I can't directly address the concerns you've raised, but for my project I have rewritten TM.py to work better within the begin/vote/finish/abort protocol framework. I've also added more documentation. John Randall F. Kern wrote:
I may just be missing something obvious here, but it seems like there is a hole in ZODB.Transaction.Transaction.commit and Shared.DC.ZRDB.TM.TM, that can cause external transactions (those that use the TM mixin class, like psycopg) to be abandoned (never get committed or rolled back).
Let's say somewhere around line 300 in Transaction.py (the call to j.commit(o, self)) we get an exception. Furthermore, let's say the TM derived database object has already been committed (the only effect of which is to move the DB into the jars mapping, since TM.tpc_begin() and TM.commit() both do nothing).
The exception dumps us down to about line 353, where we call _p_jar.abort() on all the uncommitted objects (note: it's important that the database connection isn't in this list, because TM.abort() will rollback the transaction. the way we keep the db out of this list is by having it appear in objects _before_ the object that failed the commit).
Next we reach line ~366, where we should "unwind TPC for the jars that began it". What this means is calling tpc_abort() on each jar from the objects that were already committed (which includes the database). However, TM.tpc_abort() does nothing, leaving the external database transaction open.
Does this make sense?
If this makes sense (i.e. seems bad :), does catching tpc_abort() in TM and calling TM.abort() seem like a valid fix?
Thanks, -Randy
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IN NO EVENT SHALL DIGITAL CREATIONS OR ITS # CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, # SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT # LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF # USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND # ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, # OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT # OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF # SUCH DAMAGE. # # # This software consists of contributions made by Digital Creations and # many individuals on behalf of Digital Creations. Specific # attributions are listed in the accompanying credits file. # ############################################################################## """Provide support for linking an external transaction manager with Zope's """ class TM: """Mix-in class that provides transaction management support A sub class should call self._register() whenever it performs any transaction-dependent operations (e.g. sql statements). The sub class will need to override: _begin if necessary _vote to raise an except if necessary _finish to finallize work, _abort to roll-back work """ def _begin(self): """Hook method to begin external transaction. This may be called multiple times,""" pass def _vote(self): """Hook method to vote on success of transaction commit. This will only be called once,""" pass def _finish(self): """Hook method to complete transaction work. This may be called multiple times.""" pass def _abort(self): """Hook method to undo transaction work. This may be called multiple times.""" pass _registered=None class Surrogate: "A ZODB persistent look-alike." def __init__(self, connection): self._p_jar=connection def _register(self): """This method will register a surrogate persistent object with the transaction. This surrogate will include me in the tpc_* two-phase commit process.""" if not self._registered: try: get_transaction().register(TM.Surrogate(self)) self._registered=1 except: import traceback traceback.print_exc() pass def commit(self, *ignored): "We don't need to actually do an storing." pass def tpc_begin(self, *ignored): "Connection method to begin a commit." self._begin() def tpc_vote(self, *ignored): "Connection method to vote on commit success." self._vote() def tpc_finish(self, *ignored): """Connection method to signal commit success. This should *never* fail""" try: self._finish() finally: self._registered=0 def abort(self, *ignored): """Connnection method to signal commit failure. This should *never* fail""" try: self._abort() finally: self._registered=0