from requests.exceptions import HTTPError
from etcd.common_ops import CommonOps
[docs]class LeaderMod(CommonOps):
"""'Leader' functionality for consensus-based assignment. If multiple
processes try to assign different simple strings to the given key, the
first will succeed and block the others until the TTL expires. The same
process repeats for all subsequent assignments.
"""
def __get_path(self, leader_key):
return ('/' + leader_key)
[docs] def set_or_renew(self, key, value, ttl):
self.client.debug("LEADER: Setting key [%s] with value [%s]." %
(key, value))
fq_path = self.__get_path(key)
# TODO: Why is it called "name"?
data = { 'name': value }
parameters = { 'ttl': ttl }
self.client.send(2, 'put', fq_path, data=data,
parameters=parameters, module='leader',
return_raw=True)
[docs] def get(self, key):
self.client.debug("LEADER: Getting value for key [%s]." % (key))
fq_path = self.__get_path(key)
# TODO:
#
# If this fails, we get a text response on a 200:
#
# get leader error: read lock error: Cannot reach servers after 3 time\n
#
# Raise a KeyError when this is fixed.
r = self.client.send(2, 'get', fq_path, module='leader',
return_raw=True)
if r.text == '':
return None
result = r.text
if result.startswith('get leader error:') is True:
raise KeyError(key)
return result
[docs] def delete(self, key, value):
self.client.debug("LEADER: Deleting key [%s] with value [%s]." %
(key, value))
# TODO:
#
# If this fails, we get a text response with a 500:
#
# delete leader error: release lock error: cannot find: test value
#
# Raise a KeyError when this is fixed.
fq_path = self.__get_path(key)
parameters = { 'name': value }
try:
self.client.send(2, 'delete', fq_path, module='leader',
parameters=parameters, return_raw=True)
except HTTPError as e:
if e.response.status_code == 500:
raise KeyError(key)
raise