Add cancellation support to ReadWriteLock

changelog.d/12120.misc

@@ -0,0 +1 @@
+Add support for cancellation to `ReadWriteLock`.

synapse/handlers/pagination.py

@@ -350,7 +350,7 @@ async def _purge_history(
  """
  self._purges_in_progress_by_room.add(room_id)
  try:
- with await self.pagination_lock.write(room_id):
+ async with self.pagination_lock.write(room_id):
  await self.storage.purge_events.purge_history(
  room_id, token, delete_local_events
  )
@@ -406,7 +406,7 @@ async def purge_room(self, room_id: str, force: bool = False) -> None:
  room_id: room to be purged
  force: set true to skip checking for joined users.
  """
- with await self.pagination_lock.write(room_id):
+ async with self.pagination_lock.write(room_id):
  # first check that we have no users in this room
  if not force:
  joined = await self.store.is_host_joined(room_id, self._server_name)
@@ -448,7 +448,7 @@ async def get_messages(
 
  room_token = from_token.room_key
 
- with await self.pagination_lock.read(room_id):
+ async with self.pagination_lock.read(room_id):
  (
  membership,
  member_event_id,
@@ -615,7 +615,7 @@ async def _shutdown_and_purge_room(
 
  self._purges_in_progress_by_room.add(room_id)
  try:
- with await self.pagination_lock.write(room_id):
+ async with self.pagination_lock.write(room_id):
  self._delete_by_id[delete_id].status = DeleteStatus.STATUS_SHUTTING_DOWN
  self._delete_by_id[
  delete_id

synapse/util/async_helpers.py

@@ -18,9 +18,10 @@
 import inspect
 import itertools
 import logging
-from contextlib import contextmanager
+from contextlib import asynccontextmanager, contextmanager
 from typing import (
  Any,
+ AsyncIterator,
  Awaitable,
  Callable,
  Collection,
@@ -40,7 +41,7 @@
 )
 
 import attr
-from typing_extensions import ContextManager, Literal
+from typing_extensions import AsyncContextManager, Literal
 
 from twisted.internet import defer
 from twisted.internet.defer import CancelledError
@@ -491,7 +492,7 @@ class ReadWriteLock:
 
  Example:
 
- with await read_write_lock.read("test_key"):
+ async with read_write_lock.read("test_key"):
  # do some work
  """
 
@@ -514,22 +515,24 @@ def __init__(self) -> None:
  # Latest writer queued
  self.key_to_current_writer: Dict[str, defer.Deferred] = {}
 
- async def read(self, key: str) -> ContextManager:
- new_defer: "defer.Deferred[None]" = defer.Deferred()
+ def read(self, key: str) -> AsyncContextManager:
+ @asynccontextmanager
+ async def _ctx_manager() -> AsyncIterator[None]:
+ new_defer: "defer.Deferred[None]" = defer.Deferred()
 
- curr_readers = self.key_to_current_readers.setdefault(key, set())
- curr_writer = self.key_to_current_writer.get(key, None)
+  curr_readers = self.key_to_current_readers.setdefault(key, set())
+  curr_writer = self.key_to_current_writer.get(key, None)
 
- curr_readers.add(new_defer)
+  curr_readers.add(new_defer)
 
- # We wait for the latest writer to finish writing. We can safely ignore
- # any existing readers... as they're readers.
- if curr_writer:
- await make_deferred_yieldable(curr_writer)
-
- @contextmanager
- def _ctx_manager() -> Iterator[None]:
  try:
+ # We wait for the latest writer to finish writing. We can safely ignore
+ # any existing readers... as they're readers.
+ # May raise a `CancelledError` if the `Deferred` wrapping us is
+ # cancelled. The `Deferred` we are waiting on must not be cancelled,
+ # since we do not own it.
+ if curr_writer:
+ await make_deferred_yieldable(stop_cancellation(curr_writer))
  yield
  finally:
  with PreserveLoggingContext():
@@ -538,29 +541,35 @@ def _ctx_manager() -> Iterator[None]:
 
  return _ctx_manager()
 
- async def write(self, key: str) -> ContextManager:
- new_defer: "defer.Deferred[None]" = defer.Deferred()
+ def write(self, key: str) -> AsyncContextManager:
+ @asynccontextmanager
+ async def _ctx_manager() -> AsyncIterator[None]:
+ new_defer: "defer.Deferred[None]" = defer.Deferred()
 
- curr_readers = self.key_to_current_readers.get(key, set())
- curr_writer = self.key_to_current_writer.get(key, None)
+  curr_readers = self.key_to_current_readers.get(key, set())
+  curr_writer = self.key_to_current_writer.get(key, None)
 
- # We wait on all latest readers and writer.
- to_wait_on = list(curr_readers)
- if curr_writer:
- to_wait_on.append(curr_writer)
+  # We wait on all latest readers and writer.
+  to_wait_on = list(curr_readers)
+  if curr_writer:
+  to_wait_on.append(curr_writer)
 
- # We can clear the list of current readers since the new writer waits
- # for them to finish.
- curr_readers.clear()
- self.key_to_current_writer[key] = new_defer
+  # We can clear the list of current readers since `new_defer` waits
+  # for them to finish.
+  curr_readers.clear()
+  self.key_to_current_writer[key] = new_defer
 
- await make_deferred_yieldable(defer.gatherResults(to_wait_on))
-
- @contextmanager
- def _ctx_manager() -> Iterator[None]:
+ to_wait_on_defer = defer.gatherResults(to_wait_on)
  try:
+ # Wait for all current readers and the latest writer to finish.
+ # May raise a `CancelledError` immediately after the wait if the
+ # `Deferred` wrapping us is cancelled. We must only release the lock
+ # once we have acquired it, hence the use of `delay_cancellation`
+ # rather than `stop_cancellation`.
+ await make_deferred_yieldable(delay_cancellation(to_wait_on_defer))
  yield
  finally:
+ # Release the lock.
  with PreserveLoggingContext():
  new_defer.callback(None)
  # `self.key_to_current_writer[key]` may be missing if there was another