62ac6d4309
Commit 9fd5160558 attempted to fix
races where the change cache watchers might still be running
after test shutdown. This was specific to some very short tests.
Unfortunately, one of those tests (test_concurrent_delete) exercises
a behavior where if no watch events ever reach the cache during
the test, then the cache key will still remain in the cache.
It is not clear whether this is a behavior that could occur
in reality, or if it is a side-effect of simulating two cache
actors with the same cache object. If it could happen in reality,
it may indicate a minor bug/leak in the change cache. The best
way to resolve this might be to switch the change cache to use
a persistent recursive watch (possibly via the ZuulTreeCache)
in a future change.
In the mean time, let's try a second approach to make these tests
robust: give the change cache a stop method that will abort any
calls to ZK after it is called. This should avoid the underlying
problem of delayed watch callbacks attempting to access zk after
shutdown.
Change-Id: I15133bd5b612e492ddb51e903e9ee7944279cfc3
509 lines
19 KiB
Python
509 lines
19 KiB
Python
# Copyright 2021 BMW Group
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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import abc
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import contextlib
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import json
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import logging
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import threading
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import time
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import uuid
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import hashlib
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import zlib
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from collections import defaultdict
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from collections.abc import Iterable
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from kazoo.exceptions import BadVersionError, NodeExistsError, NoNodeError
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from zuul import model
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from zuul.zk import sharding, ZooKeeperSimpleBase
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from zuul.zk.exceptions import ZuulZooKeeperException
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from zuul.zk.vendor.watchers import ExistingDataWatch
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CHANGE_CACHE_ROOT = "/zuul/cache/connection"
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class ConcurrentUpdateError(ZuulZooKeeperException):
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pass
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def str_or_none(d):
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if d is None:
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return d
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return str(d)
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class ChangeKey:
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"""Represents a change key
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This is used to look up a change in the change cache.
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It also contains enough basic information about a change in order
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to determine if two entries in the change cache are related or
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identical.
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There are two ways to refer to a Change in ZK. If one ZK object
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refers to a change, it should use ChangeKey.reference. This is a
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dictionary with structured information about the change. The
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contents can be used to construct a ChangeKey, and that can be
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used to pull the Change from the cache. The reference is used by
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other objects in ZooKeeper to refer to changes, so the
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serialization format must be stable or backwards compatible.
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The cache itself uses a sha256 digest of the reference as the
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actual cache key in ZK. This reduces and stabilizes the length of
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the cache keys themselves. Methods outside of the change_cache
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should not use this directly.
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"""
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def __init__(self, connection_name, project_name,
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change_type, stable_id, revision):
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self.connection_name = str_or_none(connection_name)
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self.project_name = str_or_none(project_name)
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self.change_type = str_or_none(change_type)
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self.stable_id = str_or_none(stable_id)
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self.revision = str_or_none(revision)
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reference = dict(
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connection_name=connection_name,
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project_name=project_name,
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change_type=change_type,
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stable_id=stable_id,
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revision=revision,
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)
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self.reference = json.dumps(reference, sort_keys=True)
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msg = self.reference.encode('utf8')
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self._hash = hashlib.sha256(msg).hexdigest()
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def __hash__(self):
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return hash(self.reference)
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def __eq__(self, other):
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return (isinstance(other, ChangeKey) and
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self.reference == other.reference)
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def __repr__(self):
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return (f'<ChangeKey {self.connection_name} {self.project_name} '
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f'{self.change_type} {self.stable_id} {self.revision} '
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f'hash={self._hash}>')
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@classmethod
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def fromReference(cls, data):
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data = json.loads(data)
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return cls(data['connection_name'], data['project_name'],
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data['change_type'], data['stable_id'], data['revision'])
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def isSameChange(self, other):
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return all([
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self.connection_name == str_or_none(other.connection_name),
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self.project_name == str_or_none(other.project_name),
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self.change_type == str_or_none(other.change_type),
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self.stable_id == str_or_none(other.stable_id),
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])
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# Convenience methods for drivers that encode old/newrev in
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# revision. Revision is not guaranteed to use this format.
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@property
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def oldrev(self):
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if '..' in self.revision:
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old = self.revision.split('..')[0]
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if old == 'None':
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return None
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return old
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return None
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@property
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def newrev(self):
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if '..' in self.revision:
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new = self.revision.split('..')[1]
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if new == 'None':
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return None
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return new
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return self.revision
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class AbstractChangeCache(ZooKeeperSimpleBase, Iterable, abc.ABC):
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"""Abstract class for caching change items in Zookeeper.
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In order to make updates atomic the change data is stored separate
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from the cache entry. The data uses a random UUID znode that is
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then referenced from the actual cache entry.
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The change data is immutable, which means that an update of a cached
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item will result in a new data node. The cache entry will then be
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changed to reference the new data.
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This approach also allows us to check if a given change is
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up-to-date by comparing the referenced UUID in Zookeeper with the
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one in the local cache without loading the whole change data.
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The change data is stored in the following Zookeeper path:
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/zuul/cache/connection/<connection-name>/data/<uuid>
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The cache entries that reference the change data use the following
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path:
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/zuul/cache/connection/<connection-name>/cache/<key>
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Data nodes will not be directly removed when an entry is removed
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or updated in order to prevent race conditions with multiple
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consumers of the cache. The stale data nodes will be instead
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cleaned up in the cache's cleanup() method. This is expected to
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happen periodically.
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"""
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def __init__(self, client, connection):
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self.log = logging.getLogger(
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f"zuul.ChangeCache.{connection.connection_name}")
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super().__init__(client)
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self._stopped = False
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self.connection = connection
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self.root_path = f"{CHANGE_CACHE_ROOT}/{connection.connection_name}"
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self.cache_root = f"{self.root_path}/cache"
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self.data_root = f"{self.root_path}/data"
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self.kazoo_client.ensure_path(self.data_root)
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self.kazoo_client.ensure_path(self.cache_root)
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self._change_cache = {}
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# Per change locks to serialize concurrent creation and update of
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# local objects.
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self._change_locks = defaultdict(threading.Lock)
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self._watched_keys = set()
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# Data UUIDs that are candidates to be removed on the next
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# cleanup iteration.
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self._data_cleanup_candidates = set()
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self.kazoo_client.ChildrenWatch(self.cache_root, self._cacheWatcher)
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def stop(self):
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self._stopped = True
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def _dataPath(self, data_uuid):
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return f"{self.data_root}/{data_uuid}"
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def _cachePath(self, key_hash):
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return f"{self.cache_root}/{key_hash}"
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def _cacheWatcher(self, cache_keys):
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# This method deals with key hashes exclusively
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cache_keys = set(cache_keys)
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deleted_watches = self._watched_keys - cache_keys
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for key in deleted_watches:
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self.log.debug("Watcher removing %s from cache", key)
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self._watched_keys.discard(key)
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with contextlib.suppress(KeyError):
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del self._change_cache[key]
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with contextlib.suppress(KeyError):
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del self._change_locks[key]
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new_keys = cache_keys - self._watched_keys
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for key in new_keys:
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if self._stopped:
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return
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ExistingDataWatch(self.kazoo_client,
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f"{self.cache_root}/{key}",
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self._cacheItemWatcher)
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self._watched_keys.add(key)
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def _cacheItemWatcher(self, data, zstat, event=None):
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if not all((data, zstat)):
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return
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key, data_uuid = self._loadKey(data)
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self.log.debug("Noticed update to key %s data uuid %s",
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key, data_uuid)
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if self._stopped:
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return
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self._get(key, data_uuid, zstat)
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def _loadKey(self, data):
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data = json.loads(data.decode("utf8"))
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key = ChangeKey.fromReference(data['key_reference'])
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return key, data['data_uuid']
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def estimateDataSize(self):
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"""Return the data size of the changes in the cache.
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:returns: (compressed_size, uncompressed_size)
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"""
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compressed_size = 0
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uncompressed_size = 0
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for c in list(self._change_cache.values()):
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compressed_size += c.cache_stat.compressed_size
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uncompressed_size += c.cache_stat.uncompressed_size
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return (compressed_size, uncompressed_size)
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def prune(self, relevant, max_age=3600): # 1h
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# Relevant is the list of changes directly in a pipeline.
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# This method will take care of expanding that out to each
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# change's network of related changes.
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self.log.debug("Pruning cache")
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cutoff_time = time.time() - max_age
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outdated_versions = dict()
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to_keep = set(relevant)
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sched = self.connection.sched
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for c in list(self._change_cache.values()):
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# Assign to a local variable so all 3 values we use are
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# consistent in case the cache_stat is updated during this
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# loop.
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cache_stat = c.cache_stat
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if cache_stat.last_modified >= cutoff_time:
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# This entry isn't old enough to delete yet
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to_keep.add(cache_stat.key)
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continue
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# Save the version we examined so we can make sure to only
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# delete that version.
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outdated_versions[cache_stat.key] = cache_stat.version
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# Changes we want to keep may have localized networks; keep
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# them together even if one member hasn't been updated in a
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# while. Only when the entire network hasn't been modified in
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# max_age will any change in it be removed.
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for key in to_keep.copy():
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source = sched.connections.getSource(key.connection_name)
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change = source.getChange(key)
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change.getRelatedChanges(sched, to_keep)
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to_prune = set(outdated_versions.keys()) - to_keep
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for key in to_prune:
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self.delete(key, outdated_versions[key])
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self.log.debug("Done pruning cache")
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def cleanup(self):
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self.log.debug("Cleaning cache")
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valid_uuids = {c.cache_stat.uuid
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for c in list(self._change_cache.values())}
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stale_uuids = self._data_cleanup_candidates - valid_uuids
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for data_uuid in stale_uuids:
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self.log.debug("Deleting stale data uuid %s", data_uuid)
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self.kazoo_client.delete(self._dataPath(data_uuid), recursive=True)
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data_uuids = set(self.kazoo_client.get_children(self.data_root))
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self._data_cleanup_candidates = data_uuids - valid_uuids
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self.log.debug("Done cleaning cache")
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def __iter__(self):
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try:
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children = self.kazoo_client.get_children(self.cache_root)
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except NoNodeError:
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return
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for key_hash in children:
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change = self._get_from_key_hash(key_hash)
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if change is not None:
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yield change
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def get(self, key):
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cache_path = self._cachePath(key._hash)
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try:
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value, zstat = self.kazoo_client.get(cache_path)
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except NoNodeError:
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return None
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_, data_uuid = self._loadKey(value)
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return self._get(key, data_uuid, zstat)
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def _get_from_key_hash(self, key_hash):
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cache_path = self._cachePath(key_hash)
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try:
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value, zstat = self.kazoo_client.get(cache_path)
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except NoNodeError:
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return None
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key, data_uuid = self._loadKey(value)
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return self._get(key, data_uuid, zstat)
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def _get(self, key, data_uuid, zstat):
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change = self._change_cache.get(key._hash)
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if change and change.cache_stat.uuid == data_uuid:
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# Change in our local cache is up-to-date
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return change
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compressed_size = 0
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uncompressed_size = 0
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try:
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with sharding.BufferedShardReader(
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self.kazoo_client, self._dataPath(data_uuid)
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) as stream:
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raw_data = zlib.decompress(stream.read())
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compressed_size = stream.bytes_read
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uncompressed_size = len(raw_data)
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except NoNodeError:
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cache_path = self._cachePath(key._hash)
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self.log.error("Removing cache key %s with no data node uuid %s",
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key, data_uuid)
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# TODO: handle no node + version mismatch
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self.kazoo_client.delete(cache_path, zstat.version)
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return None
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try:
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data = json.loads(raw_data)
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except json.JSONDecodeError:
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cache_path = self._cachePath(key._hash)
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self.log.error("Removing cache key %s with corrupt data node "
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"uuid %s data %s len %s",
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key, data_uuid, repr(raw_data), len(raw_data))
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# TODO: handle no node + version mismatch
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self.kazoo_client.delete(cache_path, zstat.version)
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return None
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with self._change_locks[key._hash]:
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if change:
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# While holding the lock check if we still need to update
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# the change and skip the update if we have the latest version.
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if change.cache_stat.mzxid >= zstat.mzxid:
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return change
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self._updateChange(change, data)
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else:
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change = self._changeFromData(data)
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change.cache_stat = model.CacheStat(
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key, data_uuid, zstat.version,
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zstat.last_modified_transaction_id, zstat.last_modified,
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compressed_size, uncompressed_size)
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# Use setdefault here so we only have a single instance of a change
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# around. In case of a concurrent get this might return a different
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# change instance than the one we just created.
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return self._change_cache.setdefault(key._hash, change)
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def set(self, key, change, version=-1):
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data = self._dataFromChange(change)
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raw_data = json.dumps(data, sort_keys=True).encode("utf8")
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compressed_size = 0
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uncompressed_size = 0
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data_uuid = uuid.uuid4().hex
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with sharding.BufferedShardWriter(
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self.kazoo_client, self._dataPath(data_uuid)) as stream:
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stream.write(zlib.compress(raw_data))
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stream.flush()
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compressed_size = stream.bytes_written
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uncompressed_size = len(raw_data)
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# Add the change_key info here mostly for debugging since the
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# hash is non-reversible.
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cache_data = json.dumps(dict(
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data_uuid=data_uuid,
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key_reference=key.reference,
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), sort_keys=True)
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cache_path = self._cachePath(key._hash)
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with self._change_locks[key._hash]:
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try:
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if version == -1:
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self.log.debug(
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"Create cache key %s with data uuid %s len %s",
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key, data_uuid, len(raw_data))
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_, zstat = self.kazoo_client.create(
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cache_path,
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cache_data.encode("utf8"),
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include_data=True)
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else:
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# Sanity check that we only have a single change instance
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# for a key.
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if self._change_cache[key._hash] is not change:
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raise RuntimeError(
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"Conflicting change objects (existing "
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f"{self._change_cache[key._hash]} vs. "
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f"new {change} "
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f"for key '{key.reference}'")
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self.log.debug(
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"Update cache key %s with data uuid %s len %s",
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key, data_uuid, len(raw_data))
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zstat = self.kazoo_client.set(
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cache_path, cache_data.encode("utf8"), version)
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except (BadVersionError, NodeExistsError, NoNodeError) as exc:
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raise ConcurrentUpdateError from exc
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change.cache_stat = model.CacheStat(
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key, data_uuid, zstat.version,
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zstat.last_modified_transaction_id, zstat.last_modified,
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compressed_size, uncompressed_size)
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self._change_cache[key._hash] = change
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def updateChangeWithRetry(self, key, change, update_func, retry_count=5,
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allow_key_update=False):
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for attempt in range(1, retry_count + 1):
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try:
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version = change.cache_version
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newkey = update_func(change)
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if allow_key_update and newkey:
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key = newkey
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self.set(key, change, version)
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break
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except ConcurrentUpdateError:
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self.log.info(
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"Conflicting cache update of %s (attempt: %s/%s)",
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change, attempt, retry_count)
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if attempt == retry_count:
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raise
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# Update the cache and get the change as it might have
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# changed due to a concurrent create.
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change = self.get(key)
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return change
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def delete(self, key, version=-1):
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self.log.debug("Deleting %s from cache", key)
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cache_path = self._cachePath(key._hash)
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# Only delete the cache entry and NOT the data node in order to
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# prevent race conditions with other consumers. The stale data
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# nodes will be removed by the periodic cleanup.
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try:
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self.kazoo_client.delete(cache_path, version)
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except BadVersionError:
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# Someone else may have written a new entry since we
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# decided to delete this, so we should no longer delete
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# the entry.
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return
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except NoNodeError:
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pass
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with contextlib.suppress(KeyError):
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del self._change_cache[key._hash]
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def _changeFromData(self, data):
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change_type, change_data = data["change_type"], data["change_data"]
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change_class = self._getChangeClass(change_type)
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project = self.connection.source.getProject(change_data["project"])
|
|
change = change_class(project)
|
|
change.deserialize(change_data)
|
|
return change
|
|
|
|
def _dataFromChange(self, change):
|
|
return {
|
|
"change_type": self._getChangeType(change),
|
|
"change_data": change.serialize(),
|
|
}
|
|
|
|
def _updateChange(self, change, data):
|
|
change.deserialize(data["change_data"])
|
|
|
|
def _getChangeClass(self, change_type):
|
|
"""Return the change class for the given type."""
|
|
return self.CHANGE_TYPE_MAP[change_type]
|
|
|
|
def _getChangeType(self, change):
|
|
"""Return the change type as a string for the given type."""
|
|
return type(change).__name__
|
|
|
|
@abc.abstractproperty
|
|
def CHANGE_TYPE_MAP(self):
|
|
"""Return a mapping of change type as string to change class.
|
|
|
|
This property cann also be defined as a class attribute.
|
|
"""
|
|
pass
|