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perf: replace RLock with Lock where re-entrant locking is not needed
Convert 7 of 8 RLock instances to plain Lock. All verified to use only flat (non-recursive) acquisition patterns: - Connection.lock (hot path: every message send/receive) - Cluster._lock (connect/shutdown) - ControlConnection._lock and _reconnection_lock - Metadata._hosts_lock and TokenMap._rebuild_lock - Host.lock and cqlengine Connection.lazy_connect_lock Session._lock is kept as RLock because run_add_or_renew_pool() uses manual release/acquire inside a 'with' block. Benchmark: RLock 'with' stmt is ~14% slower than plain Lock.
1 parent 8e6c4d4 commit fbb04b2

7 files changed

Lines changed: 216 additions & 11 deletions

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benchmarks/bench_rlock_vs_lock.py

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# Copyright DataStax, Inc.
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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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"""
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Micro-benchmark: RLock vs Lock acquire/release overhead.
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Measures the performance difference between threading.RLock and
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threading.Lock for non-recursive lock acquisition patterns.
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Run:
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python benchmarks/bench_rlock_vs_lock.py
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"""
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import timeit
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from threading import Lock, RLock
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def bench_lock_types():
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"""Compare Lock vs RLock acquire/release cycles."""
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lock = Lock()
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rlock = RLock()
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n = 2_000_000
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def use_lock():
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lock.acquire()
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lock.release()
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def use_rlock():
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rlock.acquire()
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rlock.release()
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def use_lock_with():
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with lock:
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pass
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def use_rlock_with():
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with rlock:
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pass
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t_lock = timeit.timeit(use_lock, number=n)
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t_rlock = timeit.timeit(use_rlock, number=n)
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print(f"Lock acquire/release ({n} iters): {t_lock:.3f}s ({t_lock / n * 1e9:.1f} ns/cycle)")
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print(f"RLock acquire/release ({n} iters): {t_rlock:.3f}s ({t_rlock / n * 1e9:.1f} ns/cycle)")
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print(f"RLock overhead: {(t_rlock / t_lock - 1) * 100:.0f}% ({t_rlock / t_lock:.2f}x)")
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t_lock_with = timeit.timeit(use_lock_with, number=n)
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t_rlock_with = timeit.timeit(use_rlock_with, number=n)
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print(f"\nLock 'with' stmt ({n} iters): {t_lock_with:.3f}s ({t_lock_with / n * 1e9:.1f} ns/cycle)")
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print(f"RLock 'with' stmt ({n} iters): {t_rlock_with:.3f}s ({t_rlock_with / n * 1e9:.1f} ns/cycle)")
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print(f"RLock overhead: {(t_rlock_with / t_lock_with - 1) * 100:.0f}% ({t_rlock_with / t_lock_with:.2f}x)")
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def main():
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bench_lock_types()
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if __name__ == '__main__':
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main()

cassandra/cluster.py

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1498,7 +1498,7 @@ def __init__(self,
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self.executor = self._create_thread_pool_executor(max_workers=executor_threads)
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self.scheduler = _Scheduler(self.executor)
15001500

1501-
self._lock = RLock()
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self._lock = Lock()
15021502

15031503
if self.metrics_enabled:
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from cassandra.metrics import Metrics
@@ -3540,11 +3540,11 @@ def __init__(self, cluster, timeout,
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self._token_meta_enabled = token_meta_enabled
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self._schema_meta_page_size = schema_meta_page_size
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3543-
self._lock = RLock()
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self._lock = Lock()
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self._schema_agreement_lock = Lock()
35453545

35463546
self._reconnection_handler = None
3547-
self._reconnection_lock = RLock()
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self._reconnection_lock = Lock()
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35493549
self._event_schedule_times = {}
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cassandra/connection.py

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -22,7 +22,7 @@
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import socket
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import struct
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import sys
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from threading import Thread, Event, RLock, Condition
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from threading import Thread, Event, Lock, RLock, Condition
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import time
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import ssl
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import uuid
@@ -928,7 +928,7 @@ def __init__(self, host='127.0.0.1', port=9042, authenticator=None,
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self.request_ids = deque(range(initial_size))
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self.highest_request_id = initial_size - 1
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931-
self.lock = RLock()
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self.lock = Lock()
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self.connected_event = Event()
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self.features = ProtocolFeatures(shard_id=shard_id)
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self.total_shards = total_shards

cassandra/cqlengine/connection.py

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -78,7 +78,7 @@ def __init__(self, name, hosts, consistency=None,
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self.lazy_connect = lazy_connect
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self.retry_connect = retry_connect
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self.cluster_options = cluster_options if cluster_options else {}
81-
self.lazy_connect_lock = threading.RLock()
81+
self.lazy_connect_lock = threading.Lock()
8282

8383
@classmethod
8484
def from_session(cls, name, session):

cassandra/metadata.py

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -22,7 +22,7 @@
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import logging
2323
import re
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import sys
25-
from threading import RLock
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from threading import Lock
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import struct
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import random
2828
import itertools
@@ -126,7 +126,7 @@ def __init__(self):
126126
self.dbaas = False
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self._hosts = {}
128128
self._host_id_by_endpoint = {}
129-
self._hosts_lock = RLock()
129+
self._hosts_lock = Lock()
130130
self._tablets = Tablets({})
131131

132132
def export_schema_as_string(self):
@@ -1778,7 +1778,7 @@ def __init__(self, token_class, token_to_host_owner, all_tokens, metadata):
17781778

17791779
self.tokens_to_hosts_by_ks = {}
17801780
self._metadata = metadata
1781-
self._rebuild_lock = RLock()
1781+
self._rebuild_lock = Lock()
17821782

17831783
def rebuild_keyspace(self, keyspace, build_if_absent=False):
17841784
with self._rebuild_lock:

cassandra/pool.py

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -23,7 +23,7 @@
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import random
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import copy
2525
import uuid
26-
from threading import Lock, RLock, Condition
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from threading import Lock, Condition
2727
import weakref
2828
try:
2929
from weakref import WeakSet
@@ -179,7 +179,7 @@ def __init__(self, endpoint, conviction_policy_factory, datacenter=None, rack=No
179179
raise ValueError("host_id may not be None")
180180
self.host_id = host_id
181181
self.set_location_info(datacenter, rack)
182-
self.lock = RLock()
182+
self.lock = Lock()
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184184
@property
185185
def address(self):

tests/unit/test_rlock_to_lock.py

Lines changed: 134 additions & 0 deletions
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"""
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Unit tests verifying that RLock -> Lock conversion is safe.
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Tests that the lock objects are of the correct type and that basic
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operations (connect, metadata, pool) still work correctly.
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"""
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import threading
8+
import unittest
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from unittest.mock import Mock
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11+
from cassandra.metadata import Metadata, TokenMap
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from cassandra.pool import Host
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class TestLockTypes(unittest.TestCase):
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"""Verify each converted lock is a plain Lock, not RLock."""
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def _assert_is_lock_not_rlock(self, lock_obj):
19+
"""Assert the given object is a plain Lock, not an RLock."""
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# In CPython, Lock() creates _thread.lock, RLock() creates _thread.RLock
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lock_type_name = type(lock_obj).__name__
22+
self.assertNotIn('RLock', lock_type_name,
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f"Expected plain Lock but got {type(lock_obj)}")
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def test_metadata_hosts_lock_is_plain_lock(self):
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"""Metadata._hosts_lock should be a plain Lock."""
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m = Metadata()
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self._assert_is_lock_not_rlock(m._hosts_lock)
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def test_metadata_rebuild_lock_is_plain_lock(self):
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"""TokenMap._rebuild_lock should be a plain Lock."""
32+
tm = TokenMap(
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token_class=Mock(),
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token_to_host_owner={},
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all_tokens=[],
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metadata=Mock()
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)
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self._assert_is_lock_not_rlock(tm._rebuild_lock)
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def test_host_lock_is_plain_lock(self):
41+
"""Host.lock should be a plain Lock."""
42+
import uuid
43+
h = Host(
44+
endpoint=Mock(),
45+
conviction_policy_factory=Mock(),
46+
host_id=uuid.uuid4()
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)
48+
self._assert_is_lock_not_rlock(h.lock)
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def test_cqlengine_connection_lock_is_plain_lock(self):
51+
"""CQLEngine Connection.lazy_connect_lock should be a plain Lock."""
52+
from cassandra.cqlengine.connection import Connection as CQLConn
53+
c = CQLConn.__new__(CQLConn)
54+
c.lazy_connect_lock = threading.Lock()
55+
self._assert_is_lock_not_rlock(c.lazy_connect_lock)
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class TestMetadataOperationsWithLock(unittest.TestCase):
59+
"""Verify metadata operations work correctly with plain Lock."""
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def test_add_and_get_host(self):
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"""add_or_return_host + get_host should work with plain Lock."""
63+
import uuid
64+
m = Metadata()
65+
endpoint = Mock()
66+
host = Host(endpoint=endpoint, conviction_policy_factory=Mock(),
67+
host_id=uuid.uuid4())
68+
returned, new = m.add_or_return_host(host)
69+
self.assertTrue(new)
70+
self.assertIs(returned, host)
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72+
# Second add should return same host
73+
returned2, new2 = m.add_or_return_host(host)
74+
self.assertFalse(new2)
75+
self.assertIs(returned2, host)
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77+
def test_update_host_sequential_lock(self):
78+
"""update_host acquires lock twice sequentially — must not deadlock."""
79+
import uuid
80+
m = Metadata()
81+
old_endpoint = Mock()
82+
new_endpoint = Mock()
83+
host = Host(endpoint=new_endpoint, conviction_policy_factory=Mock(),
84+
host_id=uuid.uuid4())
85+
# update_host calls add_or_return_host (acquires lock, releases),
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# then acquires lock again for endpoint update.
87+
# With plain Lock, this must NOT deadlock.
88+
m.update_host(host, old_endpoint)
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# Host should be retrievable by host_id
90+
result = m.get_host_by_host_id(host.host_id)
91+
self.assertIs(result, host)
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93+
def test_remove_host(self):
94+
"""remove_host should work with plain Lock."""
95+
import uuid
96+
m = Metadata()
97+
endpoint = Mock()
98+
host = Host(endpoint=endpoint, conviction_policy_factory=Mock(),
99+
host_id=uuid.uuid4())
100+
m.add_or_return_host(host)
101+
removed = m.remove_host(host)
102+
self.assertTrue(removed)
103+
104+
def test_all_hosts(self):
105+
"""all_hosts should work under plain Lock."""
106+
import uuid
107+
m = Metadata()
108+
hosts = []
109+
for _ in range(3):
110+
h = Host(endpoint=Mock(), conviction_policy_factory=Mock(),
111+
host_id=uuid.uuid4())
112+
m.add_or_return_host(h)
113+
hosts.append(h)
114+
all_h = m.all_hosts()
115+
self.assertEqual(len(all_h), 3)
116+
117+
118+
class TestHostLockOperations(unittest.TestCase):
119+
"""Verify Host lock operations work with plain Lock."""
120+
121+
def test_get_and_set_reconnection_handler(self):
122+
"""get_and_set_reconnection_handler should work with plain Lock."""
123+
import uuid
124+
h = Host(endpoint=Mock(), conviction_policy_factory=Mock(),
125+
host_id=uuid.uuid4())
126+
handler = Mock()
127+
old = h.get_and_set_reconnection_handler(handler)
128+
self.assertIsNone(old)
129+
old2 = h.get_and_set_reconnection_handler(Mock())
130+
self.assertIs(old2, handler)
131+
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133+
if __name__ == '__main__':
134+
unittest.main()

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