MatrixSynapse/synapse/handlers/worker_lock.py

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# Copyright 2023 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import random
from types import TracebackType
from typing import (
TYPE_CHECKING,
AsyncContextManager,
Collection,
Dict,
Optional,
Tuple,
Type,
Union,
)
from weakref import WeakSet
import attr
from twisted.internet import defer
from twisted.internet.interfaces import IReactorTime
from synapse.logging.context import PreserveLoggingContext
from synapse.logging.opentracing import start_active_span
from synapse.metrics.background_process_metrics import wrap_as_background_process
from synapse.storage.databases.main.lock import Lock, LockStore
from synapse.util.async_helpers import timeout_deferred
if TYPE_CHECKING:
from synapse.logging.opentracing import opentracing
from synapse.server import HomeServer
# This lock is used to avoid creating an event while we are purging the room.
# We take a read lock when creating an event, and a write one when purging a room.
# This is because it is fine to create several events concurrently, since referenced events
# will not disappear under our feet as long as we don't delete the room.
NEW_EVENT_DURING_PURGE_LOCK_NAME = "new_event_during_purge_lock"
class WorkerLocksHandler:
"""A class for waiting on taking out locks, rather than using the storage
functions directly (which don't support awaiting).
"""
def __init__(self, hs: "HomeServer") -> None:
self._reactor = hs.get_reactor()
self._store = hs.get_datastores().main
self._clock = hs.get_clock()
self._notifier = hs.get_notifier()
self._instance_name = hs.get_instance_name()
# Map from lock name/key to set of `WaitingLock` that are active for
# that lock.
self._locks: Dict[
Tuple[str, str], WeakSet[Union[WaitingLock, WaitingMultiLock]]
] = {}
self._clock.looping_call(self._cleanup_locks, 30_000)
self._notifier.add_lock_released_callback(self._on_lock_released)
def acquire_lock(self, lock_name: str, lock_key: str) -> "WaitingLock":
"""Acquire a standard lock, returns a context manager that will block
until the lock is acquired.
Note: Care must be taken to avoid deadlocks. In particular, this
function does *not* timeout.
Usage:
async with handler.acquire_lock(name, key):
# Do work while holding the lock...
"""
lock = WaitingLock(
reactor=self._reactor,
store=self._store,
handler=self,
lock_name=lock_name,
lock_key=lock_key,
write=None,
)
self._locks.setdefault((lock_name, lock_key), WeakSet()).add(lock)
return lock
def acquire_read_write_lock(
self,
lock_name: str,
lock_key: str,
*,
write: bool,
) -> "WaitingLock":
"""Acquire a read/write lock, returns a context manager that will block
until the lock is acquired.
Note: Care must be taken to avoid deadlocks. In particular, this
function does *not* timeout.
Usage:
async with handler.acquire_read_write_lock(name, key, write=True):
# Do work while holding the lock...
"""
lock = WaitingLock(
reactor=self._reactor,
store=self._store,
handler=self,
lock_name=lock_name,
lock_key=lock_key,
write=write,
)
self._locks.setdefault((lock_name, lock_key), WeakSet()).add(lock)
return lock
def acquire_multi_read_write_lock(
self,
lock_names: Collection[Tuple[str, str]],
*,
write: bool,
) -> "WaitingMultiLock":
"""Acquires multi read/write locks at once, returns a context manager
that will block until all the locks are acquired.
This will try and acquire all locks at once, and will never hold on to a
subset of the locks. (This avoids accidentally creating deadlocks).
Note: Care must be taken to avoid deadlocks. In particular, this
function does *not* timeout.
"""
lock = WaitingMultiLock(
lock_names=lock_names,
write=write,
reactor=self._reactor,
store=self._store,
handler=self,
)
for lock_name, lock_key in lock_names:
self._locks.setdefault((lock_name, lock_key), WeakSet()).add(lock)
return lock
def notify_lock_released(self, lock_name: str, lock_key: str) -> None:
"""Notify that a lock has been released.
Pokes both the notifier and replication.
"""
self._notifier.notify_lock_released(self._instance_name, lock_name, lock_key)
def _on_lock_released(
self, instance_name: str, lock_name: str, lock_key: str
) -> None:
"""Called when a lock has been released.
Wakes up any locks that might be waiting on this.
"""
locks = self._locks.get((lock_name, lock_key))
if not locks:
return
def _wake_deferred(deferred: defer.Deferred) -> None:
if not deferred.called:
deferred.callback(None)
for lock in locks:
self._clock.call_later(0, _wake_deferred, lock.deferred)
@wrap_as_background_process("_cleanup_locks")
async def _cleanup_locks(self) -> None:
"""Periodically cleans out stale entries in the locks map"""
self._locks = {key: value for key, value in self._locks.items() if value}
@attr.s(auto_attribs=True, eq=False)
class WaitingLock:
reactor: IReactorTime
store: LockStore
handler: WorkerLocksHandler
lock_name: str
lock_key: str
write: Optional[bool]
deferred: "defer.Deferred[None]" = attr.Factory(defer.Deferred)
_inner_lock: Optional[Lock] = None
_retry_interval: float = 0.1
_lock_span: "opentracing.Scope" = attr.Factory(
lambda: start_active_span("WaitingLock.lock")
)
async def __aenter__(self) -> None:
self._lock_span.__enter__()
with start_active_span("WaitingLock.waiting_for_lock"):
while self._inner_lock is None:
self.deferred = defer.Deferred()
if self.write is not None:
lock = await self.store.try_acquire_read_write_lock(
self.lock_name, self.lock_key, write=self.write
)
else:
lock = await self.store.try_acquire_lock(
self.lock_name, self.lock_key
)
if lock:
self._inner_lock = lock
break
try:
# Wait until the we get notified the lock might have been
# released (by the deferred being resolved). We also
# periodically wake up in case the lock was released but we
# weren't notified.
with PreserveLoggingContext():
await timeout_deferred(
deferred=self.deferred,
timeout=self._get_next_retry_interval(),
reactor=self.reactor,
)
except Exception:
pass
return await self._inner_lock.__aenter__()
async def __aexit__(
self,
exc_type: Optional[Type[BaseException]],
exc: Optional[BaseException],
tb: Optional[TracebackType],
) -> Optional[bool]:
assert self._inner_lock
self.handler.notify_lock_released(self.lock_name, self.lock_key)
try:
r = await self._inner_lock.__aexit__(exc_type, exc, tb)
finally:
self._lock_span.__exit__(exc_type, exc, tb)
return r
def _get_next_retry_interval(self) -> float:
next = self._retry_interval
self._retry_interval = max(5, next * 2)
return next * random.uniform(0.9, 1.1)
@attr.s(auto_attribs=True, eq=False)
class WaitingMultiLock:
lock_names: Collection[Tuple[str, str]]
write: bool
reactor: IReactorTime
store: LockStore
handler: WorkerLocksHandler
deferred: "defer.Deferred[None]" = attr.Factory(defer.Deferred)
_inner_lock_cm: Optional[AsyncContextManager] = None
_retry_interval: float = 0.1
_lock_span: "opentracing.Scope" = attr.Factory(
lambda: start_active_span("WaitingLock.lock")
)
async def __aenter__(self) -> None:
self._lock_span.__enter__()
with start_active_span("WaitingLock.waiting_for_lock"):
while self._inner_lock_cm is None:
self.deferred = defer.Deferred()
lock_cm = await self.store.try_acquire_multi_read_write_lock(
self.lock_names, write=self.write
)
if lock_cm:
self._inner_lock_cm = lock_cm
break
try:
# Wait until the we get notified the lock might have been
# released (by the deferred being resolved). We also
# periodically wake up in case the lock was released but we
# weren't notified.
with PreserveLoggingContext():
await timeout_deferred(
deferred=self.deferred,
timeout=self._get_next_retry_interval(),
reactor=self.reactor,
)
except Exception:
pass
assert self._inner_lock_cm
await self._inner_lock_cm.__aenter__()
return
async def __aexit__(
self,
exc_type: Optional[Type[BaseException]],
exc: Optional[BaseException],
tb: Optional[TracebackType],
) -> Optional[bool]:
assert self._inner_lock_cm
for lock_name, lock_key in self.lock_names:
self.handler.notify_lock_released(lock_name, lock_key)
try:
r = await self._inner_lock_cm.__aexit__(exc_type, exc, tb)
finally:
self._lock_span.__exit__(exc_type, exc, tb)
return r
def _get_next_retry_interval(self) -> float:
next = self._retry_interval
self._retry_interval = max(5, next * 2)
return next * random.uniform(0.9, 1.1)