[Async-sig] asyncio.Lock equivalent for multiple processes

[Ludovic Gasc]

2018-04-17 15:16 GMT+02:00 Antoine Pitrou <solipsis at pitrou.net>:

>
>
> You could simply use something like the first 64 bits of
> sha1("myapp:<lock name>")
>

I have followed your idea, except I used hashtext directly, it's an
internal postgresql function that generates an integer directly.

For now, it seems to work pretty well but I didn't yet finished all tests.
The final result is literally 3 lines of Python inside an async
contextmanager, I like this solution ;-) :

@asynccontextmanager
async def lock(env, category='global', name='global'):
    # Alternative lock id with 'mytable'::regclass::integer OID
    await env['aiopg']['cursor'].execute("SELECT pg_advisory_lock(
hashtext(%(lock_name)s) );", {'lock_name': '%s.%s' % (category, name)})

    yield None

    await env['aiopg']['cursor'].execute("SELECT pg_advisory_unlock(
hashtext(%(lock_name)s) );", {'lock_name': '%s.%s' % (category, name)})



>
> Regards
>
> Antoine.
>
>
> On Tue, 17 Apr 2018 15:04:37 +0200
> Ludovic Gasc <gmludo at gmail.com> wrote:
> > Hi Antoine & Chris,
> >
> > Thanks a lot for the advisory lock, I didn't know this feature in
> > PostgreSQL.
> > Indeed, it seems to fit my problem.
> >
> > The small latest problem I have is that we have string names for locks,
> > but advisory locks accept only integers.
> > Nevertheless, it isn't a problem, I will do a mapping between names and
> > integers.
> >
> > Yours.
> >
> > --
> > Ludovic Gasc (GMLudo)
> >
> > 2018-04-17 13:41 GMT+02:00 Antoine Pitrou <solipsis at pitrou.net>:
> >
> > > On Tue, 17 Apr 2018 13:34:47 +0200
> > > Ludovic Gasc <gmludo at gmail.com> wrote:
> > > > Hi Nickolai,
> > > >
> > > > Thanks for your suggestions, especially for the file system lock:
> We
> > > don't
> > > > have often locks, but we must be sure it's locked.
> > > >
> > > > For 1) and 4) suggestions, in fact we have several systems to sync
> and
> > > also
> > > > a PostgreSQL transaction, the request must be treated by the same
> worker
> > > > from beginning to end and the other systems aren't idempotent at
> all,
> > > it's
> > > > "old-school" proprietary systems, good luck to change that ;-)
> > >
> > > If you already have a PostgreSQL connection, can't you use a PostgreSQL
> > > lock?  e.g. an "advisory lock" as described in
> > > https://www.postgresql.org/docs/9.1/static/explicit-locking.html
> > >
> > > Regards
> > >
> > > Antoine.
> > >
> > >
> > >
> >
>
>
>
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