rei-mirrors/synapse
1
0
Fork 0
mirror of https://github.com/matrix-org/synapse.git synced 2025-10-31 12:18:24 +00:00
Code Issues Packages Projects Releases Wiki Activity

Add basic read/write lock (#15782)

Browse Source
This commit is contained in:
Erik Johnston 2023-07-05 17:25:00 +01:00 committed by GitHub
parent ce857c05d5
commit 39d131b016
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
6 changed files with 731 additions and 59 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
changelog.d/15782.misc Normal file
View File

@ -0,0 +1 @@
Add read/write style cross-worker locks.

9
synapse/_scripts/synapse_port_db.py
View File

@ -197,6 +197,11 @@ IGNORED_TABLES = {
"ui_auth_sessions",
"ui_auth_sessions_credentials",
"ui_auth_sessions_ips",
# Ignore the worker locks table, as a) there shouldn't be any acquired locks
# after porting, and b) the circular foreign key constraints make it hard to
# port.
"worker_read_write_locks_mode",
"worker_read_write_locks",
}
@ -805,7 +810,9 @@ class Porter:
)
# Map from table name to args passed to `handle_table`, i.e. a tuple
# of: `postgres_size`, `table_size`, `forward_chunk`, `backward_chunk`.
tables_to_port_info_map = {r[0]: r[1:] for r in setup_res}
tables_to_port_info_map = {
r[0]: r[1:] for r in setup_res if r[0] not in IGNORED_TABLES
}
# Step 5. Do the copying.
#

226
synapse/storage/databases/main/lock.py
View File

@ -25,6 +25,7 @@ from synapse.storage.database import (
LoggingDatabaseConnection,
LoggingTransaction,
)
from synapse.storage.engines import PostgresEngine
from synapse.util import Clock
from synapse.util.stringutils import random_string
@ -68,12 +69,20 @@ class LockStore(SQLBaseStore):
self._reactor = hs.get_reactor()
self._instance_name = hs.get_instance_id()
# A map from `(lock_name, lock_key)` to the token of any locks that we
# think we currently hold.
self._live_tokens: WeakValueDictionary[
# A map from `(lock_name, lock_key)` to lock that we think we
# currently hold.
self._live_lock_tokens: WeakValueDictionary[
Tuple[str, str], Lock
] = WeakValueDictionary()
# A map from `(lock_name, lock_key, token)` to read/write lock that we
# think we currently hold. For a given lock_name/lock_key, there can be
# multiple read locks at a time but only one write lock (no mixing read
# and write locks at the same time).
self._live_read_write_lock_tokens: WeakValueDictionary[
Tuple[str, str, str], Lock
] = WeakValueDictionary()
# When we shut down we want to remove the locks. Technically this can
# lead to a race, as we may drop the lock while we are still processing.
# However, a) it should be a small window, b) the lock is best effort
@ -91,11 +100,13 @@ class LockStore(SQLBaseStore):
"""Called when the server is shutting down"""
logger.info("Dropping held locks due to shutdown")
# We need to take a copy of the tokens dict as dropping the locks will
# cause the dictionary to change.
locks = dict(self._live_tokens)
# We need to take a copy of the locks as dropping the locks will cause
# the dictionary to change.
locks = list(self._live_lock_tokens.values()) + list(
self._live_read_write_lock_tokens.values()
)
for lock in locks.values():
for lock in locks:
await lock.release()
logger.info("Dropped locks due to shutdown")
@ -122,7 +133,7 @@ class LockStore(SQLBaseStore):
"""
# Check if this process has taken out a lock and if it's still valid.
lock = self._live_tokens.get((lock_name, lock_key))
lock = self._live_lock_tokens.get((lock_name, lock_key))
if lock and await lock.is_still_valid():
return None
@ -176,61 +187,111 @@ class LockStore(SQLBaseStore):
self._reactor,
self._clock,
self,
read_write=False,
lock_name=lock_name,
lock_key=lock_key,
token=token,
)
self._live_tokens[(lock_name, lock_key)] = lock
self._live_lock_tokens[(lock_name, lock_key)] = lock
return lock
async def _is_lock_still_valid(
self, lock_name: str, lock_key: str, token: str
) -> bool:
"""Checks whether this instance still holds the lock."""
last_renewed_ts = await self.db_pool.simple_select_one_onecol(
table="worker_locks",
keyvalues={
"lock_name": lock_name,
"lock_key": lock_key,
"token": token,
},
retcol="last_renewed_ts",
allow_none=True,
desc="is_lock_still_valid",
)
return (
last_renewed_ts is not None
and self._clock.time_msec() - _LOCK_TIMEOUT_MS < last_renewed_ts
async def try_acquire_read_write_lock(
self,
lock_name: str,
lock_key: str,
write: bool,
) -> 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).
"""
now = self._clock.time_msec()
token = random_string(6)
def _try_acquire_read_write_lock_txn(txn: LoggingTransaction) -> None:
# We attempt to acquire the lock by inserting into
# `worker_read_write_locks` and seeing if that fails any
# constraints. If it doesn't then we have acquired the lock,
# otherwise we haven't.
#
# Before that though we clear the table of any stale locks.
delete_sql = """
DELETE FROM worker_read_write_locks
WHERE last_renewed_ts < ? AND lock_name = ? AND lock_key = ?;
"""
insert_sql = """
INSERT INTO worker_read_write_locks (lock_name, lock_key, write_lock, instance_name, token, last_renewed_ts)
VALUES (?, ?, ?, ?, ?, ?)
"""
if isinstance(self.database_engine, PostgresEngine):
# For Postgres we can send these queries at the same time.
txn.execute(
delete_sql + ";" + insert_sql,
(
# DELETE args
now - _LOCK_TIMEOUT_MS,
lock_name,
lock_key,
# UPSERT args
lock_name,
lock_key,
write,
self._instance_name,
token,
now,
),
)
else:
# For SQLite these need to be two queries.
txn.execute(
delete_sql,
(
now - _LOCK_TIMEOUT_MS,
lock_name,
lock_key,
),
)
txn.execute(
insert_sql,
(
lock_name,
lock_key,
write,
self._instance_name,
token,
now,
),
)
return
try:
await self.db_pool.runInteraction(
"try_acquire_read_write_lock",
_try_acquire_read_write_lock_txn,
)
except self.database_engine.module.IntegrityError:
return None
lock = Lock(
self._reactor,
self._clock,
self,
read_write=True,
lock_name=lock_name,
lock_key=lock_key,
token=token,
)
async def _renew_lock(self, lock_name: str, lock_key: str, token: str) -> None:
"""Attempt to renew the lock if we still hold it."""
await self.db_pool.simple_update(
table="worker_locks",
keyvalues={
"lock_name": lock_name,
"lock_key": lock_key,
"token": token,
},
updatevalues={"last_renewed_ts": self._clock.time_msec()},
desc="renew_lock",
)
self._live_read_write_lock_tokens[(lock_name, lock_key, token)] = lock
async def _drop_lock(self, lock_name: str, lock_key: str, token: str) -> None:
"""Attempt to drop the lock, if we still hold it"""
await self.db_pool.simple_delete(
table="worker_locks",
keyvalues={
"lock_name": lock_name,
"lock_key": lock_key,
"token": token,
},
desc="drop_lock",
)
self._live_tokens.pop((lock_name, lock_key), None)
return lock
class Lock:
@ -259,6 +320,7 @@ class Lock:
reactor: IReactorCore,
clock: Clock,
store: LockStore,
read_write: bool,
lock_name: str,
lock_key: str,
token: str,
@ -266,13 +328,23 @@ class Lock:
self._reactor = reactor
self._clock = clock
self._store = store
self._read_write = read_write
self._lock_name = lock_name
self._lock_key = lock_key
self._token = token
self._table = "worker_read_write_locks" if read_write else "worker_locks"
self._looping_call = clock.looping_call(
self._renew, _RENEWAL_INTERVAL_MS, store, lock_name, lock_key, token
self._renew,
_RENEWAL_INTERVAL_MS,
store,
clock,
read_write,
lock_name,
lock_key,
token,
)
self._dropped = False
@ -281,6 +353,8 @@ class Lock:
@wrap_as_background_process("Lock._renew")
async def _renew(
store: LockStore,
clock: Clock,
read_write: bool,
lock_name: str,
lock_key: str,
token: str,
@ -291,12 +365,34 @@ class Lock:
don't end up with a reference to `self` in the reactor, which would stop
this from being cleaned up if we dropped the context manager.
"""
await store._renew_lock(lock_name, lock_key, token)
table = "worker_read_write_locks" if read_write else "worker_locks"
await store.db_pool.simple_update(
table=table,
keyvalues={
"lock_name": lock_name,
"lock_key": lock_key,
"token": token,
},
updatevalues={"last_renewed_ts": clock.time_msec()},
desc="renew_lock",
)
async def is_still_valid(self) -> bool:
"""Check if the lock is still held by us"""
return await self._store._is_lock_still_valid(
self._lock_name, self._lock_key, self._token
last_renewed_ts = await self._store.db_pool.simple_select_one_onecol(
table=self._table,
keyvalues={
"lock_name": self._lock_name,
"lock_key": self._lock_key,
"token": self._token,
},
retcol="last_renewed_ts",
allow_none=True,
desc="is_lock_still_valid",
)
return (
last_renewed_ts is not None
and self._clock.time_msec() - _LOCK_TIMEOUT_MS < last_renewed_ts
)
async def __aenter__(self) -> None:
@ -325,7 +421,23 @@ class Lock:
if self._looping_call.running:
self._looping_call.stop()
await self._store._drop_lock(self._lock_name, self._lock_key, self._token)
await self._store.db_pool.simple_delete(
table=self._table,
keyvalues={
"lock_name": self._lock_name,
"lock_key": self._lock_key,
"token": self._token,
},
desc="drop_lock",
)
if self._read_write:
self._store._live_read_write_lock_tokens.pop(
(self._lock_name, self._lock_key, self._token), None
)
else:
self._store._live_lock_tokens.pop((self._lock_name, self._lock_key), None)
self._dropped = True
def __del__(self) -> None:

152
synapse/storage/schema/main/delta/78/04_read_write_locks_triggers.sql.postgres Normal file
View File

@ -0,0 +1,152 @@
/* 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.
*/
-- We implement read/write style locks by using two tables with mutual foreign
-- key constraints. Note that this implementation is vulnerable to starving
-- writers if read locks repeatedly get acquired.
--
-- The first table (`worker_read_write_locks_mode`) indicates that a given lock
-- has either been acquired in read mode *or* write mode, but not both. This is
-- enforced by the unique constraint. Each instance of a lock being acquired is
-- associated with a random `token`.
--
-- The second table (`worker_read_write_locks`) tracks who has currently
-- acquired a given lock. For a given lock_name/lock_key, there can be multiple
-- read locks at a time but only one write lock (no mixing read and write locks
-- at the same time).
--
-- The foreign key from the second to first table enforces that for any given
-- lock the second table cannot have a mix of rows with read or write.
--
-- The foreign key from the first to second table enforces that we don't have a
-- row for a lock in the first table if not in the second table.
--
--
-- Furthermore, we add some triggers to automatically keep the first table up to
-- date when inserting/deleting from the second table. This reduces the number
-- of round trips needed to acquire and release locks, as those operations
-- simply become an INSERT or DELETE. These triggers are added in a separate
-- delta due to database specific syntax.
-- A table to track whether a lock is currently acquired, and if so whether its
-- in read or write mode.
CREATE TABLE worker_read_write_locks_mode (
lock_name TEXT NOT NULL,
lock_key TEXT NOT NULL,
-- Whether this lock is in read (false) or write (true) mode
write_lock BOOLEAN NOT NULL,
-- A token that has currently acquired the lock. We need this so that we can
-- add a foreign constraint from this table to `worker_read_write_locks`.
token TEXT NOT NULL
);
-- Ensure that we can only have one row per lock
CREATE UNIQUE INDEX worker_read_write_locks_mode_key ON worker_read_write_locks_mode (lock_name, lock_key);
-- We need this (redundant) constraint so that we can have a foreign key
-- constraint against this table.
CREATE UNIQUE INDEX worker_read_write_locks_mode_type ON worker_read_write_locks_mode (lock_name, lock_key, write_lock);
-- A table to track who has currently acquired a given lock.
CREATE TABLE worker_read_write_locks (
lock_name TEXT NOT NULL,
lock_key TEXT NOT NULL,
-- We write the instance name to ease manual debugging, we don't ever read
-- from it.
-- Note: instance names aren't guarenteed to be unique.
instance_name TEXT NOT NULL,
-- Whether the process has taken out a "read" or a "write" lock.
write_lock BOOLEAN NOT NULL,
-- A random string generated each time an instance takes out a lock. Used by
-- the instance to tell whether the lock is still held by it (e.g. in the
-- case where the process stalls for a long time the lock may time out and
-- be taken out by another instance, at which point the original instance
-- can tell it no longer holds the lock as the tokens no longer match).
token TEXT NOT NULL,
last_renewed_ts BIGINT NOT NULL,
-- This constraint ensures that a given lock has only been acquired in read
-- xor write mode, but not both.
FOREIGN KEY (lock_name, lock_key, write_lock) REFERENCES worker_read_write_locks_mode (lock_name, lock_key, write_lock)
);
CREATE UNIQUE INDEX worker_read_write_locks_key ON worker_read_write_locks (lock_name, lock_key, token);
-- Ensures that only one instance can acquire a lock in write mode at a time.
CREATE UNIQUE INDEX worker_read_write_locks_write ON worker_read_write_locks (lock_name, lock_key) WHERE write_lock;
-- Add a foreign key constraint to ensure that if a lock is in
-- `worker_read_write_locks_mode` then there must be a corresponding row in
-- `worker_read_write_locks` (i.e. we don't accidentally end up with a row in
-- `worker_read_write_locks_mode` when the lock is not currently acquired).
--
-- We only add to PostgreSQL as SQLite does not support adding constraints
-- after table creation, and so doesn't support "circular" foreign key
-- constraints.
ALTER TABLE worker_read_write_locks_mode ADD CONSTRAINT worker_read_write_locks_mode_foreign
FOREIGN KEY (lock_name, lock_key, token) REFERENCES worker_read_write_locks(lock_name, lock_key, token) DEFERRABLE INITIALLY DEFERRED;
-- Add a trigger to UPSERT into `worker_read_write_locks_mode` whenever we try
-- and acquire a lock, i.e. insert into `worker_read_write_locks`,
CREATE OR REPLACE FUNCTION upsert_read_write_lock_parent() RETURNS trigger AS $$
BEGIN
INSERT INTO worker_read_write_locks_mode (lock_name, lock_key, write_lock, token)
VALUES (NEW.lock_name, NEW.lock_key, NEW.write_lock, NEW.token)
ON CONFLICT (lock_name, lock_key)
DO NOTHING;
RETURN NEW;
END
$$
LANGUAGE plpgsql;
CREATE TRIGGER upsert_read_write_lock_parent_trigger BEFORE INSERT ON worker_read_write_locks
FOR EACH ROW
EXECUTE PROCEDURE upsert_read_write_lock_parent();
-- Ensure that we keep `worker_read_write_locks_mode` up to date whenever a lock
-- is released (i.e. a row deleted from `worker_read_write_locks`). Either we
-- update the `worker_read_write_locks_mode.token` to match another instance
-- that has currently acquired the lock, or we delete the row if nobody has
-- currently acquired a lock.
CREATE OR REPLACE FUNCTION delete_read_write_lock_parent() RETURNS trigger AS $$
DECLARE
new_token TEXT;
BEGIN
SELECT token INTO new_token FROM worker_read_write_locks
WHERE
lock_name = OLD.lock_name
AND lock_key = OLD.lock_key;
IF NOT FOUND THEN
DELETE FROM worker_read_write_locks_mode
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key;
ELSE
UPDATE worker_read_write_locks_mode
SET token = new_token
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key;
END IF;
RETURN NEW;
END
$$
LANGUAGE plpgsql;
CREATE TRIGGER delete_read_write_lock_parent_trigger AFTER DELETE ON worker_read_write_locks
FOR EACH ROW
EXECUTE PROCEDURE delete_read_write_lock_parent();

119
synapse/storage/schema/main/delta/78/04_read_write_locks_triggers.sql.sqlite Normal file
View File

@ -0,0 +1,119 @@
/* 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.
*/
-- c.f. the postgres version for context. The tables and constraints are the
-- same, however they need to be defined slightly differently to work around how
-- each database handles circular foreign key references.
-- A table to track whether a lock is currently acquired, and if so whether its
-- in read or write mode.
CREATE TABLE worker_read_write_locks_mode (
lock_name TEXT NOT NULL,
lock_key TEXT NOT NULL,
-- Whether this lock is in read (false) or write (true) mode
write_lock BOOLEAN NOT NULL,
-- A token that has currently acquired the lock. We need this so that we can
-- add a foreign constraint from this table to `worker_read_write_locks`.
token TEXT NOT NULL,
-- Add a foreign key constraint to ensure that if a lock is in
-- `worker_read_write_locks_mode` then there must be a corresponding row in
-- `worker_read_write_locks` (i.e. we don't accidentally end up with a row in
-- `worker_read_write_locks_mode` when the lock is not currently acquired).
FOREIGN KEY (lock_name, lock_key, token) REFERENCES worker_read_write_locks(lock_name, lock_key, token) DEFERRABLE INITIALLY DEFERRED
);
-- Ensure that we can only have one row per lock
CREATE UNIQUE INDEX worker_read_write_locks_mode_key ON worker_read_write_locks_mode (lock_name, lock_key);
-- We need this (redundant) constraint so that we can have a foreign key
-- constraint against this table.
CREATE UNIQUE INDEX worker_read_write_locks_mode_type ON worker_read_write_locks_mode (lock_name, lock_key, write_lock);
-- A table to track who has currently acquired a given lock.
CREATE TABLE worker_read_write_locks (
lock_name TEXT NOT NULL,
lock_key TEXT NOT NULL,
-- We write the instance name to ease manual debugging, we don't ever read
-- from it.
-- Note: instance names aren't guarenteed to be unique.
instance_name TEXT NOT NULL,
-- Whether the process has taken out a "read" or a "write" lock.
write_lock BOOLEAN NOT NULL,
-- A random string generated each time an instance takes out a lock. Used by
-- the instance to tell whether the lock is still held by it (e.g. in the
-- case where the process stalls for a long time the lock may time out and
-- be taken out by another instance, at which point the original instance
-- can tell it no longer holds the lock as the tokens no longer match).
token TEXT NOT NULL,
last_renewed_ts BIGINT NOT NULL,
-- This constraint ensures that a given lock has only been acquired in read
-- xor write mode, but not both.
FOREIGN KEY (lock_name, lock_key, write_lock) REFERENCES worker_read_write_locks_mode (lock_name, lock_key, write_lock)
);
CREATE UNIQUE INDEX worker_read_write_locks_key ON worker_read_write_locks (lock_name, lock_key, token);
-- Ensures that only one instance can acquire a lock in write mode at a time.
CREATE UNIQUE INDEX worker_read_write_locks_write ON worker_read_write_locks (lock_name, lock_key) WHERE write_lock;
-- Add a trigger to UPSERT into `worker_read_write_locks_mode` whenever we try
-- and acquire a lock, i.e. insert into `worker_read_write_locks`,
CREATE TRIGGER IF NOT EXISTS upsert_read_write_lock_parent_trigger
BEFORE INSERT ON worker_read_write_locks
FOR EACH ROW
BEGIN
-- First ensure that `worker_read_write_locks_mode` doesn't have stale
-- entries in it, as on SQLite we don't have the foreign key constraint to
-- enforce this.
DELETE FROM worker_read_write_locks_mode
WHERE lock_name = NEW.lock_name AND lock_key = NEW.lock_key
AND NOT EXISTS (
SELECT 1 FROM worker_read_write_locks
WHERE lock_name = NEW.lock_name AND lock_key = NEW.lock_key
);
INSERT INTO worker_read_write_locks_mode (lock_name, lock_key, write_lock, token)
VALUES (NEW.lock_name, NEW.lock_key, NEW.write_lock, NEW.token)
ON CONFLICT (lock_name, lock_key)
DO NOTHING;
END;
-- Ensure that we keep `worker_read_write_locks_mode` up to date whenever a lock
-- is released (i.e. a row deleted from `worker_read_write_locks`). Either we
-- update the `worker_read_write_locks_mode.token` to match another instance
-- that has currently acquired the lock, or we delete the row if nobody has
-- currently acquired a lock.
CREATE TRIGGER IF NOT EXISTS delete_read_write_lock_parent_trigger
AFTER DELETE ON worker_read_write_locks
FOR EACH ROW
BEGIN
DELETE FROM worker_read_write_locks_mode
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key
AND NOT EXISTS (
SELECT 1 FROM worker_read_write_locks
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key
);
UPDATE worker_read_write_locks_mode
SET token = (
SELECT token FROM worker_read_write_locks
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key
)
WHERE lock_name = OLD.lock_name AND lock_key = OLD.lock_key;
END;

283
tests/storage/databases/main/test_lock.py
View File

@ -166,4 +166,285 @@ class LockTestCase(unittest.HomeserverTestCase):
# Now call the shutdown code
self.get_success(self.store._on_shutdown())
self.assertEqual(self.store._live_tokens, {})
self.assertEqual(self.store._live_lock_tokens, {})
class ReadWriteLockTestCase(unittest.HomeserverTestCase):
"""Test the read/write lock implementation."""
def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
self.store = hs.get_datastores().main
def test_acquire_write_contention(self) -> None:
"""Test that we can only acquire one write lock at a time"""
# 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() -> None:
nonlocal in_lock
nonlocal max_in_lock
lock = await self.store.try_acquire_read_write_lock(
"name", "key", write=True
)
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_acquire_multiple_reads(self) -> None:
"""Test that we can acquire multiple read locks at a time"""
# Track the number of tasks holding the lock.
in_lock = 0
max_in_lock = 0
release_lock: "Deferred[None]" = Deferred()
async def task() -> None:
nonlocal in_lock
nonlocal max_in_lock
lock = await self.store.try_acquire_read_write_lock(
"name", "key", write=False
)
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, 3)
def test_write_lock_acquired(self) -> None:
"""Test that we can take out a write lock and that while we hold it
nobody else can take it out.
"""
# First to acquire this lock, so it should complete
lock = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
assert lock is not None
# Enter the context manager
self.get_success(lock.__aenter__())
# Attempting to acquire the lock again fails, as both read and write.
lock2 = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
self.assertIsNone(lock2)
lock3 = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=False)
)
self.assertIsNone(lock3)
# Calling `is_still_valid` reports true.
self.assertTrue(self.get_success(lock.is_still_valid()))
# Drop the lock
self.get_success(lock.__aexit__(None, None, None))
# We can now acquire the lock again.
lock4 = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
assert lock4 is not None
self.get_success(lock4.__aenter__())
self.get_success(lock4.__aexit__(None, None, None))
def test_read_lock_acquired(self) -> None:
"""Test that we can take out a read lock and that while we hold it
only other reads can use it.
"""
# First to acquire this lock, so it should complete
lock = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=False)
)
assert lock is not None
# Enter the context manager
self.get_success(lock.__aenter__())
# Attempting to acquire the write lock fails
lock2 = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
self.assertIsNone(lock2)
# Attempting to acquire a read lock succeeds
lock3 = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=False)
)
assert lock3 is not None
self.get_success(lock3.__aenter__())
# Calling `is_still_valid` reports true.
self.assertTrue(self.get_success(lock.is_still_valid()))
# Drop the first lock
self.get_success(lock.__aexit__(None, None, None))
# Attempting to acquire the write lock still fails, as lock3 is still
# active.
lock4 = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
self.assertIsNone(lock4)
# Drop the still open third lock
self.get_success(lock3.__aexit__(None, None, None))
# We can now acquire the lock again.
lock5 = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
assert lock5 is not None
self.get_success(lock5.__aenter__())
self.get_success(lock5.__aexit__(None, None, None))
def test_maintain_lock(self) -> None:
"""Test that we don't time out locks while they're still active (lock is
renewed in the background if the process is still alive)"""
lock = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
assert lock is not None
self.get_success(lock.__aenter__())
# Wait for ages with the lock, we should not be able to get the lock.
self.reactor.advance(5 * _LOCK_TIMEOUT_MS / 1000)
self.pump()
lock2 = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
self.assertIsNone(lock2)
self.get_success(lock.__aexit__(None, None, None))
def test_timeout_lock(self) -> None:
"""Test that we time out locks if they're not updated for ages"""
lock = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
assert lock is not None
self.get_success(lock.__aenter__())
# We simulate the process getting stuck by cancelling the looping call
# that keeps the lock active.
lock._looping_call.stop()
# Wait for the lock to timeout.
self.reactor.advance(2 * _LOCK_TIMEOUT_MS / 1000)
lock2 = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
self.assertIsNotNone(lock2)
self.assertFalse(self.get_success(lock.is_still_valid()))
def test_drop(self) -> None:
"""Test that dropping the context manager means we stop renewing the lock"""
lock = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
self.assertIsNotNone(lock)
del lock
# Wait for the lock to timeout.
self.reactor.advance(2 * _LOCK_TIMEOUT_MS / 1000)
lock2 = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
self.assertIsNotNone(lock2)
def test_shutdown(self) -> None:
"""Test that shutting down Synapse releases the locks"""
# Acquire two locks
lock = self.get_success(
self.store.try_acquire_read_write_lock("name", "key", write=True)
)
self.assertIsNotNone(lock)
lock2 = self.get_success(
self.store.try_acquire_read_write_lock("name", "key2", write=True)
)
self.assertIsNotNone(lock2)
# Now call the shutdown code
self.get_success(self.store._on_shutdown())
self.assertEqual(self.store._live_read_write_lock_tokens, {})