58 lines
1.9 KiB
Python
58 lines
1.9 KiB
Python
# authentic2 - versatile identity manager
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# Copyright (C) 2010-2021 Entr'ouvert
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#
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# This program is free software: you can redistribute it and/or modify it
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# under the terms of the GNU Affero General Public License as published
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# by the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU Affero General Public License for more details.
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#
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# You should have received a copy of the GNU Affero General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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import math
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import random
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import time
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from django.conf import settings
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from django.db import connection
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def poisson_random(frequency):
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'''Generate random numbers following a poisson distribution'''
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return -math.log(1.0 - random.random()) / frequency
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SAFE_GET_OR_CREATE_RETRIES = 3
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class ConcurrencyError(Exception):
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pass
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def safe_get_or_create(model, defaults=None, **kwargs):
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assert (
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getattr(settings, 'TESTING', False) or not connection.in_atomic_block
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), 'safe_get_or_create cannot be used in inside a transaction'
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defaults = defaults or {}
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exception = None
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for dummy in range(SAFE_GET_OR_CREATE_RETRIES):
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try:
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instance, created = model.objects.get_or_create(defaults=defaults, **kwargs)
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except model.MultipleObjectsReturned as e:
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exception = e
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time.sleep(max(poisson_random(1), 0.5))
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continue
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if created and model.objects.filter(**kwargs).exclude(pk=instance.pk).exists():
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instance.delete()
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time.sleep(max(poisson_random(1), 0.5))
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continue
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return instance, created
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raise exception
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