openstack
/
tooz
Code Issues Proposed changes

memcached: implement leader election 

Change-Id: I82bfdce0174410f7cb15bf594fa4c6a364881df1
Co-Authored-By: Sahid Ferdjaoui <sahid.ferdjaoui@cloudwatt.com>
This commit is contained in:
Julien Danjou 2014-04-03 12:29:42 +02:00
parent 698f554c9d
commit 57d24bd54b
1 changed files with 40 additions and 7 deletions
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47
tooz/drivers/memcached.py
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@ -80,15 +80,18 @@ class MemcachedLock(locking.Lock):
class MemcachedDriver(coordination.CoordinationDriver):
_GROUP_PREFIX = b'_TOOZ_GROUP_'
_GROUP_LEADER_PREFIX = b'_TOOZ_GROUP_LEADER_'
_MEMBER_PREFIX = b'_TOOZ_MEMBER_'
_GROUP_LIST_KEY = b'_TOOZ_GROUP_LIST'
def __init__(self, member_id, membership_timeout=30, lock_timeout=30):
def __init__(self, member_id, membership_timeout=30, lock_timeout=30,
leader_timeout=30):
super(MemcachedDriver, self).__init__()
self._member_id = member_id
self._groups = set()
self.membership_timeout = membership_timeout
self.lock_timeout = lock_timeout
self.leader_timeout = leader_timeout
@staticmethod
def _msgpack_serializer(key, value):
@ -121,6 +124,11 @@ class MemcachedDriver(coordination.CoordinationDriver):
def stop(self):
self.client.delete(self._encode_member_id(self._member_id))
map(self.leave_group, list(self._groups))
for group_id in six.iterkeys(self._hooks_elected_leader):
if self.get_leader(group_id).get() == self._member_id:
self.client.delete(self._encode_group_leader(group_id))
self.client.close()
def _encode_group_id(self, group_id):
@ -129,6 +137,9 @@ class MemcachedDriver(coordination.CoordinationDriver):
def _encode_member_id(self, member_id):
return self._MEMBER_PREFIX + member_id
def _encode_group_leader(self, group_id):
return self._GROUP_LEADER_PREFIX + group_id
@retry
def _add_group_to_group_list(self, group_id):
"""Add group to the group list.
@ -241,6 +252,10 @@ class MemcachedDriver(coordination.CoordinationDriver):
raise Retry
return MemcachedAsyncResult(None)
def get_leader(self, group_id):
return MemcachedAsyncResult(
self.client.get(self._encode_group_leader(group_id)))
def heartbeat(self):
self.client.set(self._encode_member_id(self._member_id),
"It's alive!",
@ -249,6 +264,11 @@ class MemcachedDriver(coordination.CoordinationDriver):
for lock in self._acquired_locks:
lock.heartbeat()
for group_id in six.iterkeys(self._hooks_elected_leader):
if self.get_leader(group_id).get() == self._member_id:
self.client.touch(self._encode_group_leader(group_id),
expire=self.leader_timeout)
def _init_watch_group(self, group_id):
members = self.client.get(self._encode_group_id(group_id))
if members is None:
@ -275,13 +295,13 @@ class MemcachedDriver(coordination.CoordinationDriver):
return super(MemcachedDriver, self).unwatch_leave_group(
group_id, callback)
@staticmethod
def watch_elected_as_leader(group_id, callback):
raise NotImplementedError
def watch_elected_as_leader(self, group_id, callback):
return super(MemcachedDriver, self).watch_elected_as_leader(
group_id, callback)
@staticmethod
def unwatch_elected_as_leader(group_id, callback):
raise NotImplementedError
def unwatch_elected_as_leader(self, group_id, callback):
return super(MemcachedDriver, self).unwatch_elected_as_leader(
group_id, callback)
def get_lock(self, name):
return MemcachedLock(self, name, self.lock_timeout)
@ -307,6 +327,19 @@ class MemcachedDriver(coordination.CoordinationDriver):
self._group_members[group_id] = group_members
for group_id in six.iterkeys(self._hooks_elected_leader):
lock_id = self._encode_group_leader(group_id)
# Try to grab the lock, if that fails, that means someone has it
# already.
if self.client.add(lock_id, self._member_id,
expire=self.leader_timeout,
noreply=False):
# We got the lock
self._hooks_elected_leader[group_id].run(
coordination.LeaderElected(
group_id,
self._member_id))
return result