[Freeipa-devel] [PATCH] Allow creation of new connections by unshared instances of backend.Connectible.

[Pavel Zuna]

The backend.Connectible base class was designed, so that only one instance of 
each subclass is used at a time. Connectible generates a Connection object for 
each thread and stores it in thread-local storage (context). Subclasses access 
this object through the Connectible.conn property.

This is a good thing, because one instance of the class can be shared by all 
threads and each thread has its own connection. Unfortunately, this is also a 
limitation. If a thread needs a second connection (to a different host for 
example) - it can't do it. Not even by creating a new instance of the 
Connectible subclass.

Ok, let's move from theory to practice:

The LDAP backend is currently only used by the Executioner backend, so that 
plugins can connect to the IPA DS.

In the migration plugin, we need a second connection to the DS we're migrating 
from. The last version had to use low level python-ldap calls to achieve this.

In the installer we're still using legacy code from v1. Using ldap2 would be 
simpler and we could drop ~1000 lines code. (I already started rewriting a few 
parts to see if it would work.)

Proposed solution:

Make it possible to create unshared instances of Connectible subclasses.

This would be achieved by passing shared_instance=False (couldn't come up with a 
better name) to the object constructor explicitly. Normally, Connection objects 
are stored in thread-local storage under the subclass name (e.g. "ldap2"). 
Unshared instances would store their Connection objects under subclass name + 
unique instances ID (e.g. "ldap2_218adsfka7").

This is the only solution I could come up with, that doesn't involve breaking a 
lot of stuff - it just adds a new way of using the code we already have.

The attached patches show how it would be done.

Pavel
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