Synnefo

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from django.db import transaction

from django.db import connection

from time import sleep

import logging

logger = logging.getLogger(__name__)

def with_lock(retries=3, retry_wait=1.0):

    def wrap(func):

        def inner(*args, **kwargs):

            transaction.commit()

            _retries = retries

            cursor = connection.cursor()

            locked = True

            try:

                while 1:

                    cursor.execute("SELECT pg_try_advisory_lock(1)")

                    r = cursor.fetchone()

                    if r is None:

                        m = "Impossible"

                        raise AssertionError(m)

                    locked = r[0]

                    if locked:

                        break

                    _retries -= 1

                    if _retries <= 0:

                        return False

                    sleep(retry_wait)

                return func(*args, **kwargs)

            finally:

                if locked:

                    try:

                        transaction.commit()

                    except Exception as e:

                        logger.exception(e)

                        transaction.rollback()

                    cursor.execute("SELECT pg_advisory_unlock(1)")

                    cursor.fetchall()

        return inner

    return wrap