Rip out the DNS lookup limiter (#10190)

As I've written in various places in the past (#7113, #9865) I'm pretty sure this is doing nothing useful at all.
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Richard van der Hoff 2021-06-17 16:22:41 +01:00 committed by GitHub
parent 8070b893db
commit 9cf6e0eae7
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2 changed files with 1 additions and 104 deletions

1
changelog.d/10190.misc Normal file
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@ -0,0 +1 @@
Remove redundant DNS lookup limiter.

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@ -38,7 +38,6 @@ from synapse.crypto import context_factory
from synapse.logging.context import PreserveLoggingContext
from synapse.metrics.background_process_metrics import wrap_as_background_process
from synapse.metrics.jemalloc import setup_jemalloc_stats
from synapse.util.async_helpers import Linearizer
from synapse.util.daemonize import daemonize_process
from synapse.util.rlimit import change_resource_limit
from synapse.util.versionstring import get_version_string
@ -112,8 +111,6 @@ def start_reactor(
run_command (Callable[]): callable that actually runs the reactor
"""
install_dns_limiter(reactor)
def run():
logger.info("Running")
setup_jemalloc_stats()
@ -398,107 +395,6 @@ def setup_sdnotify(hs):
)
def install_dns_limiter(reactor, max_dns_requests_in_flight=100):
"""Replaces the resolver with one that limits the number of in flight DNS
requests.
This is to workaround https://twistedmatrix.com/trac/ticket/9620, where we
can run out of file descriptors and infinite loop if we attempt to do too
many DNS queries at once
XXX: I'm confused by this. reactor.nameResolver does not use twisted.names unless
you explicitly install twisted.names as the resolver; rather it uses a GAIResolver
backed by the reactor's default threadpool (which is limited to 10 threads). So
(a) I don't understand why twisted ticket 9620 is relevant, and (b) I don't
understand why we would run out of FDs if we did too many lookups at once.
-- richvdh 2020/08/29
"""
new_resolver = _LimitedHostnameResolver(
reactor.nameResolver, max_dns_requests_in_flight
)
reactor.installNameResolver(new_resolver)
class _LimitedHostnameResolver:
"""Wraps a IHostnameResolver, limiting the number of in-flight DNS lookups."""
def __init__(self, resolver, max_dns_requests_in_flight):
self._resolver = resolver
self._limiter = Linearizer(
name="dns_client_limiter", max_count=max_dns_requests_in_flight
)
def resolveHostName(
self,
resolutionReceiver,
hostName,
portNumber=0,
addressTypes=None,
transportSemantics="TCP",
):
# We need this function to return `resolutionReceiver` so we do all the
# actual logic involving deferreds in a separate function.
# even though this is happening within the depths of twisted, we need to drop
# our logcontext before starting _resolve, otherwise: (a) _resolve will drop
# the logcontext if it returns an incomplete deferred; (b) _resolve will
# call the resolutionReceiver *with* a logcontext, which it won't be expecting.
with PreserveLoggingContext():
self._resolve(
resolutionReceiver,
hostName,
portNumber,
addressTypes,
transportSemantics,
)
return resolutionReceiver
@defer.inlineCallbacks
def _resolve(
self,
resolutionReceiver,
hostName,
portNumber=0,
addressTypes=None,
transportSemantics="TCP",
):
with (yield self._limiter.queue(())):
# resolveHostName doesn't return a Deferred, so we need to hook into
# the receiver interface to get told when resolution has finished.
deferred = defer.Deferred()
receiver = _DeferredResolutionReceiver(resolutionReceiver, deferred)
self._resolver.resolveHostName(
receiver, hostName, portNumber, addressTypes, transportSemantics
)
yield deferred
class _DeferredResolutionReceiver:
"""Wraps a IResolutionReceiver and simply resolves the given deferred when
resolution is complete
"""
def __init__(self, receiver, deferred):
self._receiver = receiver
self._deferred = deferred
def resolutionBegan(self, resolutionInProgress):
self._receiver.resolutionBegan(resolutionInProgress)
def addressResolved(self, address):
self._receiver.addressResolved(address)
def resolutionComplete(self):
self._deferred.callback(())
self._receiver.resolutionComplete()
sdnotify_sockaddr = os.getenv("NOTIFY_SOCKET")