46 lines
1.6 KiB
Python
46 lines
1.6 KiB
Python
from __future__ import absolute_import
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import logging
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import datetime
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from django.db.utils import IntegrityError
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from django.db import transaction
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from django.db import models
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from .exceptions import LockError
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logger = logging.getLogger(__name__)
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class LockManager(models.Manager):
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@transaction.commit_on_success
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def acquire_lock(self, name, timeout=None):
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logger.debug('trying to acquire lock: %s' % name)
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lock = self.model(name=name, timeout=timeout)
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try:
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lock.save(force_insert=True)
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logger.debug('acquired lock: %s' % name)
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return lock
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except IntegrityError, msg:
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transaction.rollback()
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logger.debug('IntegrityError: %s', msg)
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# There is already an existing lock
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# Check it's expiration date and if expired, reset it
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try:
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lock = self.model.objects.get(name=name)
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except self.model.DoesNotExist:
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# Table based locking
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logger.debug('lock: %s does not exist' % name)
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raise LockError('Unable to acquire lock')
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if datetime.datetime.now() > lock.creation_datetime + datetime.timedelta(seconds=lock.timeout):
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logger.debug('reseting deleting stale lock: %s' % name)
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lock.timeout = timeout
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logger.debug('trying to reacquire stale lock: %s' % name)
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lock.save()
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logger.debug('reacquired stale lock: %s' % name)
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return lock
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else:
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logger.debug('unable to acquire lock: %s' % name)
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raise LockError('Unable to acquire lock')
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