[Zope-dev] Re: Bare "except" dangerous to ZODB?

[Jeremy Hylton]

On Tue, 2003-02-11 at 04:13, zope-dev-request@zope.org wrote:
> Chris McDonough wrote:
> > Could this be done by initializing a dictionary at startup keyed on
> > thread-id that a ConflictError exception's __init__ could stick a marker
> > into, then checking that dictionary at commit time and disallowing the
> > commit if the marker still existed?
> 
> Yes, but Transaction objects are already keyed on the thread ID, so I 
> think you just have to set a "doomed" flag on the transaction.  Attempts 
> to commit doomed transactions result in either ConflictError or 
> "DoomedTransactionError". ;-)  Aborting the transaction (or beginning a 
> new transaction) resets the flag.
> 
> Shane

The doomed flag is the way zodb4 works.  Each transaction has a status
flag that can be one of: active, preparing, prepared, failed, committed,
aborting, and aborted.  Actions are only allowable in certain states. 
The only thing you can do to a failed transaction is abort it.  And the
only thing you can do to a prepared transaction is commit or abort it.

I'd like to backport that to ZODB3, but I need to finish the transaction
package for ZODB4 first.  If the current problem is perceived to be a
significant risk, we could increase the priority of the backport.  One
downside is that some people do strange things with transactions, like
joining them during the commit; that doesn't work in ZODB4.

Jeremy