summary refs log tree commit diff
path: root/synapse/handlers/worker_lock.py
blob: 72df773a8623aba908fbf485b9bcfef551b73094 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
# 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.

import random
from types import TracebackType
from typing import (
    TYPE_CHECKING,
    AsyncContextManager,
    Collection,
    Dict,
    Optional,
    Tuple,
    Type,
    Union,
)
from weakref import WeakSet

import attr

from twisted.internet import defer
from twisted.internet.interfaces import IReactorTime

from synapse.logging.context import PreserveLoggingContext
from synapse.logging.opentracing import start_active_span
from synapse.metrics.background_process_metrics import wrap_as_background_process
from synapse.storage.databases.main.lock import Lock, LockStore
from synapse.util.async_helpers import timeout_deferred

if TYPE_CHECKING:
    from synapse.logging.opentracing import opentracing
    from synapse.server import HomeServer


DELETE_ROOM_LOCK_NAME = "delete_room_lock"


class WorkerLocksHandler:
    """A class for waiting on taking out locks, rather than using the storage
    functions directly (which don't support awaiting).
    """

    def __init__(self, hs: "HomeServer") -> None:
        self._reactor = hs.get_reactor()
        self._store = hs.get_datastores().main
        self._clock = hs.get_clock()
        self._notifier = hs.get_notifier()
        self._instance_name = hs.get_instance_name()

        # Map from lock name/key to set of `WaitingLock` that are active for
        # that lock.
        self._locks: Dict[
            Tuple[str, str], WeakSet[Union[WaitingLock, WaitingMultiLock]]
        ] = {}

        self._clock.looping_call(self._cleanup_locks, 30_000)

        self._notifier.add_lock_released_callback(self._on_lock_released)

    def acquire_lock(self, lock_name: str, lock_key: str) -> "WaitingLock":
        """Acquire a standard lock, returns a context manager that will block
        until the lock is acquired.

        Note: Care must be taken to avoid deadlocks. In particular, this
        function does *not* timeout.

        Usage:
            async with handler.acquire_lock(name, key):
                # Do work while holding the lock...
        """

        lock = WaitingLock(
            reactor=self._reactor,
            store=self._store,
            handler=self,
            lock_name=lock_name,
            lock_key=lock_key,
            write=None,
        )

        self._locks.setdefault((lock_name, lock_key), WeakSet()).add(lock)

        return lock

    def acquire_read_write_lock(
        self,
        lock_name: str,
        lock_key: str,
        *,
        write: bool,
    ) -> "WaitingLock":
        """Acquire a read/write lock, returns a context manager that will block
        until the lock is acquired.

        Note: Care must be taken to avoid deadlocks. In particular, this
        function does *not* timeout.

        Usage:
            async with handler.acquire_read_write_lock(name, key, write=True):
                # Do work while holding the lock...
        """

        lock = WaitingLock(
            reactor=self._reactor,
            store=self._store,
            handler=self,
            lock_name=lock_name,
            lock_key=lock_key,
            write=write,
        )

        self._locks.setdefault((lock_name, lock_key), WeakSet()).add(lock)

        return lock

    def acquire_multi_read_write_lock(
        self,
        lock_names: Collection[Tuple[str, str]],
        *,
        write: bool,
    ) -> "WaitingMultiLock":
        """Acquires multi read/write locks at once, returns a context manager
        that will block until all the locks are acquired.

        This will try and acquire all locks at once, and will never hold on to a
        subset of the locks. (This avoids accidentally creating deadlocks).

        Note: Care must be taken to avoid deadlocks. In particular, this
        function does *not* timeout.
        """

        lock = WaitingMultiLock(
            lock_names=lock_names,
            write=write,
            reactor=self._reactor,
            store=self._store,
            handler=self,
        )

        for lock_name, lock_key in lock_names:
            self._locks.setdefault((lock_name, lock_key), WeakSet()).add(lock)

        return lock

    def notify_lock_released(self, lock_name: str, lock_key: str) -> None:
        """Notify that a lock has been released.

        Pokes both the notifier and replication.
        """

        self._notifier.notify_lock_released(self._instance_name, lock_name, lock_key)

    def _on_lock_released(
        self, instance_name: str, lock_name: str, lock_key: str
    ) -> None:
        """Called when a lock has been released.

        Wakes up any locks that might be waiting on this.
        """
        locks = self._locks.get((lock_name, lock_key))
        if not locks:
            return

        def _wake_deferred(deferred: defer.Deferred) -> None:
            if not deferred.called:
                deferred.callback(None)

        for lock in locks:
            self._clock.call_later(0, _wake_deferred, lock.deferred)

    @wrap_as_background_process("_cleanup_locks")
    async def _cleanup_locks(self) -> None:
        """Periodically cleans out stale entries in the locks map"""
        self._locks = {key: value for key, value in self._locks.items() if value}


@attr.s(auto_attribs=True, eq=False)
class WaitingLock:
    reactor: IReactorTime
    store: LockStore
    handler: WorkerLocksHandler
    lock_name: str
    lock_key: str
    write: Optional[bool]
    deferred: "defer.Deferred[None]" = attr.Factory(defer.Deferred)
    _inner_lock: Optional[Lock] = None
    _retry_interval: float = 0.1
    _lock_span: "opentracing.Scope" = attr.Factory(
        lambda: start_active_span("WaitingLock.lock")
    )

    async def __aenter__(self) -> None:
        self._lock_span.__enter__()

        with start_active_span("WaitingLock.waiting_for_lock"):
            while self._inner_lock is None:
                self.deferred = defer.Deferred()

                if self.write is not None:
                    lock = await self.store.try_acquire_read_write_lock(
                        self.lock_name, self.lock_key, write=self.write
                    )
                else:
                    lock = await self.store.try_acquire_lock(
                        self.lock_name, self.lock_key
                    )

                if lock:
                    self._inner_lock = lock
                    break

                try:
                    # Wait until the we get notified the lock might have been
                    # released (by the deferred being resolved). We also
                    # periodically wake up in case the lock was released but we
                    # weren't notified.
                    with PreserveLoggingContext():
                        await timeout_deferred(
                            deferred=self.deferred,
                            timeout=self._get_next_retry_interval(),
                            reactor=self.reactor,
                        )
                except Exception:
                    pass

        return await self._inner_lock.__aenter__()

    async def __aexit__(
        self,
        exc_type: Optional[Type[BaseException]],
        exc: Optional[BaseException],
        tb: Optional[TracebackType],
    ) -> Optional[bool]:
        assert self._inner_lock

        self.handler.notify_lock_released(self.lock_name, self.lock_key)

        try:
            r = await self._inner_lock.__aexit__(exc_type, exc, tb)
        finally:
            self._lock_span.__exit__(exc_type, exc, tb)

        return r

    def _get_next_retry_interval(self) -> float:
        next = self._retry_interval
        self._retry_interval = max(5, next * 2)
        return next * random.uniform(0.9, 1.1)


@attr.s(auto_attribs=True, eq=False)
class WaitingMultiLock:
    lock_names: Collection[Tuple[str, str]]

    write: bool

    reactor: IReactorTime
    store: LockStore
    handler: WorkerLocksHandler

    deferred: "defer.Deferred[None]" = attr.Factory(defer.Deferred)

    _inner_lock_cm: Optional[AsyncContextManager] = None
    _retry_interval: float = 0.1
    _lock_span: "opentracing.Scope" = attr.Factory(
        lambda: start_active_span("WaitingLock.lock")
    )

    async def __aenter__(self) -> None:
        self._lock_span.__enter__()

        with start_active_span("WaitingLock.waiting_for_lock"):
            while self._inner_lock_cm is None:
                self.deferred = defer.Deferred()

                lock_cm = await self.store.try_acquire_multi_read_write_lock(
                    self.lock_names, write=self.write
                )

                if lock_cm:
                    self._inner_lock_cm = lock_cm
                    break

                try:
                    # Wait until the we get notified the lock might have been
                    # released (by the deferred being resolved). We also
                    # periodically wake up in case the lock was released but we
                    # weren't notified.
                    with PreserveLoggingContext():
                        await timeout_deferred(
                            deferred=self.deferred,
                            timeout=self._get_next_retry_interval(),
                            reactor=self.reactor,
                        )
                except Exception:
                    pass

        assert self._inner_lock_cm
        await self._inner_lock_cm.__aenter__()
        return

    async def __aexit__(
        self,
        exc_type: Optional[Type[BaseException]],
        exc: Optional[BaseException],
        tb: Optional[TracebackType],
    ) -> Optional[bool]:
        assert self._inner_lock_cm

        for lock_name, lock_key in self.lock_names:
            self.handler.notify_lock_released(lock_name, lock_key)

        try:
            r = await self._inner_lock_cm.__aexit__(exc_type, exc, tb)
        finally:
            self._lock_span.__exit__(exc_type, exc, tb)

        return r

    def _get_next_retry_interval(self) -> float:
        next = self._retry_interval
        self._retry_interval = max(5, next * 2)
        return next * random.uniform(0.9, 1.1)