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800ba87cc8
Refactor and convert `Linearizer` to async. This makes a `Linearizer` cancellation bug easier to fix. Also refactor to use an async context manager, which eliminates an unlikely footgun where code that doesn't immediately use the context manager could forget to release the lock. Signed-off-by: Sean Quah <seanq@element.io>
215 lines
7.0 KiB
Python
215 lines
7.0 KiB
Python
# Copyright 2016 OpenMarket Ltd
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# Copyright 2018 New Vector Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain 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,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from typing import Callable, Hashable, Tuple
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from twisted.internet import defer, reactor
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from twisted.internet.base import ReactorBase
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from twisted.internet.defer import CancelledError, Deferred
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from synapse.logging.context import LoggingContext, current_context
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from synapse.util.async_helpers import Linearizer
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from tests import unittest
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class LinearizerTestCase(unittest.TestCase):
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def _start_task(
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self, linearizer: Linearizer, key: Hashable
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) -> Tuple["Deferred[None]", "Deferred[None]", Callable[[], None]]:
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"""Starts a task which acquires the linearizer lock, blocks, then completes.
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Args:
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linearizer: The `Linearizer`.
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key: The `Linearizer` key.
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Returns:
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A tuple containing:
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* A cancellable `Deferred` for the entire task.
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* A `Deferred` that resolves once the task acquires the lock.
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* A function that unblocks the task. Must be called by the caller
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to allow the task to release the lock and complete.
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"""
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acquired_d: "Deferred[None]" = Deferred()
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unblock_d: "Deferred[None]" = Deferred()
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async def task() -> None:
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async with linearizer.queue(key):
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acquired_d.callback(None)
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await unblock_d
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d = defer.ensureDeferred(task())
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def unblock() -> None:
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unblock_d.callback(None)
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# The next task, if it exists, will acquire the lock and require a kick of
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# the reactor to advance.
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self._pump()
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return d, acquired_d, unblock
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def _pump(self) -> None:
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"""Pump the reactor to advance `Linearizer`s."""
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assert isinstance(reactor, ReactorBase)
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while reactor.getDelayedCalls():
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reactor.runUntilCurrent()
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def test_linearizer(self) -> None:
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"""Tests that a task is queued up behind an earlier task."""
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linearizer = Linearizer()
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key = object()
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_, acquired_d1, unblock1 = self._start_task(linearizer, key)
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self.assertTrue(acquired_d1.called)
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_, acquired_d2, unblock2 = self._start_task(linearizer, key)
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self.assertFalse(acquired_d2.called)
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# Once the first task is done, the second task can continue.
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unblock1()
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self.assertTrue(acquired_d2.called)
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unblock2()
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def test_linearizer_is_queued(self) -> None:
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"""Tests `Linearizer.is_queued`.
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Runs through the same scenario as `test_linearizer`.
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"""
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linearizer = Linearizer()
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key = object()
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_, acquired_d1, unblock1 = self._start_task(linearizer, key)
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self.assertTrue(acquired_d1.called)
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# Since the first task acquires the lock immediately, "is_queued" should return
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# false.
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self.assertFalse(linearizer.is_queued(key))
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_, acquired_d2, unblock2 = self._start_task(linearizer, key)
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self.assertFalse(acquired_d2.called)
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# Now the second task is queued up behind the first.
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self.assertTrue(linearizer.is_queued(key))
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unblock1()
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# And now the second task acquires the lock and nothing is in the queue again.
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self.assertTrue(acquired_d2.called)
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self.assertFalse(linearizer.is_queued(key))
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unblock2()
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self.assertFalse(linearizer.is_queued(key))
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def test_lots_of_queued_things(self) -> None:
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"""Tests lots of fast things queued up behind a slow thing.
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The stack should *not* explode when the slow thing completes.
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"""
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linearizer = Linearizer()
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key = ""
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async def func(i: int) -> None:
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with LoggingContext("func(%s)" % i) as lc:
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async with linearizer.queue(key):
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self.assertEqual(current_context(), lc)
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self.assertEqual(current_context(), lc)
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_, _, unblock = self._start_task(linearizer, key)
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for i in range(1, 100):
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defer.ensureDeferred(func(i))
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d = defer.ensureDeferred(func(1000))
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unblock()
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self.successResultOf(d)
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def test_multiple_entries(self) -> None:
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"""Tests a `Linearizer` with a concurrency above 1."""
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limiter = Linearizer(max_count=3)
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key = object()
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_, acquired_d1, unblock1 = self._start_task(limiter, key)
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self.assertTrue(acquired_d1.called)
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_, acquired_d2, unblock2 = self._start_task(limiter, key)
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self.assertTrue(acquired_d2.called)
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_, acquired_d3, unblock3 = self._start_task(limiter, key)
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self.assertTrue(acquired_d3.called)
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# These next two tasks have to wait.
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_, acquired_d4, unblock4 = self._start_task(limiter, key)
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self.assertFalse(acquired_d4.called)
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_, acquired_d5, unblock5 = self._start_task(limiter, key)
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self.assertFalse(acquired_d5.called)
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# Once the first task completes, the fourth task can continue.
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unblock1()
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self.assertTrue(acquired_d4.called)
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self.assertFalse(acquired_d5.called)
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# Once the third task completes, the fifth task can continue.
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unblock3()
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self.assertTrue(acquired_d5.called)
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# Make all tasks finish.
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unblock2()
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unblock4()
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unblock5()
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# The next task shouldn't have to wait.
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_, acquired_d6, unblock6 = self._start_task(limiter, key)
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self.assertTrue(acquired_d6)
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unblock6()
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def test_cancellation(self) -> None:
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"""Tests cancellation while waiting for a `Linearizer`."""
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linearizer = Linearizer()
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key = object()
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d1, acquired_d1, unblock1 = self._start_task(linearizer, key)
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self.assertTrue(acquired_d1.called)
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# Create a second task, waiting for the first task.
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d2, acquired_d2, _ = self._start_task(linearizer, key)
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self.assertFalse(acquired_d2.called)
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# Create a third task, waiting for the second task.
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d3, acquired_d3, unblock3 = self._start_task(linearizer, key)
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self.assertFalse(acquired_d3.called)
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# Cancel the waiting second task.
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d2.cancel()
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unblock1()
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self.successResultOf(d1)
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self.assertTrue(d2.called)
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self.failureResultOf(d2, CancelledError)
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# The third task should continue running.
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self.assertTrue(
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acquired_d3.called,
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"Third task did not get the lock after the second task was cancelled",
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)
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unblock3()
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self.successResultOf(d3)
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