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Ensure that we never stop reconnecting to redis #9391

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Feb 11, 2021
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Ensure that we never stop reconnecting to redis #9391

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78f3afe
Ensure that we never stop reconnecting to redis
erikjohnston Feb 11, 2021
de2daff
Newsfile
erikjohnston Feb 11, 2021
38f9fb2
Don't use slots, as it breaks py3.5
erikjohnston Feb 11, 2021
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1 change: 1 addition & 0 deletions changelog.d/9391.bugfix
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fix bug where Synapse would occaisonally stop reconnecting after the connection was lost.
26 changes: 24 additions & 2 deletions synapse/replication/tcp/redis.py
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Expand Up @@ -15,8 +15,9 @@

import logging
from inspect import isawaitable
from typing import TYPE_CHECKING, Optional, Type, cast
from typing import TYPE_CHECKING, Generic, Optional, Type, TypeVar, cast

import attr
import txredisapi

from synapse.logging.context import PreserveLoggingContext, make_deferred_yieldable
Expand All @@ -42,6 +43,24 @@

logger = logging.getLogger(__name__)

T = TypeVar("T")
V = TypeVar("V")


@attr.s
class ConstantProperty(Generic[T, V]):
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Can you just use the @property decorator (or does that raise when attempting to set it?)

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Yeah, that raises. We could do continueTrying = property(lambda _: True, lambda _a, _b: True) but eww

"""A descriptor that returns the given constant, ignoring attempts to set
it.
"""

constant = attr.ib() # type: V
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FWIW we can now do the following I think?

Suggested change
constant = attr.ib() # type: V
constant: V = attr.ib()

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I thought that was py3.6?

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Oh, maybe. I'm guessing this is why you need the cast() call?

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I believe it should understand descriptors enough to understand, but empirically it didn't. Possibly because of the #type: ignore (as mypy doesn't like overriding a bool attribute with a descriptor that returns a bool...)


def __get__(self, obj: Optional[T], objtype: Type[T] = None) -> V:
return self.constant

def __set__(self, obj: Optional[T], value: V):
pass


class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
"""Connection to redis subscribed to replication stream.
Expand Down Expand Up @@ -195,6 +214,10 @@ class SynapseRedisFactory(txredisapi.RedisFactory):
we detect dead connections.
"""

# We want to *always* retry connecting, txredisapi will stop if there is a
# failure during certain operations, e.g. during AUTH.
continueTrying = cast(bool, ConstantProperty(True))

def __init__(
self,
hs: "HomeServer",
Expand Down Expand Up @@ -243,7 +266,6 @@ class RedisDirectTcpReplicationClientFactory(SynapseRedisFactory):
"""

maxDelay = 5
continueTrying = True
protocol = RedisSubscriber

def __init__(
Expand Down