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

[Ludovic Gasc]

Indeed, thanks for the suggestion :-)

Le mer. 18 avr. 2018 à 01:21, Nathaniel Smith <njs at pobox.com> a écrit :

> Pretty sure you want to add a try/finally around that yield, so you
> release the lock on errors.
>
> On Tue, Apr 17, 2018, 14:39 Ludovic Gasc <gmludo at gmail.com> wrote:
>
>> 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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>>
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