diff options
| -rw-r--r-- | changelog.d/12832.bugfix | 1 | ||||
| -rw-r--r-- | synapse/storage/databases/main/lock.py | 19 | ||||
| -rw-r--r-- | tests/storage/databases/main/test_lock.py | 54 |
3 files changed, 73 insertions, 1 deletions
diff --git a/changelog.d/12832.bugfix b/changelog.d/12832.bugfix new file mode 100644 index 0000000000..497d5184ea --- /dev/null +++ b/changelog.d/12832.bugfix @@ -0,0 +1 @@ +Fixed a bug which allowed multiple async operations to access database locks concurrently. Contributed by @sumnerevans @ Beeper. diff --git a/synapse/storage/databases/main/lock.py b/synapse/storage/databases/main/lock.py index bedacaf0d7..2d7633fbd5 100644 --- a/synapse/storage/databases/main/lock.py +++ b/synapse/storage/databases/main/lock.py @@ -13,7 +13,7 @@ # limitations under the License. import logging from types import TracebackType -from typing import TYPE_CHECKING, Optional, Tuple, Type +from typing import TYPE_CHECKING, Optional, Set, Tuple, Type from weakref import WeakValueDictionary from twisted.internet.interfaces import IReactorCore @@ -84,6 +84,8 @@ class LockStore(SQLBaseStore): self._on_shutdown, ) + self._acquiring_locks: Set[Tuple[str, str]] = set() + @wrap_as_background_process("LockStore._on_shutdown") async def _on_shutdown(self) -> None: """Called when the server is shutting down""" @@ -103,6 +105,21 @@ class LockStore(SQLBaseStore): context manager if the lock is successfully acquired, which *must* be used (otherwise the lock will leak). """ + if (lock_name, lock_key) in self._acquiring_locks: + return None + try: + self._acquiring_locks.add((lock_name, lock_key)) + return await self._try_acquire_lock(lock_name, lock_key) + finally: + self._acquiring_locks.discard((lock_name, lock_key)) + + async def _try_acquire_lock( + self, lock_name: str, lock_key: str + ) -> Optional["Lock"]: + """Try to acquire a lock for the given name/key. Will return an async + context manager if the lock is successfully acquired, which *must* be + used (otherwise the lock will leak). + """ # Check if this process has taken out a lock and if it's still valid. lock = self._live_tokens.get((lock_name, lock_key)) diff --git a/tests/storage/databases/main/test_lock.py b/tests/storage/databases/main/test_lock.py index 74c6224eb6..3cc2a58d8d 100644 --- a/tests/storage/databases/main/test_lock.py +++ b/tests/storage/databases/main/test_lock.py @@ -12,6 +12,10 @@ # See the License for the specific language governing permissions and # limitations under the License. +from twisted.internet import defer, reactor +from twisted.internet.base import ReactorBase +from twisted.internet.defer import Deferred + from synapse.server import HomeServer from synapse.storage.databases.main.lock import _LOCK_TIMEOUT_MS @@ -22,6 +26,56 @@ class LockTestCase(unittest.HomeserverTestCase): def prepare(self, reactor, clock, hs: HomeServer): self.store = hs.get_datastores().main + def test_acquire_contention(self): + # Track the number of tasks holding the lock. + # Should be at most 1. + in_lock = 0 + max_in_lock = 0 + + release_lock: "Deferred[None]" = Deferred() + + async def task(): + nonlocal in_lock + nonlocal max_in_lock + + lock = await self.store.try_acquire_lock("name", "key") + if not lock: + return + + async with lock: + in_lock += 1 + max_in_lock = max(max_in_lock, in_lock) + + # Block to allow other tasks to attempt to take the lock. + await release_lock + + in_lock -= 1 + + # Start 3 tasks. + task1 = defer.ensureDeferred(task()) + task2 = defer.ensureDeferred(task()) + task3 = defer.ensureDeferred(task()) + + # Give the reactor a kick so that the database transaction returns. + self.pump() + + release_lock.callback(None) + + # Run the tasks to completion. + # To work around `Linearizer`s using a different reactor to sleep when + # contended (#12841), we call `runUntilCurrent` on + # `twisted.internet.reactor`, which is a different reactor to that used + # by the homeserver. + assert isinstance(reactor, ReactorBase) + self.get_success(task1) + reactor.runUntilCurrent() + self.get_success(task2) + reactor.runUntilCurrent() + self.get_success(task3) + + # At most one task should have held the lock at a time. + self.assertEqual(max_in_lock, 1) + def test_simple_lock(self): """Test that we can take out a lock and that while we hold it nobody else can take it out. |