Questions

[Chris Muller]

Howdy, you have some great questions here..

> However I notice that no one explicitly holds a reference to the root
> object, except for the MagmaSession itself, 

The MagmaSession only references the root if you ask for it while in a
transaction.

> they are referencing
> other
> objects in the tree. Does this mean that if the model-tree was not
> fully
> connected, the root could be gc'd while the user continues to browse
> around the leaves? 

Yes.

> If so would a new user asking the same
> MagmaSession
> for its root, would get a fresh instance. If this new user browsed
> down
> to the same leaf as the first user, I would hope that they would both
> be
> looking at the same object within the one session.

Yes, definitely.  Each session has its own oid->object and object->oid
identity maps.  As the new user browses down to the object that
references the same leaf held by first user, the oid reference in the
buffer will cause it to "hook up" to the leaf object already previously
materialised.

> If another user goes to the same leaf in a fresh second non-shared
> magma
> session then his root-tree and leaf objects are a different
> rematerialisation of the repository, they are not the same objects as
> the first two users are looking at. Is this the case?

Yep.  Another user that has his own session has his own identity maps.

> So the first user changes the data in the leaf, the second user
> sharing
> the session with the first will see the exact same objects as the
> first
> so has no need to 'abort' to see the changes, in fact aborting is a
> bad
> idea because the first user may be in the middle of a commit:[] and
> that
> would ruin things for him.

Yes; as is committing a bad idea, since the other user might be in a
commit (causing multi-level transaction confusion).

Everyone knows my opinion about sharing MagmaSessions among web
sessions.  It might be naive, I don't do web programming, but if
someone is willing to try out the 1:1 design and experiences, I'd
prefer to profile THAT and see where improvements can be made so as to
maintain that simple design.

> The third user in his own magmaSession needs to #abort in order for
> the
> leaf object changes to be passed to his session. 

Yes.

> To see the changes I
> guess he has to let go of his own references to his view on the leaf
> objects, to back off to some safe unchanged place such as the branch,
> and then from there re-view the leaf objects which will have been
> updated. Is this correct?

No.  The leaf objects will be updated, in place, when the third user
crosses a transaction boundary.  No need to "expunge them" and
"reload";  that would not be transparent enough.

> Eventually the webserver is left alone for a while and sessions are
> discarded, I am assuming that the fact that the MagmaSession has a
> reference to its root will not stop it from being garbage collected.

Unless the sessions still have a transaction open they do not
hard-reference the root.  Otherwise, yes, despite its reference to the
root I think if the MagmaSession goes the root-reference would too.

> I
> also get the idea that it is not a good idea to store a reference to
> these persisted objects anywhere such as in a Class instance variable
> since this will simply result in the whole tree remaining memory
> resident.

Yep, don't do that.  :)

 - Chris