[Twisted-Python] laxdb - an async dbapi wrapper

[Vishal Shetye]

> Hi,
>
> In response to the announcement of the Twisted Asynchronous Database Api
> (tada), <http://www.darkarts.co.za/projects/tada/, I thought I should
> mention something I wrote.
>
> [Unfortunately, tada does not use threads correctly so it's likely to
> break. The author knows this and has added a warning to the module for
now.]
>
> A while back, I started messing around with making a standard, blocking
> db-api module appear non-blocking but with a deferred API. I called it
> laxdb and it's in my sandbox.
>
>     svn://svn.twistedmatrix.com/svn/Twisted/sandbox/mg/laxdb.py
>     http://svn.twistedmatrix.com/cvs/sandbox/mg/laxdb.py?view=markup
>
> laxdb is quite literally an async db-api interface and not a
> t.enterprise.adbapi style interface. In particular, it provides exactly
> the same API (but deferred) and it doesn't take over transaction
> management. It also doesn't wrongly call a cursor, "Transaction" ;-).
>
> I recently went back to laxdb and finished it off, also adding a
> connection pool implementation.
>
> Now, I haven't used laxdb in a real project and there are no unit tests
> but I think it's reasonably complete. It should work with any dbapi
> module that has threadsafety level 1 or higher, just like adbapi.
>
> If there's interest in this way of accessing a database then I would be
> happy to write tests etc, move it into Twisted and maintain it.
>
> Cheers, Matt

I guess there have not been any additions to this module in recent time.
I just tried to use it, sample code, actually a failure test, is as below
which does not actually do any query. Reactor is stopped without commit or
rollback.
This raises an exception in removeTrigger_BASE.
    exceptions.ValueError: list.remove(x): x not in list

I could fix it, in class WorkerThread, function _start has line
    self._shutdownTriggerId = reactor.addSystemEventTrigger('after',
'shutdown', self.shutdown)

self.shutdown is called by Connection.close() or reactor.stop(). In case of
second, reactor.stop, registered function, self.shutdown in this case,
should not do
    reactor.removeSystemEventTrigger(self._shutdownTriggerId)

However, this raises some doubts about overall code as there are no test
cases to prove the correctness.
Has anyone used this before? Can somebody provide pointers on what
scenarios/conditions should be tested?
laxdb is good match for what I want, interleaved calls and async interface
to db. Is there any alternative available?

[code]
from laxdb import ConnectionPool
from twisted.internet import reactor

pool = ConnectionPool("sqlite3", database='laxdbTest', timeout=5.0,
check_same_thread=False)

def connect(pool):
    d = pool.connect()
    d.addCallback(connected)

def connected(conn):
    curs = conn.cursor()
    reactor.stop()

reactor.callWhenRunning(connect, pool)
reactor.run()
[/code]

Regards,
vishal
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