55 lines
1.7 KiB
Python
55 lines
1.7 KiB
Python
import datetime
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from django.db import models
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from django.utils.translation import ugettext_lazy as _
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from django.db.utils import IntegrityError
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from django.db import transaction
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class LockError(Exception):
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pass
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class LockManager(models.Manager):
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@transaction.commit_manually
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def acquire_lock(self, name):
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lock = self.model(name=name)
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try:
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lock.save(force_insert=True)
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except IntegrityError:
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transaction.rollback()
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# There is already an existing lock
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# Check it's expiration date and if expired delete it and
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# re-create it
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lock = Lock.objects.get(name=name)
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if datetime.datetime.now() > lock.creation_datetime + datetime.timedelta(seconds=lock.expiration):
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release_lock(self)
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lock.save()
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else:
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raise LockError('Unable to acquire lock')
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else:
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transaction.commit()
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@transaction.commit_manually
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def release_lock(self, name):
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lock = Lock.objects.get(name=name)
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lock.delete()
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transaction.commit()
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class Lock(models.Model):
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creation_datetime = models.DateTimeField(verbose_name=_(u'creation datetime'))
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expiration_time = models.IntegerField(default=3600, verbose_name=_(u'expiration time'))
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name = models.CharField(max_length=32, verbose_name=_(u'name'), unique=True)
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objects = LockManager()
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def __unicode__(self):
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return self.name
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def save(self, *args, **kwargs):
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self.creation_datetime = datetime.datetime.now()
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super(Lock, self).save(*args, **kwargs)
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class Meta:
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verbose_name = _(u'lock')
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verbose_name_plural = _(u'locks')
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