[ZODB-Dev] Multithread app with ZODB

[Alberto Casado Martín]

Sorry again , think i didn't confirm the inscription before sending the
mail... :)

2010/6/8 Alberto Casado <alberto.casado.martin at gmail.com>

>
>
> I forgot  one step in the code, sorry.
>
>
> El 08/06/2010, a las 02:08, Alberto Casado escribió:
>
> Hi all
> I don't know if this is the list where I have to ask, if isn't it, sorry.
>
> In the last weeks I am having a lot of problems trying to figure out how
> ZODB should interact with a multithread app.
> In short,  basically the App is a GUI that receives data from sensors. It
> is a distributed system, built with  omniORB, when the info comes from the
> sensors it is store in ZODB and it is shown  in a GUI where can be modify by
> an operator (human) and this changes are commited to ZODB and send back to
> the sensor.
>
> I have a connection for each thread, due to that  sometimes the thread is
> created in c++, I don't have the control of the pool. But i am pretty sure
> that before any change is done, I create a new connection for this thread
> (and also getting the root object).
> Almost every  time i try to commit to ZODB I have an error
>  Duplicate tpc_begin calls for same transaction
>
> I have observed that when info comes from the sensors (one call, one thread
> , I am dealing only with one message now) and I update the data , different
> objects (ZODB persistent classes), these  distinct objects are registered in
> several connections, so when I try to commit them, always end up in the same
> error...
>
> As I can see in the code, the first time goes fine, but the second is going
> to fail  always, because the transaction is assigned to the storage.
>
> from _transaction.py:
> def _commitResources(self):
>         # Execute the two-phase commit protocol.
>
>         L = list(self._resources)
>         L.sort(rm_cmp)
>         try:
>             for rm in L:
>                 rm.tpc_begin(self)------- tpc_begin always with self.
>             for rm in L:
>                 rm.commit(self)
>                 self.log.debug("commit %r" % rm)
>             for rm in L:
>                 rm.tpc_vote(self)
>                 self._voted[id(rm)] = True
>
>
> from Connection.py.
>
> def tpc_begin(self, transaction):
>         """Begin commit of a transaction, starting the two-phase
> commit."""
>         self._modified = []
>
>         # _creating is a list of oids of new objects, which is used to
>         # remove them from the cache if a transaction aborts.
>         self._creating.clear()
>         self._normal_storage.tpc_begin(transaction)
>
>
>
>
>
> From BasicStorage.py
> def tpc_begin(self, transaction, tid=None, status=' '):
>         if self._is_read_only:
>             raise POSException.ReadOnlyError()
>         self._lock_acquire()
>         try:
>             if self._transaction is transaction:------------ the fisrt
> time goes fine,but the second always fail
>                 raise POSException.StorageTransactionError(
>                     "Duplicate tpc_begin calls for same transaction")
>             self._lock_release()
>             self._commit_lock_acquire()
>             self._lock_acquire()
>             self._transaction = transaction------------
>             self._clear_temp()
>
> This is killing me, I don't know if it is an error registering
> modifications that are happening in one thread, to several connections and I
> dont know why this is happening...
>
> I someone can give me some clue...
>
>
> BR.
>
> Alberto.
> PD: sorry for my English.
>
>
>
>
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