From 8027166dd546811316e7c8395deaf929110c2f3a Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <richard@matrix.org>
Date: Sat, 29 Aug 2020 00:05:25 +0100
Subject: [PATCH] Add a comment about _LimitedHostnameResolver
---
synapse/app/_base.py | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/synapse/app/_base.py b/synapse/app/_base.py
index 2b2cd795e0..a43dc5b2c9 100644
--- a/synapse/app/_base.py
+++ b/synapse/app/_base.py
@@ -334,6 +334,13 @@ def install_dns_limiter(reactor, max_dns_requests_in_flight=100):
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
--
GitLab