diff --git a/changelog.d/10190.misc b/changelog.d/10190.misc
new file mode 100644
index 0000000000..388ed3ffb6
--- /dev/null
+++ b/changelog.d/10190.misc
@@ -0,0 +1 @@
+Remove redundant DNS lookup limiter.
diff --git a/synapse/app/_base.py b/synapse/app/_base.py
index 1329af2e2b..575bd30d27 100644
--- a/synapse/app/_base.py
+++ b/synapse/app/_base.py
@@ -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")
|
