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395 lines
16 KiB
Python
395 lines
16 KiB
Python
# Copyright 2016 OpenMarket 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 AsyncContextManager, Callable, Sequence, Tuple
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from twisted.internet import defer
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from twisted.internet.defer import CancelledError, Deferred
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from synapse.util.async_helpers import ReadWriteLock
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from tests import unittest
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class ReadWriteLockTestCase(unittest.TestCase):
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def _start_reader_or_writer(
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self,
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read_or_write: Callable[[str], AsyncContextManager],
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key: str,
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return_value: str,
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) -> Tuple["Deferred[str]", "Deferred[None]", "Deferred[None]"]:
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"""Starts a reader or writer which acquires the lock, blocks, then completes.
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Args:
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read_or_write: A function returning a context manager for a lock.
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Either a bound `ReadWriteLock.read` or `ReadWriteLock.write`.
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key: The key to read or write.
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return_value: A string that the reader or writer will resolve with when
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done.
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Returns:
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A tuple of three `Deferred`s:
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* A cancellable `Deferred` for the entire read or write operation that
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resolves with `return_value` on successful completion.
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* A `Deferred` that resolves once the reader or writer acquires the lock.
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* A `Deferred` that blocks the reader or writer. Must be resolved by the
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caller to allow the reader or writer 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 reader_or_writer():
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async with read_or_write(key):
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acquired_d.callback(None)
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await unblock_d
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return return_value
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d = defer.ensureDeferred(reader_or_writer())
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return d, acquired_d, unblock_d
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def _start_blocking_reader(
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self, rwlock: ReadWriteLock, key: str, return_value: str
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) -> Tuple["Deferred[str]", "Deferred[None]", "Deferred[None]"]:
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"""Starts a reader which acquires the lock, blocks, then releases the lock.
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See the docstring for `_start_reader_or_writer` for details about the arguments
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and return values.
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"""
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return self._start_reader_or_writer(rwlock.read, key, return_value)
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def _start_blocking_writer(
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self, rwlock: ReadWriteLock, key: str, return_value: str
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) -> Tuple["Deferred[str]", "Deferred[None]", "Deferred[None]"]:
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"""Starts a writer which acquires the lock, blocks, then releases the lock.
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See the docstring for `_start_reader_or_writer` for details about the arguments
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and return values.
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"""
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return self._start_reader_or_writer(rwlock.write, key, return_value)
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def _start_nonblocking_reader(
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self, rwlock: ReadWriteLock, key: str, return_value: str
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) -> Tuple["Deferred[str]", "Deferred[None]"]:
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"""Starts a reader which acquires the lock, then releases it immediately.
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See the docstring for `_start_reader_or_writer` for details about the arguments.
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Returns:
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A tuple of two `Deferred`s:
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* A cancellable `Deferred` for the entire read operation that resolves with
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`return_value` on successful completion.
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* A `Deferred` that resolves once the reader acquires the lock.
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"""
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d, acquired_d, unblock_d = self._start_reader_or_writer(
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rwlock.read, key, return_value
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)
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unblock_d.callback(None)
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return d, acquired_d
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def _start_nonblocking_writer(
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self, rwlock: ReadWriteLock, key: str, return_value: str
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) -> Tuple["Deferred[str]", "Deferred[None]"]:
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"""Starts a writer which acquires the lock, then releases it immediately.
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See the docstring for `_start_reader_or_writer` for details about the arguments.
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Returns:
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A tuple of two `Deferred`s:
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* A cancellable `Deferred` for the entire write operation that resolves
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with `return_value` on successful completion.
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* A `Deferred` that resolves once the writer acquires the lock.
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"""
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d, acquired_d, unblock_d = self._start_reader_or_writer(
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rwlock.write, key, return_value
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)
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unblock_d.callback(None)
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return d, acquired_d
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def _assert_first_n_resolved(
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self, deferreds: Sequence["defer.Deferred[None]"], n: int
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) -> None:
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"""Assert that exactly the first n `Deferred`s in the given list are resolved.
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Args:
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deferreds: The list of `Deferred`s to be checked.
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n: The number of `Deferred`s at the start of `deferreds` that should be
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resolved.
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"""
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for i, d in enumerate(deferreds[:n]):
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self.assertTrue(d.called, msg="deferred %d was unexpectedly unresolved" % i)
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for i, d in enumerate(deferreds[n:]):
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self.assertFalse(
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d.called, msg="deferred %d was unexpectedly resolved" % (i + n)
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)
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def test_rwlock(self):
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rwlock = ReadWriteLock()
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key = "key"
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ds = [
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self._start_blocking_reader(rwlock, key, "0"),
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self._start_blocking_reader(rwlock, key, "1"),
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self._start_blocking_writer(rwlock, key, "2"),
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self._start_blocking_writer(rwlock, key, "3"),
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self._start_blocking_reader(rwlock, key, "4"),
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self._start_blocking_reader(rwlock, key, "5"),
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self._start_blocking_writer(rwlock, key, "6"),
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]
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# `Deferred`s that resolve when each reader or writer acquires the lock.
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acquired_ds = [acquired_d for _, acquired_d, _ in ds]
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# `Deferred`s that will trigger the release of locks when resolved.
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release_ds = [release_d for _, _, release_d in ds]
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# The first two readers should acquire their locks.
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self._assert_first_n_resolved(acquired_ds, 2)
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# Release one of the read locks. The next writer should not acquire the lock,
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# because there is another reader holding the lock.
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self._assert_first_n_resolved(acquired_ds, 2)
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release_ds[0].callback(None)
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self._assert_first_n_resolved(acquired_ds, 2)
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# Release the other read lock. The next writer should acquire the lock.
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self._assert_first_n_resolved(acquired_ds, 2)
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release_ds[1].callback(None)
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self._assert_first_n_resolved(acquired_ds, 3)
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# Release the write lock. The next writer should acquire the lock.
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self._assert_first_n_resolved(acquired_ds, 3)
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release_ds[2].callback(None)
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self._assert_first_n_resolved(acquired_ds, 4)
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# Release the write lock. The next two readers should acquire locks.
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self._assert_first_n_resolved(acquired_ds, 4)
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release_ds[3].callback(None)
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self._assert_first_n_resolved(acquired_ds, 6)
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# Release one of the read locks. The next writer should not acquire the lock,
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# because there is another reader holding the lock.
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self._assert_first_n_resolved(acquired_ds, 6)
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release_ds[5].callback(None)
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self._assert_first_n_resolved(acquired_ds, 6)
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# Release the other read lock. The next writer should acquire the lock.
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self._assert_first_n_resolved(acquired_ds, 6)
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release_ds[4].callback(None)
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self._assert_first_n_resolved(acquired_ds, 7)
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# Release the write lock.
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release_ds[6].callback(None)
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# Acquire and release the write and read locks one last time for good measure.
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_, acquired_d = self._start_nonblocking_writer(rwlock, key, "last writer")
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self.assertTrue(acquired_d.called)
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_, acquired_d = self._start_nonblocking_reader(rwlock, key, "last reader")
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self.assertTrue(acquired_d.called)
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def test_lock_handoff_to_nonblocking_writer(self):
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"""Test a writer handing the lock to another writer that completes instantly."""
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rwlock = ReadWriteLock()
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key = "key"
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d1, _, unblock = self._start_blocking_writer(rwlock, key, "write 1 completed")
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d2, _ = self._start_nonblocking_writer(rwlock, key, "write 2 completed")
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self.assertFalse(d1.called)
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self.assertFalse(d2.called)
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# Unblock the first writer. The second writer will complete without blocking.
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unblock.callback(None)
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self.assertTrue(d1.called)
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self.assertTrue(d2.called)
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# The `ReadWriteLock` should operate as normal.
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d3, _ = self._start_nonblocking_writer(rwlock, key, "write 3 completed")
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self.assertTrue(d3.called)
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def test_cancellation_while_holding_read_lock(self):
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"""Test cancellation while holding a read lock.
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A waiting writer should be given the lock when the reader holding the lock is
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cancelled.
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"""
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rwlock = ReadWriteLock()
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key = "key"
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# 1. A reader takes the lock and blocks.
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reader_d, _, _ = self._start_blocking_reader(rwlock, key, "read completed")
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# 2. A writer waits for the reader to complete.
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writer_d, _ = self._start_nonblocking_writer(rwlock, key, "write completed")
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self.assertFalse(writer_d.called)
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# 3. The reader is cancelled.
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reader_d.cancel()
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self.failureResultOf(reader_d, CancelledError)
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# 4. The writer should take the lock and complete.
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self.assertTrue(
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writer_d.called, "Writer is stuck waiting for a cancelled reader"
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)
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self.assertEqual("write completed", self.successResultOf(writer_d))
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def test_cancellation_while_holding_write_lock(self):
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"""Test cancellation while holding a write lock.
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A waiting reader should be given the lock when the writer holding the lock is
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cancelled.
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"""
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rwlock = ReadWriteLock()
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key = "key"
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# 1. A writer takes the lock and blocks.
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writer_d, _, _ = self._start_blocking_writer(rwlock, key, "write completed")
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# 2. A reader waits for the writer to complete.
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reader_d, _ = self._start_nonblocking_reader(rwlock, key, "read completed")
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self.assertFalse(reader_d.called)
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# 3. The writer is cancelled.
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writer_d.cancel()
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self.failureResultOf(writer_d, CancelledError)
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# 4. The reader should take the lock and complete.
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self.assertTrue(
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reader_d.called, "Reader is stuck waiting for a cancelled writer"
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)
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self.assertEqual("read completed", self.successResultOf(reader_d))
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def test_cancellation_while_waiting_for_read_lock(self):
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"""Test cancellation while waiting for a read lock.
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Tests that cancelling a waiting reader:
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* does not cancel the writer it is waiting on
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* does not cancel the next writer waiting on it
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* does not allow the next writer to acquire the lock before an earlier writer
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has finished
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* does not keep the next writer waiting indefinitely
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These correspond to the asserts with explicit messages.
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"""
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rwlock = ReadWriteLock()
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key = "key"
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# 1. A writer takes the lock and blocks.
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writer1_d, _, unblock_writer1 = self._start_blocking_writer(
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rwlock, key, "write 1 completed"
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)
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# 2. A reader waits for the first writer to complete.
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# This reader will be cancelled later.
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reader_d, _ = self._start_nonblocking_reader(rwlock, key, "read completed")
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self.assertFalse(reader_d.called)
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# 3. A second writer waits for both the first writer and the reader to complete.
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writer2_d, _ = self._start_nonblocking_writer(rwlock, key, "write 2 completed")
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self.assertFalse(writer2_d.called)
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# 4. The waiting reader is cancelled.
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# Neither of the writers should be cancelled.
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# The second writer should still be waiting, but only on the first writer.
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reader_d.cancel()
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self.failureResultOf(reader_d, CancelledError)
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self.assertFalse(writer1_d.called, "First writer was unexpectedly cancelled")
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self.assertFalse(
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writer2_d.called,
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"Second writer was unexpectedly cancelled or given the lock before the "
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"first writer finished",
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)
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# 5. Unblock the first writer, which should complete.
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unblock_writer1.callback(None)
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self.assertEqual("write 1 completed", self.successResultOf(writer1_d))
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# 6. The second writer should take the lock and complete.
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self.assertTrue(
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writer2_d.called, "Second writer is stuck waiting for a cancelled reader"
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)
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self.assertEqual("write 2 completed", self.successResultOf(writer2_d))
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def test_cancellation_while_waiting_for_write_lock(self):
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"""Test cancellation while waiting for a write lock.
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Tests that cancelling a waiting writer:
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* does not cancel the reader or writer it is waiting on
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* does not cancel the next writer waiting on it
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* does not allow the next writer to acquire the lock before an earlier reader
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and writer have finished
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* does not keep the next writer waiting indefinitely
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These correspond to the asserts with explicit messages.
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"""
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rwlock = ReadWriteLock()
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key = "key"
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# 1. A reader takes the lock and blocks.
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reader_d, _, unblock_reader = self._start_blocking_reader(
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rwlock, key, "read completed"
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)
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# 2. A writer waits for the reader to complete.
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writer1_d, _, unblock_writer1 = self._start_blocking_writer(
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rwlock, key, "write 1 completed"
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)
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# 3. A second writer waits for both the reader and first writer to complete.
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# This writer will be cancelled later.
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writer2_d, _ = self._start_nonblocking_writer(rwlock, key, "write 2 completed")
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self.assertFalse(writer2_d.called)
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# 4. A third writer waits for the second writer to complete.
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writer3_d, _ = self._start_nonblocking_writer(rwlock, key, "write 3 completed")
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self.assertFalse(writer3_d.called)
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# 5. The second writer is cancelled, but continues waiting for the lock.
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# The reader, first writer and third writer should not be cancelled.
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# The first writer should still be waiting on the reader.
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# The third writer should still be waiting on the second writer.
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writer2_d.cancel()
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self.assertNoResult(writer2_d)
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self.assertFalse(reader_d.called, "Reader was unexpectedly cancelled")
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self.assertFalse(writer1_d.called, "First writer was unexpectedly cancelled")
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self.assertFalse(
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writer3_d.called,
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"Third writer was unexpectedly cancelled or given the lock before the first "
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"writer finished",
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)
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# 6. Unblock the reader, which should complete.
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# The first writer should be given the lock and block.
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# The third writer should still be waiting on the second writer.
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unblock_reader.callback(None)
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self.assertEqual("read completed", self.successResultOf(reader_d))
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self.assertNoResult(writer2_d)
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self.assertFalse(
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writer3_d.called,
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"Third writer was unexpectedly given the lock before the first writer "
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"finished",
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)
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# 7. Unblock the first writer, which should complete.
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unblock_writer1.callback(None)
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self.assertEqual("write 1 completed", self.successResultOf(writer1_d))
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# 8. The second writer should take the lock and release it immediately, since it
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# has been cancelled.
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self.failureResultOf(writer2_d, CancelledError)
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# 9. The third writer should take the lock and complete.
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self.assertTrue(
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writer3_d.called, "Third writer is stuck waiting for a cancelled writer"
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)
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self.assertEqual("write 3 completed", self.successResultOf(writer3_d))
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