'll find that the error isn't really "random," there's a specific misuse of objects that gets you there.

Jason

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