115 lines
3.9 KiB
Python
115 lines
3.9 KiB
Python
# Copyright (C) 2015 SUSE Linux GmbH
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 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 General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License along
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# with this program; if not, write to the Free Software Foundation, Inc.,
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# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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from datetime import datetime
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import time
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import warnings
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from xml.etree import cElementTree as ET
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from osc import conf
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from osc.core import makeurl
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from osc.core import http_GET
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from osc.core import http_POST
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class OBSLock(object):
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"""Implement a distributed lock using a shared OBS resource."""
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def __init__(self, apiurl, project, ttl=3600):
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self.apiurl = apiurl
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self.project = project
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self.lock = conf.config[project]['lock']
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self.ns = conf.config[project]['lock-ns']
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# TTL is measured in seconds
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self.ttl = ttl
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self.user = conf.config['api_host_options'][apiurl]['user']
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self.locked = False
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def _signature(self):
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"""Create a signature with a timestamp."""
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return '%s@%s' % (self.user, datetime.isoformat(datetime.utcnow()))
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def _parse(self, signature):
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"""Parse a signature into an user and a timestamp."""
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user, ts = None, None
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try:
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user, ts_str = signature.split('@')
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ts = datetime.strptime(ts_str, '%Y-%m-%dT%H:%M:%S.%f')
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except (AttributeError, ValueError):
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pass
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return user, ts
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def _read(self):
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url = makeurl(self.apiurl, ['source', self.lock, '_attribute', '%s:LockedBy' % self.ns])
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root = ET.parse(http_GET(url)).getroot()
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signature = None
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try:
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signature = root.find('.//value').text
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except (AttributeError, ValueError):
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pass
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return signature
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def _write(self, signature):
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url = makeurl(self.apiurl, ['source', self.lock, '_attribute', '%s:LockedBy' % self.ns])
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data = """
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<attributes>
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<attribute namespace='%s' name='LockedBy'>
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<value>%s</value>
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</attribute>
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</attributes>""" % (self.ns, signature)
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http_POST(url, data=data)
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def acquire(self):
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# If the project doesn't have locks configured, raise a
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# Warning (but continue the operation)
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if not self.lock:
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warnings.warn('Locking attribute is not found. Create one to avoid race conditions.')
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return self
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user, ts = self._parse(self._read())
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if user and ts:
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now = datetime.utcnow()
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if now < ts:
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raise Exception('Lock acquired from the future [%s] by [%s]. Try later.' % (ts, user))
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delta = now - ts
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if delta.seconds < self.ttl:
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print 'Lock acquired by [%s] %s ago. Try later.' % (user, delta)
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exit(-1)
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# raise Exception('Lock acquired by [%s]. Try later.' % user)
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self._write(self._signature())
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time.sleep(1)
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user, ts = self._parse(self._read())
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if user != self.user:
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raise Exception('Race condition, [%s] wins. Try later.' % user)
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return self
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def release(self):
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# If the project do not have locks configured, simply ignore
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# the operation.
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if not self.lock:
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return
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user, ts = self._parse(self._read())
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if user == self.user:
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self._write('')
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__enter__ = acquire
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def __exit__(self, exc_type, exc_val, exc_tb):
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self.release()
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