[Zope] zope operations atomic?

[Clark OBrien]

This thread is getting hard to follow. The second block below that you 
attribute to me was actually Kapil's response to something I had said.

-----Original Message-----
From: Chris McDonough [mailto:chrism@zope.com]
Sent: Thursday, November 01, 2001 4:50 PM
To: Kapil Thangavelu; Clark OBrien
Cc: zope@zope.org
Subject: Re: [Zope] zope operations atomic?


Clark wrote:

> > suppose I have a method AtoB that changes every
> > letter A to B.
> > suppose I have another method BtoC that changes the
> > leter B to C.
> >
> > what is the outcome of invoking these methods in
> > different thread contexts
> > on the
> > string ABABABAB?
> >

Kapil replied:

> it depends on the concurrency. if both methods execute
> concurrently, than one will conflict and one will
> commit from trying to write on the same object. which
> one is hard to determine apriori... i'm taking a wild
> guess that it would be first one to commit. Chris,
> could you comment on this?

I'm not totally sure I understand the question (was it an allegory?)
but a literal response is:

If there is a conflict created by a first-time concurrent run of the
two methods, the string AAAAAAAA will be modified to become:

BBBBBBBB if AtoB wins the commit

or

ACACACAC if BtoC wins the commit

The "loser" of the commit would on a retry subsequently cause the
string to become:

CCCCCCCC (if BtoC was the loser)

or

BCBCBCBC (if AtoB was the loser)

(crossing fingers ;-)

Clark said:
> > >your joking, right...  besides the fact that
> > excessive locking kills
> > >performance and scalability, i *know* i don't want
> > to have to litter my
> > code
> > >with locks and thinking about concurrency. the zodb
> > greatly mitigates
> > >concurrency issues, making them almost non-existent
> > for most code. moving
> > >from this paradigm to some application level
> > locking paradigm greatly
> > >complicates code and would make it damm near
> > impossible to be productive
> > with
> > >zope, IMO.

I sorta feel like I'm answering brainteasers at this point.  Can I
help somebody solve an actual problem here? ;-)

- C